Broadcast Systems: Alamouti Index Coding

Abstract

Consider a wireless broadcast channel with a number of receivers, where each receiver possesses some side information. In an index coding problem, the transmitter aims at delivering different messages to different receivers. It is desirable to minimize the total number of message transmissions in order to improve the bandwidth efficiency. It is known that the minimum number of transmissions can be achieved by solving a minimum rank problem for a given side information graph, which is a known NP-hard problem. In this thesis, the index coding problem over additive white Gaussian noise and Rayleigh fading channels is studied. Modulation techniques, such as phase shift keying and quadrature amplitude modulation, are tested, and it is shown that a careful choice of modulation can improve the performance. It is also shown that a careful choice of a generator matrix can provide for further performance gains, in particular for ”prioritized” receivers. A probabilistic soft information detection (PSID) is compared to a simple hard decision scheme, and the PSID performance is shown superior in achieving a lower error rate. Additional improvement in performance is achieved by using diversity, when employing two transmit and two receive antenna system in conjunction with the Alamouti code. All these techniques provide for the lower error rates and higher throughput when compared to the traditional schemes.