Node Cooperation for Fixed Wireless Access

宽带互联网接入在发展中国家和发达国家都具有日益重要的经济和政治意义。宽带固定无线接入(FWA)是一种技术，它允许在与现有运营商竞争中或在几乎没有现有基础设施的地区快速且经济高效地推出宽带服务。支持多媒体的应用程序对宽带网络提出的要求要求的比特率远远超过当前无线系统可用的比特率。因此，基本的要求是能够在视线(LOS)和非视距(LOS)场景中提供数兆比特的数据速率。本提案中的合作伙伴目前正在进行一项由EPSRC资助的项目(GR/S46437/01)，该项目正在研究空时编码和空间复用技术，以提高宽带FWA系统的吞吐量和容量。然而，尽管已经在性能方面取得了有益的进展，但由于FWA频道的基本方面，进一步的改进可能会较为温和。具体地，FWA系统通常具有LOS或接近LOS传播的特征，产生缓慢的时间变化、温和的频率选择性和相关的传播路径。因此，很难有效地利用时间、频率和空间分集来提高系统性能。因此，在当前的提案中提出了一种新的FWA系统架构，它将克服以前强调的问题。特别是，节点协作分集的使用被提出为在FWA场景中改进性能的一种手段，其中更难利用其他分集技术。在节点协作分集中，节点在向目的节点的传输中相互协助。例如，目的节点将直接从源接收消息，此外还将从中继节点接收消息的副本。因此，协作系统中的分集与存在多条独立衰落的到达目的节点的路径有关。因此，节点协作分集是进一步提高FWA系统性能的关键概念之一。

Broadband Internet access is of growing economic and political importance in both developing and developed countries. Broadband fixed wireless access (FWA) is a technology which permits broadband services to be rolled-out both quickly and cost effectively in competition with incumbent operators or in areas where there is little existing infrastructure. The demands being placed upon broadband networks by multimedia-enabled applications require bit rates far in excess of that available from current wireless systems. Therefore, the fundamental requirement is to be able to deliver multi-megabit data rates in both line of sight (LOS) and non-LOS scenarios.The partners in this current proposal are presently conducting an EPSRC funded project (GR/S46437/01) that is investigating space-time coding and spatial multiplexing techniques to improve the throughput and capacity of broadband FWA systems. However, although useful gains in performance have been achieved, further improvements are likely to be more modest owing to fundamental aspects of the FWA channel. Specifically, FWA systems are in general characterized by LOS or near LOS propagation, yielding slow time variation, mild frequency selectivity and correlated propagation paths. Therefore it is difficult to exploit time, frequency and space diversity in an effective manner in order to improve system performance. Consequently, a new architecture for FWA systems is presented in this current proposal that will overcome the issues previously highlighted. Particularly, the use of node cooperation diversity is proposed as a means of improving performance in the FWA scenario where it is more difficult to exploit other diversity techniques. In node cooperation diversity, nodes assist one another in their transmission to the destination node. For example, a destination node will receive a message directly from the source and in addition a copy of the message from a relay node. Consequently, diversity in cooperative systems is associated with the existence of multiple paths to the destination node that fade independently. Therefore, node cooperation diversity is one of the key concepts to enable further improvements in the performance of FWA systems.