Network coordinated beamforming for cell-boundary users: Linear and nonlinear approaches

In this paper, low-complexity linear and nonlinear network coordinated beamforming (N-CBF) algorithms are proposed for the multi-cell downlink channel. We consider a downlink scenario with three base stations (BSs) equipped with one transmit antenna each and three mobile users, each of which has more than one receive antenna and is located on the cell-boundary. A single data stream is transmitted to all three cell-boundary users where each user receives his/her own independent data stream (called full broadcast channel), or where two users receive the same data stream while the third user receives a different data stream (called clustered broadcast channel). For full and clustered broadcast channel scenarios, we propose low-complexity linear N-CBF algorithms approaching the sum capacity realized by multi-cell dirty paper coding. We also propose low complexity nonlinear N-CBF algorithms that avoid power enhancement and maximize the effective channel gain for enhancing the bit error rate (BER). The impact of the number of receive antennas on the behavior of the proposed system is also discussed. Monte Carlo simulations are carried out to verify the sum rate and BER performances of the proposed algorithms.