복소확산부호를 이용한 OFDM 시스템의 PAPR 감소에 관한 연구

PAPR Power Reduction of OFDM via Complex Spreading Code Sequence

In this paper, a new OFDM scheme, CI/OFDM using the complex spreading code sequence, is introduced. OFDM accomodates high data rates while avoiding multipath in frequency selective channels. But its high peaks in power result from non-stable envelopes, leads to inefficient operation of the transmit power amplifier. The average power of this scheme is the same that in conventional OFDM, but the peak values are much lower. CI/OFDM system uses the N orthogonal carriers equally spaced in frequency, but each information bit is simultaneously modulated onto all carriers with the complex spreading code sequences. The performance of Cl/OFDM systems in a typical frequency selective fading channel environment, are analyzed. And it is shown that the frequency diversity benefits of this system result in significant performance enhancements relative to traditional OFDM system without causing bandwidth expansion, and the magnitude of PAPR becomes far less than that of OFDM.