Forward link capacity in smart antenna base stations with dynamic slot allocation

In this paper we consider a set of portable stations which communicate with a base station equipped with a smart antenna operating in multibeam packet-switched SDMA mode. We assume that the system operates using time division duplexing (TDD) and focus on the problem of access to the stations by the base station in the forward link direction. A polling protocol is used which permits efficient access in this type of system. The operation of the protocol is unique in that it permits dynamic slot allocation and accommodates variations in channel time coherence. In the protocol, dynamic slot assignment is integrated into the forward link beam scheduling. The results show the improvements in capacity which are possible in such systems and give insight into the degradation in protocol performance which occurs when channel coherence times decrease. We find that very large improvements in capacity are possible, especially under harsh channel conditions. We also investigate various base station queueing issues in this type of system. It is shown that care must be taken in how buffering is performed so that blocking effects do not unnecessarily degrade the forward link capacity.