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Successive relaying is a bandwidth-efficient scheme in cooperative networks. In this study, a novel distributed space-time coding (DSTC) transmission scheme for a two-path successive relay network is proposed that enjoys threshold-based selection relaying protocol. A new beamforming method is also employed alongside the proposed DSTC transmission scheme. Three scenarios are considered in this study. In the first scenario, single-input–single-output (SISO) relays are considered. In the second and third scenarios, multiple-input–multiple-output (MIMO) relays are used, but in the second case a transmission scheme named as quasi-DSTC scheme alongside employing space-time coding at each relay is proposed. A closed-form expression for the end-to-end bit error rate (BER) of the system is derived and it is shown that regardless of the fading in inter-relay channel, the proposed scheme achieves full diversity order even when there are decoding errors at the relay nodes. Simulation results show a significant saving in power of about 2.5, 3, and 4 dB at BER ( 10 − 4 ) compared with other conventional methods in the case of using SISO relays, MIMO relays in the second and third scenarios, respectively.

In this paper, a limited‐feedback decode‐and‐forward cooperative network with multiple relays is considered where each relay is equipped with multiple antennas. To combat error propagation...

Multiple access broadcasting (MABC) is a spectral efficient protocol in a two-way relay channel (TWRC). The drawback of this protocol in decode-and-forward (DF) mode is decoding complexity at the relay side. Erroneous decoding at the relay can lead to error propagation that degrades the performance of all relay networks operating in the DF mode. In this paper, a maximum likelihood (ML) detector at the multiple-antenna relay is used, and it is proved that this decoding rule can achieve full diversity order at the multiple access (MAC) phase of the MABC protocol. Then, a new beamforming algorithm named as channel alignment is proposed, and it is shown that it achieves full diversity order. A new relay selection algorithm is proposed, and a tight upper bound for the bit error rate (BER) of this scheme is derived. It is proved that it achieves full diversity order. The analytical results and BER performance of the proposed schemes are investigated and compared through simulations.

In this study, two diversity achieving schemes in two-way relay channel (TWRC) under Nakagami-m fading are proposed. A general network of N r relays is considered where each relay is equipped with N a antennas. It is also assumed that the relays operate in decode-and-forward (DF) mode. The data transmission is divided into two phases, multiple access (MAC) phase and broadcast (BC) phase. In the MAC phase, the sources send their data to the relays simultaneously and after decoding, one relay is selected with MAX–MIN relay selection criterion and then in the BC phase retransmit the decoded symbols using the proposed transmission schemes at the selected relay. With evaluating the asymptotic behaviour of the bit error rate (BER) of the proposed schemes, it is proved that the diversity order of them is N r N a m. As a result, the proposed schemes achieve full diversity order.

A cooperative network consisting of a source, one relay, and a destination is considered. The source and destination are both equipped with a single antenna. The relay is equipped with $N$ antennas and operates in decode-and-forward (DF) mode. At the relay, the detected symbols are retransmitted using a novel beamforming method proposed in this paper that assumes the relay has 2-bit quantized information about the phase of all links from the relay to the destination. At the destination, the detector combines the received signals from the source and the relay in the first and second phases of transmission, respectively. An upper bound for the bit error rate (BER) performance of the detector is derived, and it is shown that the proposed beamforming and detector achieve full diversity order. The detector is extended to a multicast system with one single antenna source, one $N$ -antenna DF relay and $M$ single antenna destinations. It is assumed that the relay has 2-bit quantized phase information and exact signal-to-noise ratio (SNR) information at all the links from the relay to the destinations. An antenna selection algorithm based on a MAX-MIN criterion at the relay is proposed, and after beamforming, the detector is used at all destinations. By deriving a rigorous upper bound for BER performance at all destinations, it is shown that the proposed scheme achieves full diversity order at all destinations. Simulation results show that the BER performance of the proposed antenna selection algorithm outperforms the well known MAX-MIN antenna selection scheme.

Two-path successive relaying is used as a method of transmission for recovering the bandwidth loss of conventional relay networks. In this paper, a new beamforming method is employed alongside the proposed distributed space-time coding (DSTC) transmission scheme in a two-path successive relay network which enjoys SNR-based selection relaying protocol. A closed-form expression for the end-to-end bit error rate (BER) of the system is derived. Regardless of the fading in inter-relay channel, the proposed scheme ensures that full rate and full diversity can be attained in the presence of decoding errors at the relay nodes. Simulation results, show a significant power saving about 2.5 dB at BER (10−4) in comparison to other conventional methods.

Cooperative communication can improve the performance of communication systems under multi-path fading conditions through relaying. Increasing the number of relays will also boost the performance of the system, but since relays transmit through orthogonal channels, this improvement is obtained at the cost of bandwidth or rate of the system. Best relay selection is a well-known technique to achieve full order of diversity and use bandwidth efficiently in a cooperative two-hop multi-relay network. A new beamforming at the relay is proposed that selects the best two among several relays and then the selected relays forward their detected symbols in a common channel to the destination. For achieving full diversity order at the destination, a modified maximal ratio combining detector is proposed. In the proposed beamforming scheme, the phase of the selected relays is adjusted in such a way to compensate the channel between the relays and the destination and achieve acceptable performance at the receiving end. The selected relays require two-bit quantised phase information of the channel gain between the relay and the destination, which can be sent to the relay by the destination. It is shown that the proposed method achieves full diversity order and has considerable performance gain in comparison with the best relay selection method.

In this paper, we consider the Hybrid Decode---Amplify---Forward protocol with the $$n$$ n th best-relay selection scheme. In the best-relay selection scheme, the best relay only forwards the source signal to the destination, regardless of working in the Amplify-and-Forward mode or the Decode-and-Forward mode. However, the best relay might be unavailable due to some reasons; hence we might bring into play the second, third or generally the $$n$$ n th best relay. We derive closed-form expression for the outage probability using the probability density function and moment generating function of the signal-to-noise ratio of the relayed signal at the destination node. Results show that with the $$n$$ n th best relay the diversity order is equal to $$(m-n+2)$$ ( m - n + 2 ) where $$m$$ m is the number of relays. Simulation results are also given to verify the analytical results.

One of the main drawbacks of cooperative communication systems with half-duplex relaying is inefficient use of spectrum. Incremental relaying is an effective technique that overcomes this limitation, particularly in the high-SNR regime. In this paper, for a multi-relay cooperative network with arbitrary number of relay nodes, we propose a spectrally-efficient incremental relaying scheme that eliminates redundant relay transmissions such that an average end-to-end bit error rate (BER) constraint is satisfied. For detect-and-forward relaying, under the assumption of error propagation from the relays to the destination, we analyze the performance of the system in terms of the end-to-end BER, the average spectral efficiency and the outage probability for Rayleigh fading environment. The performance of the system depends on a single threshold employed by the relays and the destination. We optimize this threshold such that the average spectral efficiency of the system is maximized under an average end-to-end BER constraint. This optimization criterion results in a constant-BER, variable-spectral efficiency relaying scheme. The proposed scheme makes use of spectrum as efficiently as possible, while providing the required quality of service at the destination.

One of the main drawbacks of cooperative communication systems with half-duplex relaying is inefficient use of spectrum. Incremental relaying is an effective technique that overcomes this limitation. In this study, for a single-relay regenerative system, the authors propose a spectrally-efficient incremental relaying scheme that eliminates redundant relay transmissions such that the error propagation from the relay to the destination is effectively mitigated and the full diversity is achieved. The authors examine the impact of the error propagation on the performance of the system and derive closed-form expressions for the end-to-end symbol error probability (SEP) for different modulation schemes. They also derive an approximate closed-form expression for the optimal threshold that minimises the end-to-end SEP. The high-signal-to-noise ratio (SNR) analysis demonstrates that this threshold achieves full diversity whereas neither the bandwidth-consuming cyclic redundancy check code nor the availability of the instantaneous source–relay channel state information at the destination is required in the system. Furthermore, the authors purpose a class of thresholds that are independent of the network geometry and achieve full diversity. The asymptotic behaviour of the system shows that the spectral efficiency for both the optimal and geometry-independent thresholds in the high-SNR regime tends to the maximum achievable value.

In this study, the authors investigate the hybrid decode-amplify-forward (HDAF) relaying protocol for the multiple parallel relays over independent and non-identical distribution flat Rayleigh fading channels using maximum ratio combining at the destination. They derive closed-form tight bounds for the outage probability and bit error rate (BER) of the HDAF relaying protocol. They also show that the outage probability performance of this protocol outperforms decode-forward (DF) protocol, and is very close to amplify-forward (AF) scheme. On the other hand, the BER of the HDAF scheme is superior to AF protocol, and is close to BER of DF scheme. From practical point of view, when taking into account outage and BER performance of a system together, the HDAF protocol performs better than AF and DF schemes by combining the merits of both. Also, the authors investigate power allocation among the relay nodes to minimise the system outage probability and BER under total and individual power constraints. Numerical results are provided to show the correctness of our analytical expressions.

Due to the half-duplex transmission nature of cooperative protocols, almost all cooperative diversity systems suffer from low spectral efficiency. In general, adaptive modulation can offer a good tradeoff between spectral efficiency and bit-error-probability (BEP) performance of wireless communication systems. In this paper, we propose two adaptive modulation schemes for the cooperative system with detect-and-forward relaying that simultaneously exploit the cooperative diversity gain and improve the spectral efficiency of the system. In the first scheme, which is similar to conventional selection relaying, the relay decides independently whether to forward the source messages to the destination or not by comparing the instantaneous received signal-to-noise ratio (SNR) with a predetermined fixed threshold, which is independent of the instantaneous modulation scheme. In contrast, in the second scheme, the relay and the destination jointly decide whether the relay will participate in the second phase of the protocol or remain silent. This second scheme can be viewed as a combination of selection and incremental relaying and achieves higher spectral efficiency in comparison with its nonincremental counterparts. We evaluate the performance of the protocols in terms of the end-to-end BEP, the average spectral efficiency, and the outage probability for both identically and nonidentically distributed Rayleigh fading environments. In our analysis, we consider M-ary phase-shift keying ( M-PSK) modulation, M -ary pulse-amplitude modulation (M-PAM), and M-ary quadrature-amplitude modulation ( M-QAM) schemes and examine the impact of error propagation from the relay to the destination on the end-to-end performance of the system in detail. Moreover, we derive a closed-form expression for the optimal relaying threshold that effectively mitigates error propagation and minimizes the end-to-end BEP of the system. The high-SNR analysis demonstrates that both proposed schemes provide full diversity.

Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, especially when the source-relay channel state information (CSI) is not available at the destination. In this study, the authors investigate the SNR-based selection relaying scheme in a multi-relay cooperative network (with R potential relay nodes) and examine the impact of the error propagation on the end-to-end performance of the system. The authors derive closed-form expressions for the end-to-end symbol error probability (SEP) of the system for both identically distributed and non-identically distributed Rayleigh fading environments. In the analysis, the authors consider M-ary phase shift keying (M-PSK), M-ary pulse amplitude modulation (M-PAM) and M-ary quadrature amplitude modulation (M-QAM) schemes. They also propose a class of geometry-independent thresholds that effectively mitigate the error propagation and provide full diversity of order R+1. Furthermore, for the special case of single-relay network, the authors derive closed-form expressions for the optimal thresholds that minimise the end-to-end SEPs.

Multiple Accesses Broadcasting (MABC) is a spectral efficient protocol in two-way relay channel (TWRC). The drawback of this protocol in decode-and-forward (DF) mode is decoding complexity at the relay's side. Erroneous decoding at the relay can bring about error propagation that leads to performance degradation in all of the relay networks operating in the DF mode. In this paper, we propose ML detection at the multiple antenna relay. With analytical investigation, we prove that this decoding rule can achieve full diversity order at the MAC phase of the MABC protocol. Then, we propose a new beamforming algorithm named as “Channel Alignment” and show that the proposed algorithm will result in better performance compared with the well-known MAX-MIN antenna selection method while it has full diversity order at the BC phase of the MABC protocol. The analytical results are verified through simulations and the performance of our proposed method is also compared with another method.

Transmission in frequency selective channels has some challenges due to the generated ISI which significantly deteriorates the performance of the system; hence, most of the proposed methods in literature for flat fading cannot be established in frequency selective conditions. Filter and forward strategy was proposed in AF protocol for combating the ISI in frequency selective channels. In this paper, we have proposed filter and forward strategy in DF relay networks which consists of a multi-antenna relay and destination, and with considering MMSE criterion, we have calculated the optimum filter coefficients at relay and destination. We also have verified our proposed method with simulation and compared it with some other works in literature.

In this paper, we consider adaptive quadratic amplitude modulation (QAM) for a cooperative network consists of a source, one decode-and-forward (DF) relay and a destination which are single antenna systems. For increasing the spectral efficiency of the system, we use adaptive modulation method for data transmission. We propose a new adaptive modulation scheme which has less complexity than available schemes. Then, we analyze average spectral efficiency (ASE), average bit error performance (ABEP) and outage probability of the proposed scheme. Computer simulation results corroborate our theoretical relations; furthermore, it shows that our proposed scheme has the same performance as maximum spectral efficiency scheme (MSES) with much lower complexity and has better performance than some other schemes.

This paper considers joint power and subcarrier allocation on the uplink OFDMA-based cooperative cognitive networks. We propose three schemes to maximize sum-capacity of Primary Users (Ups) in a situation that Secondary Users (SUs) relay the data of PUs and achieve subcarrier from PUs. We investigate the optimization problem under PUs peak power constraint to avoid interference with other cells with lower complexity compared to other works. The greedy algorithm is also modified to improve active PUs in the network. Our simulation results show preference of cooperative mode than non-cooperative mode in many parameters.

In this paper, we consider the fast and slow multipath fading scenarios in which the coherence time of the channel between primary transmitter and secondary receiver is compared to the sensing time. We formulate the detection problem under fast fading, then we show that there are situations in which the detection performance under the fast fading scheme outperforms that of the non-fading case (AWGN) slightly. Also, using Markov inequality, we propose a simple method in order to solve the optimization problem in the slow fading scenario, since the average probability of detection has no closed form. Finally, we observe that in low SNR rgimes the performance of detection under fast fading is significantly better in comparison to slow multipath fading.

Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, specifically when the source-relay channel state information (CSI) is not available at the destination. In this paper, we investigate the SNR-based selection relaying scheme and present a closed-form expression for the end-to-end symbol error probability (SEP) of the system for M-PSK modulation. The optimal threshold which minimizes the end-to-end SEP and provides full diversity order is also presented in closed-form. In our analysis, we examine the error propagation scenario in detail and derive a closed-form expression for the SEP under this scenario. Numerical results demonstrate that the SNR-based selection relaying scheme by employing the optimal threshold, without using error detection codes that reduce the bandwidth efficiency, effectively mitigates the error propagation and significantly improves the diversity order.

Error propagation from the relay to the destination is a major drawback of digital relaying protocols that substantially diminishes the cooperative diversity gain of the system. Appropriately designed selection relaying schemes can effectively mitigate this phenomenon and improve the diversity order, especially when the source-relay channel state information (CSI) is not available at the destination. In this study, the authors investigate the SNR-based selection relaying scheme in a multi-relay cooperative network that employs the distributed space-time coding (DSTC) strategy. The authors present a closed-form expression for the end-to-end bit error probability (BEP) of the system. It is demonstrated that the orthogonality of the space-time coded signals transmitted by the relays is not preserved under the error propagation from the relays to the destination and this gives rise to intersymbol interference at the destination. The SNR loss and intersymbol interference caused by the error propagation substantially diminish the diversity order of the system. The error propagation can be effectively mitigated by employing appropriate thresholds at the relays. The authors derive a closed-form expression for the optimal threshold that minimises the end-to-end BEP of the system. The authors also analyse the asymptotic behaviour of the BEP and demonstrate that by employing the optimal threshold the full diversity order is achieved. Furthermore, the authors propose a class of thresholds that are independent of the network geometry and also provide full diversity order. By employing these thresholds, each relay node can decide to forward or remain silent independent of other relay nodes.