Multi-carrier transmission systems

• US 6,466,629 B1
• Filed: 05/28/1999
• Issued: 10/15/2002
• Est. Priority Date: 09/02/1996
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: STMicroelectronics NV
• Inventors: Isaksson, Anders, Okvist, Goran, Ljunggren, Lis-Marie, Olsson, Lennart, Nordstrom, Tomas, Isaksson, Mikael, Isaksson, Lars-Ake, Johansson, Magnus, Bengtsson, Daniel, Tonvall, Harry, Hakansson, Siwert, Stefansson, Tomas, Wen, Ye, Ohman, Hans, Bahlenberg, Gunnar
• Primary Examiner(s): Ghayour, Mohammad H.
• Application Number:
  US09/147,756
• Time in Patent Office: 1,236 Days
• Field of Search: 375/316, 375/243, 375/245, 375/286, 375/287, 375/377, 341/155, 341/156, 341/158
• US Class Current: 375/316
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A multi-carrier transmission system. A received multi-carrier signal is sampled and digitized before FFT processing. Multi-carrier signals consist of many narrow band carrier waves which convey data via a wide band channel. The amplitude distribution of the sum of all the individual carriers is Gaussian. This means that high amplitudes occur with low probability. At the present time, analog to digital converters have a limited dynamic range. It is therefore normal practice to provide a compromise between cutting and quantization noise. The adverse affects of a course quantization have to be balanced between signal distortions caused by the loss of the low probability high amplitude signals.

Claims

1. A receiver, for use with a multi-carrier transmission system, said receiver including digitising means for sampling and quantising a received signal comprising a plurality of individual carriers, and processing means for digitally processing said sampled and quantised received signal to extract data modulated on said plurality of carriers, characterised in that said digitising means includes an analogue to digital convertor for converting said received signal to a series of digitised samples, each sample having n bits, an extremal detector for detecting when an analogue signal at an input to said analogue to digital convertor has an amplitude greater than that which can be represented by n bits, and generator means controlled by said extremal detector to generate m bits to represent each digitised sample, where m>

n.

2. A receiver, as claimed in claim 1, characterised in that said digitising means is operative to minimise cutting of said digitised signal resulting from saturation of said analogue to digital convertor.

3. A receiver, as claimed in either claim 1, characterised in that a number represented by said m bits is determined by estimation from a Gaussian distribution of amplitudes.

4. A receiver, as claimed in any previous claim 1, characterised in that said received signal is passed through analogue amplitude regulation means before passing to said input of said analogue to digital convertor.

5. A receiver, as claimed in claim 1, characterised in that said generator means is a 3-to-1 multiplexor having a first input arranged to receive an n bit output from said digital to analogue convertor, a second input arranged to receive an estimate of a positive amplitude value representative of an amplitude of a sample of said received signal greater than a positive saturation value of said analogue to digital convertor, a third input arranged to receive an estimate of a negative amplitude value representative of an amplitude of a sample of said received signal less than a negative saturation value of said analogue to digital convertor, and an output for an m bit signal representative of a predicted amplitude of said input signal.

6. A receiver, as claimed in claim 1, characterised in that said multi-carrier transmission system is an orthogonal frequency division multiplex radio transmission system.

7. A receiver, as claimed in claim 1, characterised in that said multi-carrier transmission system is a DMT transmission system.

8. A receiver, as claimed in claim 7, characterised in that said multi-carrier transmission system is a DMT based VDSL system.

9. A receiver, as claimed in claim 1, characterised in that a digitised output signal from said digitising means is passed to an input of a FFT processor means.

10. A receiver, as claimed in claim 1, characterised in that a digitised output signal from said digitising means is passed to an input of a wavelet transform processor means.

11. A transceiver, including a transmitter and a receiver, characterised in that said receiver is a receiver as claimed in claim 1.

12. A multi-carrier transmission system, characterised in that said multi-carrier transmission system includes two transceivers as claimed in claim 11.

13. A transceiver, or multi-carrier transmission system, as claimed in claim 11, characterised in that said multi-carrier transmission system is a DMT system.

14. A transceiver, or multi-carrier transmission system, as claimed in claim 13, characterised in that said multi-carrier transmission system is a DMT based VDSL system.

15. A method of digitising an analogue multi-carrier signal comprising a plurality of individual carriers each of which is modulated with a data stream, in which said signal is sampled and quantised, characterised by the steps of:

sampling and quantising said analogue multi-carrier signal to produce a sequence of digital samples each of which contains n bits representing said sample amplitude;

detecting when an analogue multi-carrier signal sample has an amplitude greater than the maximum amplitude that can be represented by n bits; and

generating a digital signal in which each sample is represented by m bits, where m>

n.

16. A method, as claimed in claim 15, characterised by minimising cutting of said digitised signal resulting from saturation of an analogue to digital convertor used for said sampling and quantization.

17. A method, as claimed in claim 15, characterised by estimating a number represented by said m bits from a Gaussian distribution of amplitudes.

18. A method, as claimed in claims 15, characterised by regulating said analogue multi-carrier signal'"'"'s amplitude prior to sampling and quantization.

19. A method, as claimed in claims 15, characterised by estimating a positive amplitude for said analogue multi-carrier signal, greater than the positive saturation value of said analogue to digital convertor, estimating a negative amplitude for said analogue multi-carrier signal, less than the negative saturation value of said analogue to digital convertor, and:

if a sample of said analogue multi-carrier signal has an amplitude lying between said positive and negative saturation values, using an output of said analogue to digital convertor to represent the amplitude of said sample of said analogue multi-carrier signal;

if a sample of said analogue multi-carrier signal has an amplitude greater than said positive saturation value, using the estimated positive value of said amplitude to represent the amplitude of said sample of said analogue multi-carrier signal; and

if a sample of said analogue multi-carrier signal has an amplitude less than said negative saturation value, using the estimated negative value of said amplitude to represent the amplitude of said sample of said analogue multi-carrier signal.

20. A method, as claimed in claims 15, characterised in that said multi-carrier signal is an orthogonal frequency division multiplex signal.

21. A method, as claimed in claim 15, characterised in that said multi-carrier transmission signal is a DMT transmission signal.