Spectrum Allocation in Cognitive Networks

Cognitive Network is a technique which is used to improve the spectrum utilization. Current network scenario is experiencing the huge spectrum scarcity problem due to the fixed assignment policy so in this method great amount of spectrum remain unused. To overcome this limitation the spectrum allocation must be in dynamic manner. In this paper the spectrum allocation is discussed thoroughly. Interference is the most important factor that needs to be considered. It is caused by the environment (noise) or by other radio users. It limits the possibility of spectrum reuse. Channel assignment is one of the techniques used to control interference in the network. There exist a trade-off between network capacity and level of contention. In cognitive radio networks spectrum assignment or spectrum allocation or frequency assignment is used to avoid interference. It is the process of simultaneous selection of operating central frequency and bandwidth. In doing so, the process of sensing the spectrum becomes very crucial; it must be reliable, accurate and efficient. The accuracy of sensing affects the overall operation of cognitive networks. Accurate results not only lead to higher utilization of the spectrum but also preserve the privacy of primary user. Accuracy of sensing is highly affected by the natural causes like noise, shadowing, fading etc. There are many other challenges as well, like, hardware requirements, hidden node problem, security, sensing frequency and duration, decision fusion etc.