A robust multimode transmission strategy for PU2RC with quantized CQI using hierarchical codebook

Per-User Unitary Rate Control (PU2RC) performs poorly when the number of users is small and suffers from the sum-rate ceiling effect in the high signal-to-noise ratio (SNR) regime. In this paper, we propose a multimode transmission (MMT) strategy to overcome these inherent shortcomings of PU2RC. In the proposed MMT strategy, the transmitter finds out the optimal transmission mode and schedules users using each user´s instantaneous channel quality information (CQI) parameters. First we assume that each user´s CQI parameters are perfectly reported in order to introduce the proposed MMT strategy. Then we consider the quantization of CQI parameters using codebooks designed by the Lloyd algorithm. Moreover, we modify the CQI parameters to improve the system´s robustness against quantization error. Finally, in order to reduce the quantization error, we design a hierarchical codebook to jointly quantize the modified CQI parameters considering the correlation between them. Simulation results show that the proposed MMT strategy effectively overcomes the shortcomings of the conventional PU2RC and is robust for CQI quantization levels.