WO1998027665A1

WO1998027665A1 - Apparatus and method for communicating voice and data between a customer premises and a central office

Info

Publication number: WO1998027665A1
Application number: PCT/US1997/022632
Authority: WO
Inventors: Gordon Bremer; Thomas Bingel
Original assignee: Paradyne Corporation
Priority date: 1996-12-17
Filing date: 1997-12-04
Publication date: 1998-06-25
Also published as: JP2001526849A; CA2272576A1

Abstract

A method and apparatus are provided for communicating data (25) across a communication link (26), in a manner that senses and dynamically adapts to the simultaneous transmission of voice information (30, 32) across the local loop. In accordance with one aspect of the invention, a method is provided for dynamically communicating data (25) over a local loop using a modem (20) comprising the steps of transmitting data in a full-band transmission state, sensing a band-limiting condition, and adjusting the transmission of data from the full-band transmission state to a band-limited transmission state, in response to the sensing step. A significant aspect of the present invention is the dynamic allocation of the data transmission bandwidth, whereby the invention senses a condition indicative of whether voice information (30, 32) is being communicated. If so, then the system shifts and/or narrows the data transmission bandwidth to allow for voice communications without interference from or with the data transmission.

Description

APPARATUS AND METHOD FOR COMMUNICATING VOICE AND DATA BETWEEN A CUSTOMER PREMISES AND A CENTRAL OFFICE

Cross-Reference to Related Applications

This application claims the benefit of U.S. Provisional Patent Application

Serial. No. 60/033.660. filed on December 17, 1996, and entitled Digital Subscriber

Loop Data Communications Method Enabling Simultaneous Data and POTS Without

POTS Filters/Splitters or Special Premise Wiring.

Background of the Invention

Field of the Invention

The present invention generally relates to modems, and more particularly to

high speed modems offering robust communication between a central office and a

customer premises.

Discussion of the Related Art

High speed digital modems, such as Rate Adaptive Digital Subscriber Loop

("RADSL^") modems are able to transfer data at high rates over the local loop, because

they use frequencies which are significantly higher than the voice band frequencies

used in Plain Old Telephone Service ("POTS"). By way of example, speech on a

POTS system generally occurs in the frequency spectrum between about 0 Hz ("DC")

and about 4 KHz. whereas RADSL modems use the frequency spectrum of between

about 20 KHz to about 1 MHz. High speed digital modems generally include error

detection circuitry which measures the errors which occur during communications.

By making such measurements, they are then able to update their statistical knowledge of the wire pair which extends between the subscriber^'s location and the

central office. Using that statistical knowledge, the modems can select optimal

operating speeds. These modems were originally proposed when it was thought that

services, such as video-on-demand, would be desirable.

As modem technology has developed, another need has arisen, in that the

Internet has become a popular medium for both personal and work related use.

While the high speeds of RADSL modems seem to be quite desirable, their

use of high frequencies mean that they also need to be protected from high frequency

noise, such as cross-talk from adjacent channels or adjacent loops in the loop cable

binder, as such noise causes them to downwardly adjust their operating speeds. In

order to avoid certain types of noise, RADSL modems typically require the use of

filters, called POTS filters, together with splitters for isolating Public Switched

Telephone Network ("PSTN") equipment from the RADSL modems. Indeed, without

POTS filters and POTS splitters. POTS signals directly interfere with the RADSL

spectrum below about 20 kilohertz and the RADSL spectrum directly interferes with

the POTS. POTS filters and POTS splitters reduce POTS signaling transients from

interfering with RADSL data transmission. In addition, the use of the high RADSL

bandwidth demands relatively high transmit power, which can cause distortions and

dynamic range overload to POTS equipment.

Unfortunately, the manufacture and installation of POTS filters and splitters

are expensive, and their use sometimes requires rewiring of the customer premises to

ensure that all PSTN equipment is properly isolated from the RADSL modems and

computing equipment. Consequently, it would be desirable to avoid the use of POTS splitters and filters, in order to avoid the expense they impose (e.g.. purchase cost and

possible rewiring of customer premises).

Accordingly, their appears to be a need for a mass market modem which has

data transfer rates greater than the 33.6 Kbps attainable by PSTN modems, yet under

the rate that requires the addition of POTS filters, splitters, etc. to address noise and

deleterious transmission line effects often encountered in high speed DSL modems.

Yet another problem which is manifest in increased Internet access and data

communications is the increasingly limited availability to the customer phone line or

local loop for its original purpose, i.e.. voice communications. Of course, one

solution is for a customer to purchase an additional phone line. This, however,

imposes an additional cost on the customer. Moreover, unless the line is dedicated by

the customer for a specific purpose (which is poor utilization), the second line may

not always be available when needed.

Accordingly, there is a need to provide an improved modem that

accommodates data transmissions, while simultaneously allowing traditional voice

operation of a telephone attached to the same line at the customer premise. It is

particularly desirable to have such a modem that does not require the use of costly

POTS filters and splitters.

Summary of the Invention

Certain objects, advantages and novel features of the invention will be set

forth in part in the description that follows and in part will become apparent to those

skilled in the art upon examination of the following or may be learned with the practice of the invention. The objects and advantages of the invention ma\ be realized

and obtained by means of the instrumentalities and combinations particularly pointed

out in the appended claims.

To achieve the advantages and novel features, the present invention is

generally directed to a method and apparatus for communicating data across a local

loop, in a manner that senses and dynamically adapts to the simultaneous transmission

of POTS (e.g.. voice or PSTN modem) information across the local loop. In

accordance with one aspect of the invention, a method is provided for dynamically

communicating data over a local loop using a modem comprising the steps of

transmitting data in a full-band transmission state, sensing a band-limiting condition,

and adjusting the transmission of data from the full-band transmission state to a band-

limited transmission state, in response to the sensing step. The step of sensing a band-

limiting condition includes both the detection of the onset of a condition indicating

that the method should enter the band-limited transmission state, as well as the

detection of the cessation of that condition, indicating that the method should enter the

full-band transmission state from the band-limited transmission state.

In accordance with the method of the present invention, data may be

transmitted by the modem across the local loop at the same time that POTS (e.g.,

voice or PSTN modem data) information is communicated across the same local loop.

A significant aspect of the present invention is the dynamic allocation of the data

transmission bandwidth, whereby the invention senses a condition indicative of

whether POTS information is being communicated. If so. then the system shifts

and/or narrows the data transmission bandwidth to allow for voice communications without interference from or with the data transmission. However, when no POTS

information is being communicated, the invention dynamically allocates the data

transmission bandwidth to utilize at least a portion, if not all. of the frequency band

otherwise used for communicating voice information.

In accordance with the preferred embodiment, the method senses an off-hook

condition of a telephone handset of a telephone electrically connected to the local

loop. In use. a local loop extending between a customer premises and a central office

branches, at the customer premise, to support multiple connections to the local loop.

In this regard, the various branches or connections are typically routed throughout a

customer premises to phone jacks, such as RJ- 1 1 jacks. Multiple telephones may be

plugged directly into these jacks for voice communication across the local loop.

Similarly, a modem constructed in accordance with the present invention may be

plugged directly into one of these jacks. The off-hook condition is preferably sensed

by detecting either a change in impedance in the telephone line, or alternatively a drop

in line voltage across the telephone line.

In accordance with one embodiment of the invention, the full-band

transmission state is defined by a transmission frequency bandwidth having a lower

frequency boundary of less than about 15-20 kilohertz (and preferable less than 4

kilohertz). In the band-limited transmission state, the transmission frequency

bandwidth has a lower frequency boundary of greater than 4 kilohertz. The

significance of these values, for purposes of the invention, is that when no voice

information is being communicated across the local loop, the transmission frequency

bandwidth invades that frequency band generally dedicated to the transmission of voice information (/ e . the 0-4 kilohertz POTS frequency band). When, however, the

invention senses that POTS information is being communicated across the local loop,

or that there is a demand for the POTS band (e g , telephone off-hook. ring. etc.). then

the embodiment shifts the lower boundary of the transmission frequency bandwidth

above the generally 4 kilohertz upper limit of the voice band. Preferably, the lower

boundan will be shifted upwardly to approximately 20 kilohertz, to allow sufficient

separation between the voice and data transmission frequency bands to that no

interference between the two is realized, either by voice information corrupting data,

or data transmission being heard in the voice band as noise.

For purposes of the preferred embodiment of the present invention, the precise

value of upper boundary of the transmission frequency bandwidth is not so

significant, as it is the dynamic adjustment of the lower boundary and/or the reduced

power in POTS mode, that realizes the inventive step. However, it will be appreciated

that the upper boundary will generally be greater than 40 kilohertz. in order to define a

meaningful transmission frequency bandwidth for data transmission. Indeed, in the

preferred embodiment, the upper frequency boundary is approximately 80 kilohertz.

It is belie\ ed that this frequency is low enough that transmissions may be effectively

implemented without the need for POTS filters or POTS splitters, and therefore

significantly reducing the cost of implementing the inventive system. Signal-to-noise

ratio is high to permit reasonable data throughput without excessive power incident on

attached POTS devices. Also, premises wiring and subscriber loop stubs do not cause

substan e nulls in the frequency response. It will be further appreciated that shifting

of the upper frequency boundary is not relevant to the present invention. That is. the upper boundary may be shifted in conjunction with the shifting of the lower frequency

boundary, or alternatively the upper frequency boundary may remain substantially

fixed.

It will be further appreciated that - depending upon loading, line conditions,

and other factors - the spectral shape of the band-limited xDSL transmission may be

varied to minimize noise, intermodulation products, or other interference within the

POTS frequency band. More particularly, it is generally understood that the power

density of xDSL transmissions is generally greater than that of POTS transmissions.

Merely shifting the xDSL transmission into the band-limited transmission state with a

lower cut-off frequency of approximately 20kHz may not always provide a wide

enough guard band to prevent interference with the POTS band. Line loading, line

conditions, and other factors (which differ among local loops) factor into this

determination. Intermodulation products are another source of noise that often is

present within the POTS band. When such noise is present within the POTS band, the

band-limited transmission state may be further configured by reducing the power-

density of the xDSL transmission. Another, related solution may be to uniquely shape

the spectral curve for xDSL transmissions. This, for example, may be done by

tapering the lower frequency portion of the curve (i.e.. that portion near the

approximately 15-20 kHz frequency).

In accordance with another aspect of the preferred embodiment, a modem is

provided for communicating data across a local loop. The modem includes an

input/output signal line that is electrically connected with the local loop (e.g.. plugged

into an RJ-1 1 phone jack). The modem also includes a processor unit that is adapted for operation in one of two states: a full-band transmission state and a band-limited

transmission state. The full-band transmission state is defined by a lower frequency

boundary at a value below approximately 15-20 kilohertz and an upper frequency

boundary generally greater than 40 kilohertz (as discussed above). The band-limited

state is defined by a lower frequency boundary greater than 4 kilohertz and an upper

frequency boundary greater than 40 kilohertz (which may or may not be the same as

the upper frequency boundary for the full-band transmission state). The modem

further includes a sensor or other sensing means for sensing that the local loop is in

POTS mode (e.g.. transmitting POTS information, or preparing to transmit POTS

information), and the data signal power and bandwidth are adaptivelv altered to

provide data without out interfering with the POTS transmission. Upon sensing the

band-limiting condition, such as an off-hook condition, the controller causes the

processor unit to upwardly shift the lower frequency boundary of the transmission

frequency band and operate in the band-limited, or reduced-power, state. Likewise.

upon sensing no band-limiting condition (or a cessation in the band-limiting

condition), the controller causes the processor unit to downwardly shift the lower

frequency boundary of the transmission frequency band, and operate in the full-band

transmission state, to maximize data throughput.

In accordance with yet a further aspect of the present invention, a method is

provided for simultaneously communicating both voice and data between a customer

premises and a central office across a local loop. In accordance with this aspect of the

invention, the method comprises the steps of: (1 ) transmitting data between the

customer premises and the central office in a first frequency band, wherein the first frequency band is defined by an upper frequency boundary and a lower frequency

boundary: (2) allocating a second frequency band for transmitting voice information

between the customer premises and the central office; (3) sensing a band-limiting

condition; and (4) dynamically shifting the lower frequency boundary of the first

frequency band in response to the sensed band-limiting condition. In accordance with

the invention, the lower frequency boundary of the first frequency band shifted to at

least partially overlap the second frequency band when no band-limiting condition

exists. The lower frequency boundary of the first frequency band is further shifted to

avoid overlapping with any portion of the second frequency band when the band-

limiting condition exists.

In accordance with yet a further aspect of the invention, a modem is provided

for communicating across a communication link capable of single-use transmissions

and multiple-use transmissions. The term single-use transmissions is used to

generally connote that a single transmission or communication is occurring across the

link. For example, a single PSTN voice call, or a single data communication

transmission. The term multiple-use transmissions is used to generally imply that

multiple transmissions or communications are occurring simultaneously. For

example, the simultaneous transmission of a data communication and a PSTN voice

call. The modem constructed in accordance with this aspect of the invention includes

an input/output signal line in communication with the communication link. It further

includes a processor unit adapted for operation in one of at least two states, a full-band

transmission state and a band-limited state, wherein the full-band transmission state

occurs when single-use transmissions are occurring across the transmission link, and the band-limited transmission state occurs when multiple-use transmissions are

occurring across the communication link.

It will be appreciated that, in accordance with a broad inventive aspect, the

present invention operates by adjusting transmit power between a band-limited

transmission state and a full-band transmission state. Generally (but not necessarily

always), the full-band transmission state occurs when the communication link is

operating in a single-use transmission mode, while the band-limited transmission state

generally occurs when the communication link is operating in a multiple-use

transmission mode. In accordance with this broad concept of the invention.

substantial transmission energy is transmitted by the modem in or near the POTS

frequency band, when the modem is transmitting in the full-band state. Conversely,

very little (ideally zero) energy is transmitted by the modem in or near the POTS

frequency band, when the modem is transmitting in the band-limited state. This

allows for simultaneous POTS transmissions (e.g.. voice. PSTN modem, etc.) in the

POTS frequency band, and band-limited modem transmissions.

Brief Description of the Drawings

The accompanying drawings incorporated in and forming a part of the

specification, illustrate several aspects of the present invention, and together with the

description serve to explain the principles of the invention. In the drawings:

FIG. 1 is an illustration of the frequency spectrum of a dual frequency band

communications system of the prior art. depicting the POTS transmission frequency

band and the xDSL transmission frequency band; FIG. 2 is a block diagram illustrating the primary components in a system

utilizing the present invention;

FIG. 3A is a frequency spectrum illustrating the full-band transmission

frequency band of the present invention;

FIG. 3B is a frequency spectrum illustrating the band-limited transmission

frequency band of the present invention;

FIG. 3C is a frequency spectrum illustrating a band-limited transmission

frequency band of an alternative embodiment of the present invention, having a

uniquely shaped xDSL transmission band:

FIG. 3D is a frequency spectrum illustrating a band-limited transmission

frequency band of an alternative embodiment of the present invention, having a reduced power xDSL transmission band;

FIG. 4 is a block diagram illustrating the primary components of a modem

constructed in accordance with the present invention;

FIG. 5 is a circuit diagram illustrating the analog front end component of the modem block diagram of FIG. 4;

FIG. 6 is a software flowchart depicting the operation of the functional

operation of the analog front end element, illustrated in FIG. 5: and

FIG. 7 is a software flowchart illustrating the top-level operation of a system

constructed in accordance with the present invention.

Detailed Description of the Preferred Embodiment of the Invention Having summarized the invention, reference will now be made in detail to the

description of the invention as illustrated in the drawings. While the invention will be

described in connection with these drawings, there is no intent to limit it to the

embodiment or embodiments disclosed therein. On the contrary, the intent is to cover

all alternatives, modifications and equivalents included within the spirit and scope of

the invention as defined by the appended claims.

Turning now to the drawings. FIG. 1 is a diagram illustrating frequency band

communications, as is known in the prior art. The term frequency band

communications is used to indicate communication of information within a certain

defined, frequency band. As is known in the prior art. plain old telephone system

(POTS) communications are transmitted in the frequency band 1 defined between

about 0 (DC) and about 4 kHz. A second transmission frequency band 14 is defined

at a higher frequency level than the POTS frequency band 12. and is used in the

transmission of digital subscriber line (DSL) communications. A guard dead band 16

is typically provided to separate the two transmission frequency bands 12 and 14. The

DSL transmission frequency band 14 is more broadly denominated as "xDSL^".

wherein the ^"x^" generically denominates any of a number of transmission techniques

within the DSL family. For example, ADSL - Asymmetric Digital Subscriber Line,

RADSL - Rate Adaptive Digital Subscriber Line. HDSL - High-Bit-Rate DSL. etc.

As is known. xDSL transmission frequency bands 14 may encompass a bandwidth of

greater than 1 MHz. As a result, and for the reasons described above, without the

addition of extra equipment such as POTS filters, splitters, etc. xDSL signals are not compatible with attached POTS type equipment, such as telephones. PSTN modems,

facsimile machines, etc.

As will be discussed in more detail below, the present invention provides an

upper transmission band having an upper frequency boundary that is much lower than

the 1 MHz frequency boundary often encountered in xDSL transmissions. Indeed, the

upper frequency boundary of the present invention is defined in a range that is readily

supported by. or compatible with, transmission systems (and attached POTS type

equipment) presently in place between a customer premises and a central office.

without the need for extraneous devices such as POTS filters and POTS splitters. In

this regard, reference is made to FIG. 2. which is a top level diagram illustrating the

principal hardware components of a system utilizing the present invention. In

accordance with one aspect of the invention, a modem 20 is provided for achieving

efficient data communications between a customer premises 22 and a central office 24

across a local loop 26. by dynamically allocating a transmission frequency bandwidth

and/or power for transmitting data. Certainly, one of the factors motivating the

development of the present invention is the expanded demand for higher speed

communications in recent years. This enhanced demand is primarily attributed to

communications over the Internet.

The present invention dynamically allocates a data transmission frequency

band and/or power spectral density (PSD) in response to POTS communications

across the same line. More particularly, the present invention may utilize the

frequency band otherwise allocated for POTS/voice transmission, at times when there

is no present demand for transmitting voice information. When, however, there is a demand for voice transmissions, then the present invention reallocates the

transmission frequency band and PSD for the data communications so that there is no

overlap or interference with the POTS transmission frequency band 12. and so that

there is not significant interference to POTS type attached equipment.

In keeping within the description of FIG. 2, the customer premises 22 may be

a single-family household having a single phone line 26 for communicating between

the customer premises 22 at a central office 24. Within the house or customer

premises 22, multiple connections branch off of the local loop 26 and are terminated

at phone jacks (such as RJ-1 1) located in various rooms of the household. In this way.

multiple telephones 30. and 32 may be plugged in and supported from the same phone

line 26. In the same way, a personal computer may be disposed in communication

with the local loop 26 by way of a modem 20.

Presently, unless a user purchases an additional phone line, or a more costly

communication service, such as xDSL. simultaneous transmissions of voice and data

to different locations are not possible. As a result, one person in a household may

have the local loop 26 tied up with data communications (such as Internet

communications), while another person at the same household is awaiting the use of

the local loop 26 for voice communication. An accordance with the present invention,

and as will be discussed in more detail below, this shortcoming is overcome.

In keeping with the description of FIG. 2, a companion modem 40. that is

compatible with the modem 20, is provided at the central office 24. As is known,

other equipment, such as wire distribution frame and standard telephone switching

equipment 42 may also be in communication with the local loop 26. Since the configuration and operation of such equipment is known in the prior art and does not

effect or impact the present invention, it will not be discussed herein. FIG. 2 also

illustrates a variety of services that may be connected at the central office 24 to the

modem 40. constructed in accordance with the present invention. These services may

include a high speed ISP service 44, a high speed LAN access service 46, etc. Again,

since the provision and operation of such services are generally understood and are

further not necessary in order to describe the operation of the present invention, they

will not be described herein.

Turning now to Figs. 3A and 3B. the dynamic allocation and deallocation of

the data transmission frequency band is illustrated. Specifically. FIG. 3 A illustrates

the data transmission frequency band 50 in a full-band transmission frequency state,

while FIG. 3B illustrates a data transmission frequency band 52 in a band-limited

(POTS compatible) transmission frequency state. As illustrated in FIG. 3A, the full-

band transmission frequency band 50 extends from approximately 0 Hz (DC) to

approximately 100 KHz. In contrast, in FIG. 3B the data transmission frequency band

52 extends from approximately 20 KFIz to approximately 100 KHz. In accordance

with an important aspect of the preferred embodiment, a modem 20 constructed in

accordance with the invention senses the need to dynamically allocate or deallocate a

portion of the transmission frequency band in order to accommodate voice

communications within the 0 to 4 KHz POTS frequency band 12. As will be

described further herein, the present invention may sense this demand for voice

transmissions (or band-limiting condition) by sensing an OFF-HOOK condition of a

telephone 30. 32. (see FIG. 2) connected to the local loop 26. Alternatively, this band-limiting condition may be detected by an impedance change on the local loop

26.

For phone compatibility, in addition to detecting RING and OFF-HOOK

conditions, the system may also be configured to detect voice conversation. Upon

voice detection, the system may increase transmit power as it shifts into the band-

limited transmission state, to increase data rate dynamically, so long as the voice

band SNR is about 30 to 40 dB. When silence is once again detected (for a

predetermined amount of time), the system will again reduce the transmit power for

good idle channel perception.

Unlike typical xDSL communications, where the data transmission frequency

band is often 1 MHz in width, the data transmission frequency band of the present

invention is much less than that. This permits relatively high-speed data

communication without the addition of expensive equipment, such as POTS splitters

and POTS filters. Importantly, this addresses a market need from consumers that do

not wish to incur, or cannot afford, the additional expenses normally incurred with

purchasing an xDSL communication service. An important aspect of the present

invention is its ability to sense when voice-band communications are not occurring, or

otherwise when a band-limiting condition is not present, and expand the transmission

frequency band into the frequency band otherwise reserved for POTS transmissions.

and/or increase transmit power to increase the data rate. As can be seen from the

illustrations in Figs. 3A and 3B, expanding the transmission frequency band from a 20

kHz cutoff (FIG. 3B) to approximately DC (FIG. 3 A) realizes a 25 percent increase in bandwidth (i.e.. from 80 kHz to 100 kHz), and thus realize a significant improvement

in performance.

FIGS. 3C and 3D illustrate alternative embodiments of the present invention.

In short. FIGS. 3C and 3D illustrate a spectrally-shaped transmission curve and an

adaptive power transmission curve, respectively. As illustrated in FIG. 3B. under

normal operating condition, the power density of the xDSL transmission band is

greater than that of the POTS transmission band. However, there may be instances

when the guard band 16 is not large enough to sufficiently separate the xDSL

transmission band 52 from the POTS frequency band 12. As a result. xDSL

transmissions may be evident in the POTS frequency band 12 as noise (audible static).

The reasons this may occur are varied, and include factors such as telephone set

sensitivity and non-linearities. Intermodulation products may also be manifest within

the POTS transmission band 12 as noise.

It will be appreciated that, consistent with the concepts and teachings of the

present invention, various adaptations of the band-limited transmission state may be

implemented to minimize or eliminate noise in the POTS transmission band 12. One

solution is to further increase the size of the guard band 16. thereby increasing the

frequency separation between the POTS transmission band 12 and the xDSL

transmission band 52. Another solution is to adaptivelv reduce the transmit power of

the xDSL transmission band. This solution is illustrated in FIG. 3D. wherein the

normal power spectrum 52 is illustrated in dashed line and the reduced power

spectrum 56 is superimposed in solid line. Reducing the transmit power in this way

reduces the amount of noise that is manifest within the POTS frequency band. The specific amount of power reduction may vary among customer premises, based upon

the attached equipment.

Yet another solution is to more particularly define the spectral shape of the

transmission band. This solution is illustrated in FIG. 3C. As shown, the power

spectrum of the xDSL transmission band 54 may be asymmetrically shaped to provide

a greater taper on the lower frequency end of the curve. This taper, ensures sufficient

attenuation of the xDSL transmission signal above the POTS frequency band 12. and

therefore minimizes intermodulation products and noise (resulting from the xDSL

transmission) within the POTS band 12. Although only one such shaped signal band

56 is illustrated in FIG. 3D. it will be appreciated that this aspect of the invention is

not so limited. Instead, other shapes may be deemed desirable, depending upon the

specific environment and line conditions.

Reference is now made to FIG. 4. which shows a block diagram of a modem

20 constructed in accordance with the present invention. As is common among

modems, the modem 20 is in communication with both a local loop 26 and computing

equipment 25. such as a personal computer. More specifically, the modem 20

communicates with the computing equipment 25 across line 60. The telephone line

26 is typically comprised of a two wire service, which wires are often denoted as TIP

62 and RING 64. The TIP 62 and RING 64 lines are input to an analog front-end

circuit 66 (see FIG. 5) as well as a monitor circuit 68. which is configured to detect an

OFF-HOOK condition of the local loop 26.

Analog to digital and digital to analog converter circuitry 70 is in

communication with the analog front end circuitry 66. and is in further communication with digital signal processor 72. Data received from the local loop 26

passes through the analog front-end 66 and is converted from analog to digital form

by the analog to digital converter of block 70. before being passed to the digital signal

processor 72. Conversely, outgoing data output from the digital signal processor 72 is

converted by the digital to analog converter of block 70. before being communicated

to the local loop 26. by way of the analog front-end 66. Finally, a Data Terminal

Equipment (DTE interface 74) is in communication with the digital signal processor

72 and in further communication across line 60, with the data terminal equipment,

such as a computer 25. The analog to digital and digital to analog converter circuitry

70. the digital signal processing 72, and the DTE interface 74 are all well known and

generally operate in accordance with the prior art. Therefore, their individual

structure and operation need not be described herein.

Indeed, a significant component of the modem 20, constructed in accordance

with the present invention, is a controller 80 that is in communication with the various

other components of the modem 20. While there are various ways to implement the

controller 80. one way, as illustrated, is to further partition the controller 80 into

functional units denoted as a processing unit 82. a memory 84 (which may further

include an executable code segment 86) and a controller 88.

For purposes of the broad concepts of the present invention, the controller 80

receives a signal from the monitor circuit 68 on line 90. which signal indicates

whether the invention should transmit data in a band-limited transmission state or a

full-band transmission state. In this regard, the monitor circuitry 68 may be

configured to detect an OFF-HOOK condition or alternatively a RING condition on local loop 26. As is known in the art. the OFF-HOOK condition may be detected by a

drop in voltage across the local loop 26. or alternatively a sudden chance in

impedance on the local loop 26. On the other hand, a RING detect condition is

identified by a low frequency oscillatory voltage on local loop 26. For example, the

voltage drops from about 48 volts (on hook) to approximately 10 volts or less (off

hook), at the customer premises end of the local loop.

In short, the controller 80 evaluates the signal received on line 90 to determine

whether data should be transmitted in the full-band transmission state or the band-

limited transmission state. Appropriate signals may. accordingly, be transmitted to

the digital signal processor 72 for formulating data transmissions (or interpreting

received data transmissions).

In accordance with an alternative embodiment of the invention, it will be

appreciated that the monitor circuitry 68 may be incoφorated within the controller 80.

whereby certain signal conditions may be evaluated to detect the band-limiting

condition. In this regard, an analog to digital converter would also be implemented as

part of the controller 80. to generate a signal in digital format which may be more

readily evaluated and processed by the processing unit 82. In this regard, the

processing unit 82 may be a microprocessor, a microcontroller, an application specific

integrated circuit (ASIC) or other digital circuitry configured to specially processed

information. In the illustrated embodiment, the controller 80 includes fundamental

components (processor unit, controller, memory) that together operate to perform

distinct computing operations. Such operations may be controlled, for example, by

executable code 86 contained within the memory 84. Reference is now made to FIG. 5, which shows a more detailed diagram of the

circuitry comprising the analog front-end 66. The preferred embodiment includes

blocking capacitors 102 and 104, which are series connected with the TIP 62 and

RING 64 signal lines, and serve to block any DC voltage otherwise carried on the TIP

62 and RING 64 lines. A transformer 106 couples alternating current to the remainder

of the circuitry, as well as provides safety and signal isolation for the remaining

circuitry in the modem. A termination resistor 108 and switch 1 10 are disposed for

series connection with each other (depending upon whether the switch 1 10 is opened

or closed), and together are connected in parallel across the secondary winding of the

transformer 106. The switch 1 10 is controlled by controller 80 (FIG. 4) to close and

therefore switch in the terminating resistor 108 when the telephones 30 and 32 (see

FIG. 2) are all ON-HOOK (as observed by the monitor circuit 68). The switch 1 10

may be open to switch out the terminating resistor 108. upon detection of an incoming

RING signal or OFF-HOOK on the local loop 26. Capacitors 102 and 104 are chosen

to pass data, block DC. and yield acceptable Ringer Equivalence Number per FCC

part 68. The switch 1 10 is generally opened to switch out the terminating resistor

when the monitor circuit 68 determines that the local loop 26 is in the OFF-HOOK

state. The reason for this is that, when one or more telephones are taken OFF-HOOK,

then the OFF-HOOK telephone will terminate the line, and the terminating resistor

108 is not needed. Optionally, the switch 1 10 can be closed in the Off-HOOK state to

improve line termination provided by the OFF-HOOK telephone.

The item represented by reference numeral 1 12 denotes circuitry that is

configured in a form of a dependent current source. The current source is prompted by the transmit signal Tx to create an outgoing transmission signal. As a current

source, the item 1 12 has a very high impedance (as seen across the secondary winding

of transformer 106) and therefore, only the termination resistor 108 operates to

terminate the line (when switched in). Similarly, amplifier 1 14 is the receive

amplifier that generates the Rx signal, as is known in the art. Like the current source

1 12. the amplifier 1 14 has an extremely high input impedance and thus does not effect

line termination.

Reference is now made to FIG. 6. which a software flow-chart illustrating the

operation of the analog front-end element of FIG. 5. Beginning at step 120. the

element determines whether the local loop 26 is ON-HOOK or OFF-HOOK. As will

be appreciated from the foregoing discussion, this decision is made by the controller

80 which outputs a signal 122 (see FIG. 4) to the analog front-end 66 indicative of the

ON-HOOK/OFF-HOOK status. If the resolution of step 120 is NO, the analog front-

end element 66 opens switch 1 12 (step 122) to remove the termination resistor 108

from the circuit. That is. if the system detects that a telephone connected to the local

loop 26 is OFF-HOOK. it will remove the termination resistor 108 from the circuit.

since the line will then be terminated by the OFF-HOOK telephone. Thereafter,

operation proceeds to step 122. wherein data is transmitted in accordance with the

band-limited transmission frequency band (e.g., 20 kHz- 100 kHz). In accordance

with one embodiment of the present invention, the system may emit periodic tones

within the audible frequency range to alert a user talking on an attached telephone the

local loop 26 is also being used for data transmissions. Thus, a person, for example,

speaking in another part of the house over a telephone hearing periodic beeps would know that someone else in the household is using a computer to communicate data,

and therefore may wish to keep his or her conversation to a minimum, in order to free

up the local loop 26. so that the present invention may obtain a full utilization of the

full-banded transmission frequency band, for maximum data throughput.

If the resolution of step 120 is YES, indicating that all telephones attached to

the local loop 26 are ON-HOOK. then the system ensures that switch 1 10 is closed

thereby placing termination resistor 108 in the circuit, so as to achieve proper line

termination (step 130). Thereafter, the system may transmit data across the local loop

utilizing the entire, full-band transmission frequency (i. e.. DC to approximately 100

KHz).

Reference is now made to FIG. 7. which is a software flow-chart illustrating

the top-level operation of a system communicating in accordance with the present

invention. Beginning at block 140. the system awaits the initiation of data

transmission. This initiation may occur either upon the instruction of a user at the

computer 25 (see FIG. 2). or alternatively from a remote user that is dialing the phone

number of computer 25 to connect up to that computer (this assumes that that

computer 25 is in auto answer mode). Once the system has been instructed to begin

data communications, it first makes a check (at step 144) to determine whether the

loop is in the OFF-HOOK state. If so, it begins the data communications in the band-

limited frequency transition state (step 146)(e.g. , 20 kFIz - 100 kHz). During the data

transmissions, the system will make continuous checks to determine whether the data

transmission has ended (step 148. or whether the band-limiting condition has subsided

(step 150). As previously mentioned, the band-limiting condition is generally identified by the OFF-HOOK detection circuitry. If the end data communications

check, at step 148. resolves to YES. then the system returns to step 140. If not. the

system proceeds to step 150 where it checks for the cessation of the band-limiting

condition. If this step resolves to YES, then the system continues the data

transmission in the full-band transmission frequency bandwidth (step 154).

Returning to the decision block 144. if, upon initiation of data communication,

the system determines that all telephones are presently ON-HOOK. then the system

proceeds to step 154 where it transmits data in accordance with the full-band data

transmission state (i.e.. utilizing the full 0 to 100 KHz transmission frequency

bandwidth). During transmission in this frequency band, the system periodically

checks to see if the data communications has terminated (step 156). or whether the

occurrence of a band-limiting condition has occurred (step 158). This latter condition

occurs, for example, when a person lifts a handset of an attached telephone. If this

occurs, the system proceeds to step 146 and continues the data transmissions in

accordance with the band-limited transmission frequency band (20 kHz - 100 kHz).

It will be appreciated from a review of the flow-chart of FIG. 7. that the

system, during data transmission, can dynamically shift back and forth between the

full-band and band-limited transmission frequency bandwidths as users may lift or

reset telephone handsets (or as RING conditions occur). It will be appreciated.

however, that other band-limiting conditions (other than RING or OFF-HOOK) may

be utilized to invoke the frequency shifting feature of the present invention, depending

upon the system configuration or other pertinent system factors. It will be appreciated that the invention described herein could provide a low-

cost solution to Internet access for the mass consumer market. In this regard. It could

fill the gap in our product offering between low-cost 33.6 kbps modems and high

speed xDSL modems, which require the addition of relatively expensive equipment

(such as POTS splitters and POTS filters) at the customer premise, and is labor

intensive. The present invention, as described above, generally achieves

transmissions rates in the range of 64 kbps to 640 kbps.

As described above, the invention utilizes the low frequency portion of the

telephone subscriber loop spectrum (roughly DC to approximately 100 KHz) to

transport user data. The modulation could be CAP. QAM. DMT. spread spectrum.

etc. as the invention is not limited to any particular form. Utilization of the lower

frequency portion of the telephone subscriber loop has the advantage of lowest

possible signal attenuation (usually the number one signal impairment in data

communications) and low cross-talk. Other advantages are reduced transmission line

concerns like reflections due to stubs.

In use. the invention requires a simple bridge (electrical parallel) connection to

the subscriber loop or premise wiring. Therefore, one unit would connect (in bridge

fashion) at the central office, and one companion unit connect at the customer

premises.

The foregoing description has been presented for purposes of illustration and

description. It is not intended to be exhaustive or to limit the invention to the precise

forms disclosed. Obvious modifications or variations are possible in light of the

above teachings. The embodiment or embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its

practical application to thereby enable one of ordinary skill in the art to utilize the

invention in various embodiments and with various modifications as are suited to the

particular use contemplated. All such modifications and variations are within the

scope of the invention as determined by the appended claims when interpreted in

accordance with the breadth to which they are fairly and legally entitled.

Claims

We Claim:

1. A modem for communicating across a communication link

comprising:

an input/output signal line in communication with the communication

link:

a processor unit adapted for operation in one of at least two states, a

full-band transmission state and a band-limited state, wherein the full-band

transmission state is defined by significant transmission energy in a frequency range

below a first frequency, and a band-limited transmission state defined by a negligible

amount of energy in the frequency range below the first frequency.

2. The modem as defined in claim 1. wherein the first frequency is

approximately 15 kilohertz.

3. The modem as defined in claim 1. wherein the communication link is a

multiple-use communication link.

4. The modem as defined in claim 1. further including:

sensing means for sensing a band-limiting condition; and

control means associated with the processor unit responsive to the

sensing means for controlling the operating state of the processor unit, wherein upon

sensing the band-limiting condition the control means causes the processor to operate in the band-limited state, and upon sensing no band-limiting condition the control

means causes the processor to operate in the full-band transmission state.

5. The modem as defined in claim 1. wherein significant energy

transmissions are transmissions substantially exceeding a audible level.

6. A modem for communicating across a communication link capable of

single-use transmissions and multiple-use transmissions comprising:

an input/output signal line in communication with the communication

link:

a processor unit adapted for operation in one of at least two states, a

full-band transmission state and a band-limited state, wherein the full-band

transmission state occurs when single-use transmissions are occurring across the

transmission link, and the band-limited transmission state occurs when multiple-use

transmissions are occurring across the communication link.

7. A modem for communicating across a communication link comprising:

an input/output signal line in communication with the communication

link:

a processor unit adapted for operation in one of at least two states, a

full-band transmission state and a band-limited state, wherein the full-band

transmission state is defined by significant energy transmission below a first

frequency and the band-limited state is defined by substantialh- zero energy

transmission below the first frequency;

sensing means for sensing a band-limiting condition; and

control means associated with the processor unit responsive to the

sensing the band-limiting condition the control means causes the processor to operate

in the band-limited state, and upon sensing no band-limiting condition the control

means causes the processor to operate in the full-band transmission state.

8. The modem as defined in claim 7. wherein the first frequency is

approximately 15 kilohertz.

9. The modem as defined in claim 7. wherein the sensing means is

configured to detect a multi-position switch, the position of which defines the band-

limiting condition.

10. The modem as defined in claim 7. wherein the sensing means is

configured to detect an off-hook condition of a telephone that is electrically connected

to the input/output signal line.

1 1. The modem as defined in claim 10. wherein the sensing means further

includes means for detecting the onset of a condition indicative of a handset of the

telephone being taken off-hook.

12. The modem as defined in claim 1 1. wherein the means for detecting

the onset of the condition is configured to detect a voltage drop on the input/output

signal line.

13. The modem as defined in claim 1 1. wherein the means for detecting

the onset of the condition is configured to detect an impedance shift in the

input/output signal line.

14. The modem as defined in claim 7. wherein the full-band transmission

state is defined by a transmission frequency bandwidth having a lower frequency

boundary of less than 4 kilohertz.

15. The modem as defined in claim 14. wherein the full-band transmission

state is defined by a transmission frequency bandwidth having a lower frequency

boundary of approximately DC.

16. The modem as defined in claim 7. wherein the full-band transmission

state is defined by a transmission frequency bandwidth having an upper frequency

boundary of greater than 50 kilohertz.

17. The modem as defined in claim 16. wherein the full-band transmission

boundary of approximately 100 kilohertz.

18. The modem as defined in claim 7. wherein the band-limited transmission state is defined by a transmission frequency bandwidth having a lower

frequency boundary of greater than 4 kilohertz.

19. The modem as defined in claim 18. wherein the full-band transmission

state is defined by a transmission frequency bandwidth having a lower frequency

boundary of approximately 20 kilohertz.

20. The modem as defined in claim 7. wherein the full-band transmission

state is defined by a first transmission frequency bandwidth and the band-limited

transmission state is defined by a second transmission frequency bandwidth, wherein

the first transmission frequency bandwidth has an upper frequency boundary that is

substantially the same an upper frequency boundary of the second frequency

bandwidth.

21. The modem as defined in claim 7. wherein the full-band transmission

different than an upper frequency boundary of the second frequency bandwidth.

22. The modem as defined in claim 7, wherein the communication link is a

two-wire telecommunications link.

23. The modem as defined in claim 7, wherein the communication link is a local loop.

24. The modem as defined in claim 7. wherein the sensing means includes a code segment containing executable code.

25. The modem as defined in claim 7, wherein the control means includes

a code segment containing executable code.

26. A modem for communicating across a communication link comprising:

an input/output signal line in communication with the communication

link;

a processor unit adapted for operation in one of two states, a full-band

transmission state and a band-limited state, wherein the full-band transmission state is

defined by a lower frequency boundary below a second frequency and an upper

frequency boundary greater than a first frequency, and the band-limited state is

defined by a lower frequency boundary greater than the second frequency and an

upper frequency boundary greater than the first frequency;

a sensor configured to detect the presence of a band-limiting condition: and

a controller associated with the processor unit and responsive to the

sensor, configured to control the operating state of the processor unit, wherein upon

sensing the band-limiting condition the controller causes the processor to operate in

the band-limited state, and upon sensing no band-limiting condition the controller

causes the processor to operate in the full-band transmission state.

27. The modem as defined in claim 26. wherein the first frequency is

approximately 50 kilohertz.

28. The modem as defined in claim 26, wherein the second frequency is

approximately 4 kilohertz.

29. A method for dynamically communicating data over a communication

link using a modem comprising the steps of:

transmitting data in a full-band transmission state;

sensing a band-limiting condition; and

adjusting the transmission of data from the full-band transmission state

to a band-limited transmission state, in response to the sensing step.

30. The method as defined in claim 29. wherein the sensing step includes

detecting the position of a multi-position switch.

31. The method as defined in claim 29. further including the step of

adaptively varying transmit power of the transmission of data to minimize

interference of data signals with a lower frequency band.

32. The method as defined in claim 29. further including the step of

uniquely shaping a power spectral transmission band of the data transmission to

minimize interference of data signals with a lower frequency band.

33. The method as defined in claim 29. further including the step of

sensing a cessation of the band-limiting condition.

34. The method as defined in claim 33. further including the step of

adjusting the transmission of data from the band-limited transmission state to the full-

band transmission state, in response to the step of sensing the cessation of the band-

limiting condition.

35. The method as defined in claim 29, wherein the step of sensing the

band-limiting condition includes sensing an incoming ring signal on the

communication link.

36. The method as defined in claim 29, wherein the step of sensing a band-

limiting condition includes sensing an off-hook condition of a telephone handset of a

telephone electrically connected to the communication link.

37. The method as defined in claim 36, wherein the step of sensing the off-

hook condition includes sensing an impedance of the communication link.

38. The method as defined in claim 36, wherein the step of sensing the off-

hook condition includes sensing a voltage on the communication link.

39. The method as defined in claim 29, wherein the full-band transmission

state is defined by a transmission frequency bandwidth having a lower frequency

boundary of less than 4 kilohertz.

40. The method as defined in claim 39, wherein the full-band transmission

state is defined by a transmission frequency bandwidth having a lower frequency

boundary of approximately DC.

41. The method as defined in claim 29, wherein the full-band transmission

boundary of greater than 50 kilohertz.

42. The method as defined in claim 41, wherein the full-band transmission state is defined by a transmission frequency bandwidth having an upper frequency

boundary of approximately 100 kilohertz.

43. The method as defined in claim 29. wherein the band-limited

frequency boundary of greater than 4 kilohertz.

44. The method as defined in claim 43. wherein the full-band transmission

state is defined by a transmission frequency bandwidth having a lower frequency

boundary of approximately 20 kilohertz.

45. The method as defined in claim 29, wherein the full-band transmission

state is defined by a first transmission frequency bandwidth and the band-limited transmission state is defined by a second transmission frequency bandwidth, wherein

substantially the same an upper frequency boundary of the second frequency

bandwidth.

46. The method as defined in claim 29, wherein the full-band transmission

different than an upper frequency boundary of the second frequency bandwidth.

47. A method for dynamically communicating data across a

communication link using a modem comprising the steps of:

transmitting data in a band-limited transmission state;

sensing a cessation in a band-limiting condition; and

adjusting the transmission of data from the band-limited transmission

state to a full-band transmission state, in response to the sensing step.

48. The method as defined in claim 47, further including the step of

sensing a band-limiting condition.

49. The method as defined in claim 48, further including the step of

adjusting the transmission of data from the full-band transmission state to the band- limited transmission state, in response to the step of sensing the band-limiting

condition.

50. A method for communicating both voice and data between a customer

premises and a central office across a communication link comprising the steps of:

transmitting data between the customer premises and the central office

in a first frequency band, wherein the first frequency band is defined by an upper

frequency boundary and a lower frequency boundary;

allocating a second frequency band for transmitting voice information

between the customer premises and the central office in the second frequency band:

sensing a band-limiting condition; and

dynamically shifting the lower frequency boundary of the first

frequency band in response to the sensed band-limiting condition.

51. The method as defined in claim 50. wherein the step of dynamically

shifting the lower frequency boundary includes shifting the lower frequency boundary

of the first frequency band to at least partially overlap between the first frequency

band and the second frequency band, when the band-limiting condition is not present.

52. The method as defined in claim 50. wherein the step of dynamically

of the first frequency band so that there is no overlap between the first frequency band

and the second frequency band, when the band-limiting condition is present.

53. The method as defined in claim 50. wherein the step of sensing a band-

limiting condition includes sensing an off-hook condition of a telephone electrically

connected to the communication link.

54. The method as defined in claim 50. further including the step of

shifting the upper frequency boundary of the first frequency band in response to the

sensed band-limiting condition.

55. The method as defined in claim 50. wherein the lower frequency boundary is less than 4 kilohertz.

56. The method as defined in claim 55. wherein the step of dynamically shifting the lower frequency boundary includes the step of shifting the lower

frequency boundary to a frequency greater than 4 kilohertz.

57. The method as defined in claim 55. wherein the lower frequency

boundary is approximately DC, and the step of dynamically shifting the lower

frequency boundary includes the step of shifting the lower frequency boundary to a

frequency greater than 4 kilohertz.

58. The method as defined in claim 57. wherein the step of dynamically shifting the lower frequency boundary includes the step of shifting the lower

frequency boundary upwardly to a frequency of approximately 20 kilohertz.

59. The method as defined in claim 50. wherein the step of sensing the

band-limiting condition includes the step of detecting the onset of a condition

indicative of demand for voice communications.

60. The method as defined in claim 50, wherein the step of sensing the

band-limiting condition includes the step of detecting the cessation of a condition indicative of the termination of voice communications.

61. The method as defined in claim 60, wherein the step of dynamically

shifting the lower frequency boundary includes the step of shifting the lower

frequency boundary from a value greater then 4 kilohertz to a value less that 4

kilohertz.

62. A computer readable storage medium containing program code for

controlling the operation of a modem used for dynamically communicating data over

a phone in accordance with a method comprising the steps of:

transmitting data in a full-band transmission state;

sensing a band-limiting condition; and

adjusting the transmission of data from the full-band transmission state

to a band-limited transmission state, in response to the sensing step.

63. A computer readable storage medium containing program code for

controlling the operation of a modem for communicating data across a communication link comprising:

a first code segment operative to transmit and receive data across an

input/output signal line in communication with the communication link;

a second code segment operative to control a processor unit for

operation in one of two states, a full-band transmission state and a band-limited state,

wherein the full-band transmission state is defined by a lower frequency boundary

below a second frequency and an upper frequency boundary greater than or equal to a

first frequency, and the band-limited state is defined by a lower frequency boundary

greater than the second frequency and an upper frequency boundary greater than or

equal to the first frequency;

a third code segment for sensing a band-limiting condition; and

a fourth code segment for controlling the operating state of the

processor unit, wherein upon sensing the band-limiting condition the control means causes the processor to operate in the band-limited state, and upon sensing no band-

limiting condition the control means causes the processor to operate in the full-band transmission state.

64. The computer readable storage medium as defined in claim 63,

wherein the first frequency is approximately 50 kilohertz.

65. The computer readable storage medium as defined in claim 63. wherein the second frequency is approximately 4 kilohertz.