MIMO Layer Shifting for LTE-Advanced Uplink

In this paper, multiple-input multiple-output (MIMO) layer shifting with cubic metric (CM) preserving precoder and downlink control signal sharing is proposed as a uplink transmission scheme for 3GPP Long Term Evolution (LTE). The design criteria for CM preserving precoder are presented and uplink precoder is designed accordingly. By sharing MCS (modulation and coding scheme) and/or HARQ (hybrid automatic repeat request) among codewords, downlink control signal sharing reduces the control signal overhead at the expense of performance degradation, which motivates this paper. The proposed MIMO layer shifting on a per SC-FDMA (single-carrier frequency division multiple access) symbol basis eliminates the discrepancy of channel quality among codewords, and thus improves the performance in the presence of MCS and/or HARQ sharing. Simulation results show that layer shifting is beneficial to both minimum mean square error (MMSE) and successive interference cancellation (SIC) receivers.

I. Introduction

Recently, multiple-input multiple-output (MIMO) has emerged as the key technology for next generation communications. It can significantly improve the coverage by diversity gain and/or increase the transmission rate by multiplexing gain. Thus, the 3GPP E-UTRA Long Term Evolution (LTE), which is a strong candidate for next generation cellular networks [1], supports the use of MIMO in the downlink [2]. Moreover, as LTE evolves to LTE-Advanced, MIMO is also considered as a uplink transmission scheme, to achieve the required spectral efficiency (15b/s/Hz) and coverage (2b/s/Hz) [3] and [4].