An improved scheme based on log-likelihood-ratio for lattice reduction-aided MIMO detection

Yunchao Song,Chen Liu,Feng Lü

doi:10.1186/s13634-016-0312-8

Abstract

Lattice reduction (LR)-aided detectors have been shown great potentials in wireless communications for their low complexity and low bit-error-rate (BER) performance. The LR algorithms use the unimodular transformation to improve the orthogonality of the channel matrix. However, the LR algorithms only utilize the channel state information (CSI) and do not take account for the received signal, which is also important information in enhancing the performance of the detectors. In this paper, we make a readjustment of the received signal in the LR domain and propose a new scheme which is based on the log-likelihood-ratio (LLR) criterion to improve the LR-aided detectors. The motivation of using the LLR criterion is that it utilizes both the received signal and the CSI, so that it can provide exact pairwise error probabilities (PEPs) of the symbols. Then, in the proposed scheme, we design the LLR-based transformation algorithm (TA) which uses the unimodular transformation to minimize the PEPs of the symbols by the LLR criterion. Note that the PEPs of the symbols affect the error propagation in the vertical Bell Laboratories Layered Space-Time (VBLAST) detector, and decreasing the PEPs can reduce the error propagation in the VBLAST detectors; thus, our LLR-based TA-aided VBLAST detectors will exhibit better BER performance than the previous LR-aided VBLAST detectors. Both the BER performance and the computational complexity are demonstrated through the simulation results.

Highlights

The multiple-input multiple-output (MIMO) technology plays an important role in increasing the spectral efficiency of wireless communications by allowing for spatial multiplexing [1]
5 Conclusions In this paper, we made a readjustment of the received signal in the Lattice reduction (LR) domain and proposed a new scheme to improve the LR algorithm
Unlike the LR algorithm which utilized the unimodular transformation to change the orthogonality of the channel matrix, the proposed scheme targeted to use the unimodular transformation to decrease the pairwise error probabilities (PEPs) of the symbols, while the PEPs affected the error propagation in the vertical Bell Laboratories Layered Space-Time (VBLAST) detectors

Summary

Introduction

The multiple-input multiple-output (MIMO) technology plays an important role in increasing the spectral efficiency of wireless communications by allowing for spatial multiplexing [1]. An improved ELR algorithm [18] is proposed to enhance the BER performance of the ELR algorithm; it brings large complexity increase. The previous LR algorithms aim to use unimodular transformation to change the orthogonality of the channel matrix, such that the gap between the suboptimal detectors and the MLD is reduced. These LR algorithms do not take the received signal into consideration. The received signal is important information in the MIMO detection It can partially reflect the received noise and is useful in enhancing the BER performance of the LR-aided detectors. We write Ai,j for the entry in the ith row and jth column of the matrix A, ai for the ith entry in a. ai and ai denote for the ith row and the ith column of the matrix A, respectively

Preliminary

LLR criterion for our transformation algorithm

The description of the LLR-based transformation algorithm

The simulation and the analysis

The BER comparison of the VBLAST detector with LLR ordering

Conclusions