Wireless Communications

14Cooperative Communications

Abstract

Physical layer technologies such as MIMO and OFDM have been proved effective in providing a higher data rate for wireless systems. However, such improvements are far from sufficient to meet the increasing demand raised by the explosive growth of mobile devices. Given the limited spectrum, a promising solution is to significantly increase the spectral efficiency of wireless networks. The large amount of distributed wireless nodes, fortunately, also provides a new platform to achieve this goal through cooperation among wireless nodes. The simplest version of node cooperation to assist data transmission can be traced back to the conventional microwave relay system. Cooperative communications, however, is different from the conventional relay system in the sense that multiple nodes will coordinate to transmit the signal and avoid interference. As a result, besides the SNR gain, cooperative communications can also help achieve diversity gain, manage interference, and, thus, greatly improve the aggregate capacity of wireless networks. Various types of node cooperation, such as multi-hop and multi-relay communication, multi-cell MIMO, and two-way relaying, have found their applications in the infrastructured (cellular) and ad hoc (sensor) networks.

14.1 A historical review

Just as any physical phenomenon, information exchange is also governed by a fundamental law. Recall that the maximum mutual information (capacity) of a single point-to-point ...