Jules Merlin Mouatcho Moualeu

Relay Selection for Coded Cooperative Networks with Outdated CSI over Nakagami-m Fading Channels

In this paper, we consider relay selection for turbo coded cooperative networks subject to Nakagami-m fading when the channel state information (CSI) is known at the receiver but is not necessarily ideal. This non-ideality may be due to a feedback delay caused by the difference between the instantaneous CSI during the transmission and the CSI at the time of relay selection, resulting in outdated CSI phenomena. The impact of the outdated CSI on the proposed scheme is well investigated. A closed-form expression for the exact outage probability is derived as well as its asymptotic expression in the high signal-to-noise (SNR) regime. Moreover, upper bounds on the bit-error rate (BER) are presented and a study of the diversity order reveals that for ideal CSI, full diversity in the number of relays and fading parameters m is achieved as opposed to outdated CSI where the achievable diversity is equivalent to the diversity of a coded cooperative network with a single relay.

Multi-Relay Turbo-Coded Cooperative Diversity Networks Over Nakagami-

This paper studies a multi-relay adaptive turbo-coded cooperative diversity scheme over Nakagami- m fading channels. In the underlying scheme, after receiving a fraction of the codeword determined by a tradeoff parameter denoted by f, all the relays decode, and only the reliable relays forward the rest of the codeword to the destination. We assume binary phase-shift keying modulation and analyze the scheme under study in terms of bit error rate (BER) and outage probability. Union bounds on the BER are derived using the transfer function bounding and the limit-before-average techniques. Furthermore, we examine the asymptotic behavior of the system in the high-signal-to-noise-ratio (SNR) regime using the derived pairwise error probability (PEP). We also derive a closed-form expression for the outage probability of the system and its high-SNR approximation to evaluate the achievable diversity order. Simulations are provided to assess the accuracy of our analytical work.

m

Since the radio-frequency spectrum is fast becoming scarce, increasing the spectral utilization is of utmost importance for the sustainable development of wireless communications systems. In an effort to improve the spectral efficiency, cooperative relaying techniques have recently been integrated into spectrum-sharing environments. In this paper, we examine the outage and bit error probabilities of dual-hop cognitive turbo-coded cooperative networks with outdated channel state information (CSI) subject to Rayleigh fading. We assume a spectrum-sharing environment where the transmit power conditions of the underlay network are governed by the combined power constraint of the interference in the primary network and the maximum allowable transmission power at the secondary network. In this network, cochannel interference from the primary transmitter on the secondary network is considered, and a single relay that maximizes the received signal-to-noise ratio (SNR) is selected among the secondary relays. To efficiently evaluate the key parameters on the system performance, we derive the analytical expressions of the end-to-end outage probability and bit error rate (BER) for the proposed scheme. Assuming binary phase-shift keying (BPSK), we obtain explicit upper bounds on the probability of bit error based on the pairwise error probability. Furthermore, we present simplified expressions of the outage probability in the high-SNR regime used to quantify the system performance in terms of diversity gain. Finally, simulation results are provided to verify the accuracy of our analytical framework.

Fading Channels

In this letter, we investigate the performance of amplify-and-forward partial relay selection in underlay cognitive radio systems with delayed channel estimates, where a direct secondary link is considered. We derive the exact outage probability using a novel mathematical approach based on the moment generating function. Unlike the previous works, our analysis shows that for varying interference-to-noise ratio (INR), i.e., γ̅_I = εγ̅, where 0 ≤ ε ≤ 1, the diversity gain is a function of ε regardless of the nature of the channel state information (CSI). Under the varying INR assumption, it is found that the diversity gain is improved for both outdated and perfect CSIs when ε → 0. The validity of our analysis is verified by computer simulations.

Cognitive Coded Cooperation in Underlay Spectrum-Sharing Networks Under Interference Power Constraints

In this paper, the best relay selection in CSI-assisted variable gain amplify-and-forward (AF) with outdated channel state information (CSI) in the presence of co-channel interference (CCI) over Rayleigh fading channels is investigated. We first derive the cumulative density function (CDF) of the effective signal-to-interference-plus-noise ratio (SINR) of both the best source-to-relay and relay-to-destination links. Subsequently, a closed-form expression for the lower bound on the end-to-end outage probability (OP) of the system under study is obtained. Moreover, we present and discuss asymptotic expressions of the OP, which reveal the diversity gain of the underlying system. In particular, it is shown that for varying interference-to-noise ratio (INR), the diversity order is reduced to zero regardless of the nature of the desired CSI (i.e., outdated or ideal), and to full diversity or diversity one for fixed INR with ideal CSI or outdated CSI, respectively. Finally, Monte-Carlo simulation results are presented to validate the accuracy of the proposed analytical framework.

Performance of AF Relay Selection With Outdated Channel Estimates in Spectrum-Sharing Systems

In this paper, we consider a cognitive radio network (CRN) with multiple primary users (PUs) and multiple SUs and propose a cooperative spectrum sensing and transmission for some selected SUs in order to avoid interference with PUs. The distributed collaboration strategy is done through a coalitional game and we present a distributed algorithm for the coalition formation. In the proposed scheme, the SUs that sense a particular channel with non-identical sensing times, form a coalition in which a coalition head is selected to determine whether or not the channel is idle. If a channel is not active, then the SU chosen as coalition head can transmit its packets through a cooperative scheme in the data transmission slot. Our simulation results show that the proposed scheme can significantly improve the average throughput compared to its non-cooperative counterpart. Moreover, it is shown that the proposed scheme is energy efficient in comparison to a scheme with fixed and identical sensing times.

Outage analysis of relay selection in AF with outdated channel information in the presence of co-channel interference

In this paper, we investigate a cross-layer relay selection approach for cooperative-diversity networks that employ the truncated automatic repeat request (ARQ) protocol. The key feature of the proposed scheme is that the criterion for the selection of relay subsets is the maximization of the link-layer throughput that takes into account both the physical and link layers characteristics. Results show that the proposed cross-layer approach which assigns transmission to relay combination that sees better channel conditions, outperforms the capacity-based cooperative transmission with the same number of reliable relays in terms of throughput gain. Furthermore, a joint optimization of constellation size and packet length is included to enhance the system throughput for both the cross-layer relay selection and capacity-based relay selection.

Energy-efficient cooperative spectrum sensing and transmission in multi-channel cognitive radio networks

We investigate a power assignment scheme in multi-relay adaptive decode-and-forward (DF) cooperative-diversity networks over non-identical Rayleigh fading channels, that integrates truncated automatic repeat-request (ARQ) at the link layer. At the cooperative level, only the reliable relays participate in the retransmission phase if necessary. In this paper, we aim at maximizing the system throughput via power optimization and we show that this can be done by minimizing the symbol-error rate (SER) of the retransmission. We derive the closed- form expressions for the exact SER of the multi-relay adaptive DF over non-identical Rayleigh fading channels as well as the asymptotic bounds for the SER. Results show that the analytical bounds for the SER corroborate with the simulated SER at high signal-to-noise ratio (SNR) and maximum throughput is achieved through optimal power allocated at the source and various reliable relays.

Cross-layer relay selection criterion for cooperative-diversity networks

Recently, cooperative relaying techniques have been integrated into spectrum-sharing systems in an effort to yield higher spectral efficiency. Many investigations on such systems have assumed that the channel state information between the secondary transmitter and primary receiver used to calculate the maximum allowable transmit secondary user transmit power to limit the interference is known to be perfect. However, because of feedback delay from the primary receiver or the time-varying properties of the channel, the channel information may be outdated, which is an important scenario to cognitive radio systems. In this paper, we investigate the impact of outdated channel state information for relay selection on the performance of partial relay selection with amplify and forward in underlay spectrum-sharing systems. We begin by deriving a closed-form expression for the outage probability of the secondary network in a Rayleigh fading channel along with peak received interference power constraint and maximum allowable secondary user transmit power. We also provide a closed-form expression for the average bit-error rate of the underlying system. Moreover, we present asymptotic expressions for both the outage probability and average bit-error rate in the high signal-to-noise ratio regime that reveal practical insights on the achievable diversity gain. Finally, we confirm our results through comparisons with computer simulations. Copyright

Power assignment in multi-relay adaptive DF cooperative networks

In this paper, we study the performance of relay selection in variable-gain amplify-and-forward (AF) turbo-coded cooperative network in the presence of channel estimation errors. In particular, we assume M-ary phase shift keying (MPSK) modulation and consider a dual multi-relay cooperative scenario where the relay selection requires global knowledge (end-to-end) of the relaying link. We derive the probability density function (PDF) of the received signal-to-noise ratio (SNR) for the underlying relaying link, and an upper bound expression of the average pairwise error probability (PEP). Furthermore, we present the diversity analysis study in which we show that the effect of erroneous channel estimates reduce the diversity order at high SNR to zero. Using these results, we evaluate the performance of the coded cooperation scenario under study in terms of bit-error rate (BER). Monte-Carlo simulation results are presented to validate the accuracy of the analytical results.