Jiangbo Si

On the Performance of Spectrum Sharing Cognitive Relay Networks with Imperfect CSI

In a spectrum sharing scenario, when the channel state information (CSI) of interference links is imperfect, the transmission of the secondary user (SU) may cause a harmful interference on the primary user (PU). To quantify the impact of imperfect CSI on the PU, we present a performance metric termed as interference probability and derive the exact closed-form expression for interference probability of the PU. It is shown that the PUs interference probability is always equal to 0.75 when the CSI of interference links is imperfect. In order to guarantee the PUs interference probability below an acceptable value, a back-off power control mechanism is adopted. Then, under the PUs interference probability constraints, the exact outage probability of partial amplify-and-forward (AF) relay selection scheme in the cognitive relay networks is derived. Finally, numerical results are provided to validate our analysis.

On the Performance of Cognitive Relay Networks Under Primary User's Outage Constraint

In this letter, we propose two relay selection schemes in cognitive relay networks. According to the proposed schemes, the number of relays involved in the opportunistic relaying is determined by the partial channel state information (CSI) of primary user link and partial CSI between the relays and the primary user receiver, so as to maintain the primary users outage probability below a predetermined value. The exact outage probabilities of the secondary user are derived over Rayleigh fading channels. Finally, simulation results validate our analysis.

Capacity Analysis of Cognitive Relay Networks with the PU's Interference

In this letter, with the primary users (PUs) interference, we investigate the performance of the secondary user (SU) in spectrum sharing cognitive relay networks. Considering the correlation among the received interference plus noise ratios (SINRs) at the relays and SU destination, closed-form expressions for the outage probability and capacity of the SU are derived. It is shown that, though the interference from the PU badly degrades the SUs performance, an increase of the number of relays can compensate the loss. Finally, simulation results are provided to validate our theoretical analysis.

Efficient Soft Decision Fusion Rule in Cooperative Spectrum Sensing

In cognitive radio (CR), the soft decision fusion (SDF) rule plays a critical role in cooperative spectrum sensing (CSS). However, the computational cost on obtaining efficient SDF rule becomes infeasible even with a small number of cooperative users. In this paper, the efficiency of SDF rule in inhomogeneous background is studied from the perspective of quantization theory. We formulate the calculation of sensing performance including the probabilities of detection and false alarm when regarding both i) the quantization impact and ii) the inhomogeneous background, and then conclude a condition under which the sensing performance can be calculated by the fast Fourier transform (FFT). Based on this condition, two novel quantization schemes with two optimization methods are proposed to guarantee both the quantizer and decision threshold of SDF rule can be obtained efficiently, at the same time, the SDF can achieve high sensing performance.

Outage Probability of Opportunistic Relaying in Rayleigh Fading Channels With Multiple Interferers

In this letter, as multiple interferers have an effect on both the relays and the destination, the exact outage probabilities for the decode-and-forward (DF) opportunistic relaying are derived in three different cases: a) with selection combining (SC) deployed at the destination, b) with maximal ratio combining (MRC) deployed at the destination, and c) with hybrid selection and maximal ratio combining (HSMC) deployed at the destination. Simulation results validate our analysis, and show that in terms of outage probability, opportunistic relaying with HSMC is much better than that with SC or MRC.

Robust AN-Aided Beamforming and Power Splitting Design for Secure MISO Cognitive Radio With SWIPT

A multiple-input single-output cognitive radio downlink network is studied with simultaneous wireless information and power transfer. In this network, a secondary user coexists with multiple primary users and multiple energy harvesting receivers. In order to guarantee secure communication and energy harvesting, the problem of robust secure artificial noise-aided beamforming and power splitting design is investigated under imperfect channel state information (CSI). Specifically, the transmit power minimization problem and the max–min fairness energy harvesting problem are formulated for both the bounded CSI error model and the probabilistic CSI error model. These problems are non-convex and challenging to solve. A 1-D search algorithm is proposed to solve these problems based on

Energy-Efficient Optimal Power Allocation for Fading Cognitive Radio Channels: Ergodic Capacity, Outage Capacity, and Minimum-Rate Capacity

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Outage Analysis of Underlay Cognitive Multiple Relays Networks with a Direct Link

under the bounded CSI error model and based on Bernstein-type inequalities under the probabilistic CSI error model. It is shown that the optimal robust secure beamforming can be achieved under the bounded CSI error model, whereas a suboptimal beamforming solution can be obtained under the probabilistic CSI error model. A tradeoff is elucidated between the secrecy rate of the secondary user receiver and the energy harvested by the energy harvesting receivers under a max–min fairness criterion.

Spatial False Alarm in Cognitive Radio Network

Green communications is an inevitable trend for future communication network design, especially for a cognitive radio network. Power allocation strategies are of crucial importance for green cognitive radio networks. However, energy-efficient power allocation strategies in green cognitive radio networks have not been fully studied. Energy efficiency maximization problems are analyzed in delay-insensitive cognitive radio, delay-sensitive cognitive radio, and simultaneously delay-insensitive and delay-sensitive cognitive radio, where a secondary user coexists with a primary user and the channels are fading. Using fractional programming and convex optimization techniques, energy-efficient optimal power allocation strategies are proposed subject to constraints on the average interference power, along with the peak/average transmit power. It is shown that the secondary user can achieve energy efficiency gains under the average transmit power constraint, in contrast to the peak transmit power constraint. Simulation results show that the fading of the channel between the primary user transmitter and the secondary user receiver and the fading of the channel between the secondary user transmitter and the primary user receiver are favorable to the secondary user with respect to the energy efficiency maximization of the secondary user, whereas the fading of the channel between the secondary user transmitter and the secondary user receiver is unfavorable to the secondary user.

Threshold Based Relay Selection Protocol for Wireless Relay Networks with Interference

In this letter, exact outage probability of decode-and-forward (DF) and incremental DF (IDF) relaying are respectively derived over underlay cognitive relay networks. Particularly, we consider both the direct link and the primary users (PUs) interference with multiple available relays. Moreover, to reveal additional insights into the performance of DF and IDF relaying, the outage gap between the two schemes is theoretically evaluated. Finally, simulation results validate our analytical studies.