OFDM-PAPR Reduction using Statistical Clipping and Window based Noise Filtering

Abstract

Orthogonal Frequency Division Multiplexing (OFDM) is an attractive modulation and multiple access technique for the channels with a non-flat frequency response, as it alleviates the need for complex equalizers. It can offer high quality performance in terms of bandwidth efficiency, robustness against the multipath fading and cost-effective implementation. It has been currently under intense research for the broadband wireless transmission due to its many advantages. The large peak to average-power-ratio (PAPR) of multiplexing OFDM transmission is one of the major drawbacks for mobile communication that requires severe power saving. A large PAPR increases the complexity of the analog to digital and digital to analog converter and it also reduces the efficiency of the radio frequency (RF) power amplifier. This thesis work presents an alternate approach for the iterative clipping and filtering (ICF) method used for the PAPR reduction in OFDM systems. As the resultant in-band noise due to clipping after z consecutive iterations is approximately proportional to the clipping noise generated in the single iteration, therefore this in-band noise obtained after first iteration is statistically scaled to measure the in-band clipping noise for z iterations. This approximated in-band clipping noise may be further used for refining the OFDM signal by using statistical clipping (SC) approach [1]. However, the out of band clipping noise is also a significant drawback for OFDM systems, which restricts the efficiency of transmitter. Therefore, the main focus of presented thesis work is on the out of band clipping noise suppression using the window based filtering, in addition to the in-band clipping noise excision using SC method, which may be termed as statistical clipping and window based filtering approach (SC-W). The simulation results are presented to compare the bit error rate (BER) performance of the underlying wireless OFDM systems using the ICF, SC, SC-W techniques for PAPR reduction. The complementary cumulative density function (CCDF) and power spectral density (PSD) characteristics are also investigated to infer the results, which depict that the proposed SC-W PAPR reduction technique meets the requirements of transmit mask specified in IEEE 802.11a. The exclusive advantage of SC-W method over ICF approach is the low computational complexity.