946 publications from this institution
We consider the sum rate maximization problem in downlink OFDMA systems subject to total transmit power and minimum user rate constraints. A low complexity suboptimal resource allocation algorithm is proposed for joint optimization of multiuser subcarrier assignment and power allocation. The algorithm is based on Lagrangian relaxation where the non-convex optimization problem is decomposed into a master problem and a subproblem. Subproblem has a similar form as standard weighted sum rate maximization subject to total transmit power. Standard subgradient method is used in the master problem and a suboptimal algorithm inspired from primal decomposition techniques is also proposed to approximately solve the subproblem. Simulations are provided to compare the performance of the proposed algorithm to fixed spectrum assignment based algorithms with adaptive power control.
Generalized Zero Forcing (GZF) will be used in emerging commercial systems for Multi-User MIMO (MU-MIMO) broadcast communications. In this paper, the user scheduling problem related to it is studied. Instead of using Singular Value Decomposition based Block Diagonalization (SVD-BD) method, we construct the GZF precoder that optimally solves the Sum Rate Maximizing (SRMax) problem by a product of a channel pseudo inverse matrix and a block diagonal matrix. Later a Suboptimal User Scheduling (SUS) algorithm with Receive Antenna Selection (RAS) is designed by using a greedy user and antenna selection under SRMax and other simplified criteria. As the channel pseudo inverse can be sequentially calculated, the proposed algorithm is computationally efficient. It also achieves higher average sum rate which is verified by numerical simulations.
