Inter-Cell Coordination, Opportunistic Beamforming and Scheduling

In high speed downlink packet access systems (HSDPA), opportunistic beamforming has been proposed as a viable technique for improving the system capacity by taking advantage of the multiuser diversity due to the time varying fluctuations of the mobile users' channels. In opportunistic beamforming with proportional fair scheduling, mobile users who have the largest rates when compared with their averaged throughputs, are scheduled over preferred spatial beams, thereby yielding improved throughput-delay tradeoffs. In this paper, we consider cellular architectures where base stations coordinate to service users. These base stations are assumed equipped with smart antenna systems which generate pilot beams according to a predefined algorithm, collect only an SINR report from the users, and provide opportunistic scheduling. We propose schemes where the base stations coordinate to generate beams that reduce the inter-cell interference to the users considered for service. Through computer simulations we show that the proposed base station coordination technique provides significant performance gains in downlink packet access cellular systems. Furthermore this is achieved with the use of only modest feedback (SINR) from the users i.e. without the need for excessive channel state information feedback.