Opportunistic Spectrum Access to 3G Wireless CDMA Networks for Cognitive Radio

In this paper, we deal with the scenario that a single secondary user (SU) attempts to opportunistically access the 3G wireless CDMA networks licensed to primary users (PUs). Different to earlier studies in which consider the channel as two state Markov process, here, we expand the channel´s availability into a multiple-state Markov process according to the transmission power of the SU. We propose a cyclical, but not periodic sensing and transmission strategy, which can be divided into two steps: 1) the SU acquires the estimation about how many PUs are in this network during a sensing period T_s; 2) Based on the estimation, the SU determines how much transmission power and how long it can transmit. Further, we derive the optimal transmission strategy which consists of different transmission power and time corresponding to different number of PUs in service. Finally, simulation results indicate that our optimal strategy is superior to the empirical strategy such as the maximum power transmission strategy and the maximum time transmission strategy, and achieves the highest throughput of SUs in the long run.