An Optimal Standard-Compliant MIMO Scheduler for LTE Downlink

Frequency domain packet scheduling (FDPS) problem is one of the crucial elements in the 3rd generation partnership project (3GPP) long term evolution (LTE) system, which has a tremendous impact on the LTE system performance. However, optimal resource allocation through FDPS is a complicated and challenging task when multiple input and multiple output (MIMO)-orthogonal frequency division multiple access (OFDMA) technology is adopted. In this paper, we propose a new FDPS scheme for the 3GPP LTE downlink channels that optimally assigns time-frequency resources to users based on the proportional fairness metric. The proposed scheme jointly considers multiple system constraints imposed by the 3GPP LTE standard that arise in the MIMO mode selection and modulation and coding scheme (MCS) selection. Such scheduling problem is considered to be among the most difficult optimization problems. Our major contribution in this paper is that we model the FDPS problem as a unique binary linear programming problem and prove that the problem is totally unimodular. With the total unimodularity property, we are able to solve the complicated FDPS problem using efficient linear programming problem solvers. Simulation results show that our proposed scheme outperforms the existing state-of-the-art MIMO proportional fair scheduling algorithms used in the FDPS problem.