Modulation Design for MIMO-CoMP HARQ

Modulation diversity (MoDiv) is a simple and practical transmission enhancement technique that utilizes different modulation mappings to reduce packet loss rate and achieve higher link throughput. MoDiv is particularly meaningful and effective in Hybrid-Automatic Repeat reQuest (HARQ) systems. We study the deployment and optimization of MoDiv for HARQ in a MIMO-coordinated multi-point scenario under Rician fading channel to mitigate packet loss. We formulate the design optimization of MoDiv into a quadratic 3-D assignment problem, then solve it using a modified iterated local search method. Numerical results demonstrate clear performance gain over simple retransmissions and over a heuristic design under fading channels.