Multi-relay Cooperative Networks Research Articles

Resource allocation algorithm for downlink secure transmission in wireless EH cooperative networks with idle relay-assisted jamming

In wireless Energy Harvesting (EH) cooperative networks, we investigate the problem of secure energy-saving resource allocation for downlink physical layer security transmission. Initially, we establish a model for a multi-relay cooperative network incorporating wireless energy harvesting, spectrum sharing, and system power constraints, focusing on physical layer security transmission in the presence of eavesdropping nodes. In this model, the source node transmits signals while injecting Artificial Noise (AN) to mitigate eavesdropping risks, and an idle relay can act as a jamming node to assist in this process. Based on this model, we formulate an optimization problem for maximizing system secure harvesting energy efficiency, this problem integrates constraints on total power, bandwidth, and AN allocation. We proceed by conducting a mathematical analysis of the optimization problem, deriving optimal solutions for secure energy-saving resource allocation, this includes strategies for power allocation at the source and relay nodes, bandwidth allocation among relays, and power splitting for the energy harvesting node. Thus, we propose a secure resource allocation algorithm designed to maximize secure harvesting energy efficiency. Finally, We validate the correctness of the theoretical derivation through Monte Carlo simulations, discussing the impact of parameters such as legitimate channel gain, power splitting factor, and the number of relays on secure harvesting energy efficiency of the system. The simulation results show that the proposed secure energy-saving resource allocation algorithm effectively enhances the security performance of the system.

Differential Modulation-Based Buffer-Aided Cooperative Relaying Network

In this article, we consider a multirelay cooperative network using a differential modulation technique. The given set-up consists of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$K$</tex-math></inline-formula> decode-and-forward (DF) relays, each equipped with a buffer of size <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$L$</tex-math></inline-formula> . All transceiver nodes in the considered cooperative network apply differential modulation for the transmission of data, hence, channel-state information is not required for decoding of the data at the receiving nodes. A priority-based max link selection approach is used for the selection of the best links for the transmission and reception of data. The Markov chain approach is used to derive the state-transition matrix of the system, which is then further used to model the evolution of buffer status. Analytical expressions of the outage probability and average bit error rate are obtained with the help of the state-transition matrix. The performance of the considered system is analyzed for different buffer sizes and a number of relays. The performance is then further compared with that of a coherent buffer-aided network and also with the nonbuffer-aided differential amplify-and-forward and DF systems. As compared to the coherent buffer-aided network, the considered buffer-aided differential system suffers a negligible signal-to-noise ratio penalty in the scenario when more than one buffer-aided relay is present in the network, which is a significant improvement when compared with the nonbuffer-aided differential cooperative systems, which suffer a performance penalty of approximately 3 dB as compared to their coherent counterpart.

A new energy harvesting scheme for multi-relay cooperative networks

Wireless networks have gone through unprecedented changes in the last decade owing to the rise in the number of users. Radio frequency (RF) energy harvesting (EH) (termed as RF-EH) can be a potential solution to encounter the energy constraints in the next generation wireless devices. In this study, we have proposed a new RF-EH technique from an RF source which was, to the best of our knowledge, not considered useful in any previous works. We have investigated the performance of an RF-EH cooperative multi-relay network by benefiting from the transmitted signal of the best relay (Rb) to the destination. In the most common RF-EH cooperative multiple relaying networks, only the relays harvest energy from the signal of source to power up themselves. However, in the proposed RF-EH technique, both the signals of source and Rb are exploited to harvest energy. In the proposed scheme, each of the relays harvests energy from the transmitted signal by source during phase-1, whereas the relays other than the Rb also harvest energy from the transmitted signal of Rb to destination during phase-2. Additionally, we have investigated our proposed scheme for both time-switching and power-splitting receiver architectures. Finally, from the simulation results, an increase in the system throughput and better outage performance is observed in the proposed scheme as compared to the conventional EH protocol in which EH is performed merely from the signal of source.

Relay selection and nonlinear energy harvesting in full-duplex multi-relay cooperative network

Energy harvesting (EH) is a promising technique to extend the lifetime energy-constrained devices in wireless networks. This paper analyses the significance of relay selection and non-linear EH in evaluating the performance of Full-duplex (FD) decode-and-forward (DF) multi-relay cooperative network. The relay selection is considered under three scenarios based on channel state information (CSI) availability. We compare the EH performance of a hybrid power-time-splitting (PTS)-based non-linear energy harvester with time-spitting (TS) and power-splitting (PS) EH at the relay node. We derive the expression of outage probability (OP) of FD DF multi-relay cooperative network over independent and identically distributed Rayleigh fading channels. Numerical results show that the outage performance of the system is significantly enhanced by deploying an ideal relay selection scheme. This paper also gives insights about the combined effect of saturation threshold of non-linear EH and residual self-interference (RSI) on the system performance. Unlike linear EH systems, the non-linear EH causes the outage floor even when the RSI is significantly small. The response of the system is also analysed for the impact of TS and PS ratios. Furthermore, we also investigate the system’s performance in terms of other system parameters like the number of relays and data transfer rate. Monte Carlo simulations are used to verify the analytical expressions.

Modeling and Analysis of Multi-Relay Cooperative Communications in C-V2X Networks

To compensate for the limitations of existing dedicated short range communications (DSRC), cellular vehicle-to-everything (C-V2X) has been proposed recently, which is also a promising technology for future intelligent transportation systems (ITS). Using stochastic geometry approach, this paper presents the modeling and analysis of success probability in multi-relay cooperative C-V2X networks. The spatial distribution of base stations (BSs) and vehicles in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathbb {R}^{2}$ </tex-math></inline-formula> are modeled as a 2D Poisson point process (PPP) and a Poisson line Cox point process (PLCPP), respectively. We focus on the success probability of a source vehicle sending a message to the nearest destination vehicle assisted by the closest BS. Each vehicle is equipped with single antenna whereas each BS is equipped with multiple antennas, which act as independent relays. We consider two decoding schemes, i.e., selection combining (SC) and maximum ratio combing (MRC), and obtain the analytical expressions for joint success probability during two continuous time slots, taking into account the interference correlation (i.e., the spatial correlation of vehicle location). The analytical model is validated using Monte Carlo simulations in MATLAB, and the effects of major parameters on success probability are investigated.

Signal Space Cognitive Cooperation

In this work, a new transmission scheme, signal space cognitive cooperation, is introduced by applying the idea of signal space diversity in an underlay spectrum sharing decode-and-forward multi-relay cooperative network. In the proposed structure, the secondary source signal is rotated by a certain angle and then the source and the secondary best relay transmit the in-phase and the quadrature components of the rotated signal. As a consequence, two source signals, rather than one, are transmitted in two-time slots which improves data rates considerably, compared to the conventional cognitive cooperative schemes. In this work, proactive relaying mode is used in which the best relay is selected based on the max-min selection criterion before executing the transmission. Considering both statistical and the instantaneous channel state information of the feedback channel between the primary receiver and the secondary network, two power allocation methods are adopted at the source. For both methods, closed-form expressions of error probability are derived. Moreover, asymptotic analysis is performed and diversity gain is obtained to provide further insights about the system performance. Finally, analytical expressions are verified by Monte-Carlo simulations.

Distributed Processing for Multi-Relay Assisted OFDM With Index Modulation

Orthogonal frequency-division multiplexing with index modulation (OFDM-IM) has become a high-profile modulation scheme for the fifth-generation (5G) wireless communications and has thus been extended to multi-hop scenarios in order to improve the network coverage and energy efficiency. However, the extension of OFDM-IM to multi-relay cooperative networks is not trivial, since it is required that a complete OFDM block should be received and decoded as an entity in one node. This requirement prevents the employment of multiple relays to forward fragmented OFDM blocks on individual subcarriers. In this regard, we propose a distributed processing scheme for multi-relay assisted OFDM-IM, by which multiple relays are selected to forward signals in a per-subcarrier manner to provide optimal error performance for two-hop decode-and-forward (DF) OFDM-IM systems. Specifically, a single selected relay only needs to decode partial information carried on certain active subcarriers and forward just as for traditional OFDM systems without IM. After receiving all signals on active subcarriers forwarded by different relays, the destination can reconstruct the complete OFDM block and retrieve the full information. We analyze the average block error rate and modulation capacity of the two-hop OFDM-IM system employing the proposed distributed DF protocol and verify the analysis by numerical simulations.

A Coalitional Formation Game for Physical Layer Security of Cooperative Compressive Sensing Multi-Relay Networks.

Cooperative relaying is an effective technology to improve the capacity of physical-layer security, in which the relay helps forward the received signal to the destination. In this paper, a cooperative compressive sensing and amplify-and-forward (CCS-AF) scheme, which combines the compressive sensing theory and amplify-and-forward strategy, is proposed to increase the secrecy capacity. To optimize the secrecy performance, a coalition formation algorithm based on coalitional game theory of optimal relay selection is proposed to maximize the secrecy capacity. Different to maximizing the individual utility based on the traditional pareto order, the max-coalition order rule is newly defined to guide the coalitional formation. Simulation results indicate that with the proposed algorithm, part of the relays could form a coalition to forward the information and the proposed algorithm could significantly improve the secrecy capacity of cooperative multi-relay networks.

Multihop Capability Analysis in Wireless Information and Power Transfer Multirelay Cooperative Networks

We study simultaneous wireless information and power transfer (SWIPT) in multihop wireless cooperative networks, where the multihop capability that denotes the largest number of transmission hops is investigated. By utilizing the broadcast nature of multihop wireless networks, we first propose a cooperative forwarding power (CFP) scheme. In CFP scheme, the multiple relays and receiver have distinctly different tasks. Specifically, multiple relays close to the transmitter harvest power from the transmitter first and then cooperatively forward the power (not the information) towards the receiver. The receiver receives the information (not the power) from the transmitter first, and then it harvests the power from the relays and is taken as the transmitter of the next hop. Furthermore, for performance comparison, we suggest two schemes: cooperative forwarding information and power (CFIP) and direct receiving information and power (DFIP). Also, we construct an analysis model to investigate the multihop capabilities of CFP, CFIP, and DFIP schemes under the given targeted throughput requirement. Finally, simulation results validate the analysis model and show that the multihop capability of CFP is better than CFIP and DFIP, and for improving the multihop capabilities, it is best effective to increase the average number of relay nodes in cooperative set.

Performance analysis of incremental hybrid decode-amplify-forward cooperative relaying with relay selection in Nakagami-m fading channels

In this paper, we investigate the performance of incremental hybrid decode-amplify-forward relaying (IHDAF) protocol for the dual-hop cooperative multi-relay networks. We deduce a tight closed-form expression for the outage probability (OP) by employing opportunistic relay selection (ORS) under Nakagami-m fading channels. We further derive an asymptotic outage expression in the high signal-to-noise ratio (SNR) regime, from which the diversity order is examined. Based on the asymptotic results, we also present an optimal relay location to minimize the overall system outage. In addition, we derive new tight closed-form expressions of ergodic capacity and asymptotic ergodic capacity for the considered system. Finally, numerical and simulation results show the correctness of our analytical findings and the performance enhancement of the considered system with ORS-IHDAF scheme compared with the other incremental ORS-based cooperative schemes.

Quantum Bee Colony Optimization and Non-dominated Sorting Quantum Bee Colony Optimization Based Multi-relay Selection Scheme

In cooperative multi-relay networks, the relay nodes which are selected are very important to the system performance. How to choose the best cooperative relay nodes is an optimization problem. In this paper, multi-relay selection schemes which consider either single objective or multi-objective are proposed based on evolutionary algorithms. Firstly, the single objective optimization problems of multi-relay selection considering signal to noise ratio (SNR) or power efficiency maximization are solved based on the quantum bee colony optimization (QBCO). Then the multi-objective optimization problems of multi-relay selection considering SNR maximization and power consumption minimization (two contradictive objectives) or SNR maximization and power efficiency maximization (also two contradictive objectives) are solved based on non-dominated sorting quantum bee colony optimization (NSQBCO), which can obtain the Pareto front solutions considering two contradictive objectives simultaneously. Simulation results show that QBCO based multi-relay selection schemes have the ability to search global optimal solution compared with other multi-relay selection schemes in literature, while NSQBCO based multi-relay selection schemes can obtain the same Pareto front solutions as exhaustive search when the number of relays is not very large. When the number of relays is very large, exhaustive search cannot be used due to complexity but NSQBCO based multi-relay selection schemes can still be used to solve the problems. All simulation results demonstrate the effectiveness of the proposed schemes.

Optimized Relay Selection and Power Allocation by an Exclusive Method in Multi-Relay AF Cooperative Networks

Optimized Relay Selection and Power Allocation by an Exclusive Method in Multi-Relay AF Cooperative Networks

Performance Analysis of Physical Layer Security of Opportunistic Scheduling in Multiuser Multirelay Cooperative Networks.

In this paper, we study the physical layer security (PLS) of opportunistic scheduling for uplink scenarios of multiuser multirelay cooperative networks. To this end, we propose a low-complexity, yet comparable secrecy performance source relay selection scheme, called the proposed source relay selection (PSRS) scheme. Specifically, the PSRS scheme first selects the least vulnerable source and then selects the relay that maximizes the system secrecy capacity for the given selected source. Additionally, the maximal ratio combining (MRC) technique and the selection combining (SC) technique are considered at the eavesdropper, respectively. Investigating the system performance in terms of secrecy outage probability (SOP), closed-form expressions of the SOP are derived. The developed analysis is corroborated through Monte Carlo simulation. Numerical results show that the PSRS scheme significantly improves the secure ability of the system compared to that of the random source relay selection scheme, but does not outperform the optimal joint source relay selection (OJSRS) scheme. However, the PSRS scheme drastically reduces the required amount of channel state information (CSI) estimations compared to that required by the OJSRS scheme, specially in dense cooperative networks.

Performance investigation of multi-relay cooperative diversity networks

In this paper, we consider a cooperative network consisting of an origin node, multiple intermediate nodes and a final node. The performance of conventional selection combining (SC) suffers degradation for the described network model. In this paper, we propose a new form of SC for multiple intermediate nodes with the use of full channel state information. An end-to-end symbol error probability is derived for the proposed SC scheme with M-ary phase shift keying modulation technique in the presence of flat Rayleigh fading channel. We use decode and forward protocol at the intermediate nodes. The origin to final node link and the intermediate to final node links are assumed to be independent and identically distributed. The results show that the proposed SC scheme performs better than the conventional SC scheme. The analytical results are validated through Monte-Carlo simulations.

Performance analysis of multirelay RF energy harvesting cooperative networks with hardware impairments

In this study, the authors analyse the outage performance of multirelay decode-and-forward cooperative networks subject to two joint practical issues of wireless communications, namely, energy constraints and transceiver hardware impairment (HI). To deal with energy constraints at relay nodes, radio-frequency (RF) energy harvesting (EH) technique is adopted. Considering the joint impacts of RF EH technique and HI, two relay selection schemes, namely, harvested energy-based relay selection (HEbS) scheme and channel quality-base relay selection (CQbS) scheme are proposed. Tight closed-form approximate expressions for the outage probability of each scheme are derived and corroborated through Monte Carlo simulations. Some representative performance comparisons are carried out and show that the diversity order achieved by the HEbS scheme is 1 and is independent of the number of relays, K, whereas that achieved by the CQbS scheme is K, which is full diversity.

Cooperative Transmission in Simultaneous Wireless Information and Power Transfer Networks

In this paper, we consider a cooperative simultaneous wireless information and power transfer (SWIPT) network with one source–destination pair and multiple energy harvesting relays. How to efficiently use these relays has been addressed in conventional cooperative networks, and this paper investigates the impact of SWIPT on the performance of such multirelay cooperative networks. In particular, the main contribution of this paper is that a closed-form expression of the outage probability achieved by the multirelay cooperative protocol is obtained, as well as its approximation at high SNR. In addition, the performance of the cooperative network with the SWIPT relays is compared with that in conventional systems with self-powered relays.

Performance Evaluation of Amplify-Quantize and Forward Protocol for Multi-relay Cooperative Networks

Fading which occurs during the process of information transmission can significantly degrade system performance. The cooperative communication system is a well-known diversity technique that is able to mitigate the impact of fading. The relay protocol is the core of such systems. In this research, we evaluated the performance of amplify-quantize and forward (AQF) relays using a hybrid of two protocols: amplify-and-forward (AF) and quantize-and-forward (QF). The outage probability and throughput of multi-relay cooperative networks were derived, and computer simulation was used to evaluate the impact of a number of parameters on the performance of the AQF relay for multi-relay cooperative networks. We also compared the outage probability and throughput of AF, QF, and direct link networks. The outage probability of AQF decreased as the number of relays increased, whereas the throughput increased. We demonstrated that amplification values and quantization levels have a significant impact on the performance of AQF multi-relay networks. Overall, AQF performed better in terms of outage probability and throughput than AF and QF, for multi-relay cooperative networks.

On the Optimization of Distributed Compression in Multirelay Cooperative Networks

In this paper, we consider multirelay cooperative networks for the Rayleigh fading channel, where each relay, upon receiving its own channel observation, independently compresses it and forwards the compressed information to the destination. Although the compression at each relay is distributed using Wyner–Ziv coding, there exists an opportunity for jointly optimizing compression at multiple relays to maximize the achievable rate. Considering Gaussian signaling, a primal optimization problem is formulated accordingly. We prove that the primal problem can be solved by resorting to its Lagrangian dual problem, and an iterative optimization algorithm is proposed. The analysis is further extended to a hybrid scheme, where the employed forwarding scheme depends on the decoding status of each relay. The relays that are capable of successful decoding perform a decode-and-forward (DF) scheme, and the rest conduct distributed compression. The hybrid scheme allows the cooperative network to adapt to the changes of the channel conditions and benefit from an enhanced level of flexibility. Numerical results from both spectrum and energy efficiency perspectives show that the joint optimization improves efficiency of compression and identify the scenarios where the proposed schemes outperform the conventional forwarding schemes. The findings provide important insights into the optimal deployment of relays in a realistic cellular network.

Wireless-Powered Cooperative Communications: Power-Splitting Relaying With Energy Accumulation

A harvest-use-store power splitting (PS) relaying strategy with distributed beamforming is proposed for wirelesspowered multi-relay cooperative networks in this paper. Different from the conventional battery-free PS relaying strategy, harvested energy is prioritized to power information relaying while the remainder is accumulated and stored for future usage with the help of a battery in the proposed strategy, which supports an efficient utilization of harvested energy. However, PS affects throughput at subsequent time slots due to the battery operations including the charging and discharging. To this end, PS and battery operations are coupled with distributed beamforming. A throughput optimization problem to incorporate these coupled operations is formulated though it is intractable. To address the intractability of the optimization,a layered optimization method is proposed to achieve the optimal joint PS and battery operation design with non-causal channel state information (CSI), in which the PS and the battery operation can be analyzed in a decomposed manner. Then, a general case with causal CSI is considered, where the proposed layered optimization method is extended by utilizing the statistical properties of CSI. To reach a better tradeoff between performance and complexity, a greedy method that requires no information about subsequent time slots is proposed. Simulation results reveal the upper and lower bound on performance of the proposed strategy, which are reached by the layered optimization method with non-causal CSI and the greedy method, respectively. Moreover, the proposed strategy outperforms the conventional PS-based relaying without energy accumulation and time switching-based relaying strategy.

Error Rate and Power Allocation Analysis of Regenerative Networks Over Generalized Fading Channels

Cooperative communication has been shown to provide significant increase of transmission reliability and network capacity while expanding coverage in cellular networks. The present work is devoted to the investigation of the end-to-end performance and power allocation of a maximum-ratio-combining based regenerative multi-relay cooperative network over non-homogeneous scattering environment, which is the realistic case in many practical wireless communication scenarios. Novel analytic expressions are derived for the end-to-end symbol-error-rate of both M -ary phase-shift keying and M -ary quadrature amplitude modulation over independent and non-identically distributed generalized fading channels are given by exact analytic expressions that involve the Lauricella function and can be readily evaluated with the aid of a proposed computing algorithm. Simple analytic expressions are also derived for the corresponding symbol-error-rate at asymptotically high signal-to-noise ratios. The derived expressions are corroborated with respective results from computer simulations and are subsequently employed in formulating a sum-power optimization problem that enhances the system performance under total sum-power constraint within the multi-relay cooperative system. It is also shown that asymptotically optimum power allocation provides substantial performance gains over the corresponding equal power allocation, particularly, when the source-relay and relay-destination paths are highly unbalanced.