System capacity of a system consisting of N classes of users is characterized by N-vectors representing the number of users that can be accommodated under a specified BER (bit error rate) constraint in each class. In this paper, system capacity of the reverse link of a wireless multimedia CDMA system with processing gain control is analyzed in the asymptotic regime, when the processing gain G, for receivers with and without CCI cancellers. A new scheme for processing gain control with an optimized power allocation is proposed and its system capacity is compared with the conventional processing gain control scheme as well as the previously discussed power control scheme. It is shown that the proposed scheme has a certain advantage over other schemes.

This paper proposes an adaptive transmission control scheme for code-division multiple-access (CDMA) cellular slotted-ALOHA systems. This scheme adaptively controls the target received power and the processing gain according to both channel load and location of the mobile station. The target received power of each mobile station is controlled so that the difference between the target received powers by distance becomes large under heavy load conditions. As the distance from the base station increases, the target received power becomes smaller. The processing gain of transmitted packets is concurrently controlled with their target received powers. The packets transmitted with low signal power are spread by a large processing gain in order to reduce the unfairness in packet reception. The radio channels with distance attenuation, shadowing, slow Rayleigh fading and imperfect power control are taken into consideration in order to evaluate the performance of this scheme in the case that mobile stations transmit short massages to the base station in cellular environments. Computer simulation validates the effectiveness of this scheme: the capture effect can be achieved under heavy channel loads, and therefore, throughput performance is improved. Detailed evaluation of throughput, packet reception probability and transmission complete probability is presented. The effect of movement of mobile stations is also discussed. Calculated results show that the proposed scheme has superior characteristics and thus can expand the allowable load area in the cellular environments with slow Rayleigh fading channels.

When wireless multi-media information which includes speech, image, data and so on are transmitted, the defference in information rate, required quality as well as traffic performance should be taken into account. A wireless spread spectrum system can achieve a flexible balance of these differences because of the inherent asynchronous capability of CDMA. In this paper, we propose a wireless multi-media CDMA system based on a processing gain control in a dynamic traffic channel. According to the priority of each medium and channel measurement information i.e. traffic, the optimal processing gain can be controlled by using Nonlinear Programming. Numerical results demonstrate that the proposed method possesses higher flexible capacity than TDMA in a dynamic multi-medea traffic channel.