Selection Amplify-and-forward Research Articles

Asymptotic Analysis of Cooperative Diversity Systems With Relay Selection in a Spectrum-Sharing Scenario

Three low-complexity relay-selection strategies, namely, selective amplify and forward (S-AF), selective decode and forward (S-DF), and amplify and forward with partial relay selection (PRS-AF) in a spectrum-sharing scenario are studied. First, we consider a scenario where perfect channel state information (CSI) is available. For these scenarios, the respective asymptotic outage behaviors of the secondary systems are analyzed, from which the diversity and coding gains are derived and compared. Unlike the coding gain, which is shown to be very sensitive with the position of the primary receiver, the diversity gain of the secondary system is the same as the nonspectrum-sharing system. In addition, depending on the cooperative strategy employed, an increase in the number of relays may lead to severe loss of the coding gain. Afterwards, the impacts of imperfect CSI regarding the interference and transmit channels on the outage behavior of the secondary systems are analyzed. On one hand, the imperfect CSI concerning the interference channels only affects the outage performance of the primary system, whereas it has no effect on the diversity gain of the secondary system. On the other hand, the imperfect CSI concerning the transmit channels of the secondary systems may reduce the diversity gain of the three relay-selection strategies to unity, which is validated by both theoretical and numerical results.

Strict suboptimality of selection amplify-and-forward relaying under global channel information

Selection amplify-and-forward (SAF) relaying, which has been shown to be optimal under the constraints of localized channel information at the relays and a constant relay power allocation (PA) template, is shown to be globally strictly suboptimal. A necessary condition for the outage optimality of the SAF PA, and an exponentially vanishing upper bound on the probability of the SAF optimality are derived.

ABEP of amplify-and-forward cooperation in Nakagami-m fading channels with arbitrary m

An asymptotic average bit error probability (ABEP) analysis is presented for amplify-and-forward (AF) cooperation with multi-branch dual-hop relays in independent Nakagami-m fading channels. The approximate probability density function (PDF) of the instantaneous dual-hop link power at high SNR region is derived, and indicates that the relay link is dominated by the more severely faded hop. Simple and general asymptotic ABEP expressions are presented for all-participate AF (AP-AF) and selective AF (S-AF) cooperation employing general Gray bitmapped constellation. The results are quite simple and general for arbitrary value of severity parameter m ges 0.5. It is shown that S-AF does not necessarily outperform AP-AF in terms of coding gain under conventional equal power allocation as in the Rayleigh fading environment. Whether or not S-AF outperforms AP-AF depends only upon the fading severity parameters and is irrelevant to the channel gains. Simulation results verify the tightness of the presented analysis at high SNR region.

Relay Selection in Amplify-and-Forward Relay Network with Multiple Antennas at the Destination

In this paper, we consider an amplify-and-forward (AF) relay network where a source node transmits information to a destination node through the cooperation of multiple relay nodes. It is shown in prior works that the outage behavior and average throughput of the selection AF (S-AF) scheme where only the best relay node is chosen to assist can outperform the conventional all-participate AF (AP-AF) scheme. Assuming multiple antennas at the destination node and single antennas at other nodes in this paper, we propose a relay selection scheme according to the criterion of maximizing receive signal to noise ratio (SNR), where a group of relays is chosen to assist in the transmission simultaneously in a manner similar to cyclic delay diversity (CDD). Compared with S-AF, the proposed scheme achieves better outage behavior and average throughput. It can be seen from simulation results that the performance improvement of symbol error rate (SER) is significant compared with S-AF.

Capacity, power allocation and partners selection for SIMO relay channels

AbstractIn this paper, we investigate the cooperative channels with one source‐destination pair and multiple partners (relays), where only the destination is equipped with multiple antennas. The achievable capacity with the optimal power allocation and partner selection is analyzed with the total transmit power constraints under the different cooperation modes, including amplify‐and‐forward (AF) and decode‐and‐forward (DF). With the partial channel state information (CSI) at the destination, we develop three algorithms to choose the possible best partner(s) for AF, repetition‐coded DF and Gaussian‐coded DF, which are called Selective AF (SAF), Selective repetition‐coded DF (SRDF), and Selective Gaussian‐coded DF (SGDF), respectively. In these algorithms, only one partner will be employed as relay for SAF and SRDF to maximize the capacity while multiple partners are selected for SGDF. An efficient quasi‐distributed protocol to support SAF, SRDF, and SGDF is also involved. We study the impact of the number of receive antennas and SNR on SAF, SRDF, and SGDF. Numerical results show that SAF and SRDF have higher spectral efficiency than direct transmission (DT), especially in low SNR regime and for the small number of receive antennas and large number of users cases, while SGDF outperforms DT evidently in every scenario. Copyright © 2007 John Wiley & Sons, Ltd.