Dynamic spreading code selection method for PAPR reduction in OFDM-CDMA systems with 4-QAM modulation

We present a new dynamic spreading code selection technique to obtain low p eak-to-average-power ratio (PAPR) of an orthogonal frequency-division multi plexing code-division multiple-access (OFDM-CDMA) system with 4-QAM modulat ion for the down-link in mobile communication. In this method, initially, e ach user is assigned a low and a high PAPR spreading code, which allows sel ecting one when the system is operating. The spreading code of each user is dynamically selected so that total PAPR level of the whole user group pres ent in the system is minimized. With the proposed technique, the PAPR level of a system with 10 users and 64 sub-carriers using 64 chip Walsh-Hadamard (WH) codes, can be limited to 15 dB while the worst case theoretical maxim um could go up to 28.1 dB. Although 64 chip WH codes are employed to evalua te the performance it can be generalized to all other sets of spreading cod es.