Multi-carrier spread spectrum modulation with reduced dynamic range

Multi-carrier (MC) modulation has been proposed for code-division multiple access (CDMA) mobile radio communications, by modulating an identical symbol on multiple carriers of same magnitude. Certain phase offsets assigned to each carrier define a code that is given to a specific user. We introduce a CDMA system based on multi-carrier spread spectrum (MC-SS) with one identical code for all users. In general, the employment of a multi-carrier transmission technique would increase the dynamic range of the correspondent lowpass time signal, and therefore would require a highly linear power amplifier. It is shown that by carefully designing the code of a MC-SS signal a significant decrease of several orders of magnitude in the dynamic range can be obtained. The dynamic range of the resulting multi-carrier signal is of the same range as of conventional direct-sequence spread-spectrum (DS-SS) signals using OQPSK combined with raised-cosine filtering. We therefore show that MCSS CDMA is an alternative to existing DS-SS techniques proposed for mobile cellular radio and PCS, and should be considered for future mobile applications