Downlink VoIP Capacity with Network-Synchronized Cyclic Beamswitching

The next generation of wireless networks (e.g., Long Term Evolution (LTE) and WiMAX) use multiple techniques to improve channel spectral efficiencies. In this paper we focus on one such technique, namely Coordinated Beam Switching (CBS). With CBS, each sector determines a sequence of beams (possibly with repetitions) over which it continuously cycles. Each sector independently determines its beam pattern with the only constraint being that all sectors use a common cycle period. A beam can be used for the entire frame or one may use different beam patterns for each subband of the frame. Therefore the interference pattern of each subband of a sector repeats with the same period and hence the channel quality can be predicted if we assume slow moving UEs (User Equipment). Such a method may not be suitable for delay sensitive applications but, in the case of VoIP, the periodic arrivals of VoIP packets can be synchronized with the periodic service provided to the UE. Furthermore, VoIP service is limited by UEs at the edge but these are precisely the UEs that benefit from beamforming. In this paper we provide algorithms for accomplishing this synchronization and illustrate the corresponding VoIP capacity gains through simulations.