Increasing performance in modems in presence of noise

• US 6,965,638 B2
• Filed: 09/12/2001
• Issued: 11/15/2005
• Est. Priority Date: 04/17/2001
• Status: Active Grant

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Warke, Nirmal
• Primary Examiner(s): Burd, Kevin
• Assistant Examiner(s): TORRES, JUAN A
• Application Number:
  US09/953,040
• Publication Number:
  US 20020150154A1
• Time in Patent Office: 1,525 Days
• Field of Search: 375/222
• US Class Current: 375/222
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A digital communications system with a built-in apparatus for improving receive path performance in the presence of noise. An analog datastream is provided to a hardware receive filter that rejects signals lying outside a frequency spectrum of interest, while a hardware equalizer flattens the channel response. An analog-to-digital converter digitizes the filtered and equalized analog datastream into a digital bitstream, which is then filtered, further channel-equalized and demodulated. The system also includes a memory, an estimator unit, having a first input coupled to the memory and a second input coupled to a 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. The compute unit, has an input coupled the estimator unit and an output coupled to the memory, and is adapted to computing a channel capacity based the selected combination of modem parameters.

Claims

1. 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-to-digital 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.

2. The digital communications system of claim 1, wherein the compute unit comprises:

a first adder, having a first input coupled to a receive noise floor estimator and a second input coupled to an 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.

3. The apparatus of claim 1, 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.

4. An apparatus of claim 3, wherein the adaptive channel equalizer coefficients calculator has an input coupled to the data input and the output coupled to the memory.

5. An apparatus of claim 3, 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.

6. An apparatus of claim 3, wherein the modem parameters are selected from the group consisting of:

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