Limited-Feedback Low-Encoding Encoding Complexity Precoder Design for Downlink of FDD Multi Multi-User Massive MIMO Systems
Abstract: We investigate a limited feedback precoder based on symbol pairwise error probability (PEP) for a block block-faded K×nt downlink multiple-input input multiple-output multiple (MIMO) channel. In the considered system, K=⌊nαt⌋ single-antenna antenna users feedback quantized channel state information to the nt-antenna antenna transmitter using B bits per-transmit-antenna antenna per user. We analytically show that for α<(1/2) , B≥1 and nt→∞ →∞ , both symbol PEP and achievable rate of each of the K downlink users almost surely converge to the symbol PEP and achievable rate of K parallel additive white Gaussian noise (AWGN) channels, respectively. We show that the encoding comple complexity of the precoder is O(ntK) . We also show that if channel coefficients estimated by the user are corrupted by AWGN noise, the symbol PEP and achievable rate of each user almost surely converge to the symbol PEP and achievable rate in a scaled AWGN chan channel with B>1 and nt→∞ . For correlated channels, we derive a condition, which enables the proposed precoder almost surely to cancel multi multi-user user interference for large nt values. Finally, we numerically compare the bit error rate, encoding complexity, and perpe user achievable rate of the proposed scheme with the existing designs.