Our publications cover several aspects of information theory, wireless communication, data compression and network security. We highlight some selected recent papers below, that are representative of these topics. Please look at a more detailed list sorted as:

Our work has also resulted in several issued patents. There have been several Ph.D. theses that have resulted from the research, which can also be found here.

  1. Abstract:
    Wireless network topologies change over time and maintaining routes requires frequent updates. Updates are costly in terms of consuming throughput available for data transmission, which is precious in wireless networks. In this paper, we ask whether there exist low-overhead schemes that produce near-optimal routes. We show that random geometric graphs and variants have a nice property that they are doubling metric spaces, with high probability. This enables us to design hierarchical routing schemes with provable performance that account for the user mobility and scale well with network size.
  2. Download: secret_keygen.pdf 
    Abstract:
    We study the secret-key capacity in a joint source-channel coding setup-the terminals are connected over a discrete memoryless channel and have access to side information, modelled as a pair of discrete memoryless source sequences. As our main result, we establish the upper and lower bounds on the secret-key capacity. In the lower bound expression, the equivocation terms of the source and channel components are functionally additive even though the coding scheme generates a single secret-key by jointly taking into account the source and channel equivocations. Our bounds coincide, thus establishing the capacity, when the underlying wiretap channel can be decomposed into a set of independent, parallel, and reversely degraded channels. For the case of parallel Gaussian channels and jointly Gaussian sources we show that Gaussian codebooks achieve the secret-key capacity. In addition, when the eavesdropper also observes a correlated side information sequence, we establish the secret-key capacity when both the source and channel of the eavesdropper are a degraded version of the legitimate receiver. We finally also treat the case when a public discussion channel is available, propose a separation based coding scheme, and establish its optimality when the channel output symbols of the legitimate receiver and eavesdropper are conditionally independent given the input.
  3. Download: on Arxiv 
    Abstract:
    We provide a complete characterization of the achievable distortion region for the problem of sending a bivariate Gaussian source over bandwidth-matched Gaussian broadcast channels, where each receiver is interested in only one component of the source. This setting naturally generalizes the simple single Gaussian source bandwidth-matched broadcast problem for which the uncoded scheme is known to be optimal. We show that a hybrid scheme can achieve the optimum for the bivariate case, but neither an uncoded scheme alone nor a separation-based scheme alone is sufficient. We further show that in this joint source channel coding setting, the Gaussian scenario is the worst scenario among the sources and channel noises with the same covariances.
  4. Abstract:
    In this paper we study two-stage Gaussian relay-interference networks where there are weak cross-links, causing the networks to behave like a chain of Z Gaussian channels. Our main result is an approximate characterization of the capacity region for such networks. We propose a new interference management scheme, termed interference neutralization, which is implemented using structured lattice codes. This scheme allows for over-the-air interference removal, without the transmitters having complete access the interfering signals.
  5. Abstract:
    This paper approximately resolves the information flow over wireless (Gaussian) relay networks to within a constant number of bits. It introduced the linear deterministic model and established a max-flow min-cut result for linear deterministic networks. The insights from the deterministic approach led to the approximate max-flow min-cut characterization for noisy Gaussian networks, through the introduction of a new relaying strategy called quantize-map-forward (QMF).
  6. Abstract:
    Approximately solves symmetric Gaussian multiple description problem to within a bit, by sandwiching the MD rate region between two polytopes separated by at most a fraction of a bit.
  7. Abstract:
    This paper introduces diversity embedded codes, which are space-time codes that simultaneously give different levels of diversity protection to different information streams. The paper provides algebraic constructions based on binary codes designed for rank distance and lifts them to the complex domain. It also gives several example of linear diversity embedded codes.
  8. Download: finbuf.pdf 
    Abstract:
    This paper was motivated by the transmission of information over finite buffer channels. Analyzing the capacity of such channels naturally led us to the study of deletion channels. In deletion channels, in contrast to erasure channels, symbols of the transmitted sequence are removed, and the receiver does not know which symbols have been deleted. This was a classic problem from the 1960s in the context of modeling synchronization errors. This paper gave the best known (at the time of publication) lower bounds to capacity of deletion channels since the 1960s. It also studied erasure channels with arbitrary memory in the erasure process. It showed that even when the erasure process has memory, feedback does not increase the capacity.
  9. Download: gc.pdf 
    Abstract:
    This paper studies the scaling capacity of asymptotically large wireless networks. It shows that even restricted one-dimensional mobility allows the total capacity of the wireless network scales linearly with the number of nodes. This implies that per-node capacity scales as a constant, demonstrating that even restricted mobility can be used to provide non-diminishing throughput for large-scale wireless networks. This is demonstrated by utilizing the multi-user diversity which is instantiated through node-mobility.
  10. Download: worstnoise.pdf 
    Abstract:
    This paper started with a simple question: is the maximum entropy noise the worst noise for additive channels? In the case of scalar channels with a power constraint on the noise, this is true, as is well known. However, we show that in the vector case, with covariance constraints, the answer is yes and no. Yes, if the transmit power is large enough and no otherwise. Along the way we give a solution to the mutual information game with covariance constraints and show that Gaussian solutions form saddle points, but there could also be other saddlepoints. We also demonstrate that the information rates can be achieved using mismatched (Gaussian) decoders.

Ph.D. theses