This study presents a system-level theoretical analysis of two different types of multirate code division multiaccess (CDMA) wireless communication systems, which include both variable spreading gain (VSG) CDMA and multicode (MCD) CDMA systems. Based on the accurate interference models, the authors derive unified expressions of the cumulative density function of the signal-to-interference-plus-noise ratio in the cases of both binary and quaternary multirate CDMA schemes. This leads us to achieve new packet error rate expressions, which consider the impacts of bit-to-bit error dependence, optimal power transmissions and random users’ distributions, for multirate-slotted packet CDMA systems. The expressions are used to investigate the system-level performance of VSG and MCD-based multicellular CDMA networks over Rayleigh fading environment.

In this paper, an efficient analytical technique for bit error rate (BER) of variable spreading gain code division multiple access (VSG CDMA) in Nakagami fading is introduced. Based on the accurate improve Gaussian approximation (IGA) technique, a new BER expression is derived in a closed form. Validated by Monte Carlo simulation, the proposed expression is used to accurately investigate the impacts of channel's conditions, power allocation and random users' distributions on the BER performance.

A new accurate mathematical analysis is presented for the efficient computation of the spectral efficiency of CDMA downlink wireless communication systems in the presence of multipath Rayleigh fading and log-normal shadowing. A new explicit expression is derived for the spectral efficiency, which is based on an accurate interference model that accounts for both intra-cell and inter-cell interferences. This is used to investigate the performance of downlink CDMA in different multipath delay profiles. The numerical results has shown that the loss of orthogonality deteriorates the spectral efficiency significantly at high signal-to-noise ratios (SNR) levels. On the other hand, the diversity gain will compensate the loss of orthogonality at low SNR levels.

This letter presents a new efficient technique to solve a throughput maximization problem on the uplink of a variable spreading gain code division multiple access (VSG-CDMA) system operated in an independent Rayleigh fading environment. A new linear set of constrains is found that enables a linear-programming solution to the problem of maximizing the overall average throughput in a multiclass system while maintaining the QoS constraints for all users

This paper presents new analytical expressions for the spectral efficiency of variable spreading gain code division multiple access (VSG CDMA) networks in a Nakagami and Rician fading environments. These are used to gain insight into the impact of fading and background noise on the optimal transmit powers. Numerical results for a dual class and 5-class system, reveal that the spectral efficiency is optimized at higher signal-to-noise ratio levels when each user is retaining the same bit energy. However, at lower levels of the signal-to-noise-ratio, the spectral efficiency would be optimized when a larger amount of energy is allocated to the classes of higher data rate, as compared to the lower rate classes