Crest Factor Reduction In Ofdm Using Blind Selected Pilot Tone Modulation
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Orthogonal frequency division multiplexing (OFDM) is a spectrally efficient multicarrier modulation technique for high speed data transmission over multipath fading channels, but has low power efficiency. OFDM signals have large crest factors, or peak-to-average power ratios (PARs) which lead to power inefficiency in the RF portion of the transmitter. Selected mapping can be used to reduce the PAR of an OFDM signal and is distortionless. A technique is disclosed that links the index of a phase rotation sequence used in selected mapping to the location of pilot tones that are used to estimate the channel. Each pilot tone location-phase sequence selection produces a different PAR value for the time-domain OFDM signal, and the signal with the lowest PAR value is transmitted. The technique is "blind" in that the optimum pilot tone location-phase sequence index is not transmitted as side information. A technique to blindly detect the optimum index at the receiver is also disclosed.
- Georgia Tech Patents