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

• US 5,970,100 A
• Filed: 03/25/1998
• Issued: 10/19/1999
• 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:
  US09/047,802
• Time in Patent Office: 573 Days
• Field of Search: 375/253, 375/254, 375/222, 375/242, 375/285, 375/295, 375/296, 341/55, 341/59, 379/93.01
• US Class Current: 375/296
• CPC Class Codes: H04L 25/4927 using levels matched to the quantisation levels of the channel

Abstract

Methods and apparatus are disclosed for shaping and controlling the spectrum of transmitted samples with a set of predetermined frequency characteristics and a predetermined set of allowable transmitted signal levels are disclosed. In particular, methods of minimizing the energy of the signal at unwanted frequencies are described. For each of the transmitted samples, the system computes a running measure of unwanted components. It then computes, for each block (or "data frame") of the transmitted samples, an objective function, for example, a running filter sum based upon a biquad filter function. It then selects, for each block or spectral shaping frame of transmitted samples, a sign combination from a sign-combination subset such that the objective function is optimized.

Claims

1. A method of spectrally shaping transmitted samples with a set of predetermined frequency characteristics and a predetermined set of allowable transmitted signal levels, wherein a transmitted sample is either of an unmodified source sample or a dependent sample, the transmitted samples being transmitted in data frames, said method comprising the steps of:

(a) calculating, for each of the transmitted samples, a Running Filter Sum of unwanted components up to the current sample, wherein said Running Filter Sum is based on a biquad filter;

(b) computing an objective function in accordance with the Running Filter Sum obtained in Step (a);

(c) selecting, for each data frame of transmitted samples, at least one redundant sample to be added or modified within the data frame such that the objective function of Step (b) is optimized.

2. The method of claim 1, wherein said step of selecting comprises selecting redundant signs to optimize the objective function.

3. The method of claim 1, wherein the transmitted samples are transmitted via a communication channel, and wherein said method further comprises the step of varying the number of redundant signs in accordance with communication channel conditions.

4. The method of claim 1, wherein the transmitted samples are transmitted at a transmit data rate, and wherein said method further comprises the step of varying the number of redundant signs in accordance with the transmit data rate.

5. The method of claim 4, wherein said varying step comprises varying the number of redundant signs such that the redundancy is lowest at a high transmit data rate and highest at a low transmit data rate.

6. The method of claim 1, wherein the transmitted samples are transmitted to a receiver via a communication channel, and wherein the number of redundant signs is determined by the receiver and sent to the transmitter during a start-up sequence.

7. The method of claim 1, wherein the transmitted samples are transmitted to a receiver via a communication channel, and wherein the number of redundant signs is determined by the receiver and sent to the transmitter during a rate renegotiation sequence.

8. A method of spectrally shaping source samples to transmitted samples based on a set of predetermined characteristics of a frequency spectrum, wherein the allowable signal levels of the transmitted samples are limited to a prescribed set, and wherein the source samples are partitioned into data frames, said method comprising the steps of:

(a) calculating, for a current data frame and a predetermined number of additional data frames, a Running Filter Sum of unwanted signal levels, wherein said Running Filter Sum is based on a biquad filter;

(b) computing an objective function in accordance with the Running Filter Sum obtained in Step (a); and

(c) selecting, for the current data frame of source samples, at least one redundant sign for optimization of the objective function computed in Step (b).

9. The method of claim 8, wherein said predetermined number of additional data frames comprises ld look-ahead frames, wherein ld is an integer between zero and three inclusive.

10. The method of claim 8, wherein the transmitted samples are transmitted via a communication channel, and wherein said method further comprises the step of varying the number of redundant signs in accordance with communication channel conditions.

11. The method of claim 8, wherein the transmitted samples are transmitted at a transmit data rate, and wherein said method further comprises the step of varying the number of redundant signs in accordance with the transmit data rate.

12. The method of claim 11, wherein said varying step comprises varying the number of redundant signs such that the redundancy is lowest at a high transmit data rate and highest at a low transmit data rate.

13. The method of claim 8, wherein the samples are transmitted by a transmitter to a receiver via a communication channel, and wherein the number of redundant signs is determined by the receiver and sent to the transmitter during a training sequence.

14. The method of claim 8, wherein the samples are transmitted by a transmitter to a receiver via a communication channel, and wherein the number of redundant signs is determined by the receiver and sent to the transmitter during a rate-renegotiation sequence.

15. The method of claim 8, wherein the objective function is computed based upon the sum of the squares of the output of the Running Filter Sum obtained in Step (a).

16. The method of claim 8, wherein the objective function is characterized by a filter function, F(z), given by:

##EQU23## wherein;

T(z) is the spectral shape filter transfer function; and

a₁, a₂, b₁, and b₂ are filter parameters having absolute values less than or equal to 1.

17. The method of claim 16, wherein the nth sample has a value x(n), and wherein the step of computing the objective function comprises the steps of:

(a) computing a value, y(n), for the nth sample, as;

space="preserve" listing-type="equation">y(n)=x(n)-b.sub.1 x(n-1)+a.sub.1 y(n-1);

(b) computing a value, v(n), for the nth sample, as;

space="preserve" listing-type="equation">v(n)=y(n)-b.sub.2 y(n-1)+a.sub.2 v(n-1);

(b) computing the objective function, w(n), as;

space="preserve" listing-type="equation">w(n)=v.sup.2 (n)+w(n-1).

18. The method of claim 16, wherein a transmitter is used to transmit the samples to a receiver, and wherein the filter parameters a₁, a₂, b₁, and b₂ are determined by the receiver and sent to the transmitter during a start-up sequence.

19. The method of claim 16, wherein a transmitter is used to transmit the samples to a receiver, and wherein the filter parameters a₁, a₂, b₁, and b₂ are determined by the receiver and sent to the transmitter during a rate-renegotiation sequence.

20. A system for controlling and shaping transmitted data samples having predetermined frequency characteristics and allowable transmit signal levels, wherein the transmitted samples are partitioned into data frames, said system comprising:

a microprocessor configured to;

(a) calculate, for a current data frame and a predetermined number of additional data frames, a Running Filter Sum to obtain a measure of unwanted signal components of source samples up to at least the current block, wherein said Running Filter Sum is based on a biquad filter;

(b) compute an objective function based on the Running Filter Sum;

(c) select, for the current data frame of source samples, at least one redundant sign to optimize the objective function; and

a semiconductor memory device for storing and enabling the microprocessor to access the Running Filter Sum, the objective function, and the redundant sample.

21. The system of claim 20, wherein:

the microprocessor is further configured to transmit the samples to a receiver over a communication channel; and

the biquad filter is characterized by a set of filter parameters chosen in accordance with the communication channel conditions.

22. The system of claim 21, wherein the microprocessor is further configured to receive filter parameters sent by the receiver during a start-up sequence.

23. The system of claim 21, wherein the microprocessor is further configured to receive filter parameters sent by the receiver during a rate-renegotiation sequence.

24. The system of claim 21, wherein the microprocessor is further configured to receive, during a start-up sequence, the number of redundant signs.

25. The system of claim 21, wherein the microprocessor is further configured to receive, during a rate-renegotiation sequence, the number of redundant signs.

26. A method of spectrally shaping transmitted samples with a set of predetermined frequency characteristics and a predetermined set of allowable transmitted signal levels, wherein each of said transmitted samples comprises an amplitude and a sign, and wherein said transmitted samples are transmitted in data frames corresponding to groups of input data bits, and wherein each of said data frames is divided into at least one spectral shaping frame, said method comprising the steps of:

(a) partitioning each of said groups of input data bits into;

a first subgroup used to select the amplitudes of said transmitted samples in said data frame; and

a second subgroup used to select a sign-combination subset for each of said spectral shaping frames in said data frame, wherein said sign-combination subsets comprise sign combinations which differ from each other by more than one sign bit;

(b) calculating, for each of said transmitted samples, a Running Filter Sum of unwanted components up to at least the current spectral shaping frame for at least two of said sign combinations in said sign-combination subset, wherein said Running Filter Sum is based on a biquad filter;

(c) computing an objective function in accordance with said Running Filter Sum obtained in step (b);

(d) selecting, for each of said spectral shaping frames of transmitted samples, a sign combination from said sign-combination subset such that said objective function of step (c) is optimized.

27. The method of claim 26, wherein each of said sign-combination subsets comprises two sign combinations.

28. The method of claim 26, wherein said data frame comprises six transmitted samples, and wherein each of said spectral shaping frames comprises 2, 3, or 6 transmitted samples.

29. The method of claim 26, wherein said sign combinations in said sign-combination subsets are chosen so as to maximize the Hamming distance between sign combinations in the subsets, considering the signs as 0'"'"'s and 1'"'"'s of a binary codeword.

30. The method of claim 26, wherein said transmitted samples are transmitted via a communication channel, further comprising the step of varying a level of redundancy used for spectral shaping in accordance with communication channel conditions.

31. The method of claim 26, wherein said transmitted samples are transmitted at a transmit data rate, further comprising the step of varying a level of redundancy used for spectral shaping in accordance with the transmit data rate.

32. The method of claim 31, wherein said step of varying is performed such that said redundancy is lowest at a high transmit data rate and highest at a low transmit data rate.

33. The method of claim 26, wherein said transmitted samples are transmitted to a receiver by a transmitter via a communication channel, and wherein a level of redundancy used for spectral shaping is determined by said receiver and sent to said transmitter during a start-up sequence.

34. The method of claim 26, wherein said transmitted samples are transmitted to a receiver by a transmitter via a communication channel, and wherein a level of redundancy used for spectral shaping is determined by said receiver and sent to said transmitter during a rate renegotiation sequence.

35. The method of claim 26, wherein said transmitted samples are transmitted to a receiver by a transmitter via a communication channel, and wherein said biquad filter is characterized by a set of filter parameters determined by said receiver and sent to said transmitter during a start-up sequence.

36. The method of claim 26, wherein said transmitted samples are transmitted to a receiver by a transmitter via a communication channel, and wherein said biquad filter is characterized by a set of filter parameters determined by said receiver and sent to said transmitter during a rate-renegotiation sequence.