Primary User Protection Research Articles

Utility‐based opportunistic spectrum access for cognitive radio sensor networks: joint spectrum sensing and random access control

This study formulates a novel optimisation problem for joint spectrum sensing and random access control (JS 2 RAC) in cognitive radio sensor networks (CRSNs). The JS 2 RAC is formulated as a network utility maximisation problem, which aims to maximise the sum of utilities over all links in the network but subject to the primary user protection constraint, the energy constraint, and the physical constraint. Due to the non-separable and non-convex nature of the JS 2 RAC problem, the authors propose a primal-decomposition-based iterative (PDI) algorithm which decomposes the JS 2 RAC problem into a spectrum sensing subproblem and a random access control subproblem, and solve the two subproblems iteratively. Then, the authors prove the convergence of the PDI algorithm and show its distributed implementation in practice. Simulations demonstrate the fast convergence and the near-optimal nature of the PDI algorithm and show its significant improvement in the network utility of CRSNs in comparison with the method of optimising spectrum sensing and random access separately.

Opportunities for a more Efficient Use of the Spectrum based in Cognitive Radio

Different studies about the use of radio spectrum have shown the existence of underutilized bands, like the ones destined to television broadcasting. This provides an interesting opportunity considering the exponential growth in wireless communications and applications, which results in an important demand for higher bandwidth to achieve an adequate performance. To operate in bands that are already licensed, it is necessary to ensure that this operation does not cause any interference to the primary user, and always gives priority to it. In this context the IEEE has been defining a standard with functionalities of Cognitive Radio that allows operation in licensed bands opportunistically, and without causing interference. From there comes the IEEE 802.22 standard, which has a set of features and procedures to measure, monitor and manage the radio spectrum, essential to ensure the protection of primary user's transmissions. Some pilot projects have demonstrated the potential of this standard to provide broadband services comparable to classical ADSL services, especially in remote or rural areas inaccessible to deploy fixed networks. One of the great challenges to install such systems commercially, is to achieve the permissions for the operation and to have a defined regulation for these systems, decisions that are in the hands of the telecommunications services regulators in each country. This paper presents an overview of these issues with the intention of promoting a more efficient use of the spectrum.

Mobility-Enhanced Reliable Geographical Forwarding in Cognitive Radio Sensor Networks.

The emergence of the Internet of Things and the proliferation of mobile wireless devices has brought the area of mobile cognitive radio sensor networks (MCRSN) to the research spot light. Notwithstanding the potentials of CRSNs in terms of opportunistic channel usage for bursty traffic, the effect of the mobility of resource-constrained nodes to route stability, mobility-induced spatio-temporal spectral opportunities and primary user (PU) protection still remain open issues that need to be jointly addressed. To this effect, this paper proposes a mobile reliable geographical forwarding routing (MROR) protocol. MROR provides a robust mobile framework for geographical forwarding that is based on a mobility-induced channel availability model. It presents a comprehensive routing strategy that considers PU activity (to take care of routes that have to be built through PU coverage), PU signal protection (by the introduction of a mobility-induced guard (mguard) distance) and the random mobility-induced spatio-temporal spectrum opportunities (for enhancement of throughput). It also addresses the issue of frequent route maintenance that arises when speeds of the mobile nodes are considered as a routing metric. As a result, simulation has shown the ability of MROR to reduce the route failure rate by about 65% as against other schemes. In addition, further results show that MROR can improve both the throughput and goodput at the sink in an energy-efficient manner that is required in CRSNs as against compared works.

A Novel Cooperative Spectrum Sensing scheme with primary user protection

A Novel Cooperative Spectrum Sensing scheme with primary user protection

Wideband Spectrum Sensing by Model Order Selection

Spectrum sensing is an essential functionality in cognitive radio (CR) systems allowing us to discover spectrum opportunities and enabling primary user (PU) protection. Wideband spectrum sensing (WS) improves the awareness of the surrounding radio environment by jointly monitoring multiple frequency bands. In this paper we propose a WS approach based on the observation of a frequency domain representation of the received signal and the adoption of model order selection (MOS) to identify the occupied frequency components. We provide a general formulation of the problem valid for any kind of spectral representation and then focus on the case in which discrete Fourier transform (DFT) is used. This choice is motivated by the fact that DFT blocks are available in many wireless systems, such as OFDM receivers and recently proposed software radio architectures. We provide analytical expressions for the maximum probability of correct selection of the occupied sub-bands valid for MOS approaches encompassed within the generalized information criterion (GIC). We then propose a method for designing the selection algorithm to balance overestimation and underestimation. Numerical results show that the MOS scheme derived for DFT can be successfully applied also when more accurate frequency representations, such as multitaper (MT) spectrum estimates, are adopted.

Throughput maximization by alternative use of single and double thresholds based energy detection method

Cognitive radio (CR) offers solution to the problem of spectrum underutilization by opportunistic spectrum access. Spectrum sensing is one of the important functions of CR as it affects both Primary Users (PUs) protection and Secondary Users (SUs) achievable throughput. In this paper, we are introducing a spectrum sensing scheme which selects either single threshold or double threshold energy detection method based on the estimated Signal to Noise Ratio (SNR) value of the channel. This scheme achieves a better tradeoff between sensing performance and achievable throughput as compared to conventional methods that works purely on single threshold or double threshold energy detection method.

Performance evaluation of improved double-threshold energy detector over Rayleigh-faded sensing and imperfect reporting channels

Cognitive radio (CR) has been viewed as a promising solution to spectrum scarcity. In order to design a reliable CR system, many improvements have been proposed to enhance spectrum sensing performance of secondary users (SUs) in a CR network (CRN). Sensing reliability and transmission throughput of SUs are two important performance criteria, which should be optimized to enhance signal protection of primary user (PU) as well as spectrum utilization rate. In this paper, we consider Rayleigh-faded sensing channels and SUs use improved energy detector (IED) to make their local decisions. The final decision is made in a fusion center (FC) through the cooperative spectrum sensing (CSS) scheme with erroneous reporting channels. We show that the improved double-threshold energy detector (IDED) outperforms the conventional energy detector (CED) in terms of the total error rate. Furthermore, we evaluate the transmission throughput of the CRN through various ED schemes with detection constraints over both perfect and imperfect reporting channels. We show that the IDED has the highest achievable throughput among different ED schemes over imperfect reporting channels.

Towards trustworthy collaboration in spectrum sensing for ad hoc cognitive radio networks

Cognitive radio networks (CRN) make use of dynamic spectrum access to communicate opportunistically in frequency bands otherwise licensed to incumbent primary users such as TV broadcast. To prevent interference to primary users it is vital for secondary users in CRNs to conduct accurate spectrum sensing, which is especially challenging when the transmission range of primary users is shorter compared to the size of the CRN. This task becomes even more challenging in the presence of malicious secondary users that launch spectrum sensing data falsification (SSDF) attacks by providing false spectrum reports. Existing solutions to detect such malicious behaviors cannot be utilized in scenarios where the transmission range of primary users is limited within a small sub-region of the CRN. In this paper, we present a framework for trustworthy collaboration in spectrum sensing for ad hoc CRNs. This framework incorporates a semi-supervised spatio-spectral anomaly/outlier detection system and a reputation system, both designed to detect byzantine attacks in the form of SSDF from malicious nodes within the CRN. The framework guarantees protection of incumbent primary users' communication rights while at the same time making optimal use of the spectrum when it is not used by primary users. Simulation carried out under typical network conditions and attack scenarios shows that our proposed framework can achieve spectrum decision accuracy up to 99.3 % and detect malicious nodes up to 98 % of the time.

Maximizing Throughput with Wireless Spectrum Sensing Network Assisted Cognitive Radios

In a cognitive radio network (CRN), secondary users (SUs) utilize primary users (PUs) licensed spectrum in an opportunistic manner. Spectrum sensing is of the utmost importance in CRN to find and use the available spectrum without harmful interference to the PUs. Conventionally, to implement spectrum utilization, SUs are required to sense the primary spectrum first and then transmit data on the available spectrum. In this paper, we propose a dedicated wireless spectrum sensing network (WSSN), eliminating sensing overhead from SUs with the aim of improving achievable throughput. With WSSN assistance, we eliminate sensing time from the SUs frame, hence increasing the transmission time, which maximizes the achievable throughput. Additionally, the sensing duration is increased by deploying a dedicated WSSN, decreasing the probability of false alarm and achieving a targeted high probability of detection. A low probability of false alarm increases the spectrum utilization, improving the achievable throughput, while a high detection probability ensures PUs protection. Moreover, the proposed technique also addresses hidden and exposed terminal problems along with smooth spectrum mobility. Finally, we provide simulation results to demonstrate the proposed techniques, effectiveness. In the results, we have compared the achievable throughput of the proposed scheme with that of conventional CRN.

Statistical Delay QoS Protection for Primary Users in Cooperative Cognitive Radio Networks

In cooperative cognitive radio networks, where secondary users (SU) can relay the signal of primary user (PU) in exchange for PU's licensed spectrum, most existing works employ deterministic quality-of-service (QoS) guarantee in terms of minimum required transmission rate for PU's protection. In this letter, we adopt the statistical QoS requirement characterized by queue-length bound violation probability for PU's delay QoS provisioning. By applying the effective capacity theory, we further convert PU's queue-length bound violation probability requirement to the equivalent effective capacity constraint and formulate the corresponding SU's throughput maximization problem. Then, we obtain the optimal joint time-slot allocation scheme, where the time-slot division adapts to both channel conditions and PU's delay QoS requirements, such that not only PU's statistical delay QoS requirement can be well guaranteed, but also SU's throughput can be optimized. Moreover, we also develop a fixed time-slot allocation scheme that only varies with PU's delay QoS requirements. Simulation results show that both the optimal and fixed allocation schemes can flexibly perform time-slot divisions according to the delay QoS requirements of PU's traffic, but the developed optimal scheme outperforms the fixed time-slot allocation scheme.

Bounds on Secondary User Connectivity in Cognitive Radio Networks

We consider a large-scale cognitive radio network (CRN) in a Rayleigh fading environment. Errors of spectrum sensing by secondary users (SUs) are considered in the letter. Cumulative inter-network interference (between primary and secondary networks) is calculated and outage probability of primary users (PUs) is derived in the closed-form. The upper and lower bounds on the percolation area are obtained and analyzed, within which the secondary network percolates while the PU's outage probability is kept below a tolerable threshold. The bounds depend on SU's correct detection and false alarm probabilities, and PU's transmit power and protection radius. Further we find that the percolation area that percolates SUs and meanwhile provides protection for PUs does not always exist.

Measurement-Based Spectrum Database for Flexible Spectrum Management

In this paper, we propose the novel concept of a spectrum database for improving the efficiency of spectrum utilization. In the current design of TV white space spectrum databases, a propagation model is utilized to determine the spectrum availability. However, this propagation model has poor accuracy for radio environment estimation because it requires a large interference margin for the PU coverage area to ensure protection of primary users (PUs); thus, it decreases the spectrum sharing efficiency. The proposed spectrum database consists of radio environment measurement results from sensors on mobile terminals such as vehicles and smart phones. In the proposed database, actual measurements of radio signals are used to estimate radio information regarding PUs. Because the sensors on mobile terminals can gather a large amount of data, accurate propagation information can be obtained, including information regarding propagation loss and shadowing. In this paper, we first introduce the architecture of the proposed spectrum database. Then, we present experimental results for the database construction using actual TV broadcast signals. Additionally, from the evaluation results, we discuss the extent to which the proposed database can mitigate the excess interference margin.

Optimal energy-efficient sensing in cooperative cognitive radio networks

In a cognitive radio network (CRN), when the secondary users (SUs) are battery-powered devices, the concept of energy-efficient design is very important. The sensing time and the number of cooperative SUs in the cooperative spectrum sensing could greatly affect energy consumption and throughput of the system. In this paper, we propose an energy utility function by formulating the achievable data rate of a cooperative CRN in terms of the energy consumption by the CRN. The maximization of the energy utility function is obtained by jointly designing the sensing time, sensing threshold, and number of cooperative SUs with the constraint of sufficient protection for primary user (PU). Numerical results show that the CRN can achieve almost the maximum achievable data rate with significant energy saving through the joint optimization.

Efficient transceiver beamforming in multiple‐input–multiple‐output cognitive radio network

Owing to the ability of improving spectrum utilisation and quality-of-service (QoS) in wireless communications, multiple-input–multiple-output (MIMO) cognitive radio (CR) network has been identified as an excellent choice for the next generation communication. To protect primary users (PUs) from excessive interference while ensuring a meaningful QoS of secondary users (SUs), one key challenge of such system is the joint design of transceiver beamforming for SUs. In this study, the authors investigate the beamforming in MIMO CR network, and two optimisation problems in terms of the minimisation of the total transmission power and the maximisation of the smallest received signal-to-interference-plus-noise ratio (SINR) are considered. The problems can be formulated as indefinite quadratic optimisation programs which are known to be non-convex NP-hard. Hence, a distributed algorithm based on semi-definite programming and minimum-mean-squared-error is proposed to achieve the optimal beamforming weight vector. The findings of this study demonstrated that the proposed algorithm outperforms the existing ones with respect to the total transmitted power and SUs SINR.

A Joint Routing and Time-Slot Assignment Algorithm for Multi-Hop Cognitive Radio Networks with Primary-User Protection

Cognitive radio has recently emerged as a promising technology to improve the utilization efficiency of the radio spectrum. In cognitive radio networks, secondary users (SUs) must avoid causing any harmful interference to primary users (PUs) and transparently utilize the licensed spectrum bands. In this paper, we study the PUprotection issue in multi-hop cognitive radio networks. In such networks, secondary users carefully select paths and time slots to reduce the interference to PUs. We formulate the routing and time-slot assignment problem into a mixed integer linear programming (MILP). To solve the MILP which is NP-Hard in general, we propose an algorithm named RSAA (Routing and Slot Assignment Algorithm). By relaxing the integral constraints of the MILP, RSAA first solves the max flow from the source to the destination. Based on the max flow, RSAA constructs a new network topology. On the new topology, RSAA uses branch and bound method to get the near optimal assignment of time slots and paths. The theoretical analyses show that the complexity of our proposed algorithm is O(N^4). Also, simulation results demonstrate that our proposed algorithm can obtain near-optimal throughputs for SUs.

Optimal Sensing Interval Considering Per-primary Transmission Protection in Cognitive Radio Networks

Sufficient protection of primary user is a challenging issue in cognitive radio networks. The probability of detection and the interference ratio (probability of collision) have been considered as the main constraints for primary protection in the literature. Based on the sensing parameters designed to comply with these constraints, secondary users are often considered to be able to use licensed bands without giving harmful interference to primary users. However, satisfying these constraints might not guarantee that each primary transmission (i.e., each busy period) is sufficiently protected. Obviously, if a large fraction of a busy period is interfered, the busy period may be subject to the useless transmission potentially degrading the quality of service of primary users. We suggest that the busy period impaired more than a certain ratio of so-called required per-transmission interference ratio (PTIR) is subject to the primary transmission failure (PTF), which has not been considered in the literature. As the first attempt, with the assumption of perfect sensing, the effect of sensing interval on the PTIR and PTF is investigated. The probability of PTF is derived as a function of sensing interval given the required PTIR. Then, given the required PTIR and probability of PTF, the optimal sensing interval that maximizes the throughput for secondary users is derived. Performance evaluation shows that primary users can be more protected with the optimal sensing interval obtained by using the proposed constraint.

Power Control Algorithm for Cognitive Radio Based on Chaos Particle Swarm Optimization

Power control is one of key technologies for Cognitive Radio Networks (CRNs) since it can protect Primary Users (PUs) in the networks and guarantee Quality of Service (QoS) requirements for Second Users (SUs). In this paper, for an underlay CRNs in the scenario of the presence of multiple SUs and PUs, a novel power control approach with the objective to minimize total power consumption of SUs is proposed based on Chaos Particle Swarm Optimization (CPSO). The approach takes three constraints (minimum accepted SINR, maximum transmit power of SUs as well as maximum tolerated interference power for PUs) into account. The utility functions and constraints of original optimization problem are transformed into a related penalty function by CPSO approach. Simulation results indicate that the proposed CPSO algorithm can reduce total transmit power consumption, obtain faster convergence rate and improve searching quality compared with the standard Particle Swarm Optimization (PSO) and the Adaptation Particle Swarm Optimization (APSO) algorithms respectively.

Cognitive Radio-Based Vehicular Ad Hoc and Sensor Networks

Current advancements in vehicular networking lead to amplifying the issue of spectrum scarcity. Cognitive radio (CR) has emerged as the key technology that enables flexible, efficient, and reliable spectrum exploiting by unlicensed networks to use licensed spectrum bands in an opportunistic manner to alleviate the spectrum scarcity issue. We have already proposed vehicular ad hoc and sensor networks (VASNET) as a new networking paradigm for vehicular communication by utilizing wireless sensor nodes in two mobile and stationary modes. The nodes are employed to sense vehicles' activity, for example, car crashes. Like other unlicensed networks, VASNET is supposed to operate over unlicensed spectrum bands. However, due to emergency nature of accident alarms in VASNET that must be received in minimum period of time and avoiding packet loss, in this paper we investigate CR-based VASNET, named as CR-VASNET. Various challenges and issues are discussed in details. In order to save stationary nodes' power and enlarge the network lifetime, an optimization technique for relay node selection is proposed. Furthermore, for primary users (PU) protection, an energy detection-based scheme is suggested to calculate the probability of PU arrival. Our theoretical discussions and simulation results proved the efficient functionality of the proposed CR-VASNET as a promising vehicular networking paradigm.

Spectrum Hole Utilization in Cognitive Two-way Relaying Networks

This paper investigates the spectrum hole utilization of cooperative schemes for the two-way relaying model in order to improve the utilization efficiency of limited spectrum holes in cognitive radio networks with imperfect spectrum sensing. We propose two specific bidirectional secondary data transmission (BSDT) schemes with two-step and three-step two-way relaying models, i.e., two-BSDT and three-BSDT schemes, where the spectrum sensing and the secondary data transmission are jointly designed. In the proposed cooperative schemes, the best two-way relay channel between two secondary users is selected from a group of secondary users serving as cognitive relays and assists the bi-directional communication between the two secondary users without a direct link. The closed-form asymptotic expressions for outage probabilities of the two schemes are derived with a primary user protection constraint over Rayleigh fading channels. Based on the derived outage probabilities, the spectrum hole utilization is calculated to evaluate the percentage of spectrum holes used by the two secondary users for their successful information exchange without channel outage. Numerical results show that the spectrum hole utilization depends on the spectrum sensing overhead and the channel gain from a primary user to secondary users. Additionally, we compare the spectrum hole utilization of the two schemes as the varying of secondary signal to noise ratio, the number of cognitive relays, and symmetric and asymmetric channels.

Optimized energy limited cooperative spectrum sensing in cognitive radio networks

In cognitive radio networks, it is well known that the cooperative spectrum sensing can overcome damaging effects of fading and shadowing. However, it also increases the amount of energy consumption which is a critical factor in low powered wireless communications. In this paper based on bi-threshold energy detection, we maximize the network throughput such that the energy consumption is below a predefined value and also sufficient protection of primary users against interference is guaranteed. Convex optimization analysis is presented to jointly obtain the optimal values of sensing time and detection thresholds. Simulation results show that the proposed method is very flexible such that a good tradeoff between achievable throughput and energy efficiency can be established, while it often outperforms the conventional sensing method significantly.