Presence Of Multiple Primary Users Research Articles

Performance Analysis of Full-Duplex Multirelaying Energy Harvesting Scheme in Presence of Multiuser Cognitive Radio Network

This paper investigates the outage performance of secondary receiver with an energy harvesting cognitive radio network employing multiple full-duplex (FD) relaying protocol in presence of multi-user spectrum sharing environment. Under this energy harvesting aided FD relaying network scenario, adaptive transmit power policies for the secondary user (SU) source, secondary FD relays and exact outage probability of the secondary user are derived analytically in presence of multiple primary users and multiple secondary destinations. Impact of self interference at the receive antenna of each FD relay in addition to all the transmitting interference at all receive nodes is being addressed. A comparative study considering all the interference together in an FD relaying protocol with that of conventional half-duplex (HD) relaying protocol is carried out. With the same diversity order, a trade-off between FD multi-relay and multi-destination is shown. Closed form expressions of secondary outage probability for FD energy harvested relay equipped CR network has also been evaluated. Maintaining quality of service (QoS) of multiple primary users (PUs), power allocation strategies at each secondary transmitting node is taken care of. Finally, all the analytical closed form expressions have been validated through Monte-Carlo simulations.

NOMA-Based Integrated Satellite-Terrestrial Relay Networks Under Spectrum Sharing Environment

With the increasing requirements for efficient utilization of satellite resources, both non-orthogonal multiple access (NOMA) scheme and cognitive radio (CR) have been recognized as one of the promising solutions, particularly, for the enhancement of spectrum efficiency. This letter investigates the performance of NOMA-based integrated satellite-terrestrial relay network (ISTRN) in the presence of multiple primary users (PUs) under spectrum sharing environment. Specifically, we derive the closed-form expressions of outage probability (OP) and ergodic capacity (EC) of the considered system under the interference constraint imposed by multiple adjacent PUs. To get further insights, the asymptotic analysis for OP at high signal-to-noise ratios (SNRs) is also obtained. Numerical results are provided to verify our analysis and reveal the impacts of key parameters on system performance.

Outage and Throughput Analysis of Spectrum Sharing Cognitive Radio Network Incorporating Energy Harvesting Hybrid Relay

In this paper, cooperative spectrum sharing in cognitive radio (CR) network is incorporated with multi-antenna based RF energy harvesting relays (EH). The performance has been analyzed in the presence of multiple primary users. The relays can harvest energy from source signal and interference from primary transmitter. The relays follow adaptive hybrid protocol (AHR) for forwarding the received signal from source to destination. Outage probability and achievable throughput have been analyzed using a time-splitting relaying (TSR) scheme at the destination where best relay selection (BRS) strategy is used. The outage performances of energy harvesting and non-energy harvesting model have been compared. Throughput and outage performance comparison for AF, DF and AHR have been analyzed. The effect of the number of primary users is also investigated. A trade-off is shown between the number of relays and the number of antennas to achieve the desired throughput. The results depict that the use of energy harvesting strategy in cognitive radio network can result in an energy-efficient solution for future wireless communication.

Interference Alignment in Multi-Hop Cognitive Radio Networks under Interference Leakage

In this work, we examine the interference alignment (IA) performance of a multi-input multi-output (MIMO) multi-hop cognitive radio (CR) network in the presence of multiple primary users. In the proposed architecture, it is assumed that linear IA is adopted at the secondary network to alleviate the interference between primary and secondary networks. By doing so, the secondary source can communicate with the secondary destination via multiple relays without causing any interference to the primary network. Even though linear IA can suppress the interference in CR networks considerably, interference leakages may occur due to a fast fading channel. To this end, we focus on the performance of the secondary network for two different cases: (i) the interference is perfectly aligned; (ii) the impact of interference leakages. For both cases, closed-form expressions of outage probability and ergodic capacity are derived. The results, which are validated by Monte Carlo simulations, show that interference leakages can deteriorate both system performance and the diversity gains considerably.

Cooperative spectrum sharing with multi-antenna based adaptive hybrid relay in presence of multiple primary users

Performance analysis of cooperative spectrum sharing network using multi-antenna based Adaptive Hybrid Relay (AHR) scheme in presence of multiple primary users under non-identical Rayleigh fading channel has been studied in this paper. An Adaptive Hybrid Relay equipped with multiple antennas at the input employs selection combining (SC) on the signals received from secondary user source (S) via multiple receiving antennas at the input and forwards the received signal to secondary user destination (D). The outage probability has been evaluated at the secondary destination where best relay selection (BRS) scheme is used. The comparison between outage performances of cooperative spectrum sharing for Amplify-and-Forward (AF), Decode-and-Forward (DF) and Adaptive Hybrid Relay (AHR) scheme is also presented. The effects of number of relay antennas (L), number of relays (K) and number of primary users (M) on the system performance have also been studied. It is seen that the outage performance improves considerably with increase in number of primary users (PUs). It is also observed that increase in number of primary users compensate the negative impact of high channel rate (R). A trade-off between number of relay and number of antenna at each relay is also shown.

An Efficient Zero-Forcing Precoding Design for Cognitive MIMO Broadcast Channels

We consider linear precoding design for an underlay cognitive radio multiple-input multiple-output broadcast channel in the presence of multiple primary users (PUs). Under the assumption of imperfect channel state information (CSI) of the PUs, the objective of this letter is to maximize the sum rate of the secondary system, subject to the power budget at the secondary base station and the interference power constraints at the PUs. The design problem is non-convex, and thus is difficult to solve in general. Herein, we first convert a non-convex constraint related to the imperfect CSI of the PUs into a convex constraint, and then invoke a rank relaxation method to transform the considered problem into a convex–concave problem based on a downlink–uplink duality result. Simulation results are provided to demonstrate the effectiveness and robustness of the proposed design against CSI imperfection.

Design and implementation of spectrum sensing for cognitive radios with a frequency-hopping primary system

In this work, spectrum sensing for cognitive radios is considered in the presence of multiple Primary Users (PU) using frequency-hopping communication over a set of frequency bands. The detection performance of the Fast Fourier Transform (FFT) Average Ratio (FAR) algorithm is obtained in closed-form, for a given FFT size and number of PUs. The effective throughput of the Secondary Users (SU) is formulated as an optimization problem with a constraint on the maximum allowable interference on the primary network. Given the hopping period of the PUs, the sensing duration that maximizes the SU throughput is derived. The results are validated using Monte Carlo simulations. Further, an implementation of the FAR algorithm on the Lyrtech (now, Nutaq) small form factor software defined radio development platform is presented, and the performance recorded through the hardware is observed to corroborate well with that obtained through simulations, allowing for implementation losses.

Underlay cognitive relay networks with imperfect channel state information and multiple primary receivers

In this study, the authors investigate the effect of imperfect channel state information (CSI) on underlay cognitive radio networks in the presence of multiple primary users (PUs). Particularly, with multiple proactive partial decode-and-forward (DF) relays available, both the relay selection channels and interference channels are assumed to be imperfect. In this context, firstly, based on the instantaneous CSI (ICSI) of interference channels, exact closed form expressions for the outage probability (OP) and the interference probability (IP) are derived, where IP is used as a performance metric to quantify the impact of harmful interference caused by secondary user (SU) on PUs. It is shown that, when the ICSI of interference channels are imperfect, the secondary networks always interfere with PUs' communications. Then, to reduce the harmful interference caused by secondary nodes, we propose an adaptive power control scheme relying on the partial CSI (PCSI) of interference channels. Finally, simulation results verify the accuracy and effectiveness of the author's analytical study, and indicate the proposed scheme strikes a good tradeoff between the interference introduced by secondary nodes on PUs and SU's performance.

Multiantenna Spectrum Sensing in the Presence of Multiple Primary Users over Fading and Nonfading Channels

The basis of this paper is Wei and Tirkkonen, 2012, in which expressions for the key performance metrics of the sphericity test applied to the multiantenna cooperative spectrum sensing of multiple primary transmitters in cognitive radio networks over nonfading channels are provided. The false alarm and the detection probabilities were derived in Wei and Tirkkonen, 2012, based on approximations obtained by matching the moments of the test statistics to the Beta distribution. In this paper we show that the model adopted in Wei and Tirkkonen, 2012, does not apply directly to fading channels, yet being considerably inaccurate for some system parameters and channel conditions. Nevertheless, we show that the original expressions from Wei and Tirkkonen, 2012, can be simply and accurately applied to a modified model that considers fixed or time-varying channels with any fading statistic. We also analyze the performance of the sphericity test and other competing detectors with a varying number of primary transmitters, considering different situations in terms of the channel gains and channel dynamics. Based on our results, we correct several interpretations from Wei and Tirkkonen, 2012, in what concerns the performance of the detectors, both over a fixed-gain additive white Gaussian noise channel and over a time-varying Rayleigh fading channel.

Adaptive Network Coding for Spectrum Sharing Systems

In this paper, we propose an adaptive network coding scheme for cognitive relay networks comprising multiple secondary sources communicating with a common destination in the presence of multiple primary users. Conventional network coding schemes developed for cognitive radio networks normally use global encoding kernels to achieve the minimum end-to-end outage probability. Finding the global kernel is computationally inefficient especially when the number of nodes in a network changes. To this end, we propose a network coding scheme that evenly groups the codewords into multiple subsets, linearly combines the network encoded codewords over the reduced subset, and dynamically adjusts the encoding set size to minimize the end-to-end outage probability. An advantage of the proposed network coding scheme is that it achieves lower end-to-end outage probability as compared to the conventional network coding scheme over the whole signal-to-noise ratio (SNR) range with a small additional overhead. We derive closed-form expressions for the link outage probability while taking the interference constraints into consideration. We also derive the exact end-to-end outage probability of the proposed scheme and compare its performance to that of conventional fixed network coding. We show that the proposed scheme provides a trade-off between the probability of relay cooperation and network coding gain. We demonstrate through numerical examples that the proposed adaptive network coding scheme achieves gains of more than 4 dB at a target outage probability of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> as compared to conventional fixed network coding schemes.

Spectrum Sensing in the Presence of Multiple Primary Users

We consider multi-antenna cooperative spectrum sensing in cognitive radio networks, when there may be multiple primary users. A detector based on the spherical test is analyzed in such a scenario. Based on the moments of the distributions involved, simple and accurate analytical formulae for the key performance metrics of the detector are derived. The false alarm and the detection probabilities, as well as the detection threshold and Receiver Operation Characteristics are available in closed form. Simulations are provided to verify the accuracy of the derived results, and to compare with other detectors in realistic sensing scenarios.

Outage probability analysis of partial AF relay selection in spectrum-sharing scenario with multiple primary users

In the presence of multiple primary users (PUs), the exact outage probability of partial amplify-and-forward (AF) relay selection in the spectrum-sharing relay networks is investigated. To gain more insight, a simple and accurate outage probability approximation is also derived in the high signal-to-noise ratio (SNR) region. It is shown that, at high SNR, the outage probability is affected only by the channel gain ratio between relay-destination links to relay-PU links, regardless of the number of relays. Moreover, when more PUs are present, it causes outage performance degradation on the secondary system. Finally, simulation results are presented to verify the analysis.

Dynamic Spectrum Management for Multiple-Antenna Cognitive Radio Systems: Designs with Imperfect CSI

In this paper, we study the problem of resource allocation and optimization for multiple-input multiple-output (MIMO) cognitive radio (CR) systems under the assumption of imperfect channel state information (CSI) of the channels between the secondary users (SUs) and the primary users (PUs) at the SUs. We formulate robust design optimization problems for CR systems with one or more SUs communicating over a single or multiple frequency carriers in the presence of multiple PUs. We propose a linear matrix inequality (LMI) transformation that facilitates proper treatment of channel uncertainty at the SU transmitter and we provide solutions to the design problems based on convex optimization and Lagrange dual decomposition techniques. Finally, we demonstrate the importance of the proposed formulations and the implications of ignoring channel uncertainties when designing for CR systems.