On The Performance of Underlay Relay Cognitive Networks

The bit error rate (BER) performance of underlay relay cognitive networks in the presence of Rayleigh fading is thoroughly analyzed in this paper. New exact and asymptotic analytic expressions under consideration of both interference power constraint and maximum transmit power constraint are derived in closed-form and are extensively corroborated by Monte-Carlo simulations. These expressions facilitate in evaluating effectively the network performance behaviour in key operation parameters as well as in optimizing system parameters. A multitude of analytical results expose that underlay relay cognitive networks experience the performance saturation phenomena while their performance considerably depends on the number of hops for the linear network model. Additionally, optimum relay position is significantly dependent of maximum transmit power, maximum interference power, and licensee location. Moreover, the appropriate order of locating unlicensees with different maximum transmit power levels can dramatically improve the network performance

Exact Outage Performance Analysis of Multiuser Multi-relay Spectrum Sharing Cognitive Networks

In this paper, we investigate the outage performance of dual-hop multiuser multi-relay cognitive radio networks under spectrum sharing constraints. Using an efficient relay-destination selection scheme, the exact and asymptotic closed-form expressions for the outage probability are derived. From these expressions it is indicated that the achieved diversity order is only determined by the number of secondary user (SU) relays and destinations, and equals to M+N (where M and N are the number of destination nodes and relay nodes, respectively). Further, we find that the coding gain of the SU network will be affected by the interference threshold $bar I$ at the primary user (PU) receiver. Specifically, as the increases of the interference threshold, the coding gain of the considered network approaches to that of the multiuser multi-relay system in the non-cognitive network. Finally, our study is corroborated by representative numerical examples

Application of non-orthogonal multiple access in cooperative spectrum-sharing networks over Nakagami-m fading channels

This paper proposes a novel non-orthogonal multiple access (NOMA)-based cooperative transmission scheme for a spectrum-sharing cognitive radio network, whereby a secondary transmitter (ST) serves as a relay and helps transmit the primary and secondary messages simultaneously with employing NOMA signaling. This cooperation is particularly useful when the ST has good channel conditions to a primary receiver but lacks of the radio spectrum. To evaluate the performance of the proposed scheme, the outage probability and system throughput for the primary and secondary networks are derived in closed forms. Simulation results demonstrate the superior performance gains for both networks thanks to the use of the proposed NOMAbased cooperative transmission scheme. It is also revealed that NOMA outperforms conventional orthogonal multiple access and achieves better spectrum utilization

Physical Layer Security of Cooperative NOMA for IoT Networks under I/Q Imbalance

In this paper, we investigate the reliability and security of cooperative dual-hop non-orthogonal multiple access (NOMA) for internet-of-thing (IoT) networks, in which the transceivers consider a detrimental factor of in-phase and quadrature-phase imbalance (IQI). The communication between the source and destination is accomplished through a decode-and-forward (DF) relay in the presence of an eavesdropper. In order to characterize the performance of the considered system, exact analytical expressions for the outage probability (OP) and intercept probability (IP) are derived in closed-form. Furthermore, to better understanding the performance of the considered system, we further derive the asymptotic expressions of OP in the high signal-to-noise ratio (SNR) regime and IP at the high main eavesdropping ratio (MER) region. A large number of analysis and Monte Carlo simulation results show that the existence of IQI usually increases the corresponding OP and reduces the IP, which means that reduces the reliability of the system and improves the security. In addition, the provided results provide useful insights into the trade-off between reliability and security of secure cooperative communication systems

Proactive and Reactive DF Relaying for Cognitive Network with Multiple Primary Users

In this paper, the outage performance of a cognitive radio network with a pair of secondary transmitter and receiver is investigated in the presence multiple primary users over a number of licensed frequency band and multiple secondary relays (SRs). Two decode and forward (DF) schemes are considered for the relays, namely proactive and reactive DF schemes. An adaptive power allocation scheme for secondary transmitter and secondary relays is formulated under the joint constraints of the primary user outage and peak transmit power of the secondary users. Based on these strategies, analytical expressions for the outage probability of proactive and reactive DF schemes are derived. More precisely, our results demonstrate the impact of number of the active primary users (PUs) over a number of available licensed frequency bands on the outage performance of secondary network. Further, it is observed that the performance of the secondary network can be improved by extending the bandwidth of the primary users

Relay Selections for Cooperative Underlay CR Systems with Energy Harvesting

In this work, we consider a cooperative underlay cognitive radio system in which one secondary user (S) transmits its data to a secondary receiver with the assistance of multiple relays. In the considered underlay spectrum sharing scenario, the transmit power levers at S and forwarding relays are adjusted simultaneously according to a given threshold interference power that the primary user can tolerate. We also consider that relays adopt threshold decode-and-forward relay scheme and harvest energy from the primary transmitter with finite energy storage capacity under time switching scheme. Three best relay selection schemes, optimal source-relay link with wireless energy harvesting (WEH), optimal relay-destination link with WEH and optimal source-relay-destination link with WEH schemes, are proposed and studied. Closed-form analytical expressions for the outage probability of these three best relay selection schemes are derived, respectively. Finally, our analytical results are verified by Monte-Carlo simulations

A unified performance analysis of cooperative NOMA with practical constraints: hardware impairment, imperfect SIC and CSI

Non-orthogonal multiple access (NOMA) has been a strong candidate to support massive connectivity in future wireless networks. In this regard, its implementation into cooperative relaying, named cooperative-NOMA (CNOMA), has received tremendous attention from researchers. However, most of the existing CNOMA studies have failed to address practical constraints since they assume ideal conditions. Particularly, the error performance of CNOMA schemes with imperfections has not been investigated yet. In this paper, we provide an analytical framework for error and outage performance of CNOMA schemes under practical assumptions where we take into account imperfect successive interference canceler (ipSIC), imperfect channel state information (ipCSI), and hardware impairments (HWI) at the transceivers. We derive analytical expressions of bit error rate (BER) expressions in CNOMA schemes whether the direct links between source and users exist or not which is, to the best of the authors' knowledge, the first study in the open literature. We also derive the outage probability (OP) expressions for CNOMA schemes with and without direct links under practical assumptions. For comparisons, we provide BER and OP expressions for downlink NOMA with practical constraints which also have not been given in the literature, yet. The theoretical BER and OP expressions are validated with computer simulations where the perfect match is observed. Finally, we discuss the effects of the system parameters (e.g., power allocation, HWI level, ipCSI factor) on the performance of CNOMA schemes to reveal fruitful insights for society. The results demonstrate that the HWI, ipCSI and ipSIC have a significant effect on the performance of the systems

A Survey on Approximations of One-Dimensional Gaussian Q-Function

Predicting the digital communication system performance plays a very important role in the process of system design. This performance is usually quantified by symbol error probability or bit error probability. Computing these probabilities in presence of Additive White Gaussian Noise requires to work with integrals involving the Gaussian Qfunction, which cannot be expressed in closed-form in terms of elementary functions. As a result, approximating the Gaussian Q-function in closed-form expressions with high accuracy becomes a necessity. In this paper, we give an overview about the Gaussian Q-function approximations and via some illustrating examples, we discuss their accuracy, tractability as well as their computational complexit