Louis Sibomana

Wireless information and power transfer in an underlay cognitive radio network

In this paper, we consider a secondary network with simultaneous wireless information and power transfer in a spectrum sharing scenario. In particular, a secondary user (SU) transmitter communicates with multiple SU receivers (SU-Rxs) under the peak interference power constraint of the primary user receiver and the SU maximum transmit power limit. We apply a channel quality-based threshold and exploit opportunistic scheduling. Specifically, an SU-Rx with best channel condition among a set of SU-Rxs satisfying the threshold is scheduled for data transmission. The remaining SU-Rxs with channel condition below the threshold, harvest the radio frequency energy. Analytical expressions of the SU ergodic capacity, symbol error rate, throughput, and energy harvesting are obtained. An optimal threshold satisfying a given target outage probability is determined. Numerical results are provided to investigate the impact of different parameters on the secondary network performance.

Packet transmission time for cognitive radio networks considering interference from primary user

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.

On physical layer security for reactive DF cognitive relay networks

This paper analyzes the physical layer security for cognitive relay networks under the peak interference power constraint of the primary user receiver. In particular, a secondary user (SU) transmitter communicates with an SU receiver through the help of multiple secondary relays (SRs) using a decode-and-forward (DF) protocol. There exist multiple eavesdroppers (EAVs) who illegally listen to the secondary network communication. We consider a reactive DF scheme, and only the SRs that satisfy a decoding threshold participate in the relay selection. Analytical expressions of the probability of existence of secrecy capacity and secrecy outage probability are obtained. Numerical results are provided to evaluate the impact of the number of SRs, number of EAVs and channel mean powers on the secondary system security. We also investigate the effect of the interference from the primary network to the secondary network performance. Moreover, the performance of proactive DF is analyzed for the purpose of comparison.

On the performance of cognitive radio networks with DF relay assistance under primary outage constraint using SC and MRC

In this paper, we analyze the performance of a cognitive radio network (CRN) that is assisted by a single relay. In particular, the secondary user (SU) transmitter (SU-Tx) and the secondary relay (SR) utilize the licensed frequency band of the primary user (PU). To protect the PU from harmful interference, the SU-Tx and SR must regulate their transmit power to satisfy the outage probability constraint of the PU. System performance in terms of outage probability is analyzed for selection combining (SC) and maximal ratio combining (MRC). Specifically, a power allocation policy and analytical expressions for the outage probability with SC and MRC are derived. Our results show that the upper bound of the outage probability corresponding to MRC is equal to the exact expression for the outage probability for SC.

Performance Analysis of a Cognitive Radio Network With a Buffered Relay

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) with the help of a secondary relay (SR). In particular, we assume that the SU-Tx and the SR are subject to the joint constraint of the timeout probability of the primary user (PU) and the peak transmit power of the secondary users (SUs). On this basis, we investigate the impact of the transmit power of the PUs and channel mean power 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 end-to-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 power of the interference links of the networks is small and if the SR peak transmit power is set to a high value.

Cognitive radio network with secrecy and interference constraints

In this paper, we investigate the physical-layer security of a secure communication in single-input multiple-output (SIMO) cognitive radio networks (CRNs) in the presence of two eavesdroppers. In particular, both primary user (PU) and secondary user (SU) share the same spectrum, but they face with different eavesdroppers who are equipped with multiple antennas. In order to protect the PU communication from the interference of the SU and the risks of eavesdropping, the SU must have a reasonable adaptive transmission power which is set on the basis of channel state information, interference and security constraints of the PU. Accordingly, an upper bound and lower bound for the SU transmission power are derived. Furthermore, a power allocation policy, which is calculated on the convex combination of the upper and lower bound of the SU transmission power, is proposed. On this basis, we investigate the impact of the PU transmission power and channel mean gains on the security and system performance of the SU. Closed-form expressions for the outage probability, probability of non-zero secrecy capacity, and secrecy outage probability are obtained. Interestingly, our results show that the strong channel mean gain of the PU transmitter to the PUs eavesdropper in the primary network can enhance the SU performance.

On physical layer security for cognitive radio networks with primary user interference

In this paper, we investigate the secondary network physical layer security under the outage constraint of the primary user (PU) receiver and interference from the PU transmitter to the secondary network. In particular, a secondary user (SU) transmitter sends confidential messages to trusted multiple SU receivers (SU-Rxs) in the presence of multiple eavesdroppers (EAVs). Further, we exploit multiuser diversity where the SU-Rx with best channel condition is scheduled for transmission. Then, analytical expressions of the probability of existence of non-zero secrecy capacity and secrecy outage probability are obtained. Analytical and simulation results are provided to evaluate the effect of the number of SU-Rxs and number of EAVs on the secondary system. Interestingly, the numerical results show that the interference from the primary network to the secondary network is an important parameter to improve the secondary network security.

Impact of secondary user communication on security communication of primary user

Cognitive radio network concept has been considered as a promising solution to improve the spectrum utilization. However, it may be vulnerable to security problems as the primary user PU and secondary user SU access the same resource. In this paper, we consider a system model where an eavesdropper EAV illegally listens to the PU communication in the presence of a SU transmitter SU-Tx communicating with a SU receiver SU-Rx. The SU-Tx transmit power is subject to the peak transmit power constraint of the SU and outage probability constraint of the PU. Given this context, the effect of the interference from the SU-Tx to the EAV on the primary system security is investigated. In particular, analytical expressions of the probability of existence of non-zero secrecy capacity and secrecy outage probability of the PU are derived. Moreover, the performance analysis of the secondary network is examined where closed-form expressions of the symbol error probability and achievable rate are presented. Numerical examples are provided to evaluate the impact of the primary system parameters and channel conditions among users on the system performance of secondary and primary networks. Interestingly, our results reveal a fact that the security of the primary network strongly depends on the channel condition of the SU-Tx to the EAV link and the transmit power policy of the SU-Tx. Copyright

A Framework for Packet Delay Analysis of Point-to-Multipoint Underlay Cognitive Radio Networks

This paper presents a queueing analytical framework for the performance evaluation of the secondary user (SU) packet transmission with service differentiation in a point-to-multipoint underlay cognitive radio network. The transmit power of the SU transmitter is subject to the joint outage constraint imposed by the primary user receivers (PU-Rxs) and the SU maximum transmit power limit. The analysis considers a queueing model for secondary traffic with multiple classes, and different types of arrival and service processes under a non-preemptive priority service discipline. The SU quality of service (QoS) is characterized by a packet timeout threshold and target bit error rate. Given these settings, analytical expressions of the packet timeout probability and average transmission time are derived for opportunistic and multicast scheduling. Moreover, expressions of the average packet waiting time in the queue and the total time in the system for each class of traffic are obtained. Numerical examples are provided to illustrate the secondary network performance with respect to various parameters such as number of PU-Rxs and SU receivers, SU packet arrival process, QoS requirements, and the impact of interference from the primary network to the secondary network.

Symbol error probability and effective capacity of an underlay CRN over α-μ fading channels

This paper analyses the performance of an underlay cognitive radio network (CRN) over α-μ fading channels in terms of symbol error probability (SEP) and effective capacity (EC). The α-μ distribution allows for a more general fading model with an increased level of generality compared to well-known models such as Nakagami-m and Rayleigh fading. The SEP and EC at the secondary user receiver are therefore evaluated for different fading parameters α and μ. In the considered underlay CRN, the secondary user transmit power is subject to a peak interference power constraint in order to limit the interference to the primary user receiver. Given this setting, analytical expressions for the SEP and EC are derived for the general case of α-μ fading channels. Numerical results are provided to illustrate the performance of the considered underlay CRN on different fading channels.