An Efficient Signaling Method over MIMO Broadcast Channels

A simple signaling method for multi-antenna broadcast channel is proposed. In the proposed method, for each user, a direction in which that user has the maximum gain is determined. The base station selects the best user in terms of the larger maximum gain, and allocates the corresponding direction to that user. In each step, the maximization is performed in the null space of the former selected coordinates. Finally, the transmitted signal is a superposition of the selected coordinates. It is shown that in this method, the later selected user has no interference on the former users. A dirty paper pre-coding on top of the system eliminates the remaining interferences. Note that, in this method, the set of active users and the power allocated to each of them is easily determined, which is a significant advantage in the case of large number of users in the system. Furthermore, this method exploits multiuser diversity. Further, the proposed algorithm is modified to work with partial side information at the base station. Simulations show that the achieved rate is close to the sum-rate capacity. In addition, the asymptotic analysis shows that the increase of the sum-rate with number of transmit antenna is linear and with the number of users, K, is proportional to log log(K).