Primary User Protection Research Articles

Protecting Primary Users in Cognitive Radio Networks with Effective Capacity Loss Constraint

Cognitive radio (CR) in spectrum sharing mode allows secondary user (SU) to share the same spectrum simultaneously with primary user (PU), as long as the former guarantees no harmful interference is caused to the latter. This letter proposes a new type of constraint to protect the PU systems that are carrying delay-sensitive applications, namely the PU effective capacity loss constraint, which sets an upper bound on the maximum effective capacity loss of the PU due to the SU transmission. In addition, the PU effective capacity loss constraint is approximately transformed to the interference temperature (power) constraint, to make it easier to be implemented. As an example, we obtain a closed form expression of the SU effective capacity under the approximated peak interference power constraint and the results of simulations validate the proposed PU protection criterion.

A Distributed Sensor Selection Mechanism for Cooperative Spectrum Sensing

In a cognitive sensor network (CSN), selfish sensors can choose to conduct cooperative spectrum sensing (CSS) or local spectrum sensing (LSS). CSS usually improves sensing performance at the price of delay and energy consumption. A selfish sensor only decides to conduct CSS if it is more profitable than performing LSS. A key issue is how to achieve a desired decision outcome that maximizes spectrum utilization under the requirement of self-interest maximization and primary user (PU) protection. To address this problem, we formulate the interactive deciding of sensors as a noncooperative game, and Nash equilibrium (NE) corresponds to a stable decision outcome that no sensor has an incentive to resist unilaterally. It is shown that the desired decision outcome can be obtained by solving a constrained nonlinear 0-1 programming problem. We derive the desired decision outcome for homogenous sensors, and then develop a sensor selection mechanism for heterogeneous sensors to achieve the desired decision outcome in a distributed fashion. The proposed mechanism is shown to have a relatively low complexity. Computer simulations are carried out to validate the effectiveness of the proposed approaches.

Dynamic Sensing Strategies for Efficient Spectrum Utilization in Cognitive Radio Networks

For cognitive radio (CR) networks with user hierarchy, the sensing strategy with "listen-before-talk" (LBT) policy plays a key role in spectrum utilization and primary user (PU) protection. However, existing sensing strategies do not handle satisfactorily the randomness of both user locations and channel conditions in the network environment, resulting in inefficient spectrum utilization. To cope with such randomness, this paper develops three dynamic sensing strategies that can adaptively schedule the sensing slots/cycles according to the online link conditions without assuming knowledge of the PU traffic model. The proposed strategies can improve the efficiency of spectrum utilization while being robust with respect to the uncertainty in the PU traffic pattern. To maximize spectrum utilization, the proposed strategies are formulated through closed-form expressions. Efficient methods are introduced to compute the optimal values of the parameters used in the strategies, such as sensing time and sensing threshold. Simulations verify that the proposed sensing strategies offer an evident improvement on the spectrum utilization of the CR network.

Power allocation in heterogeneous networks: Limited spectrum-sensing ability and combined protection

In this paper, we investigate the problem of power allocation in a heterogeneous network that is composed of a pair of cognitive users (CUs) and an infrastructure-based primary network. Since CUs have only limited effective spectrum-sensing ability and primary users (PUs) are not active all the time in all locations and licensed bands, we set up a new multi-area model to characterize the heterogeneous network. A novel combined interference-avoidance policy corresponding to different PU-appearance situations is introduced to protect the primary network from unacceptable disturbance and to increase the spectrum secondary-reuse efficiency. We use dual decomposition to transform the original power allocation problem into a two-layer optimization problem. We propose a low-complexity joint power-optimizing method to maximize the transmission rate between CUs, taking into account both the individual power-transmission constraints and the combined interference power constraint of the PUs. Numerical results show that for various values of the system parameters, the proposed joint optimization method with combined PU protection is significantly better than the opportunistic spectrum access mode and other heuristic approaches.

Energy-Efficient Channel Management Scheme for Cognitive Radio Sensor Networks

In designing a cognitive radio sensor network (CRSN), we need to take account of energy both efficiency and primary user (PU) protection since the CRSN consumes additional energy to support CR functionality such as channel sensing and switching, which can shorten the network lifetime. In this paper, we propose a new channel management scheme for CRSNs, which heightens the energy efficiency while not greatly disturbing a PU. The CRSN with the proposed scheme adaptively selects its operation mode among channel sensing, channel switching, and data transmission/reception, according to the channel-sensing outcome. Considering that the sensing outcome can be erroneous due to noise uncertainty, we design the proposed scheme on the basis of the partially observable Markov decision process framework. The simulation results show that the proposed scheme energy-efficiently operates while properly protecting a PU.

OFDM-Based Common Control Channel Design for Cognitive Radio Ad Hoc Networks

Cognitive radio (CR) technology allows devices to opportunistically use the vacant portions of the licensed wireless spectrum. However, the available spectrum changes dynamically with the primary user (PU) activity, necessitating frequent PU sensing coordination and exchanging network topology information in a multihop CR ad hoc network. To facilitate these tasks, an always-on, out-of-band common control channel (CCC) design is proposed that uses noncontiguous OFDM subcarriers placed within the guard bands separating the channels of the licensed spectrum. First, the task of choosing the OFDM-specific parameters, including the number, power, and bandwidth of the subcarriers is formulated as a feasibility problem to ensure that the CCC does not adversely interfere with the PU operation. Second, for unicast messaging between a given pair of users, a subset of the guard bands may be chosen, which allows an additional measure of protection for the adjacent PU spectrum. For this, the multiarm bandit algorithm is used that allows the guard band selection to evolve over time based on the observed interference from the PU. Results reveal that our proposed CCC ensures connectivity and improved PU protection with a limited trade-off in data rate when compared to frequency-hopping and cluster-based CCC schemes.

Cooperative Incumbent System Protection MAC Protocol for Multi-channel Ad-hoc Cognitive Radio Networks

Cognitive radio (CR) MAC protocol provides access control of unused spectrum resources without causing interference to primary users. To achieve this goal, in this paper a TDMA based cooperative multi-channel cognitive radio MAC (MCR-MAC) protocol is proposed for wireless ad hoc networks to provide reliable protection for primary users by achieving cooperative detection of incumbent system signals around the communication pair. Each CR node maintains transmission opportunity schedules and a list of available channels that is employed in the neighbor discovery period. To avoid possible signal collision between incumbent systems and cognitive radio ad hoc users, we propose a simple but efficient emergency notification message exchanging mechanism between neighbor CR nodes with little overhead. Our simulation results show that the proposed MCR-MAC can greatly reduce interference with primary users and remarkably improve the network throughput.

Integration of Cooperative Sensing and Transmission

In this article, some aspects of cognitive radio (CR) technologies and cooperation strategies are discussed. The findings show that cooperative sensing enhances decision making by collaborating cognitive users (CUs). Primary users (PU) protection increases by OR rule and opportunistic access increases for CUs if collaborated using AND rule. It can also be observed that cooperative relaying benefits from path-loss saving, power gain due to the fact that the relay may add additional transmit power, and diversity gain in the presence of fading. In addition, the network performance is also enhanced by the increase in achievable data rates when using cooperative relay when compared with the rates achieved without relay. Cooperative communication technique can further enhance the transmission capacity of a communication system, while CR technique can improve the spectrum utilization ratio. Doubtless, the integration of the two technologies will have a great impact on network architecture, terminals, service models, and applications of future wireless mobile communication.

Efficient QoS support for secondary users in cognitive radio systems [Dynamic Spectrum Management

The fundamental condition for the legal approval of dynamic spectrum access approaches is the protection of the primary user. However, for dynamic spectrum access to become an attractive service reality, it is crucial to also ensure some quality of service support for the secondary user communication. In this article we discuss sensing-based opportunistic spectrum access approaches, in which primary user protection is achieved by a properly organized sensing process and secondary user communication reconfiguration. While the required reliability of the sensing process can be expressed in terms of rarely enough overlooking the primary user, we assume that the proper QoS for the secondary user is given by maintaining - with a given confidence level - a minimum bandwidth availability for the secondary user in spite of primary user dynamics. In this article we present an overview of approaches that might be used to achieve these objectives. In addition, we point out that both the sensing process and the secondary link maintenance (necessary to keep the required bandwidth in spite of reconfiguration due to detected primary users) require significant spectrum overhead. We identify and elaborate a fundamental trade-off in using these overheads in either sensing or link maintenance, and present examples of its optimization.

Multi-channel transmission strategy for dynamic spectrum access

Cognitive radio is a promising technology that deals with the scarcity of radio spectrum. In this paper, we propose a new multi-channel transmission strategy for dynamic spectrum access in cognitive radio network. Starting with the model of spectrum activities, we present the multi-channel transmission strategy which has primary user’s protection mechanism to improve the spectrum efficiency and study its performance under perfect and imperfect sensing. Numerical example results reveal that the performance of the proposed strategy has the superiority with respect to capacity performance of cognitive users and the protection of primary users.

Efficient Power Allocation for Multiuser Cognitive Radio Networks

Cognitive radio has been recently considered as a flexible spectrum usage model to improve the spectrum efficiency. In this paper, we develop a new power allocation approach by geometric programming (GP) to realize the coexistence of a primary user (PU) and multiple cognitive users (CUs) in the same frequency band. The objective is to minimize the total power consumption of CUs while guaranteeing the not only protection of PU but also the quality of service (QoS) of multiple CUs, which is different from previous works. In order to facilitate the centralized computation, a distributed algorithm is developed to adaptively adjust the transmit power of each CU. Numerical results are provided to show the effectiveness of the proposed algorithm in power saving.

Optimal Transmission Strategies for Dynamic Spectrum Access in Cognitive Radio Networks

Cognitive radio offers a promising technology to mitigate spectrum shortage in wireless communications. It enables secondary users (SUs) to opportunistically access low-occupancy primary spectral bands as long as their negative effect on the primary user (PU) access is constrained. This PU protection requirement is particularly challenging for multiple SUs over a wide geographical area. In this paper, we study the fundamental performance limit on the throughput of cognitive radio networks under the PU packet collision constraint. With perfect sensing, we develop an optimum spectrum access strategy under generic PU traffic patterns. Without perfect sensing, we quantify the impact of missed detection and false alarm, and propose a modified threshold-based spectrum access strategy that achieves close-to-optimal performance. Moreover, we develop and evaluate a distributed access scheme that enables multiple SUs to collectively protect the PU while adapting to behavioral changes in PU usage patterns. Our results provide useful insight on the trade-off between the protection of the primary user and the throughput performance of cognitive radios.

Hybrid power control scheme in hierarchical spectrum sharing network for cognitive radio

Recently, Hierarchical Spectrum Sharing Network (HSSN) has been proposed to efficiently and flexibly unitize available spectrum resource in cognitive radio context. In the HSSN, available spectrum bands are classified into two types to support both centralized and distributed communications simultaneously. A stable and efficient power control scheme is required to fully make use of the potential of HSSN. An effective power control scheme in the HSSN faces several challenges, such as low power emission, high level of quality of service (QoS), and suitability for the hybrid architecture of the HSSN. To effectively meet these requirements, a novel hybrid power control scheme is proposed in this paper. The proposed scheme is composed of three parts: a centralized power control scheme, a distributed power control scheme, and a coordination policy to coordinate these two types of power control schemes when both of them are exploited in the same channels. In the centralized power control design, we propose a Two-Step Fair Allocation (TSFA) scheme. In its first step, resources, such as channels and powers, are allocated by cognitive radio base station (CRBS) based on fairness and QoS requirements to obtain the maximum available resources of cognitive radio users (CRUs). In the second step, to get the final resource and reduce algorithm complexity, the allocation task is accomplished by each CRU simultaneously. In the distributed power control design, we propose Utility based Power Control algorithm combined with Admission Control (UPCAC). We also provide a protocol to effectively implement UPCAC. We formulate a utility function, i.e., payoff function minus price function, to measure the requirements of primary users (PUs) and CRUs. The payoff function represents CRUs’ signal-to-interference-plus-noise ratio (SINR) objectives, and the price function specifies protection for PUs and CRUs’ power consumptions. By analyzing the geometric characteristics of the payoff and price functions, we properly set the parameters of the utility function. Further, we propose coordination policy to combine centralized power control scheme with distributed power control scheme when they are exploited in the same channels. Simulation results show that the proposed hybrid power control scheme can meet the requirements of low emission power as well as high QoS level.

Capacity Optimization for Local and Cooperative Spectrum Sensing in Cognitive Radio Networks

The dynamic spectrum allocation solutions such as cognitive radio networks have been proposed as a key technology to exploit the frequency segments that are spectrally underutilized. Cognitive radio users work as secondary users who need to constantly and rapidly sense the presence of primary users or licensees to utilize their frequency bands if they are inactive. Short sensing cycles should be run by the secondary users to achieve higher throughput rates as well as to provide low level of interference to the primary users by immediately vacating their channels once they have been detected. In this paper, the throughput-sensing time relationship in local and cooperative spectrum sensing has been investigated under two distinct scenarios, namely, constant primary user protection (CPUP) and constant secondary user spectrum usability (CSUSU) scenarios. The simulation results show that the design of sensing slot duration is very critical and depends on the number of cooperating users under CPUP scenario whereas under CSUSU, cooperating more users has no effect if the sensing time used exceeds 5% of the total frame duration.

Game Theoretic Analysis of Joint Rate and Power Allocation in Cognitive Radio Networks

Spectrum sharing is an essential enabling functionality to allow the coexistence between primary user (PU) and cognitive users (CUs) in the same frequency band. In this paper, we consider joint rate and power allocation in cognitive radio networks by using game theory. The optimum rates and powers are obtained by iteratively maximizing each CU’s utility function, which is designed to guarantee the protection of primary user (PU) as well as the quality of service (QoS) of CUs. In addition, transmission rates of some CUs should be adjusted if corresponding actual signal-to-interference-plus-noise ratio (SINR) falls below the target SINR. Based on the modified transmission rate for each CU, distributed power allocation is introduced to further reduce the total power consumption. Simulation results are provided to demonstrate that the proposed algorithm achieves a significant gain in power saving.