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The multi-tone CDMA is a spectrum-efficient multiuser transmission technique, and regarded as a promising platform for multimedia communications. We study the multi-rate physical-layer transmissions, based on multi-code (MC) and variable-spreading-length (VSL) access. A general and systematic system model accommodating both access methods with multiuser detection (MUD) is constructed, which is useful for programmable system integration. We investigate the system characteristics under multi-rate transmission, including multiple access interference (MAI) and intercarrier interference (ICI), and the performance comparisons between MC and VSL schemes in frequency-selective Rayleigh fading channels are studied.