Research On Peak-to-average Power Ratio In Orthogonal Wavelet Packet Multiplexing System

Orthogonal Wavelet Packet Multiplexing (OWPM) system has higher spectralefficiency, better anti-interference ability, and more flexible subchannel configurationperformance than Orthogonal Frequency Division Multiplexing(OFDM) system, aswell as can support various rates of signal transmission and so on, thus attractingcommunication workers’ sight. However, as a new multicarrier modulation technique,OWPM system also needs to solve the problem of high peak-to-average power ratio(PAPR). The high PAPR will bring forward higher requirement to the linear region offront-end power amplifier, once the signal into the non-linear region, it will cause thesignal distortion and simultaneously generate intermodulation interference andout-of-band radiation, and then destroy the orthogonality between subcarriers,eventually resulting in the deterioration of system performance. Therefore, it is veryessential to research how to reduce PAPR of OWPM system.In this dissertation, three common PAPR suppression techniques are mainlystudied, including threshold clipping, μ-law companding and Partial TransmitSequence(PTS) technology. Firstly, pointing to the problem of high bit error rate(BER) of threshold clipping, an improved threshold clipping is proposed, andsimulation results demonstrate the improved scheme under the condition of smallsignal to noise ratio can better reduce PAPR of the sending end, and hardly affecttingthe BER performance of system; Secondly, pointing to the problem of difficulthardware implementation of μ-law companding, an improved μ-law compandingmethod is put forward, theoretical analysis and simulation results confirm thatimproved μ-law companding not only reduces the complexity of the system hardwareimplementation, but also can better improve the PAPR suppression performance;Finally, aiming at the high computational complexity and insufficient PAPRsuppression effect of PTS technology, three improvement projects are raisedrespectively, namely PTS technology based on improved threshold searching method,PTS technology based on improved artificial bee colony algorithm, and PTS technology based on pruning wavelet packet transform. Simulation results show thatthe first two schemes can effectively reduce the computational complexity whileinhibit PAPR, especially for the second scheme, the bigger the system, the moreobvious the effect; and the third way aiming at the optimization of wavelet packetbinary tree structure is a good way to cut the computational complexity of system, atthe same time well enhance the PAPR suppression performance and does not destroythe original BER. Due to the defects in any kind of algorithms, two kinds of jointalgorithms are also proposed in this paper to reduce the PAPR on transmit side,finally realizing the balance of BER performance, PAPR suppression performanceand computational complexity.