A Signal-Time Coding Approach to Relay Networks

In this paper, we first investigate the network information flow over a relay network topology and find that the reliable achievable information rate is beyond the achievable upper bound using the conventional encoding/modulation techniques when the relay and the destination are with carrier sensing. We then propose a signal-time coding approach which combines the traditional encoding/modulation mode in the signal domain with the signal pulse phase modulation in time domain. Such a hybrid signal-time coding approach can be considered as an integrated codec/modem processing in the two dimensional combinatorial space: Signal domain and temporal domain. The main feature of the proposed signal-time coding is that one can separately design the codec/modem in the signal domain and in the time domain. Therefore, the well known efficient codec/modems, such as LDPC, Turbo coding, TCM etc. in the signal domain can be employed here. A tight lower bound is explicitly presented for the signal phase coding/modulation efficiency in the time domain. In addition, we also present an iterative method to construct the code book for the signal phase coding/modulation in the time domain. Finally, consider its applications in the additive white Gaussian noisy (AWGN) relay networks and obtain some interesting results.