Modular multiplicative data rate modem and method of operation

• US 6,065,060 A
• Filed: 06/30/1997
• Issued: 05/16/2000
• 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:
  US08/884,958
• Time in Patent Office: 1,051 Days
• Field of Search: 379/93.14, 379/399, 379/28, 709/233, 370/80, 370/341, 370/494, 364/705.05, 375/39, 375/377, 375/222, 375/350
• US Class Current: 709/233
• CPC Class Codes: G06F 15/163 Interprocessor communication
• CPC Class Codes: H04L 5/143 for modulated signals H04L5/1469 takes precedence
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data
• CPC Class Codes: H04Q 2213/13039 Asymmetrical two-way transmission, e.g. ADSL, HDSL

Abstract

A high speed modem is provided which targets the use of a selectable, desirable portion of the total available bandwidth of a channel for achieving a data rate which nevertheless far exceeds that of conventional voice-band modems. In a preferred embodiment, the invention is implemented in an Asymmetric Digital Subscriber Loop (ADSL), and the nominal data rate is achieved using an analog front end (AFE) with subband filtering which causes an upstream transceiver to use only a selected number of available sub-channels for downstream data transmission and allows slower sampling rate for the AFE. The data rate of the modem is increased in a multiplicative fashion through modular expansion of a bank of AFEs to increase the number of transmitted downstream sub-channels.

Claims

1. A high speed communications transciever for communicating with an upstream transciever transmitting an analog data transmission signal using M data carrying signals within a bandwidth F through a digital subscriber line channel to said system, said transceiver comprising:

a digital subscriber line channel interface circuit for coupling to and receiving said analog data signal from the digital subscriber line channel, said analog data signal being carried separately from a voice band signal in the digital subscriber line; and

a modular bank front end receiving circuit comprised of L separate front end circuits for sampling the analog data signal and generating L separate digital signals based on such analog data signal, each of the L digital signals being generated by a separate one of said L separate front end circuits operating on a corresponding separate portion of said analog data signal and each of said digital signals including data from a corresponding one of L separate bandwidth portions of said bandwidth F, such that said L digital signals combined contain a number N data carrying signals, where N<

=M; and

a bus interface circuit for transmitting at least the L digital signals to a host processing device; and

wherein the modular bank front end receiving circuit can be expanded by capacity of said L separate front end circuits such that said N data carrying signals can be taken from additional portions of said bandwidth F so that all of said M data carrying signals can be used for carrying data in the digital subscriber line channel.

2. The transceiver of claim 1, wherein each of the L front end circuits includes (i) a sub-band filter for passing said corresponding separate bandwidth portion of said bandwidth F;

(ii) and an analog to digital converter for converting said corresponding separate portion of said analog data signal into one of said L digital signals.

3. The transciever of claim 2, wherein said L separate front end circuits each sample a portion of said analog data signal corresponding to a first frequency bandwith portion f1, such that L first frequency bandwidth portions f1 are sampled, and L·

f1<

=F.

4. The transciever of claim 3, wherein N/L data carrying signals are contained within each of said L first frequency bandwidth portions f1.

5. The transceiver of claim 1, wherein each of said L separate front end circuits operates at a rate slower than the Nyquist rate required by an analog to digital converter to sample said bandwidth F.

6. The transciever of claim 1, further including a front end transmitting circuit for transmitting control information to cause said upstream transceiver to transmit downstream data only using the N data carrying signals.

7. The transceiver of claim 6, wherein the control information transmitted to the upstream transceiver includes feedback information from the host processing device indicating to the upstream transceiver that only N of the M data carrying signals are desirable for downstream data transmission, even if said digital subscriber line channel is capable of supporting more than N data carrying signals.

8. The transceiver of claim 7, wherein the front end transmitting circuit transmits an upstream data transmission using a second frequency bandwidth F2 and M'"'"' upstream data carrying signals, and where M'"'"'<

M.

9. The transceiver of claim 1, further including a host signal processor circuit contained within the host processing device, which host signal processor circuit executes a signal processing routine to assist in demodulating data from said L digital signals containing said N data carrying signals.

10. The transceiver of claim 9, wherein said host signal processor circuit includes a microprocessor, a programmable memory coupled to the microprocessor, and said signal processing routine located in the memory which can be executed by the microprocessor;

and further wherein a signal processing performance capability of said signal processing routine can be adjusted based on allocating differing amounts of computing resources of said microprocessor to said signal processing routine.

11. A high speed communications system for receiving selected data contained in a number of modulated sub-channels N from a remote transceiver capable of transmitting a number of modulated sub-channels M through a channel to said system, said system comprising:

a channel interface circuit for coupling to and receiving said analog data signal from the channel, said analog data signal being separate from a voice band signal carried in the channel; and

an analog front end circuit for sampling the analog data signal and converting it to L separate digital signals based on sampling L separate portions of said analog data signal, the front end circuit including L separate front end circuits, and each of said L separate front end circuits having an anti-aliasing filter and an analog to digital converter, and wherein said L digital signals combined include data only from said number of sub-channels N, where N<

=M; and

a bus interface circuit for transmitting the L digital signals to a host processing device so that selected data can be demodulated from the N sub-channels using a software signal processing routine executed by said host processing device; and

wherein the front end receiving circuit can be expanded by modular additions so that the sampling of the analog data signal can be increased by increasing a number of said L separate front end circuits, such that the data rate and the number of sub-channels N used in the channel can also be expanded.

12. The system of claim 11, wherein the rati o of N to M is approximately 0.5 or less.

13. The system of claim 11, wherein each of said L separate front end circuits includes (i) a filter for passing N/L sub-channels;

(ii) and an analog to digital converter for converting said corresponding separate portion of said analog data signal into one of said L digital signals.

14. The system of claim 13, wherein said L separate front end circuits each bandpass a first frequency portion f1 of a maximum available bandwidth F in the channel, such that N/L sub-channels are carried within said first frequency portion f1, and L·

f1<

=F.

15. The system of claim 14, wherein each of said L separate front end circuits operates at a rate slower than the Nyquist rate required by an analog to digital converter to sample said full bandwidth F.

16. The system of claim 11, 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.

17. The system of claim 11, wherein the control information transmitted to the upstream transceiver includes feedback information permanently masking out all the available sub-channels except the N sub-channels for any subsequent downstream data transmissions.

18. The system of claim 11, wherein said host processing device includes a host processor circuit, said host processor circuit including a microprocessor, a programmable memory coupled to the microprocessor, and said signal processing routine located in the memory which can be executed by the microprocessor;

and further wherein a signal processing performance capability of said signal processing routine can be adjusted based on allocating differing amounts of computing resources of said microprocessor to said signal processing routine.

19. The system of claim 11, wherein the remote transceiver uses discrete multi-tone (DMT) modulation for generating the M modulated sub-channels, and the channel supports asymmetric digital subscriber loop (ADSL) transmission standards.

20. The system of claim 16, wherein the front end transmitting circuit can transmit an upstream data transmission using a second set of modulated sub-channels M'"'"', where M'"'"'<

M.

21. An interface device configured for transferring selected data between a remote data transceiver and a host processing device, the remote data transceiver being capable of transmitting an analog data signal through a channel using a bandwidth F, and the host processing device capable of processing a digital signal to extract the selected data, the interface device comprising:

a channel interface circuit for coupling to and receiving said analog data stream transmission, said analog data stream transmission being carried separately from a voice band frequency signal in the channel; and

an analog front end receiving circuit comprised of L separate front end circuits for filtering L separate frequency portions of the analog data signal with L respective sub-band filters and generating L respective digital signals with L respective A/D converters, each of said L respective digital signals being based on one of said L separate frequency portions of said analog data signal; and

a bus interface circuit for transmitting at least the L digital signals to said host processing device to undergo a demodulation operation to extract the selected data from said L digital signals; and

an analog front end transmitting circuit for transmitting a control signal to cause said remote transmitter to transmit using only using a combination of said L separate frequency portions; and

wherein a data rate in the channel can be varied by sampling a variable portion of the bandwidth F occupied by the analog data signal, said variable portion corresponding to said combination of said L separate frequency portions.

22. A method of processing data transmitted on a digital subscriber link comprising the steps of:

(a) receiving an analog data signal having a frequency bandwidth F, which analog data signal contains up to M DMT modulated sub-channels;

(b) splitting said analog data signal into L separate analog signals, where L is an integer >

=2;

(c) generating L filtered analog signals from said L separate analog signals, said L filtered analog signals being associated with one of L different frequency portions of said frequency bandwidth F, and one of L different subsets of said M DMT modulated sub-channels;

(d) converting said L filtered analog signals into L digital signals using L separate A/D converters, one for each of said L filtered analog signals, and each of which L separate A/D converters uses a data sampling rate that is at least L times less than a sampling rate required by a single A/D converter to perform an A/D conversion on an analog data signal having a frequency bandwidth F;

(e) transmitting said L digital signals to a signal processor so that signal processing operations can be performed on said L digital signals to receive the data by demodulating said up to M DMT modulated sub-channels.

23. The method of claim 22, wherein said signal processing is performed by a software routine executing on a host processing device.

24. The method of claim 22, wherein analog data signal is transmitted in accordance with T1.413 signal data protocols.

25. The method of claim 22, wherein L is intentionally selected such that only a sub-set N of said M DMT modulated sub-channels (N<

M) are demodulated.

26. The method of claim 22, wherein as L is increased more of said M DMT modulated sub-channels can be demodulated.

27. A front end circuit for use with an ADSL transceiver, which transceiver processes up to M DMT based subchannels transmitted by a remote transceiver using an analog data signal, the front end circuit comprising:

(a) a bandpass filter for generating a filtered analog data signal from the analog data signal, said bandpass filter being configurable such that all or a portion of said analog data signal can be passed through said filter;

(b) an analog to digital converter for converting said filtered analog data signal to a digital signal which digital signal contains modulated data for up to a number N sub-channels taken from the M sub-channels, where N is configured based on signal processing capabilities of the transceiver to have a value <

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

=1;

wherein said analog front end circuit can be configured by the ADSL transceiver to process an analog data signal carrying all of said M sub-channels and/or an analog data signal carrying a reduced number of said M sub-channels consisting of said N sub-channels.

28. The front end circuit of claim 27, wherein said bandpass filter consists of L separate bandpass filters, each of said bandpass filters operating on a separate portion of said analog data signal such that L separate filtered analog data signals are generated.

29. The front end circuit of claim 28, wherein said analog to digital converter consists of L separate analog to digital converters, each of said L analog to digital converters operating on a separate one of said L filtered analog data signals such that L separate digital signals are generated.

30. The front end circuit of claim 29, wherein said L bandpass filters and said L analog to digital converters can be modularly expanded in number such that a greater number of sub-channels can be recovered and demodulated by the transceiver.

31. The front end circuit of claim 30, wherein each of said L separate analog to digital converters operates at a rate that is a L times slower than the Nyquist rate required by an analog to digital converter to sample all of said analog data signal.

32. A front end circuit for use with a scalable rate T1.413 compatible transceiver, which transceiver receives an analog data signal containing a received number of sub-channels consisting of a subset (N) and/or all of number (M) of DMT subchannels transmitted by a remote transceiver, and which analog data signal has a transmitted frequency range which varies based on a number of sub-channels transmitted by the remote transceiver, the front end circuit comprising:

(a) a bandpass filter for generating a filtered analog data signal from the analog data signal said bandpass filter being configurable to use a bandpass frequency range corresponding to the transmitted frequency range; and

(b) an analog to digital converter for converting said filtered analog data signal to a digital signal, which digital signal contains modulated data for the received number of sub-channels, such that either the subset (N) and/or all (M) the sub-channels are made available for demodulation by the scalable rate transceiver;

wherein said analog front end circuit can be configured by the T1.413 compatible transceiver to process a variable number of sub-channels ranging from N to M.

33. The front end circuit of claim 32, wherein said bandpass filter consists of L separate bandpass filters, each of said bandpass filters operating on a separate portion of said analog data signal such that L separate filtered analog data signals are generated.

34. The front end circuit of claim 33, wherein said analog to digital converter consists of L separate analog to digital converters, each of said L analog to digital converters operating on a separate one of said L filtered analog data signals such that L separate digital signals are generated.

35. The front end circuit of claim 34, wherein said L bandpass filters and said L analog to digital converters can be modularly expanded in number such that a greater number of sub-channels can be recovered and demodulated by the transceiver.

36. The front end circuit of claim 34, wherein each of said L separate analog to digital converters operates at a rate that is a L times slower than the Nyquist rate required by an analog to digital converter to sample all of said analog data signal.

37. The front end circuit of claim 32, wherein N is approximately M/2.

38. The front end circuit of claim 32, wherein N is configured during an initialization process.