Robust feedback scheme for precoding systems based on finite-rate feedback

In a multiple-input multiple-output (MIMO) precoding system based on finite-rate feedback, the receiver sends a precoding matrix to the transmitter via a feedback channel. The overall system performance is degraded due to feedback error. In this paper, we propose a robust feedback scheme that employs the index permutation technique to provide the system with redundancy-free protection against the feedback error. The wireless channel is assumed to experience Rayleigh fading, and the feedback channel is modeled as a discrete memoryless channel (DMC). Using the average chordal distance as a metric, the design of the index permutation in the feedback scheme is formulated into a minimization problem. An upper bound on the average chordal distance is derived, and the permutation design problem is simplified based on the bound. A modified binary switching algorithm is then developed to search for good permutations. Simulation results show that the proposed feedback scheme well compensates for the performance degradation caused by feedback error.