Page 239 - From Smart Grid to Internet of Energy

212 From smart grid to internet of energy

the spectrum and wireless networks [20]. The CR user is merely authorized to
exploit unoccupied spectrum in order to prevent causing interference or colli-
sion with the PUs. In addition, several spectrum measurement reports indicate
that it is not appropriate for existing wireless communication systems to con-
sider only one spectrum policy [8–10]. Since the transceivers of CR systems
can actively update their system configurations such as modulation type, band-
width, and transmission power, they remarkably differ from conventional com-
munication systems [21]. Before CR devices update their system configurations
according to changes of the radio environments, they should obtain several
information from the network. Therefore, CRs need to have two important fea-
tures called “cognitive capability” and “reconfigurability” to accomplish
opportunistic spectrum access (OSA) [2, 11]. The cognitive capability can be
described as the ability to perceive radio environment, consider the perceived
information and make a decision according to the considered information. The
perceived information are related to network protocol, spectrum, transmitted
waveform, communication network type, geographical information, locally
available resources and services, user needs, security policy, and so forth. On
the other hand, after these required information are collected from the surround-
ing radio environment, the CR devices reconfigure their system parameters in
accordance with perceived data that is called as reconfigurability feature of the
CR systems.
Inactive spectrum bands of the PUs are called as “spectrum holes” or “white
spaces” that are illustrated in Fig. 6.1. A spectrum hole (or white space) is char-
acterized in [2] as “a band of frequencies assigned to a primary user (licensed
user), but, at a particular time and specific geographic location, the band is not
being utilized by that user.” In the event of the PU reclaims the spectrum, CR
device(s) should move another white space or continues to employ this band by

FIG. 6.1 Spectrum hole or white space concept in the CR technology.