Synthesis of Gaussian Trees with Correlation Sign Ambiguity: An Information Theoretic Approach

In latent Gaussian trees the pairwise correlation signs between the variables are intrinsically unrecoverable. Such information is vital since it completely determines the direction in which two variables are associated. In this work, we resort to information theoretical approaches to achieve two fundamental goals: First, we quantify the amount of information loss due to unrecoverable sign information. Second, we show the importance of such information in determining the maximum achievable rate region, in which the observed output vector can be synthesized, given its probability density function. In particular, we model the graphical model as a communication channel and propose a new layered encoding framework to synthesize observed data using upper layer Gaussian inputs and independent Bernoulli correlation sign inputs from each layer. We find the achievable rate region for the rate tuples of multi-layer latent Gaussian messages to synthesize the desired observables.Comment: 14 pages, 9 figures, part of this work is submitted to Allerton 2016 conference, UIUC, IL, US

Half-duplex active eavesdropping in fast-fading channels: A block-markov wyner secrecy encoding scheme

In this paper, we study the problem of half-duplex active eavesdropping in fast-fading channels. The active eavesdropper is a more powerful adversary than the classical eavesdropper. It can choose between two functional modes: eavesdropping the transmission between the legitimate parties (Ex mode), and jamming it (Jx mode)-the active eavesdropper cannot function in full duplex mode. We consider a conservative scenario, when the active eavesdropper can choose its strategy based on the legitimate transmitter-receiver pair\u27s strategy, and thus, the transmitter and legitimate receiver have to plan for the worst. We show that conventional physical-layer secrecy approaches perform poorly (if at all), and we introduce a novel encoding scheme, based on very limited and unsecured feedback-the Block-Markov Wyner encoding scheme-which outperforms any schemes currently available. © 2012 IEEE

Jamming games in fast-fading wireless channels

In this paper, we adopt outage probability (A- capacity) in fast fading channels as a pay-off function in a zero- sum game between a legitimate transceiver pair and an uncorre- lated Gaussian jammer. The transmitter aims at minimizing the outage probability, while the jammer attempts to maximize the outage probability. We consider both peak (over each codeword) and average (over all codewords) power constraints. For peak power constraints, a transmission rate is either supported by the system, or if too large, causes the whole transmission to fail. By imposing average power constraints, large rates can be supported at the cost of positive probability of codeword error. Maxmin and minimax power control strategies are developed, which show that no Nash equilibrium of pure strategies exists under average power constraints. © 2008 IEEE

Mixed anti-jamming strategies in fixed-rate wireless systems over fast fading channels

We study the problem of jamming in a fixed-rate wireless system over fast fading channels. Both transmitter and jammer are subject to long term (average) power constraints. Our jamming problem is formulated as a zero-sum game with the probability of outage as pay-off function and power control functions as strategies. We consider both the case with full channel state information (CSI) at all parties (available from a training and feedback protocol), and the case when no CSI is fed back from the receiver. Nash equilibria of mixed strategies are found by solving the generalized form of an older problem dated back to Bell and Cover (1]. © 2009 IEEE

Active eavesdropping in fast fading channels

In this paper we study the problem of active eavesdropping in fast fading channels. The active eavesdropper is a more powerful adversary than the classical eavesdropper. It can choose between two functional modes: eavesdropping the transmission between the legitimate parties (Ex mode), and jamming it (Jx mode) the active eavesdropper cannot function in full duplex mode. In this paper we only consider the best-case scenario, when the transmitter knows the eavesdropper\u27s strategy in advance - and hence can adaptively choose an encoding strategy. We show that, even under these most optimistic assumptions, an active eavesdropper can induce moderate to severe degradation of the achievable secrecy rate. ©2009 IEEE