Improved Link Adaptation using Truncated Channel Inversion for MU-MIMO Systems

In this work, we propose a link adaptation scheme called truncated channel inversion (TCI) as an effective power allocation strategy for block adaptive modulation, coding, and spatial mode (AMCS). Since water-filling based power allocation is no longer optimal to minimize bit error rate (BER) in block modulation system, block AMCS is considered as a practical link adaptation scheme. We first investigate the BER bound for multiuser multiple-input multiple-output bit-interleaved coded orthogonal frequency division multiplexing (MU-MIMO BIC-OFDM), and the optimal power allocation solution that minimizes the bound is derived. By showing that the solution from the BER minimization and the result from TCI are equal, we verify the suitability of TCI for MU-MIMO BIC-OFDM system with block modulation. Then, we propose a block AMCS algorithm that integrates TCI, and selects the optimal MCS and the corresponding power allocation which maximize the throughput under a packet error rate (PER) constraint. Improved transmission performance of the proposed algorithm is verified through simulation results.