Trellis coded modulation for informed receivers
Xuepeng Xiao, Yi Hong, Emanuele Viterbo, Anindya Gupta · 2017
We consider the following variant of the index coding problem. A transmitter wishes to communicate several messages, each of which is k bit long, to multiple informed receivers over a noisy broadcast link. Each informed receiver already knows some of the messages a priori, which is called its side information, and demands to know the rest of the messages. However, unlike in an index coding problem, the transmitter is oblivious of the side information available at the receivers. We propose a trellis coded modulation (TCM) based scheme, called TCM for informed receivers (TCMIR), for this scenario. The transmitter jointly encodes the messages using a k/k+1 convolutional code and transmits the k + 1 coded bits as a signal from a 2k+1point constellation. New bit labeling rules are given to guarantee that the performance gain of any receiver is independent of the actual bit value of the side information. Compared to the uncoded case, each receiver can decode the required messages more reliably. Moreover, the receivers with side information can recover the remaining messages more reliably compared to a receiver with no side information. Next, the performance of TCMIR is compared with that of nested codes available in the literature and it is shown that TCMIR outperforms the nested codes for a receiver with side information.