# Laboratory

Department of Electrical Engineering

 Date 11/6/2013 Time-Place 4:15 PM @ 13A EE West Presenter Kaya Tutuncuoglu Title Bits Through Bufferless Queues Abstract We will be discussing the following paper: Mehrnaz Tavan, Roy D. Yates, and Waheed U. Bajwa, "Bits Through Bufferless Queues," accepted for publication in Proceedings of 51st Annual Allerton Conference on Communication, Control, and Computing, Monticello, Illinois, Oct. 2013. Abstract: This paper investigates the capacity of a channel in which information is conveyed by the timing of consecutive packets passing through a queue with independent and identically distributed service times. Such timing channels are commonly studied under the assumption of a work-conserving queue. In contrast, this paper studies the case of a bufferless queue that drops arriving packets while a packet is in service. Under this bufferless model, the paper provides upper bounds on the capacity of timing channels and establishes achievable rates for the case of bufferless M/M/1 and M/G/1 queues. In particular, it is shown that a bufferless M/M/1 queue at worst suffers less than 10% reduction in capacity when compared to an M/M/1 work-conserving queue.

 Date 10/15/2013 Time-Place 4:15 PM @ 13A EE West Presenter Ahmed Zewail Title Finite State Channels With Time-Invariant Deterministic Feedback Abstract We will continue discussing the following paper: Haim Henry Permuter, Tsachy Weissman and Andrea J. Goldsmith, "Finite State Channels With Time-Invariant Deterministic Feedback," IEEE Transactions on Information Theory, vol. 55, no. 2, pp.644-662, Feb. 2009. We will also discuss the following paper: James L. Massey, "Causality, Feedback and Directed Information," in Proceedings of the International Symposium on Information Theory and Its Applications, ISITA'90, Waikiki, HI, Nov. 1990, pp. 303-305. Abstract: It is shown that the "usual definition" of a discrete memoryless channel (DMC) in fact prohibits the use of feedback. The difficulty stems from the confusion of causality and statistical dependence. An adequate definition of a DMC is given, as well as a definition of using a channel without feedback. A definition, closely based on an old idea of Marko, is given for the directed information flowing from one sequence to another. This directed information is used to give a simple proof of the well-known fact that the use of feedback cannot increase the capacity of a DMC. It is shown that, when feedback is present, directed information is a more useful quantity than the traditional mutual information.

 Date 10/8/2013 Time-Place 4:15 PM @ 13A EE West Presenter Basak Guler Title Finite State Channels With Time-Invariant Deterministic Feedback Abstract We will be discussing the following paper: Haim Henry Permuter, Tsachy Weissman and Andrea J. Goldsmith, "Finite State Channels With Time-Invariant Deterministic Feedback," IEEE Transactions on Information Theory, vol. 55, no. 2, pp.644-662, Feb. 2009. Abstract: We consider capacity of discrete-time channels with feedback for the general case where the feedback is a time-invariant deterministic function of the output samples. Under the assumption that the channel states take values in a finite alphabet, we find a sequence of achievable rates and a sequence of upper bounds on the capacity. The achievable rates and the upper bounds are computable for any N, and the limits of the sequences exist. We show that when the probability of the initial state is positive for all the channel states, then the capacity is the limit of the achievable-rate sequence. We further show that when the channel is stationary, indecomposable, and has no intersymbol interference (ISI), its capacity is given by the limit of the maximum of the (normalized) directed information between the input X^N and the output Y^N, i.e., C = lim_{N -> inf} (1/N) max I(X^N -> Y^N) where the maximization is taken over the causal conditioning probability Q(x^N || z^{N-1}) defined in this paper. The main idea for obtaining the results is to add causality into Gallager's results on finite state channels. The capacity results are used to show that the source-channel separation theorem holds for time-invariant determinist feedback, and if the state of the channel is known both at the encoder and the decoder, then feedback does not increase capacity.

 Date 9/24/2013 Time-Place 4:15 PM @ 13A EE West Presenter Burak Varan Title Maximizing the Spread of Influence through a Social Network Abstract We will be discussing the following paper: David Kempe, Jon Kleinberg and Eva Tardos, "Maximizing the Spread of Influence through a Social Network," in Proc. 9th ACM SIGKDD int. conf. on Knowledge discovery and data mining, 2003 (pp. 137-147). Abstract: Models for the processes by which ideas and influence propagate through a social network have been studied in a number of domains, including the diffusion of medical and technological innovations, the sudden and widespread adoption of various strategies in game-theoretic settings, and the effects of "word of mouth" in the promotion of new products. Recently, motivated by the design of viral marketing strategies, Domingos and Richardson posed a fundamental algorithmic problem for such social network processes: if we can try to convince a subset of individuals to adopt a new product or innovation, and the goal is to trigger a large cascade of further adoptions, which set of individuals should we target?We consider this problem in several of the most widely studied models in social network analysis. The optimization problem of selecting the most influential nodes is NP-hard here, and we provide the first provable approximation guarantees for efficient algorithms. Using an analysis framework based on submodular functions, we show that a natural greedy strategy obtains a solution that is provably within 63% of optimal for several classes of models; our framework suggests a general approach for reasoning about the performance guarantees of algorithms for these types of influence problems in social networks.We also provide computational experiments on large collaboration networks, showing that in addition to their provable guarantees, our approximation algorithms significantly out-perform node-selection heuristics based on the well-studied notions of degree centrality and distance centrality from the field of social networks.

 Date 6/3/2013 Time-Place TBA @ 13A EE West Presenter Basak Guler Title Interactive Data Compression Abstract We will be discussing the following paper: Abbas El Gamal and Alon Orlitsky, "Interactive Data Compression," in Proc. 25th Ann. symp. Foundations Computer Science, l984 (pp. 100-108) Abstract: Let X and Y be two random variables with probability distribution p(z,y), joint entropy H(X,Y) and conditional entropies H(X|Y) and H(Y|X). Person Px knows X and person Py knows Y. They communicate over a noiseless two-way channel so that both know Xand Y. It is proved that, on the average, at least H(X|Y) + H(Y|X) bits must be exchanged and that H(X,Y) + 2 bits are sufficient. If p(z,y) > 0 for all (x,y), then at least H(X,Y) bits must be communicated on the average. However, if p(z,y) is uniform over its support set, the average number of bits needed is close to H(X|Y) + H(Y|X). Randomized protocols can reduce the amount of communication considerably but only when some probability of error is acceptable.

 Date 5/20/2013 Time-Place 2:00 PM @ 13A EE West Presenter Kaya Tutuncuoglu Title Communication Schemes with Constrained Reordering of Resources Abstract We will be discussing the following paper: Petar Popovski, Zoran Utkovski, and Kasper F. Trillingsgaard, "Communication Schemes with Constrained Reordering of Resources," accepted for publication in IEEE Transactions on Communications, Nov. 2012. Abstract: This paper introduces a communication model inspired by two practical scenarios. The ?rst scenario is related to the concept of protocol coding, where information is encoded in the actions taken by an existing communication protocol. We investigate strategies for protocol coding via combinatorial reordering of the labelled user resources (packets, channels) in an existing, primary system. However, the degrees of freedom of the reordering are constrained by the operation of the primary system. The second scenario is related to communication systems with energy harvesting, where the transmitted signals are constrained by the energy that is available through the harvesting process. We have introduced a communication model that covers both scenarios and elicits their key feature, namely the constraints of the primary system or the harvesting process. We have shown how to compute the capacity of the channels pertaining to the communication model when the resources that can be reordered have binary values. The capacity result is valid under arbitrary error model in which errors in each resource (packet) occur independently. Inspired by the information-theoretic analysis, we have shown how to design practical error-correcting codes suited for the communication model. It turns out that the information-theoretic insights are instrumental for devising superior design of error-control codes.

 Date 3/27/2013 Time-Place 4:15 PM @ 13A EE West Presenter Mohamed Nafea Title Real Interference Alignment with Real Numbers Abstract We will be discussing the following paper: Abolfazl S. Motahari, Shahab Oveis Gharan and Amir K. Khandani, "Real Interference Alignment with Real Numbers," submitted to IEEE Transactions on Information Theory. Abstract: A novel coding scheme applicable in networks with single antenna nodes is proposed. This scheme converts a single antenna system to an equivalent Multiple Input Multiple Output (MIMO) system with fractional dimensions. Interference can be aligned along these dimensions and higher Multiplexing gains can be achieved. Tools from the field of Diophantine approximation in number theory are used to show that the proposed coding scheme in fact mimics the traditional schemes used in MIMO systems where each data stream is sent along a direction and alignment happens when several streams arrive at the same direction. Two types of constellation are proposed for the encoding part, namely the single layer constellation and the multi-layer constellation. Using the single layer constellation, the coding scheme is applied to the two-user $X$ channel and the three-user Gaussian Interference Channel (GIC). In case of the two-user $X$ channel, it is proved that the total Degrees-of-Freedom (DOF), i.e. 4/3, of the channel is achievable almost surely. This is the first example in which it is shown that a time invariant single antenna system does not fall short of achieving its total DOF. Using the multi-layer constellation, the coding scheme is applied to the symmetric three-user GIC. Achievable DOFs are derived for all channel gains. As a function of the channel gain, it is observed that the DOF is everywhere discontinuous.

 Date 3/20/2013 Time-Place 4:15 PM @ 13A EE West Presenter Burak Varan Title The Degrees of Freedom of Compute-and-Forward Abstract We will be discussing the following paper: Urs Niesen and Phil Whiting, "The Degrees of Freedom of Compute-and-Forward," IEEE Transactions on Information Theory, vol. 58, no. 8, August 2012 Abstract: We analyze the asymptotic behavior of compute-andforward relay networks in the regime of high signal-to-noise ratios. We consider a section of such a network consisting of K transmitters and K relays. The aim of the relays is to reliably decode an invertible function of the messages sent by the transmitters. An upper bound on the capacity of this system can be obtained by allowing full cooperation among the transmitters and among the relays, transforming the network into a KxK multiple-input multiple-output (MIMO) channel. The number of degrees of freedom of compute-and-forward is hence at most K. In this paper, we analyze the degrees of freedom achieved by the lattice coding implementation of compute-and-forward proposed recently by Nazer and Gastpar. We show that this lattice implementation achieves at most 2/(1+1/K) \leq 2 degrees of freedom, thus exhibiting a very different asymptotic behavior than the MIMO upper bound.This raises the question if this gap of the lattice implementation to the MIMO upper bound is inherent to compute-and-forward in general. We answer this question in the negative by proposing a novel compute-and-forward implementation achieving K degrees of freedom.

 Date 1/18/2013 Time-Place 3:45 PM @ 13A EE West Presenter Basak Guler Title Interactive Interference Alignment Abstract We will be discussing the following paper: Quan Geng, Sreeram Kannan, and Pramod Viswanath, "Interactive Interference Alignment," available at arXiv:1211.0985 Abstract: We study interference channels (IFC) where interaction among sources and destinations is enabled, e.g., both sources and destinations can talk to each other. The interaction can come in two ways: 1) for half-duplex radios, destinations can talk back to sources using either simultaneous out-of-band (white spaces) transmission or in-band half-duplex transmission; 2) for full-duplex radios, both sources and destinations can transmit and listen in the same channel simultaneously. The flexibility afforded by interaction among sources and destinations allows for the derivation of interference alignment (IA) strategies that have desirable "engineering properties": insensitivity to the rationality or irrationality of channel parameters, small block lengths and finite SNR operations. We show that for several classes of interference channels the interactive interference alignment scheme can achieve the optimal degrees of freedom. We also give simulation results on the finite SNR performance of interactive interactive alignment for 3-user and 4-user half-duplex interference channels.

 Date 1/11/2013 Time-Place 3:45 PM @ 13A EE West Presenter Mohamed Nafea Title On the Secrecy Capacity of Fading Channels Abstract We will be discussing the following paper: Praveen Kumar Gopala, Lifeng Lai, and Hesham El Gamal, "On the Secrecy Capacity of Fading Channels," IEEE Transactions on Information Theory, vol, 54, no. 10, October 2008 Abstract: We consider the secure transmission of information over an ergodic fading channel in the presence of an eavesdropper. Our eavesdropper can be viewed as the wireless counterpart of Wyner's wiretapper. The secrecy capacity of such a system is characterized under the assumption of asymptotically long coherence intervals. We ?rst consider the full channel state information (CSI) case, where the transmitter has access to the channel gains of the legitimate receiver and the eavesdropper. The secrecy capacity under this full CSI assumption serves as an upper bound for the secrecy capacity when only the CSI of the legitimate receiver is known at the transmitter, which is characterized next. In each scenario, the perfect secrecy capacity is obtained along with the optimal power and rate allocation strategies. We then propose a low-complexity on/off power allocation strategy that achieves near-optimal performance with only the main channel CSI. More speci?cally, this scheme is shown to be asymptotically optimal as the average signal-to-noise ratio (SNR) goes to in?nity, and interestingly, is shown to attain the secrecy capacity under the full CSI assumption. Overall, channel fading has a positive impact on the secrecy capacity and rate adaptation, based on the main channel CSI, is critical in facilitating secure communications over slow fading channels.

 Date 11/28/2012 Time-Place 2:00 PM @ 13A EE West Presenter Basak Guler Title The Two-Armed-Bandit Problem With Time-Invariant Finite Memory Abstract We will be discussing the following paper: Thomas M. Cover and Martin E. Hellman, "The Two-Armed-Bandit Problem With Time-Invariant Finite Memory," IEEE Transactions on Information Theory, vol, 16, no. 2, March 1970 Abstract: This paper solves the classical two-armed-bandit problem under the finite-memory constraint described below. Given are probability densitiesp_0andp_1, and two experimentsAandB. It is not known which density is associated with which experiment. Thus the experimental outcomeYof experimentAis as likely to be distributed according top_0as it is to be distributed according top_1. It is desired to sequentially choose an experiment to be performed on the basis of past observations according to the algorithmT_n = f(T_{n-1}, e_n, Y_n), e_n = e(T_{n-1}), whereT_n in {1, 2, cdots, m}is the state of memory at timen, e_n in {A, B}is the choice of experiment, andY_n, is the random variable observation. The goal is to maximize the asymptotic proportionrof uses of the experiment associated with densityp_0. Letl(y) = p_0 (y) / p_1 (y), and letbar{l}andbar{bar{l}}denote the almost everywhere greatest lower bound and least upper bound onl(y). Let1 = max {bar{bar{l}}, 1/bar{l}}. Then the optimal value ofr, over allm-state algorithms(f, e), will be shown to bel^{m-1} / (l^{m-1} + 1). Ane-optimal family ofm-state algorithms will be demonstrated. In general, optimal algorithms do not exist, ande-optimal algorithms require artificial randomization.

 Date 11/21/2012 Time-Place 2:00 PM @ 13A EE West Presenter Kaya Tutuncuoglu Title Communicating Using an Energy Harvesting Transmitter: Optimum Policies Under Energy Storage Losses Abstract We will be discussing the following paper: Kaya Tutuncuoglu and Aylin Yener, "Communicating Using an Energy Harvesting Transmitter: Optimum Policies Under Energy Storage Losses," ArXiv:1208.6273, August 2012 Abstract: In this paper, short-term throughput optimal power allocation policies are derived for an energy harvesting transmitter with energy storage losses. In particular, the energy harvesting transmitter is equipped with a battery that loses a fraction of its stored energy. Both single user, i.e. one transmitter-one receiver, and the broadcast channel, i.e., one transmitter-multiple receiver settings are considered, initially with an infinite capacity battery. It is shown that the optimal policies for these models are threshold policies. Specifically, storing energy when harvested power is above an upper threshold, retrieving energy when harvested power is below a lower threshold, and transmitting with the harvested energy in between is shown to maximize the weighted sum-rate. It is observed that the two thresholds are related through the storage efficiency of the battery, and are nondecreasing during the transmission. The results are then extended to the case with finite battery capacity, where it is shown that a similar double-threshold structure arises but the thresholds are no longer monotonic. A dynamic program that yields an optimal online power allocation is derived, and is shown to have a similar double-threshold structure. A simpler online policy is proposed and observed to perform close to the optimal policy.

 Date 11/14/2012 Time-Place 2:00 PM @ 13A EE West Presenter Ye Tian Title Elements of Cellular Blind Interference Alignment -- Aligned Frequency Reuse, Wireless Index Coding and Interference Diversity Abstract We will be discussing the following paper: Syed A. Jafar, "Elements of Cellular Blind Interference Alignment -- Aligned Frequency Reuse, Wireless Index Coding and Interference Diversity," ArXiv:1203.2384, March 2012 Abstract: We explore degrees of freedom (DoF) characterizations of partially connected wireless networks, especially cellular networks, with no channel state information at the transmitters. Specifically, we introduce three fundamental elements - aligned frequency reuse, wireless index coding and interference diversity - through a series of examples, focusing first on infinite regular arrays, then on finite clusters with arbitrary connectivity and message sets, and finally on heterogeneous settings with asymmetric multiple antenna configurations. Aligned frequency reuse refers to the optimality of orthogonal resource allocations in many cases, but according to unconventional reuse patterns that are guided by interference alignment principles. Wireless index coding highlights both the intimate connection between the index coding problem and cellular blind interference alignment, as well as the added complexity inherent to wireless settings. Interference diversity refers to the observation that in a wireless network each receiver experiences a different set of interferers, and depending on the actions of its own set of interferers, the interference-free signal space at each receiver fluctuates differently from other receivers, creating opportunities for robust applications of blind interference alignment principles.

 Date 11/7/2012 Time-Place 2:00 PM @ 13A EE West Presenter Mohamed Nafea Title On The Z-Interference Channel: Diversity-Multiplexing-Delay Trade-off Abstract In this thesis, we first analyze the diversity gain region (DGR) of the single antenna Rayleigh fading Z-interference channel (ZIC). More specifically, we characterize the achievable DGR of the fixed power split Han-Kobayashi (HK) approach under these assumptions. Our characterization comes in a closed form and demonstrates that the HK scheme with only a common message is a singular case, which achieves the best DGR among all HK schemes for certain multiplexing gains. We also show that a generalized time sharing, with variable rate and power assignments for the common and private messages, does not improve the achievable DGR. Next, we analyze the fundamental performance trade off of automatic re-transmission request (ARQ) ZIC. Specifically, we characterize the achievable three-dimensional trade off between diversity (reliability), multiplexing (throughput), and delay (maximum number of re-transmissions) of two ARQ protocols: A non-cooperative protocol and a cooperative one. Considering no cooperation exists, we study the achievable trade off of the fixed-power split HK approach. Interestingly, we demonstrate that if the second user transmits the common part only of its message in the event of its successful decoding and a decoding failure at the first user, communication is improved over that achieved by keeping or stopping the transmission of both the common and private messages. We obtain closed-form expressions for the achievable trade off under the HK splitting. Under cooperation, two special cases of the HK are considered for static and dynamic decoders. The difference between the two decoders lies in the ability of the latter to dynamically choose which HK special-case decoding to apply. Cooperation is shown to dramatically increase the achievable first user diversity. Two papers related to his work can be found here: http://arxiv.org/pdf/1202.1740.pdf http://arxiv.org/pdf/1202.2561v2.pdf

 Date 10/31/2012 Time-Place 2:00 PM @ 13A EE West Presenter Burak Varan Title Cooperative Compute-and-Forward Abstract We will be discussing the following paper: Matthew Nokleby and Behnaam Aazhang, "Cooperative Compute-and-Forward," ArXiv:1203.1695, March 2012 Abstract: We examine the bene?ts of user cooperation under compute-and-forward. Much like in network coding, receivers in a compute-and-forward network recover ?nite-?eld linear combinations of transmitters' messages. Recovery is enabled by linear codes: transmitters map messages to a linear codebook, and receivers attempt to decode the incoming superposition of signals to an integer combination of codewords. However, the achievable computation rates are low if channel gains do not correspond to a suitable linear combination. In response to this challenge, we propose a cooperative approach to compute-and-forward. We devise a lattice-coding approach to block Markov encoding with which we construct a decode-and-forward style computation strategy. Transmitters broadcast lattice codewords, decode each other's messages, and then cooperatively transmit resolution information to aid receivers in decoding the integer combinations. Using our strategy, we show that cooperation offers a signi?cant improvement both in the achievable computation rate and in the diversity-multiplexing tradeoff.

 Date 10/26/2012 Time-Place 4:45 PM @ 13A EE West Presenter Basak Guler Title Quickest Detection POMDPs With Social Learning: Interaction of Local and Global Decision Makers Abstract We will be discussing the following paper: Vikram Krishnamurthy, "Quickest Detection POMDPs With Social Learning: Interaction of Local and Global Decision Makers," Information Theory, IEEE Transactions on , vol.58, no.8, pp.5563-5587, Aug. 2012. Abstract: We consider how local and global decision policies interact in stopping time problems such as quickest time change detection. Individual agents make myopic local decisions via social learning, that is, each agent records a private observation of a noisy underlying state process, selfishly optimizes its local utility and then broadcasts its local decision. Given these local decisions, how can a global decision maker achieve quickest time change detection when the underlying state changes according to a phase-type distribution? This paper presents four results. First, using Blackwell dominance of measures, it is shown that the optimal cost incurred in social-learning-based quickest detection is always larger than that of classical quickest detection. Second, it is shown that in general the optimal decision policy for social-learning-based quickest detection is characterized by multiple thresholds within the space of Bayesian distributions. Third, using lattice programming and stochastic dominance, sufficient conditions are given for the optimal decision policy to consist of a single linear hyperplane, or, more generally, a threshold curve. Estimation of the optimal linear approximation to this threshold curve is formulated as a simulation-based stochastic optimization problem. Finally, this paper shows that in multiagent sensor management with quickest detection, where each agent views the world according to its prior, the optimal policy has a similar structure to social learning.

 Date 10/10/2012 Time-Place 2:00 PM @ 13A EE West Presenter Kaya Tutuncuoglu Title Capacity and coding for the Gilbert-Elliott channels Abstract We will be discussing the following paper: Mushkin, M.; Bar-David, I.; , "Capacity and coding for the Gilbert-Elliott channels," Information Theory, IEEE Transactions on , vol.35, no.6, pp.1277-1290, Nov. 1989. Abstract: The Gilbert-Elliott channel is a varying binary symmetric channel with crossover probabilities determined by a binary-state Markov process. In general, ruch a channel has a memory that depends on the transition probabilities between the states. First, a method of calculating the capacity of this channel is introduced and applied to several examples; then the question of coding is addressed. In the conventional usage of varying channels, a code suitable for memoryless channels is used in conjunction with an interleaver, with the decoder considering the deinterleaved symbol stream as the output of a derived memoryless channel. The transmission rate in such uses is limited by the capacity of this memoryless channel, which is, however, often considerably less than the capacity of the original channel. In this work a decision-feedback decoding algorithm, that completely recovers this capacity loss, is introduced. It is shown that the performance of a system incorporating such an algorithm is determined hi an equivalent genie-aided channel, the capacity of which equals that of the original channel. Also, the calculated random coding exponent of the genie-aided channel indicates a considerable increase in the cutoff rate over the conventionally derived memoryless channel.

 Date 8/17/2012 Time-Place 2:30 PM @ 13A EE West Presenter Ye Tian Title Signal Space Alignment and Degrees of Freedom for the Two-Cluster Multi-way Relay Channel Abstract This paper investigates the degrees of freedom (DoF) of the multi-way relay channel. Specifically, the focus is on the case when there are two clusters and each cluster has two users that wish to exchange messages within the cluster with the help of the relay. It is assumed that the relay has N antennas and each of the users has M antennas. A DoF outerbound is derived and it is shown that for several scenarios of interests the DoF outerbound can be achieved. Specifically, when N < M, a network coding based two-way relaying approach with time division multiplex access (TDMA) is sufficient to achieve the DoF outerbound. When M < N < 4M/3, the signal space alignment with multiple access and broadcast transmission between the clusters can achieve the DoF outerbound. It is also show that when N>4M, the DoF outerbound can be achieved by just using multiple access and broadcast transmission between the users.

 Date 4/18/2012 Time-Place 4:00 PM @ 13A EE West Presenter Kaya Tutuncuoglu Title Information Theory of DNA Sequencing Abstract We will be discussing the following paper: Abolfazl Motahari, Guy Bresler and David Tse, "Information Theory of DNA Sequencing," available on ArXiv: 1203.6233. Abstact: DNA sequencing is the basic workhorse of modern day biology and medicine. Shotgun sequencing is the dominant technique used: many randomly located short fragments called reads are extracted from the DNA sequence, and these reads are assembled to reconstruct the original sequence. A basic question is: given a sequencing technology and the statistics of the DNA sequence, what is the minimum number of reads required for reliable reconstruction? This number provides a fundamental limit to the performance of any assembly algorithm. By drawing an analogy between the DNA sequencing problem and the classic communication problem, we formulate this question in terms of an information theoretic notion of sequencing capacity. This is the asymptotic ratio of the length of the DNA sequence to the minimum number of reads required to reconstruct it reliably. We compute the sequencing capacity explicitly for a simple statistical model of the DNA sequence and the read process. Using this framework, we also study the impact of noise in the read process on the sequencing capacity.

 Date 4/11/2012 Time-Place 3:00 PM @ 13A EE West Presenter Burak Varan Title Aligned Interference Neutralization and the Degrees of Freedom of the 2x 2x 2 Interference Channel Abstract We will be discussing the following paper: Tiangao Gou, Syed A. Jafar, Sang-Woon Jeon, Sae-Young Chung, "Aligned Interference Neutralization and the Degrees of Freedom of the 2x2x2 Interference Channel," available on ArXiv: 1012.2350. Abstact: We show that the 2x2x2 interference network, i.e., the multihop interference network formed by concatenation of two 2-user interference channels achieves the min-cut outer bound value of 2 DoF, for almost all values of channel coefficients, for both time-varying or fixed channel coefficients. The key to this result is a new idea, called aligned interference neutralization, that provides a way to align interference terms over each hop in a manner that allows them to be cancelled over the air at the last hop.

 Date 3/28/2012 Time-Place 3:00 PM @ 13A EE West Presenter Khashayar Kotobi Title User Cooperation Diversity—Part I: System Description Abstract We will be discussing the following paper: Andrew Sendonaris, Elza Erkip, and Behnaam Aazhang, "User Cooperation Diversity—Part I: System Description," IEEE Transactions on Communications, vol. 51, no. 11, Nov 2003. Abstact: Mobile users’ data rate and quality of service are limited by the fact that, within the duration of any given call, they experience severe variations in signal attenuation, thereby necessitating the use of some type of diversity. In this two-part paper, we propose a new form of spatial diversity, in which diversity gains are achieved via the cooperation of mobile users. Part I describes the user cooperation strategy, while Part II focuses on implementation issues and performance analysis. Results show that, even though the interuser channel is noisy, cooperation leads not only to an increase in capacity for both users but also to a more robust system, where users’ achievable rates are less susceptible to channel variations.

 Date 3/14/2012 Time-Place 3:00 PM @ 13A EE West Presenter Basak Guler Title Linear precoder designs for K-user interference channels Abstract We will be discussing the following paper: H. Sung, S. Park, K. Lee and I. Lee, "Linear precoder designs for K-user interference channels," IEEE Transactions on Wireless Communications, Jan 2010. Abstact: This paper studies linear precoding and decoding schemes for K-user interference channel systems. It was shown by Cadambe and Jafar that the interference alignment (IA) algorithm achieves a theoretical bound on degrees of freedom (DOF) for interference channel systems. Based on this, we first introduce a non-iterative solution for the precoding and decoding scheme. To this end, we determine the orthonormal basis vectors of each user's precoding matrix to achieve the maximum DOF, then we optimize precoding matrices in the IA method according to two different decoding schemes with respect to individual rate. Second, an iterative processing algorithm is proposed which maximizes the weighted sum rate. Deriving the gradient of the weighted sum rate and applying the gradient descent method, the proposed scheme identifies a local-optimal solution iteratively. Simulation results show that the proposed iterative algorithm outperforms other existing methods in terms of sum rate. Also, we exhibit that the proposed non-iterative method approaches a local optimal solution at high signal-to-noise ratio with reduced complexity.

 Date 2/29/2012 Time-Place 3:00 PM @ 13A EE West Presenter Insoo Koo Title Cooperative Spectrum Sensing in Cognitive Radios Abstract Developing an effective cooperative spectrum sensing (CSS) scheme in Cognitive Radio (CR) network is necessary. In this talk, I’d like to discuss with research issues related to CCS such as how to reduce delay time for gathering sensing data in CCS, how to reduce transmission overhead in the control channel, how to be robust to malicious users, and how to combine local decisions without any requirement of priori network information. I also introduce a recent work titled by “Cluster-Based Selective Cooperative Spectrum Sensing in Cognitive Radio. The paper is attached to the announcement email.

 Date 2/22/2012 Time-Place 3:00 PM @ 13A EE West Presenter Min Li Title Relaying for Multiuser Networks in the Absence of Codebook Information Abstract We will be discussing the following paper: Y. Tian and A. Yener, "Relaying for Multiuser Networks in the Absence of Codebook Information," submitted to IEEE Transactions on Information Theory, Jan 2012. Abstract: This work considers relay assisted transmission for multiuser networks when the relay has no access to the codebooks used by the transmitters. The relay is called oblivious for this reason. Of particular interest is the generalized compress-and-forward (GCF) strategy, where the destinations jointly decode the compression indices and the transmitted messages, and their optimality in this setting. The relay-to-destination links are assumed to be out-of-band with finite capacity. Two models are investigated: the multiple access relay channel (MARC) and the interference relay channel (IFRC). For the MARC with an oblivious relay, a new outerbound is derived and it is shown to be tight by means of achievability of the capacity region using GCF scheme. For the IFRC with an oblivious relay, a new strong interference condition is established, under which the capacity region is found by deriving a new outerbound and showing that it is achievable using GCF scheme. The result is further extended to establish the capacity region of M-user MARC with an oblivious relay, and multicast networks containing M sources and K destinations with an oblivious relay.

 Date 2/15/2012 Time-Place 3:00 PM @ 13A EE West Presenter Igor Stanojev Title Efficient Power Control via Pricing in Wireless Data Networks Abstract We will be discussing the following paper: C.U. Saraydar, N.B. Mandayam and D.J. Goodman, "Efficient power control via pricing in wireless data networks," IEEE Transactions on Communications, vol.50, no.2, pp.291-303, Feb 2002. "It is a very important game-theoretic paper, with over 800 citations. Most importantly, the group members will have the opportunity to grasp the fundamental game-theoretic concepts such as Nash equilibrium and Pareto optimality, and its most common application for wireless communications - the distributed uplink power control for multiple access channel." -- Igor

 Date 2/1/2012 Time-Place 3:00 PM @ 13A EE West Presenter Ye Tian Title Completely Stale Transmitter Channel State Information is Still Very Useful Abstract We will be discussing the following paper: Mohammad Ali Maddah-Ali and David Tse, "Completely Stale Transmitter Channel State Information is Still Very Useful," Forty-Eighth Annual Allerton Conference, UIUC, Illinois, September 2010. Abstract: Transmitter channel state information (CSIT) is crucial for the multiplexing gains offered by advanced interference management techniques such as multiuser MIMO and interference alignment. Such CSIT is usually obtained by feedback from the receivers, but the feedback is subject to delays. The usual approach is to use the fed back information to predict the current channel state and then apply a scheme designed assuming perfect CSIT. When the feedback delay is large compared to the channel coherence time, such a prediction approach completely fails to achieve any multiplexing gain. In this paper, we show that even in this case, the completely stale CSI is still very useful. More concretely, we showed that in a MIMO broadcast channel with K transmit antennas and K receivers each with 1 receive antenna, K/(1+1/2+...+1/K) (> 1) degrees of freedom is achievable even when the fed back channel state is completely independent of the current channel state. Moreover, we establish that if all receivers have identically distributed channels, then this is the optimal number of degrees of freedom achievable. In the optimal scheme, the transmitter uses the fed back CSI to learn the side information that the receivers receive from previous transmissions rather than to predict the current channel state. Our result can be viewed as the first example of feedback providing a degree-of-freedom gain in memoryless channels.

 Date 11/1/2011 Time-Place 11:00 AM @ 13A EE West Presenter Kaya Tutuncuoglu and Ertugrul N. Ciftcioglu Title Asilomar and MILCOM rehearsals Abstract Kaya and Ertugrul will be presenting the following papers: Kaya Tutuncuoglu and Aylin Yener, Optimal Power Control for Energy Harvesting Transmitters in an Interference Channel, to appear in Proceedings of Asilomar Conference on Signals, Systems, and Computers, Pacific Grove, CA, November 2011. Ertugrul N. Ciftcioglu and Aylin Yener, Quality-of-Information Aware Transmission Policies with Time-Varying Links, to appear in IEEE Military Communications Conference (MILCOM) 2011, Baltimore, MD, November 2011.

 Date 10/26/2011 Time-Place 4:00 PM @ 13A EE West Presenter Ye Tian Title Diversity and Multiplexing: A Fundamental Tradeoff in Multiple-Antenna Channels Abstract We will be discussing the following paper: Lizhong Zheng and David Tse, "Diversity and Multiplexing: A Fundamental Tradeoff in Multiple-Antenna Channels," IEEE Transactions on Information Theory, vol. 49, no. 5, May 2003. Abstract: Multiple antennas can be used for increasing the amount of diversity or the number of degrees of freedom in wireless communication systems. In this paper, we propose the point of view that both types of gains can be simultaneously obtained for a given multiple-antenna channel, but there is a fundamental tradeoff between how much of each any coding scheme can get. For the richly scattered Rayleigh-fading channel, we give a simple characterization of the optimal tradeoff curve and use it to evaluate the performance of existing multiple antenna schemes.

 Date 9/6/2011 Time-Place 5:00 PM @ 13A EE West Presenter Ertugrul Necdet Ciftcioglu Title A Stochastic Approximation Method Abstract We will be discussing the following paper: Herbert Robbins and Sutton Monro, "A Stochastic Approximation Method," Annals of Mathematical Statistics 22, #3, pp. 400–407, September 1951. Abstract: Let M(x) denote the expected value at level x of the response to a certain experiment. M(x) is assumed to be a monotone function of x but is unknown to the experimenter, and it is desired to find the solution x = \theta of the equation M(x) = \alpha, where \alpha is a given constant. We give a method for making successive experiments at levels x_1,x_2,... in such a way that x_n will tend to \theta in probability.

 Date 9/1/2011 Time-Place 4:00 PM @ 13A EE West Presenter Igor Stanojev Title A Coding Scheme for Additive Noise Channels with Feedback-Part I: No Bandwidth Constraint Abstract We will be discussing the following paper: J. P. M. Schalkwijkand, T. Kailath, "A Coding Scheme for Additive Noise Channels with Feedback-Part I: No Bandwidth Constraint" IEEE Transactions on Information Theory, vol. IT-12, no. 2, Apr. 1966. Abstract: In some communication problems, it is a good assumption that the channel consists of an additive white Gaussian noise forward link and an essentially noiseless feedback link. In this paper, we study channels where no bandwidth constraint is placed on the transmitted signals. Such channels arise in space communications. It is known that the availability of the feedback link cannot increase the channel capacity of the noisy forward link, but it can considerably reduce the coding effort required to achieve a given level of performance. We present a coding scheme that exploits the feedback to achieve considerable reductions in coding and decoding complexity and delay over what would be needed for comparable performance with the best known (simplex) codes for the one-way channel. Our scheme, which was motivated by the Robbins-Monro stochastic approximation technique, can also be used over channels where the additive noise is not Gaussian but is still independent from instant to instant. An extension of the scheme for channels with limited signal bandwidth is presented in a companion paper (Part II).

 Date 8/25/2011 Time-Place 4:00 PM @ 13A EE West Presenter Min Li Title Lattice Strategies for the Dirty Multiple Access Channel Abstract We will be discussing the following paper: T. Philosof, R. Zamir, U. Erez and A. J. Khisti, "Lattice Strategies for the Dirty Multiple Access Channel," IEEE Transactions on Information Theory, August 2011. Abstract: In Costa's dirty-paper channel, Gaussian random binning is able to eliminate the effect of interference which is known at the transmitter, and thus achieve capacity. We examine a generalization of the dirty-paper problem to a multiple access channel (MAC) setup, where structured (lattice-based) binning seems to be necessary to achieve capacity. In the dirty-MAC, two additive interference signals are present, one known to each transmitter but none to the receiver. The achievable rates using Costa's Gaussian binning vanish if both interference signals are strong. In contrast, it is shown that lattice-strategies (“lattice precoding”) can achieve positive rates, independent of the interference power. Furthermore, in some cases—which depend on the noise variance and power constraints—high-dimensional lattice strategies are in fact optimal. In particular, they are optimal in the limit of high SNR—where the capacity region of the dirty MAC with strong interference approaches that of a clean MAC whose power is governed by the minimum of the users' powers rather than their sum. The rate gap at high SNR between lattice-strategies and optimum (rather than Gaussian) random binning is conjectured to be ${1over 2}log_2(pi e/6)approx 0.254$ bit. Thus, the doubly dirty MAC is another instance of a network setting, like the Körner-Marton problem, where (linear) structured coding is potentially better than random binning.

 Date 4/26/2011 Time-Place 4:00 PM @ 13A EE West Presenter Ye Tian Title Degree of freedom region for the MIMO X channel Abstract We will be discussing the following paper: S. A. Jafar, S. Shamai(Shitz), "Degree of freedom region for the MIMO X channel," IEEE Transactions on Information Theory, vol. 54, no. 1, January 2008. Abstract: We provide achievability as well as converse results for the degrees of freedom region of a multiple-input multiple-output (MIMO) X channel, i.e., a system with two transmitters, two receivers, each equipped with multiple antennas, where independent messages need to be conveyed over fixed channels from each transmitter to each receiver. The inner and outer bounds on the degrees of freedom region are tight whenever integer degrees of freedom are optimal for each message.With M = 1 antennas at each node, we find that the total (sum rate) degrees of freedom are bounded above and below as 1 < eta_X < 4/3. If M > 1 and channel matrices are nondegenerate then the precise degrees of freedom eta_X = 4/3 M. Thus, the MIMO X channel has noninteger degrees of freedom when M is not a multiple of 3. Simple zero forcing without dirty paper encoding or successive decoding, suffices to achieve the 4/3 M degrees of freedom. If the channels vary with time/frequency then the X channel with single antennas (M = 1) at all nodes has exactly 4/3 degrees of freedom. The key idea for the achievability of the degrees of freedomis interference alignment—i.e., signal spaces are aligned at receivers where they constitute interference while they are separable at receivers where they are desired.We also explore the increase in degrees of freedomwhen some of themessages are made available to a transmitter or receiver in the manner of cognitive radio.

 Date 4/19/2011 Time-Place 4:00 PM @ 13A EE West Presenter Basak Guler Title Price-Based Resource Allocation for Spectrum-Sharing Femtocell Networks: A Stackelberg Game Approach Abstract We will continue discussing the following paper: X. Kang, R. Zhang and M. Motani, "Price-Based Resource Allocation for Spectrum-Sharing Femtocell Networks: A Stackelberg Game Approach," Arxiv preprint arXiv:1103.2240, 2011.

 Date 4/12/2011 Time-Place 4:00 PM @ 13A EE West Presenter Basak Guler Title Price-Based Resource Allocation for Spectrum-Sharing Femtocell Networks: A Stackelberg Game Approach Abstract We will be discussing the following paper: X. Kang, R. Zhang and M. Motani, "Price-Based Resource Allocation for Spectrum-Sharing Femtocell Networks: A Stackelberg Game Approach," Arxiv preprint arXiv:1103.2240, 2011. Abstract: This paper investigates the price-based resource allocation strategies for the uplink transmission of a spectrum-sharing femtocell network, in which a central macrocell is underlaid with distributed femtocells, all operating over the same frequency band as the macrocell. Assuming that the macrocell base station (MBS) protects itself by pricing the interference from the femtocell users, a Stackelberg game is formulated to study the joint utility maximization of the macrocell and the femtocells subject to a maximum tolerable interference power constraint at the MBS. Especially, two practical femtocell channel models: sparsely deployed scenario for rural areas and densely deployed scenario for urban areas, are investigated. For each scenario, two pricing schemes: uniform pricing and non-uniform pricing, are proposed. Then, the Stackelberg equilibriums for these proposed games are studied, and an effective distributed interference price bargaining algorithm with guaranteed convergence is propsed for the uniform-pricing case. Finally, numerical examples are presented to verify the proposed studies. It is shown that the proposed algorithms are effective in resource allocation and macrocell protection requiring minimal network overhead for spectrum-sharing-based two-tier femtocell networks.

 Date 4/5/2011 Time-Place 4:00 PM @ 13A EE West Presenter Fatih Kocak Title Toward Quality of Information Aware Rate Control for Sensor Networks Abstract We will be discussing the following paper: Z. Charbiwala, S. Zahedi, Y. Kim, M.B. Srivastava, Y.H. Cho, "Toward Quality of Information Aware Rate Control for Sensor Networks," Fourth International Workshop on Feedback Control Implementation and Design in Computing Systems and Networks, 2009. Abstract: In sensor networks, it is the Quality of Information (QoI) delivered to the end user that is of primary interest. In general, measurements from different sensor nodes do not contribute equally to the QoI because of differing sensing modalities, node locations, noise levels, sensing channel conditions, fault status, and physical process dynamics. In addition, metrics of QoI are highly application dependent, such as probability of detection of an event or fidelity of reconstruction of a spatio-temporal process. Despite these considerations, traditional data dissemination protocols in sensor networks have been designed with a focus on metrics such as throughput, packet delivery ratio, latency, and fair division of bandwidth, and are thus oblivious to the importance and quality of sensor data and the target application. In this paper, we argue for sensor network protocols that are cognizant of and use feedback from the sensor fusion algorithms to explicitly optimize for application-relevant QoI metrics during network resource allocation decisions. Through analysis and simulation we demonstrate the application-level performance benefits accruing from such a QoI-aware approach to network resource management in the context of a centralized sensor rate selection mechanism for an event detection application scenario.

 Date 3/29/2011 Time-Place 4:30 PM @ 13A EE West Presenter Kaya Tutuncuoglu Title Capacity of Channels with Action-Dependent States Abstract We will be discussing the following paper: T. Weissman, "Capacity of Channels with Action-Dependent States," IEEE Transactions on Information Theory, vol.56, no.11, pp.5396-5411, Nov. 2010. Abstract: We consider channels with action-dependent states: Given the message to be communicated, the transmitter chooses an action sequence that affects the formation of the channel states, and then creates the channel input sequence based on the state sequence. We characterize the capacity of such a channel both for the case where the channel inputs are allowed to depend non-causally on the state sequence and the case where they are restricted to causal dependence. Our setting covers previously considered scenarios involving transmission over channels with states known at the encoder, as well as various new coding scenarios for channels with a ‘rewrite’ option that may arise naturally in storage for computer memories with defects or in magnetic recoding. A few examples are worked out in detail.

 Date 3/22/2011 Time-Place 4:00 PM @ 13A EE West Presenter Ertugrul N. Ciftcioglu Title Operational Information Content Sum Capacity: Formulation and Examples Abstract This work considers Quality-of-Information (QoI) aware rate allocation policies for multiple access channels. QoI is a recently introduced composite metric which is impacted by a number of attributes including accuracy and timeliness of delivery of information communicated from the source(s) to the destination(s), and as such differs from traditional quality-of-service metrics considered to date. The focus of this work is defining the Operational Information Content Sum Capacity (OICC-S) of a network, as the set of QoI-vectors supported which maximize sum utility of the system. This utility is defined as a function of the QoI attributes provided by the source input, as well as the channel induced attributes that impact the QoI delivered to the destination(s). Optimum rate allocation to maximize the output sum utility and achieve OICC-S of the network is provided, and demonstrated to differ from the solution that provides maximum throughput. Finally, we discuss dynamic QoI-adaptation policies for time-varying links, as well as QoI-aware scheduling schemes for multihop relay networks.

 Date 3/15/2011 Time-Place 4:30 PM @ 13A EE West Presenter Igor Stanojev Title Optimal Beamforming in Interference Networks with Perfect Local Channel Information Abstract We will be discussing the following paper: Mochaourab, R.; Jorswieck, E.A.;, "Optimal Beamforming in Interference Networks with Perfect Local Channel Information," IEEE Transactions on Signal Processing, vol.59, no.3, pp.1128-1141, March 2011. Abstract: We consider settings in which T multi-antenna transmitters and K single-antenna receivers concurrently utilize the available communication resources. Each transmitter sends useful information only to its intended receivers and can degrade the performance of unintended systems. Here, we assume the performance measures associated with each receiver are monotonic with the received power gains. In general, the joint performance of the systems is desired to be Pareto optimal. However, designing Pareto optimal resource allocation schemes is known to be difficult. In order to reduce the complexity of achieving efficient operating points, we show that it is sufficient to consider rank-1 transmit covariance matrices and propose a framework for determining the efficient beamforming vectors. These beamforming vectors are thereby also parameterized by T(K-1) real-valued parameters each between zero and one. The framework is based on analyzing each transmitter's power gain-region which is composed of all jointly achievable power gains at the receivers. The efficient beamforming vectors are on a specific boundary section of the power gain-region, and in certain scenarios it is shown that it is necessary to perform additional power allocation on the beamforming vectors. Two examples which include broadcast and multicast data as well as a cognitive radio application scenario illustrate the results.

 Date 2/22/2011 Time-Place 4:30 PM @ 13A EE West Presenter Min Li Title Noisy Network Coding Abstract This talk is the continuation of last week's talk, focusing on the paper below: Sung Hoon Lim; Young-Han Kim; El Gamal, A.; Sae-Young Chung; , "Noisy network coding," Information Theory Workshop (ITW), 2010 IEEE , vol., no., pp.1-5, 6-8 Jan. 2010.

 Date 2/15/2011 Time-Place 5:00 PM @ 13A EE West Presenter Min Li Title Cooperative Transmission in the Relay Channel without or with State Abstract This talk is divided into two major parts. In the first part, we together study the noisy network coding scheme recently proposed by Lim, Kim, El Gamal and Chung. The scheme is devised for sending multiple sources over a general noisy network. Three main techniques are involved in the proposed scheme: message repetition coding, relay signal compression, and simultaneous decoding. It is shown that the scheme unifies and extends previous results on network coding and its extensions, and on compress-and-forward for the relay channels. Specifically, I will explain how this coding scheme works in a conventional three-node relay channel. In the second part, a state-dependent relay channel is studied in which strictly causal channel state information is available at the relay and no state information is available at the source and destination. The source and the relay are connected via two unidirectional out-of-band orthogonal links of finite capacity, and a state-dependent memoryless channel connects the source and the relay, on one side, and the destination, on the other. Via the orthogonal links, the source can convey information about the message to be delivered to the destination to the relay while the relay can forward state information to the source. This exchange enables cooperation between the source and the relay on transmission of message and state information to the destination. First, two achievable schemes are proposed that exploit both message and state cooperation. It is shown that a transmission scheme inspired by noisy network coding performs better than a strategy based on block Markov coding and backward decoding. Next, based on the given achievable schemes and appropriate upper bounds, capacity results are identified for some special cases. Finally, a Gaussian model is studied, along with corresponding numerical results that illuminate the relative merits of state and message cooperation. Reference: Lim, S. H. and Kim, Y. H. and El Gamal, A. and Chung, S. Y., Noisy network coding, available online at http://arxiv.org/abs/1002.3188v2, 2010. (I recommend that we should read this paper at least up to Section III. )

 Date 2/1/2011 Time-Place 4:30 PM @ 3A EE West Presenter Ye Tian Title Harnessing Interference with an Out-of-Band Relay: An Approximate Capacity Result Abstract This work studies the Gaussian interference channel (IC) with a relay, which transmits and receives in a band that is orthogonal to the IC. The channel associated with the relay is thus an out-of-band relay channel (OBRC). The focus is on a symmetric channel model, in order to understand the fundamental impact of the OBRC on the signal interaction of the IC, in the simplest possible setting. First, the linear deterministic model is investigated and the sum capacity of this channel is established for all possible channel parameters. In particular, it is observed that the impact of OBRC, as its links get stronger, is similar to that of output feedback for the IC. The insights obtained from the deterministic model are then used to design achievable schemes for the Gaussian model. The interference links are classified as extremely strong, very strong, strong, moderate, weak, and very weak. For strong and moderate interference, separate encoding is near optimal. For very strong and extremely strong interference, the interference links provide side information to the destinations, which can help the transmission through the OBRC. Specifically, when the interference is extremely strong, the channel acts as if there are two disjoint OBRCs helping each source-destination pair. For weak or very weak interference, we use the Han-Kobayashi scheme for the IC where the messages are split into common and private. We find that it is beneficial to further split the common message into two parts, and the OBRC plays an important role in decoding the common message. It is shown that our strategy achieves the symmetric capacity to within 1.14625 bits per channel use for all channel parameters.

 Date 12/13/2010 Time-Place 5:00 PM @ 3A EE West Presenter Igor Stanojev Title Topics in Collaborative Communications and Distributed Resource Allocation Abstract The major motivation behind this presentation is to introduce you to my research experience. Thus, instead of elaborating on a single or a few topics (which is usually a good idea), I have decided to take the unconventional approach and cover most of my work, providing you with a motivation behind each of the topics, the basic approach I took to solve the problem and interesting conclusions (if any). The presentations is divided in two major parts (as is my research history), namely the Cooperative Retransmission Protocols and Distributed Resource Allocation (with applications of game theory). You will hear, among other topics, about the way that the circuitry consumption harms the energy efficiency in wireless networks (and how it can be solved), about the concepts of exchanging the spectrum for relaying services in cognitive radio, relaying-motivation approach and self-configurable interference-avoiding networks.

 Date 11/29/2010 Time-Place 4:30 PM @ 3A EE West Presenter Gul Ezgi Arslan Title Modeling and Solution of Fingerprinting Games Abstract This will be the continuation of the last talk. (See below)

 Date 11/17/2010 Time-Place 5:00 PM @ 3A EE West Presenter Gul Ezgi Arslan Title Modeling and Solution of Fingerprinting Games Abstract The topic of this talk is the fingerprinting games. The fingerprinting games are essentially designed for protecting the copyrighted software or content reliably to possible attacks. In order to ensure this protection, the distributor of the content digitally embeds a unique fingerprint in the content and knows which copy is given to which customer. If one of the customers try to distribute the content without authorization, then the distributor will detect that user. The problem gets complicated if some the users cooperate and attempt the unauthorized distribution using their fingerprint information. The several copies of the content give more information about the fingerprints, therefore pirates could change the content with leaving only weak traces. A two player zero-sum game is constructed to solve this problem. In this game, the distributor aims to maximize the number of users that a fingerprinting code can support and ensure the detection of the attackers. In contrast, the group of pirates aims to minimize this fingerprinting capacity. Saddle point solution is shown to be optimal for this fingerprinting game.

 Date 11/8/2010 Time-Place 5:30 PM @ 3A EE West Presenter Ertugrul N. Ciftcioglu Title Quality of Information Aware Scheduling in Task Processing Networks Abstract We investigate Quality of Information (QoI) aware scheduling in task processing networks. Specifically, we consider the scenario where a network sequentially receives tasks from an end user, utilizes its resources to process them, and sends back its response. The utility derived by the end user from this response depends on both the accuracy and the freshness of the information. There is often a tradeoff between these two attributes and we present a model that quantifies this dependence. Using dynamic programming and optimal stopping theory, we characterize the optimal scheduling policy that maximizes the time average utility delivered by the network. We show that for many scenarios of practical interest, the optimal policy has a simple threshold structure. We also propose a method to approximately compute the threshold in closed-form. This work takes a step towards incorporating application aware objectives in making optimal scheduling decisions.

 Date 11/1/2010 Time-Place 4:30 PM @ 3A EE West Presenter Fatih Kocak Title Time-Delay Estimation in Cognitive Radio and MIMO Systems Abstract The time-delay estimation problem is studied for cognitive radio systems, multiple-input single-output (MISO) systems, and cognitive single-input multiple-output (SIMO) systems. A two-step approach is proposed for cognitive radio and cognitive SIMO systems in order to perform time-delay estimation with significantly lower computational complexity than the optimal maximum likelihood (ML) estimator. In the first step of this two-step approach, an ML estimator is used for each receiver branch in order to estimate the unknown parameters of the signal received via that branch. Then, in the second step, the estimates from the first step are combined in various ways in order to obtain the final time-delay estimate. The combining techniques that are used in the second step are called optimal combining, signal-to-noise ratio (SNR) combining, selection combining, and equal combining. It is shown that the performance of the optimal combining technique gets very close to the Cramer-Rao lower bound (CRLB) at high SNRs. These combining techniques provide various mechanisms for diversity combining for time-delay estimation and extend the concept of diversity in communications systems to the time-delay estimation problem in cognitive radio and cognitive SIMO systems. Simulation results are presented to evaluate the performance of the proposed estimators and to verify the theoretical analysis. For the solution of the time-delay estimation problem in MISO systems, ML estimation based on a genetic global optimization algorithm, namely, differential evolution (DE), is proposed. This approach is proposed in order to decrease the computational complexity of the ML estimator, which results in a complex optimization problem in general. A theoretical analysis is carried out by deriving the CRLB. Simulation studies for Rayleigh and Rician fading scenarios are performed to investigate the performance of the proposed algorithm.

 Date 10/11/2010 Time-Place 5:00 PM @ 3A EE West Presenter Kaya Tutuncuoglu Title Optimal transmission policies for energy harvesting battery limited nodes Abstract Energy harvesting from the environment significantly improves the lifetime of battery powered wireless nodes. However the unknown nature of the recharge process calls for transmission policies to adapt to this setting. Mainly, the average power constraint in traditional transmission problems is replaced with a set of energy constraints based on the stochastic energy arrivals and battery capacity. We set out to find optimal transmission policies for wireless transmitters with power control. We consider the two problems of throughput maximization until a deadline and transmission completion time minimization for a packet. A concave power-rate function is assumed, as the case in the AWGN channel. First, optimal offline power allocation policies are developed on a static channel with non-causally known energy arrivals, and the relationship between the two problems are shown. Then, the solution is extended to fading channels with an intuitive directional water-filling algorithm. Finally online algorithms using dynamic programming and other approaches are suggested.

 Date 10/07/2010 Time-Place 4:00 PM @ 225 EE West Presenter Dr. Osvaldo Simeone, New Jersey Institute of Technology Title Cooperating without codebook information Abstract A standard assumption in network information theory is that all nodes are informed at all times of the operations carried out (e.g., of the codebooks used) by any other terminal in the network. In this talk, information theoretic limits are presented under the assumption that, instead, some nodes are not informed about the codebooks used by other terminals. Specifically, capacity results are derived for a relay channel in which the relay is oblivious to the codebook used by the source (oblivious relaying), and an interference relay channel with oblivious relaying and in which each destination is possibly unaware of the codebook used by the interfering source (interference-oblivious decoding). Extensions are also discussed for a related scenario with standard codebook-aware relaying but interference-oblivious decoding.

 Date 10/05/2010 Time-Place 5:30 PM @ EE West 3A Presenter Ye Tian Title Sum Capacity of the Deterministic Interference Channel with an Out-of-Band Relay Abstract We consider the linear deterministic model for the two user interference channel (IC) with an out-of-band relay (OBR). In this model, each user has access to two orthogonal bands, where one band forms the IC, and the other band is assisted by a half-duplex relay, i.e., the relay receives and transmits in orthogonal bands. The channel is assumed to be symmetric. We first derive new outerbounds using genie arguments, and then construct optimal relaying strategies. As a result, we characterize the sum capacity of this model for all channel parameters. In particular, it is shown that similar to the case of the IC with output feedback (and without a relay), the “W” curve for the sum capacity of the IC becomes “V” curve as the strength of the links in the OBRC grows. The interference links are classified as extremely strong, very strong, strong, moderate, weak, and very weak. For the IC without the relay, it is known that some signal spaces are left unused for the sum-capacity-optimal transmission strategy. We show that, with an OBR, these spaces can be utilized to achieve the sum capacity of this model improving upon that of the IC without the OBR. We show that for very strong and extremely strong interference, the interference is useful to improve the achievable rates. For weak or very weak interference, the unused signal spaces of the IC can be utilized to transmit new information bits.

 Date 09/13/2010 Time-Place 5:00 PM @ EE West 3A Presenter Satashu Goel Title Percolation theory and its applications to network security Abstract Percolation theory was developed to model diffusion process in materials. In the recent years, several researchers have used the tools from percolation theory to analyze connectivity in wireless networks. This talk will present a brief introduction to percolation theory. Two applications of percolation theory to secrecy graphs will be presented. In the first example, we consider end-to-end secure communication in a large wireless network, where the locations of eavesdroppers are uncertain. Our framework attempts to bridge the gap between physical layer security under uncertain channel state information of the eavesdropper and network level connectivity under security constraints, by modeling location uncertainty directly at the network level as correlated node and link failures in a secrecy graph. In a secrecy graph, link connectivity is determined using information theoretic secrecy models. Bounds on the percolation threshold are obtained for square and triangular lattices, and bounds on mean degree are obtained for Poisson secrecy graphs. Both analytic and simulation results show the dramatic effect of uncertainty in location of eavesdroppers on connectivity in a secrecy graph. In the second example, we consider time-varying security failures and recoveries in a secrecy graph, where security is provided using cryptographic keys. Queuing theory is used to model the time-varying nature of security compromises, and percolation theory is used to analyze connectivity in the secrecy graph. Numerical results demonstrate that in order to obtain a low probability of connectivity outage, the system must be designed for a large probability of key recovery rather than a large average key recovery rate.
 Date 04/19/2010 Time-Place 6:00 PM @ 101 EE East Presenter Aditya Kurve Title Congestion control, rate allocation and fairness criteria Abstract I will be presenting some issues of charging, rate control and congestion control for arbitrary networks with elastic traffic. I will first discuss the general idea of rate control, efficiency versus fairness and fairness criteria. Then I will focus on [1] which decomposes the optimization problem of throughput maximization of the system into distributed problems which can be solved at the users and the network manager. I will also try to touch upon the main ideas of [2] which models the network resource allocation as a game. References: [1] Kelly F.P. (1997) Charging and rate control in elastic traffic: European Transactions onTelecommunications. [2] R. Johari and J. Tsitsiklis Efficiency Loss in a Network Resource Allocation Game Mathematics of Operations Research 29(3), 407-435, 2004.
 Date 04/12/2010 Time-Place 6:00 PM @ 101 EE East Presenter Basak Guler Title Femtocells: Home Base Stations Abstract The emerging next generation wireless systems have revealed the problem of poor indoor coverage and high capacity demand of indoor users. Apparently, studies show that most of the data transmission occurs indoor, which requires the highest data rate. This talk will give a brief overview on HomeNodeBs (Home Base Stations), or femtocells, the data access points installed by home users to get better indoor coverage . The key technical problems of tiered cellular networks as well as problems arising from the ad-hoc nature of femtocells will be addressed. Recent research results about interference avoidance, coverage and access issues will be provided.
 Date 04/05/2010 Time-Place 6:00 PM @ 101 EE East Presenter Ezgi Arslan Title Information Theoretic Security of Gaussian MIMO Wiretap Channels Abstract The previous presentation was an overview on the seminal results on information theoretic secrecy. It began with the motivation and definiton of of security in wiresless communication systems, continued with single antenna wiretap channel model where one sender is sending a confidential message to an intended receiver in the presence of an eavesdropper. Finally, the some of the studies on MIMO wiretap channels are presented. This week, I will give a brief summary of the previous results and then focus on the paper listed in the references. Achievable rates and capacity achieving schemes for the Gaussian wiretap channels are studied in this paper when there are multiple transmit antennas at the sender, multiple receive antennas at the intended receiver and multiple antennas at the eavesdropper.
 Date 03/29/2010 Time-Place 6:00 PM @ 101 EE East Presenter Gang Xiong (PhD from Lehigh University ) Title Spectrum Sensing in Cognitive Radio Networks: Performance Evaluation and Optimization Abstract This talks will focus on the optimal system design and performance evaluation for cooperative spectrum sensing in cognitive radio networks. First we address optimal spectrum sensing in cognitive radio networks considering its system level cost that accounts for the local processing cost of sensing (sample collection and energy calculation at each secondary user) as well as the transmission cost (forwarding energy statistic from secondary users to fusion center). The optimization problem solves for the appropriate number of samples to be collected and amplifier gains at each secondary user to minimize the global error probability subject to a total cost constraint. In particular, closed-form expressions for optimal solutions are derived and a generalized water-filling algorithm is proposed when number of samples or amplifier gains are fixed and additional constraints are imposed. Furthermore, when jointly designing the number of samples and amplifier gains, optimal solution indicates that only one secondary user needs to be active, i.e., collecting samples for local energy calculation and transmitting energy statistic to fusion center. Second, we investigate the system level performance evaluation for cooperative spectrum sensing in cognitive radio networks. Three performance criteria are quantitively analyzed for cooperative spectrum sensing. First, the average error probability is determined given fixed amplifier gains for a fixed number of secondary users by considering all possible channel realizations. Second, the asymptotic error probability is computed in a power constrained cognitive radio network when the number of secondary user approaches infinity. Third, the outage probability is examined when instantaneous error probability is greater than a predefined threshold.
 Date 03/01/2010 Time-Place 12:15 PM @ 3A EE West Presenter Ertugrul Ciftcioglu and Kaya Tutuncuoglu Title Control of Wireless Networks with Rechargeable Batteries Abstract We consider the problem of cross-layer resource allocation for wireless networks operating with rechargeable batteries under general arrival, channel state and recharge processes. The objective is to maximize total system utility, defined as a function of the long-term rate achieved per link, while satisfying energy and power constraints. A policy with decoupled admission control and power allocation decisions is proposed that achieves asymptotic optimality for sufficiently large battery capacity to maximum transmission power ratio (explicit bounds are provided). We present first a downlink resource allocation scenario; the analysis is then extended to multihop networks. The policy is evaluated via simulations and is seen to perform very well even in the non-asymptotic regime. This policy is particularly suitable for sensor networks, which typically satisfy the asymptotic conditions required by our methodology.

 Date 02/22/2010 Time-Place 6:00 PM @ 101 EE East Presenter Ezgi Arslan Title Information Theoretic Security of Wiretap Channels Abstract The broadcast nature of wireless communication systems makes it vulnerable to eavesdroppping. To protect the system from eavesdropping, secrecy in communication systems is recently a very interesting topic. This presentation will address information theoretic approach for establishing secrecy in wiretap channels. Beginning with defining the wiretap channels and introducing information theoretic security, it will essentially provide theory and some important results starting from the seminal paper of Wyner up to secrecy in MIMO Gaussian wiretap channels.
 Date 02/15/2010 Time-Place 6:00 PM @ 101 EE East Presenter Aditya Kurve Title Decentralized Decision Making in Networks Abstract This presentation will be introductory in nature. It will start with an introduction to the field of decentralized decision making, also known as distributed optimization. The theory behind it is useful in characterizing and modelling large and complicated networks with autonomous nodes that work towards a common goal. I will try to give a brief overview of the theory, models, applications and some important results in this field. References: Problems in Decentralized Decision Making and Computation - J.N. Tsitsiklis Ph.D. Thesis, EECS, MIT, 1984; Consensus and Cooperation in Networked Multi-Agent Systems R Olfati-Saber, JA Fax, RM Murray - Proceedings of the IEEE, 2007.
 Date 11/09/2009 Time-Place 4:30 PM @ 101 EE East Presenter Vaneet Aggarwal (PhD from Princeton University, invited talk) Title Interference Channels with a Local View: Impact of Distributed Decisions Abstract A key element of mobile wireless networks is their distributed nature, which implies that often nodes only have a local view of the network. This leads to a situation where the ground truth for each node is different from other nodes. Yet, they have to make decisions about their transmission parameters like rate and power, such that their collective decision does not violate network capacity limits but still maximize spectral efficiency. In this talk, we will first formulate a message-passing protocol which allows the information about the network to trickle via local message forwarding. The protocol naturally gives rise to networks where nodes have different amount of local information. We will then consider the performance of wireless systems with this local view. More precisely, we would quantify the information needed at nodes to come up with distributed strategies that match the sum capacity as the centralized strategy and the protocols associated to learn this knowledge.

 Date 11/02/2009 Time-Place 4:30 PM @ 101 EE East Presenter Min Li Title An Overview on Cognitive Radio Channels: Fundamental Capacity Limits Aspect Abstract Cognitive radio (CR) holds tremendous promise for increasing spectral efficiency in wireless communication systems. It spurred an explosion of interest for the past few years. Many key issues on CR have been well studied, such as efficient spectrum sensing and spectrum management schemes. However, there are still lots of questions and aspects to be tackled before CR can be seamlessly and opportunistically put into practice. Among them, one fundamental problem is that: what are the fundamental limits of communication in the presence of one or more cognitive radios in the network? In this talk, I will present some existing results on fundamental limits on CR. First, the basic concepts and different paradigms of CR will be introduced. Then I will talk about some key issues for interweave and underlay CR paradigms. Next, existing results on the achievable rates and capacity regions of overlay CR channel will be mainly discussed. Through the whole talk, intuitive ideas and key coding techniques will be highlighted and compared to show how to explore the benefits of cognition and cooperation in wireless communication network.

 Date 10/05/2009 Time-Place 4:30 PM @ 101 EE East Presenter Ye Tian Title The Gaussian Interference Channel with a Potent Relay Abstract We consider the Gaussian interference channel (GIFRC) with an intermediate relay. We first briefly review the known achievable schemes for relay channel and interference channel, and then we discuss the genie techniques when upperbounding the channel capacity. In particular, we study the "smart and useful" genie method. To find a good upperbound for the GIFRC, we consider the case when the relay is assumed to have abundant power and is named potent for that reason. By setting the power of the relay constraint to infinity, we observe that the capacity region is asymptotically equivalent to the case when the relay-destination links are noiseless and orthogonal to other links. The capacity region of the latter provides an outerbound for the GIFRC with finite relay power. We then show the sum capacity of the former can be upper bounded by a single-input-multiple-output interference channel with an antenna common to both receivers. We study both weak and strong interference cases. Both results, in turn, serve as upperbounds for the sum capacity of the GIFRC with finite relay power. Although our tight results are for when the relay has infinite power, numerical results show that with finite relay power, the performance is better than the cutset bound and our bounds are close to the known achievable sum rates for many scenarios of interest.

 Date 09/28/2009 Time-Place 4:30 PM @ 101 EE East Presenter Xiang He Title Interference Channels with Strong Secrecy Abstract It is known that given the real sum of two independent uniformly distributed lattice points from the same nested lattice codebook, the eavesdropper can obtain at most 1 bit of information per channel regarding the value of one of the lattice points. In this work, we study the effect of this $1$ bit information on the equivocation expressed in three commonly used information theoretic measures, i.e., the Shannon entropy, the Renyi entropy and the min entropy. We then demonstrate its applications in an interference channel with a confidential message. In our previous work, we showed that nested lattice codes can outperform Gaussian codes for this channel when the achieved rate is measured with the weak secrecy notion. Here, with the Renyi entropy and the min entropy measure, we prove that the same secure degree of freedom is achievable with the 'strong' secrecy notion as well. A major benefit of the new coding scheme is that the strong secrecy is generated from a single lattice point instead of a sequence of lattice points. Hence the mutual information between the confidential message and the observation of the eavesdropper decreases much faster with the number of channel uses than previously known strong secrecy coding methods for nested lattice codes.

 Date 09/08/2009 Time-Place 11:00 AM @ EE West 3A Presenter Satashu Goel Title Delay Constrained Communication Over Fading Channels: A Queued-Code Approach Abstract Wireless communication system design must contend with several impairments in the wireless channel, such as time-varying channel gains, which makes it extremely challenging to provide performance guarantees for communication over these channels. Performance guarantees for delay-sensitive applications, in terms of data rate, delay and probability of violation, have traditionally been provided either through the pure (physical layer) channel coding approach, or through the pure (link layer) queuing approach. The pure channel coding approach uses long codewords which span the entire allowable delay, to average over time-varying channel gains, and hence, guarantees low decoding error probability. However, this approach results in pessimistic performance guarantees, since it does not allow rate adaptation. On the other hand, the pure queuing approach allows rate adaptation, and hence, permits improved performance under a delay constraint. However, this approach results in overly optimistic performance guarantees, since it uses short codewords to allow rate adaptation across codewords, but ignores the decoding errors. In this talk, I will present a novel queued-code system design which combines ideas from channel coding and queuing approaches to overcome their individual limitations. The queued-code balances the requirements of the coding system and the queuing system to balance the errors in the two systems. A practical implementation of the queued-code based on low density parity check (LDPC) codes will also be presented.

# List of Weekly Discussions in Spring 2008

 Title Presenter Talk 1 "Performance Bounds for Bi-Directional Coded Cooperation Protocols" by Sang Joon Kim, Patrick Mitran, and Vahid Tarokh Min Chen Talk 2 "Communication Over Fading Channels With Delay Constraints" by Randall A. Berry and Robert G. Gallager Ertugrul Ciftcioglu Talk 3 "Stability Properties of Constrained Queueing Systems and Scheduling Policies for Maximum Throughput in Multihop Radio Networks" by Leandros Tassiulas and Anthony Ephremides Xiang He Talk 4 "On the Capacity of Interference Channels with One Cooperating Transmitter" by I. Maric, A. Goldsmith, G. Kramer and S. Shamai Ye Tian Talk 5 "Decentralized Cognitive MAC for Opportunistic Spectrum Access in Ad Hoc Networks: A POMDP Framework" by Q. Zhao, L. Tong, A. Swami, and Y. Chen Min Chen Talk 6 "Energy Optimal Control for Time Varying Wireless Networks" by M. J. Neely Ertugrul Ciftcioglu

# List of Weekly Discussions in Fall 2007

 Title Presenter Talk 1 Secure Transmission with Multiple Antennas: The MISOME Wiretap Channel, by Ashish Khisti and Gregory Wornell Ender Tekin Talk 2 Capacity Scaling for MIMO Two-Way Relaying, by Rahul Vaze and Robert W. Heath Jr. Min Chen Talk 3 Cognitive Radio: An Information-Theoretic Perspective, by Aleksandar Jovicic and Pramod Viswanath Kyounghwan Lee Talk 4 Opportunistic Cooperation by Dynamic Resource Allocation, by D. Gunduz and E. Erkip. Xiang He Talk 5 Optimal Energy and Delay Tradeoffs for Multi-User Wireless Downlinks, by Michael J. Neely Ertugrul Ciftcioglu Talk 6 Capacity limits of cognitive radio with distributed and dynamic spectral activity, by Syed A. Jafar and S. Srinivasa Ye Tian Talk 7 Interference Alignment and the Degrees of Freedom for the K User Interference Channel, by Viveck R. Cadambe and Syed A. Jafar Min Chen

# List of Weekly Discussions in Spring 2007

 Title Presenter Talk 1 Optimal Relay Functionality for SNR Maximization in Memoryless Relay Networks Min Chen Talk 2 Duality and Capacity Region of AF Relay MAC and BC Ertugrul Ciftcioglu Talk 3 Network Information Flow Xuan Jiang Talk 4 Space–Time Diversity Enhancements Using Collaborative Communications Kyounghwan Lee Talk 5 Cooperative Relay Broadcast Channels Yeon-ho Chung Talk 6 Power, Spatio-Temporal Bandwidth and Distortion in Large Sensor Networks Lauren Huie Talk 7 A General Coding Scheme for the Two-Way Channel Xiang He Talk 8 On Capacity Under Receive and Spatial Spectrum-Sharing Constraints Chien-Jen Huang Talk 9 The Feedback Capacity Region of a Class of Discrete Memoryless Multiple Access Channels Ender Tekin

# List of Bi-Weekly Discussions in Fall 2006

 Title Presenter Talk 1 Chp 2.1-2.5 of Cover&Thomas Lauren Huie Talk 2 Chp 2.6-2.11 of Cover&Thomas Xuan Jiang Talk 3 Chp 3 of Cover&Thomas Jibum Kim Talk 4 Chp 4 of Cover&Thomas Xiang He Talk 5 Chp 5 of Cover&Thomas Ertugrul Ciftcioglu

# List of Bi-Weekly Discussions in Spring 2006

 Title Presenter Talk 1 Capacity of Correlated Jamming Channels Ender Tekin Talk 2 Outage Analysis of Coded Cooperation Min Chen Talk 3-5 Communication Over Fading Channles With Delay Constraints Chien-Jen Huang Chip McArtor Talk 6 On the Throughput Scaling of Wireless Relay Networks Mikhail Lisovich Talk 7 Information-Theoretic Upper Bounds on the Capacity of Large Extended Ad Hoc Wireless Networks Kyounghwan Lee

# List of Weekly Discussions in Fall 2005

 Title Presenter Talk 1 The Capacity of Wireless Networks Mikhail A. Lisovich Talk 2 Optimum Power Allocation for Relay Assisted F/TDMA Ad Hoc Networks Semih Serbetli Talk 3 On Secure Signaling for the Gaussian Multiple Access Wire-Tap Channel Ender Tekin Talk 4 Achievable Rates in Low-Power Relay Links Over Fading Channels Chien-Jen Huang Kyounghwan Lee Talk 5 Block Markov Code Chien-Jen Huang Kyounghwan Lee Talk 6 Distributed Power Allocation for Parallel Relay Networks Min Chen Talk 7 M.S. Thesis Defense: Transmit Strategies for Lifetime Maximization of Wireless Sensor Networks Sandeep Bethanabhotla

# List of Weekly Discussions in Spring 2005

 Title Presenter Week 1 Joint Scheduling and Resource Allocation in CDMA Systems Changyoon Oh Week 2 Correlated Sources Over Wireless Channels: Cooperative Source-Channel Coding Sandeep Bethanabhotla Week 3 Maximum Lifetime Routing in Wireless Sensor Networks Chip McArtor Week 4 An Exact Analysis and Performance Evaluation of Framed ALOHA with Capture Girish Khandelwal Week 5 Capacity Scaling Laws in MIMO Relay Networks Kyounghwan Lee Week 6 Capture Models for Mobile Packet Radio Networks Sung-Min Bae Week 7 Capacity Bounds and Power Allocation for the Wireless Relay Channel Ender Tekin Week 8 On the Capacity of Large Gaussian Relay Networks Semih Serbetli Week 9 Cooperative Strategies and Capacity Theorems for Relay Networks Min Chen Week 10 Multihop Diversity in Wireless Relaying Channels Chien-Jen Huang Week 11 Modeling and Optimization of Transmission Schemes in Energy Constrained Wireless Sensor Networks Sandeep Bethanabhotla Week 12 Ph.D. Thesis Defense: Efficient Transmit Strategies for Multiuser Multiple Antenna Systems Semih Serbetli Week 13 Medium Access Control With Coordinated Adaptive Sleeping for Wireless Sensor Networks Chip McArtor Week 14 Ph.D. Thesis Defense: Resource Allocation Techniques for Performance Improvement of Multiuser Systems Changyoon Oh

# List of Weekly Discussions in Fall 2004

 Title Presenter Week 1 Energy Efficient Transmission over a Wireless Link via Lazy Packet Scheduling Changyoon Oh Week 2 Design Guidelines for Wireless Sensor Networks: communication, clustering and aggregation Sandeep Bethanabhotla Week 3 A novel feedback scheme to increase throughput in multiple access radio systems Girish Khandelwal Week 4 Coded Cooperation in Wireless Communications: Space-Time Transmission and Iterative Decoding Min Chen Week 5 Power optimal routing in wireless networks Chien-Jen Huang Week 6 Fading Relay Channels: Performance Limits and Space–Time Signal Design Kyounghwan Lee Week 7 Distributed space-time-coded protocols for exploiting cooperative diversity in wireless networks Semih Serbetli Week 8 Correlated Jamming on MIMO Gaussian Fading Channels Ender Tekin Week 9 An Energy Efficient Hierarchical Clustering Algorithm for Wireless Sensor Networks Sandeep Bethanabhotla Week 10 Efficient Mermoryless Protocol for Tag Identification Girish Khandelwal Week 11 Practical Relay Networks: A Generalization of Hybrid-ARQ Min Chen Week 12 Symbol Error Probabilities for General Cooperative Links Chien-Jen Huang

Transmit Strategies for Multiuser MIMO MAC (Talk by Prof. Yener given on May 7, 2004 at University of Maryland, College Park; and on May 11, 2004: Ohio State University)

List of Biweekly Discussions and Relevant Colloqui ( Spring 2003 - Spring 2004)

 Date 02/06/2003 Time-Place 16:15 @ Willard 267 (EE Colloquium) Presenter Dr. Phil Whiting, Bell Labs Title Dynamic Channel-Sensitive Scheduling Algorithms for Wireless Data Throughput Optimization Abstract The relative delay tolerance of data applications, together with the bursty traffic characteristics, opens up the possibility for scheduling transmissions so as to optimize throughput. An attractive approach,in fading environments, is to exploit channel variations and transmit to the user with the currently best' channel. We show that the best' user may be identified as the maximum-rate user when the feasible rates are weighed with some appropriately determined coefficients. Interpreting the coefficients as shadow prices, or reward values, the optimal strategy may thus be viewed as a revenue-based policy, which always assigns the transmission slot to the user yielding the maximum revenue. Calculating the optimal revenue vector directly is a formidable task, requiring detailed information on the channel statistics. Instead, we present adaptive algorithms for determining the optimal revenue vector on-line in an iterative fashion, without the need for explicit knowledge of the channel behavior. In the last part of the talk, asymptotic results for the proportional fair scheduling algorithm will be reviewed but not presented in detail.

 Date 02/25/2003 Time-Place 18:00 @ EE West 209 Presenter Semih Serbetli Title Signature and Beamformer Optimization for MIMO-CDMA Based on the Mean Squared Error Criterion Abstract We consider the uplink of a CDMA system where the transmitters as well as the receiver are equipped with multiple antennas. Each user transmits a weighted form of its symbol through its transmit antennas. In this work, we adopt the system-wide mean squared error as the performance measure and propose an alternating minimization based iterative algorithm to find the jointly optimum beamformers, signatures and the corresponding optimum receivers for each user. The convergence and the performance of the algorithm are investigated through numerical results.

 Date 02/25/2003 Time-Place 18:30 @ EE West 209 Presenter Onder Filiz Title Rank Constrained Temporal-Spatial Filters for CDMA Systems with Base Station Antenna Arrays Abstract Efficient interference suppression techniques are needed to maximally utilize the potential gains of code division multiple access (CDMA) systems. In this paper, we consider a minimum mean-squared error (MMSE) based receiver structure which combines multiuser detection (temporal filtering) and receiver beamforming (spatial filtering). We model the receiver as a matrix filter. Motivated by the high computational complexity we propose rank constrained temporal-spatial filters which are simpler and near optimum. The proposed filters are found by minimizing the mean-squared error subject to a structural constraint on the filters. The constraint on the receiver matrix filter narrows down the solution space, which helps to solve the optimization problem more efficiently. The constraint can be set appropriately by the system designer to achieve a desired tradeoff between performance and complexity. Numerical results indicate that a performance close to that of the optimum filter can be achieved with less complexity even in highly loaded systems. The adaptive implementations that use training bits are formulated and their convergence properties are investigated.

 Date 04/1/2003 (defense 04/3/2003) Time-Place 18:00 @ EE West 209 Presenter Battal Ozdemir - M.S. Paper Defense Title Adaptive Probing Based Medium Access Control (PMAC) Protocol for Wireless Ad Hoc Networks Abstract In this research, we have developed an adaptive medium access control (MAC) protocol based on channel probing and distributed power control. In contrast with the reservation based medium access protocols of current wireless local area network (WLAN) standards such as IEEE 802.11b, the new protocol enables concurrent transmissions on the shared radio channel by allowing reallocation of link powers in a distributed manner as long as it is feasible to accommodate all users' quality of service requirements . The new protocol utilizes the radio resources more efficiently; since all links are maintained with only the necessary amount of power by the adaptive power control scheme. In the simulations, we have observed that the proposed MAC protocol improves the channel utilization under heavy load, reduces the end-to-end packet delay and guarantees better energy consumption performance with respect to the current CSMA/CA based MAC protocol.

 Date 04/03/2003 Time-Place 18:00 @ EE West 209 Presenter Ender Tekin Title Capacity Of Multiuser Channels Abstract This was a brief presentation summarizing three important papers on differing capacity concepts for multiuser channels: "Capacity Region Of Gaussian CDMA Channels: The Symbol Synhronous Case" by S. Verdu (1986), "Optimum Sequence Multisets for Synhronous Code-Division Multiple-Access Channels" by M. Rupf and J.L. Massey (1994) and "Spectral Efficiency Of CDMA with Random Spreading" by S. Verdu and S. Shamai (1999).

 Date 04/09/2003 Time-Place 16:15 @ Willard 267 (EE Colloquium) Presenter Dr. Philip Schniter, Professor of electrical engineering at OSU Title A Low-Complexity Receiver for OFDM in Doubly-Selective Channels Abstract Orthogonal frequency division multiplexing (OFDM) is a convenient technique for communication over multipath channels with large delayspread. In OFDM, high-rate data is transmitted in parallel using a large number of low-rate narrowband subcarriers, thereby preventing the manifestation of inter-symbol interference that would otherwise result from the dispersive channel. OFDM is made practical by the fast Fourier transform (FFT), which offers a computationally efficient way to modulate data onto the orthogonal narrowband subcarriers. When OFDM systems with large FFT length are used in fast-fading multipath channels, however, orthogonality is lost and significant inter-carrier interference (ICI) may result. Due to the large FFT size, the standard approaches to data detection in the presence of ICI (e.g., maximum likelihood, minimum mean-squared error, or zero-forcing methods) become prohibitively complex. To tackle this problem, we propose a detection strategy based on optimal linear pre-processing and iterative MMSE estimation. In addition to significant computational savings, simulation results indicate performance that far surpasses the linear MMSE detector.

 Date 04/22/2003 Time-Place 18:00 @ EE West 209 Presenter Group Discussion Title Joint Power and Rate Control in Multiaccess Systems with Multirate Services Reference Karakayali M. K., Yates R., Razumov L. "Joint Power and Rate Control in Multiaccess Systems with Multirate Services", Proceedings of CISS'03, Baltimore, MD., March 2003

 Date 05/06/2003 Time-Place 18:00 @ EE West 209 Presenter Group Discussion Title Performance enhancement of multiuser MIMO wireless communication systems Reference Wong, Kai-Kit, Murch, R.D., Letaief, K.B. "Performance enhancement of multiuser MIMO wireless communication systems". IEEE Transactions on Communications, Jan 2001, 49(1), pp. 195-206.

 Date 06/17/2003 Time-Place 09:00 @ EE West 209 Presenter Group Discussion Title A framework for uplink power control in cellular radio systems Reference Yates, R.D. "A framework for uplink power control in cellular radio systems". IEEE Journal on Selected Areas in Communications, Sept. 1995, 13(7), pp. 1341-1347.

 Date 07/01/2003, 07/08/2003 Time-Place 09:00 @ EE West 209 Presenter Group Discussion Title Capacity limits of MIMO channels Reference Goldsmith, A., Jafar, S.A., Jindal, N., Vishwanath, S. "Capacity limits of MIMO channels", IEEE Journal on Selected Areas in Communications, June 2003, 21(5), pp. 684-702.

 Date 07/01/2003 Time-Place 14:00 @ EE East129 Presenter Onder Filiz - M.S. Thesis Defense Title Rank Constrained Temporal-Spatial Filtering for CDMA Systems Abstract Efficient interference suppression techniques are needed to maximally utilize the potential gains of code division multiple access (CDMA) systems. In this thesis, a receiver structure which combines multiuser detection (temporal filtering) and receiver beamforming (spatial filtering) is considered. The receiver is modelled as a linear matrix filter and the minimum mean-squared error (MMSE) is used as the performance criterion. Motivated by the high complexity of the optimum receiver, we propose rank constrained temporal-spatial filters which are simpler and near-optimum. The mean-square error (MSE) is minimized subject to a structural constraint, using an iterative algorithm based on alternating minimization. The constraint on the receiver matrix filter narrows down the solution space, which helps to solve the optimization problem more efficiently. The constraint can be set appropriately by the system designer to achieve the desired trade-off between performance and complexity. Numerical results indicate that a performance close to that of the optimum filter can be achieved with a simple iterative structure, even in highly loaded systems. A new adaptive scheme is proposed which is a combination of the alternating minimization and the least mean squares (LMS) methods and the convergence properties are investigated. The approach is then extended to multiuser systems with multipath channels, with the resulting receivers being able to utilize the inherent multipath diversity.

 Date 08/27/2003 Time-Place 10:00 @ EE East 129 Presenter Atul Divakaran - M.S. Paper Defense Title An Adaptive Channel Allocation Strategy for Wireless Multimedia Qos - "Best-Fit" Abstract Third generation wireless standards are aimed to enable the launch of numerous broadband multimedia services with high Quality of Service (QoS). It is worthwhile to note that with the advent of third generation cellular technologies, comes the need for large scale system changes such as carriers with greater bandwidth, complex modulation techniques, new hardware and software installations etc. and hence, in a sense, there is a need to reinvent the wheel. This paper discusses an adaptive channel allocation algorithm, based on existing 2.5 G standards, for efficient and fair utilization of precious wireless network resources, without the need to reinvent the wheel. This resource (channel) allocation scheme, called “Best-Fit”, is particularly suited to TDMA based packet switched data bearers, and provides certain advantages over its contemporary 2.5 G (and 2G) standards such as GPRS, HSCSD (and GSM). The goal of this algorithm is to share the available wireless bandwidth between the maximum number of connections, and offer the maximum QoS to each of them depending on the connections state. It is able to support more users on the same time slot architecture of GPRS and HSCSD with lower blocking probabilities and higher total throughput attainable for all users combined, without drastically reducing the individual throughputs of existing users.

 Date 10/03/2003 Time-Place 10:30 @ EE East 129 Presenter Group Discussion Title Optimum Power Control For CDMA with Deterministic Sequences in Fading Channels Reference Kaya, O., Ulukus, S. "Optimum Power Control for CDMA with Deterministic Sequences in Fading Channels", IEEE Transactions on Information Theory, submitted December 2002.

 Date 10/23/2003 Time-Place 16:15 @ Willard 367 (EE Colloquium) Presenter Dr. Milica Stojanovic,Massachusettes Institute of Technology, Cambridge, MA Title High Speed Wireless Underwater Communications Abstract Wireless information transmission through the ocean is one of the enabling technologies for the development of future ocean-observation systems, whose applications include gathering of scientific data, pollution control, climate recording, detection of objects on the ocean floor, and transmission of images from remote sites. Implicitly, wireless signal transmission is crucial for control of autonomous underwater vehicles (AUVs) which will serve as mobile nodes in the future information networks of distributed underwater sensors. Wireless communication provides advantages of collecting data without the need to retrieve instruments, and maneuvering underwater vehicles and robots without the burden of cables. Acoustic wireless communications are governed by three factors: limited bandwidth, time-varying multipath propagation, and low speed of sound in the ocean. Together, these factors result in a communication channel of poor quality and high latency. To achieve high information throughput on such channels, coherent modulation/detection techniques, such as PSK and QAM, must be considered because of their bandwidth efficiency. Signal processing methods for underwater acoustic channels are based on the same principles as those for radio communications; yet, they differ substantially due to the amount of time-spreading introduced by the channel, as well as frequency-spreading introduced by the system mobility. Signal processing methods for high speed underwater communications have been a topic of extensive research over the past decade, resulting in the development of first underwater acoustic modems. In this presentation, we focus on signal processing methods of adaptive equalization, digital synchronization, and diversity combining for bandwidth-efficient underwater communication systems. We also address methods for multiple-access underwater communications, which form the basis of future underwater wireless communication networks. The performance of various techniques is discussed through a series of experimental results, which include transmission over distances ranging from a few kilometers in shallow water to hundreds of kilometers in deep water, at highest bit-rates demonstrated to date.

 Date 10/31/2003 Time-Place 10:30 @ EE East 129 Presenter Group Discussion Title Optimum Sequence Multisets For Synchronous Code-Division Multiple-Access Channels Reference Rupf, M., Massey, J.L. "Optimum Sequence Multisets For Synchronous Code-Division Multiple-Access Channels", IEEE Transactions on Information Theory, July 1994, 40(4), pp. 1261-1266.

 Date 11/7/2003 Time-Place 10:30 @ EE West 111C Presenter Changyoon Oh Title Further Results on Adaptive CDMA Cell Sectorization with Linear Multiuser Detection Abstract We consider the adaptive sectorization problem for uplink CDMA system under the imperfect directional antenna. Specifically, given the number of sectors and terminal locations, and assuming base station employs linear multiuser detection, we investigate how to appropriately sectorize the cell, such that the total transmit power is minimized, while each user has acceptable quality of service. We have observed uplink/downlink duality. Then, we extend this problem to the imperfect directional antenna. We propose MMSE power control to suppress both the intrasector interference and the intersector interference. As the optimum solution for arbitrary signature sets may have high complexity, we also propose simpler suboptimum methods. The results suggest that by intelligently combining adaptive cell sectorization, power control and temporal linear multiuser detection, we are able to increase the uplink user capacity of the cell. We provide numerical results showing the robustness of optimum sectorization against Gaussian channel estimation error.

 Date 01/20/2004, 02/05/2004, 02/12/2004, 02/26/2004 Time-Place 16:30 @ EE West 209, 17:30@ EE West 209, 17:30@ EE East 129, 17:30@ EE East 129 Presenter Girish Khandelwal Title Short Range Wireless Systems Abstract Short range wireless refers to a group of technologies that enable wireless data networking across distances between one and a few hundred meters. In recent years, the short range wireless marketplace has expanded to a wide base of technologies and standards supporting a diverse range of requirements and applications. These applications are driven by the cost of solution, data rates, frequency band, power requirements, interference with other technologies and target client base. The presentation will focus on the technologies in this space. Essentially, it will touch upon the basic specifications and the working model of these technologies in the physical model. Technologies discussed are: Bluetooth, IEEE802.11, Ultra Wide Band (2 Proposals), IrDA, RFID and RTLS.

 Date 03/02/2004 Time-Place 16:15 @ EE West 225 (E/M Seminar (organized by Prof. Mittra)) Presenter Aylin Yener Title Performance Enhancement of CDMA Systems Using Smart Antennas: Joint temporal-spatial designs Reference Talk slides

 Date 03/15/2004 Time-Place 17:00 @ EE East 129 Presenter Semih Serbetli Title Signature and Beamformer Design for MIMO-CDMA with Various Levels of Feedback Abstract We investigate the signature and beamformer design problem for multiple antenna CDMA (MIMO-CDMA) systems with sum capacity as the performance metric. We first find upper bounds for the sum capacity by relaxing a set of structural constraints. We construct an iterative algorithm to find the jointly optimum temporal signatures and transmit beamformers under the assumption of perfect temporal signature and transmit beamforming feedback. Next, motivated by milder feedback requirements, a low complexity orthogonal temporal signature assignment algorithm is presented that aims to approach the capacity upper bound for given transmit beamformers. The transmit beamformers can be shaped depending on the channel state information available at the transmitter. We next investigate the cases of various different levels of feedback, and combine the proposed orthogonal temporal signature assignment algorithm with antenna selection, eigen transmit beamforming and perfectly controlled transmit beamforming models. We observe that as the available feedback level is increased, the performance of the algorithms approach the upper bounds developed. In particular, a substantial sum capacity gain is attained when the individual channel state information is available at the transmitter side.

 Date 03/15/2004 Time-Place 17:40 @ EE East 129 Presenter Semih Serbetli Title The Effect of Channel Estimation on Transceiver Design for MIMO Systems with QoS Constraints Abstract We investigate the transceiver design problem for a multiple input multiple output (MIMO) link considering the effect of channel estimation. We work with the total mean squared error as the performance measure and develop transceiver structures considering the effect of maximum likelihood (ML) channel estimation. The proposed transceiver structures are optimum in the sense of minimizing the total MSE and distributing the MSE equally among the parallel data streams. Next, an upper bound for the number of data streams that can be transmitted for a given target MSE is derived. Motivated by the substantial effect the channel estimation process can have on the system performance, we next investigate the problem of how the MIMO link should distribute its total available power between power expended for channel estimation versus data transmission. The optimum power allocation between the training sequences for ML estimation of the channel and data transmission is derived given the total power budget. Numerical results supporting the analysis and the power allocation schemes are presented.

 Date 03/25/2004 Time-Place 16:15 @ Willard 267 (EE Colloquium) Presenter Prof. Sennur Ulukus, University of Maryland, College Park Title Optimum Resource Allocation and Signalling Schemes in Fading CDMA Channels Abstract Fading may be an important limiting factor in wireless communication networks unless appropriate resource allocation is applied to exploit the variations in the channel gains to the advantage of the network capacity. The resources that we concentrate on allocating optimally in this talk are the transmit powers of the users. We also determine the optimum signalling directions by choosing the transmit waveforms (signature sequences) of the users. We will first focus on the power control problem for a given fixed set of signature sequences, and propose an iterative waterfilling algorithm that converges to the power allocation that maximizes the ergodic sum capacity of the network. We will then talk about the jointly optimum power control and signature sequence assignment problem, and present a closed form solution as well as an iterative algorithm that converges to the optimum configuration.

 Date 04/06/2004 Time-Place 17:00 @ EE West 206 Presenter Min Chen Title A tour of detection and decoding for coded CDMA Abstract In the past decades, increasing attention has been devoted to the development of multi-user detection technologies for combating the multi-user interference. In recent years, much attention has been paid to joint multi-user detection and decoding which exploits error control coding to aid in multi-user detection. In this presentation, the BCJR algorithm, an optimal decoding method which minimizes the symbol error probability, is introduced. Then some multi-user receivers for coded CDMA systems are discussed.

 Date 04/27/2004 Time-Place 17:00 @ EE West 206 Presenter Kyounghwan Lee Title Cooperative Diversity in Wireless Networks Abstract In wireless networks, signal fading resulting from multi-path propagation is a severe form of interference that can be mitigated by the use of diversity. Cooperative diversity is a network-based diversity (not rely on physical arrays) achieved by exploiting space diversity available through cooperating terminals' relaying signals. Unlike conventional relaying networks where the relay nodes are pure forwarders in a relay chain, the cooperative relaying consider combining of repeated signals in destination node for averaging out fading effect and improving the performance. The presentation will discuss the outage performance of the various cooperative diversity protocols.