Dynamic spectrum access in cognitive radio

In recent years, demand for wireless communication services has grown far beyond earlier predictions, raising serious concerns about future radio spectrum shortages. Current spectrum management policy is characterised by static spectrum allocation where radio spectrum is allocated on a long term for large geographical regions on exclusive basis. This is an effective way to prevent interference, but it leads to highly inefficient use of radio spectrum. This paper investigates possibilities of policy change towards dynamic spectrum access. Cognitive radio technology is proposed as a key technology enabling this policy change, but ensuring compatibility with legacy wireless systems. Based on hierarchical overlay model of co-existence between primary licensed users and secondary cognitive users interference avoidance constraints are presented.