Sdudy On Linear Transform Approaches For Reducing The Peak-to-Average Power Ratio Of OFDM Signal

Orthogonal Frequency Division Multiplexing (OFDM) is an attractive technology for wireless communications, due to its ability against multi-path fading, immunity to impulse interference and high spectral efficiency, OFDM has been adopted in a number of physical layer standards for high data rate wireless communications, and it has become a key technology of 4G. However, one of the main drawbacks is the high peak-to-average power ratio (PAPR) of the OFDM transmitting signals. The signal with high PAPR in time domain will be distorted due to HPA working in unlinear scope, then decreases the power effenciency and BER of OFDM system. The distortion caused by high PAPR is the biggest obstacle of the RF communications design. Therefore, it is essential to reduce the PAPR of the OFDM signal to improve the power efficiency and decrease the bit error rate.We focused on the linear transformed methods to inhibit PAPR of the original OFDM signal throughout the transmitter in this dissertation, include system design and performance analysis of the non-distortion transformation technology. A kind of linear technology based on matrix transform was presented for PAPR reduction which can inprove the PAPR performance with low computational complexity.On the Partial Transmit Sequences (PTS) method based on multiple signal representation, we proposed two kinds of technology, first, an enhanced iterative flipping agrithms was presented, which can greatly decrease the computational complexity of PTS system. Combined with the pre-set threhold, we can choose the most appropriate parameter for the practical application. Then tradeoff between PAPR performance and computational complexity can be well balanced. A similar performance and a significantly reduced computational complexity can be abtained by ultilizing the presented searching approach. Secondly, in order to solve the problems that transmission of side information (SI) will increase the system overhead and reduce the effective data rate, a PTS scheme without transmitting side information was presented, the SI was embedded in the pilots of transmitting signals. The receiver should reconstruct the weighting factors using received combinated information. The implement scheme and control strategies of system were proposed at the same time. By utilizing the proposed PTS-OFDM scheme, PAPR of OFDM signal and BER performance can be improved without a little loss of data rate, and not subject to the modulation mode.Pulse Shaping(PS) is an efficient method for PAPR reduction of OFDM signal, which can shape the spectrum of transmitting signal to decrease the BER and reduce the PAPR at same time. While different shaping pulse has different performance. A novel Nyquist shaping pulse was presented which can flexiblely reduce the PAPR of OFDM signal by adjusting the roll-off factor. At the same time, the system BER was decreased and frenquency sectrum effenciency was increased. The presented pulse was much better than the traditional raised cosine pulse and the inverted exponent pulse on overall performance, which was an effective solution with low complexity. In addition, we gave out theoretical analysis and derivation in-depth around the optimization problems of Nyquist pulse shaping. And then we proposed a Nyquist shaping pulse selection criteria, the Nyquist pulse which meet the criterion can guarantee the system BER performance and not subject to the influence of the roll-off factor.PTS and PS are two effective linear transforming methods to solve PAPR problem of OFDM system which optimize system performance by reducing the occurrence probability of the signals with high PAPR, that have the advantages of flexibility and effectiveness of no distortion. However, PS technology should extend the frequency bandwidth and reduce the effective data rate, PTS has the drawback of high calculational complexity. To solve these fixed problems, a combined PS-PTS technology was presented which utilized the advantages of each method and got better PAPR performance at the condition of same frequency expense. With Comparison to PTS, this method improved PAPR reduction performance with lower complexity and decreased BER with pulse shaping at the same time.On block coding methods, we proposed an optimizing method using LDPC code for PAPR reduction of OFDM signal, which can improve the PAPR and BER performance of the multipule-input multiple-output OFDM system. The performance of the OFDM system could be improved by using low-density parity-check codes as an alternative to turbo and RS coding in mtitgating the PAPR problems which had been used in previous works. In this paper, LDPC codes was introduced into the area of PAR suppression, we proposed an efficient construction method of check matrix H which could reduce the LDPC coding complexity. In addition, the implementation scheme of MIMO-OFDM system by using LDPC to reduce the PAPR was proposed to successfully resolve the problem that linear block codes could not be used for PAPR suppression in the OFDM system with large number of carriers.