The exact outage probability (OP) of cognitive dual-hop relay networks equipped with a single amplify-and-forward (AF) relay and a selection combining receiver at the destination is derived under spectrum sharing constraint on a primary user. The tractable closed-form OP readily enables evaluation of system performance, which indicates the significance of using a relay in cognitive radio networks with a spectrum sharing approach. The proposed analysis is validated by numerical examples.Introduction: Cognitive radio technology is a promising approach to improve the utilisation of scarce radio frequency spectrum. The concept of relaying communication in cognitive radio networks with cooperative spectrum sharing has attracted much attention [1-3]. All of these works investigated the cognitive relay networks with decodeand-forward (DF) relaying operation. In particular, for adaptive DF relays, the exact and tight bounds for outage probability (OP) were derived in [1] and [2], respectively. Besides DF, the amplify-andforward (AF) relay is also an important protocol where the relay just simply forwards the signal to the destination without performing any regenerating operation. Recently, the OP of cognitive relay networks with AF relay has been derived [4]. By approximating the end-to-end signal-to-noise ratio (SNR) as the harmonic mean of two random variables, the tight lower bound of OP was derived in the high SNR regime. However, it is important to note that such approximation is not feasible in practical cognitive radio scenarios since the underlay spectrum sharing system must operate in the low SNR regime to avoid causing any harmful interference on the primary networks. To circumvent this drawback, the closed-form expression of exact OP for cognitive AF relay networks has been presented [5]. However, the work in [5] has not considered the direct link of secondary networks which can be utilised for diversity combining with a relaying link to increase network reliability.Inspired by all of the above, this Letter presents, for the first time, cooperative spectrum sharing with AF relay and selection combining (SC). In the cooperative spectrum sharing model, the existence of a common random variable, i.e. the channel fading coefficient from SU transmitter (SU-Tx) to primary user (PU), results in a dependence between the two SNR terms, which is cumbersome for the analysis. This Letter proposes a new analytical approach to solve this problem by taking into account the conditioned statistics on the fading coefficient from SU-Tx to PU. Specifically, the exact OP is obtained in a tractable closed-form expression (containing only elementary functions). This result readily allows us to investigate the advantage of deploying AF relay in a cognitive spectrum sharing environment. In fact, the performance of the considered cognitive cooperation significantly outperforms both direct communications and AF relaying transmission without a direct link.
In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source’s radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks.
Most of the research in spectrum sharing has neglected the effect of interference from primary users. In this reported work, the performance of spectrum sharing amplify-and-forward relay networks under interference-limited environment, where the interference induced by the transmission of primary networks is taken into account, is investigated. In particular, a closed-form expression tight lower bound of outage probability is derived. To reveal additional insights into the effect of primary networks on the diversity and array gains, an asymptotic expression is also obtained.Introduction: Spectrum sharing relay networks have recently attracted much attention for providing higher reliability over direct transmission under scarce and limited spectrum conditions [1 -4]. Specifically, the performance of decode-and-forward (DF) relay networks in spectrum sharing environments has been reported [1 -3]. Recently, we have investigated the outage probability (OP) for spectrum sharing networks with amplify-and-forward (AF) relaying [4]. It has been shown in [1][2][3][4] that utilising DF/AF relaying significantly enhances system performance in such constrained transmission power conditions. However, most of the previous works have neglected the effect of the primary transmitter (PU-Tx), which significantly deteriorates the performance of the secondary network. In this Letter, to evaluate this interference effect, we derive a closed-form expression for OP and further calculate an asymptotic expression. We show that under fixed interference from primary networks, the diversity order remains unchanged and the loss only occurs in the array gain, which is theoretically quantified. However, when the interference is linearly proportional to the signal-to-noise ratio (SNR) of the secondary network, the system is severely affected, leading to an irreducible error floor of OP.
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