Primary User Band Research Articles

Delay and Throughput Oriented Continuous Spectrum Sensing Schemes in Cognitive Radio Networks

Periodic spectrum sensing over the entire primary user (PU) band always interrupts the secondary user (SU) data transmission in the sensing interval, which may degrade the quality of service of the SU. To alleviate this problem, we divide the PU band into two subbands, one for opportunistic SU data transmission, and the other for continuous spectrum sensing. Based on the PU band division, we propose a delay oriented continuous spectrum sensing (DO-CSS) scheme for delay sensitive SU services. In the DO-CSS scheme, the average SU transmission delay is reduced by selecting the proper bandwidth for spectrum sensing within each frame. Since different SUs may have different requirements on their quality of services, we further propose a throughput oriented continuous spectrum sensing (TO-CSS) scheme. In the TO-CSS scheme, the achievable average SU throughput is maximized by choosing the optimal sensing bandwidth within multiple adjacent frames. Both theoretical analyses and simulation results show that compared with the conventional periodical spectrum sensing scheme, the average transmission delay of the SU is reduced without degradation in the maximum achievable throughput by using the proposed DO-CSS scheme, and both the delay performance and achievable SU throughput are further improved by using the proposed TO-CSS scheme.

Distributed Power Allocation for Secondary Users in a Cognitive Radio Scenario

The major contribution of this paper is distributed power allocation for a multi-user multi-channel Cognitive Radio (CR) network which deploys overlay spectrum sharing by the Primary Users (PUs) and Secondary Users (SUs), and Frequency Division Multiplexing Access (FDMA) for the SUs. The transmit power of each SU is constrained by an individual node power budget, the interference threshold on the PU band, as well as the interference caused to the neighboring SUs. Motivated by the non-convex structure of the problem and the need to execute the power allocation distributedly, the problem is cast within a game theoretic frame-work. Pay-off functions for the SUs are formulated to suit the system model, and the Nash Equilibrium for the game is analyzed. Simulation results are provided to validate the mathematical concepts and to evaluate the performance of the proposed distributed power control algorithm in comparison with other relevant schemes.

Power Allocation in OFDM Cognitive Radio System in Presence of Relay

This paper proposes power allocation algorithm in orthogonal frequency division multiplexing (OFDM) based cognitive radio (CR) system using decode and forward (DF) relay. It is reported in the literature that both classical i.e. uniform power loading scheme and water filling methods that allocate power on OFDM subcarriers based on the channel gain are not effective for cognitive radio network (CRN) as the schemes introduce large interference to primary user (PU). To this aim, the present work proposes a simple, computationally efficient yet effective power loading scheme that maximizes the transmission capacity of CR while keeping the interference introduced to the PU below acceptable limits. To meet the objective, proposed power allocation to subcarriers not only considers channel gains but also the relative distances between CR subcarriers and PU band. This capacity performance is further improved significantly using DF relay, where our research direction focuses on optimal sharing of power between CR and relay using maximal ratio combiner (MRC) at destination receiver. Performance for the proposed power allocation schemes are compared with OFDM based hybrid power allocation as well as joint subcarrier and power adaptation methods reported in the literature. Numerical results show that the relative gain on CR's capacity are 3.7 times and 2.3 times, respectively compared to the optimal and hybrid OFDM power allocation schemes, while for interference introduced to PU is set at 3 times 10-6 (in watt). Finally, a few related research problems are also highlighted as future scope of works.

Collaborative Spectrum Sensing in the Presence of Byzantine Attacks in Cognitive Radio Networks

Cognitive radio (CR) has emerged as a solution to the problem of spectrum scarcity as it exploits transmission opportunities in the under-utilized spectrum bands of primary users. Collaborative (or distributed) spectrum sensing has been shown to have various advantages in terms of spectrum utilization and robustness. The data fusion scheme is a key component of collaborative spectrum sensing. In this paper, we analyze the performance limits of collaborative spectrum sensing under Byzantine Attacks where malicious users send false sensing data to the fusion center leading to increased probability of incorrect sensing results. We show that above a certain fraction of Byzantine attackers in the CR network, data fusion scheme becomes completely incapable and no reputation based fusion scheme can achieve any performance gain. We present optimal attacking strategies for given attacking resources and also analyze the possible counter measures at the fusion center (FC). Based on these analyses, we also propose a novel and easy to implement technique to counter Byzantine attacks in CRNs. In this approach, the FC identifies the attackers and removes them from the data fusion process. Our analysis indicates that the proposed scheme is robust against Byzantine attacks and can successfully remove the Byzantines in a short time span.

An Efficient Power-Loading Scheme for OFDM-Based Cognitive Radio Systems

We study the bit and power-allocation problem for an orthogonal frequency-division multiplexing (OFDM)-based cognitive radio (CR) system in which the spectrum is licensed to a primary user (PU) pair consisting of one transmitter and one receiver. CR pairs (CRPs) may use both active and nonactive PU bands as long as the generated interference powers are within the interference temperature limits of the PUs. The optimal solution and a low-complexity suboptimal solution are proposed. It is found that significant improvements can be achieved compared with systems in which CRPs only use the nonactive PU bands.

Throughput analysis for a contention-based dynamic spectrum sharing model

In this paper we present throughput analysis for a contention-based dynamic spectrum sharing model. We consider two scenarios of allocating channels to primary users, fixed allocation and random allocation. In fixed allocation, the number of primary users allocated to a channel is fixed all the time, but the number of users in different channels may be different. In random allocation, each primary user dynamically and randomly selects a channel in each time slot. We assume that the spectrum band of primary users is divided into multiple channels and the time is slotted. Primary users allocated to a specific channel compete to access this channel in each time slot. Secondary users are able to dynamically detect the idle channels in each time slot, and compete to access these channels. We develop analytical models for the throughput of primary users and secondary users in both scenarios and examine the impact of the number of secondary users on the throughput of the system. For a given number of primary users, channels and traffic generation probability, we aim to find the number of secondary users to maximize the total throughput of both primary users and secondary users. Our solutions match closely with the numerical results.

Computationally Efficient Power Allocation Algorithm in Multicarrier-Based Cognitive Radio Networks: OFDM and FBMC Systems

Cognitive Radio (CR) systems have been proposed to increase the spectrum utilization by opportunistically access the unused spectrum. Multicarrier communication systems are promising candidates for CR systems. Due to its high spectral efficiency, filter bank multicarrier (FBMC) can be considered as an alternative to conventional orthogonal frequency division multiplexing (OFDM) for transmission over the CR networks. This paper addresses the problem of resource allocation in multicarrier-based CR networks. The objective is to maximize the downlink capacity of the network under both total power and interference introduced to the primary users (PUs) constraints. The optimal solution has high computational complexity which makes it unsuitable for practical applications and hence a low complexity suboptimal solution is proposed. The proposed algorithm utilizes the spectrum holes in PUs bands as well as active PU bands. The performance of the proposed algorithm is investigated for OFDM and FBMC based CR systems. Simulation results illustrate that the proposed resource allocation algorithm with low computational complexity achieves near optimal performance and proves the efficiency of using FBMC in CR context.

Sensing-Throughput Tradeoff for Cognitive Radio Networks

In a cognitive radio network, the secondary users are allowed to utilize the frequency bands of primary users when these bands are not currently being used. To support this spectrum reuse functionality, the secondary users are required to sense the radio frequency environment, and once the primary users are found to be active, the secondary users are required to vacate the channel within a certain amount of time. Therefore, spectrum sensing is of significant importance in cognitive radio networks. There are two parameters associated with spectrum sensing: probability of detection and probability of false alarm. The higher the probability of detection, the better the primary users are protected. However, from the secondary users' perspective, the lower the probability of false alarm, the more chances the channel can be reused when it is available, thus the higher the achievable throughput for the secondary network. In this paper, we study the problem of designing the sensing duration to maximize the achievable throughput for the secondary network under the constraint that the primary users are sufficiently protected. We formulate the sensing-throughput tradeoff problem mathematically, and use energy detection sensing scheme to prove that the formulated problem indeed has one optimal sensing time which yields the highest throughput for the secondary network. Cooperative sensing using multiple mini-slots or multiple secondary users are also studied using the methodology proposed in this paper. Computer simulations have shown that for a 6 MHz channel, when the frame duration is 100 ms, and the signal-to-noise ratio of primary user at the secondary receiver is -20 dB, the optimal sensing time achieving the highest throughput while maintaining 90% detection probability is 14.2 ms. This optimal sensing time decreases when distributed spectrum sensing is applied.