Cooperative diversity in downlink of cellular CDMA systems using maximum ratio precoding

Cooperative communication is an efficient technique for improving the performance and coverage of cellular mobile networks. In this paper, we consider signal transmission in downlink of cooperative cellular direct sequence code division multiple access (DS-CDMA) systems. In this case, signal is transmitted to the destination mobile terminals via direct links, i.e. links from the base station to users, and also from a cooperative link via the partner mobile terminal to the destination. Our purpose is to shift the spatial processing from the user terminal to the transmitter of the base station. We proposed two different precoding schemes. In the first scheme, we assume that the inter-user channel state information is available at the relay mobile terminals and the base station only has information about the direct links. In the second scheme, we assume that all direct and inter-user channel state information are available at the base station. We derive different linear precoding techniques for two schemes and evaluate their performance by computer simulations. We show that both proposed cooperation schemes improve the performance of the system with respect to the case when no cooperation is used in the system. In addition it will be shown that the proposed schemes can achieve maximum diversity with low complexity requirements at the mobile receivers.