The PAPR Reduction Algorithm In WOFDM Systems

Wavelet-based Orthogonal Frequency Division Multiplexing (WOFDM) is a multi-car-rier modulation technique which integrates wavelet theory and OFDM. WOFDM can obtainthe same perfect performance like OFDM. Furthermore, WOFDM can assign sub-channelsmore flexibly and can satisfy multi-rate signal transmission more conveniently. WOFDMcan eliminate the Inter-Symbol Interference (ISI), the impulse interference and theInter-Carrier Interference (ICI) more efficiently. The WOFDM technique can improve thecapacity and performance of the system much better. The Peak-to-Average Power Ratio(PAPR) of the WOFDM signal is very high. And the high PAPR signal need utilize thepower amplifiers and other devices which have better performance. Therefore, the researchon the reduction of high PAPR of WOFDM signals in essence is very necessary.To solve the high PAPR problem in WOFDM systems, several algorithms are proposedin this paper to reduce the high PAPR of WOFDM signals using full-tree wavelet packetbasis and ignoring the optimal wavelet packet tree problem. The major research contents areoutlined as follows:1. Taking account of the similarity of the OFDM system and WOFDM system, theCompressing and Expanding Transform, the Selective Mapping (SLM) algorithm and thePartial Transmit Sequences (PTS) algorithm which are typical PAPR reduction algorithmsof OFDM system are utilized in WOFDM system. And the performance of these algorithmsis compared by analysis and simulation.2. The computational complexity of the PTS algorithm is very high. According to thecharacteristics and advantages of the three division ways of the PTS algorithm, the randomdivision and the adjacent division are combined to divide the PTS sequence. The iterationPTS (IPTS) algorithm based on this new combined division is proposed. The simulationresults show that the improved algorithm can still improve the PAPR distribution of thesystem effectively with low complexity and does not affect the Bit Error Rate (BER)performance of the WOFDM system.3. The H matrix could be used as the weighting coefficients set in PTS algorithm. Thena new algorithm called Hadamard PTS (HPTS) algorithm based on the combined division isproposed. The H matrix could cut down the correlation of the signal as the weightingcoefficients set, so the PAPR value of the signal is reduced. The order of the H matrix andthe number of segmentations of the signal sequence are the same. Therefore, the improvedalgorithm could reduce the times of searching for the weighting coefficients. And theimproved algorithm utilizes the line number of the H matrix as side information, the amountof computation is reduced and the bandwidth efficiency of the system is increased at the same time. In addition, the improved algorithm could diminish the signal processing timegreatly by parallel computing.