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 report 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.
2. Literature Survey
Spectrum Allocation in Cognitive Radio Networks – The aim of this approach is to limit the interference so that the capacity and performance of the network can be improved. This process is related with spectrum sensing. Spectrum sensing is responsible for finding the available frequency band then spectrum decision or spectrum assignment is based on the parameters like fairness, quality of service requirement, throughput, spectrum efficiency etc. and the constraint is, interference to the primary user as well as secondary users must be avoided. The task of spectrum assignment is carried out by selecting the central frequency and bandwidth (according to requirement) simultaneously.
The process of spectrum assignment is divided into three parts. First is define the objective function that is criteria to solve this problem then the suitable modelling is chosen and the third step is the selection of technique that will simplify the SA problem.
There are three different aspects of Spectrum Allocation Phenomenon.
• Spectral Efficiency
• Interference / Power
• Energy Efficiency
• Network Connectivity
• PU not considered
• PU considered
• Cluster Based
• Graph Theory
• Game Theory
• Fuzzy logic
Table-1 Different Criteria ofSpectrumAllocation
Criterion Objective Function Constraints References
Interference It should be minimized at the primary user and other secondary users as well. Quality of service requirements must be satisfied. ,,
Power It must be controlled at the secondary user so that primary user can be protected. Quality of service requirements must be satisfied. ,
Spectrum efficiency It must be maximized, either by increasing number of secondary users or number of channels. Its complexity is high and it can be done only in centralized spectrum allocation algorithm. ,
Throughput It must be maximized i.e. network or user...