No abstract

Frequency spectrum is a limited resource and the increasing demand caused by emerging services, augmented number of wireless users along with the demand for high-quality multimedia applications have resulted in the overcrowding of the allocated spectrum bands. The overcrowding of spectrum bands has exacerbated by the current spectrum licensing policy which has emerged as a bottleneck to efficient spectrum utilization, due to its inflexibility, resulting in most of the licensed spectrum being severely under-utilized. However, the problem of scarcity of spectrum bands and the inefficient utilization of the already allocated radio spectrum can be smartly addressed through spectrum sharing by enabling opportunistic usage of the underutilized frequency bands. One of the most exciting ways of spectrum sharing is cognitive radio technology which allows a wireless node to sense the environment, detect the network changes, and then make intelligent decisions by dynamically changing its reception or transmission parameters to communicate while ensuring that no interference is affected to the licensed users. It thus improves the spectrum utilization by reusing the unused or underutilized spectrum owned by the incumbent systems (primary systems). In this paper, a comprehensive survey and review of recent research about the advances in cognitive radio technology will be carried out. We will also evaluate the various spectrum sensing techniques in a cognitive radio network in the UHF/VHF bands allocated for TV broadcasting.

The demand for wireless connectivity is increasing exponentially resulting in an unprecedented demand on the limited radio spectrum. Due to the current fixed spectrum licensing scheme, it is becoming increasingly arduous to find extra spectrum resulting in a paradigm shift towards efficient utilization of radio spectrum in order to address the spectrum scarcity. The transition from analogue to digital terrestrial television has freed-up some spectrum thereby creating unique opportunities for exploitation of locally underused portions of the TV bands referred to as TV white spaces (TVWS) and their exploitation offers an attractive way of making efficient use of radio spectrum as long as the secondary users do not interfere with the primary users. This is enabled by employing cognitive radio technology that allows for dynamic spectrum access. This paper investigates the aspect of interference in TV White spaces and the possibility of mutual coexistence between primary users and secondary users operating in TV White spaces. The impact of interfering signals is undertaken to show the probability of interference in both same channel and different adjacent channels scenarios. The interference analysis is carried out using the SEAMCAT simulation software. Simulation results show that in a power limited secondary network, vacation of cognitive users from active spectrum bands is crucial for ensuring coexistence. The various interference mitigation mechanisms employed by CR networks are also reviewed. In TV white spaces, mitigating interference is vital not only for primary user protection, but also for ensuring the quality of service of the secondary users.

No abstract