Sum-rate maximization for spectrum-sharing cognitive multiple access channels without successive interference cancellation

In this paper, the sum-rate of a cognitive multiple access channel (C-MAC) is studied, where a secondary network (SN) with multiple secondary users (SUs) transmitting to a secondary base station (SBS) shares the spectrum band with a primary user (PU). An interference power constraint (IPC) is imposed on the SN to protect the PU. Under the IPC and the individual transmit power constraint (TPC) imposed on each SU, we investigate the power allocation strategies to maximize the sum-rate of the C-MAC without successive interference cancellation (SIC). We prove that the optimal solution must be at the extreme points of the feasible region. We show that Dynamic Time Division Multiple Access (D-TDMA) is optimal with high probability when the number of SUs is large. Furthermore, we show through simulations that the optimal power allocation to maximize the sum-rate of the C-MAC with SIC is optimal or near-optimal for our setting when D-TDMA is not optimal.