Some fundamental problems in the development of wireless relay networks

干扰、衰落和信号衰减是无线通信中的主要困难。为了构建高效的无线网络，可以利用中继节点来缩短通信范围、提高频谱利用率、增加空间分集和充分利用可用信号。然而，为了实现这些目标，必须使用更高级的编码方案和合作策略。随着更多的节点参与，更多的信号传输，更多的相关引入，无线组网问题变得更加具有挑战性。解码转发是一种中继策略，在该策略中，中继节点需要在转发消息之前对其进行解码。这具有从接收的信号中消除噪声的优点，并且即使在多次继电之后也不会积累噪声。在文献中已经有很多关于译码转发中继方案的研究，并且在单一信源的情况下获得了令人满意的结果。然而，在多个信号源的情况下，由于它们之间的相互干扰，这个问题更具挑战性。我们打算开发一种多信源情况下的最优译码转发中继框架。压缩转发是另一种中继策略，不需要在中继处进行解码。相反，中继器只是在量化后转发接收的信号。虽然在没有解码的情况下，接收信号中的噪声也将被转发，但中继器不会对通信速率施加限制。对于某些网络问题，此中继策略的性能明显优于解码转发。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，确定适用于一般无线网络的最优压缩转发中继方案。最后，比较不同的中继策略，并为不同的网络问题确定最佳选择是非常有意义的。尽管已经对每种接力策略进行了广泛的研究，但如何从它们中进行最佳选择，或者它们的任何组合，仍然缺乏一般指导。我们打算开发这样的通用指南，这将对实际无线中继网的设计非常重要。

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.