Power Allocation for Underlay Device-to-Device Communication Over Multiple Channels

In underlay device-to-device (D2D) communication, a D2D pair reuses the cellular spectrum, causing interference to existing cellular users. The achieved D2D rate and the added interference to cellular users need to be jointly considered for optimal resource and power allocations. Unlike most existing work which only consider the simplified scenario of assigning each D2D pair a single channel or resource block (RB), we consider multiple RBs from different cellular users can be assigned to each D2D pair. We formulate the problem of optimal power allocation over multiple RBs at the D2D transmitter to maximize the sum-rate of D2D and cellular users, under the D2D transmitter power constraint and minimum signal-to-noise-and-interference ratio (SINR) requirement at each reused RB for all affected cellular users in all cells. To further lower the required overhead in a practical setting, we consider a second optimization problem for power allocation solution to maximize the D2D rate under the same constraints as the sum-rate maximization problem. We obtain the asymptotic power solution for the sum-rate maximization and the semiclosed-form optimal power solution for the D2D rate maximization. Our proposed optimization solutions are applicable to both uplink and downlink cellular spectrum sharing as well as to mutlicell with multiple D2D pairs scenarios. Our simulation studies demonstrates the effectiveness of the two proposed methods for both uplink and downlink resource sharing, and further shed light into how the maximum rate is impacted by the system parameters such as available D2D transmit power, number of D2D pairs, minimum SINR requirements, and the cell size.