This paper analyzes the ergodic capacity of secondary point-to-multipoint communications under the outage constraint of multiple primary user receivers (PU-Rxs) and the secondary user (SU) maximum transmit power limit. We first derive analytical expressions of the ergodic capacity for three scheduling schemes, that is, round robin, Max-signal-to-interference-plus-noise-ratio (Max-SINR) and Min-SINR, and compare their performance. Numerical examples show that when the number of SU receivers (SU-Rxs) increases in the presence of a single PU-Rx and at high SINR, the Min-SINR outperforms the Max-SINR scheme. As the number of PU-Rxs increases, the Max-SINR performs better than the Min-SINR scheduling. When the number of SU-Rxs becomes large, the system capacity is enhanced but so is the feedback load. To exploit the Max-SINR transmission while reducing the feedback load, we assume a threshold based on the channel quality where the SU-Rxs with the instantaneous SINR above the threshold participate in the Max-SINR scheduling; otherwise, an SU-Rx is selected randomly. Then, an analytical expression of the average capacity is derived. Numerical results illustrate that the capacity with limited feedback is approximately the same as for the case of Max-SINR with full feedback when the SU threshold for feedback condition is set to low and medium values.

In this paper, we consider a point-to-multipoint underlay cognitive radio network under the joint constraint of the primary user peak interference power and maximum transmit power limit of the secondary user (SU). Analytical expressions for the secondary outage capacity are obtained based on exact as well as approximate expressions of the first and second moments of the channel capacity. Numerical results are provided to assess the effect of the number of SU receivers and a given SU outage probability. We also evaluate the impact of the primary network parameters on the secondary network performance.

This paper analyzes the secondary network performance under the joint constraint of the primary user (PU) peak interference power and maximum transmit power limit of the secondary user (SU). In particular, N SU transmitters (SU-Txs) communicate with an SU receiver in the presence of a primary network with a PU transmitter and multiple PU receivers. Moreover, we exploit opportunistic scheduling where the SU-Tx with the best channel condition is scheduled for transmission. Analytical expressions of the outage probability and symbol error probability of the SU are obtained considering either perfect or statistical knowledge of the PU channel gains. Furthermore, we analyze the SU throughput for delay constrained applications with two hybrid automatic repeat request protocols, namely, repetition time diversity and incremental redundancy. Numerical results are provided to assess the effect of the number of SU-Txs and number of packet retransmissions on the secondary network performance. In addition, the impact of the primary network parameters on the secondary network is investigated.

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.

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.

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.