Some fundamental problems in the development of wireless relay networks

干扰、衰落和信号衰减是无线通信的主要难点。为了构建高效的无线网络，可以利用中继节点缩短通信距离，提高频谱复用，增加空间分集，充分利用可用信号。然而，为了实现这些目标，必须使用更先进的编码方案和合作策略。随着涉及的节点越来越多，传输的信号越来越多，引入的关联也越来越多，无线网络问题变得越来越具有挑战性。解码转发是一种中继策略，中继节点在转发消息之前需要对消息进行解码。这样做的好处是消除了接收到的信号中的噪声，即使经过多次中继，噪声也不会累积。文献中对译码转发中继方案进行了大量的研究，并在单源情况下获得了令人满意的结果。然而，在多信号源相互干扰的情况下，这个问题更具挑战性。我们打算在多源情况下开发一个最佳的译码转发中继框架。压缩转发是另一种中继策略，不需要在中继上进行解码。相反，继电器只是将接收到的信号进行量化后转发。虽然没有解码，接收信号中的噪声也会被转发，但中继对通信速率没有限制。对于某些网络问题，这种中继策略的性能明显优于译码转发。然而，最优的压缩转发方案尚未确定。我们最近在这方面取得了一些进展，并打算进一步研究这一基本问题，并确定通用无线网络的最佳压缩转发中继方案。最后，比较不同的中继策略，并确定针对不同网络问题的最佳选择是很有意义的。尽管每种接力策略已经被广泛地研究过，但关于如何从它们中进行最佳选择或它们的任何组合的一般指导仍然缺失。我们打算制定这样一个通用指南，这对实际的无线中继网络的设计是非常重要的。

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.