Abstract: To increase the capacity of the mobile communication system and consider the concurrence of CDMA and GSM systems for a long term, we put forward the scheme that the two systems share a common radio-band. First, at the transmitter, GSM signals will be multiplied by PN sequences to be transferred from the TDMA mode to the CDMA/TDMA mode. Then they will transmit with CDMA signals on the same bandwidths, so the U_m interface combination problem of these two systems can be solved. At the receiver, CDMA/TDMA signals will be multiplied by the same PN sequences to be transferred to the TDMA mode, the these two signals can be separated. It can be seen from theoretical analysis and simulation resuls that this method can double the total system capacity.

Key words: shared common band, system capacity, GSM, CDMA