Increasing performance in modems in presence of noise

• US 20020150154A1
• Filed: 09/12/2001
• Published: 10/17/2002
• Est. Priority Date: 04/17/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Warke, Nirmal
• Granted Patent: US 6,965,638 B2
• Time in Patent Office: Days
• US Class Current: 375/222
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

Method and apparatus for improving receive path performance in digital communication modems and total system bandwidth utilization by setting parameters of various signal processing components within said modems with consideration given to the effect on the overall communications channel characteristics of each of the signal processing components. The parameters of various signal processing components include filter type, filter order, corner frequency, equalizer slope, equalizer coefficients, and combinations thereof.

Claims

1. A method of training a modem for optimal receive channel performance, the method comprising:

A. selecting a combination of modem parameters;

B. determining channel capacity based on the combination of modem parameters;

C. repeating A and B for other combinations of modem parameters; and

D. selecting a specific combination of modem parameters providing a highest channel capacity.

2. The method of claim 1, wherein the repeating comprises repeating A and B for all other combinations of modem parameters.

3. The method of claim 1, the method further comprising estimating a first received signal power and noise floor estimate before the selecting the combination of modem parameters,

wherein the selecting a combination of modem parameters comprises determining an initial set of modem parameters based on the estimated signal and noise powers, and

wherein the repeating comprises repeating A and B for remaining combinations of modem parameters which differ from the original set of modem parameters by less than a specified threshold.

4. The method of claim 1, wherein the determining channel capacity comprises:

determining channel signal-to-noise ratio (SNR); and

calculating the channel capacity using the channel SNR.

5. The method of claim 1, wherein the determining channel capacity comprises:

estimating channel response;

estimating channel noise;

estimating receive signal power;

calculating channel signal-to-noise ratio (SNR) using the estimated channel noise and the estimated receive signal power; and

calculating the channel capacity using the channel SNR.

6. The method of claim 1, further comprising calculating adaptive channel equalizer coefficients.

7. The method of claim 1, wherein the modem parameters are selected from the group consisting of:

filter type, filter order, corner frequency, equalizer slope, equalizer coefficients, and combinations thereof.

8. The method of claim 5, wherein the estimating channel noise comprises:

estimating inter-symbol interference spectral power;

estimating a receive noise floor with a set of calculated adaptive channel equalizer coefficients; and

adding the estimated inter-symbol interference spectral power to the receive noise floor estimate, producing a total channel noise estimate.

9. The method of claim 5, wherein the calculating channel SNR is performed for each subchannel within an operating frequency band.

10. The method of claim 5, wherein the calculating channel SNR is performed by dividing the estimated receive signal power by the channel noise estimate.

11. The method of claim 5, wherein the calculating channel capacity is performed by summing the Log₂(1+channel SNR) for each subchannel within an operating frequency band.

12. The method of claim 5, wherein the estimating channel response is performed with an adaptive channel equalizer set to perform no equalization.

14. The apparatus of claim 13, wherein the compute unit comprises:

a first adder, having a first input coupled to the receive noise floor estimator and a second input coupled to the inter-symbol interference estimator and an output coupled to a divider, adapted to adding the two inputs;

the divider, having a first input coupled to the receive signal power estimator and a second input coupled to the first adder and an output coupled to a second adder, adapted to dividing the output of the receive signal power calculator with the output of first adder;

the second adder, having a first input coupled to the divider and a second input coupled to a constant value of 1.0 and an output coupled to a logarithm calculator, adapted to adding the two inputs;

the logarithm calculator, having an input coupled to the second adder and an output coupled to an accumulator, adapted to calculating the logarithm of the input; and

the accumulator, having a first input coupled to the logarithm calculator and an output coupled to the memory, adapted to summing the input.

15. The apparatus of claim 13, wherein the estimator unit comprises:

a modem parameter selector, coupled to the memory, adapted to selecting a combination of modem parameters from a set of modem parameters;

a channel response estimator adapted to calculating the receive path'"'"'s channel response, having an input coupled to the data input and an output coupled to an adaptive channel equalizer coefficients calculator and the output coupled to an inter-symbol interference estimator;

a receive noise floor estimator, having an input coupled to the data input and an output coupled to adaptive channel equalizer coefficients calculator and the output coupled to a compute unit, adapted to calculating the receive path'"'"'s total noise floor;

the adaptive channel equalizer coefficients calculator, having an input coupled to the channel response estimator and a second input coupled to the receive noise floor estimator and an output coupled to the memory, adapted to calculating a set of adaptive channel equalizer coefficients;

a receive signal power estimator, having an input coupled to the data input and an output coupled to the compute unit, adapted to calculating the signal power of the digital bitstream from the data input; and

an inter-symbol interference estimator, having an input coupled to the data input and an output coupled to the compute unit, adapted to calculating inter-symbol interference spectral power in the digital bitstream from the data input.

16. An apparatus of claim 15, wherein the adaptive channel equalizer coefficients calculator has an input coupled to the data input and the output coupled to the memory.

17. An apparatus of claim 15, wherein the inter-symbol interference estimator has an input coupled to the channel response estimator and a second input coupled to the adaptive channel equalizer coefficients calculator and the output coupled to the compute unit.

18. An apparatus of claim 15, wherein the modem parameters are selected from the group consisting of:

filter type, filter order, corner frequency, equalizer slope, equalizer coefficients, and combinations thereof.

20. The digital communications system of claim 19, wherein the compute unit comprises:

a first adder, having a first input coupled to the receive noise floor estimator and a second input coupled to the inter-symbol interference estimator and an output coupled to a divider, adapted to adding the two inputs;

the divider, having a first input coupled to the receive signal power estimator and a second input coupled to the first adder and an output coupled to a second adder, adapted to dividing the output of the receive signal power calculator with the output of first adder;

the second adder, having a first input coupled to the divider and a second input coupled to a constant value of 1.0 and an output coupled to a logarithm calculator, adapted to adding the two inputs;

the logarithm calculator, having an input coupled to the second adder and an output coupled to an accumulator, adapted to calculating the logarithm of the input; and

the accumulator, having a first input coupled to the logarithm calculator and an output coupled to the memory, adapted to summing the input.

21. The apparatus of claim 19, wherein the estimator unit comprises:

a modem parameter selector, coupled to the memory, adapted to selecting a combination of modem parameters from a set of modem parameters;

a channel response estimator adapted to calculating the receive path'"'"'s channel response, having an input coupled to the data input and an output coupled to an adaptive channel equalizer coefficients calculator and the output coupled to an inter-symbol interference estimator;

a receive noise floor estimator, having an input coupled to the data input and an output coupled to adaptive channel equalizer coefficients calculator and the output coupled to a compute unit, adapted to calculating the receive path'"'"'s total noise floor;

the adaptive channel equalizer coefficients calculator, having an input coupled to the channel response estimator and a second input coupled to the receive noise floor estimator and an output coupled to the memory, adapted to calculating a set of adaptive channel equalizer coefficients;

a receive signal power estimator, having an input coupled to the data input and an output coupled to the compute unit, adapted to calculating the signal power of the digital bitstream from the data input; and

an inter-symbol interference estimator, having an input coupled to the data input and an output coupled to the compute unit, adapted to calculating inter-symbol interference spectral power in the digital bitstream from the data input.

22. An apparatus of claim 21, wherein the adaptive channel equalizer coefficients calculator has an input coupled to the data input and the output coupled to the memory.

23. An apparatus of claim 21, wherein the inter-symbol interference estimator has an input coupled to the channel response estimator and a second input coupled to the adaptive channel equalizer coefficients calculator and the output coupled to the compute unit.

24. An apparatus of claim 21, wherein the modem parameters are selected from the group consisting of:

filter type, filter order, corner frequency, equalizer slope, equalizer coefficients, and combinations thereof.

13. An apparatus for increasing receive path performance in the presence of noise, comprising:

a data input, adapted to providing a digital bitstream;

a memory, adapted to storing digital data;

an estimator unit, having a first input coupled to the memory and a second input coupled to the data input, and an output coupled to a compute unit, the estimator unit is adapted to providing estimates of signal power, channel noise and channel response; and

the compute unit, having an input coupled to the estimator unit and the compute unit having an output coupled to the memory, adapted to computing a channel capacity based on a selected combination of modem parameters.

19. A digital communications system with a built-in apparatus for improving receive path performance in the presence of noise, comprising:

an analog input, adapted to providing an analog datastream;

a hardware receive filter, having an input coupled to the analog input and an output coupled to a hardware equalizer, adapted to filtering the analog datastream and rejecting signals lying outside a frequency spectrum of interest;

the hardware equalizer, having an input coupled to the hardware receive filter and an output coupled to an analog-to-digital converter, adapted to making the channel response of a communications channel flat as function of frequency;

the analog-to-digital converter, having an input coupled to the hardware equalizer and an output coupled to a software receive filter, adapted to digitizing the analog datastream into a digital bitstream;

the software receive filter, having an input coupled to the analog-todigital converter and an output coupled to an adaptive channel equalizer, adapted to further filter desired data signal from undesired noise;

the adaptive channel equalizer, having an input coupled to the software receive filter and an output coupled to a baseband processor, adapted to equalizing the channel response of a communications channel;

the baseband processor, having an input coupled to the adaptive channel equalizer and an output coupled to a digital device, adapted to demodulating and error detection and correction on the digital bitstream;

the apparatus, having a data input coupled to the adaptive channel equalizer and an output coupled to the hardware receive filter and the hardware equalizer and the software receive filter and the adaptive channel equalizer, adapted to optimally setting the signal processing modem parameters for improving the receive path performance, wherein the apparatus further comprising;

a memory, adapted to storing digital data;

an estimator unit, having a first input coupled to the memory and a second input coupled to the data input, and an output coupled to a compute unit, the estimator unit is adapted to providing estimates of signal power, channel noise and channel response; and

the compute unit, having an input coupled the estimator unit and the compute unit having an output coupled to the memory, adapted to computing a channel capacity based the selected combination of modem parameters.