Speech and data multiplexor optimized for use over impaired and bandwidth restricted analog channels

• US 4,757,495 A
• Filed: 03/05/1986
• Issued: 07/12/1988
• Est. Priority Date: 03/05/1986
• Status: Expired due to Term

• Current Assignee: Telebit Corp. (Cisco Systems, Inc.)
• Original Assignee: Telebit Corp. (Cisco Systems, Inc.)
• Inventors: Mueller, Frederick L., Flowers, Mark B., Freret, Payne, Hughes-Hartogs, Dirk, Decker, Dwight W.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Chin, Wellington
• Application Number:
  US06/836,438
• Time in Patent Office: 860 Days
• Field of Search: 370/69.1, 370/76, 370/110.1, 375/98, 375/97, 375/5
• US Class Current: 370/477
• CPC Class Codes: H04L 5/0005 Time-frequency
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04L 5/0053 Allocation of signaling, i.e. of overhead other than pilot signals
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

The present invention relates to an apparatus and method for the simultaneous transmission of analog speech and modulated data, such apparatus and method being optimized for use over impaired and bandwidth restricted analog channels, or digital representations of such channels. In each instance of use, an evaluation is made of the available channel bandwidth, with a frequency division multiplex scheme allocating a voice sub-band, with data transmission allocated to sub-bands above, below, or around, this selected voice sub-band. The speech and data sub-band allocations are made by the multiplexor in response to user input of either a requested speech quality, a requested data rate, or a value indicating the relative user weighting of speech quality and data rate. A multi-carrier multi-mode modulation scheme is employed for data transmission, with this scheme having the ability to fully utilize the remaining bandwidth, and further, being capable of adapting to the impairments most likely present on the fringes of bandwidth restricted analog channels. When the analog channel employed is the standard voice-grade telephone circuit, good speech quality simultaneously with 3000 bps data transmission may be expected. The further ability to automatically switch to full bandwidth data transmission when voice transmission is not being attempted is also provided.

Claims

1. A speech and data multiplexor for use over imparied and bandwidth restricted analog channels or digital representative of such channels, said multiplexor comprising,

allocating means for alllocating a speech sub-band in a central poriton of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band, within the available bandwidth and on a border of the speech sub-band and in a portion of the available bandwidth separate and distinct from the portion of the bandwidth containing the speech sub-band, for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attenuation and/or group delay are common in the data sub-band, and

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and independent of any speech signals and/or channel impairments existing or occurring in the speech sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments in the data sub-band and within the limt of the power available or allocated for the transmission.

8. The invention defined in claim 1 wherein the allocating means permit user selection of the boundaries of the speech sub-band.

9. The invention defined in claim 8 wherein the multiplexor includes a data port and the user selection of the speech sub-band to be utilized is accomplished by means of information transmitted through the data port.

10. The invention defined in claim 1 including transmitting means for transmitting speech in the speech sub-band.

11. The invention defined in claim 1 including transmitting means for transmitting data in the speech sub-band.

12. The invention defined in claim 11 wherein the transmitting means include modem means for transmitting data through the use of a conventional data set, such as, for example, a 300BPS Bell 103 compatible data set or a 1200 BPS Bell 212 compatible data set.

13. The invention defined in claim 1 wherein the selecting means select a single data sub-band above the speech sub-band.

14. The invention defined in claim 1 wherein the selecting means select a single data sub-band below the speech sub-band.

15. The invention defined in claim 1 wherein the selecting means select two data sub-bands, one data sub-band above the speech sub-band and the other data sub-band below the speech sub-band.

19. The invention defined in claim 1 including separating means for separating the speech and data energies that are present in the speech sub-band and data sub-band.

20. The invention defined in claim 19 wherein the separating means include filter means.

21. The invention defined in claim 20 wherein the filter means include programmable, active filter means for selecting the edge frequencies of the sub-bands.

22. The invention defined in claim 21 wherein the multiplexor includes an ensemble modem operatively associated with the filter means for allowing the ensemble modem to select the edge frequencies of the sub-bands.

23. The invention defined in claim 20 wherein the filter means include passive bi-directional filters.

24. The invention defined in claim 1 wherein the analog channel is a telephone channel having a restricted bandwidth in the general range of 0-4000 Hz.

25. The invention defined in claim 24 wherein the speech sub-band is allocated in the frequency range of about 300 Hz to 2700 Hz.

28. The invention defined in claim 24 wherein the multiplexor has three ports--a channel port, a speech port and a data port--and filtering means for separating speech and data energies that are present in the sub-bands and wherein the filter means are active programmable filter means operatively associated with the data port for permitting user selection of the edges of the sub-bands to be employed by the multiplexor.

29. The invention defined in claim 24 wherein the analog channel is a public switched telephone network circuit, and a local multiplexor is used at one end of the circuit and a remote multiplexor is used at the other end of the circuit and both the local and remote multiplexors are identical.

30. The invention defined in claim 24 wherein the analog channel is a loaded (or unloaded) local loop, a local multiplexor is used at one end of the channel and a remote multiplexor is used at a telephone company central office.

2. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating mean for allocating a speed sub-band in a central portion of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attentuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and wherein the adaptive means include evaluating means for determination of the total available bandwith for data transmission, said evaluating means being operatively associated with the selecting means for said selection of the data sub-band.

3. A speech and data multiplexor for use over impaired and bandwidth restrited analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in a central portion of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attentuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and wherein the adaptive means include multiple signal carriers uniformly spaced apart in small increments of frequency and wherein said adaptive means are effective both to select certain carriers for transmitting the data and also to select a particular modulation scheme for each selected carrier in order to optimize the overall rate of data transmission in the presence of any impairments existing in the data sub-band.

4. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in a central portion of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attentuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and wherein the adaptive means include an ensemble modem which utilizes multiple signal carriers and a multimode modulation scheme for transmitting the data in the data sub-band.

5. The invention defined in claim 4 wherein the multiple signal carriers are uniformly spaced apart in small increments of frequency and wherein the ensemble modem depolys the allowable available transmission power by choosing certain carriers for transmission for data and also by choosing a modulation scheme employed on each chosen carrier.

6. The invention defined in claim 5 wherein the selection of the signal carriers adapts to induced power and telephone equipment noise in a low frequency data sub-band, provides carrier by carrier demodulation to permit compensation for frequency dependent attenuation in both low and high frequency data sub-bands, and provides a long symbol period modulation with an associated guardtime to make the transmission of data insensitive to frequency dependent group delay.

7. The invention defined in claim 4 wherein the ensemble modem includes testing means for testing the analog channel transmission characteristics during a training phase to determine the attenuation and the background noise experienced by each of the carriers transmitted within the data sub-band and wherein the modem then optimizes the transmission of data by deploying the available power over selected carrier frequencies and with a modulated number of bits on each selected carrier to obtain the most efficient use of the data sub-band for the transmission of data in view of the existing analog channel transmission characteristics.

16. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in a central portion of the available bandwith for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attentuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmisison of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and wherein the selecting means select a single data sub-band above the speech sub-band and including detecting means for detecting the absence of speech transmission on the analog channel and effective in combination with the selecting means for selecting all of the available bandwith for the transmission of data in the absence of speech.

17. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in a central portion of the available bandwith for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attentuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and wherein the selecting means select a single data sub-band below the speech sub-band and including detecting means for detecting the absence of speech transmission on the analog channel and effective in combination with the selecting means for selecting all of the available bandwidth for the transmission of data in the absence of speech.

18. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means or allocating a speech sub-band in a central portion for the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attentuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optmize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and wherein the selecting means select two data sub-bands, one data sub-band above the speech sub-band and the other data sub-band below the speech sub-band and including detecting means for detecting the absence of speech transmission on the analog channel and effective in combination with the selecting means for selecting all of the available bandwidth for the transmission of data in the absence of speech.

26. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in a central portion of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attenuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmisison of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and wherein the analog channel is a telephone channel having a restricted bandwith in the general range of 0-4000 Hz and wherein the edges of the speech sub-band are allocated to permit all dual tone multi-frequency (DTMF) and call progress signalling without the need to switch the speech or data sub-bands.

27. The invention defined in claim 26 wherein the analog channel is a standard public-switched telephone network circuit and wherein the multiplexor includes circuit components which insure that no impairment is made to those signals that would normally be present on such telephone network circuits.

31. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representations of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in a cental portion of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attenuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission,

said adaptive means including evaluating means for determination of the total available bandwidth for data transmission, said evaluating means being operatively associated with the selecting means for said selecting of the data sub-band,

said adaptive means including an ensemble modem which utilizes multiple signal carriers and a multimode modulation scheme for transmitting the data in the data sub-band,

filter means for separating the speech and data energies that are present in the speech sub-band and data sub-band, said filter means including programmable, active filter means for selecting the edge frequencies of the sub-bands, and wherein the ensemble modem is operatively associated with the filter means for allowing the ensemble modem to select the edge frequencies of the sub-bands, and

wherein the analog channel is a telephone channel having a restricted bandwidth in the general range of 0-4000 Hz and the edges of the speech sub-band are allocated to permit all dual tone multi-frequency (DTMF) signalling without the need to switch the speech or data sub-bands.

32. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in a central portion of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attentuation and/or group delay are common in the data sub-band,

adaptive means for adapting the transmission of the data in the data sub-band to any impairments existing in the data sub-band and effective to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and including user input means for inputting a requested speech quality signal, a requested data rate signal or a value indicating the relative user weighting of speech quality and data rate and wherein said allocating means and selecting means determine the edge frequencies of the speech and data sub-bands in response to the signal which is input by said user input means.

33. A speech and data multiplexor for use over impaired and bandwidth restricted analog channels or digital representatives of such channels, said multiplexor comprising,

allocating means for allocating a speech sub-band in the middle part of the available bandwidth for the transmission of speech,

selecting means for selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the transmission of data,

said analog channel being an analog channel of the kind in which impairments of induced noise, attenuation and/or group delay are common in the data sub-band,

elvaluating means for determination of the total available bandwidth for data transmission, said evaluating means being operatively associated with the selecting means for said selecting of the data sub-band, and

multicarrier data transmitting means for transmitting data in the data sub-band on a plurality of carriers.

34. A method of multiplexing speech and data over impaired and bandwidth restricted analog channels or digital representations of such channels, said method comprising,

allocating a speech sub-band in the middle part of the available bandwidth for the transmission of speech,

selecting at least one data sub-band, within the available bandwidth and on a border of the speech sub-band and in a portion of the available bandwidth separate and distinct from the portion of the bandwidth containing the speech sub-band, for the transmission of data, and

adapting the transmission of the data in the data sub-band to the impairments of induced noise and attenuation that may be present in the data sub-band and independently of any speech signals and/or channel impairments existing or occurring in the speech sub-band to optimize the transmission of data in the data sub-band in the presence of said impcirments in the data sub-band and within the limit of the power available or allocated for the transmission.

35. The invention defined in claim 34 wherein the adapting step includes evaluating the total available bandwidth for selecting said data sub-band.

36. A method of multiplexing speech and data over impaired and bandwidth restricted analog channels or digital representations of such channels, said method comprising,

allocating a speech sub-band in the middle part of the available bandwidth for the transmission of speech,

selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the the transmission of data,

adapting the transmission of the data in the data sub-band to be impairments of induced noise and attenuation that may be present in the data sub-band to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and including utilizing multiple signal carriers uniformly spaced apart in small increments of frequency for transmitting data in the data sub-band and including selecting certain carriers for the transmission of data and also selecting a particular modulation scheme for each selected carrier (to determine the number of data bits modulated on each carrier) for said optimization of the overall rate of data transmission in the presence of any impairments existing in the data sub-band.

37. A method of multiplexing speech and data over impaired and bandwidth restricted analog channels or digital representations of such channels, said method comprising,

allocating a speech sub-band in the middle part of the available bandwidth for the transmission of speech,

selecting at least one data sub-band within the available bandwidth and on a border of the speech sub-band for the the transmission of data,

adapting the transmission of the data in the data sub-band to be impairments of induced noise and attenuation that may be present in the data sub-band to optimize the transmission of data in the data sub-band in the presence of said impairments and within the limit of the power available or allocated for the transmission, and including determining the edge frequencies of the speech and data sub-bands in response to a user requested speech quality, a user requested data rate or a value indicating the realtive user weighting of speech quality and data rate.