Variable rate and power M-QAM for DPS/DPB CoMP with adaptive modulation

Dynamic point selection/dynamic point blanking (DPS/DPB)-based coordinated multipoint (CoMP) has attracted lots of interest because of the significant performance improvement with a particular low complexity. In this paper, we first investigate the average spectral efficiency (ASE) of M-ary quadrature amplitude modulation (M-QAM) satisfying instantaneous bit error rate constraint for DPS/DPB CoMP system with 3 different adaptive modulation strategies. Closed-form expressions of the ASE for continuous-rate M-QAM are obtained in which calculus of variations is used to obtain the optimal power allocation policy. We also analyze the ASE for discrete-rate M-QAM which is more useful for the practical DPS/DPB CoMP wireless communication systems. Average bit error rate for DPS/DPB CoMP discrete-rate M-QAM is also investigated in this paper. Monte Carlo simulations are used to verify the correctness of our analysis. The results reveal that in M-QAM DPS/DPB CoMP systems, when the channel condition is unfavorable, the transmit power is the crucial parameter to enhance the ASE, otherwise the transmit rate is the key parameter. We can also notice that by using adaptive modulation, DPS/DPB CoMP has an obvious channel capacity improvement compared to the case without coordination among different transmission points.