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Reduction of Peak-to-Average Power Ratio in OFDM-CDMA Systems with Different Spreading Codes
Recently, Code Division Multiple Access (CDMA) has been extensively applied to various kinds of new-type wireless communication system. Orthogonal Frequency Division Multiplexing-Code Division Multiple Access (OFDM-CDMA), which is a very popular communication technological in multi-carrier system, is considered the important technology of the mobile communication in future generation. The major advantage of OFDM and CDMA is to counteract frequency selective fading and has high efficiency use in spectrum, respectively. OFDM-CDMA consists of OFDM and CDMA technology to satisfy these advantages of OFDM and CDMA. OFDM-CDMA has high peak-to-average power ratio (PAPR) due to combine with OFDM. High PAPR, which is the cause of non-linear distortion output of high power amplifier, influences communication quality and consumes much power to transmit signal. Therefore, an interesting issue for multi-carrier system is how to reduce high PAPR. %This paper proposes a new method to analyze two sets of orthogonal spreading code which are Walsh Hadamard sequence %and Reed Muller code; the method analyzes the combination of spreading code sequence according to the number of %active user. We try to find the combination of spreading code sequence which produces high PAPR; these sequences %can be completely ruled out for using as the combination of spreading code sequence. As a result of the autocorrelation %function and the power spectrum density becomes Fourier pair each other. Therefore, we analyze these combinations of %spreading code sequence by cross-correlation function; and find out some regulation to avoid choosing the combination %of spreading code which produces high PAPR. This paper proposed new orthogonal spreading codes in first order Reed-Muller code and to reduce high PAPR in OFDM-CDMA system. The method analyzes the combination of spreading code sequence according to the number of active user. We try to find the combinations of spreading code sequence and find rules out which produces highPAPR; these sequences can be completely ruled out for using as the combination of spreading code sequence.
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