Abstract: A gradient sensitivity based method is described for reducing Peak to Average Power Ratio in multicarrier communication systems. The method involves definition of a differentiable penalty function which has non-zero values whenever there is a peak violation. The gradient of the function with respect to the symbol magnitudes and phases is evaluated at the given symbol vector. Symbol perturbations are computed in the opposite direction of the gradient in such a way that the peaks are reduced and the amount of errors introduced in the symbols is not large enough to affect the decoding process. In order to reduce computation, a variant of the method is proposed where a peak reduction kernel is precomputed and stored. The kernel is rotated to the location of the peak and added with proper sign to reduce PAR.

Abstract: A method and apparatus is provided that computes an optimal estimate of known clock frequency error between the transmitter and receiver using a known pilot signal and the statistics of the noise process. The estimate is computed such that the residual clock error is below the least count (the smallest frequency correction that can be imparted) of the VCXO that controls the receiver sample clock. A tracking technique based on a measure of drift in taps of frequency domain equalizers of different sub-carriers is disclosed. This tracking ensures that the residual mean square error is within a predefined bound. Finally, the least count effects in digitally controlled oscillators (DAC controlled VCXOs and Numerically Controlled Oscillators (NCXO)) are addressed by a dithering mechanism. The dithering mechanism involves imparting positive and negative clock corrections for different lengths of time in such a manner that the residual clock error becomes zero mean.