Frequency planning strategies for frequency hopping GSM

The GSM system has two type of frequency carriers, namely the frequencies that carry the broadcast control channels (BCCH) and the frequencies carrying only traffic channel (TCH). Two basic frequency planning alternatives can be distinguished: one can either divide the available spectrum into two dedicated parts for BCCH and TCH frequencies respectively or use the entire band for both BCCH and TCH frequencies. The goal with this study has been to investigate which one to prefer, from an interference point of view, in a tightly planned frequency hopping system. Simulations of an interference limited system have been performed. The focus is on the downlink performance, i.e. it is assumed that the downlink is the limiting link in the system. The results show that using dedicated frequency bands for the BCCH and TCH is superior in the downlink. The second strategy, using the entire band for both BCCH and TCH frequencies, will suffer from heavy disturbance in the downlink mainly from BCCH transmitters and the gain from power control and discontinuous transmission cannot be fully utilized. Multiple reuse patterns, a frequency planning concept based on the dedicated bands method has also been analysed.