Cooperative Amplify-and-forward Research Articles

Optimal Secure Channel Access in Distributed Cooperative Networks With Untrusted Relay

This paper investigates optimal channel access strategies to improve secure communications over a distributed cooperative wireless network with multiple user pairs and an untrusted amplify-and-forward (AF) relay. The user pairs communicate directly or via the relay. To enable secure communication, we formulate a channel access problem to maximize the average secrecy system throughput with destination-based jamming. Using optimal sequential planned decision theory, we propose an optimal channel access strategy where the winning user pair uses direct transmission, cooperative AF relaying, or cooperative jamming in an adaptive manner. We rigorously prove the optimality of the solution and provide a distributed channel access algorithm based on the pure threshold structure, which is easy to implement. Numerical results demonstrate effectiveness and efficiency of the proposed strategy compared to alternatives.

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.

Coded Assisted Transmit and Receive IQ Mismatch Compensation With Channel Estimation for AF Cooperative OFDM Systems

Amplify-and-forward (AF) orthogonal frequency division multiplexing (OFDM) transmissions encounter a significant difficulty in the form of in-phase and quadrature phase (IQ) mismatch. Previous reports on this problem have solely been discussed in the context of uncoded transmissions. In addition, in these precedent studies, IQ equalization must be conducted following the estimation stage for accurate detection of data symbols. This research delves into the issue of the IQ mismatch between transmission and reception in AF-OFDM systems in the context of channel coding. We design a magnificent code-aided approach to predict the overall channel impulse responses (CIRs), which encompass the actual CIRs and IQ mismatch originating at the source, relay, and destination. Instead of using a collection of algorithms, the proposed approach can be utilized to estimate nine parameters simultaneously. Due to the impractical nature of the precise maximum-likelihood (ML) strategy to this situation, we instead utilize an expectation-maximization (EM) process as a low complexity strategy to predict the parameters under consideration. The suggested estimation approach uses an iterative process to improve predictions exploiting the a priori knowledge gained from the soft information supplied by the channel decoder. In addition, we demonstrate how to carry out data detection by making use of the estimated parameters. The simulation results verify the effectiveness of the proposed estimator and detector for usage in real-world settings, with superiority over the conventional ones.

Performance Analysis of AF Cooperative Relaying Networks with SWIPT

Cooperative communication networks have received more attention due to its ability to improve the signal quality of terminal devices by spatial diversity. Under recent advance in internet of things, In order to extend the service life of terminal devices powered by battery, simultaneous wireless information and power transfer (SWIPT) technique has been emphasize. The terminal devices can harvest energy and decode information from the same radio frequency (RF) signal using by SWIPT technique. In this paper, we combine both techniques to study the performance of both conventional cooperative relaying networks without SWIPT and cooperative relaying networks with SWIPT under an amplify-and-forward (AF) relaying network. To the best of our knowledge, no one simultaneously studies and compares the performance of both systems. Therefore, the outage probabilities of both systems are carried out, and numerical results are compared in this paper. The main results include: (1) Compared with conventional cooperative communication, the cooperative communication with SWIPT has better outage probability only when the distance between relay node and source node is less than one. It implies that, to outperform the conventional cooperative communication, the relay node should harvest enough energy for signal transmission. (2) With the diversity of direct path and relay path, the outage probability of cooperative communication with EH under an AF relaying network has been significantly reduced.

Physical Layer Performance of a Cooperative Amplify and Forward Scheme for MIMO WLANs

This paper proposes a novel cooperative amplify and forward (CAF) architecture for MIMO WLANs to improve their coverage and transmission rates, without requiring any modifications in the IEEE 802.11 standards at the clients. System models are used for analyzing the physical layer of CAF networks, and compared with the conventional amplify-and-forward (AF) and decode-and-forward (DF) networks. Numerical results demonstrate that the CAF network clearly outperforms conventional 802.11 networks, and AF and DF networks in terms of coverage and throughput.

Exact SEP and performance bounds for orthogonal space‐time block codes in cooperative multiantenna AF relaying networks

SummaryIn this paper, we derive a moment generating function (MGF) for dual‐hop (DH) amplify‐and‐forward (AF) relaying networks, in which all nodes have an arbitrary number of antennas, with orthogonal space‐time block code (OSTBC) transmissions over Rayleigh fading channels. We present an exact error rate expression based on the derived MGF and another analytical approach to derive achievable performance bounds as closed‐forms of symbol error rate, outage probability, and normalized channel capacity. Furthermore, we derive the asymptotic behavior of symbol error rate and outage probability. From this asymptotic behavior, it is shown that the diversity order and its dependence on antenna configurations can be explicitly determined. Simulation results are also presented to verify their accuracy by comparing with numerical results and to provide an insight to the relationship between relaying networks' antenna configuration and diversity order. It is confirmed that the transmit antenna gain of the source node and the receive antenna gain of the relay node can be obtained only when the relay is close to the destination, and then, the transmit antenna gain of the relay node and the receive antenna gain of the destination node can be obtained only when the relay is close to the source.

Cooperative AF relaying with energy harvesting in Nakagami-[formula omitted] fading channel

In this paper, the bit error performance of an energy harvesting (EH) cooperative amplify-and-forward (AF) relaying system, in which the relay harvests energy from radio frequency source signal and then uses this energy to transmit its signal to the destination in the presence of a direct link between the source and the destination, is investigated in Nakagami- m fading channel. A unified approach to the analysis of bit error probability (BEP) is presented for the cases where the relay harvests energy based on power splitting (PS), time switching (TS) and ideal operational modes. Simulation results validate the theoretical analysis performed for coherent M-PSK and M-QAM and different system parameters. Dual-hop EH and conventional non-EH cooperative AF relaying systems are considered for comparison purposes. The obtained results show that the system bit error rate performance is mostly dependent on the channel parameter m and the energy harvesting parameters.

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.

Destination Assisted Jamming and Beamforming for Improving the Security of AF Relay Systems

In this paper, we propose a destination-assisted jamming and beamforming (DAJB) scheme for physical layer security in a one-way cooperative amplify-and-forward (AF) relay communication system. The system model consists of one source, one destination, one eavesdropper, and N relay nodes, with the individual power constraint of each relay node and the destination-assisted jamming node as well as unknown instantaneous channel state information (CSI) of the eavesdropper. Due to the half-duplex constraint of the relay nodes, there are two phases in our proposed DAJB scheme. In the first phase, the source node broadcasts information signal and all N relay nodes listen simultaneously. In the meantime, the destination node transmits the jamming signal to confuse the potential eavesdropper. In the second phase, all N relay nodes amplify and forward the received signals, covered by the artificial noise (AN), to the destination using the distributed beamforming technology. The optimal beamformer weights and power allocation are obtained by solving the second-order convex cone programming (SOCP) together with a linear programming (LP) problem. Furthermore, the performance of the DAJB scheme is analyzed in terms of the achievable secrecy rate. Compared with the scheme that selects a relay node as the jammer, we obtain larger power gain to achieve higher secrecy rates. Finally, the simulation results verify that the DAJB scheme greatly improves the secrecy rate of a one-way cooperative AF relay communication system.

Efficient Analysis of the Ergodic Capacity of Cooperative Non-Regenerative Relay Networks Over Generalized Fading Channels

In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight approximate moment applicable to myriad of fading environments including mixed and composite fading channels. Three distinct adaptive source transmission policies were considered in our analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading environments (especially for the analysis of the mixed fading case)and provides significant advantage to model wireless system for mixed and composite fading channel. In addition to simplifying computation complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.

Power Allocation and Relay Selection for AF Cooperative Relay Systems With Imperfect Channel Estimation

In this paper, we investigate power-allocation and relay-selection algorithms for amplify-and-forward (AF) cooperative relay systems under imperfect channel estimation. Based on maximizing a tight capacity lower bound, a closed-form formula for optimal power allocation under a given relay is first derived and then used to establish an optimal relay-selection algorithm. By exploring the asymptotic behavior of the capacity lower bound, a suboptimal but reduced-complexity relay-selection algorithm is further presented. Simulation results demonstrate that significant capacity gains can be achieved by using the proposed optimal and suboptimal algorithms.

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 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.

Performance Improvement of Non-Regerative Cooperative Relay Networks with Optimal Power Allocation and Adaptive M-QAM/M-PSK Modulation Over Generalized Fading Channels

This paper analyzes the performance of Channel Side Information (CSI)-assisted cooperative amplify-andforward (CAF) relay networks that employ both the node placement (i.e., relay position) based optimal power allocation policy among collaborating nodes and adaptive M-ary quadrature amplitude modulation (M-QAM)/ M-ary phase shift keying (M-PSK) techniques in generalized wireless fading environments. In particular, we advocate a simple yet unified numerical approach based on the marginal moment generating function (MGF) of the total received Signal to Noise Ratio (SNR) to derive analytical expressions for the average bit error rate (ABER), mean achievable spectral efficiency, and outage probability performance metrics. The proposed analytical framework is sufficiently general and flexible to characterize the performance of adaptive-link CAF relay networks over a wide range of fading distributions (i.e., not restricted to Rayleigh fading or independent identically distributed (i.i.d) Nakagami-m fading ) with independent but non-identically distributed (i.n.d) fading statistics across the spatially distributed diversity paths. Additionally, we further simplify the computational complexity, by employing the use of an “approximate MGF expression” to compute the system performance metrics over the generalized fading channel. Employing the above novel approach based on “approximate MGF” in conjunction derived analytical frameworks allows us to simplify the computation complexity of achievable spectral efficiency as well as ABER of CAF relay system in the generalized fading environments by simply replacing appropriate single channel MGF which is readily available.

Performance Analysis of the Link-Adaptive Cooperative Amplify-and-Forward Relay Networks with Opportunistic Relaying Strategy

This paper analyzes the performance of cooperative amplify-and-forward (CAF) relay networks that employ adaptive M-ary quadrature amplitude modulation (M-QAM)/M-ary phase shift keying (M-PSK) digital modulation techniques in Nakagami-m fading channel. In particular, we present and compared the analysis of CAF relay networks with different cooperative diversity and opportunistic routing strategies such as regular Maximal Ratio Combining (MRC), Selection Diversity Combining (SDC), Opportunistic Relay Selection with Maximal Ratio Combining (ORS-MRC) and Opportunistic Relay Selection with Selection Diversity Combining (ORS-SDC). We advocate a simple yet unified numerical approach based on the marginal moment generating function (MGF) of the total received SNR to compute the average symbol error rate (ASER), mean achievable spectral efficiency, and outage probability performance metrics.

Joint-Design of Link-Adaptive Modulation and Coding with Adaptive ARQ for Cooperative Amplify and Forward Relaying System

This paper analyzes the efficiency of a joint-design of an adaptive modulation and coding (AMC) at the physical (PHY) layer with an adaptive R max -truncated selective-repeat automatic repeat request (ARQ) protocol at the medium access control (MAC) layer to maximize the throughput of cooperative nonregenerative relay networks under prescribed delay and/or error performance constraints. Particularly, we generalize the existing design model/results for cross-layer combining of AMC along with truncated ARQ in non-cooperative diversity networks in three-folds: (i) extension of the cross-layer PHY/MAC design or optimization to cooperative diversity systems; (ii) generalization/unification of analytical expressions for various network performance metrics to generalized block fading channels with independent but nonidentically distributed (i.n.d) fading statistics among the spatially distributed nodes; (iii) analysis of the effectiveness of joint-adaptation of the maximum retransmission limit R max of ARQ protocol and cooperative diversity order N for delay-insensitive applications. Our insightful numerical results reveal that the average throughput can be increased significantly by judiciously combining two additional degrees of freedom (N and R max ) that are available in cooperative amplify-and-forward (CAF) relay networks besides employing AMC at the PHY layer, especially in the most challenging low signal-to-noise ratio (SNR) regime.

A 60GHz Wireless Cooperative Communication System Based on Switching Beamforming

The challenge of penetrating obstacles along with impact from weak multipath effects makes 60GHz signal very difficult to be transmitted in non-line of sight (NLOS) channel. So 60GHz system is vulnerable to obstructions and thus likely results in link interruption. While the application of cooperative technology to solve link blockage problemin 60GHz system should consider the characteristic of directional transmission for 60GHz signal. Therefore in this paper a system is proposed to solve the link blockage problem in 60GHz NLOS communication environment based on the concept of cooperation and also the beamforming technology, which is the basis of directional transmission for 60GHz communication system. The process of anti-blockage solution with cooperative communication is presented in detail, and the fast switching and recovery schemes are well designed. The theoretical values of symbol error rate (SER) using decode and forward (DF) cooperation and amplify and forward (AF) cooperation are presented respectively when the common channel interference exists. Simulation results demonstrate that the performance based on DF cooperation is better than the performance based on AF cooperation when directional transmission is used.

Bit error rate performance of IR‐UWB ED‐PPM system using cooperative dual‐hop AF strategy

This study presents a novel analytical approach for evaluation of bit error rate (BER) performance of an impulse radio-ultra-wideband (IR-UWB) energy detector-pulse position modulation (ED-PPM) system, using dual-hop cooperative amplify and forward (AF) relaying strategy with optimum diversity combining, over IEEE 802.15.4a UWB channel. An approximate expression for BER has been derived based on energy detection principle. The analytical BER expression thus derived is validated with computer simulations, which confirm the accuracy in approximation used in investigation of BER. Furthermore, it is observed that the BER performance of IR-UWB ED-PPM system, improves substantially using dual-hop cooperative AF scheme, compared with non-cooperative scheme. Despite its poor BER performance, ED systems are preferred over AC systems, because of simplicity and low complexity.

Resource Allocation for Multiuser Improved AF Cooperative Communication Scheme

Joint power and bandwidth allocation of an improved amplify and forward (AF) cooperative communication scheme is proposed to utilize the spectrum efficiently. Each user adapts to a mixed strategy transmission using frequency division multiplexing (FDM), where part of the data is transmitted using AF relaying with diversity, and the other part is transmitted using direct transmission without diversity. The resource allocation problem aimed at maximizing the sum rate of a multi-user up-link scenario using the improved scheme is formulated. Both flat and frequency-selective fading channels are addressed. The resource allocation problem of the power and bandwidth profiles is non-convex and difficult to solve. In this sense, a two-step iterative algorithm is proposed, which alternates between solving either power allocation sub-problem for a given bandwidth profile or a bandwidth allocation sub-problem for a given power profile. The convergence and optimality of the proposed algorithm are discussed using game theory framework. Numerical simulations show the merits of the proposed improved AF cooperative communication scheme and the proposed iterative algorithm.

Distributed Beamforming for Spectrum-Sharing Systems With AF Cooperative Two-Way Relaying

We consider in this paper distributed beamforming for two-way cognitive radio networks in an effort to improve the spectrum efficiency and enhance the performance of the cognitive (secondary) system. In particular, we consider a spectrum sharing system where a set of amplify-and-forward (AF) relays are employed to help a pair of secondary transceivers in the presence of multiple licensed (primary) users. The set of relays participate in the beamforming process, where the optimal beamformer weights are obtained via a linear optimization method. For this system, we investigate the transmission protocols over two and three time-slots. To study and compare the performance tradeoffs between the two transmission protocols, for both of them, we derive closed-form expressions for the cumulative distribution function (CDF) and the moment generating function (MGF) of the equivalent end-to-end signal-to-noise ratio (SNR) at the secondary receiver. We analyze the performance of the proposed methods where closed-form expressions for the user outage probability and the average error probability are derived for independent and identically distributed Rayleigh fading channels. Numerical results demonstrate the efficacy of beamforming in enhancing the secondary system performance in addition to mitigating the interference to the primary users. In addition, our results show that the three time-slot protocol outperforms the two time-slot protocol in certain scenarios where it offers a good compromise between bandwidth efficiency and system performance.