Performance study of opportunistic scheduling in multiuser cognitive relay network

The problem of optimal power allocation with best relay selection in a two-hop amplify and forward (AF) cognitive radio relay network over independent Rayleigh fading channels is considered. We take into consideration of the transmit power allocation between the secondary transmitter and the secondary relay for a given power budget and the primary user's interference limitation. To improve the performance of the secondary link, based on the analysis of maximizing the achievable SINR, we re-formulate the power allocation and relay selection (PARS) problem and finally the optimal solution is achieved. To reduce the computation complexity, furthermore, a suboptimal scheme is proposed with negligible performance loss. Simulation results confirm the effectiveness of the proposed schemes.

This paper analyzes outage performance of opportunistic relay selection in cognitive radio networks with primary user's interference and direct channel over independent non-identically distributed fading channels and under maximum transmit power constraint and interference power constraint. Exact analysis is firstly proposed and then extended to asymptotic analysis to have insights into important performance metrics such as coding gain and diversity order. The proposed analysis can also be applied to corresponding analysis for opportunistic relay selection in cognitive radio networks with PU's interference and without direct channel to highlight the usefulness of direct channel in relaying communications without any sacrifice of power and bandwidth. A multitude of results illustrate an achievable full diversity order, a considerable system performance deterioration due to primary user's interference but this deterioration can be drastically remedied by increasing the number of involved relays, and the superiority of opportunistic relay selection with direct channel to that without it.

This paper advocates the performance of wireless multiuser relay networks (MRNs) equipped with a single amplify-and-forward (AaF) relay. For such networks, we focus on opportunistic scheduling, in which the destination with the highest instantaneous end-to-end signal-to-noise ratio (SNR) is scheduled for transmission. The scheduled destination can receive either directly from the source or indirectly through the relay, based on cooperative selection diversity (CSD). Assuming Rayleigh fading channels, we first derive a new expression for the cumulative distribution function (CDF) of the received instantaneous end-to-end SNR. Then, relying on this statistical result, we present new exact expressions for the outage probability and symbol error rate (SER), both of which are obtained in closed-form. Furthermore, we derive simple yet valuable closed-form asymptotic expressions for the outage probability and SER in the high SNR regime. Our results explicitly reveal the impacts of CSD and opportunistic scheduling on the diversity order and array gain. Numerical results are presented to validate the analysis.

Cognitive relay network is a method for optimizing frequency spectrum utilization. What’s important in these networks is to transmit data such that none of primary and secondary users cause destructive interference to other users. Although primary interference affect cognitive network performance, but is neglected in former researches. In this paper, we show cognitive network performance by calculating outage probability. We consider both primary and secondary interference links. Finally, our study is corroborated by representative numerical example. Simulation results demonstrate that increasing interference threshold increase outage probability and increasing data transmit rate cause outage probability increase.

In this study, the authors investigate the performance of opportunistic scheduling for the dual‐hop amplify‐and‐forward multi‐user cognitive relaying network. Expressions are derived for the cumulative distribution function (CDF) and probability density function of the equivalent signal‐to‐noise ratio (SNR). From the derived CDF, the outage performance of the cognitive network is investigated. Then, an expression for average error probability is derived. Furthermore, simple and generic asymptotic expressions for the outage and error probabilities are obtained and discussed. In addition, a closed‐form expression for the system's ergodic capacity is derived. Their asymptotic results show that opportunistic scheduling has no impact on diversity gain. It is confirmed that the array gain determines the SNR advantage of opportunistic scheduling over the single‐user scenario. Moreover, they study adaptive power allocation under the total transmit power constraint in order to minimise the average error probability. As expected, the results show that optimum power allocation improves system performance compared with uniform power allocation. Finally, numerical results and Monte Carlo simulations are also provided to support the correctness of the analytical calculations.

In this paper, energy efficiency (EE) was investigated for a cognitive radio network (CRN) where massive multiple-input multiple-output (MIMO) was combined with femto cells. A heterogeneous network was considered to maximise EE, while massive MIMO was implemented to increase spatial reuse and focus energy into smaller spatial regions. Cooperation between femto cell based relay stations (RS) and a micro cell based secondary base station (SBS) allowed for secondary user (SU) quality-of-service (QoS) requirements to be met and also for control over primary user (PU) interference. Two key issues were addressed by the proposed model, namely improved CRN EE and reduced PU interference. The formulated EE optimisation problem was non-convex and thus converted into a semi-definite problem. Simulation results show that combining massive MIMO at the micro cell level with femto cells, lead to a CRN EE improvement. The addition of femto cells also lead to a reduction in PU interference.

This paper investigates the power allocation between the cognitive transmitter (CT) and the cognitive relay (CR) in a cognitive Amplify-and-Forward (AF) full-duplex relay network. To maximize the cognitive capacity, we firstly obtain a closed form expression of the optimal power allocation with the instantaneous interference channel information. Then considering limited cooperation between the primary and the cognitive networks, we develop an efficient iterative search algorithm to obtain the optimal power allocation with the statistical rather than the instantaneous interference channel information. Furthermore, considering absolutely no cooperation between the primary and the cognitive networks, we develop a sensing-based iterative search algorithm to obtain the optimal power allocation without any interference channel information. Simulation results show the capacity of the cognitive AF full-duplex relay network may achieve up to 50% improvement compared with the cognitive AF half-duplex relay network on the condition that the mean value of the self-interference channel gain is lower than −25 dB.

Adaptive channel and power allocation of downlink multi-user MC-CDMA systems

In this paper, we address the problem of beamforming (BF) design in a cognitive relay network (CRN), where the cognitive network not only shares the spectrum with the primary one but also acts as a relay to assist the primary signal transmission. Considering that all of the wireless channels are subject to the correlated Rayleigh fading distribution, we first formulate a constrained optimization problem to minimize the total transmit power of the cognitive base station (CBS) with multiple antennas, while guaranteeing the quality-of-service (QoS) of the primary and secondary users and keeping the mutual interference below an acceptable level. Then, by adopting the available partial channel state information (CSI), and proposing an approximation method to relax the constraints, a support vector machine (SVM) based algorithm is presented to solve the optimization problem for the BF weight vectors. The benefit of the new approach is that the slow change of the partial CSI can be taken into account. Finally, computer simulation results are provided to confirm the superiority of the proposed BF design strategy.

An adaptive and QoS-based spectrum awareness framework for CR networks

In cognitive relay networks, the interferences from secondary users (SUs) and relays to primary users are constrained to be lower than a threshold. The interference constraints are difficult to satisfy when the channel state information (CSI) is imperfect. In this paper, we propose a robust beamforming scheme for the multi-antenna non-regenerative cognitive relay network where the multi-antenna relay with imperfect CSIs helps the communication of single-antenna SU. Our objective is to design a robust beamforming scheme which maximizes the system capacity subject to transmit power constraint and interference constraints. The bounded channel uncertainties are modeled using the worst-case model. The robust beamforming problem, neglecting the correlation of channel uncertainties, is reformulated as a convex semidefinite programming (SDP) by rank-one relaxation. This convex SDP is related with the worst-case relay transmit power minimization problem, which is further reformulated as a convex SDP, whose rank-one solution is proved to exist. Thus, we propose the suboptimal solution to the robust beamforming problem which is found effectively by solving two convex SDPs. Simulation results are provided to demonstrate the effectiveness of the proposed scheme.

The difference between cognitive wireless network and traditional wireless network lies in the function of spectrum sensing and channel switching. In cognitive networks, cognitive users must sense the spectrum. When the primary users access, it must switch to another channel in order to avoid the interference to the primary users. Therefore, it is necessary to improve the traditional TCP to make it adapt to the spectrum sensing and channel switching in cognitive network. The cross-layer designing between TCP and MAC can eliminate retransmission problems caused by the spectrum sensing, and the proposed "TCP-improved algorithm" can solve the problems of low utilization rate of bandwidth or network congestion when cognitive users switch its channel. The experimental results show that the "TCP-improved algorithm" has the best performance in cognitive network.

Outage performance of cognitive DF relay networks with nonidentical Rayleigh fading channels and maximal ratio combining

In this paper, signal space diversity (SSD) is introduced in an underlay cognitive two-way relay network where two secondary source terminals communicate with each other directly and via an intermediate secondary relay in the presence of a primary user. SSD is applied at all transmitting nodes in the secondary network to rotate and interleave the signal components before transmission that enables both source terminals and intermediate relay to transmit different symbols. Therefore, SSD enhances the mutual information of the SSD-based underlay cognitive two-way relay network compared to the conventional one. Thus, performance analysis and results of the proposed system are different than that of the conventional system. It is shown that the proposed system improves the outage performance and spectral efficiency of the underlay cognitive two-way relay network. Moreover, the closed-form expression for exact outage probability of the proposed system is derived over Rayleigh fading channels. Monte Carlo simulations are carried out to validate the analytical work. In all analysis, interference power constraints and correlation among signal-to-noise ratios are taken into consideration to provide accurate results. Furthermore, the impact of channel estimation error on the outage probability of the system is investigated and the closed-form expression of the outage probability is derived.

NOMA-based cognitive radio network with hybrid FD/HD relay in industry 5.0