An Achievable Rate Region for Three-Pair Interference Channels with Noise

An achievable rate region for certain noisy three-user-pair interference channels is proposed. The channel class under consideration generalizes the three-pair deterministic interference channel (3-DIC) in the same way as the Telatar-Tse noisy two-pair interference channel generalizes the El Gamal-Costa injective channel. Specifically, arbitrary noise is introduced that acts on the combined interference signal before it affects the desired signal. This class of channels includes the Gaussian case. The rate region includes the best-known inner bound on the 3-DIC capacity region, dominates treating interference as noise, and subsumes the Han-Kobayashi region for the two-pair case.Comment: 9 pages, 3 figures; abbreviated version to be presented at IEEE International Symposium on Information Theory (ISIT 2012

A Unified Approach for Network Information Theory

In this paper, we take a unified approach for network information theory and prove a coding theorem, which can recover most of the achievability results in network information theory that are based on random coding. The final single-letter expression has a very simple form, which was made possible by many novel elements such as a unified framework that represents various network problems in a simple and unified way, a unified coding strategy that consists of a few basic ingredients but can emulate many known coding techniques if needed, and new proof techniques beyond the use of standard covering and packing lemmas. For example, in our framework, sources, channels, states and side information are treated in a unified way and various constraints such as cost and distortion constraints are unified as a single joint-typicality constraint. Our theorem can be useful in proving many new achievability results easily and in some cases gives simpler rate expressions than those obtained using conventional approaches. Furthermore, our unified coding can strictly outperform existing schemes. For example, we obtain a generalized decode-compress-amplify-and-forward bound as a simple corollary of our main theorem and show it strictly outperforms previously known coding schemes. Using our unified framework, we formally define and characterize three types of network duality based on channel input-output reversal and network flow reversal combined with packing-covering duality.Comment: 52 pages, 7 figures, submitted to IEEE Transactions on Information theory, a shorter version will appear in Proc. IEEE ISIT 201

Is non-unique decoding necessary?

In multi-terminal communication systems, signals carrying messages meant for different destinations are often observed together at any given destination receiver. Han and Kobayashi (1981) proposed a receiving strategy which performs a joint unique decoding of messages of interest along with a subset of messages which are not of interest. It is now well-known that this provides an achievable region which is, in general, larger than if the receiver treats all messages not of interest as noise. Nair and El Gamal (2009) and Chong, Motani, Garg, and El Gamal (2008) independently proposed a generalization called indirect or non-unique decoding where the receiver uses the codebook structure of the messages to only uniquely decode its messages of interest. Non-unique (indirect) decoding has since been used in various scenarios. The main result in this paper is to provide an interpretation and a systematic proof technique for why indirect decoding, in all known cases where it has been employed, can be replaced by a particularly designed joint unique decoding strategy, without any penalty from a rate region viewpoint

On Cyclic Delay Diversity OFDM Based Channels

Orthogonal Frequency Division Multiplexing, so called OFDM, has found a prominent place in various wireless systems and networks as a method of encoding data over multiple carrier frequencies. OFDM-based communication systems, however, lacking inherent diversity, are capable of benefiting from different spatial diversity schemes. One such scheme, Cyclic Delay Diversity (CDD) is a method to provide spatial diversity which can be also interpreted as a Space-Time Block Coding (STBC) step. The main idea is to add more transmit antennas at the transmitter side sending the same streams of data, though with differing time delays. In [1], the capacity of a point-to-point OFDM-based channel with CDD is derived for inputs with Gaussian and discrete constellations. In this dissertation, we use the same approach for an OFDM-based single-input single-output (SISO) two-user interference channel (IC). In our model, at the receiver side, the interference is treated as noise. Moreover, since the channel is time-varying (slow-fading), the Shannon capacity in the strict sense is not well-defined, so the expected value of the instantaneous capacity is calculated instead. Furthermore, the channel coefficients are unknown to the transmitters. Thus, in this setting, the probability of outage emerges as a reasonable performance measure. Adding an extra antenna in the transmitters, the SISO IC turns into an MISO IC, which results in increasing the diversity. Both the continuous and discrete inputs are studied and it turns out that decoding interference is helpful in some cases. The results of the simulations for discrete inputs indicate that there are improvements in terms of outage capacity compared to the ICs with single-antenna transmitters