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.