Ali Afana

On the Performance of Cooperative Relaying Spectrum-Sharing Systems with Collaborative Distributed Beamforming

In this paper, we use joint distributed beamforming and cooperative relaying in cognitive radio relay networks in an effort to enhance the spectrum efficiency and improve the performance of the cognitive (secondary) system. In particular, we consider a spectrum sharing system where a set of potential relays are employed to help a pair of secondary users in the presence of a licensed (primary) user. Among the available relays, only the reliable ones participate in the beamforming process, where the beamformer weights are obtained based on a linear optimization method. We investigate two well-known strategies, namely, selection decode-and-forward (SDF) and amplify-and-forward (AF) relaying in conjunction with distributed optimal beamforming. However, given the complexity of the performance analysis with optimal beamforming, we use zero forcing beamforming (ZFB), and compare both approaches through simulations. In this context, for SDF, we derive expressions for the probability density function (PDF) of the received signal-to-interference noise ratio (SINR) at the relays as well as at the secondary destination. As for the AF scheme, we obtain the exact expression for the cumulative distribution function (CDF) and the moment generating function (MGF) of the equivalent end-to-end SNR at the secondary destination. For both schemes, we derive closed-form expressions for the outage probability and bit error rate (BER) over independent and identically distributed Rayleigh fading channels for binary phase shift keying (BPSK) and M-ary quadrature amplitude modulation (M-QAM) schemes. Numerical results demonstrate the efficacy of the proposed scheme in improving the outage and BER performance of the secondary system while limiting the interference to the primary system. In addition, the results show the effectiveness of the combination of the cooperative diversity and distributed beamforming in compensating for the loss in the secondary systems performance due to the primary users co-channel interference (CCI).

Distributed Beamforming for Spectrum-Sharing Systems With AF Cooperative Two-Way Relaying

We consider in this paper distributed beamforming for two-way cognitive radio networks in an effort to improve the spectrum efficiency and enhance the performance of the cognitive (secondary) system. In particular, we consider a spectrum sharing system where a set of amplify-and-forward (AF) relays are employed to help a pair of secondary transceivers in the presence of multiple licensed (primary) users. The set of relays participate in the beamforming process, where the optimal beamformer weights are obtained via a linear optimization method. For this system, we investigate the transmission protocols over two and three time-slots. To study and compare the performance tradeoffs between the two transmission protocols, for both of them, we derive closed-form expressions for the cumulative distribution function (CDF) and the moment generating function (MGF) of the equivalent end-to-end signal-to-noise ratio (SNR) at the secondary receiver. We analyze the performance of the proposed methods where closed-form expressions for the user outage probability and the average error probability are derived for independent and identically distributed Rayleigh fading channels. Numerical results demonstrate the efficacy of beamforming in enhancing the secondary system performance in addition to mitigating the interference to the primary users. In addition, our results show that the three time-slot protocol outperforms the two time-slot protocol in certain scenarios where it offers a good compromise between bandwidth efficiency and system performance.

Spatial Modulation in MIMO Limited-Feedback Spectrum-Sharing Systems With Mutual Interference and Channel Estimation Errors

This letter investigates spatial modulation (SM) in multiple-input multiple-output (MIMO) spectrum-sharing systems in an effort to improve the overall spectral efficiency. Specifically, we study the secondary system performance adopting the SM technique under mutual primary-secondary interferences and channel estimation errors (CEEs). With limited feedback from the primary receiver, a closed-form expression for the average pairwise error probability, a tight upper bounded average bit error rate expression, and an approximate simple, yet accurate expression are derived over Rayleigh fading channels. Simulation results, which corroborate the numerical ones, show the importance of SM in improving the overall secondary performance and its robustness to CEEs.

Cooperative relaying in spectrum-sharing systems with beamforming and interference constraints

In this paper, we use a distributed Zero Forcing Beamforming (ZFB) method in cognitive radio relay networks in an effort to enhance the spectrum efficiency and improve the performance of the cognitive (secondary) system. In particular, we consider a spectrum sharing system where a set of decode-and-forward (DF) relays are employed to help a pair of secondary users in the presence of a licensed (primary) user. In this context, we derive expressions for the probability density functions (PDFs) of the received signal-to-noise ratio (SNR) at the relays as well as at the secondary destination. We also derive closed form expressions for the outage and bit error rate (BER) probabilities over independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical results demonstrate the efficacy of beamforming in improving the outage and BER performance.

Distributed Beamforming for Two-Way DF Relay Cognitive Networks Under Primary–Secondary Mutual Interference

In this paper, we consider collaborative beamforming for a cooperative two-way relay spectrum-sharing system where a pair of secondary transceivers communicates via a set of secondary decode-and-forward (DF) relays in the presence of multiple primary transceivers. Among the available relays, only those that receive the signals reliably participate in the cooperative beamforming process and use network coding to simultaneously transmit the weighted signals to the transceivers. Two practical two-way relaying strategies are investigated, namely, DF- xoring and DF-superposition. The former is based on bitwise-level xoring of the detected signals at the relays, whereas the latter is based on symbolwise-level addition at the relays. For each relaying strategy, we derive general optimal beamforming vectors at the relays to keep the interference inflicted on the primary receivers to a predefined threshold. Employing zero-forcing beamforming as a special case, we present an analytical framework of the performance of the secondary system considering the effect of the primary-secondary mutual cochannel interference (CCI). In particular, we derive closed-form expressions for the outage probability, bit error rate (BER), and achievable sum rates over independent and identically distributed Rayleigh fading channels. Numerical results demonstrate the effectiveness of beamforming in compensating for the cognitive system performance loss due to CCI in addition to mitigating the interference to the primary receivers. Simulation results also show that, when the received signals at the relays are equally weighted, DF- xor always outperforms both DF-superposition and amplify-and-forward (AF) relaying.

Enhancing the performance of spectrum-sharing systems via collaborative distributed beamforming and AF relaying

In this paper, we use a distributed beamforming method in cognitive radio relay networks in an effort to enhance the spectrum efficiency and improve the performance of the cognitive (secondary) system. In particular, we consider a spectrum sharing system where a set of potential relays are employed to help a pair of secondary users in the presence of a licensed (primary) user. A selection relaying scenario in an amplify and forward (AF) scheme is investigated. In this context, we obtain the exact expressions for the cumulative distribution function (CDF) and the moment generating function (MGF) of the equivalent end-to-end SNR at the secondary destination. Then, to analyze the performance, we derive closed-form expressions for the outage probability and bit error rate (BER) over independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical results demonstrate the efficacy of beamforming in improving the secondary system performance in addition to limiting the interference to the primary users.

Cooperative AF Relaying With Beamforming and Limited Feedback in Cognitive Radio Networks

This letter studies cooperative beamforming for dual-hop amplify and forward cognitive relay networks comprising a pair of secondary source-destination and multiple antenna relay in the presence of a pair of primary transmitter-receiver. The aim of this work is to improve the secondary system performance with limited feedback from the primary receiver while using a mean value-based power allocation strategy. We derive closed-form expressions for the outage probability and average error probability over Rayleigh fading channels. Numerical and simulation results demonstrate the impact of the limited feedback on the secondary system performance and show that an acceptable performance is achieved when compared with the case of perfect channel state information.

Cooperative two-way selective relaying in spectrum-sharing systems with distributed beamforming

We consider in this paper distributed beamforming for two-way cognitive radio networks in an effort to improve the spectrum efficiency and enhance the performance of the cognitive (secondary) system. In particular, we consider a spectrum sharing system where a set of decode-and-forward (DF) relays are employed to help a pair of secondary transceivers in the presence of multiple licensed (primary) users. Among the available relays, only those that receive the signals reliably participate in the beamforming process, where the optimal beamformer weights are obtained via a linear optimization method. We derive closed-form expression for the probability distribution function (PDF) of the total end-to-end signal-to-noise ratio (SNR) at the secondary transceiver. We also derive closed-form expressions for the outage and error probabilities over independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical results show the effect of beamforming in enhancing the secondary system performance in addition to mitigating the interference to the primary users.

On the performance of spectrum sharing two-way relay networks with distributed beamforming

In this paper, we consider distributed beamforming for two-way spectrum-sharing system in an effort to enhance the performance of the secondary system and improve the bandwidth efficiency. In particular, we consider a cognitive radio network where a set of amplify-and-forward (AF) relays are employed to help a pair of secondary transceivers in the presence of multiple primary receivers. This set of the available relays participate in the beamforming process, where the beamformer weights are obtained via a convex optimization method. We analyze the performance of the proposed methods where closed-form expressions for the end-to-end outage and average error probabilities are derived for independent and identically distributed (i.i.d.) Rayleigh fading channels. Numerical results demonstrate the vitality of beamforming in enhancing the secondary system performance in addition to mitigating the interference to the primary users.

Quadrature Spatial Modulation for Cooperative MIMO 5G Wireless Networks

In this paper, quadrature spatial modulation (QSM) is used in a cooperative decode-and-forward (DF) diversity systems in order to enhance the overall reliability and energy efficiency. In particular, a multi-antenna source communicates with a single-antenna destination with the help of a multi-antenna DF relay in the presence of a direct link. To study the system performance, we derive a closed-form expression for the average pairwise error probability ({PEP}) over Rayleigh fading channels. A tight upper bounded average bit error rate is obtained using the {PEP} expression. Moreover, simple approximate expressions are obtained to get insights on the system diversity. Numerical results, which match with simulations, show that QSM offers about 3 dB gain over the conventional spatial modulation in DF relaying systems.