Coding schemes for deterministic interference channels [electronic resource]
Keywords: Electrical Engineering

One of the canonical unsolved problems in network information theory is to find the capacity region of the interference channel. The problem is motivated by today's wireless communication systems which have experienced a steep growth in participant density and thus increasingly operate in the interference-limited regime. Data rates are no longer limited by propagation path loss and thermal noise, but instead, by simultaneous transmissions in the same frequency band. The interference channel models such concurrent communication among several transmitter-receiver pairs using a shared medium. Its capacity region describes the optimal trade-off between simultaneously achievable data rates. While considerable progress has been made in characterizing the capacity region for the case with two sender-receiver pairs, much less is known for interference channels with three or more user pairs. This dissertation contributes to this area by investigating a class of deterministic (noise-free) interference channels with three user pairs. A series of three coding schemes and corresponding achievable rate regions is developed, each of which subsumes and improves upon its predecessor. As a baseline, a first transmission scheme is considered where point-to-point random codes are combined with receivers that disregard the special statistical structure of the interfering signals and simply treat them as white noise. It is shown that despite its simplicity, this scheme achieves the sum capacity for an important subclass of channels. The baseline scheme is not optimal in general. In order to overcome its shortfalls, two different viewpoints on the interference channel are taken. The receiver-centric view states that each received signal is composed of multiple independent structured transmissions, among which only the desired one must be decoded correctly. An approach is developed that allows the receivers to exploit the structure of the combined interference signal without insisting to decode any of the interfering messages partly or fully. This interference decoding scheme results in a second achievable rate region that is shown to strictly dominate treating interference as noise. In addition, it also contains as a special case the scheme that decodes the undesired messages uniquely. The complementary view of the interference channel is transmitter-centric. The observation that each sender affects all receivers, but needs to convey a message only to one of them while minimizing the disturbance caused at the others leads to a new model of communication with disturbance constraints. Disturbance is measured by a mutual information expression that represents the rate of unwanted information flow from the transmitter to the side receivers. The disturbance-constrained communication problem is first studied in isolation, and its optimal coding schemes are identified. The rate-disturbance trade-off is established for the single constraint case, where the optimal encoding scheme turns out to be the same as the Han-Kobayashi scheme for the two user-pair interference channel. For the case of communication with two disturbance constraints, the best known encoding scheme involves rate splitting, Marton coding and superposition coding, and is shown to be optimal in several nontrivial cases. Finally, the two viewpoints are consolidated by applying the codebook structure from communication with two disturbance constraints in the three-user-pair interference channel and combining it with interference-decoding receivers. This yields a third achievable rate region that is the central result of this dissertation. It is strictly larger than the two previous inner bounds to the capacity region. Furthermore, it is shown to achieve the capacity region of each two-user-pair subchannel embedded within the three-pair interference channel, and as such, the coding scheme generalizes the Han-Kobayashi scheme to more than two user pairs. While the results are presented in the framework of the deterministic interference channel with three user pairs, the modular approach of separating the transmitter- and receiver-centric viewpoints as well as the new coding schemes apply in principle to general discrete memoryless interference channels.