Peak to average power ratio reduction in communication systems
View Patent ↗A system and method for reducing peak to average power ratio (PAR) in single and multi-carrier transmitters while accounting for the effect of the transmit filters without significantly affecting a requisite transmission Power Spectral Density (PSD) mask. To this end, in a multicarrier communication system, a DSL transmitter is provided that transmits a multicarrier symbol having a controlled peak-to-average power ratio (PAR) and which is a function of a plurality of information signals. The transmitter has a power reducer that reduces the PAR of the multicarrier symbol by modifying a selected information signal of a plurality of information signals, the modified signal including an information component, a peak reduction component, and a transmission channel response component.
1. A transmitter for use in a multicarrier communication system where a symbol transmitted by a transmitter has peak to average power ratio as a function of a plurality of signals, each one of the plurality of signals being centered at one of plurality of frequencies wherein a subset of the plurality of signals are configured to reduce the PAR before the symbol is transmitted along a transmission channel and where the subset of signals are further configured to include a response of the transmission channel, said transmitter comprising:
(a) an encoder for encoding a first set of data into a plurality of sets of data;
(b) a modulator coupled to the encoder for receiving the plurality of sets of data and (c) modulating each set of data of the plurality of the sets of data to produce the plurality of signals which are combined;
(c) a first inverse Fourier transformer coupled to the modulator, the inverse Fourier transformer operative to perform an inverse Fourier transform on the combined plurality of signals producing a transformed signal;
(d) a first power reducer coupled to the inverse transformer, wherein the power reducer is operative to analyze the transformed signal and to detect any peaks in the transformed signal, and if a peak is detected, the power reducer being operative to apply a kernel to the peak of the transformed signal by adjusting the kernel, wherein the kernel is an approximation of an impulse response generated from the subset of the plurality of signals such that the kernel is adjusted by scaling and time shifting; and
(e) a second power reducer coupled to receive a weighted transformed signal and a weighted kernel for analyzing the weighted transformed signal and for detecting any peaks therein if a peak is detected, the second power reducer being operative to apply the weighted kernel to the weighted transformed signal by applying scale and shift values to the weighted kernel such that said scale and shift values are used by said first power reducer for respectively scaling and time shifting said kernel, such that said weighed kernel includes the effects of said transmission channel.
2. A transmitter as defined in claim 1 , wherein the transmitter is an XDSL transmitter.
3. A transmitter for use in a multicarrier communication system where a symbol transmitted by a transmitter has peak to average power ratio as a function of a plurality of signals, each one of the plurality of signals being centered at one of plurality of frequencies wherein a subset of the plurality of signals are configured to reduce the PAR before the symbol is transmitted along a transmission channel and where the subset of signals are further configured to include a response of the transmission channel, said transmitter comprising:
(f) a cyclic prefix insertion module coupled to said inverse Fourier transformer;
(g) a filter for receiving an output from said cyclic prefix insertion module; and
(h) a power reducer coupled to the output of said filter, wherein the power reducer is operative to analyze the output from said cyclic prefix insertion module to detect peaks in the signal, and if a peak is detected, the power reducer is operative to apply a modified kernel to the peak of the signal by adjusting the modified kernel wherein the kernel is an approximation of an impulse response generated from the subset of the plurality of signals such that the kernel is adjusted by modifying the subset of plurality of signals and wherein the kernel is further modified using the impulse response of the filter to produce the modified kernel whereby the effect of the filter is included in the reduced PAR of the symbol.
4. A transmitter as defined in claim 3 , wherein the transmitter is an XDSL transmitter.