Subspace Quantization Based Combining for Limited Feedback Block-Diagonalization

Abstract

Spatial multiplexing of multiple users in a multiantenna broadcast system, i.e., multi-user MIMO, is a promising technique for improving the spectral efficiency of cellular networks. Still, practical implementations struggle with the difficulty of obtaining sufficiently accurate channel state information at the transmitter (CSIT), due to restrictions on the capacity of the CSI feedback links from the users. Without accurate CSIT, residual multi-user interference diminishes the potential performance gain of multi-user MIMO, challenging its value for practical realizations. In this work we show that the CSI feedback overhead can be significantly reduced if the number of spatially multiplexed data streams per user is less than the number of receive antennas, and the antenna outputs are appropriately combined. We propose an interference-unaware antenna combining algorithm that minimizes the CSI quantization error, which has the effect of minimizing multi-user interference at the price of reducing the received signal power. We mathematically analyze the performance of the proposed algorithm, substantiating its value for limited feedback systems. Numerical simulations confirm the potential of the proposed algorithm in comparison to a traditional technique that maximizes the received signal power.Index Terms-Limited feedback, quantized feedback, multiuser MIMO, block-diagonalization, antenna combining.

Adaptive quantization on the Grassmann-manifold for limited feedback multi-user MIMO systems

“…In [7][8][9] it has been shown that this error is directly related to the rate loss of the limited feedback system compared to perfect CSIT.…”

“…Accurate CSIT is central in interference limited multi-user systems, because CSI imperfections increase the multi-user interference and strongly deteriorate the throughput. It has been shown that a linear increase in the number of feedback bits with the signal to noise ratio (SNR) (in [dB]) is required to maintain a constant rate-gap to perfect CSIT [6][7][8][9]. Several multi-user precoding techniques require knowledge about the This work has been funded by A1 Telekom Austria AG and the Institute of Telecom., Vienna Univ.…”

Robust full-dimension MIMO transmission based on limited feedback angular-domain CSIT

“…BD precoding is very sensitive to CSI imperfections since it relies on destructive multipath interference to eliminate multi-user interference [71][72][73]. It also has heavy CSI requirements as it requires knowledge of the entire channel matrix H u of each user.…”

Achievable rates of SVD‐based codebooks for zero‐forcing and Tomlinson‐Harashima precoding schemes with limited feedback MU‐MIMO system

“…Thereby motivated by these problems, in this paper, we pose some questions such as: what kind of codebooks are required instead of existing codebooks [5][6][7][8][9][10][11][12][13][14] to precisely improve the channel at the Tx side? What will be the closed-form solution of the achievable rates for the proposed codebooks to efficiently apply precoding schemes?…”