Amplify-and-forward Cooperative Networks Research Articles

User-relay Assignment based Antenna Selection Scheme in Multi-user Multi-relay AF Cooperative Communication Network

In this paper, the user-relay assignment based antenna selection scheme for multi-user cooperative network is proposed to improve the transmission bit rate and system performance. The low complexity suboptimal user-relay assignment algorithm is first proposed to simultaneously improve both the system performance and individual user’ performance in the multi-user amplify-and-forward (AF) cooperative user-relay network, where each user can fairly select its best relay according to the instantaneous channel state information (CSI). Based on the user-relay assignment scheme and space shift keying (SSK), we further present the antenna selection scheme to further enhance the system performance for the multi-user AF cooperative user-relay network. In order to minimize the system bit error rate (BER), three antenna selection criteria based on the maximum likelihood (ML) detection have been proposed. Numerical results and theoretical analysis show that the proposed schemes can effectively improve the average system sum rate, the outage probability of the worst user, and the system BER performance, compared with the other schemes.

Performance Analysis of Two-Way AF Cooperative Networks with the Nth Relay Selection

In this letter, we propose a novel two-way amplifyand-forward (AF) relay selection scheme over independent flat Nakagami-m fading channels. In the proposed schemes, two users first sequentially broadcast their respective information to all the relays. Then, the Nth best-relay perform AF protocol on the received signals sent from the two users and forward them to both users. The Nth best-relay is selected to optimize the end-toend performance of the system transmission. The performance of the proposed system is quantified by deriving the lower bound of the overall outage probability and average symbol error rate (SER). The effectiveness of our proposed selection scheme and analytical results is verified by simulations.

Finite‐state Markov modelling for wireless cooperative networks

Finite-state Markov chain (FSMC) models can capture the essence of time-varying fading channels and they are important tools for wireless network protocol design and performance study. How to build FSMC models for multi-hop and multi-path wireless systems remains an open issue. In this study, the FSMC models are developed for amplify-and-forward (AF) cooperative systems with selection combining (SC) and maximum ratio combining (MRC) techniques, respectively. First, the second-order statistics, the level-crossing rate and the average fade duration, are derived based on the statistical properties of each individual path, for the AF cooperative systems with SC and MRC, respectively. The results reveal that, in addition to improving the average received signal-to-noise ratio, the diversity combining schemes also improve its second-order statistical properties. Simulation results are given to verify the accuracy of the developed FSMC models. Finally, the models are used to optimise the configuration for scalable video streaming in an AF cooperative network. Experimental results show the feasibility and advantage of applying the proposed FSMC models for assisting protocol design and optimisation in wireless cooperative networks.

Performance of Incremental AF Relaying Cooperative Networks with the nth Best Relay over Rayleigh Fading Channels

Cooperative diversity networks have recently been proposed as a promising technology to improve performance over fading channels. In this paper, we consider incremental amplify-and-forward (AF) cooperative diversity networks which employ the N th best relay when the best relay is unavailable due to issues such as scheduling or load balancing. The end-to-end performance is analyzed over independent and identical (i.i.d.) and nonidentical (i.n.d.) Rayleigh fading channels. Closed form expressions for the bit error rate and channel capacity are derived, and results are presented to illustrate the performance. According to the analysis, The incremental AF strategy can reduce BER greatly when comparing to the conventional direct communication without cooperative, although it can not get the capacity of conventional direct communication, which is with the power as the total power of soure and N th best relay node in AF cooperative network. The incremental AF strategy with N th best relay can improve the capacity in high SNR region comparing to the complete cooperative with N th best relay when BER can be accepted by setting different threshold for SNR of the direct link between source node S and destination node D . The incremental N th best relay cooperative protocol can be useful when considering improving the error rate and bandwidth efficiency at the same time comparing to the conventional direct system and complete cooperative

Transceiver Design for Distributed STBC Based AF Cooperative Networks in the Presence of Timing and Frequency Offsets

In multi-relay cooperative systems, the signal at the destination is affected by impairments such as multiple channel gains, multiple timing offsets (MTOs), and multiple carrier frequency offsets (MCFOs). In this paper we account for all these impairments and propose a new transceiver structure at the relays and a novel receiver design at the destination in distributed space-time block code (DSTBC) based amplify-and-forward (AF) cooperative networks. The Cramer-Rao lower bounds and a least squares (LS) estimator for the multi-parameter estimation problem are derived. In order to significantly reduce the receiver complexity at the destination, a differential evolution (DE) based estimation algorithm is applied and the initialization and constraints for the convergence of the proposed DE algorithm are investigated. In order to detect the signal from multiple relays in the presence of unknown channels, MTOs, and MCFOs, novel optimal and sub-optimal minimum mean-square error receiver designs at the destination node are proposed. Simulation results show that the proposed estimation and compensation methods achieve full diversity gain in the presence of channel and synchronization impairments in multi-relay AF cooperative networks.

Two-Way Relaying in Interference-Limited AF Cooperative Networks Over Nakagami- $m$ Fading

The performance of dual-hop amplify-and-forward (AF) two-way relaying systems with multiple cochannel interferers at the AF relay and two noisy end-sources is investigated. Assuming a Nakagami- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$m$</tex></formula> fading environment, closed-form approximate expressions for the outage probability, average error probability, and achievable sum rate are derived, yielding results which, in practice, are indistinguishable from the exact analysis. In addition, the derived approximate expressions are evaluated instantaneously, regardless of the number of interferers, highly contrasting with the intricacy and computational inefficiency inherent to the exact formulations, which requires the evaluation of nested multiple integrals, i.e., a problem that becomes computationally intractable as the number of interferers increases. Our analysis allows for general operating scenarios with distinct integer-value Nakagami- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$m$</tex></formula> fading parameters and unequal average fading power values between the hops. Monte Carlo simulation results are presented to corroborate the tightness of the proposed approximations.

Two-stage power allocation for amplify-and-forward cooperative networks with distributed GABBA space–time codes

This study presents a two-stage power allocation for the amplify-and-forward (AF) cooperative networks with distributed generalised ABBA (GABBA) space–time codes. The new power allocation scheme first determines the transmit power between the source node and the relay nodes by maximising the instantaneous rate, and thereafter optimises the power distribution among the relay nodes via the water-filling. Also, a maximum-likelihood detection, which makes use of the encoding structure of the distributed GABBA space–time codes, is addressed to alleviate the computational overhead. Moreover, a performance analysis including the array gain and the diversity gain is also scrutinised to provide further insights into the cooperative networks considered, where the destination is equipped with multiple antennas. Conducted simulations show that the GABBA coded AF cooperative networks incorporated with the proposed two-stage power allocation can attain close or even superior performance compared with previous works but with substantially reduced computational complexity.

Power allocations in minimum-energy SER-constrained cooperative networks

In this paper, we propose minimum power allocation strategies for repetition-based amplify-and-forward (AF) relaying, given a required symbol error rate (SER) at the destination. We consider the scenario where one source and multiple relays cooperate to transmit messages to the destination. We derive the optimal power allocation strategy for two-hop AF cooperative network that minimizes the total relay power subject to the SER requirement at the destination. Two outstanding features of the proposed schemes are that the power coefficients have a simple solution and are independent of knowledge of instantaneous channel state information (CSI). We further extend the SER constraint minimum power allocation to the case of multibranch, multihop network and derive the closed-form solution for the power control coefficients. For the case of power-limited relays, we propose two iterative algorithms to find the power coefficients for the SER constraint minimum-energy cooperative networks. However, this power minimization strategy does not necessarily maximize the lifetime of battery-limited systems. Thus, we propose two other AF cooperative schemes which consider the residual battery energy, as well as the statistical CSI, for the purpose of lifetime maximization. Simulations show that the proposed minimum power allocation strategies could considerably save the total transmitted power compared to the equal transmit power scheme.

A Novel Power Allocation and Relay Selection Scheme in AF Cooperative Networks with Mean Channel Gain Information

In this letter, a novel power allocation scheme is proposed to improve the outage performance of an amplify-and-forward (AF) cooperative communication network with multiple potential relays under the assumption that only mean channel gains are available at the transmitters. In this scheme, power allocation is studied jointly with a relay selection algorithm which has low computational complexity. Simulation results demonstrate the performance improvement of the proposed scheme in terms of outage behavior.

Performance Analysis and Power Allocation for Amplify-and-Forward Cooperative Networks over Nakagami-m Fading Channels

In this paper, we consider a dual-hop wireless cooperative network with amplify-and-forward (AF) relaying. The output signal-to-noise ratio (SNR) at the destination of the AF cooperative networks is in the form of the sum of harmonic mean of the source-relay channel SNR and the relay-destination channel SNR. Instead of deriving the exact probability density function (PDF) of the output SNR, we study the series expansion of this PDF around zero. This result is then applied to evaluate the performance of the AF cooperative systems over Nakagami-m fading channels, and closed-form high-SNR approximations of the average symbol error rate (SER) and the outage probability are derived. Next, we investigate the optimal power allocation (OPA) among the source node and the relays to minimize the approximate SER as well as the outage probability. It is shown that the optimal power allocation depends on the channel mparameters and the ratio of the source-relay channel gain to the relay-destination gain. In addition to the optimal power allocation, we also propose a low complexity sub-optimal power allocation (SubOPA) scheme. The performance improvement with optimal and sub-optimal power allocation is analyzed and validated by numeric results. It is shown that equal power allocation is near optimal when the relays are close to the source, while significant performance improvement is observed by both the optimal and sub-optimal power allocation schemes when the relays are close to the destination.