Companding System Based on Time Clustering for Reducing Peak Power of OFDM Symbol in Wireless Communications

Osamu TAKYU  Tomoaki OHTSUKI  Masao NAKAGAWA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E89-A   No.7   pp.1884-1891
Publication Date: 2006/07/01
Online ISSN: 1745-1337
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Multi-dimensional Mobile Information Networks)
peak power problem,  OFDM symbol,  compressing and expanding (companding) system,  

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This paper proposes a novel compressing and expanding (companding) system for OFDM wireless communications that minimizes the compression distortion and so reduces the peak power of OFDM symbols. OFDM systems suffer from large variations in instantaneous peak power. Such transients distort the signals when they are passed through a nonlinear high power amplifier (HPA) prior to transmission. Existing companding systems are far from perfect since the receiver can not accurately estimate the degree of compression applied by the transmitter and thus can not regenerate the original signal by expansion; the key problems are the band pass filter (BPF), HPA, and the noise component enhanced by the channel compensation filter. In the proposed companding system, each symbol is divided into segments, and series of consecutive segments are grouped into clusters. Each cluster is multiplied by a weight equal to the inverse of the largest instantaneous power within the cluster. The receiver estimates the weight used for each time cluster. The weights for all clusters are averaged to mitigate the weight estimation error. As a result, the proposed expander can accurately estimate the weights used and thus well suppress the compression distortion.