Jointly optimal base station assignment for up- and downlink CDMA through space division duplex

Nonuniform traffic can severely degrade the performance of CDMA cellular systems. To alleviate this, load balancing schemes have been proposed which let the neighboring cells accommodate the traffic of a heavily loaded cell. Most of the previous works have addressed load balancing for the uplink since it was considered to be the bottleneck of the system performance. In fact it is very likely for the uplink to become congested before the downlink in the presence of conventional symmetric services (e.g. voice). However emergence of the new highly asymmetric services has put much more demand on the downlink and there may be many cases where the downlink of a cell is heavily loaded without significant uplink-loading. This motivates us to perform downlink load balancing by assigning an appropriate base station to each user. In this paper we propose an algorithm based on space division duplex which assigns optimal base stations for the up- and downlink independently.