Optimality and Feasibility of Equal Power Allocation of IDMA Systems

Interleave-division multiple access (IDMA) is a recently developed multiple access technique for wireless communications. A power allocation problem of IDMA is to find a power vector (a vector of the received powers of the signals transmitted by all users) with the minimum total power. The feasible set of this global optimization problem contains all power vectors satisfying a performance requirement. Because the problem is non-convex, finding an optimal solution unavoidably requires a lots of computation and a sophisticated solver. As we observe in the literature, it is sometimes preferable to simply require the received powers for all users to be equal. This approach is not necessarily optimal, but optimality is sacrificed in exchange for significantly cheaper computation and a simpler implementation. However, we are not aware of any systematic study on the optimality and feasibility of this approach. In this paper, we derive conditions that can be used to determine the optimality and feasibility of the equal power allocation for IDMA. The conditions suggest that the equal power allocation is not only feasible, but also optimal if the number of users is small enough.