The Joint CDMA/PRMA (JCP) protocol, proposed by Brand and Aghvami, is modified to increase the capacity for mobile communication systems. To reduce multiuser interference, the modified JCP uses an access channel additionally to the traffic channels, on which each mobile terminal reserves a unique slot and code. Furthermore, the modified JCP employs receiver-based code scheme. In the case of voice-only traffic, the throughput increases by up to 15% compared to that of the conventional JCP, when Ploss is 0.01. Also, for the mixed traffic case, the throughput increases about 20%.