Multi-carrier LAN adapter device using interpolative equalizer

• US 6,891,887 B1
• Filed: 06/20/2001
• Issued: 05/10/2005
• Est. Priority Date: 05/27/1998
• Status: Expired due to Fees

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Dobson, William Kurt
• Primary Examiner(s): Ha, Dac V.
• Application Number:
  US09/885,220
• Time in Patent Office: 1,420 Days
• Field of Search: 575/219, 575/220, 575/222, 575/229, 575/257, 575/258, 455/509, 455/517, 370/465, 370/468
• US Class Current: 375/220
• CPC Class Codes: H04L 25/022 of frequency response
• CPC Class Codes: H04L 25/0232 by interpolation between sounding signals
• CPC Class Codes: H04L 25/03159 operating in the frequency domain H04L25/03165, H04L25/03178 take precedence
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01

Abstract

A LAN adapter device using an interpolative equalizer. The LAN adapter device allows LAN computing devices to connect to the LAN medium. The adapter devices are internal or external to the LAN devices and provide a transceiver and protocol stacks for the LAN devices to communicate with each other. The physical layer of the transceivers includes transmitter having a DMT modulator and demodulator that is dynamically configurable with respect to data rate and spectrum usage. Within the receiver is an equalizer that equalizes the received signal with a simple yet effective equalizer training method, thereby obviating the need for extensive equalizer training and long-term coefficient storage. The equalizer trains on known symbols transmitted on specific carriers that arc spaced apart in the frequency domain and then determines the channel response at those frequencies. The remaining carriers that are modulated with data are equalized based on an estimate of the channel response determined from interpolating between the points previously determined from the known symbols.

Claims

1. A system for interconnecting a plurality of computing devices comprising:

a shared communication medium;

a plurality of transceivers having a first and second port, the first port for connection to one of a plurality of computing devices and the second port for connection to said shared communication medium, each of said plurality of transceivers further comprising a transmitter and a receiver for transmitting and receiving time domain signals representing data, said time domain signals comprising a plurality of modulated carriers of predetermined frequency, over said shared communication medium to at least any one of other said plurality of transceivers;

said receiver having a signal transformer for generating a frequency domain signal from the received time domain signal, and a frequency domain equalizer for operating on said frequency domain signal, said frequency domain equalizer comprising a single tap filter for each carrier of said plurality of modulated carriers received by said receiver;

said transmitter transmitting at least one known symbol on at least two non-adjacent carriers and transmitting data symbols on carriers between said at least two non-adjacent carriers, and wherein said frequency domain equalizer generates filter taps for said each carrier in response to said at least one known symbol on said at least two non-adjacent carriers.

2. The system of claim 1 wherein said transmitter transmits said at least one known symbol on every N^th carrier, where N is any integer greater than 1.

3. The system of claim 1 wherein said frequency domain equalizer generates said filter taps by interpolating points between the received said at least one known symbol.

4. The system of claim 1 wherein said frequency domain equalizer updates said filter taps by calculating averages of said at least one known symbol for each of said at least two non-adjacent carriers and interpolating points between said averages.

5. The system of claim 4 wherein said at least two non-adjacent carriers are equally spaced among said plurality of modulated carriers.

6. The system of claim 1 wherein said transmitter does not transmit energy in a Plain Old Telephone Service (POTS) frequency range.

7. The system of claim 1 wherein each of said plurality of transceiver selectively transmits on fewer than all of said plurality of predetermined frequencies.

8. A network adapter device for connecting a computing device to a shared electrical signaling medium comprising:

a first physical interface for connection to a computing device;

a second physical interface for connection to a shared electrical signaling medium; and

a transceiver connected to the first and second physical interfaces for transmitting and receiving data on said first physical interface and transmitting and receiving modulated multi-carrier data bursts over said second physical interface, wherein each of said modulated multi-carrier data bursts comprises a plurality of frames, said transceiver including a signal transformer for converting received time domain signals to frequency domain signals, and a frequency domain equalizer connected to said signal transformer for processing said frequency domain signals, said frequency domain equalizer comprising a single tap filter for each carrier of said modulated multi-carrier data bursts received by said transceiver;

wherein said frequency domain equalizer generates said equalizer taps for each carrier by interpolating a channel response from received known symbols.

9. The network adapter device of claim 8 wherein said first physical interface is a standard computer internal bus interface.

10. The network adapter device of claim 8 wherein said first physical interface is a standard external bus interface.

11. The network adapter device of claim 8 wherein said equalizer taps are updated ay averaging received known symbols and re-interpolating a channel impulse response.

12. The network adapter device of claim 8 wherein said signal transformer performs a discrete Fourier transform.

13. The network adapter device of claim 8 wherein said transceiver operates in a frequency range above a frequency range of a Plain Old Telephone Service (POTS).

14. The network adapter device of claim 8 wherein said transceiver utilizes a plurality of predetermined carrier frequencies and selectively transmits on less than all of said plurality of predetermined carrier frequencies.

15. A method of transferring data among a plurality of computing devices connected to a shared communication medium comprising the steps of:

receiving data from a computing device;

mapping the data to a plurality of sets of signal points where each signal point is assigned a carrier, and including predetermined signal points assigned to predetermined carriers in at least one set where the signal points are spaced at an interval of every N^th carrier, wherein N is an integer greater than 1;

transforming each signal point set to a time domain signal;

transmitting the time domain signals to a plurality of computing devices over a shared communication medium;

receiving the time domain signals from the shared communication medium;

converting the time domain signals to frequency domain signals;

interpolating equalizer filter taps based on the predetermined signal points; and

filtering said frequency domain signals using the interpolated equalizer filter taps.

16. The method of claim 15 where the step of transforming includes performing a frequency domain to time domain transform.

17. The method of claim 15 wherein the interval of every N^th carrier is an integer selected from 2, 4, 6, and 8.

18. The method of claim 15 further comprising the step of updating the equalizer after every frame using the most recently received set of signal points.

19. The method of claim 15 wherein the shared communication medium is standard Plain Old Telephone Service (POTS) wiring.

20. The method of claim 15 wherein the predetermined signal points are assigned to predetermined carriers in every frame.