System for controlling and shaping the spectrum and redundancy of signal-point limited transmission

• US 6,278,744 B1
• Filed: 11/26/1996
• Issued: 08/21/2001
• Est. Priority Date: 11/15/1996
• Status: Expired due to Term

• Current Assignee: Modern Telecom Systems, LLC (Ideahub, Inc.)
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Olafsson, Sverrir, Zhou, Zhenyu, Zhang, Xuming
• Primary Examiner(s): Bocure, Tesfaldet
• Application Number:
  US08/756,383
• Time in Patent Office: 1,729 Days
• Field of Search: 375/253, 375/254, 375/285, 375/242, 375/295, 375/296, 375/346, 375/222, 375/258, 341/55, 341/59
• US Class Current: 375/296
• CPC Class Codes: H04L 25/4927 using levels matched to the quantisation levels of the channel

Abstract

A method and apparatus for controlling and shaping the spectrum of transmitted signal samples having predetermined frequency characteristics and allowable transmit signal levels. A running measure of unwanted components is measured and, for each block of the transmitted samples, an objective function based on the previously calculated running measure is computed. Depending upon the measurements, redundancy is determined and selected for each block of the transmitted samples. Accordingly, at least one redundant sample may be added or, the sign of the sample modified, at structured or randomized locations within the block to optimize the objective function.

Claims

1. A method of lossless spectral shaping or coding of source samples to transmitted samples based on a set of predetermined characteristics of a frequency spectrum, where the allowable signal levels of the transmitted samples are limited to a prescribed set, and wherein the transmitted samples are transmitted via a communication channel, said method comprising the steps of:

a) for each source sample, calculating any one of the following;

i) an RDS, to obtain a measurement of the DC component of the source sample up to a current block;

ii) a RDFT or RFFT, to obtain a measure of unwanted signal components of the source sample up to the current block;

iii) a Running Filter Sum, to obtain a measure of unwanted signal components of the source sample up to the current block;

b) for every block of a determined plurality (“

N”

) of source samples, computing an objective function based on the measure obtained from Step a), wherein said objective function shapes the source samples to a predetermined spectrum characterized by a set of filter coefficients associated with a transmitter of said transmitted samples;

c) for every block of said determined plurality (“

N”

) of source samples, selecting one of;

i) at least one redundant sample,

ii) at least one redundant sign, or

iii) both of at least one redundant sample and at least one redundant sign, to optimize the objective function in Step b); and

d) varying the redundancy of the sample or the sign according to communication channel conditions and characteristics.

2. An apparatus comprising a microprocessor for performing the steps of claim 1, and a semiconductor memory device in communication with the microprocessor for storing the measurement calculated in step (a) and the objective function of steb (b).

3. The method of claim 1, wherein said selecting step comprises the step of:

selecting the location of the redundant sample such that the location is encoded within the transmitted sequence.

4. The method of claim 1, wherein the objective function is the sum of the squares of the output of the running measure over the block of transmitted samples.

5. A method of lossless spectral shaping or coding of source samples to transmitted samples based on a set of predetermined characteristics of a frequency spectrum, where the allowable signal levels of the transmitted samples are limited to a prescribed set, and wherein the transmitted samples are transmitted at a transmit data rate, said method comprising the steps of:

a) for each source sample, calculating any one of the following;

i) an RDS, to obtain a measurement of the DC component of the source sample up to a current block;

ii) a RDFT or RFFT, to obtain a measure of unwanted signal components of the source sample up to the current block;

iii) a Running Filter Sum, to obtain a measure of unwanted signal components of the source sample up to the current block;

b) for every block of a determined plurality (“

N”

) of source samples, computing an objective function based on the measure obtained from Step a), wherein said objective function shapes the source samples to a predetermined spectrum characterized by a set of filter coefficients associated with a transmitter of said transmitted samples;

c) for every block of said determined plurality (“

N”

) of source samples, selecting one of;

i) at least one redundant sample,

ii) at least one redundant sign, or

iii) both of at least one redundant s ample and at least one redundant sign, to optimize the objective function in Step b); and

d) varying the redundancy of the sample or the sign according to the transmit data rate.

6. A method according to claim 5, wherein said redundancy is determined to be lowest at a high transmit data rate and highest at a low transmit data rate.

7. The method of claim 5, wherein the objective function is the sum of the squares of the output of the running filter sum or running digital sum over the block of samples.

8. A system for controlling and shaping, transmitted data samples having predetermined frequency characteristics and allowable transmit signal levels, wherein the transmitted samples are transmitted by a transmitter, and are arranged in blocks having structured or random locations, the system comprising:

a microprocessor for

calculating for each of the transmitted samples, a running measure of unwanted components up to a current sample,

computing for each block of the transmitted samples, an objective function based on the running measure, wherein said objective function shapes the source samples to a predetermined spectrum characterized by a set of filter coefficients associated with said transmitter,

selecting, for each block of the transmitted samples, at least one redundant sample to be added or at least on transmitted sample within the corresponding block to be modified to optimize the objective function; and

a semiconductor memory device for storing and enabling the microprocessor to access the running measure, the objective function, and the redundant sample.

9. A system according to claim 8, wherein each block includes structured or random locations of transmitted sample, such that the location of the redundant sample may be fixed, scrambled, or random.

10. A communications system having, a limited number of signal points, for controlling and shaping the spectrum of data samples transmitted at a transmit data rate over a communications channel between a transmitter and a receiver, the receiver providing measurements of channel conditions, wherein the data samples are transmitted in blocks, the system comprising:

a microprocessor in communication with the transmitter, for

processing the receiver measurements,

determining a desired amount of redundancy to be added to the sample blocks in accordance with the receiver measurements,

adding the desired redundancy to the sample blocks to shape the sample blocks to a predetermined spectrum characterized by a set of filter coefficients associated with said transmitter; and

a semiconductor memory device receiving and storing the receiver measurements, and the desired amount of redundancy determined by the microprocessor.

11. A system according to claim 10, wherein the channel conditions may include detection of nonlinear transformer-hybrid distortion, additive tonal interference, and noise spectrum, such that in response to such channel conditions, the microprocessor causes the desired amount of redundancy to be increased.

12. A system according to claim 11, wherein the receiver measurements include estimates of non-linear distortion.

13. A system according to claim 11, wherein the receiver measurements include estimates of channel frequency response.

14. A system according to claim 11, wherein the receiver measurements include estimates of noise spectrum.

15. A system according to claim 11, wherein the receiver measurements include estimates of signal-to-noise ratio.

16. A system according to claim 10, wherein the data samples are defined by a plurality of bits and are transmitted in blocks, further wherein, at high transmit data rates, a redundancy of one, six, eight, twelve, or sixteen bits every 16 samples is added, and at lower transmit data rates, the redundancy is increased.

17. A system according to claim 10, wherein, at high transmit data rates, where the receiver measurements indicate that the channel conditions are good, minimal redundancy is added.

18. A system according to claim 10, wherein the amount of redundancy to be added varies in accordance with the transmit data rate.

19. A method for spectrally shaping transmitted samples having a predetermined set of frequency characteristics and a predetermined set of allowable transmitted signal levels, wherein N transmitted samples form a block of transmitted samples, comprising the steps of:

a) selecting the amplitudes of signal levels in a block based upon user data;

b) selecting an M-element subset of the 2^N possible sign combinations based upon user data;

c) computing an objective function for each of the M sign combinations by applying the signs to the amplitudes of the transmitted signal levels, wherein said objective function shapes the transmitted samples to a predetermined spectrum characterized by a set of filter coefficients associated with a transmitter of said transmitted samples;

d) selecting the sign combination that best optimizes the objective function, wherein the M element sign combinations differ in more than one sign bit;

e) transmitting the signal points using the selected sign combination.

20. The method of claim 19, wherein the 2^N sign combinations are partitioned into M-element subsets in such a way as to maximize the Hamming distance between elements in the subsets, considering the signs as 0'"'"'s and 1'"'"'s of a binary codeword.

21. The method of claim 19, wherein M is a power of 2.

22. The method of claim 19, wherein N=2, 3, or 6, and M=2^N−

1.