Random Cognitive Radio Networks Research Articles

An Energy-Efficient Model of Random Cognitive Radio Network: Rayleigh-Lognormal Environment

Motivated by the current demand for improvements in transmission rate and energy efficiency of random wireless cellular networks, we investigate the theoretical model of random cognitive radio network in Rayleigh-lognormal fading environment. In such a network, we derive an analytical expression for the connection probability, transmission rate, and energy efficiency of a secondary network in a single-tier downlink scenario, considering the probabilities of unoccupied channel selection and of successful transmission, where source-destination pairs are randomly located according to Poisson point processes. Moreover, we approach the problem of optimization of transmission rate and energy efficiency using a required connection probability constraint to improve the system performance. Our numerical results indicate that there exists an optimal combination of transmission power and secondary transmitter density where transmission rate and energy efficiency are maximized.

Spectral Efficiency of Energy Harvesting Random Cognitive Radio Networks in Dual-slope Model

This research article evaluates the performance of an energy harvesting random cognitive radio network employing a dual-slope path-loss model in terms of spectral efficiency. It derives the mathematical expression of spectral efficiency by means of stochastic geometry for secondary receivers presen

Two-slope path-loss design of energy harvesting in random cognitive radio networks

There has recently been substantial interest in applying the principles of wireless radio frequency energy harvesting in battery-operated devices to cognitive radio networks. Although implementation of energy harvesting technique increases the complexity of network planning, it reduces battery power usage and enables eco-friendly cognitive radio network. In this paper, we report a comprehensive study of energy harvesting cognitive radio network where locations of users of primary and secondary networks follow a Poisson point process. In the design of random cognitive radio network, we focus on the two-slope path-loss function so as to have a realistic scenario of propagation environments. First, a new expression of outage probability is theoretically derived for secondary receiver in active mode. Second, we obtain an explicit expression of harvested energy for secondary receiver in active and inactive modes. Finally, we investigate the harvested energy maximization problem under a particular outage probability constraint, and also obtain an optimal solution of transmission power and density of secondary transmitters. Numerical results for outage probability, harvested energy, and maximization of harvested energy are presented for evaluation of the performance and characteristics of this network.

Towards Secure and Energy-Efficient CRNs Via Embracing Interference: A Stochastic Geometry Approach

In a cognitive radio network (CRN), the interference caused by secondary users (SUs) is conventionally regarded as an obstacle to the throughput of the primary network. However, when considering security, the interference brings potential benefits to the secrecy throughput of the primary network. For a stand-alone primary network, the secrecy guard zone, including the cooperative mode and non-cooperative mode, has been shown as an efficient method to enhance the network security. The cooperative mode is traditionally thought to outperform the non-cooperative mode due to the jamming effect of the artificial noise generated by primary transmitters on eavesdroppers. However, allowing SUs to access the licensed spectrum, the resulting interference can be used as a source of the artificial noise instead of that generated on purpose by primary transmitters, which in return benefits the energy efficiency of the primary network. Inspired by the two benefits brought by SUs, this paper considers a random underlay CRN with eavesdroppers overhearing primary transmissions. To enhance both the security and energy efficiency of the primary network, we apply a secrecy guard zone around each primary transmitter, and adopt the non-cooperative mode. We exploit the stochastic geometry to model such a random CRN and analyze the connection/secrecy probability of primary links. We propose a criterion for guaranteeing the performance of secure primary network. The main idea is that compared with the primary network with the cooperative mode, the access of SUs should not reduce the secrecy throughput and energy efficiency of the primary network with the non-cooperative mode. Based on the obtained analytical results, we design the optimal secondary link scheduling schemes under the criterion. Both analytical and numerical results show that the interference from SUs can be exploited toward a secure and energy-efficient primary network and provide SUs with extra transmission opportunities.

Outage and energy-efficiency analysis of cognitive radio networks: A stochastic approach to transmit antenna selection

Cognitive radio networks have recently attracted significant research attention owing to their promise for application in future cellular communication. In this light, given the intense power consumption of wireless networks, considerable research is now being directed at designing random cognitive radio networks with enhanced energy efficiency. In this study, we investigate the outage probability and energy efficiency in a cognitive radio network, modeling the locations of the primary users and cognitive users as a Poisson point process. We derive closed-form expressions for the outage probability and energy efficiency with consideration of the probabilities of unoccupied (not utilized by the primary users) channel selection and successful transmission for imperfect detection in an interference-limited environment of cognitive radio network. Furthermore, we propose a transmit antenna selection method for the cognitive transmitter in such networks and accordingly develop closed-form expressions for the outage probability and energy efficiency. The study reported here highlights the importance of combining the capabilities of unoccupied channel selection and successful transmission in cognitive radio networks to achieve optimal performance regarding outage probability and energy efficiency. In terms of energy efficiency, there is an optimal threshold that maximizes the energy efficiency. For implementation in transmit antenna selection, the outage probability can be significantly decreased by increasing the number of transmit antennas, even though the energy efficiency is maximized at the target outage probability.

Opportunistic relay selection improves reliability–reliability tradeoff and security–reliability tradeoff in random cognitive radio networks

This study investigates the physical-layer security in random cognitive radio network (CRN) consisting of randomly distributed primary nodes, secondary nodes, relay nodes and eavesdroppers, where the secondary nodes share the spectrum of the primary nodes and the eavesdroppers attempt to intercept the secondary transmissions. The authors develop a framework to analysis the reliability-reliability tradeoff (RRT) and security-reliability tradeoff (SRT) in the random CRNs, where the security and reliability are quantified in terms of secrecy outage probability and connection outage probability. The RRT evaluates performance tradeoff between the primary and the secondary networks and the SRT evaluates the performance tradeoff inside the secondary network. Furthermore, they propose an opportunistic relay selection (ORS) scheme to enhance the secondary confidential transmission. It is demonstrated that the ORS scheme significantly improves the RRT and SRT as the density of relays increases, and outperforms the conventional direct transmission when the density of relays is larger than a certain value. This actually promotes the understandings of the performance tradeoffs and provides direct insights on system design for the practical CRNs.

On the Performance of Cooperative Spectrum Sensing in Random Cognitive Radio Networks

This paper investigates the performance of cooperative spectrum sensing in cognitive radio networks using the stochastic geometry tools. In order to cope with the diversity of received signal-to-noise ratios at secondary users, a practical and efficient cooperative spectrum sensing model is proposed and investigated based on the generalized likelihood ratio test detector. In order to investigate the cooperative spectrum sensing system, the theoretical expressions of the probabilities of false alarm and detection of the local decision are derived. The optimal number of cooperating secondary users is then investigated to achieve the minimum total error rate of the final decision by assuming that the secondary users follow a homogeneous Poisson point process. Moreover, the theoretical expressions for the achievable ergodic capacity and throughput of the secondary network are derived. Furthermore, the technique of determining an appropriate number of cooperating secondary users is proposed in order to maximize the achievable ergodic capacity and throughput of the secondary network based on a target total error rate requirement. The analytical and simulation results validate the chosen optimal number of collaborating secondary users in terms of spectrum sensing, achievable ergodic capacity, and throughput of the secondary network.

Throughput Maximization of CSMA in Cognitive Radio Networks with Cooperative Spectrum Sensing

This study aims the throughput maximization of carrier sense multiple access (CSMA) in random access cognitive radio networks (CRNs) by using cooperative spectrum sensing. In the cooperative spectrum sensing, multiple cognitive radio (CR) users individually monitor the spectrum for the primary users (PUs)' activities and send their local decisions to the CR access point. Upon receiving the individual decisions, the CR access point gives the final decision about the PU's presence at the spectrum and sends it to all CR users in the network. At decision stage, CR access point utilizes the k-out-of-N decision fusion rule with optimal k value in order to obtain maximum CRN throughput. In this paper, we model a CRN utilizing CSMA medium access control scheme and focus on analyzing the throughput performance of it. Throughput performances of our CRN model which separately utilizes AND, OR, MAJORITY fusion rules and k-out-of-N decision fusion rule with the optimum k value are obtained and compared under the same network level probability of detection constraint. The throughput results obtained show that our CRN model utilizing k-out-of-N decision fusion rule with the optimum k value achieves higher throughput performance than AND, OR and MAJORITY fusion rules when they all have the same CRN load.

On the Secure Spectral-Energy Efficiency Tradeoff in Random Cognitive Radio Networks

Spectrum efficiency (SE) and energy efficiency (EE) in secure communications have attracted much attention recently due to the fact that future wireless networks need to address the issues of high throughput, low power consumption, and high level of security. However, maximizing EE and SE are conflicting objectives, which can hardly be achieved simultaneously. In this paper, we develop a framework to study the SE and EE for secure transmission in underlay random cognitive radio (CR) networks where the primary, secondary, and eavesdropper nodes are randomly distributed according to Poisson point processes. We first analyze the connection outage probability and the secrecy outage probability of the typical links in the random CR network. Then, we evaluate the secure SE and EE in the secondary network based on the outage probability analysis. It is demonstrated that the scheduling scheme of the secondary network (i.e., the transmission power and the intensity of secondary transmitters arouses a tradeoff between the secure SE and EE. Furthermore, applying a unified secure SE-EE tradeoff metric, which condenses the secure SE and EE into a single utility function with a tradeoff factor, we formulate the joint secure SE and EE optimization problem with respect to the scheduling scheme of the secondary network. An iterative algorithm is proposed based on the separation optimization of the transmission power and the intensity. The analytical and simulation results show the effects of system parameters on the optimal solutions and secure SE-EE tradeoff. We also verify that the optimal scheduling scheme can improve the secure SE-EE tradeoff. Using these results, one can easily understand and make the secure SE-EE tradeoff in random CR networks.

Secure transmission in the random cognitive radio networks with secrecy guard zone and artificial noise

The authors study the secure transmission design in random cognitive radio networks where the primary users, the secondary users and the eavesdroppers are randomly distributed according to Poisson point processes. Centring on this scenario, the authors propose a simple and decentralised secure transmission scheme by jointly incorporating the secrecy guard zone and artificial noise. In particular, this transmission scheme helps to enhance secrecy performance via differentiating between secondary transmitters in accordance with the eavesdropping environment. They then analyse the connection outage and secrecy outage performance of the secondary network, based on which they obtain the closed-form expression of the secrecy throughput. They further determine the optimal transmission power of the secondary transmitters and the optimal power allocation between the information-bearing signal and artificial noise to maximise the secrecy throughput of the secondary network under primary and secondary outage constraints. The authors’ analysis highlights that introducing secrecy guard zone provides better security performance, and artificial noise performs as additional interference to insert a control between the reliability and security. Numerical results show how the system parameters affect the achievable maximum secrecy throughput, the optimal transmission power and the optimal power allocation between the information-bearing signal and the artificial noise.