Peak power and bandwidth efficient linear modulation
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In portable wireless communication systems, power consumption is of major concern. Traditional modulation and coding schemes have been designed from the standpoint of minimizing average power. However, for linear power amplifiers needed for spectrally efficient modulation formats, amplifier efficiency and hence power consumption are determined by the peak power of the transmitted signal. This paper looks into modulation formats which minimize peak power and retain high spectral efficiency. Peak power is broken into a sum (in terms of decibels) of average power and a peak-to-average power ratio, and a variety of modulation formats are evaluated in terms of peak power efficiency in both a Gaussian noise and Rayleigh fading channel. A generalized phase shift keying (PSK) modulation format is developed and shown to offer superior peak power efficiency relative to that of commonly used linear modulation formats. Two schemes are presented for reducing the peak-to-average power ratio of various modulation formats. First, data translation codes are used to avoid data sequences which cause large peaks in the transmitted signal. This approach was found to be most productive in quadrature amplitude modulation (QAM) formats. A reduction of up to 2.0 dB reduction in peakto-average power is obtained for 16 QAM modulation at the cost of a small decrease (10-15%) in throughput or, alternatively, a slight increase in occupied bandwidth. Finally, an adaptive peak suppression algorithm is presented which further reduces the peak-to-average power ratios of the PSK and generalized PSK formats. It was found that using this scheme on the generalized PSK format produced a 4-bit/symbol modulation technique which was 2.8-4.0 dB superior to 16 QAM in terms of peak power over a Rayleigh fading channel. The peak suppression algorithm is also applicable to vr/4-QPSK and was found to improve peak power efficiency ofthat format by about 1.25 dB over a Rayleigh fading channel. 1998 IEEE.
