OFDM 시스템에서 파일롯 톤을 이용한 부가 정보 송신 기법

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is a special multi-carrier modulation technology for high speed data transmission and efficient spectrum applications over the multipath fading channels. It also provides the probability to eliminate the need for equalizers, where efficient hardware implementation can be realized using fast Fourier transform (FFT). However, the high peak-to-average power ratio (PAPR) of the transmit signal is one of the main disadvantages of OFDM when multi-carriers are added up coherently. An OFDM signal with high PAPR causes nonlinear distortion and requires significant back-off of the average operating power of a RF power amplifier (PA) if the signal is to be linearly amplified. The distortionless Selected Mapping (SLM) technique which generates a set of sufficiently different candidate data blocks representing the same information as the original one and selects the most suitable data block with the lowest PAPR for transmission is a promising technique to effectively reduce the PAPR of an OFDM signal. However, side information representing the index of the vector matrix of the phase rotation sequences for SLM is also needed to be transmitted to the receiver for demodulation. In the conventional scheme, side information is transmitted by occupying the data subcarriers; hence, the transmission data rate will be reduced seriously. Considering the power disparity between pilot tones and the data bits, a blind side information transmission scheme which links the index of the vector matrix to the location information of pilot tones is proposed. Because this scheme is not suitable for the big vector matrix of SLM phase rotation sequences or unequal-phase shift keying (e.g., 16-QAM and 256-QAM), another improved side information transmission scheme using half of pilot tones to transmit side information instead of occupying the data subcarriers is also proposed. To reduce the degradation of channel estimation caused by only half of pilot tones are used in the proposed scheme, a special receiver utilizing iterative channel estimation is designed, additionally. The numerical analysis and simulation result demonstrate that the proposed system could successfully reduce PAPR in OFDM systems and could also get a high transmission data rate as well as a reliable BER performance.