In this paper, we consider the power splitting relaying (PSR) and time switching relaying (TSR) protocols for decode-and-forward (DF)-based relay networks consisting of a source, a relay, and a destination. For the networks, the relay is assumed to have a rechargeable battery with a certain amount of remaining energy for energy harvesting through the received signal transmitted from the source. Specifically, for the PSR protocol with and without the direct-path, we present the outage probability expression with a given power splitting coefficient, and we obtain the optimum power splitting coefficient to maximize the transmission rate and derive its transmission rate and outage probability, where the optimum coefficient depends on channel conditions and remaining energy. For the TSR protocol with and without the direct-path, we present the outage probability expression with a given time switching coefficient, and we obtain the optimum time switching coefficient to maximize the transmission rate and derive its transmission rate, where the optimum coefficient also depends on channel conditions and remaining energy.

In this paper, we investigate two different relay selection schemes, opportunistic relaying (OR) and selection cooperation (SC), for decode-and-forward (DF)-based relay networks consisting of a source, multiple relays, and a destination in the presence of multiple co-channel interferers, where each terminal has a single antenna and operates in a half-duplex mode. For the network, we first extend the conventional OR and SC to relay networks with the direct-path and multiple co-channel interferers, and obtain the exact and closed-form outage probability of the OR. Then, we show that the SC is equivalent to the OR in terms of outage performance for relay networks with the direct-path and multiple co-channel interferers. Finally, we show that the SC and OR are outage-optimal under the aggregate power consumption constraint at the relays for relay networks with the direct-path and multiple co-channel interferers.

In this letter, we offer the secrecy outage probability of the amplify-and-forward (AF) transmission, which consists of one source, one destination, one relay, and one passive eavesdropper. Particularly, we consider that the relay is equipped with multiple antennas while other terminals is utilized with single antenna and apply some diversity techniques (for both the reception and the transmission) in the relay to achieve gains in a secrecy outage performance. Additionally, we analyze the exact secrecy outage probability of the proposed systems in a one-integral form. Finally, some numerical examples are given to verify our provided analytical results for different system conditions.

We study a new relay selection scheme in nonregenerative relay networks consisting of a source, a destination, an eavesdropper, and multiple relays, where each terminal has a single antenna and operates in a half duplex mode. In these networks, it is desirable to protect the confidential message from the source to the destination against the eavesdropper with the help of a single selected relay. Specifically, we begin by investigating one scenario: instantaneous signal to noise ratios (SNRs) related to the eavesdropper are available. For the scenario, we propose relay selection to maximize the secrecy capacity of nonregenerative networks with and without direct paths. For networks with direct-paths, we derive a closed-form approximation of the secrecy outage probability. As a special case, for networks without direct-paths, we derive the exact secrecy outage probability expression in integral form and offer as well a closed-form approximation.

Two-way relaying (TWR) has recently received a great deal of attention since it can recover the loss in spectral efficiency that characterizes conventional half-duplex transmission systems operating within cooperative networks. Additionally, when relay selection is considered in multiple relay network, outdated channel state information (CSI) due to feedback delays can create important challenges from a practical point of view. In this paper, we study the outage performance of an amplify-and-forward (AF)-based TWR system with multiple relays where a single relay selection is performed based on outdated CSI. Specifically, we consider a single relay selection scheme in AF-based TWR system under outdated CSI conditions and offer a statistical analysis of the signal-to-noise ratio per hop with the given policy. For the analysis of the outage probability with asymmetric outage thresholds, we offer an accurate closed-form approximation based on the provided statistical/joint statistical analyses of a dual-hop AF transmission. Finally, we verify our analytical results with some selected computer-based simulation results.

In this paper, we study the outage performance of an amplify-and-forward (AF)-based two-way relaying (TWR) system with multiple relays where a single relay selection is performed based on outdated channel state information (CSI). Specifically, we propose a single relay selection scheme in AF-based TWR system under outdated CSI conditions. With this policy, we offer a statistical analysis of the signal-to-noise ratio per hop and analyze the outage probability with asymmetric outage thresholds based on CSI-assisted AF protocol. Additionally, we provide the exact and asymptotic expressions based on the provided statistical/joint statistical analyses of a dual-hop AF transmission. Finally, we verify our analytical results with some selected computer-based simulation results.

In this letter, we propose two-way amplify-and-forward relaying in conjunction with adaptive modulation in order to improve spectral efficiency of relayed communication systems while monitoring the required error performance. We also consider a multiple relay network where only the best relay node is utilized so that the diversity order increases while maintaining a low complexity of implementation as the number of relays increases. Based on the best relay selection criterion, we offer an upper bound on the signal-to-noise ratio to keep the performance analysis tractable. Our numerical examples show that the proposed system offers a considerable gain in spectral efficiency while satisfying the error rate requirements.

In this paper, we propose and study a cooperative transmission scheme for amplify-and-forward (AF) relaying system with adaptive modulation. Unlike the conventional incremental relaying with adaptive modulation (IR-AM) scheme, which improves the spectral efficiency with the minimum usage of relaying, our proposed scheme adaptively utilizes cooperative relaying to maximize the system spectral efficiency. We quantify the average spectral efficiency performance of the proposed scheme through statistical analysis and obtain the closed-form solutions for some practical scenarios of interest. Selected numerical results demonstrate that the spectral efficiency gain of the proposed scheme over the IR-AM scheme occurs mainly over the median signal-to-noise ratio range.

Cooperative diversity has been recently presented as a new technique to improve the link performance of wireless communication systems. However, a loss in spectral efficiency due to half-duplex relaying can be a significant weak-point for high data rate communications. In this paper, we propose two-way amplify-and-forward relaying in conjunction with adaptive modulation in order to improve spectral efficiency of relayed communication systems while monitoring the required error performance. By using the ideal-scaled gain at the relay instead of the more practical power-scaled gain, we provide an approximate but a very accurate performance analysis of our proposed system. Our numerical examples show that the proposed system offers a considerable gain in the spectral efficiency and outage probability while satisfying the error rates requirements.

We consider, in this paper, channel allocation and rate adaptation scheme for relayed transmission over correlated fading channels via cross-layer design. Specifically, jointly considering the data link layer buffer occupancy and channel quality at both the source and relay nodes, we develop an optimal channel allocation and rate adaptation policy for a dual-hop relayed transmission. As such the overall transmit power for the relayed system is minimized while a target packet dropping rate (PDR) due to buffer over flows is guaranteed. In order to find such an optimal policy, the channel allocation and rate adaptation transmission framework is formulated as a constraint Markov decision process (CMDP). The PDR performance of the optimal policy is compared with that of two conventional suboptimal schemes, namely the channel quality based and the buffer occupancy based channel allocation schemes. Numerical results show that for a given power budget, the optimal scheme requires significantly less power than the conventional schemes in order to maintain a target PDR.

In this paper, we study two-way amplify-and-forward relaying in conjunction with adaptive modulation over a multiple relay network. In order to keep the diversity order equal to the number of relays and maintain a low complexity, we consider the best relay selection scheme in this work. Based on the proposed selection criterion for the best relay, we analyze the average spectral efficiency by its approximated upper bound. In addition, we extend the proposed scheme to the case where a direct path between source and destination exists. Our numerical examples show that the proposed system offers a considerable gain in the spectral efficiency while satisfying the error rates requirements.

In this paper, we consider two-way amplify-and-forward relaying communication over a multiple relays network in which the best relay node is selected among others. Our proposed scheme picks for duplex communication between the source and the destination only the relay which provides the best end-to-end performance based on the instantaneous channel information. Similar to the relay selection method proposed, our scheme also does not require any explicit communications among the relays. Based on the proposed relay selection criterion, we offer the performance bounds on the average sum-rate, average symbol error rate, outage probability over identically, independent distributed Rayleigh fading channels. Further, our numerical examples show that our proposed scheme provides considerable sum-rate gains and offers an increasing a diversity order as the number of relay candidates increases.

In this paper, we propose a low complexity cooperative communication systems with the amplify-and-forward protocol over a multiple distributed relay network where only one relay among relay candidates is selected according to a certain threshold. By setting different values of their threshold, we consider two different relay selection schemes: (i) achieving the maximum spectral efficiency and (ii) minimizing system complexity. From our provided statistics of the combined output signal-to-noise ratio and our analysis of the system complexity, we show that our proposed node selection schemes provide considerable spectral efficiency gain and outage performance while it has a relatively low complexity comparing to other schemes known in the literatures.

In this paper, we consider an incremental relaying protocol based on an amplify-and-forward transmission in conjunction with the best relay selection scheme over non-identically distributed relay channels. In order to satisfy the spectral efficiency and the bit error rate (BER) requirements, adaptive modulation is applied to our proposed scheme. We derive the average spectral efficiency, average BER and outage probability for the performance analysis of our proposed scheme. For a more tractable analysis, we start with an upper bound for the combined signal-to-noise ratio at the destination and provide closed-form expressions for independent non-identically distributed Rayleigh fading conditions. Our analytical-based numerical results are validated by some computer-based simulations. These results show that our proposed scheme leads to a considerable improvement in the performance of cooperative diversity systems.

In this paper we propose joint antenna selection MIMO and adaptive modulation scheme for high spectral efficiency and power efficiency wireless transceiver design. In our proposed scheme the number of active receive antennas for spatial multiplexing MIMO detection is determined at the rate of the large scale channel variation which is a function of the path loss and shadowing parameters, while the link adaptation is updated as fast as the coherence time. Hence, in our proposed scheme, the rate of antenna selection is slower than the link adaptation, which is motivated by the fact that the portion of the power consumption is dominated by RF chains during the initial period of the switched-on terminal and some wireless service does not require the large scale mobility. From our analysis we determine the number of the active receive antennas to achieve a certain target ergodic capacity as well as a target link performance and evaluate bit error rate, average spectral efficiency and the outage probability for two MIMO detection schemes such as maximum likelihood and zero-forcing. Some selected numerical examples are finally presented and discussed to illustrate the tradeoff offered by this scheme.

In this paper, we consider an incremental relaying protocol based on an amplify-and-forward transmission in conjunction with a best relay selection scheme over non-identically distributed relay channels. In order to satisfy the spectral efficiency and the bit error rate (BER) requirements, adaptive modulation is applied to our proposed scheme. We derive the average spectral efficiency, average BER and outage probability for the performance analysis of our proposed scheme. For a more tractable analysis, we start with an upper bound for the combined signal-to-noise ratio at the destination and provide closed-form expressions for independent non-identically distributed Rayleigh fading conditions. Our analytical-based numerical results are validated by some computer-based simulations. These results show that our proposed scheme leads to a considerable improvement in the performance of cooperative diversity systems.

Opportunistic relaying with cooperative diversity has been introduced in as a simple alternative protocol to the distributed space-time coded protocol while achieving the same diversity-multiplexing tradeoff performance as a point-to- point multiple-input multiple-output scheme. In this paper, we derive an upper and lower bound on the per hop output signal-to- noise ratio cumulative distribution function, probability density function and moment generating function. We also derive approximate but tight closed-form expressions for the lower and upper bounds of the outage probability of opportunistic relaying based on decode-and-forward transmission under the assumption of unbalanced/balanced hops and independent, identical distributed Rayleigh fading channels.

Opportunistic relaying with cooperative diversity has been introduced in as a simple alternative protocol to the distributed space-time coded protocol while achieving the same diversity-multiplexing tradeoff performance as a point-to-point multiple-input multiple-output scheme. In this paper, we derive the upper and lower bounds for the cumulative distribution function of the signal-to-noise ratio per hop, and then provide their probability density function and moment generating function.We also derive approximate but tight closed-form expressions for the lower and upper bounds of the outage probability of opportunistic relaying based on decode-and-forward transmission under the assumption of unbalanced/balanced hops and independent, identically distributed Rayleigh fading channels.

The opportunistic relaying in [1] was proposed as an efficient cooperative protocol in the wireless multi-hop systems. However, the opportunistic relaying may still have high complexity as the number of relay nodes increases since the link quality of the paths generated by multiple relay nodes should be monitored. In this paper, we propose a novel multi-hop relay protocol named "switch and examine node selection"(SENS), where the relay node is selected if its link quality is above a certain threshold which is set to satisfy the required performance and the selected link is maintained unless its link quality does not fall below the threshold. From our derived statistics of the received output signal-to-noise ratio (SNR), we obtain the optimal threshold in terms of the link performance such as the average output SNR, the outage probability, and average error rate. Using the optimalthreshold, we show from the analytical and numerical results that the performance of our proposed SENS protocol provides the same performance as the opportunistic relaying protocol while the complexity of our proposed scheme is much lower than the one of opportunistic system.

Recently, the cooperative diversity systems, based on the distributed space-time coding (DSTC), have been presented to provide the spatial diversity gain in the wireless networks. Although the performance of DSTC cooperative diversity systems is quite attractive in terms of the link performance, the complexity and the power consumption at each node are the main practical issues for the deployment of the systems, in particular, when the number of nodes is large. In this paper, we propose the suboptimal relay selection algorithm where a predetermined threshold is set both at the relay node and the destination node, and the node selection is performed only when the signal quality of either relay node or destination node is below a predetermined threshold, which has less complexity than the opportunistic relaying in while satisfying the required performance. We provide the closed-form expression of statistics of the output SNR and study the complexity of the proposed scheme. Based on our analytical results we show several selected numerical examples to show the efficiency of our proposed schemes.