FDMA-based multiuser transmit optimization for broadcast channels

We analyze the general problem of multiuser transmit optimization for a Gaussian broadcast channel with ISI under the FDMA restriction. Due to the FDMA restriction, the resulting problem is combinatorial in nature and hard to solve. However, by relaxing the FDMA restriction, we obtain a convex reformulation that allows for efficient computation of the optimal solution. By enforcing a constant-energy restriction, further reduction in computational complexity is achieved. We present the optimal and one suboptimal constant-energy method with bandwidth optimization. Simulation results show that these methods suffer from negligible performance loss even at low SNRs where the constant-energy approximation is not valid