Data-precoded algorithm for multiple-relay-assisted systems

Sara Teodoro,Atílio Gameiro,Adão Silva,João M Gil

doi:10.1186/1687-6180-2012-22

Abstract

A data-precoded relay-assisted (RA) scheme is proposed for a system cooperating with multiple relay nodes (RNs), each equipped with either a single-antenna or a two-antenna array. The classical RA systems using distributed space-time/frequency coding algorithms, because of the half-duplex constraint at the relays, require the use of a higher order constellation than in the case of a continuous link transmission from the base station to the user terminal. This implies a penalty in the power efficiency. The proposed precoding algorithm exploits the relation between QPSK and 4 L -QAM, by alternately transmitting through L relays, achieving full diversity, while significantly reducing power penalty. This algorithm explores the situations where a direct path (DP) is not available or has poor quality, and it is a promising solution to extend coverage or increase system capacity. We present the analytical derivation of the gain obtained with the data-precoded algorithm in comparison with distributed space-frequency block code (SFBC) ones. Furthermore, analysis of the pairwise error probability of the proposed algorithm is derived and confirmed with numerical results. We evaluate the performance of the proposed scheme and compare it relatively to the equivalent distributed SFBC scheme employing 16-QAM and non-cooperative schemes, for several link quality scenarios and scheme configurations, highlighting the advantages of the proposed scheme.

Highlights

The use of relays is considered an important technology for future wireless systems, because of its potential to increase capacity, extend coverage, and improve access fairness, as well as to provide additional flexibility in the upgrading of the networks [1]
In this algorithm there is no need to transmit through the direct link, in alternative to the non-orthogonal algorithms proposed previously
The algorithm mitigates some of the penalty resulting from the half-duplex constraint at the relays and asymptotically achieves the same performance as the one obtained when a direct continuous link is available

Summary

Introduction

The use of relays is considered an important technology for future wireless systems, because of its potential to increase capacity, extend coverage, and improve access fairness, as well as to provide additional flexibility in the upgrading of the networks [1]. We extend the work of [19] on data precoded for two-relay-assisted scheme, to data precoded for a generic multiple L-relay case, where each RN is equipped with either one or two antennas In this algorithm there is no need to transmit through the direct link, in alternative to the non-orthogonal algorithms proposed previously. In the case of the single-antenna relay the gain decreases when the number of RNs goes from 3 to 4 or from 5 to 6 Note that in those situations we are increasing the cardinality of modulation in a factor 4, because of the lower spectral efficiency of this scheme, since in those cases we need an additional time phase for another Alamouti code implementation

PEP derivation for data-precoded algorithm

Numerical results

Discussion and conclusions