Investigation Of PAPR Problem And The Crossponding PTS Algorithms In OFDM System

As a special technique of multi-carrier modulation (MCM), orthogonal frequency division multiplexing (OFDM) offers a considerable high spectral efficiency, multipath delay spread tolerance, immunity to the frequency selective fading channels and power efficiency. As a result, OFDM has been widely deployed in many wireless communication standards such as Digital Audio Broadcasting (DAB), Digital Video Broadcasting(DVB), Wireless Local Area Network(WLAN), Asymmetric Digital Subscriber Line(ADSL), High Definition Television(HDTV), and so on. However, one of the main drawbacks of OFDM system is the high Peak-to-Average Power Ratio (PAPR). To solve this problem, many domestic and foreign scholars have done lots of work, aiming at PAPR reduction.In this thesis, the principle of the OFDM system is firstly discussed, followed by detailed PAPR problem analysis. The current research status of PAPR reduction techniques are then reviewed with the emphasis on the clipping & filtering and the probabilistic technologies, especially the Partial Transmit Sequence (PTS) technology.It is known that the traditional clipping technique will result in the in-band noise and out-band radiation, as well as the regrowth of PAPR after deep sampling. This thesis then investigates a clipping algorithm which uses bidirectional FFT operation to filter in the frequency domain, and its PAPR reduction ability is simulated and analyzed under different Clipping Ratio (RC). Moreover, a repeated clipping and filtering method based on the previous clipping algorithm is discussed. It is demonstrated that, by clipping and filtering more times, the performance can be further improved.Aiming at the drawback of high complexity of the PTS algorithm, two low-complexity PTS methods are simulated, which are called Cimini iterative and the Peak Cancelation. Then, their performance including implementation complexity are simulated and analyzed. Then, the concatenated structure of the clipping algorithm and PTS algorithm is discussed. Simulation results show that the best cascade scheme is to the linear PTS algorithm first, followed by the non-liner clipping algorithm.Finally, as PTS algorithm needs to transmit Side Information (SI), one low complexity PTS without SI algorithm based on Pilot Tone is studied. On this basis, an improved algorithm is proposed in this thesis. By further calculating the sum of the imaginary and real parts of the pilot tone, the expanded range of the transmitted phase factors can be estimated very well, thus the PAPR can be significantly reduced, at almost no impact on the system BER performance complexity.