Blind and semi-blind equalization for generalized space-time block codes

This paper presents a general framework for space-time codes (STCs) that encompasses a number of previously proposed STC schemes as special cases. The STCs considered are block codes that employ arbitrary redundant linear precoding of a given data sequence together with embedded training symbols, if any. The redundancy introduced by the linear precoding imposes structure on the received data that under certain conditions can be exploited for blind or semi-blind estimation of the transmitted sequence, a linear receiver that recovers the sequence, or both simultaneously. Algorithms based on this observation are developed for the single-user flat-fading case and then extended to handle multiple users, frequency-selective fading, as well as situations where the channel is rank deficient, or there are fewer receive than transmit antennas.

I. Introduction

The advantages of using multiple antennas at both the transmit and receive ends of a wireless communications link have recently been noted [1], [2]. A number of space-time codes (STCs) have been proposed that exploit the potential for increased throughput and diversity that such systems offer. For most algorithms, these gains can only be realized when that the multiple-input multiple-output (MIMO) channel separating the transmitter and receiver has been identified. While training data can be used to estimate the channel, this approach consumes precious bandwidth and reduces throughput. One approach to overcoming this difficulty is the use of differential STCs [3], [4], although such techniques incur a 3-dB penalty in SNR.