Trade-offs Between the Quality of Service, Computational Cost and Cooling Complexity in Interference-Dominated Multi-User SDMA Systems

The future 5G systems will aim to design low-cost phased array base station antenna systems at mm-waves for simultaneous multiple beam forming with enhanced spatial multiplexing, limited interference, acceptable power consumption, suitable processing complexity and passive cooling. In this paper, a multi-user space division multiple access (SDMA) model is developed to investigate the trade-offs between the quality of service (QoS), computational complexity in beamforming and cooling requirements for various use cases and number of users. The QoS at the user ends is rated by assessing the statistical signalto-interference-plus-noise ratios (SINRs). Two beamforming algorithms, namely Conjugate Beamforming (CB) and Zero-Forcing (ZF), are considered and compared. Depending on the deployment scenario, rotated and optimized array layouts are proposed to be used in CB with the least computational complexity while providing relatively good QoS. Different reduced-complexity ZF algorithms are introduced as a compromise between the SINR performance and computational burden. The impact of the number of simultaneously served users on the thermal management in active integrated 5G base station antenna arrays is investigated as well.