Combinatorial Orthogonal Beamforming for Joint Processing and Transmission

Coordinated multiple point transmission (CoMP) technologies have recently been proposed to improve the performance of cell-edge users who suffer strong inter-cell interference. Nevertheless, as more transmitters get involved in cooperation, the complexity associated with the selection of multi-dimensional parameters increases exponentially. In this work, we investigate efficient multi-cell cooperation based on CoMP-joint processing and transmission (CoMP-JPT) with orthogonal beamforming using limited feedback. Through the utilization of combinatorial optimization, optimal user scheduling for joint transmission via multiple transmitters is accomplished, while the computational complexity is significantly reduced. In particular, a generalized beam assignment problem (GBAP) is formulated and solved using a combinatorial algorithm that is generalized in terms of the number of transmitters omathcal{B}o. The performance of the combinatorial orthogonal beamforming (COBF) scheme is mathematically analyzed so as to demonstrate its superiority and capability to maintain fairness among users in a multi-cell environment. In the simulation results, a performance gain of more than 50% for cell-edge users is obtained without a loss in the average throughput for the total number of users. In addition, the COBF method can reduce the complexity by more than 60% when compared to the conventional exhaustive search technique.