Asynchronous Network Coding for Multiuser Cooperative Communications

In this paper, we present an asynchronous network coding (ANC) transmission strategy for multiuser co-operative networks. In particular, we consider a relay network comprised of multiple sources and mutiple relays. The sources all transmit simultaneously. The relay receives a sum of the signals with different delays. The decoded signals at the relay are network-coded by asynchronous delays and transmitted to the destination. We first present a decoding strategy for our ANC. We also compare our proposed ANC to complex field network coding and show the superiority of our proposed scheme in terms of decoding complexity and bit error rate (BER) performance. Next, we develop three relay selection strategies with different complexity in conjunction with the proposed ANC scheme. The proposed full selection and joint selection (JS) schemes consider both channel quality and delay effect in the selection. But the proposed individual selection scheme only considers channel quality in the selection. We derive an end-to-end (E2E) BER expression in terms of worst E2E SNR for the JS scheme. We also theoretically show that the proposed schemes achieve full diversity. In addition, we compare the performance of the three proposed relay selection schemes by simulations.