US 7,079,610 B1 · Telecommunications transmission systems

Abstract

In a multi-carrier system employing OFDM, for example DMT, an adaptive channel equalizer is normally used, operating in the frequency domain. The sampling clock is controlled so that the time delay between the transmitter and the receiver is effectively eliminated. If the information used to control the sampling clock is received from the equalized data stream, it will introduce an ambiguity between the operation of the channel equalizer and the mechanism used to control the sampling clock. Operation of the equalizer can mask an increasing time difference, between transmitter and receiver, which the sample clock controller should be tracking. The present invention eliminates the ambiguities in the operation of the equalizer and sample clock controller by preventing the equalizer from accepting time differences which should be corrected by operation of the sample clock controller.

Claims38

Dependent claims

A receiver, for use in an Orthogonal Frequency Division Multiplexing (OFDM) transmission system, comprising an adaptive channel equalizer means, detector means, equalization parameter updating means, a sampling clock and a sampling clock control means, the equalization parameter updating means responding to outputs of the detector means and the adaptive channel equalizer means to provide an equalizer parameter to the adaptive channel equalizer means, the equalization parameter updating means including an ambiguity prevention mechanism to prevent said adaptive channel equalizer means from operating on time differences between the receiver and a transmitter which should be corrected by operation of said sampling clock control means,

the equalizer parameter having an equalizer parameter argument function and said adaptive channel equalizer means being prevented from operating on said time differences by forcing a slope of a linear part of the equalizer parameter argument function to be always zero,
said sampling clock having a sampling clock frequency, said adaptive channel equalizer means providing an equalizer output vector U, and said detector means providing a quantized vector Y, said sampling clock frequency being controlled by a feed-back signal generated from an estimated slope of an argument function, Y*.U which is the element-by-element product of the equalizer output vector U and the conjugate of the quantized vector Y.

In an Orthogonal Frequency Division Multiplexing (OFDM) transmission system having a transmitter and a receiver, said receiver having an adaptive channel equalizer, a detector, a sampling clock and a sampling clock controller, and said transmitter having a sampling clock, a method of maintaining synchronization between said receiver sampling clock and said transmitter sampling clock, comprising the steps of:

preventing said adaptive channel equalizer from operating on time differences between the receiver and the transmitter which should be corrected by operation of said sampling clock controller;
controlling said adaptive channel equalizer with an equalizer parameter having an equalizer parameter argument function, and preventing said adaptive channel equalizer from operating on said time differences by forcing a slope of a linear part of the equalizer parameter argument function to be always zero;
wherein said receiver sampling clock has a sampling clock frequency, said adaptive channel equalizer provides an equalizer output vector U, and said detector provides a quantized vector Y, further comprising controlling said sampling clock frequency with a feed-back signal generated from an estimated slope of an argument function, Y*.U which is the element-by-element product of the equalizer output vector U and the conjugate of the quantized vector Y.

Dependencies are inferred from the claim text.

Telecommunications transmission systems

Life of this patent

Telecommunications transmission systems

Life of this patent

Abstract

Claims38