Channel capacity of a cognitive radio network in GSM uplink band

Cognitive radio technology enables the reuse of locally vacant frequency bands for better spectrum utilization and improved overall bandwidth efficiency. In this paper we analyze the practical capacity limits achievable by the (unlicensed) secondary users (SU) sharing bandwidth with (licensed) primary users in 850 MHz GSM uplink frequency band. The achievable capacity limits per user are compared under different constraints and interference scenarios. In order to minimize the impact on PU, we limit the instantaneous interference power from SU to PU in all cases of the investigation. The results show that the additional limit on the SU transmit power to 27 dBm results in a 10% drop in channel capacity, whereas treating PU interference as additive Gaussian noise results in a 50% capacity drop. The effects on the capacity by PU channel occupancy, location of secondary user cell, and log-normal fading spread are also studied. Results show that the average channel capacity is rather insensitive to secondary cell locations. A significant capacity gain can be achieved when PU channel occupancy drops from 50% to 10% or the standard deviation of log normal fading decreases from 8 to 4 dB.