1 Cognitive Radio with Spectrum Sensing for Future Networks
Nabil Giweli, Seyed Shahrestani, and Hon Cheung
CONTENTS
1.1 Introduction and Background
1.2 Cognitive Radio Technology
1.2.1 Cognitive Radio Definition
1.3 Cognitive Radio Functions and Cycle
1.4 Cognitive Radio Challenges
1.4.1 Spectrum Sensing and White Space Determination: The Challenges
1.4.2 The Impact of Sensing Operations on the QoS of Applications
1.4.3 Spectrum Management Challenges
1.4.4 Spectrum Mobility Challenges
1.4.5 Spectrum Sharing Challenges
1.4.6 Other CR System Challenges
1.5 Sensing Methods
1.5.1 No Prior Information Required (Blind Sensing)
1.5.1.1 Energy Detection
1.5.1.2 Covariance-Based Detection
1.5.1.3 Based on Prior Information
1.5.1.4 Cyclostationary Feature Detection
1.5.1.5 Correlation Detection
1.5.1.6 Radio Identification–Based Sensing
1.5.1.7 Matched Filtering
1.5.1.8 Based on SU Cooperation
1.6 Factors Affecting the Selection of a Proper Sensing Method
1.6.1 CR Device Capability
1.6.2 QoS Required for Applications Running on the CR Device
1.6.3 A Priori Information
1.6.4 Level of Protection Required for the PU
1.6.5 CR Network Mode and Capability
1.7 CR Standardization Efforts with Sensing Consideration
1.8 Spectrum Sensing Implementation Issues in White-Fi Networks
1.8.1 Distinguishing a PU Transmission from SU Transmissions
1.8.2 Distinguishing White-Fi SUs from Other SUs
1.8.2.1 Pure White-Fi SUs
1.8.2.2 Heterogeneous SUs
1.8.3 Complications of Operational Adjustments
1.8.4 QoS Degradation
1.8.5 Selecting the Proper Sensing Method and Parameters
1.9 Conclusion
References
1.1 INTRODUCTION AND BACKGROUND
Traditionally, the radio frequency spectrum (RFS) is divided into frequency bands and regulated in most countries by their governments. Each country has a spectrum management process for allocating the frequency bands to licensed users based on technical and economic aspects. Although each country is independently allocating its RFS, governments regulate their RFSs in compliance with international and regional standards. In general, RFS bands are statically allocated as licensed or unlicensed. Each licensed band is strictly assigned to a licensed user. On the other hand, an unlicensed RFS band can be accessed and shared freely by anyone within some transmission constraints. Therefore, unlicensed bands are in high demand as many wireless technologies and radio devices are designed to work in these free RFS bands. The industrial, scientific, and medical (ISM) bands are well-known examples of unlicensed RFS bands that include the frequency bands 902–928 MHz, 2400–2483.5 MHz, and 5725–5850 MHz. These bands are widely used, especially by wireless devices and systems based on Wi-Fi and Bluetooth communication technologies, under several specific regulations regarding operational requirements, such as power transmission and antenna gain (Cui and Weiss, 2013). As a result of regulation for the RFS bands, many licensed RFS bands are underutilized, in terms of frequency, time, and location, as found by several surveys on RFS occupancy conducted in different regions around the world (Barnes et al., 2013; Palaios et al., 2013; SiXing et al., 2012). In the near future, current RFS regulations may not be able to handle the rapidly growing usage of wireless communication technologies for various applications with highly expected increases in transmission data rate requirements. Therefore, the wireless research community and RFS regulatory organizations face the challenges of achieving high utilization of the overall RFS and need to overcome capacity scarcity in high-demand frequency bands. To overcome these challenges, there will most likely be innovative wireless technologies and revisions of the RFS regulations (Masonta et al., 2013).
From a technical perspective, cognitive radio (CR) technology is a promising solution for achieving significant RFS utilization and to open a new opportunity in the sharing of the unlicensed RFS. The concept of CR was introduced in 1999 by Joseph Mitola (Mitola and Maguire, 1999). Under the CR concept, a radio device, called the CR device, enables an unlicensed user, called the secondary user (SU) or CR user, to use a licensed RFS band without harming the operation of the licensed user, also called the primary user (PU). A licensed band is generally underutilized by the primary user, as mentioned before. This underutilization usually results in the licensed band having possible unoccupied periods, called holes or white spaces (WSs). These unoccupied spectrum holes may be present based on time, frequency, and space. By the use of CR technology, SUs are able to opportunistically share access to these holes of the licensed bands, in addition to unrestricted access to the unlicensed bands. Therefore, more bandwidth is available to the increasing number of mobile and wireless users and the increasing number of internetworking applications.
The remainder of this chapter is organized as follows: the CR concept and its main functions are explained in Section 1.2. Several challenges facing each of the CR functions are discussed in Section 1.3. Different typ...
