System and method for peak to average power ratio reduction

Abstract

A system and method for performing peak-to-average power ratio reduction in a transmitter using pulse amplitude modulation (PAM) encoding. Broadly, a transmitter is configured to perform active digital filtering to detect encoded data symbols that if uncorrected would lead to relatively high analog signal peaks in the data transmission. A prediction is made of the peak values that would be applied at the digital to analog converter (DAC) if the original output of the Tomlinson precoder was sent into the shaping filter. If the absolute value of the predicted peak value exceeds a threshold, a correction of a full 2L step is applied for one sample of the Tomlinson precoded stream. The correction step is applied in such a way as to reduce the resulting peak output. Two methods of predicting the peak values are presented. The first method segments the shaping filter into causal and non causal portions so that no extra delay is introduced. The second method uses a two-stage approach where a first pass provides symbols without correction, then corrected symbols are injected in a duplicate modulation filter (this implies an extra delay equal to the filter delay). A variation of the two-stage approach takes advantage of the linear aspects of the Tomlinson preceding.