Impact of partial relay selection on the capacity of communications systems with outdated CSI and adaptive transmission techniques

Bin Zhong,Zhongshan Zhang,Yan Li,Xu Zhang,Keping Long

doi:10.1186/1687-1499-2013-24

Abstract

AbstractThe impact of outdated channel state information (CSI) on the capacity of amplify-and-forward (AF) partial relay selection systems is studied in this article. The closed-form expressions for the distribution of received signal-to-noise ratio (SNR) in a multi-relay cooperative communications system is first derived, with independent and identically distributed (i.i.d.) Rayleigh fading channels being assumed in each wireless link. After that, the theoretical closed-form expressions for both outage probability and channel capacity of partial relay selection are derived, with four classical adaptive transmission techniques, including the constant power with optimal rate adaption (ORA), the optimal power and rate adaption (OPRA), the channel inversion with fixed rate (CIFR) and truncated channel inversion with fixed rate (TIFR), being considered. Numerical analysis proves that the channel capacity of partial relay selection is impacted considerably by some critical parameters, including the number of relays, the channel correlation coefficient and the end-to-end SNR, etc. It’s also exhibited in the numerical results that among the four adaptive transmission techniques, the diversity order of OPRA is larger than that of TIFR, and the OPRA outperforms TIFR with about 0.15 bits/s/Hz in terms of average channel capacity.

Highlights

Cooperative communications technique, where distributed multiple nodes form a virtual multiple-antenna array, has the potential of offering a number of significant performance benefits, such as an expanded wireless coverage, a system-wide power saving, a throughput improvement, and a better immunity against severe channel fading [1,2,3]
Relay selection techniques in cooperative communications systems can be classified as two modes, i.e., the opportunistic relay selection [19,20] and the partial relay selection [21], where in the former, the signal-to-noise ratio (SNR) of both the source-to-relay (S → R) and relay-to-destination (R → D) links must be considered by the central unit, but in the latter, the SNR of only the S → R link or R → D link is necessarily considered
The main contributions of this article as compared to the existing works are exhibited as follows: (1) the S → D channel is employed in the proposed cooperative transmission to improve the spatial diversity gain, with variant figures of merit, such as channel capacity, outage probability, being analyzed; (2) in consideration of the fact that an outdated channel state information (CSI) may be obtained due to Doppler Shift or feedback delay, relay selection with an outdated CSI is studied; (3) considering the CSI feedback load reduction in relay selection, partial relay selection instead of full opportunistic relaying is studied in this article, with a closed-form expression of the channel capacity for each adaptive transmission technique being derived

Summary

Introduction

Cooperative communications technique, where distributed multiple nodes form a virtual multiple-antenna array, has the potential of offering a number of significant performance benefits, such as an expanded wireless coverage, a system-wide power saving, a throughput improvement, and a better immunity against severe channel fading [1,2,3]. The main contributions of this article as compared to the existing works are exhibited as follows: (1) the S → D channel is employed in the proposed cooperative transmission to improve the spatial diversity gain, with variant figures of merit, such as channel capacity, outage probability, being analyzed; (2) in consideration of the fact that an outdated CSI may be obtained due to Doppler Shift or feedback delay, relay selection with an outdated CSI is studied; (3) considering the CSI feedback load reduction in relay selection, partial relay selection instead of full opportunistic relaying is studied in this article, with a closed-form expression of the channel capacity for each adaptive transmission technique being derived. MX(s) represents the moment generating function (MGF) of RV X

System model

Conclusions