Method and apparatus for peak limiting in a modulator

A peak limiter for peak limiting in a modulator that generates from input symbols a frequency-multiplexed composite signal including a plurality of symbols, the peak limiter comprising:

• a processing system coupled to the frequency-multiplexed composite signal for processing the input symbols to peak limit the frequently-multiplexed composite signal,
• wherein the processing system is programmed to:
• define a signal template specifying a plurality of allowable distortion amounts for a corresponding plurality of symbol types;
• locate in the frequency-multiplexed composite signal a portion of the frequency-multiplexed composite signal whose amplitude exceeds a predetermined threshold by an amplitude excess;
• record characteristics including the amplitude excess, a phase angle, and a time of the portion;
• determine an input symbol corresponding to the time, the input symbol being of a symbol type included in the plurality of symbol types;
• and
• adjust the input symbol in accordance with one of the plurality of allowable distortion amounts corresponding to the symbol type, and further in accordance with the amplitude excess and the phase angle, thereby bringing the amplitude below the predetermined threshold.

A transmitter for generating an amplified radio frequency (RF) signal, the transmitter comprising:

• a modulator for generating from input symbols a frequency-multiplexed composite signal including a plurality of symbols;
• an upconverter coupled to the modulator for upconverting the frequency-multiplexed composite signal to generate an RF signal;
• and
• a power amplifier coupled to the upconverter for amplifying the RF signal to produce the amplified RF signal;
• wherein the modulator includes a peak limiter, comprising:
• a processing system coupled to the frequency-multiplexed composite signal for processing the input symbols to peak limit the frequency-multiplexed composite signal,
• wherein the processing system is programmed to:
• define a signal template specifying a plurality of allowable distortion amounts for a corresponding plurality of symbol types;
• locate in the frequency-multiplexed composite signal a portion of the frequency-multiplexed composite signal whose amplitude exceeds a predetermined threshold by an amplitude excess;
• record characteristics including the amplitude excess, a phase angle, and a time of the portion;
• determine an input symbol corresponding to the time, the input symbol being of a symbol type included in the plurality of symbol types;
• and
• adjust the input symbol in accordance with one of the plurality of allowable distortion amounts corresponding to the symbol type, and further in accordance with the amplitude excess and the phase angle, thereby bringing the amplitude below the predetermined threshold.