Daniel Benevides da Costa

Cognitive Amplify-and-Forward Relay Networks Over Nakagami-

In this correspondence, the outage probability (OP) of dual-hop cognitive amplify-and-forward (AF) relay networks subject to independent non-identically distributed (i.n.i.d.) Nakagami-m fading is examined. We assume a spectrum-sharing environment, where two different strategies are proposed to determine the transmit powers of the secondary network. Specifically, the transmit power conditions of the proposed spectrum-sharing network are governed by either the combined power constraint of the interference on the primary network and the maximum transmission power at the secondary network or the single power constraint of the interference on the primary network. Closed-form lower bounds and asymptotic expressions for the OP are derived. Regardless of the transmit power constraint, we reveal that the diversity order is strictly defined by the minimum fading severity between the two hops of the secondary network. This aligns with the well-known result for conventional dual-hop AF relaying without spectrum sharing. Furthermore, the impact of the primary network on the diversity-multiplexing tradeoff is investigated. We confirm that the diversity-multiplexing tradeoff is independent of the primary network.

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In this paper, we investigate the end-to-end performance of dual-hop relaying systems with beamforming over Nakagami-m fading channels. Our analysis considers semi-blind (fixed-gain) relays with single antennas, and source and destination nodes equipped with multiple antennas. Closed-form expressions for the outage probability (OP), moment generating function (MGF), and generalized moments of the end-to-end signal-to-noise ratio (SNR) are derived. The proposed expressions apply to general operating scenarios with distinct Nakagami-m fading parameters and average SNRs between the hops. The influence of the power imbalance, fading parameters, and antenna configurations on the overall system performance are analyzed and discussed through representative numerical examples. Furthermore, the exactness of our formulations is validated by means of Monte Carlo simulations.

Fading

This paper investigates several important performance metrics of cognitive amplify-and-forward (AF) relay networks with a best relay selection strategy and subject to non-identical Rayleigh fading. In particular, assuming a spectrum sharing environment consists of one secondary user (SU) source, K SU relays, one SU destination, and one primary user (PU) receiver, closed-form expressions for the outage probability (OP), average symbol error probability (SEP), and ergodic capacity of the SU network are derived. The correctness of the proposed analysis is corroborated via Monte Carlo simulations and readily allows us to evaluate the impact of the key system parameters on the end-to-end performance. An asymptotic analysis is also carried out and reveals that the diversity gain is defined by the number of relays pertaining to the SU network (i.e., K), being therefore not affected by the interference power constraint of the PU network.

Cooperative dual-hop relaying systems with beamforming over nakagami-m fading channels

The end-to-end performance of dual-hop cooperative links using semi-blind (fixed gain) relays and partial relay selection is investigated. The selection scheme considers that the source monitors the connectivity among the nodes (relays) of the first hop only. This scheme is interesting in practical ad-hoc and sensor networks. In our analysis, compact closed-form expressions are obtained for the outage probability, probability density function, moment generating functions, and generalized moments of the end-to-end signal-to-noise ratio(SNR), from which other relevant statistics that well-describe the distribution of the end-to-end SNR, such as mean, variance, kurtosis, skewness, and amount of fading, can also be deduced. Furthermore, the dynamic behavior of the end-to-end envelope is investigated, and the corresponding level crossing rate and average fade duration are obtained in an exact manner. Also, tight lower and upper bounds for these second-order statistics are presented in closed-form. Numerical results illustrating the systems performance in terms of the above metrics are provided, and the influence of the relay selection on performance is analyzed and discussed. For instance, it is shown that the power imbalance between the hops may have positive or negative effects on the overall system performance irrespective of the number of selected relays.

Cognitive Amplify-and-Forward Relaying with Best Relay Selection in Non-Identical Rayleigh Fading

In this paper, the outage behavior of dual-hop multiuser multirelay cognitive radio networks under spectrum-sharing constraints is investigated. In the proposed cognitive radio network, the secondary network is composed of one secondary-user (SU) source that communicates with one out of L destinations through a direct link and also via the help of one out of N relays by using an efficient relay-destination selection scheme. Additionally, a selection combining (SC) scheme to select the best link (direct or dual-hop link) from the SU source is employed at the selected SU destination. Adopting an underlay approach, the SU communication is performed accounting for an interference constraint, where the overall transmit power is governed by the interference at the primary-user (PU) receiver, as well as by the maximum transmission power available at the respective nodes. Closed-form expressions for the outage probability are derived, from which an asymptotic analysis reveals that the diversity order of the considered system is not affected by the interference and is equal to N + L for both decode-and-forward (DF) and amplify-and-forward (AF) relaying protocols. The analytical results are corroborated by Monte Carlo simulations, and insightful discussions are provided.

End-to-end performance of dual-hop semi-blind relaying systems with partial relay selection

In this letter, we investigate the outage performance of dual-hop decode-and-forward (DF) cooperative systems in an interference-limited Nakagami-m fading environment. More specifically, assuming the presence of Nakagami-m faded multiple co-channel interferers at the DF relay and a noisy destination, simple accurate closed-form approximations for the end-to-end outage probability are derived. To this end, moment-based estimators are used to attain the appropriate Nakagami-m fading parameters. Simulation results are presented in order to confirm the accuracy of the proposed approximations.

Multiuser and Multirelay Cognitive Radio Networks Under Spectrum-Sharing Constraints

In this letter, the outage performance of dualhop cooperative spectrum sharing systems with a direct link is investigated. A selection combining receiver is employed at the destination in order to combine the signals received from the decode-and-forward (DF) relay and from the source. Assuming independent non-identically distributed Nakagami-m fading channels, exact and asymptotic closed-form expressions are derived for the outage probability. Our results reveal that the diversity order of the considered system is solely determined by the fading severity parameters of the secondary network, being equal to min(m1, m2) + m0, where m0, m1, and m2 represent the fading severity parameters of the secondary nodes i.e., source→destination, source→relay, and relay→destination links, respectively.

Interference-Limited Relaying Transmissions in Dual-Hop Cooperative Networks over Nakagami-m Fading

In this Letter, tight closed-form approximations for the ergodic capacity of dual-hop fixed-gain relaying systems are derived. Our analysis allows for independent Nakagami-m fading channels, with partial relay selection being employed in the first-hop transmission. Simulation results are presented in order to confirm the accuracy of the proposed approximations. It is noteworthy that our formulations can be easily extended for the outage capacity analysis and guidelines for such are provided.

Outage and Diversity of Cognitive Relaying Systems under Spectrum Sharing Environments in Nakagami-m Fading

Novel expressions for the average channel capacity (ACC) of single-branch receivers operating in generalized fading channels, namely eta-mu and kappa-mu, are derived. The expressions are written in terms of the well-known Meijers G-functions, which are easily implemented in the most popular computing softwares. In addition, it is shown that, for any given fading condition, the Nakagami-m ACC defines regions of capacity: it lowerbounds the eta-mu ACC and it upperbounds the kappa-mu ACC. In the same way, it lowerbounds the alpha-mu ACC for alpha < 2 and mu > m, and it upperbounds the alpha-mu ACC for alpha > 2 and mu < m.

Capacity analysis of cooperative systems with relay selection in Nakagami-m fading

This paper proposes a new efficient scheme for the combined use of cooperative diversity and multiuser diversity. Considering a decode-and-forward (DF) opportunistic relaying strategy, we first study the outage behavior of the joint source-relay-selection scheme with/without direct links, from which the significance of the direct links is recognized. Motivated by the crucial role of these links on the system performance, a two-step selection scheme is proposed, which first selects the best source node based on the channel quality of the direct links and then selects the best link from the selected source to the destination. The proposed scheme significantly reduces the amount of channel estimation while achieving comparable outage performance to that using the joint selection scheme. Most importantly, the achieved diversity order is the same as that using the joint selection scheme. In addition, assuming an amplify-and-forward (AF) opportunistic relaying strategy, the outage behavior of this two-step scheme is also analyzed, and its availability is confirmed as well.