Green Communications for Multi-cell Systems: A Joint User Grouping, Beamforming and Power Control Perspective

Future wireless communication systems have been imposed high requirement on power efficiency for operator's profitability as well as to alleviate ICT global carbon emission. To conform with the requirement of green communications, the power consumption minimization problem for a generic multi-cell multiple input and single output non-orthogonal multiple access (MISO-NOMA) system is studied in this work. The associated joint user grouping, beamforming (BF) and power control problem is a mixed integer non-convex programming problem, which is tackled by an iterative distributed methodology. First, the BF vectors and BF users are determined for each cell using only local information. Specifically, the near-optimal zero-forcing (ZF) BF is adopted, and semiorthogonal user selection (SUS) is applied to select BF users. Then, two distributed user grouping strategies are proposed. The first one, called CCUC, performs user grouping in each cell based on the channel conditions. This is conducted independently of the power control part and has low computational complexity. Another algorithm, called PCUC, uses both the channel conditions and inter-cell interference information to minimize each cell's power consumption. In contrary to CCUC, PCUC is optimized jointly with the power control. Finally, with the obtained user grouping and BF vectors, the resultant power allocation problem is optimally solved via an iterative algorithm, whose convergence is mathematically proven given that the problem is feasible. We perform Monte-Carlo simulation and numerical results show that the proposed resource management methods outperform conventional MISO scheme in several aspects, including power consumption, outage probability, energy efficiency, and connectivity efficiency.