Overlay Cognitive Radio Networks Research Articles

Spectrum Allocation based on Auction in Overlay Cognitive Radio Network

In this paper, a mechanism for spectrum allocation in overlay cognitive radio networks is proposed. In overlay cognitive radio networks, the secondary users (SUs) must first sense the activity of primary users (PUs) to identify unoccupied spectrum bands. Based on their different contributions for the spectrum sensing, the SUs get payoffs that are computed by the fusion center (FC). The unoccupied bands will be auctioned and SUs are asked to bid using payoffs they earned or saved. Coalitions are allowed to form among SUs because each SU may only need a portion of the bands. We formulate the coalition forming process as a coalition forming game and analyze it by game theory. In the coalition formation game, debtor-creditor relationship may occur among the SUs because of their limited payoff storage. A debtor asks a creditor for payoff help, and in return provides the creditor with a portion of transmission time to relay data for the creditor. The negotiations between debtors and creditors can be modeled as a Bayesian game because they lack complete information of each other, and the equilibria of the game is investigated. Theoretical analysis and numerical results show that the proposed auction yields data rate improvement and certain fairness among all SUs.

Joint Optimization of Cooperative Spectrum Sensing and Resource Allocation in Multi-channel Cognitive Radio Sensor Networks

Cooperative spectrum sensing (CSS) that utilizes multi-user diversity to mitigate channel instability and noise uncertainty is a promising technique in cognitive radio networks (CRNs). However, the spectrum-sensing parameters which affect the channel-access opportunities of secondary users (SUs) are conventionally regarded as static and treated independently from the resource-allocation strategies. In this paper, joint optimization of CSS, channel access and resource allocation is investigated in an overlay CRN in which each SU carries multi-channel spectrum sensing and transmits the detected energy to a fusion centre in the imperfect reporting channel. An access factor is introduced to describe the channel-access strategies in both cooperative and non-cooperative schemes. Based on the aggregate interference and the transmit power constraints, an optimization problem of multi-channel CSS is formulated to obtain the optimal transmit powers, allocation-access strategies, and sensing threshold of CR system for maximization of the opportunistic throughput. To solve the non-convex problems in both the single and multiple CR systems, the efficient iterative algorithms are developed by exploiting the hidden convexity of the optimization problems. Numerical results show that the performance of our approaches yields a significant enhancement compared with the equal channel-access and equal power-allocation strategy.

Spectrum sensing scheme for overlay cognitive radio networks

Considering the effects of primary user traffic, timing misalignment and multiple arrival and departure issues in a sensing period should be addressed for spectrum sensing in future overlay cognitive radio (CR) networks, such as femtocell networks. To achieve this goal, division of the whole sensing duration into multiple windows is proposed. For each window, a two-step detection scheme, i.e. coarse and fine detection, is proposed to improve the performance of the conventional energy detector (ED) in the overlay CR scenario.

A dynamic channel access strategy for underlay cognitive radio networks: Markov modelling and performance evaluation

AbstractUnlike in overlay cognitive radio networks, secondary users in underlay cognitive radio networks can access licensed spectrum even at the presence of a primary user, given that the interference caused by the secondary transmission is lower than a pre‐specified threshold. Based on this underlay access principle, we propose in this paper a dynamic channel access strategy for multi‐channel cognitive radio networks. Different from existing underlay access techniques, channel assembling, spectrum adaptation and restricted channel occupancy are also considered in the proposed strategy in order to achieve better performance in the secondary network. Accordingly, a partial channel occupancy mode, which allows secondary users to access a portion of a channel when co‐existing with a primary user, is introduced in this study. The size of this portion is adjusted by selecting an appropriate value of a configurable parameter α in the partial channel occupancy mode. The system performance is evaluated for both primary and secondary networks, and a comparison analysis is carried out to assess the cost against the gain. Numerical results demonstrate that the proposed underlay channel access strategy outperforms the corresponding overlay strategy in terms of secondary network capacity, blocking probability and dropping probability. The cost and gain analysis identifies appropriate traffic conditions under which the overall system performance could be improved by employing the proposed underlay strategy. Copyright © 2015 John Wiley & Sons, Ltd.

Cooperative waiting‐time reduction for cognitive radio networks using Stackelberg game

Waiting time occupies an important position in user's quality-of-service (QoS) evaluation system. However, in conventional overlay cognitive radio networks (CRN), the secondary users are not permitted to transmit any personal information whenever the spectrum is occupied by primary users. It follows that the waiting time of users depends heavily on the primary spectrum occupancy, which, in turn, cannot guarantee the QoS of the secondary users. To remedy this, a game theoretical cooperative waiting-time reducing method (CWTRM) is proposed in a self-generated CRN to meet users’ waiting-time demands. The proposed scheme divides the users to temporary primary and secondary groups instead of introducing an extraneous secondary network. Specifically, waiting users are served as temporary secondary users. The cooperation between them and the temporary primary users is proceeded in each frame to make reuse of the unused time fractions, thereby reducing the global waiting time of the network. The optimal relay power, pricing and corresponding cooperating strategies are determined with the utilisation of Stackelberg game and Hungarian method. Finally, the superiority of the proposed CWTRM over non-cooperative schemes is validated through simulations.

Distributed Opportunistic Interference Alignment Using Threshold-Based Beamforming in MIMO Overlay Cognitive Radio

To achieve the full multiplexing gain of a K-multiuser multiple-input-multiple-output (MIMO) overlay cognitive radio (CR) network, a distributed opportunistic interference alignment (DOIA) technique using a new beamforming algorithm, namely, threshold-based beamforming (TBF), is proposed. The MIMO overlay CR system consists of one primary user (PU) and K secondary users (SUs) where the local channel state information is available at both the transmitters and receivers of SUs. Assuming that the receiver and the transmitter of the PU have perfect knowledge of their own channel matrix, the PU uses a maximum eigenmode beamforming (MEB) scheme for its data transmission to release some of its eigenmodes for the SUs. For this virtual cooperation, the SUs align their transmitted signals to the spatial directions (SDs) associated with the unused PU's eigenmodes to ensure orthogonality between the links of the PU and the SUs. In addition, the MEB scheme overcomes the limitation of the conventional water-filling power allocation (WPA) in releasing the PU's eigenmodes for the SUs at high signal-to-noise ratios (SNRs). A noniterative and distributed power-allocation strategy, namely, TBF, is proposed, in which the SUs' links with a maximum eigenvalue above a certain threshold transmit data at full power, and the rest remain silent. This protocol, along with the MEB scheme, enables the MIMO overlay CR system to enhance the throughput of the network described as the average sum rate of both the PU and SUs. The proposed DOIA-TBF protocol allows the opportunistic SUs to use the same frequency band of a preexisting PU and guarantees that no interference is imposed on the PU's performance for such a MIMO overlay CR system.

Secondary User Power Saving in Overlay Cognitive Radio Networks

The secondary user power saving in the overlay based Hybrid Automatic Repeat request cognitive radio has been investigated. The effect of the power splitting ratio on the secondary transmissions has been studied and a simple power saving technique for secondary users is proposed. Extensive simulation runs have been carried out to validate our results. General Terms:

Spatial Throughput Characterization in Cognitive Radio Networks with Threshold-Based Opportunistic Spectrum Access

This paper studies the opportunistic spectrum access (OSA) of the secondary users in a large-scale overlay cognitive radio (CR) network. Two threshold-based OSA schemes, namely the primary receiver assisted (PRA) protocol and the primary transmitter assisted (PTA) protocol, are investigated. Under the PRA/PTA protocol, a secondary transmitter (ST) is allowed to access the spectrum only when the maximum signal power of the received beacons/pilots sent from the active primary receivers/transmitters (PRs/PTs) is lower than a certain threshold. To measure the resulting transmission opportunity for the secondary users by the proposed OSA protocols, the concept of spatial opportunity, which is defined as the probability that an arbitrary location in the primary network is detected as a spatial spectrum hole, is introduced and then evaluated by applying tools from stochastic geometry. Based on spatial opportunity, the coverage (non-outage transmission) performance in the overlay CR network is analyzed. With the obtained results of spatial opportunity and coverage probability, we finally characterize the spatial throughput, which is defined as the average spatial density of successful transmissions in the primary/secondary network, under the PRA and PTA protocols, respectively.

QoS provisioning energy saving dynamic access policy for overlay cognitive radio networks with hidden Markov channels

Dynamic spectrum access policy is crucial in improving the performance of overlay cognitive radio networks. Most of the previous works on spectrum sensing and dynamic spectrum access consider the sensing effectiveness and spectrum utilization as the design criteria, while ignoring the energy related issues and QoS constraints. In this article, we propose a QoS provisioning energy saving dynamic access policy using stochastic control theory considering the time-varying characteristics of wireless channels because of fading and mobility. The proposed scheme determines the sensing action and selects the optimal spectrum using the corresponding power setting in each decision epoch according to the channel state with the objective being to minimise both the frame error rate and energy consumption. We use the Hidden Markov Model (HMM) to model a wireless channel, since the channel state is not directly observable at the receiver, but is instead embedded in the received signal. The procedure of dynamic spectrum access is formulated as a Markov decision process which can be solved using linear programming and the primal-dual index heuristic algorithm, and the obtained policy has an index-ability property that can be easily implemented in real systems. Simulation results are presented to show the performance improvement caused by the proposed approach.

TDCS-Based Cognitive Radio Networks with Multiuser Interference Avoidance

For overlay cognitive radio networks (CRNs), transform domain communication system (TDCS) has been proposed to support multiuser communications through spectrum bin nulling and frequency domain spreading. In TDCS-based CRNs, each user is assigned a specific pseudorandom spreading sequence. However, the existence of multiuser interference (MUI) is one of main concerns, due to the non-zero cross-correlations between any pair of TDCS signals. In this paper, a novel framework of TDCS-based CRNs with the joint design of sequences and modulation schemes is presented to realize MUI avoidance. With the uncertainty of spectrum sensing results in CRNs, we first introduce a unique sequence design through two-dimensional time-frequency synthesis and obtain a class of almost perfect sequences. That is, periodic auto-correlation and cross-correlations are identically zero for most circular shifts. These correlation properties are further exploited in conjunction with a specially-designed cyclic code shift keying in order to achieve the advantage of MUI avoidance. Numerical results demonstrate that the proposed TDCS-based CRNs are considered as preferable candidates for decentralized networks against the near-far problem.

Sequential search based power allocation and beamforming design in overlay cognitive radio networks

We consider the problem of power allocation and linear beamforming design in overlay cognitive radio (CR) networks where the cognitive user is admitted to transmit simultaneously with the primary user. To compensate the interference caused at the primary receiver (PR), the secondary transmitter (ST) uses part of its power to forward the primary user's message. The objective of cognitive user is to design a joint power allocation and beamforming scheme such that the signal-to-interference-plus-noise ratio (SINR) at the secondary receiver (SR) is maximized. We propose algorithms based on uniform quantization and sequential search to solve the corresponding non-convex optimization problems. We perform sequential search over at most three real variables for the case of single-input multiple-output (SIMO) cognitive link, and four real variables for the case of multiple-input single-output (MISO) cognitive link, respectively. It is shown that the computational complexity for solving the formulated problems does not increase significantly with the number of receive (transmit) antennas in the cognitive link. Simulation results show that the multiple-antenna configurations yield improved system performance compared to the case of single-input single-output (SISO) cognitive link. In the case of transmit beamforming, the proposed beamforming scheme shows much better performance than the traditional zero-forcing (ZF) beamforming.

Improving the Sensing–Throughput Tradeoff for Cognitive Radios in Rayleigh Fading Channels

In-band spectrum sensing (SS) in overlay cognitive radio networks requires that the secondary users (SUs) periodically suspend their communication to determine whether the primary user (PU) has started to utilize the channel. In contrast, in spectrum monitoring (SM), the SU can detect the emergence of the PU from its own receiver statistics such as receiver error count (REC). Previously, it has been shown that in additive white Gaussian noise channels, a hybrid SS/SM system significantly improves the channel utilization of SUs and the detection delay of PUs. In this paper, we investigate the problem of SM in the presence of fading, where the SU employs diversity combining to mitigate the channel fading effects. We show that a decision statistic based on the REC alone does not provide good performance. Next, we introduce new decision statistics based on the REC and the combiner coefficients. It is shown that the new decision statistic achieves significant improvement in the case of maximal ratio combining (MRC). However, for equal gain combining and selection combining, the inclusion of combiner coefficients does not improve the performance over REC alone. In the case of MRC, we evaluate the receiver operating characteristics (ROCs) from analysis and compare the results with those from simulations using a BCH code as well as a convolutional code. The results show a close match between analysis and simulation results. Channel utilization and detection delay are evaluated from simulations which show that with MRC and the proposed decision statistic, the hybrid SS/SM system significantly outperforms the SS alone.

Energy-aware joint power and rate control in overlay cognitive radio networks: a Nash bargaining perspective

We investigate a joint energy-aware power and rate control scheme for overlay spectrum sharing cognitive radio networks, and we expect to achieve an optimal performance tradeoff between individual fairness and network energy efficiency. Therefore, a quality of energy efficiency-based Nash bargaining cooperative game (QoE2-NBCG) is formulated with the aid of a newly-built ‘energy-per-bit’ individual utility function in this paper. Mathematically, a multi-constrained optimisation problem is formulated with the novel individual QoE2 utility function. To reduce the implementation complexity, we utilise decomposition techniques to decouple this multi-constrained problem. Meanwhile, an iterative dynamic bargaining algorithms (IDBA) with limited information exchange is developed based on the derived closed-form of power and rate solutions. In addition, the existence and uniqueness of socially optimal Nash bargaining solutions are validated via theorems. Numerical results verify the convergence of the proposed algorithm, the overall performance improvement and the optimal tradeoff between transmission rate and ‘energy-per-bit’ efficiency.

Interference-Driven Linear Precoding in Multiuser MISO Downlink Cognitive Radio Network

We consider linear precoding in the downlink of a multiuser multiple-input-single-output (MISO) overlay cognitive radio (CR) network, wherein a primary base station (PBS) and a cognitive base station (CBS) share the same frequency band to transmit to a number of primary users (PUs) and secondary users. Conventionally, linear precoding techniques in a CR network aim to limit or completely cancel interference to the PUs while achieving maximum downlink throughput of the CR system. In this paper, we investigate novel adaptive linear precoding techniques at the CBS to exploit the interference to the primary and secondary systems, instead of its cancellation, by exploring the potential of making use of interference energy when the interference between the two systems is mutually constructive on an instantaneous basis. By doing so, the received signal-to-noise ratio (SNR) is enhanced by the signal energy gleaned from the constructive interference. In this direction, constructive-interference-based adaptive linear precoding techniques are proposed for the CR network, assuming a simple zero-forcing precoder at the PBS and noncausal knowledge of the primary message at the CBS. The presented analysis and simulations show that the proposed precoding techniques outperform conventional techniques, as the CR transmission actively enhances the performance of the PUs through constructive interference while achieving significant throughput for its own transmission.

A Mixed SINR-Balancing and SINR-Target-Constraints-Based Beamformer Design Technique for Spectrum-Sharing Networks

We propose a transmitter beamformer design technique for a spectrum-sharing network with mixed quality-of-service requirement. In particular, the proposed algorithm has the ability to jointly design multiple beamformers, so that a specific subset of users attains certain target signal-to-interference-plus-noise ratios (SINRs) whereas the SINRs of the remaining users are balanced subject to multiple linear constraints. The design framework considered is applicable to both the overlay cognitive radio network (CRN) and the underlay CRN; however, the algorithm is described for the example of an underlay CRN to include a very general mathematical framework. We maximize the worst-case users' SINR of a particular set of users while satisfying the target SINRs of the remaining users subject to the total transmission power and the interference leakage constraints. This algorithm is solved using the uplink-downlink duality and subgradient method. The condition for convergence is analytically derived. The simulation results are provided to validate the optimality and the convergence of the proposed algorithm.

Tuning radio resource in an overlay cognitive radio network for TCP: Greed isn't good

In this article we illustrate the performance of Transmission Control Protocol in an overlay cognitive radio network under dynamic spectrum access. We show that the performance of TCP in overlay CR networks that implement DSA to be quite different from its performance in conventional networks, which do not allow DSA. The key difference is that secondary users in an overlay CR network have to cope with a new type of loss called service interruption loss, due to the existence of primary users. We demonstrate on an NS2 simulation testbed the surprising result: Excessive radio resource usage leads to a decrease in aggregate TCP throughput. This behavior is in contrast to the behavior of TCP in conventional networks, where throughput increases monotonically with the available radio resource.