Amplify-and-forward Cooperative Systems Research Articles

Mixed RF/FSO SWIPT-Based OSLMD Coded AF Cooperative Communication System: Performance Analysis

In this paper, the performance analysis of simultaneous wireless information and power transfer (SWIPT) using time switching (TS) protocol-based amplify-and-forward (AF) dual-hop mixed radio-frequency/free-space optic (RF/FSO) coded and uncoded communication system (CC and UC) is investigated. Specifically, we look at using the One-Step Majority-Logic Decodable (OSMLD) codes at the source and a majority logic decoding algorithm (MLGD) at the destination, jointly with the use of maximal-ratio combining and SWIPT/TS techniques at the relay. Furthermore, the RF link undergoes Nakagami- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m$ </tex-math></inline-formula> model, while the second-hop is subject to Máalaga- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {M}$ </tex-math></inline-formula> atmospheric turbulence with the effect of pointing errors. Closed-form and asymptotic formulations for the average bit error probability (ABEP) are obtained in terms of the system parameters for both CC and UC scenarios in addition of the average channel capacity analysis. Computer-based Monte Carlo simulations were used to numerically validate all of the obtained mathematical formulations. Expectedly, it is shown that significant coding gains are achieved using OSMLD codes in comparison with UC. In addition, above a specific threshold of energy efficiency, the system performance gets steady in the high signal-to-noise-ratio regime. Moreover, the decoding method used in this work has been shown to be suitable for the SWIPT/TS-assisted RF/FSO coded AF cooperative communication system where high performance alongside low computational complexity are required.

Capacity analysis of cooperative amplify and forward multiple‐input multiple‐output systems

AbstractThe capacity and mutual information of amplify and forward (AF) cooperative multiple‐input multiple‐output (MIMO) systems with direct link are studied and analyzed in this article. Specifically, the capacities of space modulation techniques (SMTs)‐AF and spatial multiplexing (SMX)‐AF cooperative systems are derived, and the conditions under which the capacity is accomplished are discussed and interpreted. The impact of varying system and channel parameters on the capacity is studied and discussed. As well, the impact of the presence or the absence of the direct link on the capacity performance is discussed. It is revealed that the capacity can be attained if the distribution of both direct and cooperative links follow complex Gaussian distribution. The capacity of SMTs‐AF systems is shown to be higher than that of SMX‐AF counterparts. As well, the capacity of SMTs‐AF is shown to be independent of the fading channel distribution as the channel is a source of spatial symbols in SMTs. Additionally, it is disclosed that the capacity performance is significantly enhanced in the presence of the direct link and adding more AF relays enhances the performance.

Capacity Analysis of an AF Relay Cooperative NOMA System Using MRC

Non-orthogonal multiple access (NOMA) is widely studied in both academia and industry due to its high spectral efficiency over orthogonal multiple access (OMA). To effectively improve spectrum efficiency, an amplify-and-forward (AF) cooperative NOMA system is proposed as well as a novel detection scheme is proposed, in which we first perform successive interference cancellation (SIC) twice at U1 for the two signals received from two time slots to remove interference from symbol 2, then two new signals apply max ratio combining (MRC). In addition, a closed-form upper bound approximation for the ergodic capacity of our proposed system is derived. Monte-Carlo simulations and numerical analysis illustrate that our proposed system has better ergodic capacity performance than the conventional cooperative NOMA system with decode-forward (DF) relay, the conventional cooperative NOMA system with AF relay and the proposed AF cooperative NOMA system in [16]. In addition, we can see that ergodic capacity of all NOMA cooperative systems increase with the increase of transmit SNR. Finally, simulations display that power allocation coefficients have little effect on ergodic capacity of all NOMA cooperative systems. This is due to this fact that ergodic capacity of two symbols can be complementary with changing of power allocation coefficients.

A Partial Amplify and Forward Cooperative Communication Strategy Based on Blind Signal Detection

Due to the great potential in extending propagation distance and enhancing the link reliability, amplify and forward (AF) cooperative communications have attracted much attention recently. However, the existing studies mainly focus on the energy consumption analysis and optimization, and also the channels used in communications are based on Rayleigh/Rician fading model, and/or it was usually supposed that the channel state information (CSI) is known or can be acquired by a training sequence. In this paper, blind signal detection for AF cooperative communication systems based on time division multiple access (TDMA) is studied, in which the channels are modeled as frequency selective fading and the CSI are unknown. A blind signal detection algorithm of partial amplify and forward (PAF) cooperative communication is proposed based on semidefinite relaxation (SDR). This method can recover the data without the training sequence and need not to implement blind equalization for the unknown channels. With the correlation between data of different links, the proposed method can obtain the optimal solution efficiently and achieve better performance of signal detection than the traditional algorithm. By simulations, the energy consumption efficiency as well as the overall system performance of the proposed strategy are verified.

THE PERFORMANCE OF CONVOLUTIONAL CODING BASED COOPERATIVE COMMUNICATION: RELAY POSITION AND POWER ALLOCATION ANALYSIS

Wireless communication faces adversities due to noise, fading, and path loss. Multiple-Input Multiple-Output (MIMO) systems are used to overcome individual fading effect by employing transmit diversity. Duo to user single-antenna, Cooperation between at least two users is able to provide spatial diversity. This paper presents the evaluation of the performances of the Amplify and Forward (AF) cooperative system for different relay positions using several network topologies over Rayleigh and Rician fading channel. Furthermore, we present the performances of AF cooperative system with various power allocation. The results show that cooperative communication with convolutional coding shows an outperformance compared to the non-convolutional, which is a promising solution for high data-rate networks such as (WSN), Ad hoc, (IoT), and even mobile networks. When topologies are compared, the simulation shows that, linear topology offers the best BER performance, in contrast when the relay acts as source and the source take the relay place, the analysis result shows that, equilateral triangle topology has the best BER performance and stability, and the system performance with inter-user Rician fading channel is better than the performance of the system with inter-user Rayleigh fading channel.

Exact error rate analysis of two-hop AF Rayleigh fading cooperative systems with variable amplification gain

A careful exploration of literature confirms that exact symbol-error-rate (SER) performance of amplify-and-forward (AF) wireless cooperative communication systems with variable amplification gain has not been analyzed before; even for simple models with single relay (i.e, two-hop systems) and Rayleigh fading channels. The main source of this mathematical intractability is the appearance of the modified Bessel function of the second type Kν(·) in the statistics of these systems end-to-end SNR. Here, however, we aim at filling this literature gap by proposing a novel theoretical method that helps in examining, for the first time, the exact SER performance of two-hop AF systems, where, as a case study, we assume Rayleigh quasi-static fading environment with perfect channel estimation. Specifically, we derive two new exact expressions for the system’s SER performance, which involve rapidly convergent infinite summation(s) and efficiently computable special functions. Furthermore, for the same system, we obtain new approximate closed-form SER expression, which outperforms its literature counterpart. The obtained analytical results are useful to gain insight about the actual error performance of variable gain AF systems. The presented methodologies can form a generic framework for exact SER performance evaluation of other variable gain AF cooperative system models.

Enhanced Performance of Amplify and Forward Cooperative OFDM System in a Hostile Environment

This paper introduces a cooperative orthogonal frequency division multiplexing (CO-OFDM) based on amplify and forward (AF) relay and utilizing a fast low complexity T-transform as a subcarriers modulation scheme. The proposed cooperative system is developed by changing the modulation/demodulation algorithms which significantly enhanced the immunity of the system to deep notches of the multipath channels. Thereafter, the paper presents a mathematical analytic model for the proposed amplify and forward CO-T-OFDM scheme. The use of T-transform in the transceiver of the proposed system enhances the signal diversity. Therefore, the presented AF cooperative system is efficient in enhancing the signal diversity, mitigating the effects of multipath fading channels and achieving more reliable bit-error-rate (BER) performance than the state-of-the-art cooperative system. It also moderates the peaks power of the signal. The BER of the developed AF cooperative system is evaluated by Monte Carlo simulation over frequency-selective multipath channels when AF relay is used, and compared with the BER performance of the standard AF cooperative system. The results show that the developed AF cooperative technology achieves better BER than the classic CO-OFDM under different transmission scenarios.

Ergodic Channel Capacity Analysis of Downlink in the Hybrid Satellite-Terrestrial Cooperative System

In this paper, the ergodic channel capacity of the downlink is analyzed for a hybrid satellite-terrestrial cooperative system, which consists of a satellite (the source), a mobile terminal (the destination), and several gap fillers (the relays) located at the ground. The links between the satellite and the relays and the link between the satellite and the destination experience independent shadowed Rician fading, and the links between the relays and the destination experience Rayleigh fading. The maximal ratio combining technique is used at the destination to combine the direct signal received from the satellite and the relayed signals from relays with different cooperative protocols, namely amplify-and-forward (AF) and decode-and-forward (DF). The moment generating function (MGF)-based approach is adopted to derive the closed-form expressions of the ergodic downlink channel capacity of the hybrid satellite-terrestrial cooperative system. The numerical results are compared with Monte Carlo simulations and numerical results calculated with the existing analytical expressions. Comparison results show that the analytical expression derived with the MGF-based approach can achieve a higher accuracy in the low signal-to-noise ratio (SNR) regime for the single relay scenario, and significantly reduce the computational complexity with a little loss of accuracy for multiple relays scenario. On the other hand, the ergodic downlink channel capacity of the hybrid satellite-terrestrial DF cooperative system is generally higher than that of the AF cooperative system. Moreover, the ergodic channel capacity of the hybrid satellite-terrestrial cooperative system decreases as the number of participating relays increases, which can be overcome using the best relay selection strategy. In addition, the ergodic downlink channel capacity of the hybrid satellite-terrestrial cooperative system increases when the channel condition of the link between the satellite and the relay goes better, and is larger than that of the no relay land mobile satellite system when the transmitted SNR is below a certain value.

A Novel Equivalent Definition of Modified Bessel Functions for Performance Analysis of Multi-Hop Wireless Communication Systems

A statistical model is derived for the equivalent signal-to-noise ratio of the Source-to-Relay-to-Destination (S-R-D) link for Amplify-and-Forward (AF) relaying systems that are subject to block Rayleigh-fading. The probability density function and the cumulated density function of the S-R-D link SNR involve modified Bessel functions of the second kind. Using fractional-calculus mathematics, a novel approach is introduced to rewrite those Bessel functions (and the statistical model of the S-R-D link SNR) in series form using simple elementary functions. Moreover, a statistical characterization of the total receive-SNR at the destination, corresponding to the S-R-D and the S-D link SNR, is provided for a more general relaying scenario in which the destination receives signals from both the relay and the source and processes them using maximum ratio combining (MRC). Using the novel statistical model for the total receive SNR at the destination, accurate and simple analytical expressions for the outage probability, the bit error probability, and the ergodic capacity are obtained. The analytical results presented in this paper provide a theoretical framework to analyze the performance of the AF cooperative systems with an MRC receiver.

A PAPR Joint Optimization Algorithm in AF Cooperative Multicarrier System

In this paper, to reduce PAPR (Peak-to-Average Power Ratio) in AF (Amplify and Forward) cooperative multicarrier system, an SLM-TR (Selective Mapping-Tone Reservation) joint optimization algorithm based on CAZAC (Constant Amplitude Zero Auto-Correlation) sequence is proposed. In our proposed method, several carriers are reserved for tone candidates, and then SLM (Selective Mapping) algorithm is utilized for the remaining data carriers. In SLM procedure, CAZAC sequences are utilized as the initial phase vector candidates and phase vector optimization is further processed by using feedback phase rotation algorithm for data carriers. After that, in continued TR (Tone Reservation) operation, random sequence is considered as the initial tone sequence and further optimized and subtracted from the modified data signal for peak cancelling using cyclic transposition searching algorithm to further reduce PAPR. Finally, the signal with the lowest PAPR is transmitted. By doing so, not only exhausting searching for optimal phase vectors is avoided efficiently, but also additional PAPR reduction is achieved by tone sequence modification. Simulation results show that the proposed method can reduce PAPR considerably and improve BER (Bit Error Rate) performance effectively, with insurance of high spectrum efficiency, low complexity and low loss in power efficiency. The influences of several conditions such as HPA (High power Amplifier) type, initial phase vector number, tone carrier number and sequence type are discussed to improve system QoS(Quality of Service).

Performance analysis of OFDM based AF cooperative systems in selection combining receiver over Nakagami‐m fading channels with nonlinear power amplifier

SummaryIn this paper, performance analysis of orthogonal frequency division multiplexing (OFDM) based amplify‐and‐forward (AF) cooperative relaying network with selection combining (SC) scheme over independently but not necessarily identically distributed (i.n.i.d.) frequency selective Nakagami‐m fading channels is investigated. Theoretical analysis of closed‐form expressions for outage probability and average symbol error rate (ASER) have been proposed, while considering nonlinear distortions (NLD) introduced by nonlinear power amplifier (NLPA) at the relay node. Asymptotic behavior of outage probability is also analyzed in high signal‐to‐noise ratio (SNR) regime to evaluate the diversity order of the system under several conditions. Further, impacts of fading parameter and NLD are highlighted on the outage probability, ASER and the diversity order of the system under different situations. The derived theoretical results are compared with Monte' Carlo simulations and verify the correctness of theoretical results for different system configurations and SNR levels. The derived expressions are generalized, and hence, can be easily used for analysis over variety of fading environments. Copyright © 2016 John Wiley &amp; Sons, Ltd.

Research on Overlapped Time Division Multiplexing in the Amplify-and-Forward Cooperative Mode

In order to improve spectrum efficiency of cooperative communication system, Overlapped Time Division Multiplexing (OVTDM) is applied to Amplify-and-Forward (AF) cooperative communication system. The simulation results under Additive White Gaussian Noise (AWGN) channel show that the performance of new system is superior to that of corresponding AF cooperative communication system.

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.

Dual‐hop amplify‐and‐forward cooperative relaying in the presence of Tx and Rx in‐phase and quadrature‐phase imbalance

In this study, dual-hop channel state information-assisted amplify-and-forward (AF) cooperative systems in the presence of in-phase and quadrature-phase (I/Q) imbalance, which refers to the mismatch between components in the I and Q branches, are investigated. First, the authors analyse the performance of the considered AF cooperative protocol without compensation for the I/Q imbalance as the benchmark. Then, a compensation algorithm for the I/Q imbalance is proposed, which makes use of the received signals at the destination, from the source and the relay nodes, together with their conjugations to detect the transmitted signal. Moreover, the authors study the considered AF cooperative system implemented with the opportunistic relay selection and the proposed compensation mechanism for the I/Q imbalance. The performance of the AF cooperative system under study is evaluated in terms of average symbol error probability, which is derived by considering transmission in a Rayleigh fading environment. Numerical results are provided and show that the proposed compensation algorithm can efficiently mitigate the effect of the I/Q imbalance. On the other hand, it is observed that the AF cooperative system with opportunistic relay selection acquires a performance gain beyond that without relay selection.

Low-Complexity End-to-End Performance Optimization in MIMO Full-Duplex Relay Systems

In this paper, we deal with the deployment of full-duplex relaying in amplify-and-forward (AF) cooperative networks with multiple-antenna terminals. In contrast to previous studies, which focus on the spatial mitigation of the loopback interference (LI) at the relay node, a joint precoding/decoding design that maximizes the end-to-end (e2e) performance is investigated. The proposed precoding incorporates rank-1 zero-forcing (ZF) LI suppression at the relay node and is derived in closed-form by solving appropriate optimization problems. In order to further reduce system complexity, the antenna selection (AS) problem for full-duplex AF cooperative systems is discussed. We investigate different AS schemes to select a single transmit antenna at both the source and the relay, as well as a single receive antenna at both the relay and the destination. To facilitate comparison, exact outage probability expressions and asymptotic approximations of the proposed AS schemes are provided. In order to overcome zero-diversity effects associated with the AS operation, a simple power allocation scheme at the relay node is also investigated and its optimal value is analytically derived. Numerical and simulation results show that the joint ZF-based precoding significantly improves e2e performance, while AS schemes are efficient solutions for scenarios with strict computational constraints.

Coalition-Assisted Resource Allocation in Large Amplify-and-Forward Cooperative Networks

This paper considers the problem of resource allocation for a large-scale wireless network consisting of multiple amplify-and-forward (AF) cooperative links. To effectively manage interlink interference and achieve efficient resource allocation, we propose a novel two-stage game model in which links form coalitions in the first stage, and in the second stage, they engage in a noncooperative game given the coalition structure determined in the first stage. This model is distinct from the classic coalitional game theory as it captures the important possibilities of externalities across coalitions. In the coalitional game formulation, we have derived an analytical expression for the asymptotic throughput of an AF cooperative system in the regime of large number of relays and have incorporated opportunistic relaying as an effective technique to combat harmful interferences. In the sequential noncooperative game formulation, the uniqueness of the Nash equilibrium has been established for the general <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> -player case, which generalizes previous works on the two-player game. Simulation results demonstrate over 200% sum rate enhancement relative to the noncooperative approach, primarily due to the improved pattern of frequency reuse and the benefit of multiuser diversity.

Outage probability for cooperative diversity with selective combining in cellular networks

AbstractThis paper analyzes the outage probability for amplify‐and‐forward (AF) and decode‐and‐forward (DF) cooperative diversity systems with selective combining, for the case of a log‐normal Nakagami faded desired signal and log‐normal Rayleigh faded co‐channel interferers. The outage probability is compared to that of a dual‐receive antenna system also with selective combining. The results of this paper show that the proposed cooperative diversity systems can result in a lower outage probability than the corresponding dual‐receive antenna system, but only when the relay is located in a particular region of the cell with respect to the destination mobile station location. Moreover, this paper shows that the AF cooperative diversity system is more robust than the DF cooperative diversity system for the composite channel condition and multiple interferers. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Ergodic Channel Capacities for the Amplify-and-Forward Half-Duplex Cooperative Systems

In this paper, the ergodic channel capacities are established for the amplify-and-forward (AF) half-duplex cooperative systems, which consist of a source node, a destination, and multiple-relay nodes. The relay nodes assist the transmission from the source node to the destination. Since the channel matrices for the cooperative systems involve product of Gaussian random variables, which are no longer Gaussian, the approach in obtaining the ergodic channel capacity for conventional multiple-input-multiple-output (MIMO) Gaussian channels (Telatar, 1999) is not applicable. By using a novel approach, we have arrived at the following conclusions about the ergodic channel capacities for the AF cooperative systems. For the single antenna AF relay systems in which all nodes are equipped with one antenna, the optimal covariance matrix of the input signals to achieve the ergodic channel capacity is diagonal, and the diagonal elements are obtained by solving optimization problems of multidimensional integrals. These diagonal entries are not all equal even if all the channel gains in the cooperative systems are independent and identically distributed (i.i.d.) Gaussian with unit variance. Therefore, a white input signal for the AF cooperative system may not achieve the ergodic channel capacity of the system. This is in direct contrast to the case of conventional multiple-input-single-output (MISO) systems having i.i.d. Gaussian channel gains of unit variance, in which case, the ergodic capacity is achieved if the input covariance matrix is a scaled identity matrix. For the MIMO relay system in which the nodes have multiple antennas, the input covariance matrix to achieve the ergodic capacity is block diagonal and each block diagonalizes the autocorrelation of channel matrix from the source to the destination. This is different from the case of conventional MIMO systems, where the input covariance matrix to achieve the ergodic channel capacity diagonalizes the channel autocorrelation matrix of the MIMO system (Tulina, Lozano, and Verdu, 2006). If the channel gains in conventional MIMO systems are correlated Gaussian random variables, the input covariance matrix is a full matrix, not block diagonal; and if the channel gains are i.i.d. Gaussians, the optimal input covariance matrix is a scaled identity. The observations obtained in this paper reveal useful insights of how the AF cooperative systems ldquomimicrdquo the conventional MISO and MIMO systems from the ergodic channel capacity perspective.

Parameter Optimization for Amplify-and-Forward Relaying Systems with Pilot Symbol Assisted Modulation Scheme

Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with a pilot symbol as-sisted modulation (PSAM) scheme. It is assumed that a linear minimum mean square estimator (LMMSE) is used for the channel estimation at the receiver. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative communication systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the parameter optimization in the PSAM scheme. We discuss how the pilot spacing and the length of the Wiener ?lter should be chosen under the constraint of a tradeoff between pilot overhead, estimation accuracy, and receiver complexity. We also formulate an power allocation problem for the considered system. It is shown that the power allocation problem can optimally be solved by means of a gradient search method. Numerical simulations are presented to verify the correctness of the theoretical results and to demonstrate the benefits of the parameter optimization.

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.