Multi-relay Cooperative Communication Research Articles

On the capacity of a SIM-based cooperative NLOS UVC system with best relay selection

Ultraviolet communication (UVC) is a promising technology due to its ability to operate in non-line-of-sight (NLOS) mode thereby eliminating the pointing acquisition and tracking (PAT) requirement as needed by infrared and visible light communications. However, NLOS UVC suffers from very high attenuation and turbulence-induced fading when operated over a long distance. Due to these limitations, the existing literature on the NLOS UVC is mostly restricted to short-distance communications only. Therefore, this paper addresses these challenges by proposing an outdoor subcarrier-intensity-modulation (SIM) based multi-relay cooperative communication system employing the best relay selection and decode-and-forward (DF) relaying protocol. The turbulence-induced fading is modelled using lognormal distribution under weak atmospheric turbulence conditions. We derive novel closed-form analytical expressions of outage probability and ergodic capacity. Correctness of the derived analytical expressions is validated through numerical simulations.

Deep-Learning-Assisted IoT-Based RIS for Cooperative Communications

Reconfigurable intelligent surfaces (RISs) are software-controlled passive devices that can be used as relay (R) systems to reflect incoming signals from a source (S) to a destination (D) in a cooperative manner with optimum signal strength to improve the performance of wireless communication networks. The configurability and flexibility of an RIS deployed in an Internet-of-Things (IoT)-based network can enable network designers to devise stand-alone or cooperative configurations that have considerable advantages over conventional networks. In this paper, two new deep neural network (DNN)-assisted cooperative RIS models, namely, DNNR-CRIS and DNNR,D-CRIS, are proposed for cooperative communications. In DNNR-CRIS model, the potential of RIS deployment as an IoT-based relay element in a next-generation cooperative network is investigated using deep learning (DL) techniques for RIS phase optimization. In addition, to reduce the maximum likelihood (ML) complexity at D, a new DNN-based symbol detection method is presented with the DNNR,D-CRIS model combined with DNN-assisted phase optimization. For a different number of relays and receiver configurations, the bit error rate (BER) performance results of the proposed DNNR-CRIS and DNNR,D-CRIS models and traditional cooperative RIS (CRIS) scheme (without a DNN) are presented for a multi-relay cooperative communication scenario with path loss effects. It is revealed that the proposed DNN-based models show promising results in terms of BER, even in high-noise environments with low system complexity.

Efficient Polar Coded Selective Decode-and-Forward with Cooperative Decision Threshold in Cooperative Multi-Relay Transmissions

In some satellite Internet of Things (IoT) devices with terrain shielding, the qualities of the direct source-destination (S-D) channel are poor, requiring cooperative communications with multi-relays to be employed. In order to solve error propagation of current decode-and-forward (DF) on such occasions, an efficient polar coded selective decode-and-forward (SDF) cooperation method is proposed with a new decision threshold derived from channel state information (CSI). First, the proposed threshold is derived from the CSI by exploiting the channel gain ratio of optimal relay-destination link (R-D) with source-relay (S-R) link. The above R-D link possesses good channel quality among all links in the system. Second, when the channel gain ratio of certain relay links is larger than the aforementioned decision threshold, the source and all these relays cooperatively send messages together to the destination to accomplish perfect SDF transmission. Otherwise, all relays are frozen and the messages are directly transmitted through the S-D link. If it fails anyway, a retransmission is subsequently tried in the next transmission cycle. In addition, a polar code for fading channels is designed and adaptively adjusted to a proper code rate according to channel quality to attain good bit error rate (BER) performance. Simulation results show that the proposed scheme achieves about 0.9 and 0.5 dB gain at BER of 10-4, respectively, in multi-relay cooperative communications with multi-path fading channels compared with those of non-cooperation and existing polar coded cooperation channels. Therefore, the proposed polar coded SDF (PCSDF) scheme can improve both the BER and the outage probability (OP) performance in multi-relay cooperative systems, making it quite suitable for heterogeneous network applications in cooperative satellite IoT systems involving sixth-generation (6G) communications.

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.

Outage Probability Analysis of Multi-relay Cooperative Decode-and-Forward System Over Generalized η–μ and κ–μ Fading Channels

Cooperative communication has occurred to be a promising technology for future wireless networks. Characterizing its performance, in terms of symbol error rate, outage probability, data rate, etc. over the generalized fading channels are essential to wholly attain its benefits. In this paper, the closed form expressions for the outage probability of the multi-relay cooperative communication using decode-and-forward protocol over generalized fading channels ( $$\eta-\mu$$ and $$\kappa-\mu$$ ) has been derived in terms of gamma function. Firstly, the outage probability for generalized $$\eta-\mu$$ and $$\kappa-\mu$$ fading channels are computed, followed by the outage probability expression for the overall system. The final expressions are in the form of infinite series which converges very rapidly and hence it is accurately approximated by considering finite number of terms in summation. Analytical results are plotted to demonstrate the the impact of various channel parameters. It is also shown that how the outage performance improves with the number of relays. The obtained outage probability expressions for generalized fading environment can be readily extended for any generalized system model.

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.

Design of Distributed Protograph LDPC Codes for Multi-Relay Coded-Cooperative Networks

This paper studies protograph low-density parity-check coded cooperation (CC) schemes for two-hop multi-relay systems with $L$ relays over Nakagami- $m$ quasi-static fading (QSF) channels. We propose two CC schemes, namely schemes I and II, with different maximum code rates to satisfy different transmission requirements. We further design a family of distributed rate-compatible root-protograph (RCRP) codes to achieve full diversity in CC-based multi-relay QSF channels. In particular, our RCRP codes with $L+1$ sub-codewords can realize full diversity in scheme I, and our RCRP codes with two sub-codewords can achieve full diversity in scheme II with a maximum-ratio combiner. In addition, we estimate the asymptotic word error rate and bit error rate of our RCRP codes using a generalized protograph extrinsic information transfer algorithm, which is able to characterize the error performance of finite-length codewords accurately. Analysis and simulation show that our RCRP codes can achieve outage-limit-approaching performance in both multi-relay CC architectures. This makes the RCRP coding framework extremely attractive for multi-relay cooperative communication applications with slow-varying fading.

Symbol error rate of QO‐STBC based decode‐and‐forward cooperative communication system over generalised – and – fading channels

In this study, the authors derive the closed form expressions for symbol error rate (SER) of a quasi-orthogonal space-time block code (QO-STBC) based multi-relay cooperative communication system using M-ary phase-shift keying (M-PSK) modulation over generalised – fading channel. For the same system over – fading channel, due to the unobtainability of the closed form SER expressions, the analysis is restricted to binary-PSK and the bit error rate (BER) has been derived. The authors employ decode-and-forward protocol at the relays and maximal ratio combiner at the destination. For the ease of analysis, the authors consider a three relay cooperative network and the SER has been derived which could be extended to any number of relays or QO-STBCs. First, the expressions of SER were expressed in terms of moment generating function (MGF) and finally, the available closed form expression for MGF of – and – channel distributions are used to obtain the final expression of theoretical BER/SER. The validity of the obtained BER/SER expressions for a three relay cooperative system are verified through Monte–Carlo simulations by varying the channel parameters of – and – fading channels.

A Multi-relay Cooperative Communication Using Space Time Spatial Phase Coding Based on OFDM

Among schemes to obtain diversity gain, space-time block code (STBC) and spatial phase coding (SPC) have been widely studied for the cooperative wireless relaying system. However, conventional STBC has a problem that cannot deal with change in the number of relays due to low throughput. In this paper, we propose a SPC that multi-relay transmission is possible and a space-time spatial phase coding (STSPC) using the proposed SPC scheme and STBC. The STSPC scheme provides improved bit error rate performance and full rate.

Efisiensi Daya Protokol Quantize and Forward Pada Sistem Komunikasi Kooperatif Multi-relay

One of effective diversity techniques to combat fading on wireless channel is a cooperative communication system in which a source sends information through several relays and then forward it to a destination. A cooperative communication system has shown increased the system performance and reduced the energy consumption. However, it depends on the used relay mechanism that is relay protocols such as quantize and forward (QF) and amplify and forward (AF). In the previous research, energy efficiency of AF relay has investigated for a single-relay cooperative system, but multi-relay is more practical. Therefore, this research focuses on power efficiency in multi-relay cooperative communication system using QF protocol. The research method used is mathematical analysis and computer simulation for outage probability and power efficiency in the multi-relay QF. Simulation result found that multi-relay QF system could provide a high power efficiency, but the efficiency is reduced when the distance ratio increases. Power efficiency can be increased by adding the number of relays in the system. A comparison of power efficiency for QF and AF protocols has simulated, in which power efficiency of multi-relay QF is higher than that of multi-relay AF at distance ratio and power transmit. Thus, multi-relay QF system can provide high performance and power efficiency in the cooperative communication system.

Full duplex techniques for 5G networks: self-interference cancellation, protocol design, and relay selection

The wireless research community aspires to conceive full duplex operation by supporting concurrent transmission and reception in a single time/frequency channel for the sake of improving the attainable spectral efficiency by a factor of two as compared to the family of conventional half duplex wireless systems. The main challenge encountered in implementing FD wireless devices is that of finding techniques for mitigating the performance degradation imposed by self-interference. In this article, we investigate the potential FD techniques, including passive suppression, active analog cancellation, and active digital cancellation, and highlight their pros and cons. Furthermore, the troubles of FD medium access control protocol design are discussed for addressing the problems such as the resultant end-to-end delay and network congestion. Additionally, an opportunistic decode-andforward- based relay selection scheme is analyzed in underlay cognitive networks communicating over independent and identically distributed Rayleigh and Nakagami-m fading channels in the context of FD relaying. We demonstrate that the outage probability of multi-relay cooperative communication links can be substantially reduced. Finally, we discuss the challenges imposed by the aforementioned techniques and a range of critical issues associated with practical FD implementations. It is shown that numerous open challenges, such as efficient SI suppression, high-performance FD MAC-layer protocol design, low power consumption, and hybrid FD/HD designs, have to be tackled before successfully implementing FD-based systems.

Power Control Game in Multisource Multirelay Cooperative Communication Systems With a Quality-of-Service Constraint

In this paper, we propose a game-theoretic power control algorithm to minimize the total power consumption in a cooperative communication network that transmits information from multiple sources to a destination via multiple relays to save energy and improve communication performance. Under the amplify-and-forward relaying scheme, the proposed approach not only selects the best source-relay pair but also obtains the optimal transmission power, while satisfying the communication quality-of-service requirements. Using a game-theoretic model, the impacts of the number of relays on the total power consumption are also analyzed. Finally, numerical results are provided to corroborate our theoretical results and demonstrate the performance of the proposed approach.

The Research on Sparse Channel Estimation in Multi-Relay Cooperative Communication System

In a frequency selective fading environment amplify and forward relay system, the channel estimation algorithm and least squares (LS) estimation of mean square error is relatively high. And when using the compressed sensing (CS) which was proposed recently in orthogonal matching pursuit algorithm (OMP) for the single relay channel and multi relay system estimation, in order to reduce the mean square error of the system. In multi-relay cooperative communication system, allocated the power to the relay node, then respectively using the LS and OMP for channel estimation. The results show that, the orthogonal matching pursuit algorithm can greatly reduce the system mean square error, and the same channel estimation algorithm was used for the relay power allocation is also effectively reduce the estimation error, to further improve the accuracy of channel estimation.

Tensor-Based Channel Estimation for Cooperative Diversity Scheme in the Presence of Timing and Frequency Offsets

The distributed nature of cooperative networks may result in multiple carrier frequency offsets (MCFOs) and multiple timing offsets (MTOs), which overshadow the diversity gains promised by cooperative communications. So the estimation of MCFOs and MTOs is an important implementation issue in practice. In this paper we propose a new channel estimation both at the relays and the destination in distributed space-time block code (DSTBC) based amplify-and-forward (AF) cooperative networks in the presence of MCFOs and MTOs. We propose tensor-based channel estimation (TENCE) scheme, which does not assume any perfect frequency or timing synchronization. Moreover, the canonical polyadic (CP) decomposition for the tensor, associated with channel gains, frequency offsets and timing offsets, is proposed in the cooperative communication systems. We also demonstrate that TENCE can be improved by the iteration. Simulation results show that the proposed TENCE scheme can achieve a better performance in the presence of channel and synchronization impairments in multi-relay AF cooperative communications. Depending on the scenario, we also show that the significant improvements in estimation accuracy are achievable by TENCE iterations

Research on Relay Selection Based on Two-Hop Multi-Relay Networks

A relay selection criteria was proposed based on time division non-orthogonal cooperation, aiming at solving the problem of relay selection in the two-hop multi-relay cooperative communication to predigest the system design. The system BER (bit error rate) expression was obtained with its performance analysis under the condition of high SNR. Furthermore, computer simulations was conducted to show that the system diversity order is increased with the increase of the relay number under the condition of the distributed relay selection criterion, and diversity gain can be obtained significantly with the BER of the system significant decreasing.

Variable packet splitting transmission in multi-relay cooperative communications with DF and DAF for SC-FDMA

In recent years, cooperative communications are widely studied. Cooperative communications can obtain the space diversity as multiple-input multiple-output (MIMO) systems. In cooperative communications, the relay method is important as decode-and-forward (DF) and decode-amplify-forward (DAF). The multi-relay cooperative communications can improve the system performance. In the multi-relay cooperative communications, the optimum packet splitting method is effective. Moreover, the multi-relay cooperative communications can more improve the system performance by using the power allocation (PA). However, the PA method requires large feedback information (FBI). To solve this problem, in this article, we propose the optimum packet splitting method based on the time domain channel state information (CSI) in the multi-relay cooperative communication with DF and DAF.

Impact of partial relay selection on the capacity of communications systems with outdated CSI and adaptive transmission techniques

AbstractThe impact of outdated channel state information (CSI) on the capacity of amplify-and-forward (AF) partial relay selection systems is studied in this article. The closed-form expressions for the distribution of received signal-to-noise ratio (SNR) in a multi-relay cooperative communications system is first derived, with independent and identically distributed (i.i.d.) Rayleigh fading channels being assumed in each wireless link. After that, the theoretical closed-form expressions for both outage probability and channel capacity of partial relay selection are derived, with four classical adaptive transmission techniques, including the constant power with optimal rate adaption (ORA), the optimal power and rate adaption (OPRA), the channel inversion with fixed rate (CIFR) and truncated channel inversion with fixed rate (TIFR), being considered. Numerical analysis proves that the channel capacity of partial relay selection is impacted considerably by some critical parameters, including the number of relays, the channel correlation coefficient and the end-to-end SNR, etc. It’s also exhibited in the numerical results that among the four adaptive transmission techniques, the diversity order of OPRA is larger than that of TIFR, and the OPRA outperforms TIFR with about 0.15 bits/s/Hz in terms of average channel capacity.

Performance Analysis of Differential Modulation and Relay Selection with Detect-and-Forward Cooperative Relaying

This letter analyzes the performance of a multi-relay cooperative communication scheme with differential modulation and relay-selection (DM-RS). The scheme consists of a source, N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> relays, and a destination, where the best relay is selected to forward the source node's signal with detect-and-forward (DetF) protocol. The capacity outage probability (COP) and symbol error rate (SER) of the scheme are investigated. In particular, a closed-form COP and an approximation at large signal-to-noise ratio (SNR) are derived. The COP approximation shows that the scheme can achieve a full diversity order of N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</sub> +1. Furthermore, a closed-form SER approximation of the scheme with multiple phase shift keying (MPSK) modulation is derived. Simulation results confirm the presented mathematical analysis.

Optimal power allocation with AF and SDF strategies in dual-hop cooperative MIMO networks

Dual-hop cooperative Multiple-Input Multiple-Output (MIMO) network with multi-relay cooperative communication is introduced. Power allocation problem with Amplify-and-Forward (AF) and Selective Decode-and-Forward (SDF) strategies in multi-node scenario are formulated and solved respectively. Optimal power allocation schemes that maximize system capacity with AF strategy are presented. In addition, optimal power allocation methods that minimize asymptotic Symbol Error Rate (SER) with SDF cooperative protocol in multi-node scenario are also proposed. Furthermore, performance comparisons are provided in terms of system capacity and approximate SER. Numerical and simulation results confirm our theoretical analysis. It is revealed that, maximum system capacity could be obtained when powers are allocated optimally with AF protocol, while minimization of system’s SER could also be achieved with optimum power allocation in SDF strategy. In multi-node scenario, those optimal power allocation algorithms are superior to conventional equal power allocation schemes.

Novel multi-relay cross-layer cooperative communication strategy based on Jackson queuing model

A novel multi-relay cooperative communication strategy based on Jackson queuing model is proposed, which is implemented via a cross-layer design between the physical (PHY) layer and the medium access control (MAC) layer. In the PHY layer, we focus mainly on system outage performance by analyzing in detail the relationship between the SNR threshold and the outage probabilities. While in the MAC layer, system model is treated as a Jackson queuing network, and the queue discipline for each node is assumed to be GI/M/1 model. System throughput and delay performance for the proposed strategy are also illustrated. Simulation results of the proposed cross-layer scheme are presented to validate our theoretical derivations. It is revealed that, the number of cooperative nodes influences system outage performance at high spectral efficiency regimes in the PHY layer while the proposed strategy provides a better throughput and delay performance than conventional schemes in the MAC layer.