Opportunistic Frequency Reuse in Cooperative Wireless Cellular Systems

Abstract

The mutual interference among co-channel users greatly limits the performance of cellular wireless systems. In particular, if a tight frequency reuse is employed, intercell interference must be properly handled. In this paper, we propose a cross-layer approach to the interference management, by using a random beamforming strategy and a smart scheduler with joint processing of signals related to different users in the network. Random beamforming is performed at each base station of the system, partial CSI is collected and shared by the network of interfering transmitters, and a scheduler chooses a subset of the users to be transmitted to. Optimization of beamforming in broadcast MIMO channels is precluded by the amount of feedback and complexity required. In this paper we propose to reduce the feedback by employing a random beamforming where a stream can be linearly preceded before being transmitted on the antenna array of each transmitter and the users with channel/interference matched to the beamforming configurations are scheduled at each time. In MIMO system the users can further improve the overall throughput by minimizing the co-channel interference. The feedback necessary to employ the spatial multiplexing can be limited to the signal to interference ratios for a subset of users that are compatible for the random beamforming configuration. In practice, a form of adaptive frequency reuse is performed on the basis of the spatial signal-to-interference ratio distribution among the users. We provide numerical results to compare the performance of our scheme with a form of dynamic channel allocation and opportunistic beamforming