Efficiently allocating the scarce and expensive radio resources is a key challenge for advanced radio communication systems. To this end, cognitive radio (CR) has emerged as a promising solution which can offer considerable improvements in spectrum utilization. Furthermore, cooperative communication is a concept proposed to obtain spatial diversity gains through relays without requiring multiple antennas. To benefit from both CR and cooperative communications, a combination of CR networks (CRNs) with cooperative relaying referred to as cognitive cooperative relay networks (CCRNs) has recently been proposed. CCRNs can better utilize the radio spectrum by allowing the secondary users (SUs) to opportunistically access spectrum, share spectrum with primary users (PUs), and provide performance gains offered by cooperative relaying. In this thesis, a performance analysis of underlay CRNs and CCRNs in different fading channels is provided based on analytical expressions, numerical results, and simulations. To allocate power in the CCRNs, power allocation policies are proposed which consider the peak transmit power limit of the SUs and the outage probability constraint of the primary network. Thus, the impact of multiuser diversity, peak transmit power, fading parameters, and modulation schemes on the performance of the CRNs and CCRNs can be analyzed. The thesis is divided into an introduction and five research parts based on peer-reviewed conference papers and journal articles. The introduction provides fundamental background on spectrum sharing systems, fading channels, and performance metrics. In the first part, a basic underlay CRN is analyzed where the outage probability and the ergodic capacity of the network over general fading channels is derived. In the second part, the outage probability and the ergodic capacity of an underlay CRN are assessed capturing the effect of multiuser diversity on the network subject to Nakagami-m fading. Considering the presence of a PU transmitter (PU-Tx), a power allocation policy is derived and utilized for CRN performance analysis under Rayleigh fading. In the third part, the impact of multiple PU-Txs and multiple PU receivers (PU-Rxs) on the outage probability of an underlay CCRN is studied. The outage constraint at the PU-Rx and the peak transmit power constraint of the SUs are taken into account to derive the power allocation policies for the SUs. In the fourth part, analytical expressions for the outage probability and symbol error probability for CCRNs are derived where signal combining schemes at the SU receiver (SU-Rx) are compared. Finally, the fifth part applies a sleep/wake-up strategy and the min(N; T) policy to an underlay CRN. The SUs of the network operate as wireless sensor nodes under Nakagami-m fading. A power consumption function of the CRN is derived. Further, the impact of M/G/1 queue and fading channel parameters on the power consumption is assessed.

In this study, packet scheduling schemes, both in downlink and uplink of 3GPP Long Term Evolution (LTE) are evaluated. The main purpose of packet scheduling in LTE systems is to distribute resources among users in a fair and efficient way to maximize the system throughput. 3GPP LTE networks use advanced features of signal processing including Orthogonal Frequency Division Multiplexing Access (OFDMA), Single Carrier Frequency Division Multiplexing Access (SC-FDMA) and Multiple-Input Multiple-Output (MIMO) systems. In many literature, there is a gap between the physical-layer issues such as MIMO gains, Adaptive Modulation and Coding (AMC) and system-level issues focusing more on Medium Access Control (MAC) layer such as scheduling. The gap is still significant, making the optimal design of resource allocation and scheduling by a cross-layer approach in MIMO-OFDMA systems a challenging task. Different packet scheduling algorithms have different impacts on the performance of systems with MIMO links in terms of throughput, fairness, packet delay, packet loss, etc. We evaluate the performance of scheduling schemes in a downlink shared channel of 3GPP LTE Single-Input Single-Output (SISO) and MIMO networks. However, while MIMO systems can provide spatial diversity and higher system capacity, which exactly meets the growing demand for high data rate, to obtain spatially uncorrelated channels, the distance between adjacent antennas should be larger than 10 times of the wavelength of the carrier frequency. Due to this limitation of the size of user equipment (UE), it is difficult to employ the conventional technique of spatial multiplex in practice. To permit a considerable increase in throughput for uplink, scheduling schemes in Virtual MIMO (VMIMO) are proposed. The VMIMO scheduling schemes analyzed are multiuser pairing schemes where the system throughput and fairness for both orthogonal defect and capacity maximization pairing scheduling are investigated.

This paper analyses the performance of an underlay cognitive radio network (CRN) over alpha-mu fading channels in terms of symbol error probability (SEP) and effective capacity (EC). The alpha-mu 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 alpha and mu 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 alpha-mu fading channels. Numerical results are provided to illustrate the performance of the considered underlay CRN on different fading channels.

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, we analyze the power consumption of wireless sensor nodes with min(N, T) policy and M/G/1 queue in the presence of Nakagami-m fading. In particular, this system setting is applied to a wireless sensor node operating in a cognitive radio system as secondary user in the presence of a primary user. As such, not only the queue policy influences the power consumption but also the interference power constraint imposed on the wireless sensor node by the primary user. Thus, a queued sleep/wake-up strategy is analyzed in order to mitigate the average power consumption of a sensor node using min(N, T) policy in the context of an M/G/1 queue and a spectrum sharing environment in the presence of signal fading. Numerical examples are presented to illustrate the impact of queuing parameters and fading channel on the power consumption of a wireless sensor node.

In this paper, we analyze the power consumption of wireless sensor nodes with min(N,T) policy and M/G/1 queue in the presence of Nakagami-m fading. In particular, this system setting is applied to a wireless sensor node operating in a cognitive radio system as secondary user in the presence of a primary user. As such, not only the queue policy influences the power consumption but also the interference power constraint imposed on the wireless sensor node by the primary user. Thus, a queued sleep/wake-up strategy is analyzed in order to mitigate the average power consumption of a sensor node using min(N,T) policy in the context of an M/G/1 queue and a spectrum sharing environment in the presence of signal fading. Numerical examples are presented to illustrate the impact of queuing parameters and fading channel on the power consumption of a wireless sensor node.

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.

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 consider a cognitive cooperative relay network (CCRN) that utilizes a decode-and-forward relay in the presence of multiple primary users. Given this system setting, we study the effect of multiple primary transmitters (PU-Txs) and multiple primary user receivers (PU-Rxs) on the outage probability of the considered CCRN. Specifically, power allocation policies for the secondary user transmitter (SU-Tx) and the secondary relay (SR) are formulated, subject to the outage constraint which is imposed by the PU-Rxs as well as the peak transmit power limits given at the SU-Tx and SR. On the basis of these power allocation policies for the SU-Tx and SR, an expression for the outage probability of the CCRN is derived. Numerical examples are presented to show the effect of different system parameters on the outage probability of the CCRN.

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 consider a spectrum sharing system where a secondary user (SU) transmitter (SU-Tx) communicates with an SU receiver (SU-Rx) with the help of multiple secondary relays (SRs) in the presence of a single primary network link. In particular, the SU-Tx and SR are subject to their maximum transmit power limits and the timeout constraint of the primary user (PU). Moreover, we assume that the relay selection is based on either best relay selection (BRS) or max-max relay selection (MMRS). In BRS, a single relay having the best end-to-end channel condition among the SRs is selected for cooperation between the source and the destination. However, the selected relay may not experience the best source-relay channel and relay-destination channel at the same time. To overcome the limitation of selecting the same relay for both reception and transmission, MMRS uses the best relay of the SU-Tx→SR link for reception at the relay and the best relay of the SR→SURx link for transmission to the destination. Specifically, we compare the performance for BRS and MMRS in terms of the outage probability, and study the impact of the number of SRs, PU transmit power and different channel mean powers of interference links on the secondary network performance. Furthermore, based on the performance of the MMRS and assuming that automatic repeat request (ARQ) is implemented for packet retransmission, we investigate the outage probability for delay limited applications. The numerical results indicate that the MMRS outperforms BRS when more than one SRs are deployed. The secondary network outage probability is reduced when the number of SRs and the number of retransmissions become large. It is also shown that the interference from the PU has a significant impact on the secondary network performance.

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.