Study On Power Control Algorithm In Cognitive Radio

Recently with the rapid development of communication technology, the available spectrum resources get exhausted day by day. However, at the same time, the current static spectrum allocation mode allows idle spectrum resources appearing in the primary band, leading to serious spectrum resource waste. Cognitive Radio(CR) can perceive the surrounding communication environment, detect un-used spectrum, get access to idle spectrum intelligently and improve the utilization efficiency of the spectrum.Generally speaking, white spectrum and some gray spectrum can be reused, which can divide spectrum model into overlay and underlay. The power control, a key technology in the cognitive radio, can not only efficiently increase the secondary users’ demand for signal-to-interference ratio, but can also decrease the interference among users and save the energy of battery.On the underlay model, secondary users come into the spectrum being utilized by primary user. The power control algorithms applied to underlay model need to satisfy the secondary users’ demand for signal-to-interference ratio and strictly control their transmission power to decrease interference to primary user. In view of the above considerations, an improved power control algorithm based on non-cooperative game is proposed through designing a opening type utility function under the condition of satisfying the secondary users’ demand for signal-to-interference ratio and the target power constraint. Simulation results show that, the proposed algorithm is more adaptive to the change of cognitive radio environment. Under the condition of ensuring regular communication of primary user, the proposed algorithm can not only better meet the secondary users’ demand for signal-to-interference ratio with less transmission power,but also has faster convergence rate.On the overlay model, secondary users compete for spectrum resources not utilized by primary user, but there still has some secondary users who can not meet the demand for signal-to-interference ratio when their transmission power reach maximum. To solve the above problem, an improved power control algorithm based on signal-to-interference ratio is proposed, it requires the base station controls some secondary users’ transmission power under the consideration of the system interference after getting the Nash equilibrium from the improved Foschini-Miljanic algorithm.Simulation results show that, the proposed algorithm can reduce the interference ofcognitive system efficiently and allows more secondary users to reach their target signal-to-interference ratio.