Theory And Methods For PAPR Reduction Of OFDM Signals With High Spectrum Efficiency

Orthogonal frequency division multiplexing (OFDM) has been widely employed inwireless communication systems, due to the immunity to the frequency selective fadingand the inter-carrier interference. However, one disadvantage of OFDM systems is thehigh peak-to-average power ratio (PAPR) of the OFDM signals. The high poweramplifier (HPA) introduces the inter-band and outer-band interferences to the signals,caused by the non-linear distortion of the OFDM signals, and results in the decrease ofthe system performance. Hence, we propose two methods to reduce the PAPR of OFDMsystems.First, we propose a constellation reshaping method for PAPR reduction in OFDMsystems. The key idea of the proposed method is to generate a reshaped quadratureamplitude modulation (R-QAM) constellation, in which the minimum distance of theR-QAM is the same as that of the traditional QAM constellation. When the novelR-QAM constellation is employed with the traditional partial transmit sequence (PTS)and selected mapping (SLM) methods in OFDM systems, called as the R-PTS andR-SLM methods in this paper, respectively, the mean square errors between theconstellations of the received data and each R-QAM rotated by different phase rotationfactors are calculated at the receiver, and the phase rotation factor with the minimummean square error is selected to recover the original data without side information.Therefore, the flexibility in phase rotation choice and the ability to avoid data rate lossmake the R-PTS and R-SLM methods more suitable for good bit-error-rate performancein OFDM systems. Theoretical analysis and simulation results show that the R-PTS andR-SLM methods could provide the same PAPR reduction and bit-error-rate as those ofthe conventional PTS and SLM methods with perfect side information, respectively. Then, we propose a novel scheme of combined multi-sequences for the PAPRreduction in multi-input multi-output (MIMO) OFDM systems with space frequencyblock coding (SFBC). The key idea of the proposed scheme is keeping the advantage ofthe SFBC structure to generate some alternative multi-sequences via combining thesignals at different transmit antennas. Specifically, when the proposed scheme isemployed in SFBC MIMO-OFDM systems with QAM, one of the big advantages is thatthe side information does not need to be sent to the receiver. Theoretical analysis andsimulation results validate that the proposed scheme has good abilities of large PAPRreduction, low bit error rate and low computational complexity without side informationin SFBC MIMO-OFDM systems.The common point of the proposed methods in this paper is that the signal isnon-distortion without side information. The traditional signal non-distortion schemeshave to transmit side information via several subcarriers, in order to recover the originaldata in the receiver. The proposed methods without side information achieves lower errorrate than the methods with transmitted side information, which improves the bit error rateperformance and the spectrum efficiency.