xDSL DMT modem using sub-channel selection to achieve scaleable data rate based on available signal processing resources

• US 6,092,122 A
• Filed: 06/30/1997
• Issued: 07/18/2000
• Est. Priority Date: 06/30/1997
• Status: Expired due to Term

• Current Assignee: Realtek Semiconductor Corp.
• Original Assignee: Integrated Telecom Express, Inc.
• Inventors: Chen, Steve, Liu, Ming-Kang, Liu, Young Way
• Primary Examiner(s): Asta, Frank J.
• Assistant Examiner(s): VU, THONG H
• Application Number:
  US08/884,979
• Time in Patent Office: 1,114 Days
• Field of Search: 379/93.14, 379/399, 395/200.63, 341/118, 375/219, 375/377, 375/233, 375/522, 370/281, 370/522, 348/6, 709/227, 709/223, 709/225, 709/233
• US Class Current: 709/227
• CPC Class Codes: G06F 15/163 Interprocessor communication
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

A high speed modem is provided which uses a selectable, desirable portion of the total available bandwidth of a transmission channel. In a preferred embodiment, the invention is incorporated in a dedicated hardware circuit which is connected on one end to a data processor and on the other end to an upstream transceiver through a channel supporting an Asymmetric Digital Subscriber Loop (ADSL) standard. The achievable target data rate of the modem is based on the capabilities of an analog front end (AFE) used in the modem, and a signal processor within the dedicated hardware. In particular, the modem AFE contains subband filtering which causes an upstream transceiver to use only a selected number of available sub-channels for downstream data transmission. The data rate of the modem is increased by upgrading the AFE or the signal processor in order to increase the number of processable transmitted downstream sub-channels.

Claims

1. A high speed communications system for receiving transmitted data from a remote transceiver, which transceiver is capable of transmitting an analog signal using up to M separate subchannels within a bandwidth F through a channel to said system, said system being configured to operate within a personal computer system including a host processing device for executing user application programs, said system comprising:

a channel interface circuit for coupling to and receiving said analog signal from the channel; and

a front end receiving circuit for sampling the analog signal and generating a digital signal based on such analog signal;

a digital signal processing circuit for processing the digital signal, said digital signal processing circuit being implemented at least in part by signal processing software executed by the host processing device, the digital signal including data from a first frequency bandwidth portion f1 of said bandwidth F containing N separate subchannels, which N separate sub-channels are a subset of said M separate subchannels; and

a bus interface circuit for transmitting said digital signal to the host processing device through a data bus associated with said personal computer system so that said signal processing software can also process such digital signal; and

wherein the transmitted data is extracted based on an evaluation by the digital signal processing circuit of performance characteristics of said data carrying signals; and

further wherein said system supports a maximum number of said N separate sub-channels, which maximum number is based on transmission characteristics of said channel, signal processing power of said host processing device, and loading conditions experienced by said host processing device.

2. The system of claim 1, wherein a sampling rate required by the front end circuit to generate the digital signal from the N sub-channels is reduced by an integer factor k from that required to generate a digital signal from the M sub-channels, and where k=M/N.

3. The system of claim 2, wherein the N subchannels can be selected during an initialization process setting up a data link to the remote transceiver, from a set of M/k sub-channels.

4. The system of claim 1, wherein an additional number of data carrying signals P from the M data carrying signals (N+P<

M) can be processed if transmission characteristics of said channel, signal processing power of said host processing device, and loading conditions experienced by said host processing device permit such processing.

5. The system of claim 4, further including one or more anti-aliasing filters for passing the N+P subchannels and an analog to digital converter.

6. The system of claim 1, wherein the front end receiving circuit includes:

(I) a bandpass filter for passing the first frequency bandwidth portion f1 of said bandwidth F;

(ii) and an analog to digital converter; and

wherein the digital signal processing circuit also includes a digital signal processor coupled to a programmable memory.

7. The system of claim 1, wherein a data received rate of the system can be increased by modularly augmenting either or both of:

(i) the front end receiving circuit to include additional bandwidth and analog to digital conversion capacity;

(ii) the digital signal processing circuit, such that an additional number of subchannels P from the M subchannels (N+P<

M) can be processed.

8. The system of claim 7, wherein the front end receiving circuit has a programmable frequency response.

9. The system of claim 1, further including a front end transmitting circuit for transmitting control information to cause said remote transceiver to transmit downstream data only using the N sub-channels, so that selection of said N sub-channels, and control of a data rate in the channel, is controlled by the system, and not the remote transceiver.

10. The system of claim 9, wherein the control information transmitted to the remote transceiver includes feedback information from the digital signal processing circuit indicating that only N of the M sub-channels are to be loaded with data for data transmission, even if said channel is capable of supporting more than N sub-channels.

11. The system of claim 10, wherein the control information transmitted to the remote transceiver further includes feedback information indicating that:

(i) the system and remote transceiver have compatible transmission signal protocol characteristics; and

(ii) that they are connected through a channel having substantial signal attenuation characteristics for sub-channels other than the N sub-channels.

12. The system of claim 1, further including a front end transmitting circuit for transmitting a data transmission to the remote transceiver using a second frequency bandwidth F2 different from F, and L sub-channels.

13. A high speed communications system for receiving selected data contained in N Discrete Multi-Tone (DMT) modulated sub-channels from a remote transceiver capable of transmitting an analog signal containing up to M DMT modulated sub-channels through a channel to said system, said system comprising:

a channel interface circuit for coupling to and receiving said analog signal from the channel;

an analog front end circuit for sampling the analog signal and converting it to a digital signal, the front end circuit including an anti-aliasing filter and an analog to digital converter;

a digital signal processing circuit for extracting said selected data by demodulating sub-channels in said digital signal, said demodulating being performed by signal processing software executing on a host processing device the digital signal including data only from said N DMT sub-channels, where N is a subset of the M DMT modulated sub-channels, such that N<

=M;

an interface circuit for coupling said analog front end circuit to a data bus within a personal computer system associated with said host processing device so that said demodulating of said digital signal can be performed by said signal processing software; and

wherein said system supports a maximum number of said N separate DMT sub-channels, which maximum number is based on transmission characteristics of said channel, signal processing power of said host processing device, and loading conditions experienced by said host processing device.

14. The system of claim 13, wherein a sampling rate required by the analog front end circuit to generate the digital signal from the N sub-channels is reduced by an integer factor k from that required to generate a digital signal from the M sub-channels, and where k=M/N.

15. The system of claim 14, wherein the N sub-channels can be selected during an initialization process setting up a data link to the remote transceiver.

16. The system of claim 13, wherein the selected data can be altered to further include data obtained from an additional second number of sub-channels P taken from the set of M subchannels, so that an additional number of sub-channels (N+P<

M) can be demodulated if transmission characteristics of said channel, signal processing power of said host processing device, and loading conditions experienced by said host processing device permit processing of said additional second number of subchannels P.

17. The system of claim 16, further including one or more anti-aliasing filters for passing the first number N and second number P of said sub-channels.

18. The system of claim 13, wherein the front end receiving circuit includes:

(i) a bandpass filter for passing the N sub-channels; and

(ii) and an analog to digital converter; and

wherein the digital signal processing circuit further includes a digital signal processor coupled to a programmable memory.

19. The system of claim 13, wherein a data received rate of the system can be increased by modularly augmenting either or both of:

(i) the front end circuit to include additional bandwidth and analog to digital conversion capacity;

(ii) the digital signal processing circuit, such that an additional second number of sub-channels P taken from the M sub-channels (N+P<

M) can be demodulated when said host processing device is upgraded to have a signal processing performance sufficient to process said additional second number of subchannels P.

20. The system of claim 19, wherein the front end receiving circuit has a programmable frequency response.

21. The system of claim 13, further including a front end transmitting circuit for transmitting control information to cause said upstream transceiver to transmit downstream data only using the N sub-channels, such that selection of said N subchannels, and control of a data rate in the channel, is controlled by the system, and not the remote transceiver.

22. The system of claim 21, wherein the control information transmitted to the remote transceiver includes feedback information indicating that only N of the M sub-channels are to be loaded with data for downstream data transmission, even during times when said channel is capable of supporting more than N sub-channels.

23. The system of claim 22, wherein the control information transmitted to the remote transceiver further includes feedback information indicating that:

(i) the system and transceiver have compatible transmission signal protocol characteristics; and

(ii) that the system and remote transceiver are connected through a channel with substantial signal attenuation characteristics for sub-channels other than the N sub-channels.

24. The system of claim 13, wherein the channel supports T1.413 asymmetric digital subscriber loop (ADSL) transmission standards.

25. The system of claim 13, further including a front end transmitting circuit for transmitting data transmission to the remote transceiver using a second set of modulated sub-channels L separate from the M sub-channels, and where L<

M.

26. A high speed T.413 capable communications data receiver for receiving data through a channel at a first data rate X from a remote T1.413 capable transmitter, which remote transmitter is capable of transmitting an analog signal carrying a data stream at a rate Y, where Y is a rate achievable by a full rate T1.413 capable transmitter, and Y>

X, the receiver comprising;

a channel interface circuit for coupling to and receiving said data stream;

an analog front end circuit for data sampling the analog signal and converting it to a digital signal;

a processing circuit for extracting selected data from the digital signal, and for generating a transmission control signal for causing said remote transmitter to transmit at a data rate substantially equal to said data rate X during a data stream transmission, and using an initialization and transmission protocol in conformance with T1.413 ADSL transmission standards;

an interface circuit for coupling said analog front end circuit to said personal computer system data bus;

wherein data sampling circuitry requirements of the analog front end circuit and extracting circuitry requirements of the processing circuit reduced from that otherwise required to support data rate Y because data sampling and extracting is only performed for a fractional portion of the total data stream that can be transmitted by said remote transmitter; and

further wherein a maximum value of said data rate X achievable by said receiver is limited according to availability of signal processing resources to said processing circuit and transmission conditions of the channel.

27. The system of claim 26, wherein the analog front end circuit further includes anti-aliasing filter for filtering the analog signal to generate the fractional portion of the data stream that requires data sampling and extracting.

28. The system of claim 26, further including a front end transmitting circuit for transmitting the transmission control signal from the processing circuit to cause said remote transceiver to transmit downstream data only at said data rate X so that selection and control of said data rate X in the channel is controlled by the system, and not the remote transceiver.

29. The system of claim 26, further including a front end transmitting circuit for transmitting a data transmission to the remote transceiver using a transmit data rate intentionally constrained by the system to be less than a maximum receive rate of the remote transceiver.

30. The system of claim 26, wherein the ratio of X to Y is approximately 0.5 or less, and this ratio can be varied by allocating different amounts of signal processing resources to said processing circuit.

31. A high speed communications system for communicating data to a host processing device from a remote transceiver capable of transmitting M Discrete Multi-Tone (DMT) modulated subchannels embodied in an analog data transmission signal using up to a bandwidth F in a channel coupled to said system, said system comprising:

a channel interface circuit for coupling to and receiving said analog data signal from the channel; and

a front end receiving circuit for processing the analog data signal and converting it to a digital signal; and

a digital signal processing circuit for extracting selected data from the digital signal, the digital signal including data from a first frequency bandwidth portion f1 of said bandwidth F, and which data corresponds to a number N of said M DMT modulated subchannels, where N<

=M/k, and where k is an integer >

=2;

said digital signal processing circuit also generating feedback information indicating to the remote transceiver that the bandwidth other than f1 is unsuitable for data transmission even when said channel can support said bandwidth F, and for indicating to said remote transceiver that said system is a reduced rate but otherwise fully compliant T.1413 transceiver; and

a bus interface circuit for transmitting said selected data to the host processing device; and

wherein a maximum value of subchannels N supported by said system is limited according to availability of signal processing resources to said digital signal processing circuit and transmission conditions of the channel.

32. The system of claim 31, wherein the feedback information contains intentionally altered channel characteristic information.

33. The system of claim 32, wherein the feedback information, including the size and center of first frequency bandwidth portion f1, can be controlled by the host processing device, such that selection of said N subchannels, and control of a data rate in the channel, is controlled by the system, and not the remote transceiver.

34. The system of claim 33, wherein the ratio of f1 to F is approximately 0.5 or less, and this ratio can be increased through modular additions to the front end receiving circuit and/or to the processing circuit.

35. A method of operating a high speed communications system that is coupled through a channel to a remote transceiver, said transceiver capable of supporting an analog data transmission signal having up to a bandwidth F, said method comprising:

(a) configuring said system to achieve a data receive rate X; and

(b) receiving an analog initialization signal from the remote transceiver through the channel; and

(c) generating a digital signal based on a first frequency bandwidth portion f1 sufficient to meet data receive rate X; and

(d) transmitting said digital signal across a digital data bus to a host processing device which is located within a computer system incorporating the high speed communications system; and

(e) executing a signal processing routine using said host processing device so as to process the digital signal to extract information relating to characteristics of data carrying signals contained within first frequency bandwidth portion f1; and

(f) executing an initialization routine using said host processing device for generating feedback information indicating to the remote transceiver that bandwidth other than the first frequency bandwidth f1 should not be used for data transmission; and

(g) receiving an analog data transmission signal having a bandwidth f1 from said remote transceiver; and

(h) generating a digital data transmission signal based on sampling the analog data transmission signal; and

(i) repeating step (e) above for said digital data transmission signal, and for every other digital data transmission signal received thereafter by the system; and

wherein a maximum data receive rate is limited according to availability of signal processing resources to said host processing device and transmission conditions of the channel.

36. The method of claim 35, further including a step:

determining an optimal size and location of first frequency bandpass portion f1 in response to a determination of an amount of processing required to extract the data from the digital signal.

37. The method of claim 35, wherein the system transmits feedback information containing intentionally altered channel characteristic information.

38. The method of claim 35, wherein the analog data transmission is comprised of M separately modulated sub-channels, and the selected data is contained in a subset N of the M sub-channels, where N<

M.

39. The method of claim 38, further including a step:

determining an optimal set of said N sub-channels based on the channel characteristics and an amount of processing required to extract the data from the digital signal.

40. The method of claim 39, further including a step wherein protocol information pertaining to standards applicable to Asymmetric Digital Subscriber Loops is transmitted between the remote data transceiver and the system so as to set up a T1.413 compatible data link.

41. A software based modem for use in a personal computer system, comprising:

a channel interface circuit for coupling to and receiving an analog signal from the channel, said analog signal being comprised of N separately modulated sub-carriers; and

a front end receiving circuit for sampling the analog signal and generating a digital signal based on such analog signal, the digital signal including received data from said N separately modulated sub-carriers;

a bus interface coupled to said front end receiving circuit, and configured for transmitting said received data across a data bus within the personal computer system to a host processing device;

a software digital signal processing routine adapted for execution on the host processing device and for generating an extracted data stream by processing said received data, said software digital signal processing routine processing said received data at a rate related to a maximum amount of signal processing resources available to said software digital signal processing routine during a transmission session; and

wherein the software modem can achieve a receive data rate during said transmission session that exceeds 500 Kb/s in said channel when said maximum amount of signal processing resources are available to said host processing device and transmission conditions in the channel support such receive data rate.

42. The software modem of claim 41, further wherein said software digital signal processing routine performs data pump operations associated with extracting a data stream from an T1.413 modulated signal.

43. The software modem of claim 42, wherein said software digital signal processing routine also performs initialization operations associated with establishing a T1.413 compatible data link.

44. The software modem of claim 41, further wherein a maximum number of subchannels M are supportable in the channel, and said N subchannels are selected from a reduced set of said subchannels M, such that N<

=M/k, where k is an integer scaling factor.

45. The software modem of claim 41, further wherein said maximum amount of signal processing resources available to said software digital signal processing routine can be allocated by a user of said personal computer system.

46. A high speed system for communicating with an ANSI T1.413 compatible remote transceiver, which remote transceiver is capable of transmitting a first analog signal using up to M discrete multi-tone (DMT) modulated subchannels within an available bandwidth F through a channel to said system, said system comprising:

a digital processing circuit, said digital processing circuit being configured;

(i) for receiving a first digital signal from a channel interface circuit coupled to the remote transceiver, said first digital signal being derived from said first analog signal;

(ii) for extracting a data stream from the first digital signal, the first digital signal including data from N variable DMT modulated sub-channels located within a receive frequency bandwidth portion f1 of the bandwidth F, where N<

=M/k, and where k is an integer >

=1;

(iii) for setting up a data link with the ANSI T1.413 compatible remote transceiver which complies with T1.413 signal protocols;

wherein the system can set up a bi-directional data link with the ANSI T1.413 compatible remote transceiver, such that both a transmit and receive data rate in said bi-directional data link is configured by said system and not the ANSI T1.413 compatible remote transceiver; and

further wherein the bi-directional data link is intentionally constrained by the system to use less than the available transmit bandwidth F available to the remote transceiver.

47. The system of claim 46, further wherein M is >

200, k>

=2, and N can be varied between 1 and a value >

100 depending on processing characteristics of said digital processing circuit, loading on said digital processing circuit, and channel transmission conditions.

48. The system of claim 46, wherein said system operates as a full rate or reduced rate T1.413 compliant transceiver.

49. The system of claim 46, further wherein portions of said digital processing circuit are implemented by a software routine executed by a host processing device within a personal computer system.

50. The system of claim 49, further wherein said channel interface circuit is physically separated from said host processing device but electrically connected through a personal computer system bus.

51. A high speed system for communicating with a remote transceiver, which remote transceiver supports a T1.413 ADSL data link by transmitting a first analog signal using up to a number M discrete multi-tone (DMT) modulated subchannels within an available bandwidth F through a channel to said system, said high speed system comprising:

a channel interface circuit for receiving said analog signal from the channel; and

a front end receiving circuit coupled to said channel interface circuit, said front end circuit being adapted for;

(i) sampling the first analog signal; and

(ii) generating a first received digital signal based on such first analog signal; and

a digital signal processing circuit coupled to said front end receiving circuit, said digital signal processing circuit being configured;

(i) for extracting a data stream from the first digital signal, the first digital signal including data from N DMT subchannels located within a receive frequency bandwidth portion f1 of the bandwidth F (f1<

=F), where N is a variable subset of the M subchannels, and N can be configured by the high speed system to have a value between 1 and M; and

(ii) for signaling to said remote transceiver that the high speed system supports only a reduced data rate, said reduced data rate being only a fractional portion of that of a full rate T1.413 ADSL transceiver; and

(iii) for adjusting said reduced data rate depending on computational resources available to said digital signal processing circuit for extracting said data stream from said first digital signal and depending on signal transmission conditions in the channel.

52. The system of claim 51, further wherein M is >

200.

53. The system of claim 51, wherein said system operates as a full rate or reduced rate T1.413 compliant transceiver.

54. The system of claim 51, further wherein portions of said digital signal processing circuit are implemented by a software routine executed by a host processing device within a personal computer system.

55. The system of claim 54, further wherein said channel interface circuit and analog front end circuit are physically separated from said host processing device but electrically connected through a personal computer system bus.

56. A high speed system for maintaining a data link with an ANSI T1.413 compatible remote transceiver through a data channel, said system comprising:

a digital signal processing circuit, said digital signal processing circuit being configured;

(i) for setting up the data link with the ANSI T1.413 compatible remote transceiver which data link complies with T1.413 data signal protocols; and

(iv) for supporting a variable channel data rate which can vary from a full data rate achievable by an ANSI T1.413 compatible ADSL transceiver connected in such data channel to such system, to a fractional portion of such full data rate;

(ii) for achieving said variable channel data rate by varying a number of sub-channels N used for carrying data in the data channel, where M is a maximum number of sub-channels supportable in the data channel, k is an integer >

=1, and N<

=M/k;

wherein N is configured based on computing resources available to said digital signal processing circuit, performance characteristics of the ANSI T1.413 compatible remote transceiver, and transmission conditions in the channel.

57. The system of claim 56, further wherein M is >

200.

58. The system of claim 56, wherein said system operates as a full rate or reduced rate T1.413 compliant transceiver.

59. The system of claim 56, further wherein portions of said digital signal processing circuit are implemented by a software routine executed by a host processing device within a personal computer system.

60. The system of claim 59, further including a channel interface circuit and analog front end circuit that are physically separated from said host processing device but electrically connected through a personal computer system bus.

61. A high speed system for communicating with a remote transceiver, which remote transceiver operates at a data transmission sampling rate B, and can transmit a first analog signal using up to a maximum number M modulated subchannels within an available bandwidth F through a channel to said system, the high speed system comprising:

a channel interface circuit for coupling to and receiving said analog signal from the channel; and

a front end receiving circuit coupled to said channel interface circuit, said front end circuit being adapted for;

(iii) sampling the first analog signal, said sampling being performed at a sampling rate B'"'"', where B'"'"'=B/k, and where k is an integer >

=2; and

(iv) generating a first received digital signal based on such first analog signal; and

a digital signal processing circuit coupled to said front end receiving circuit, said digital signal processing circuit being configured;

(iv) for extracting a data stream from the first digital signal, the first digital signal including data from N subchannels located within a receive frequency bandwidth portion f1 of the bandwidth F (f1<

=F), where N is a subset of the maximum number of M subchannels, N<

=M/k; and

(v) for signaling to said remote transceiver that the high speed system supports a subset of the maximum number of subchannels M.

62. The system of claim 61, where M>

200.

63. The system of claim 61, wherein said system operates as a full rate or reduced rate T1.413 compliant transceiver.

64. The system of claim 61, further wherein portions of said digital signal processing circuit are implemented by a software routine executed by a host processing device within a personal computer system.

65. The system of claim 64, further wherein said channel interface circuit and front end circuit are physically separated from said host processing device but electrically connected through a personal computer system bus.

66. A method of communicating data based on DMT modulation as specified in T1.413 between a local transceiver and a remote transceiver coupled through a data channel, the method comprising the steps of:

(a) determining an amount of computing resources available for processing discrete multi-tone (DMT) modulated subchannels; and

(b) determining data sampling capabilities of an analog front end circuit associated with the local transceiver; and

(c) determining data capacity of the data channel, including a maximum number M of DMT modulated subchannels supported by the data channel; and

(d) determining data transmission capabilities of the remote transceiver during an initialization routine, including a maximum number of DMT modulated subchannnels supported by the remote transceiver; and

(e) selecting a subset of the M subchannels for data transmissions between the local transceiver and the remote transceiver, said subset constituting a number N of said M subchannels, where N<

=M, and N is selected by evaluating said amount of computing resources, said data sampling capabilities, said data capacity, and said data transmission capabilities of the remote transceiver.

67. The method of claim 66, where N<

=M/k, and k is an integer.

68. The method of claim 67, wherein said analog front end circuit associated with the local transceiver uses a sampling rate B that is reduced by said integer k from a sampling rate B'"'"' used by the remote transceiver, such that B=B'"'"'/k.

69. The method of claim 66, wherein during step (a), a measurement is made of signal processing capabilities of a host processor within a personal computer system used for demodulating said N subchannels.

70. The method of claim 66, wherein subchannels other than said number N are filtered by said analog front end circuit.