One of the most important capacity parameters in the DS-CDMA cellular systems is the system reliability on which the reverse link capacity is usually limited by a prescribed lower bound. In this letter, the effect of the system reliability as well as imperfection of the power control on the system capacity is quantitatively considered using sensitivity analysis in a multimedia DS-CDMA cellular system. As a result, an analytical close-form formula is presented in terms of the standard deviation of the received SIR and the system reliability. In a numerical example, sensitivity with respect to the system reliability on the system capacity has the value ranging from 5 to 50 between 95% and 99% the range in we are interested.

Orthogonal Multi-Carrier-Code Division Multiple Access (OMC-CDMA) is a scheme that combines multi-carrier modulation with Direct Sequence Spread Spectrum (DS-SS) and allows the efficient utilization of the bandwidth, the resistance against frequency selective fading in broadband mobile radio channels and the efficient implementation by the FFT algorithm. In this paper, we analyze the bit error probability (BER) of OMC-CDMA on two-ray Rayleigh multipath fading channels with the delay time and compare the BER performances of OMC-CDMA according to the number of users (M) and subcarriers (N), and the power of delayed path. We found that the performance of OMC-CDMA depends greatly on the power of delayed signal. If the power of delayed signal is increased from 10% to 50% as compared with the direct path power, the capacity of OMC-CDMA is decreased approximately by 40% at BER=10-3, N=256 and SNR=12 dB. And, though more subcarriers are used in the circumstance that the power of delayed signal is relatively great, the performance is not significantly improved.

In this paper, we propose an activity-based estimation scheme to determine the received signal power disparity, that enhances the BER performance of the SIC scheme in a DS/CDMA system considering a practical voice activity factor, and compare BER performance with those of other schemes with or without estimation. Numerical analysis results show that the SIC scheme with the proposed activity-based estimation improves the BER performance compared with that without considering voice activity, and it approaches to that of the ideal estimation as the total number of concurrent users increases. In addition, the higher becomes the maximum attainable SNR, the better becomes the BER performance of the proposed activity-based estimation scheme.

In this paper, we investigate the bit error rate (BER) of OMC-CDMA (Orthogonal Multi-Carrier-Code Division Multiple Access) with Maximal Ratio Combining (MRC) scheme on two-ray Rayleigh multipath fading channels, and compare the MRC scheme with the Equal Gain Combing (EGC) scheme according to not only the number of users (M) and subcarriers (N) but also the power of delayed signal. We found that the MRC scheme outperforms the EGC scheme, and the BER of OMC-CDMA depends greatly on the power of delayed signal. If the delayed path power is increased from 10% to 50%, as compared with the direct path power, CDMA capacity is decreased approximately by 30% at BER=10-3, N=256 and SNR=15 dB. When the system is heavily loaded by users in large decaying parameter, the performance of OMC-CDMA with the MRC scheme can not increase the BER significantly compared to that with the EGC scheme.