Some fundamental problems in the development of wireless relay networks

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Interference, fading and signal attenuation are the major difficulties in wireless communications. To build highly efficient wireless networks, relay nodes can be used to shorten communication range, improve spectrum reuse, increase spatial diversity and fully exploit available signals. However, in order to achieve these goals, more advanced coding schemes and cooperation strategies have to be used. With more nodes involved, more signals transmitted, more correlations introduced, the wireless networking problem becomes more challenging. Decode-and-forward is a relay strategy where a relay node needs to decode the message before forwarding it. This has the advantage of eliminating noise from the signal received, and noise will not be accumulated even after many relays. There have been many studies of decode-and-forward relay schemes in the literature, and satisfying results have been obtained in the case of a single source. However, the problem is much more challenging in the case of multiple sources due to their mutual interference. We intend to develop an optimal decode-and-forward relay framework in the case of multiple sources. Compress-and-forward is another relay strategy, where, decoding at the relay is not needed. Instead, the relay simply forwards the received signal after quantization. Although without decoding, noise in the received signal will also be forwarded, no constraints on the communication rate will be exerted by the relay. This relay strategy can significantly outperform decode-and-forward for some networking problems. However, the optimal compress-and-forward scheme has not been determined yet. We made some progress on this topic recently, and intend to further investigate this fundamental problem and determine the optimal compress-and-forward relay scheme for general wireless networks. Finally, it is of great interest to compare different relay strategies, and determine the best choice for different networking problems. Although each relay strategy has been studied extensively, a general guidance on how to optimally select from them, or any combinations of them is still missing. We intend to develop such a general guidance, which will be very important for the design of practical wireless relay networks.