RAC: Range Adaptive Cognitive Radio Networks

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Abstract

In recent years, cognitive radio has received a great attention due to tremendous potential to improve the utilization of the radio spectrum by efficiently reusing and sharing the licensed spectrum bands, as long as the interference power inflicted on the primary users of the band remains below a predefined threshold level. Cognitive radio allows the secondary users in the cognitive radio network to access the licensed spectrum of the primary users opportunistically. In this paper, an autonomous distributed adaptive transmission range control scheme for cognitive radio networks which is called the RAC is proposed. The RAC considers the QoS requirements of both the primary and the secondary users simultaneously. The cognitive user's maximization of its achievable throughput without interfering the primary user by adapting transmission range of the secondary users dynamically is the key feature of the RAC. One of the advantages of using the proposed scheme is its implementation simplicity. The RAC is compared to other cognitive radio schemes in a simulation environment by using ns2. Simulations indicate that, the RAC can well fit into the mobile cognitive radio ad hoc networks and improve the network performance. Having compared to the other schemes utilizing contemporary cognitive radio technology, the RAC provides better adaptability to the environment and maximizes throughput and minimizes data delivery latency.

Research highlights

► An autonomous distributed adaptive transmission range control scheme for cognitive radio networks is proposed. ► RAC is based on self-adjusting variable transmission range of secondary users to find an alternative path to keep communication link alive. ► It is a simple yet an efficient approach to utilize throughput and reduce end-to-end delay. ► We provide simulative performance analysis that proves the adaptability and efficiency of the scheme.

Introduction

It is known that communication frequency spectrum is underutilized. According to the Federal Communication Commission (FCC) measurements, roughly 90% of the frequency spectrum is not actively in use [1]. On the other hand, the “spectrum shortage” is often complained about in wireless communications arena essentially because of the use of outdated spectrum assignment policies such as allocating spectrum portions statically, which allow little sharing [2]. New promising technologies are required to accomplish a dynamic spectrum usage ruled by the licensing authorities such as FCC [3]. The introduction of cognitive radio (CR) techniques to assign spectrum provide promising approach to overcome the “spectrum shortage” bottleneck. CR, a term first introduced by Mitola [4], is proposed to overcome this bottleneck produced by allocating spectrum portions statically by enabling more efficient distributed decision making algorithms on how spectrum should be shared. Note that, traditionally for wireless communication, a regulator assigns the spectrum by granting licenses to operators, resulting in exclusive access to certain separate frequency allocations.

There are two classes of users in CR networks, primary (licensed) and secondary (unlicensed). Primary users hold the license for the frequency and as their name indicates they own the frequency using rights and they have the priority over the others. Primary users usually do not utilize the frequency continuously and gaps of different lengths become available. Secondary users, which hold no license, would like to share the licensed radio frequency with primary users by exploiting those spectrum gaps intelligently. Consequently, determining the interference impact of the secondary users on primary receivers from a new transmitter activation is vital, especially between systems with diverse transmission ranges. In a CR system, a secondary link is activated along with the primary link in a way that it does not disrupt the primary link. There have been three essential approaches for the cognitive transmission in the literature: the interweave, the underlay and the overlay approaches [5], [6]. In the underlay approach, the cognitive radio transmits in a manner that its interference at the primary receivers is negligible. In the overlay approach the cognitive radio imposes non-negligible interference at the primary receiver but it makes up the performance degradation in the primary radio with the help of its non-causal access to the primary users data. The interweave technique is based on the idea of opportunistic communication. There exist temporal spectrum gaps which are also called as spectrum holes that are not in use by the primary owners and consequently can be used for secondary communication.

In this paper, a wireless fading system with a cognitive radio that is concurrently transmitting with a primary user is considered. The primary user operates with a constant power and utilizes an adaptive modulation and coding scheme satisfying a bit error rate requirement. The successful operation of the cognitive radio network will be disturbed, if a primary user detected due to their priority in spectrum access, the operations of primary users should not be affected by unlicensed users. Regardless of the used scheme, frequent interruption in a selected route would degrade the performance in terms of the quality of service (QoS) of the communication. Thus, an important concern is to design a communication protocol that provides QoS guarantee which will allow a path to be retained during a data communication session along that path between secondary nodes. RAC: Range Adaptive Cognitive Radio Networks is proposed to achieve this objective by utilizing an adaptive transmission range scheme. Because of active primary user detection, a secondary node involved in the communication process may not be able to continue its transmission, thus disturbing the communication link. The RAC mechanism is based on self-adjusting variable transmission range of secondary users to find an alternative path to keep communication link alive. No negotiation, i.e. no handshaking or messaging, between users is required and the optimization procedure is done at the cognitive radio in the RAC. It may be claimed that a low transmission range will not guarantee proper connectivity among users to ensure effective communication when there is not sufficient number of secondary users in the network. Such a claim is an important issue to be discussed in a system consisting of only primary users. However, providing communication among secondary users in the presence of primary user communication proposes a totally different environment and trying to keep connection even with a reduced range improves the overall network performance for the secondaries. On the other hand, if the transmission range is higher than the optimum value, it will ensure connectivity but will increase the probability of encountering a primary user in the transmission range, cause harmful interference to more primary users, increase collision and congestion of control packets.

There has been an interest in the recent years for determining an optimal transmission range which is also called as optimum power interchangeably for a fixed number of secondary nodes distributed over an operating area [7], [8], [9], [10]. To the best of our knowledge, all of these studies tries to find and allocate an optimal range (power) and assigns it statically for a given scenario. Neither of them adjusts the transmission range adaptively during a communication session as the RAC. However, in a CR network environment, the number of both secondary and primary nodes as well as the concentration (density) of nodes in different areas of the operating zone varies. We believe that the RAC, which is a scheme based on adaptive transmission range would be an effective solution in such a changing environment due to varying primary node activities.

The remaining part of the paper is organized as follows. In Section 2, related work in this area is reviewed. Details of the RAC is given in Section 3. The simulation and performance analysis of the RAC is presented in Section 4. Finally, conclusions and future research directions are provided in Section 5.

Section snippets

Related work

Cognitive radio is a flexible and intelligent wireless system that is aware of its surrounding environment and changes its transmission or reception parameters to communicate efficiently avoiding interference with the primary or secondary users. The secondary users will benefit from this CR to utilize the licensed band of the primary system as long as the licensee's operation is not compromised [4], [11], [12]. Based on the CR's interaction with the primary network system, transmission modes

RAC

The RAC is a simple yet an efficient approach to utilize throughput and reduce end-to-end delay by dynamically changing transmission range when needed. As soon as primary user communication is detected by the cognitive radio engine, each communicating secondary node that interferes with the detected primary node reduces its transmission range trying to retain the communication path while decreasing the interference on the detected primary user. Range adaptivity is realized in a distributed

Simulation and performance analysis

Through simulations implemented in ns2 [23], the performance and functional correctness of RAC and its relative performance compared to that of SORP [19] and STOD-RP [20] are evaluated. Unless otherwise noted, simulations are run with the following parameters. Two-ray ground propagation model is used at the radio layer. The bit rate for each channel is 2 Mbps. Variable number of mobile nodes up to 100 moving in a rectangular area 1800 m × 1800 m in dimension is modeled. Each node picks a random spot

Conclusion

In this paper, Cognitive Radio Ad Hoc Networks are investigated and RAC: Range Adaptive Cognitive Radio Networks is proposed to enhance throughput of these networks. The RAC is an autonomous distributed adaptive transmission range control scheme for cognitive radio networks that simultaneously considers the QoS requirements of primary and secondary users. It is a simple yet an efficient approach to utilize throughput by dynamically changing transmission range when needed. The key feature of the

A. Cagatay Talay received his B.Sc. degree in Computer Science and Engineering in 2001 from Yildiz Technical University, Istanbul, Turkey and his M.Sc. degree in Computer Engineering in 2004 from Istanbul Technical University, Istanbul, Turkey. He is currently pursuing his Ph.D. degree in Computer Engineering at Istanbul Technical University where he also serves as a research assistant. From May 2008 to January 2009, he was a visiting researcher at the Wireless Communication and Signal

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  • Cited by (3)

    • Self adaptive routing for dynamic spectrum access in cognitive radio networks

      2013, Journal of Network and Computer Applications
      Citation Excerpt :

      Since SOPs change temporally and spatially, the secondary transmitters need to have a real-time functionality for monitoring spectrum and detecting the SOPs (Akyildiz et al., 2009; Lee et al., 2008; Kim and Shin, 2008; Yucek and Arslan, 2009) prior to accessing the licensed frequencies opportunistically. In this paper, a novel self adaptive routing algorithm (SAR), which is designed for efficient data transportation in CR ad hoc networks by making use of dynamic transmission range adaptivity (Talay and Altilar, 2012), and appropriate metrics (Talay and Altilar, 2011) that provide link modeling and ensure interference avoiding, is proposed. Although link modeling, interference avoiding and different transmission ranges with relaying methods have been previously adapted separately, to the best of our knowledge, SAR is the first routing protocol that incorporates all of them into a single routing protocol for CR networks.

    A. Cagatay Talay received his B.Sc. degree in Computer Science and Engineering in 2001 from Yildiz Technical University, Istanbul, Turkey and his M.Sc. degree in Computer Engineering in 2004 from Istanbul Technical University, Istanbul, Turkey. He is currently pursuing his Ph.D. degree in Computer Engineering at Istanbul Technical University where he also serves as a research assistant. From May 2008 to January 2009, he was a visiting researcher at the Wireless Communication and Signal Processing (WCSP) group under the guidance of Dr. Huseyin Arslan, University of South Florida, USA. A.Cagatay Talay’s research interests are next generation wireless technologies with emphasis on cognitive radios and cognitive wireless networks with a special focus on routing, cross-layer design, adaptation and optimization and Quality of Service (QoS) control. A.Cagatay Talay is a member of IEEE.

    D. Turgay Altilar received his Ph.D. degree in 2002 from Queen Mary, University of London. He was involved with several EU projects related to parallel multimedia processing during his Ph.D. research. He has been assigned as an Assistant Professor in 2003 at the Computer Engineering Department of Istanbul Technical University. Dr. Altilar's research interests are related to wireless sensor networks, cognitive radio, real-time systems, pervasive computing, parallel, distributed and grid computing. The current research interests are routing protocol design in cognitive radio networks, data dissemination on multimedia sensor networks, MAC and routing protocol design for multichannel sensor networks, resource management Grid Computing and naturally tolerant parallel algorithm design and heterogeneous network based GPGPU computing. He has served as technical program committee chair, technical program committee member, session and symposium organizer, and workshop chair in several conferences. Dr. Altilar is a member of IEEE.

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