In this chapter, Joint Radio Resource Management (JRRM) issues in cognitive networks are discussed presenting the TV White Spaces (TVWS) spectrum exploitation use case. TVWS are portions of UHF spectrum, which will be released and interleaved according to the geographical region due to the gradual switch-off of analogue TV and the adoption of digital TV. With the availability of TVWS and their temporary lease, traditional network planning and RRM design rationale points need to be enhanced. This chapter provides state-of-the-art work for existing cognitive radio network architectures, while a reference architecture for commons and secondary TVWS trading is proposed. Subsequently, JRRM concepts for heterogeneous Radio Access Technologies’ extension over TVWS aiming to continuously guarantee the QoS, the network key performance indicators, and at the same time targeting the overall highest system capacity, are presented. Finally, a thorough classification of existing admission control and scheduling techniques are provided, outlining the need for including continuously more cognitive and context-aware features in JRRM algorithms being applicable in advanced Heterogeneous Networking (HetNet) environments.
Top1. Introduction
Emerging types of wireless network services and applications, rich in multimedia content with increased requirements for network resources and guaranteed end-to-end QoS provisioning, raise the needs for higher frequency availability and create new challenges in radio-spectrum (i.e. the fundamental resource in wireless telecommunication networks) management and administration. While the utilization of advanced digital signal processing techniques enable for efficient radio-spectrum exploitation, even under the traditional “command-and-control” spectrum administration/management policy, there is a worldwide recognition that such methods have reached their limit and are no longer optimal. In fact, radio-spectrum utilization studies have resulted that most of the licensed spectrum is under-utilized (McHenry et al., 2004), and considerable parts of it would be available when both space and time dimensions are taken into account. An example of under-utilized radio-spectrum, is the so-called “television white spaces” (TVWS) that comprise of VHF/UHF frequencies, either released/freed by the digital switchover process (“Spectrum/Digital Dividend”), or being totally unexploited, mainly at local level, due to frequency planning issues and/or network design principles (“Interleaved Spectrum”) (Australian Communication & Media Authority, 2007). TVWS include tenths of MHz at local/regional level (OFCOM, 2008), enable for low cost and low power systems design, provide superior propagation conditions for building penetration, while at the same time their sufficiently short wavelength facilitate the construction of resonant antennas, at a size and shape that is acceptable for many handheld devices. Therefore, TVWS are well suited for wireless network applications and services, provided by sophisticated telecommunication systems. However, the current “command-and-control” administration/management policy allows only for primary (i.e. licensed) systems to exploit TVWS for the provision of primary services, such as terrestrial digital video broadcasting (DVB-T), handheld digital video broadcasting (DVB-H), interactive (iTV), Programme Making and Special Events (PMSE), while prohibiting any other secondary transmission. Hence, the problem of spectrum scarcity, as perceived today, is due to inefficient radio-spectrum management/administration, rather than the wireless resources shortage. The envisioned frameworks and schemes that are proposed in this book chapter include policies (Unlicensed Operation in the TV broadcast bands, 2009) in which secondary (i.e. unlicensed) systems are allowed to opportunistically utilize the underused primary TV channels. TVWS spectrum exploitation paradigm will be used as a vehicle in order to address joint radio resource management (JRRM) issues in cognitive radio networks, too.
Cognitive Radio (CR) techniques provide the ability in a network to share the available radio spectrum, under an opportunistic basis. Cognitive radio networks adapt their transmitter parameters, based on real-time interaction with their spectral environment, by exploiting portions of frequency bands that are unused at a specific time or a geographical location. The choice of radio spectrum selection has to be performed, under an efficient process without causing interference with other licensed systems operating in the same frequency band. A cognitive radio network can be set to transmit and receive on a variety of different frequencies, exploiting alternative access technologies supported by its hardware design. Through this ability, the most optimum radio spectrum band and the most appropriate operating parameters can be selected and reconfigured.
Towards making full use of cognitive radio networks benefits and improving spectrum efficiency, cognition, intelligent decision-making and the reconfiguration abilities are adopted based on a cognition cycle. More specifically, cognition ability includes acquisition of multi-domain environment cognition information, efficient cognition information transmission and usage. Intelligent decision making ability includes the ability of making decision adaptively, according to the dynamic changing environment and the ability of improving the end-to-end efficiency. Reconfiguration ability includes the reconfiguration of cognitive radio networks, according to previous intelligent decisions for an end-to-end efficiency purpose. Finally, cognition cycle is also exploited, in order to observe the network, perceive current network conditions and make an optimum decision.