AbstractThe transmission quality of mobile radio communications is strongly affected by fading with rapid fluctuations in the envelope and phase of the received signal, in addition to the effect of thermal noise. This paper considers a multiple access system (DS‐CDMA system) using the spread spectrum technique with direct spread, and presents a method of deriving the approximate average bit error rate in a frequency‐selective fading environment (the n‐ray Rayleigh fading model), with the maximum Doppler frequency, the delay time of the delayed wave, and the number of stations simultaneously utilizing the channel as parameters. The two‐wave model and the IMT2000 model are considered as examples, and the validity of the proposed method is demonstrated by the fact that the results obtained by the approximate formula agree well with the simulation results even if the parameters are varied. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(1): 90–100, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.1185