Interplay Between Delayed CSIT and Network Topology for Secure MISO BC

We study the problem of secure transmission over a Gaussian two-user multi-input single-output (MISO) broadcast channel under the assumption that links connecting the transmitter to the two receivers may have unequal strength statistically. In addition to this, the state of the channel to each receiver is conveyed in a strictly causal manner to the transmitter. We focus on a two state topological setting of strong v.s. weak links. Under these assumptions, we first consider the MISO wiretap channel and establish bounds on generalized secure degrees of freedom (GSDoF). Next, we extend this model to the two-user MISO broadcast channel and establish inner and outer bounds on GSDoF region with different topology states. The encoding scheme sheds light on the usage of both resources, i.e., topology of the model and strictly causal channel state information at the transmitter (CSIT); and, allows digitization and multi-casting of overheard side information, while transmitting confidential message over the stronger link. Furthermore, for a special class of channels, we show that the established bounds agree and so we characterize the sum GSDoF.Comment: Under submission. arXiv admin note: text overlap with arXiv:1503.0633

Capacity Bounds and a Certain Capacity Region for Special Three-Receiver Broadcast Channels with Side Information

The fact that the results for 2-receiver broadcast channels (BCs) are not generalized to the 3-receiver ones is of information theoretical importance. In this paper we study two classes of discrete memoryless BCs with non-causal side information (SI), i.e. multilevel BC (MBC) and 3-receiver less noisy BC. First, we obtain an achievable rate region and a capacity outer bound for the MBC. Second, we prove a special capacity region for the 3-receiver less noisy BC. Third, the obtained special capacity region for the 3-receiver less noisy BC is extended to continuous alphabet fading Gaussian version. It is worth mentioning that the previous works are special cases of our works.Comment: 24 pages, 2 figures, Submitted to IET Communications Journal for possible publicatio

Capacity Bounds for Wireless Ergodic Fading Broadcast Channels with Partial CSIT

The two-user wireless ergodic fading Broadcast Channel (BC) with partial Channel State Information at the Transmitter (CSIT) is considered. The CSIT is given by an arbitrary deterministic function of the channel state. This characteristic yields a full control over how much state information is available, from perfect to no information. In literature, capacity derivations for wireless ergodic fading channels, specifically for fading BCs, mostly rely on the analysis of channels comprising of parallel sub-channels. This technique is usually suitable for the cases where perfect state information is available at the transmitters. In this paper, new arguments are proposed to directly derive (without resorting to the analysis of parallel channels) capacity bounds for the two-user fading BC with both common and private messages based on the existing bounds for the discrete channel. Specifically, a novel approach is developed to adapt and evaluate the well-known UV-outer bound for the Gaussian fading channel using the entropy power inequality. Our approach indeed sheds light on the role of broadcast auxiliaries in the fading channel. It is shown that the derived outer bound is optimal for the channel with perfect CSIT as well as for some special cases with partial CSIT. Our outer bound is also directly applicable to the case without CSIT which has been recently considered in several papers. Next, the approach is developed to analyze for the fading BC with secrecy. In the case of perfect CSIT, a full characterization of the secrecy capacity region is derived for the channel with common and confidential messages. This result completes a gap in a previous work by Ekrem and Ulukus. For the channel without common message, the secrecy capacity region is also derived when the transmitter has access only to the degradedness ordering of the channel.Comment: 20 page

On Index Coding in Noisy Broadcast Channels with Receiver Message Side Information

This letter investigates the role of index coding in the capacity of AWGN broadcast channels with receiver message side information. We first show that index coding is unnecessary where there are two receivers; multiplexing coding and superposition coding are sufficient to achieve the capacity region. We next show that, for more than two receivers, multiplexing coding and superposition coding alone can be suboptimal. We give an example where these two coding schemes alone cannot achieve the capacity region, but adding index coding can. This demonstrates that, in contrast to the two-receiver case, multiplexing coding cannot fulfill the function of index coding where there are three or more receivers.Comment: Authors' final version (to appear in IEEE Communications Letters

On the Capacity of Interference Channels with Degraded Message sets

This paper is motivated by a sensor network on a correlated field where nearby sensors share information, and can thus assist rather than interfere with one another. A special class of two-user Gaussian interference channels (IFCs) is considered where one of the two transmitters knows both the messages to be conveyed to the two receivers (called the IFC with degraded message sets). Both achievability and converse arguments are provided for this scenario for a class of discrete memoryless channels with weak interference. For the case of the Gaussian weak interference channel with degraded message sets, optimality of Gaussian inputs is also shown, resulting in the capacity region of this channel

Compound Multiple Access Channels with Partial Cooperation

A two-user discrete memoryless compound multiple access channel with a common message and conferencing decoders is considered. The capacity region is characterized in the special cases of physically degraded channels and unidirectional cooperation, and achievable rate regions are provided for the general case. The results are then extended to the corresponding Gaussian model. In the Gaussian setup, the provided achievable rates are shown to lie within some constant number of bits from the boundary of the capacity region in several special cases. An alternative model, in which the encoders are connected by conferencing links rather than having a common message, is studied as well, and the capacity region for this model is also determined for the cases of physically degraded channels and unidirectional cooperation. Numerical results are also provided to obtain insights about the potential gains of conferencing at the decoders and encoders.Comment: Submitted to IEEE Transactions on Information Theor

MIMO Broadcast Channel with an Unknown Eavesdropper: Secrecy Degrees of Freedom

We study a multi-antenna broadcast channel with two legitimate receivers and an external eavesdropper. We assume that the channel matrix of the eavesdropper is unknown to the legitimate terminals but satisfies a maximum rank constraint. As our main result we characterize the associated secrecy degrees of freedom for the broadcast channel with common and private messages. We show that a direct extension of the single-user wiretap codebook does not achieve the secrecy degrees of freedom. Our proposed optimal scheme involves decomposing the signal space into a common subspace, which can be observed by both receivers, and private subspaces which can be observed by only one of the receivers, and carefully transmitting a subset of messages in each subspace. We also consider the case when each user's private message must additionally remain confidential from the other legitimate receiver and characterize the s.d.o.f.\ region in this case.Comment: Accepted to IEEE Transactions on Communication

On the Secrecy Capacity of the Broadcast Wiretap Channel with Limited CSI Feedback

In this paper, we investigate the problem of secure broadcasting over block-fading channels with limited channel knowledge at the transmitter. More particularly, we analyze the effect of having imperfect channel state information (CSI) via a finite rate feedback on the throughput of a broadcast channel where the transmission is intended for multiple legitimate receivers in the presence of an eavesdropper. First, we partially characterize the ergodic secrecy capacity of the system when the source broadcasts the same information to all the receivers, i.e., common message transmission. Then, we look at the independent messages case, where the transmitter broadcasts multiple independent messages to the legitimate receivers. For this case, we present lower and upper bounds on the ergodic secrecy sum-capacity. In both scenarios, we show that the proposed lower and upper bounds coincide asymptotically as the capacity of the feedback links becomes large, hence, fully characterizing the secrecy capacity in this case.Comment: 8 pages, reference adde

Hybrid Digital-Analog Codes for Source-Channel Broadcast of Gaussian Sources over Gaussian Channels

The problem of broadcasting a parallel Gaussian source over an additive white Gaussian noise broadcast channel under the mean-squared error distortion criterion is studied. A hybrid digital-analog coding strategy which combines source coding with side information, channel coding with side information, layered source coding, and superposition broadcast channel coding is presented. When specialized to the open problem of broadcasting a white Gaussian source over an additive white Gaussian noise broadcast channel with bandwidth mismatch which has been the subject of several previous investigations, this coding scheme strictly improves on the state-of-the-art.Comment: 24 pages, 9 figure

Relay Strategies Based on Cross-Determinism for the Broadcast Relay Channel

We consider a two-user Gaussian multiple-input multiple-output (MIMO) broadcast channel with a common multiple-antenna relay, and a shared digital (noiseless) link between the relay and the two destinations. For this channel, this paper introduces an asymptotically sum-capacity-achieving quantize-and-forward (QF) relay strategy. Our technique to design an asymptotically optimal relay quantizer is based on identifying a cross-deterministic relation between the relay observation, the source signal, and the destination observation. In a relay channel, an approximate cross deterministic relation corresponds to an approximately deterministic relation, where the relay observation is to some extent a deterministic function of the source and destination signals. We show that cross determinism can serve as a measure for quantization penalty. By identifying an analogy between a deterministic broadcast relay channel and a Gaussian MIMO relay channel, we propose a three-stage dirty paper coding strategy, along with receiver beamforming and quantization at the relay, to asymptotically achieve an extended achievable rate region for the MIMO broadcast channel with a common multiple-antenna relay.Comment: Presented at 42nd Allerton Conference on Communications, Control, and Computing, Allerton, IL, 201