Secure Communications for the Two-user Broadcast Channel with Random Traffic

In this work, we study the stability region of the two-user broadcast channel (BC) with bursty data arrivals and security constraints. We consider the scenario, where one of the receivers has a secrecy constraint and its packets need to be kept secret from the other receiver. This is achieved by employing full-duplexing at the receiver with the secrecy constraint, so that it transmits a jamming signal to impede the reception of the other receiver. In this context, the stability region of the two-user BC is characterized for the general decoding case. Then, assuming two different decoding schemes the respective stability regions are derived. The effect of self-interference due to the full-duplex operation on the stability region is also investigated. The stability region of the BC with a secrecy constraint, where the receivers do not have full duplex capability can be obtained as a special case of the results derived in this paper. In addition, the paper considers the problem of maximizing the saturated throughput of the queue, whose packets does not require to be kept secret under minimum service guarantees for the other queue. The results provide new insights on the effect of the secrecy constraint on the stability region of the BC. In particular, it is shown that the stability region with secrecy constraint is sensitive to the coefficient of self-interference cancelation under certain cases.Comment: Submitted for journal publicatio

Multiple Unicast Capacity of 2-Source 2-Sink Networks

We study the sum capacity of multiple unicasts in wired and wireless multihop networks. With 2 source nodes and 2 sink nodes, there are a total of 4 independent unicast sessions (messages), one from each source to each sink node (this setting is also known as an X network). For wired networks with arbitrary connectivity, the sum capacity is achieved simply by routing. For wireless networks, we explore the degrees of freedom (DoF) of multihop X networks with a layered structure, allowing arbitrary number of hops, and arbitrary connectivity within each hop. For the case when there are no more than two relay nodes in each layer, the DoF can only take values 1, 4/3, 3/2 or 2, based on the connectivity of the network, for almost all values of channel coefficients. When there are arbitrary number of relays in each layer, the DoF can also take the value 5/3 . Achievability schemes incorporate linear forwarding, interference alignment and aligned interference neutralization principles. Information theoretic converse arguments specialized for the connectivity of the network are constructed based on the intuition from linear dimension counting arguments.Comment: 6 pages, 7 figures, submitted to IEEE Globecom 201

Capacity Bounds for Two-Hop Interference Networks

This paper considers a two-hop interference network, where two users transmit independent messages to their respective receivers with the help of two relay nodes. The transmitters do not have direct links to the receivers; instead, two relay nodes serve as intermediaries between the transmitters and receivers. Each hop, one from the transmitters to the relays and the other from the relays to the receivers, is modeled as a Gaussian interference channel, thus the network is essentially a cascade of two interference channels. For this network, achievable symmetric rates for different parameter regimes under decode-and- forward relaying and amplify-and-forward relaying are proposed and the corresponding coding schemes are carefully studied. Numerical results are also provided.Comment: 8 pages, 5 figures, presented in Allerton Conference'0

Gaussian Multiple Access via Compute-and-Forward

Lattice codes used under the Compute-and-Forward paradigm suggest an alternative strategy for the standard Gaussian multiple-access channel (MAC): The receiver successively decodes integer linear combinations of the messages until it can invert and recover all messages. In this paper, a multiple-access technique called CFMA (Compute-Forward Multiple Access) is proposed and analyzed. For the two-user MAC, it is shown that without time-sharing, the entire capacity region can be attained using CFMA with a single-user decoder as soon as the signal-to-noise ratios are above $1+\sqrt{2}$. A partial analysis is given for more than two users. Lastly the strategy is extended to the so-called dirty MAC where two interfering signals are known non-causally to the two transmitters in a distributed fashion. Our scheme extends the previously known results and gives new achievable rate regions.Comment: to appear in IEEE Transactions on Information Theor

Lattice Codes for Many-to-One Interference Channels With and Without Cognitive Messages

A new achievable rate region is given for the Gaussian cognitive many-to-one interference channel. The proposed novel coding scheme is based on the compute-and-forward approach with lattice codes. Using the idea of decoding sums of codewords, our scheme improves considerably upon the conventional coding schemes which treat interference as noise or decode messages simultaneously. Our strategy also extends directly to the usual many-to-one interference channels without cognitive messages. Comparing to the usual compute-and-forward scheme where a fixed lattice is used for the code construction, the novel scheme employs scaled lattices and also encompasses key ingredients of the existing schemes for the cognitive interference channel. With this new component, our scheme achieves a larger rate region in general. For some symmetric channel settings, new constant gap or capacity results are established, which are independent of the number of users in the system.Comment: To appear in IEEE Transactions on Information Theor