Cooperative transmission protocols for wireless broadcast channels

In this paper, cooperative transmission protocols are proposed for wireless broadcast channels, a fundamental building block of wireless communication networks. The concepts of cognitive radio and precoding have been introduced to broadcast channels in order to improve system performance. Information theoretic metrics, such as outage probability and diversity-multiplexing tradeoff, are developed to facilitate performance evaluation. In the absence of direct S-D links, the proposed protocols can achieve a multiplexing gain close to one, whereas the traditional two-hop scheme only achieves a diversity gain of 1/2. In the presence of direct S-D links, the proposed protocol can still outperform the comparable scheme, particularly at high multiplexing gains. Regarding to the channel state information (CSI) assumptions, in the absence of direct S-D links, the source does not need to know CSI, but it is assumed that the relays have access to their own incoming and outgoing channel information. In the presence of direct S-D links, the use of precoding requires an extra assumption that the global CSI is available at the source.