Most of the research in spectrum sharing has neglected the effect of interference from primary users. In this reported work, the performance of spectrum sharing amplify-and-forward relay networks under interference-limited environment, where the interference induced by the transmission of primary networks is taken into account, is investigated. In particular, a closed-form expression tight lower bound of outage probability is derived. To reveal additional insights into the effect of primary networks on the diversity and array gains, an asymptotic expression is also obtained.

In this paper, we derive analytical expressions for outage probability and ergodic capacity of a spectrum sharing system with multiuser diversity under Nakagami-m fading. In particular, multiuser diversity effects in such systems where several secondary users utilize the licensed spectrum of the primary user are considered. The best and worst channel quality scenarios are investigated for transmission from a number of secondary transmitters. Numerical analysis and simulations are shown to reveal the effects of multiusers and fading parameters on the considered system.

In this paper, the effective capacity, a link-layer model supporting Quality of Service (QoS) metrics such as user data rate, packet loss rate and service delay, is analyzed. We consider an underlay cognitive cooperative relay network (CCRN) subject to independent non-identically distributed aH fading. An analytical expression of the effective capacity is derived by means of Fox H-functions and Meijer G-functions along with the Mellin transform of the product of two H-functions. The network performance is analyzed against the QoS exponent and the peak interference power constraint imposed by primary users.

In this paper, we investigate the ergodic capacity for an underlay cognitive relay network over α-µ fading channels. In particular, we assume the channels to be independent non-identically distributed α-µ random variables and analyze the system performance subject to a peak interference power constraint. Numerical results are presented to evaluate the effect of fading parameters on the ergodic capacity of the system.

In this paper, we investigate the performance of an underlay cognitive relay network over α-μ fading channels. In particular, we assume non-identical fading parameters and derive an analytical expression for the outage probability of a dual-hop underlay system subject to a peak interference power constraint. Numerical and simulation results are presented to evaluate the effect of fading parameters on the outage probability of the system.

In this paper, we consider a spectrum sharing system in which a primary transmission coexists with a secondary network composed of a secondary base station (SBS) and multiple secondary user receivers (SU-Rxs). The secondary user (SU) can access the spectrum licensed to the primary user (PU) as long as the SU does not cause any harmful interference to the PU. Among all available SU-Rxs, only the best SU-Rx with highest signal-to-interference-plus-noise ratio (SINR) is selected to receive the transmit signals from the SBS. We derive an analytical expression for the outage probability (OP) of the SU-Rx with highest SINR. Moreover, we derive an approximation of the ergodic capacity at the SU-Rx. In order to meet the requirements at the PU receiver (PU-Rx), at the same time, satisfying the quality of the SU link, an adaptive power allocation strategy is developed. The power allocation policy imposes the SU transmitter (SU-Tx) to adapt its transmit power in order to avoid harmful interference at the PU receiver (PU-Rx), with a PU predefined outage constraint.

In this paper, we analyze the performance of cognitive amplify-and-forward (AF) relay networks with beamforming under the peak interference power constraint of the primary user (PU). We focus on the scenario that beamforming is applied at the multi-antenna secondary transmitter and receiver. Also, the secondary relay network operates in channel state information assisted AF mode, and the signals undergo independent Nakagami-m fading. In particular, closed-form expressions for the outage probability and symbol error rate (SER) of the considered network over Nakagami-m fading are presented. More importantly, asymptotic closed-form expressions for the outage probability and SER are derived. These tractable closed-form expressions for the network performance readily enable us to evaluate and examine the impact of network parameters on the system performance. Specifically, the impact of the number of antennas, the fading severity parameters, the channel mean powers, and the peak interference power is addressed. The asymptotic analysis manifests that the peak interference power constraint imposed on the secondary relay network has no effect on the diversity gain. However, the coding gain is affected by the fading parameters of the links from the primary receiver to the secondary relay network.

In this article, the authors study the effect of peak interference power constraint given by the primary receiver on the performance of multi-hop cognitive amplify-and-forward (AF) relay networks. The athours assume that all involved channels are subject to independent, not necessarily identically distributed Nakagami-m fading and the secondary multi-hop relay network operates in channel state information-assisted AF mode. An analysis of the system performance in terms of outage probability and symbol error rate (SER) is presented. Accordingly, closed-form expressions for the tightly bounded outage probability and SER are formulated which are used for quantifying the impact of the fading channels, the interference power constraint and the number of hops on system performance. More importantly, an asymptotic performance analysis, which intuitively reveals benefits of cooperative diversity of the secondary relay network, is established. The analysis shows that the diversity gain of the considered cognitive relay networks is equal to the minimum of the fading severity parameters of all relaying hops. Also, the interference power constraint imposed by the primary receiver only affects the coding gain of the secondary relay network.

In this paper, we consider a spectrum sharing cognitive radio network (CRN) in the presence of an eavesdropper (EAV) who illegally listens to the primary user (PU) communication. Under the PU outage and the secondary user (SU) peak transmit power constraints, the adaptive transmit power policy of the SU transmitter (SU-Tx) is obtained. Then, expressions for the probability of existence of a non-zero secrecy capacity of the primary network and the outage probability of the secondary network are derived. Numerical results are provided to investigate the impact of the SU-Tx peak transmit power, PU average transmit power and channel mean powers among users on the outage probability and probability of existence of a nonzero secrecy capacity. Our results illustrate that the probability of existence of a non-zero secrecy capacity strongly depends on the channel conditions among users and SU-Tx adaptive transmit power policy.

In this paper, we investigate a downlink model for underlay cognitive radio networks (CRNs). In particular, we assume that the secondary transmitter (SU-Tx) sends common packets to secondary receivers (SU-Rx) under the outage constraint of a single primary user (PU) and the peak transmit power constraint of the SU-Tx. All channels undergo Rayleigh fading. Given these settings, an adaptive transmit power policy for the SU-Tx is considered. Moreover, the cumulative distribution function (CDF) and probability density function (PDF) for packet transmission time are derived to analyze the timeout probability, the average packet transmission time and the average time a packet spends in the system for the SU-Rx having the best channel condition. Numerical results are provided to investigate the impact of the PU transmit power and channel mean powers on secondary network performance. The results show that when the number of SU-Rx becomes large, the timeout probability and the packet average time in the system decrease to a minimum.

Cognitive radio networks (CRNs) promise solutions to increase the spectrum utilization in wireless systems. In underlay cognitive radio spectrum sharing, the non-licensed users referred to as secondary users (SUs) are allowed to transmit simultaneously over the same frequency of licensed users known as primary users (PUs) as long as the interference to the primary receiver (PU-Rx) caused by the secondary transmitter (SU-Tx) remains below a predefined threshold. In this work, we investigate a downlink model for CRN. In particular, we assume that the SU-Tx sends common packets to secondary receivers (SU-Rx) under the outage constraint of a single PU and the peak transmit power constraint of the SU-Tx. All channels undergo Rayleigh fading. Given these settings, an adaptive transmit power policy for the SU-Tx is obtained. Moreover, we derive the cumulative distribution function (CDF) for minimum packet transmission time to analyze the timeout probability for SU-Rx having the best channel condition. Numerical results are provided to investigate the impact of PU transmit power and channel mean power gain on secondary network performance. The secondary system performance does not only depend on the outage constraint imposed by the PU and the SU peak transmit power but also on the interference from PU-Tx to SU-Rx. By increasing the number of SU-Rx, the timeout probability decreases to a minimum value.

In this paper, we analyze the secondary network transmission given a packet timeout threshold and a target bit error rate (BER) in a downlink multiservice spectrum sharing cognitive radio network (CRN). Under the joint constraint of primary user (PU) outage probability and secondary user (SU) peak transmit power, the adaptive transmit power policy of the SU transmitter (SU-Tx) is obtained. The throughput is maximized by transmitting to the secondary receiver (SU-Rx) having the best channel condition. We maintain fairness with a minimum resource guarantee assigned to each packet of a class of service. Accordingly, the average packet transmission time is determined. In addition, employing an M/G/1/B queueing model, the packet blocking probability is given to develop expressions of the average throughput and packet loss probability for the secondary class of service. Moreover, the quality of experience (QoE) is evaluated based on the relationship between the packet loss probability and mean opinion score (MOS). The results show that the secondary network achieves the stable transmission quality and minimizes packet loss when the number of SU-Rx becomes large.

In our paper published in [1], the delay performance of cognitive radio networks for point-to-point and point-to-multipoint communications have been studied. In this report, additional numerical results are provided to give more insights into the impact of system parameters on the delay performance of the considered cognitive radio network scenarios.

To support the rapidly increasing number of mobile users and mobile multimedia services, and the related demands for bandwidth, wireless communication technology is facing a potentially scarcity of radio spectrum resources. However, spectrum measurement campaigns have shown that the shortage of radio spectrum is due to inefficient usage and inflexible spectrum allocation policies. Thus, to be able to meet the requirements of bandwidth and spectrum utilization, spectrum underlay access, one of the techniques in cognitive radio networks (CRNs), has been proposed as a frontier solution to deal with this problem. In a spectrum underlay network, the secondary user (SU) is allowed to simultaneously access the licensed frequency band of the primary user (PU) as long as the interference caused by the SU to the PU is kept below a predefined threshold. By doing so, the spectrum utilization can be improved significantly. Moreover, the spectrum underlay network is not only considered as the least sophisticated in implementation, but also can operate in dense areas where the number of temporal spectrum holes is small. Inspired by the above discussion, this thesis provides a performance analysis of spectrum underlay networks which are subject to interference constraints. The thesis is divided into an introduction part and five parts based on peer-reviewed international research publications. The introduction part provides the reader with an overview and background on CRNs. The first part investigates the performance of secondary networks in terms of outage probability and ergodic capacity subject to the joint outage constraint of the PU and the peak transmit power constraint of the SU. The second part evaluates the performance of CRNs with a buffered relay. Subject to the timeout probability constraint of the PU and the peak transmit power constraint of the SU, system performance in terms of end-to-end throughput, end-to-end transmission time, and stable transmission condition for the relay buffer is studied. The third part analyzes a cognitive cooperative radio network under the peak interference power constraint of multiple PUs with best relay selection. The obtained results readily reveal insights into the impact of the number of PUs, channel mean powers of the communication and interference links on the system performance. The fourth part studies the delay performance of CRNs under the peak interference power constraint of multiple PUs for point-to-point and point-to-multipoint communications. A closedform expression for outage probability and an analytical expression for the average waiting time of packets are obtained for point-to-point communications. Moreover, the outage probability and successful transmission probability for packets in point-to-multipoint communications are presented. Finally, the fifth part presents work on the performance analysis of a spectrum underlay network for a general fading channel. A lower bound on the packet timeout probability and the average number of transmissions per packet are obtained for the secondary network.

In this article, we analyze the packet transmission time in spectrum sharing systems where a secondary user (SU) simultaneously accesses the spectrum licensed to primary users (PUs). In particular, under the assumption of an independent identical distributed Rayleigh block fading channel, we investigate the effect of the peak interference power constraint imposed by multiple PUs on the packet transmission time of the SU. Utilizing the concept of timeout, exact closed-form expressions of outage probability and average packet transmission time of the SU are derived. In addition, employing the characteristics of the M/G/1 queuing model, the impact of the number of PUs and their peak interference power constraint on the stable transmission condition and the average waiting time of packets at the SU are examined. Moreover, we then extend the analysis for point-to-point to point-to-multipoint communications allowing for multiple SUs and derive the related closed-form expressions for outage probability and successful transmission probability for the best channel condition. Numerical results are provided to corroborate our theoretical results and to illustrate applications of the derived closed-form expressions for performance evaluation of cognitive radio networks.

In this paper, we investigate the performance of a single-input and multiple-output cognitive radio network over Rayleigh fading. In particular, we assume that secondary transmitter (SU-Tx) and primary transmitter (PU-Tx) are equipped with a single antenna while secondary receiver (SU-Rx) and primary receiver (PU-Rx) have multiple antennas. Additionally, the SU-Tx transmit power is subject to outage constraint of the primary network and peak transmit power of the secondary network. Given these settings, an adaptive transmit power allocation policy for the SU-Tx, a closed-form expression for outage probability, and an approximation for ergodic capacity are obtained. These formulas will be used to examine the impact of the PU-Tx transmit power, the number of antennas at receivers, and channel mean powers on the performance of the secondary network. More importantly, our results reveal that the SU-Tx using the power allocation policy can obtain optimal performance.

In this study, we investigate the impact of a secondary user on the security of the primary user in a cognitive radio network. In particular, we consider a spectrum underlay network consisting of a pair of primary users, a pair of secondary users, and an eavesdropper, operating in the same spectrum. The secondary user is allowed to simultaneously access the licensed frequency bands of the primary user as long as the outage probability of the primary user is kept below a predefined threshold, while the eavesdropper illegally listens to the communication of the primary network. Given these settings, an adaptive transmit power allocation policy, a closed-form expression for the outage probability, and an analytical expression for the probability of existence of non-zero secrecy capacity are formulated. Simulations show that the existence of a secondary network can enhance the probability of non-zero secrecy capacity of the primary network by causing interference to the eavesdropper.

In this paper, the outage performance of a cognitive radio network under the joint constraint of multiple primary users (PUs) and a secondary user (SU) is investigated. More specifically, the SU can adjust its transmit power to satisfy the outage probability constraint of multiple PUs and its own transmit power constraint for communication. The adaptive transmit power policy and closed-form expression for the outage probability are derived. On the basis of these formulas, the impact of the channel gains of the PUs and those of the interference links from the PUs to the SU on the performance of the secondary network is evaluated. Especially, our results show a relationship between the number of the active PUs on the licensed frequency bands and the outage performance of the secondary network. Also, the performance of secondary network can be improved by extending the bandwidth over a number of licensed frequency bands.

In this paper, we examine the delay performance in cognitive radio networks (CRNs) over general fading channels where secondary users are allowed to simultaneously access the spectrum licensed by primary users. In particular, subject to the peak interference power constraint, we investigate the effect of general fading channels on the delivery delay of data packets and acknowledgements (ACKs). A lower bound of outage probability and an upper bound of average transmission time are derived by utilizing the concept of timeout. Specifically, we apply the above results to investigate the quality of experience (QoE) for various fading channels, such as one-sided Gaussian, Rayleigh, Nakagami-m and Weibull channels. The numerical results indicate that the delay of ACKs under severe fading leads to a degradation of system performance.

In this paper, we study the performance of cognitive cooperative radio networks under the peak interference power constraints of multiple primary users (PUs). In particular, we consider a system model where the secondary user communication is assisted by multiple secondary relays (SRs) that operate in the decode-and-forward mode to relay the signal from a secondary transmitter to a secondary receiver. Moreover, we assume that the transmit powers of the secondary transmitter and the SRs are subject to the peak interference power constraints of multiple PUs that operate in their coverage range. Given this system setting, we first derive the cumulative distribution function of the instantaneous end-to-end signal-to-noise ratio. Then, we obtain a closed-form expression for the outage probability and an exact expression for the symbol error probability of the considered network. These tractable formulas enable us to examine the impact of the presence of multiple PUs on the performance of the considered spectrum sharing system. Furthermore, our numerical results show that system performance is improved significantly when the number of SRs increases or the channel mean power from the secondary user to the PUs is low. Also, any increase in the number of PUs in the coverage range of the secondary transmitter or the SRs leads to degradation in system performance. Finally, Monte Carlo simulations are provided to verify the correctness of our analytical results.

In this paper, outage performance of cognitive cooperative radio networks using two decode-and-forward (DF) schemes is investigated. Subject to the joint outage constraint of the primary user and the peak transmit power constraint of the secondary user, adaptive power allocation policies for the secondary transmitter and secondary relays are studied. Based on these strategies, expressions for the outage probability of proactive and reactive DF schemes are obtained. Interestingly, our results show that an increase in the transmit power of the primary transmitter (PU-Tx) does not always degrade the performance of the secondary network. In fact, the PU-Tx transmit power is a substantial parameter that the secondary users can adapt to in order to improve the system performance. The numerical results additionally show that the performance of the reactive DF scheme outperforms the proactive DF scheme if the outage threshold in the first hop of the reactive DF scheme is less than that of the proactive scheme.

In this paper, we study the impact of the number of antennas and distances among users on the performance of a spectrum sharing system. In particular, we assume that a secondary transmitter is equipped with a single antenna while both secondary receiver and primary receiver have multiple antennas. Also, it is assumed that the secondary users are subject to the peak interference power constraint. On this basis, the cumulative distribution function and probability density function for the signal-to-noise ratio are derived for Rayleigh fading channels. Moreover, using these results, we obtain closed-form expressions for the outage probability, ergodic capacity and an exact expression for symbol error probability. These formulas allow us to examine the impact of the number of antennas of the SU-Rx, the PU-Rx and distance among users on the system performance. Finally, Monte-Carlo simulations are provided to verify our analytical results.

In this paper, we analyze the packet transmission time in a cognitive cooperative radio network (CCRN) where a secondary transmitter (SU-Tx) sends packets to a secondary receiver (SU-Rx) through the help of a secondary relay (SR). In particular, we assume that the SU-Tx and SR are subject to the joint constraint of the timeout probability of the primary user (PU) and the peak transmit powers of the secondary users. On this basis, we investigate the impact of the transmit power of the PUs and channel mean powers on the packet transmission time of the CCRN. Utilizing the concept of timeout, adaptive transmit power allocation policies for the SU-Tx and SR are considered. More importantly, analytical expressions for the endto- end throughput, end-to-end packet transmission time, and stable condition for the SR operation are obtained. Our results indicate that the second hop of the considered CCRN is not a bottleneck if the channel mean powers of the interference links of the networks are small and the SR peak transmit power is set to a high value.

In this paper, we consider the outage performance of a cognitive cooperative radio network (CCRN) in which the secondary base station (SBS) transmits signals to multiple secondary receivers (SU-Rx) through the help of multiple secondary relays (SRs). It is assumed that the SRs are geographically distributed in clusters and that the considered network operates in a Rayleigh environment. In addition, we assume that the transmit powers of the SBS and SRs are subject to peak interference power constraints of the primary users (PUs) in their respective coverage range. Specifically, a closed-form expression for the outage probability of the SU-Rx with the worst channel condition is derived for independently distributed Rayleigh fading. The obtained outage expression is further utilized to examine the impact of the channel mean powers, the number of SRs distributed in each cluster and the number of clusters on the system performance.

The performance of cognitive networks (CNs) has been significantly improved by deploying a third-party, namely relay, to assist the direct communication. However, under a limited transmit power governed by the maximum tolerable interference at the primary network, the cognitive relay network still suffers a performance loss compared to its non-cognitive counterpart. To alleviate this shortcoming, this paper has pro-posed a technique to optimally deploy the relay in CNs. In particular, by assuming the decode-and-forward (DF) relay, we first derive an exact expression for the outage probability (OP) of CNs with spectrum-sharing environment over Nakagami-m channels. Then, using the exact formula, we obtain the asymptotic OP expression which further reveals the impact of networks' parameters on the performance. In addition, the optimal relay placement, i.e., minimizing the system OP, is also investigated by utilizing the asymptotic OP result. We have shown through some representative scenarios that given a fixed coordinate of a primary receiver, the optimal relay deployment significantly outperforms the two conventional approaches, i.e., uniform and random topologies.

This paper presents a new optimal window design method with a general window design specification for the passband and stopband. The design problem is formulated as a semi-infinite linear programming problem. With suitable discretizations, an exchange algorithm is employed. The convergence of the proposed algorithm is established. In the formulation, since the stopband is minimized, the method can be employed for the design of very highly optimized windows.