WO2000010317A9

WO2000010317A9 - Apparatus and method for communicating data using a supervised, derived channel system

Info

Publication number: WO2000010317A9
Application number: PCT/US1999/018312
Authority: WO
Inventors: Harry Stephey; Walt Jehnert
Original assignee: Numerex Investment Corp; Harry Stephey; Walt Jehnert
Priority date: 1998-08-14
Filing date: 1999-08-13
Publication date: 2000-05-18
Also published as: AR021773A1; WO2000010317A1; TW425807B; AU5557399A

Abstract

The supervisory signal of a derived channel data reporting system is used as a primary, data communicating signal. The data communicating signal can be implemented as a single tone, or as plural tones having a frequency (e.g., from 200 Hz to 300 Hz) which is capable of being transmitted by existing telephone network equipment, including digital transmission equipment, and an attenuated level. As an alternative, the data reporting signal can be implemented at a reduced frequency (e.g., at an audible frequency of less than 150 Hz) to be compatible with existing, high-speed modems. Such operation can be achieved in a simplex mode, or in a half-duplex or full-duplex mode, as preferred. The data reporting signal can further be implemented in such a way that multiple applications can be supported by a single telephone line or switchboard grouping, by using different signals to avoid interference between multiple subscriber terminal units associated with the system. The data rate achievable with the data reporting signal can be increased to transmit increased amounts of data by increasing the bit rate of the communicating signal, preferably using modulation techniques such as quaternary phase shift keying (QPSK), 8-phase shift keying or discrete multi-tone (DMT) modulation, to yield multiple bits per baud while maintaining a low channel baud rate.

Description

APPARATUS AND METHOD FOR COMMUNICATING DATA USING A SUPERVISED, DERIVED CHANNEL SYSTEM

Background of the Invention

The present invention generally relates to data communicating systems, and in particular, to data communications that can be performed in conjunction with a supervised, derived channel system.

A variety of data reporting systems are available to protect and/or remotely monitor residential and commercial sites. This is conventionally accomplished by placing appropriate detectors (contact switches, motion detectors, smoke detectors, fire detectors, parameter monitoring devices, etc.) at desired locations at the site to be monitored (the "subscriber's premises") and coupling the deployed detectors with an event communicating panel. The event communicating panel is configured to monitor the deployed detectors to determine the initiation of, or changes in conditions at the subscriber's premises (responsive to a change in state of one of the detectors).

In this way, the event communicating panel is made capable of monitoring the condition of the subscriber's premises, and of providing a local signal (e.g., an alarm) responsive to signals received from the deployed detectors. In most cases, it will additionally be desirable to alert a remote facility of the detected change in conditions. For example, a detected break in a contact sensor or detected movement associated with a motion detector may signify an attempted break-in at the subscriber's premises, calling for police intervention. Similarly, a detected change in state of a smoke detector or a fire detector may signify a fire, calling for intervention by a fire department. A detected change in a parameter monitoring device may signify a need to service an apparatus located at the subscriber's premises.

This is accomplished by establishing a communicating link between the event communicating panel at the subscriber's premises and a remotely stationed monitoring facility. This communicating link is preferably established by telephone due to the availability and adaptivity of telephone-based systems to the remote reporting of monitored conditions.

A basic system for accomplishing such a result establishes a one-way (so-called "unsupervised") connection between the event communicating panel and the central monitoring facility, to advise (report) the monitoring facility of any detected changes in conditions. The monitoring facility is then responsible for dispatching an appropriate response (police, fire, service, etc.). However, in practice, it has been found that such basic systems are prone to false alarms, and are easily defeated by severing the telephone connection (either intentionally, by an intruder, or through damage to the telephone system).

This gave rise to the development of so-called "supervised" systems for providing added assurances of the detection of such conditions, in turn permitting a more assured response to such conditions. One such system which has found wide acceptance in the industry is the "VerSuS®" System which is presently marketed by DCX Systems, Inc. of Willow Grove, Pennsylvania. The "VerSuS®" System is also described in U.S. Patent No. 4,442,320 (James et al.), which is incorporated by reference as if fully set forth herein.

In brief, the VerSuS® System creates a "derived channel" by coupling a "subscriber terminal unit" (STU®) with the event communicating panel and its associated detectors, which are located at each subscriber's premises, and by coupling a "scanner" with the telephone switch equipment which is located at the telephone company central office. The scanner in turn communicates with the remote monitoring facility, also using the telephone network. The scanner at the central office and the subscriber terminal units deployed at the subscribers' premises to be monitored combine to supervise the detection of signals representing changes in conditions in a way which minimizes the potential for false reports, and for compromising such systems.

To this end, the scanner operates to periodically poll (by a telephone connection) each of the subscriber terminal units located at each of the subscriber's premises to be monitored. Although various types of signals may be used for this purpose, frequency shift keyed (FSK) signals are disclosed for such purposes in U.S. Patent No. 4,442,320. Such polling signals are directed to the subscriber terminal unit, which monitors the event communicating panel at the subscriber's premises, to ascertain the status of the detectors located at the subscriber's premises. Such periodic polling also operates to verify the viability of the telephone connection which couples the subscriber terminal unit, and its associated event communicating panel, with the scanner. The subscriber terminal unit is additionally made capable of communicating with the scanner (i.e., two-way communications) to immediately advise of a change in condition detected at the subscriber's premises. While such supervised communications operate to significantly improve the assurances of an effectively monitored premises, and an effectively reported change in condition, FSK signalling (and other signalling systems) occurs at a frequency which causes an audible signal to be placed on the telephone line. When the telephone at the subscriber's premises is not in use (a so-called "on-hook" condition), this does not present a problem. However, the placement of an audible signal on the telephone line is considered unacceptable when the telephone at the subscriber's premises is in use (a so-called "off-hook" condition). To meet this limitation while maintaining the supervisory function of the data reporting system, an alternative operating mode is used when the telephone is off-hook and in use.

In this alternative mode, polling signals and responses in the audible frequency range are suspended, and a sub-audible tone is monitored to determine the status of the remotely stationed event communicating panel. The sub-audible tone is produced by the subscriber terminal unit, and is monitored by the scanner. The presence of the sub-audible tone indicates an absence of any changes in conditions, justifying a continued suspension of any polled responses. Upon the occurrence of a change in condition, the sub-audible tone is discontinued by the subscriber terminal unit. Upon detecting a discontinued sub- audible tone for a particular subscriber's premises, the scanner then initiates a polling sequence, inquiring into the status of the premises. This inquiry is accomplished using the same (audible) signals which are normally employed during on-hook conditions (when the telephone is not in use). However, in the presence of a potentially serious occurrence (e.g., an alarm event), it is acceptable for audible signals to be placed on the telephone line, even though in use, and the polled response which is obtained operates to provide a positive assurance of a validly reported change in condition. The presence of the sub-audible tone during normal telephone usage additionally operates to verify the integrity of the telephone connection since suspension of the sub-audible tone (responsive to a broken line) would itself constitute a change in condition calling for appropriate action by the remote monitoring facility. The result is a positive monitoring of changing conditions during all modes of telephone usage. The sub-audible tone suggested for use by U.S. Patent No.

4,442,320 is a 25 Hz tone. In practice, a 36 Hz tone has been found to provide an optimum result. In either case, the tone is sub-audible and readily transmitted by conventional analog switch equipment. However, to meet the demands of present technological requirements, the trend has been to replace analog transmission equipment with digital transmission equipment (so-called "digital loop carrier systems"). As part of their operation, digital loop carrier systems convert the analog signals developed by conventional telephone equipment, including data reporting equipment, to a digital form which is better suited to transmitting larger quantities of information using the relatively hmited available bandwidth of conventional telephone equipment (typically 300 to 3200 Hz). However, as part of this analog to digital conversion process, the analog signal is subjected to band pass filtering. In practice, it has been found that such filtering tends to eliminate the sub-audible (36 Hz) signal which is used for purposes of supervising data reporting equipment as previously described, precluding the supervisory function of the sub- audible tone during off-hook telephone conditions.

As an alternative to the sub-audible tone, and in order to supervise a derived channel data reporting system in the presence of digital telephone network equipment, U.S. Patent No. 5,822,423 discloses implementation of the supervisory signal as a tone having a frequency which is capable of being transmitted by a digital loop carrier system, but which is transmitted at an attenuated level sufficient to minimize, if not practically eliminate interference with normal telephone usage (including off-hook conditions of the telephone). Such a supervisory signal preferably has a frequency which lies outside of the conventional 300 to 3200 Hz pass band, but which is still within the pass band of a digital loop carrier system, and which is capable of operating in conjunction with biphase modulated (BPSK), frequency shift keyed (FSK) and multi- tone modulated (MLT) polling systems. Supervisory signals having a frequency of from 200 Hz to 300 Hz are specified for such purposes, with frequencies approaching 200 Hz being particularly preferred.

Since conventional digital loop carrier systems are generally considered to pass frequencies in a range of from 300 to 3200 Hz, it has been found that frequencies of 200 Hz to 300 Hz are effectively communicated by such systems, although at an attenuated level. Such attenuation is sufficient to avoid unsatisfactory interference with active (off-hook) telephone usage, and telephone company signalling, yet the resulting signal is of a sufficient magnitude to be detected by the scanner of a supervised, derived channel data reporting system. U.S. Patent No. 5,822,423 further discloses that the basic supervisory tone previously used in conjunction with such data reporting systems can be replaced with a supervisory signal which is capable of transmitting useful data. Added assurances of reliable reporting are provided by transmitting active data, as distinguished from the more limited, essentially binary indication of state (i.e., tone present or absent) provided by previous supervisory tones. Encrypted data can be used to further increase the security which is provided.

In practice, implementation of the supervisory signal at a frequency which is capable of being transmitted by existing, band-limited telephone network equipment, at an attenuated level, whether for purposes of providing a binary indication of state or for purposes of transmitting useful data, has been found to work well in providing a variety of practical applications. However, it has also been found that such systems are capable of various improvements, to offer even greater versatility in terms of their implementation.

Summary of the Invention

It is therefore the primary object of the present invention to provide a supervisory signal useful with derived channel data reporting systems which can provide primary data communications as well as supervisory signaling. It is also an object of the present invention to provide a supervisory signal useful with derived channel data reporting systems which can be implemented in a simplex mode, or in a half-duplex or full- duplex mode to provide additional supervisory functions. It is also an object of the present invention to provide a supervisory signal useful with derived channel data reporting systems which can be varied in configuration to permit multiple applications (including alarm reporting, meter reading and home automation) to be supported by a single system. It is also an object of the present invention to provide a supervisory signal useful with derived channel data reporting systems which is compatible with ancillary telephone equipment such as modems and high-speed modems.

It is also an object of the present invention to provide a primary, data carrying signal useful with derived channel data reporting systems which is capable of exhibiting the foregoing improvements.

It is also an object of the present invention to provide a data carrying signal useful with derived channel data reporting systems which is capable of being implemented either as a separate component associated with existing telephone equipment or as an integral part of such equipment.

These and other objects which will become apparent are achieved in accordance with the present invention by providing alternative modes for implementing the supervisory signal, to permit the associated derived channel data reporting system to perform a desired function, or series of functions. For example, the supervisory signal can be implemented as a single tone, or as a pair of tones having a frequency (e.g., from 200 Hz to 300 Hz) which is capable of being transmitted by the existing telephone network equipment, but which is transmitted at an attenuated level, to supervise biphase modulated (BPSK), frequency shift keyed (FSK) and multi-tone modulated (MLT) polling systems in a simplex mode of operation. Similar supervision can be achieved in a half-duplex mode or in a full-duplex mode by providing the scanner and the subscriber terminal units associated with the derived channel data reporting system with appropriate data transmitting and data receiving components for developing the particular operating mode which is desired. As a further alternative, the supervisory signal can be operated at a reduced frequency (e.g., at an audible frequency of less than 150 Hz) which is compatible with existing, high-speed modems (e.g., ITU type V.34 modems) that characteristically occupy a broader bandwidth. The supervisory signal can also be used to provide primary data communications, in association with the derived channel data reporting system, to perform yet other desired functions. For example, the supervisory signal can be used as the primary data-transmitting signal of a derived channel data reporting system, allowing alarm status information to be communicated between the scanner and the subscriber terminal units associated with the derived channel data reporting system. Such a supervisory signal can be implemented in a simplex mode, in a half-duplex mode or in a full-duplex mode, by providing the scanner and the subscriber terminal units associated with the derived channel data reporting system with appropriate data transmitting and data receiving components for developing the operating mode which is desired for a particular application. The supervisory signal can further be operated at a reduced frequency (e.g., at an audible frequency of less than 150 Hz) which is compatible with existing, high-speed modems (e.g., ITU type V.34 modems) that characteristically occupy a broader bandwidth.

Using the supervisory signal to provide primary data communications further allows the data carrying signal to serve as the exclusive means for providing low-band communications between the subscriber's premises and the monitoring facility. This, in turn, allows audible signaling components (e.g., FSK signaling) and hook status detection to be eliminated from the system.

The supervisory signal can further be implemented in such a way that multiple applications can be supported by a single telephone line. This can include support for multiple functions (e.g., alarm reporting, meter reading and/or home automation functions) at a single subscriber's premises, or support for multiple subscriber terminal units associated with a single switchboard grouping (e.g., a "Centrex Group"). This is preferably accomplished by using different signals to supervise those subscriber terminal units that are capable of communicating with a given telephone line, to avoid interference between the multiple subscriber terminal units associated with the telephone line. The data rate achievable with the supervisory signal can be increased, to transmit increased amounts of data, by increasing the bit rate of the communicating signal. Preferably, this is accomplished using modulation techniques such as quaternary phase shift keying (QPSK), 8- phase shift keying or discrete multi-tone (DMT) modulation techniques, that can yield multiple bits per baud while maintaining a channel baud rate which is as low as possible.

The foregoing data communicating systems can be implemented as separate components which are capable of being coupled with existing telephone equipment, as was previously the common practice. However, if desired, such data communicating systems can also be implemented as an integral part of such equipment, leading to additional versatility in the applications which can be developed with such systems. For further detail regarding the supervisory signal of the present invention, and systems for its implementation, reference is made to the detailed description which is provided below, taken in conjunction with the following illustrations.

Brief Description of the Drawings

Figure 1 is a schematic illustration of a supervised, derived channel alarm reporting system suitable for implementing the improvements of the present invention.

Figure 2 is a schematic illustration of modifications of the system of Figure 1, for implementing the improvements of the present invention.

Figure 3A is a block diagram showing transmitting portions of the system of Figure 2, for use with biphase modulated transmissions. Figure 3B is a block diagram showing receiving portions of the system of Figure 2, for use with biphase modulated transmissions.

Figure 4A is a block diagram showing transmitting portions of the system of Figure 2, for use with frequency shift keyed transmissions.

Figure 4B is a block diagram showing receiving portions of the system of Figure 2, for use with frequency shift keyed transmissions. Figure 5 is a schematic illustration similar to Figure 2, showing modifications of the system of Figure 2 for purposes of implementing a half-duplex or a full-duplex mode of operation.

Figures 6A and 6B are schematic illustrations of supervised, derived channel alarm reporting systems capable of having more than one subscriber terminal unit coupled with a single telephone line.

Figure 7 is a block diagram showing receiving portions of a data reporting system configured for use with biphase modulated (BPSK), quadrature phase modulated (QPSK) and 8-phase modulated transmissions.

Detailed Description of Preferred Embodiments

The improvements of the present invention will find applicability to any of a variety of data reporting (i.e., alarm reporting and/or signal monitoring) systems, employing different event communicating panels, different data reporting facilities, and different interfacing devices. However, for purposes of illustrating the improvements of the present invention, reference will be made to the supervised derived channel system disclosed in U.S. Patent No. 4,442,320. A detailed description of this system may be had with reference to U.S. Patent No. 4,442,320. The following will summarize portions of the disclosed system which are pertinent to the present description, in the context of an alarm reporting system. A discussion of the system of the present invention in the context of an alarm reporting system is provided only for purposes of convenience in description, and it is to be understood that corresponding improvements will be similarly achievable for other types of data reporting systems (i.e., data communicating systems), as will be described more fully below.

Figure 1 schematically illustrates a telephone network 10 which, itself, is entirely conventional in all respects. This is desirable since alarm reporting systems in general, and the supervised derived channel system to be described below, should be compatible with all types of telephone systems and should not interfere with the use of such telephone systems. The network 10 includes a plurality of subscriber telephone handsets (or equivalent terminations), which are respectively designated by the reference numerals 11, 12 and 13. Each of the telephones 11, 12, 13 is respectively connected to its designated local telephone line, or loop, which are respectively designated by the reference numerals 14, 15 and 16. The several telephone loops 14, 15, 16 communicate with a telephone network switch 17, which is normally located at a central office maintained by a telephone company or associated with a privately or govemmentally owned facility (possibly, with the mediation of local switches for directing communications between the telephone loops 14, 15, 16 and the central office switch 17). To this point, all of the components previously described are known, and any of a variety of conventional devices may be used for their implementation. Particularly pertinent to the improvements of the present invention is that the network 10 is primarily analog in design.

Additional components are mated with the telephone network 10 to effectively interface alarm systems at the premises of the subscribers to the telephones 11, 12, 13 with a central monitoring facility which is remote from the subscribers' premises and which is charged with the responsibility of monitoring the premises for alarm conditions.

To this end, a scanner 18 is provided at a convenient location for connection (the connections 19, 20, 21) to the individual subscriber telephone loops 14, 15, 16. The scanner 18 is also located at a point remote from the subscribers' premises to avoid tampering with the scanner 18. Generally, the scanner 18 will be located at the central office where the telephone network switch 17 is located (i.e., at the telephone company central office, or associated with a privately or govemmentally owned facility).

Subscriber terminal units 22, 23, 24 are additionally located at each of the subscriber's premises, and are coupled with the respective telephone loops 14, 15, 16. Each of the subscriber terminal units 22, 23, 24 in turn communicates with (interfaces with) an alarm panel 25, 26, 27, which may be any of a variety of alarm reporting systems which are presently available. Each of the alarm panels 25, 26, 27 will in turn communicate with desired sensors at the subscriber's premises, for monitoring various conditions including those pertinent to security, smoke and fire detection, and the monitoring of equipment at the subscriber's premises, as well as any other parameter, the control of which is desired by the subscribers to such services.

Each of the components previously described is known, both in its specific configuration and in its interaction with the other components identified. Consequently, a further description of these components is unnecessary. However, an overview of the interactive operation of these components is appropriate to an understanding of the present invention. In conjunction with this illustrative description, it will be noted that only three telephone loops 14, 15, 16 have been shown, together with three corresponding series of telephones, subscriber terminal units and alarm panels. However, this has been done only for purposes of simplification. The actual number of systems communicating with the telephone network switch 17 and the scanner 18 will vary, and will generally be significantly greater in number. In operation, usage of the telephones 11, 12, 13 is entirely conventional. The telephones 11, 12, 13 will remain in their dormant, so- called "on-hook" mode until such time as the use of one of the telephones 11, 12, 13 is desired. At that point, the handset will be removed from the telephone, placing the telephone in the so-called "off-hook" mode of operation. Communications will then take place across the respective telephone loop 14, 15, 16, and will be appropriately routed by the telephone network switch 17 in conventional fashion.

When the respective telephones are on-hook, and not otherwise in use (e.g., by modems and the like), the scanner 18 is given a free opportunity to communicate with the subscriber terminal units 22, 23, 24, as necessary. To this end, the scanner includes a transmitting and receiving (T/R) section 18a which is capable of transmitting polling signals and receiving polled responses in accordance with a sequence of operations controlled by the scanner 18. The subscriber terminal units 22, 23, 24 are correspondingly provided with modulating and demodulating (MOD/DEMOD) sections 22a, 23a, 24a, respectively, which operate to demodulate signals received from the T/R section 18a of the scanner 18, and to respond to these signals with a modulated (encoded) reply including an indication of the condition of the various sensors associated with the alarm panel coupled with the subscriber terminal unit which is being polled. The T/R section 18a of the scanner 18 is configured to separately receive the modulated response signals from the MOD/DEMOD sections 22a, 23a, 24a of the subscriber terminal units 22, 23, 24, completing the desired inquiry. Such polled responses are performed on a periodic basis, and preferably in sequential fashion. In this way, the scanner 18 operates to ascertain the condition of the several subscriber terminal units 22, 23, 24, and accordingly, the alarm panels 25, 26, 27 with which they are associated. The scanner 18 in turn communicates with the central monitoring facility 28 which is charged with the responsibility of monitoring the alarm panels 25, 26, 27, in accordance with the polled responses which are obtained.

A variety of different modulation techniques may be used to accomplish the inquiries (polled responses) previously described. This would include prevailing systems such as biphase modulated (BPSK), frequency shift keyed (FSK) and multi-tone modulated (MLT) systems, as well as other systems which may presently be in service or which may later be developed. However, a characteristic of these systems is that the signals sent to initiate a polled response, as well as the response which is received, will be detectable (audible) on conventional telephone equipment. When the telephones 11, 12, 13 are on-hook, this presents no difficulty since the telephone is not in use and the audible modulated signals present no interference with such use. However, when the telephones 11, 12, 13 are off-hook, and in use, these audible modulated signals will produce impermissible interference with normal telephone use (i.e., unwanted sounds on the telephone line).

For this reason, an alternative mode of operation is used to monitor subscriber premises when the subscriber's telephone is in service (off-hook). To this end, each of the subscriber terminal units 22, 23, 24 is caused to emit a sub-audible tone, which is not detectable by the user of an off -hook telephone, and operations of the T/R section 18a of the scanner 18 are suspended (disabled) to the extent that polling signals are not produced. Instead, the T/R section 18a operates to receive the sub- audible tone produced by the subscriber terminal units 22, 23, 24.

During periods when a telephone is off-hook, and the scanner 18 receives a sub-audible tone from the corresponding subscriber terminal unit, a polling signal is not initiated and polled responses are not provided. Instead, it is presumed that the alarm panel is in operation, the subscriber's loop is functioning properly, and there is no alarm condition to report. As a result, there is no interference with normal off-hook telephone usage. In the event that the scanner 18 no longer detects a sub- audible tone from a particular subscriber terminal unit, an assumption is made that either the telephone loop 14, 15, 16 has been tampered with (e.g., a cut line) or an alarm condition has occurred (which causes the subscriber terminal unit to discontinue the sub-audible tone, responsive to the detected alarm event). In such case, the scanner 18 activates the T/R section 18a, and makes an inquiry into (polls) the status of the subscriber terminal unit responsive to its change in state (loss of the sub-audible tone). An alarm event is determined to exist (either a break in the telephone line or an actual alarm event) and the central monitoring facility 28 is appropriately notified. The operations associated with this polled response will most probably be heard by the user of the telephone which is then off-hook. However, this is acceptable due to the presence of an alarm condition, and is in fact considered to be beneficial since the user is, in essence, notified of a potential alarm event.

The system disclosed in U.S. Patent No. 4,442,320 calls for the use of a sub-audible tone having a frequency of approximately 25 Hz. In the practical implementation of such a system, a frequency of approximately 36 Hz is preferably used. Such signals have worked well in performing their intended function in conjunction with the predominant analog loop carrier systems in service. This is because such frequencies are readily transmitted by such systems.

However, developments in telephone technology have led to an increased use of digital loop carrier systems. Examples of this are the "D4 Channel Bank", "SLC-96" and "SLC Series 5" systems (AT&T/Lucent) which are presently employed by many telephone companies. However, as a result of filtering (band pass filtering) performed during the procedures which are used to convert the analog signals associated with many types of telephone equipment to digital form, it is a characteristic of such digital systems that a narrower band of frequencies is passed than with the prior analog systems. In particular, such digital systems are generally intended to pass frequencies of from 300 to 3200 Hz. Frequencies below 300 Hz are attenuated, and frequencies below 200 Hz are generally attenuated to such an extent that they cannot be effectively detected. As a result, conventional sub-audible tones on the order of 36 Hz will not be effectively communicated by a digital loop carrier system. This problem can be solved by replacing the sub-audible tones that are useful in conjunction with analog systems with tones that are capable of being transmitted by a digital loop carrier system and that are capable of being detected by derived channel equipment such as the subscriber terminal units 22, 23, 24 and the scanner 18 previously described (with suitable modifications). For such applications, signals having a frequency of from 200 Hz to 300 Hz are preferred. Continuous signals, and signals with frequencies approaching 200 Hz are particularly preferred for such purposes since for a given signal level, such signals have been found to occupy the lowest possible band width, and to be the least audible. In practice, such frequencies produce signals which do not materially interfere with normal (off-hook) telephone usage, yet which are of a sufficient amplitude to be detected by the derived channel equipment. As a result, the foregoing functions of a supervised alarm reporting system are preserved in the presence of a digital loop carrier system.

Such improvements can be accomplished with minimal modifications to the prior system illustrated in Figure 1. For example, and referring to Figure 2, the scanner 18 retains a T/R section 18a, although the T/R section 18a is modified from the prior configuration as will be discussed more fully below. A subscriber terminal unit 30 is provided which is substantially similar in configuration to the subscriber terminal units 22, 23, 24 of Figure 1, except that the MOD/DEMOD sections 22a, 23 a, 24a are replaced with a transmitting and receiving (T/R) section 30a. The scanner 18 and the subscriber terminal unit 30 communicate over a telephone network 31 (which may be analog or digital in operation) in similar fashion to the communications discussed in conjunction with the prior embodiment of Figure 1. Such communications are implemented by the T/R sections 18a, 30a, as follows. Figure 3A shows a transmitter 35 for use with biphase modulated communications (BPSK). The transmitter 35 will form part of the T/R section 18a of the scanner 18 and part of the T/R section 30a of the subscriber terminal unit 30, permitting two-way communications between these two components. The BPSK functions to be performed are preferably implemented with a microprocessor configured for digital signal processing (DSP). While similar functions may be implemented using other techniques, including digital and analog circuit designs, the use of a DSP microprocessor is considered preferred due to its versatility (making the resulting system largely independent of hardware). To this end, and using techniques which are themselves known, the BPSK transmitter 35 is caused to implement the functions which follow. To be noted is that the specific parameters associated with the following circuits (including voltage level, frequency and sample rate) are provided for purposes of illustration, and can be varied to suit a particular application, as desired (responsive to programming of the DSP microprocessor). A numerically controlled oscillator 36 (NCO) is provided to develop a desired carrier frequency. Preferred frequencies for implementing this carrier signal include 210 Hz, 230 Hz, 250 Hz, 270 Hz and 290 Hz. A "sine table" look-up method is used to control the phase of this carrier signal. An input data timer 37 is provided which includes a polarity converter and which serves as an input for the data 38 which is to be transmitted over the telephone network 31. A data rate of 10 bits per second (bps) is generally sufficient for such purposes. The input data timer 37 operates to cause changes in the data received responsive to detected transitions (0 to 1, 1 to 0) in the signal 38, preferably producing a bipolar swing (+1 to -1) as opposed to a unipolar transition. The resulting output, at 39, is then applied to a "raised cosine" pulse shaping filter 40. To this end, the bipolar data signal 39 is preferably passed through a finite impulse response (FIR) linear phase filter to minimize inter-symbol interference (ISI) at the receiver (to be described below). The filter 40 is preferably implemented at a sample rate of 125 Hz. The output of the NCO 36 and the FIR filter 40 are combined in a modulator, at 41. To this end, the filtered data signal is multiplied by the carrier signal to produce a modulated transmission carrier signal, at 42.

Figure 3B shows a receiver 45 for use with the BPSK transmitter 35 of Figure 3A, to filter and demodulate the transmitted signal. The receiver 45 will also form part of the T/R section 18a of the scanner 18 and part of the T/R section 30a of the subscriber terminal unit 30, complementing the operations of the opposing transmitter (of the subscriber terminal unit 30 and the scanner 18, respectively). The receiver 45 is also preferably implemented with a DSP microprocessor, and performs the functions which follow. The specific parameters associated with the following circuits are again provided for purposes of illustration, and can be varied to suit a particular application, as desired.

A numerically controlled oscillator 46 (NCO) is controlled by the output of an integrate and dump filter 47, which operates in conjunction with a threshold detection circuit 48. The resulting signal is multiplied (multiplexer 49) with the received (input) signal 50, producing in-phase (I) and quadrature (Q) components. This operates to maintain synchronization between the input signal 50 and the resident oscillator 46. The phase constellation of the resulting signal consists of two points. However, only one phase component is processed to extract the data. To this end, the Q signal is introduced to a second integrate and dump filter 47', and to a low pass filter 51. The integrate and dump filter 47' communicates with the threshold detection circuit 48, and operates to assist in removing the effects of in-band (e.g., voice) energy present in the signal (removing more of these effects than would a single loop system). In its preferred embodiment, the filter 51 is an 85 Hz low pass, infinite impulse response (IIR) filter operating at a primary sample rate of 8 KHz. The filtered signal is further introduced to a low pass filter 52, which operates at a lower rate to extract the original (10 bps, 5 Hz) data from the input signal 50. To this end, a 5 Hz low pass infinite impulse response (IIR) filter operating at a sample rate of 250 Hz is preferred. The resulting signal is then tested against a threshold (threshold detector 53) and processed by a bit synchronization timer 54 (internal synchronization seeking finite 1-0 transitions) to produce an output bit stream 55. The output bit stream 55 is then assembled, at 56, by a known data recovery function (which may include suitable data error detection, if desired), yielding the desired data output at 57.

Figure 4A shows a transmitter 60 for use with frequency shift keyed (FSK) communications. The transmitter 60 will form part of the T/R section 18a of the scanner 18 and part of the T/R section 30a of the subscriber terminal unit 30, permitting two-way communications between these two components. The FSK functions to be performed are again preferably implemented with a microprocessor configured for digital signal processing (DSP). While similar functions may be implemented using other techniques, including digital and analog circuit designs, the use of a DSP microprocessor is considered preferred due to its versatility (making the resulting system largely independent of hardware). To this end, and again using techniques which are themselves known, the FSK transmitter 60 is caused to implement the following functions. To be noted is that the specific parameters associated with the following circuits (including voltage level, frequency and sample rate) are again provided for purposes of illustration, and can be varied to suit a particular application, as desired (responsive to programming of the DSP microprocessor). Two numerically controlled oscillators 61, 62 (NCO) are provided to develop each of the two frequencies used for modulating the output signal. Preferred frequencies for this purpose include 190 Hz and 215 Hz, respectively. A "sine table" look-up method is again used to control the phase of each of the carrier signals. An input data timer 63 is combined with a phase coherent carrier switch 64. As transitions in the data received at 65 are detected, the carrier frequency is switched from mark (1 = 215 Hz) to space (0 = 190 Hz) responsive to operations of the phase coherent carrier switch 64. The phasing must be coherent to minimize harmonics produced by the instantaneous changes in carrier frequency which result. The switched signals are summed at 66, developing an output transmission carrier signal at 67. The carrier signal 67 may be digitally filtered to minimize harmonic transmissions, if desired.

Figure 4B shows a receiver 70 for use with the FSK transmitter 60 of Figure 4A, to filter and demodulate the transmitted signal. The receiver 70 will also form part of the T/R section 18a of the scanner 18 and part of the T/R section 30a of the subscriber terminal unit 30, complementing the operations of the opposing transmitter (of the subscriber terminal unit 30 and the scanner 18, respectively). The receiver 70 is also preferably implemented with a DSP microprocessor, and performs the functions which follow. The specific parameters associated with the following circuits are again provided for purposes of illustration, and can be varied to suit a particular application, as desired.

A low pass (preferably 250 Hz) filter operates to receive a carrier input 71, primarily for the purpose of rejecting speech and other signals outside of the range of the input FSK signal. The filtered signal is then introduced to an automatic gain control (AGC) circuit 73, to set the received carrier signal level to a known range. This is done to simplify the data decision process which is to take place downstream. The resulting signal is then delayed by 90 degrees, preferably by using a zero phase delay (FIR) filter 74 in combination with a multiplexer 75. The delayed signal 76 is multiplied with the signal 77 received from the AGC 73, essentially performing an auto-correlation function. The resulting (correlated) signal is then introduced to a low pass filter 78, to remove higher frequency components, yielding the desired data. The yielded data bit stream (10 bps) is then introduced to a data slicer and timing control circuit 79, for extracting the output data, at 80, and for checking the timing of the output data 80 (which may include suitable data error detection, if desired).

Various changes can be made to the above-described system components to satisfy the system requirements appropriate to a particular application. For example, and as previously indicated, implementation of the foregoing functions, and the specific means for doing so, may be varied as desired, and may be associated with systems for reporting alarm conditions as well as other conditions requiring remote monitoring, such as the remote monitoring of specified parameters. Also capable of variation is the type of data communicating function used, which may itself call for suitable variation of the foregoing operations. Other, additional functions may be provided where desired to achieve a particular result. For example, the system of the present invention relies on a transmission of signals at a relatively low level (e.g., on the order of -35 to -40 dBm) to minimize the audibility of the supervisory (200 to 300 Hz) signal placed on the telephone line. However, a signal of this magnitude is prone to detection error in the presence of speech or other signals on the carrier. To reduce such error while avoiding unnecessary interference with telephone usage, the T/R section 18a of the scanner 18 and the T/R section 30a of the subscriber terminal 30 may be provided with means for dynamically adjusting the level of the transmitted supervisory signal responsive to the presence or absence of additional signals on the line due to operations of the telephone network 31. Referring to the transmitters 45, 70 of Figures 3 A and 4 A, such dynamic adjustment is preferably performed responsive to an energy detector 85, which communicates with the output of the transmitter to determine the level of signals present on the telephone line. The energy detector 85 communicates with a level adjusting circuit 86 capable of increasing and decreasing the level of the transmitted signal responsive to corresponding increases and decreases in the energy level detected on the telephone line. Such means are themselves known, and are not unlike the dynamic adjustment means used with cellular telephone networks to dynamically adjust signal levels responsive to changes in the distance of the mobile site from the communicating cell site (i.e., an automatic gain control).

Dynamic adjustment of the transmitted signal has the advantage that a supervisory signal with an increased (stronger) signal level will not be noticed in the presence of speech or the like, and will offer a signal of increased level for detection by the derived channel system (improving receiver performance and lowering the bit error rate). However, the level of the supervisory signal would be reduced during quiet periods, to avoid interference with normal telephone usage. Similar benefits can be achieved by adjusting the frequency of the supervisory signal (between 200 Hz and 300 Hz) responsive to changes in the carrier signal, either alone or in conjunction with a dynamic adjustment of signal level, to obtain the least audible signal possible. Dynamic frequency control would also be useful in cases where two subscribers in communication with one another each have a subscriber terminal unit 30 in accordance with the present invention, to minimize the potential for interference with normal telephone usage (resulting from the cumulative effects of two carrier signals having the same, or similar frequencies), using techniques that will be discussed more fully below.

The relatively low level signals (-35 to -40 dBm) used to minimize the audibility of the supervisory signal of the present invention can also adversely effect the ability of the system to determine the hook status condition of the subscriber's telephone, to in turn determine the operating mode for the system. For this reason, the system of the present invention preferably does not utilize a high impedance source for detecting changes in amplitude to indicate hook status condition, as did the prior system of Figure 1. Instead, the hook status condition of the subscriber's telephone is preferably detected by the subscriber terminal unit (at the subscriber's premises), and communicated to the scanner as part of the data (the response message) produced by the subscriber terminal unit. This poll/response protocol may also be used to identify losses in communications with the scanner, to allow the subscriber terminal unit to establish an alternative communications path (e.g., a cellular back-up system) responsive to such conditions (to provide an added measure of security), as will also be discussed more fully below.

In addition to the supervisory signal of the present invention, a hook status carrier signal is additionally useful in allowing a faster detection of changes in hook status and alarm conditions. As an example, this would be useful in applications where the reporting system requires a detection of changes in hook status conditions at a rate that may be faster than the data transmission rate. To this end, a tone (e.g., 310 Hz) is generated by the subscriber terminal unit. This tone is transmitted continuously when the subscriber's telephone is on-hook. However, in the off-hook condition, no tone is transmitted. Hook status conditions are detected by the subscriber terminal unit, by monitoring transmitted signal levels. Under normal conditions, the system of the present invention should not interfere with normal voice communications (including telephone company signalling such as DTMF, MF and call progress signals, among others), or with other (e.g., data) communications associated with the telephone network. However, in the event that the system of the present invention causes interference with a particular instrumentality, the T/R section 18a of the scanner 18 and the T/R section 30a of the subscriber terminal unit 30 may be provided with means for recognizing activity corresponding to the instrumentality in question, and for discontinuing operations of the system of the present invention (i.e., polling and/or supervisory signaling) pending such operations. For example, let it be assumed that the system of the present invention in some way interferes with data transmissions being performed by a modem. Suitable means would be provided to detect such data transmissions (e.g., equivalent to the energy detection circuit 85), and in such case, suitable means would be provided to suspend further operations of the system of the present invention (e.g., equivalent to the level adjusting circuit 86, set to zero). This would allow the data transmissions to proceed in an uninterrupted fashion, and operations of the system of the present invention would only have to be discontinued for a limited period of time (while the data transmissions are in progress), minimizing down-time of the associated alarm reporting system. For added security, steps can be taken to immediately initiate an inquiry (a polled response or a verification of the presence of the supervisory signal) following discontinuance of the interfering event. This is considered useful to immediately ascertain the status of the remote premises, while minimizing the potential for any loss of data. As an alternative to the discontinuance of system functions, the transmission of short signal bursts capable of fitting within the timing requirements for the scanner could also be used to minimize system interference. In practice, it has been found that the bandwidth limitations of digital loop carrier systems can limit operations of high-speed modems, especially modems that operate at speeds of 28.8 kbps and higher (e.g., modems conforming to present ITU type V.34 standard). This is because such modems typically require a bandwidth of from 150 to 3750 Hz to operate at their highest possible speeds, in turn requiring a bandwidth in excess of that provided by such band-limited, digital loop carrier systems. This further tends to interfere with communications in the preferred range of 200 Hz to 300 Hz, referred to previously, as well as FSK signaling. Efforts to bypass the bandwidth restrictions of digital loop carrier systems (using analog, "copper" loops) have not solved this problem.

For purposes of compatibility with these high-speed modems, the previously described derived channel equipment can be modified to communicate using carrier frequencies that lie outside of the applicable modem bandwidth, i.e., at a frequency at or below 150 Hz. A frequency of 80 Hz is presently preferred for such purposes. For derived channel systems that utilize multiple frequencies, as previously mentioned, frequencies of 80 Hz, 90 Hz or 100 Hz are presently considered preferred. Except for selection of the operative frequency (or frequencies), the same signaling and modulation techniques are used as those which have previously been described, but at the reduced (selected) canier frequency (or frequencies). Because such modem activity will also interfere with the (audible frequency) polling sequences of a derived channel system, such data communications are also preferably moved to a frequency outside of the modem's operating band using modulation techniques that will be more fully described below.

The previously described derived channel systems use a supervisory signal which is generated by the subscriber terminal units and which is detected by the system's scanner. For example, detection of the supervisory signal by the scanner 18 provides an indication that communications are functional (i.e., the telephone network 31 of Figure 2 is intact) and that the conesponding subscriber terminal unit 30 does not have a message (e.g., an alarm signal) to send. However, in this mode of operation (i.e., a "simplex" mode), the subscriber terminal unit 30 does not itself know whether the telephone network 31 (the telephone line) is intact. For applications where such functionality is desirable, communications can be implemented in a "half-duplex" mode (i.e., supervision in two directions, with the subscriber terminal unit and the scanner operating one at a time) or in a "full-duplex" mode (i.e., supervision in two directions, with the subscriber terminal unit and the scanner capable of operating at the same time), to permit supervision of the telephone line by the subscriber terminal units as well as the associated scanner. This also permits the subscriber terminal units to signal an alarm condition, either locally (at the monitored premises) or using a separate communications channel, in the event of a compromised (presumably cut) telephone line.

To provide either half-duplex or full-duplex operation of the supervisory signal, and referring to Figure 5, it is necessary to provide a scanner 18' with an additional transmitter 18b (e.g., the BPSK transmitter 35 of Figure 3A) and to provide the subscriber terminal unit 30' with an additional receiver 30b (e.g., the BPSK receiver 45 of Figure 3B). This enables two-way communications, which in turn provide a means for exchanging encryption key information during initialization of the system, and for supervision of the telephone network 31 by the subscriber terminal unit 30' during normal operations. To support full- duplex operation, the subscriber terminal unit 30' and the scanner 18' must operate (transmit and receive) at different carrier frequencies. To ensure compatibility with digital loop carrier systems, presently preferred frequencies for the subscriber terminal units would include the previously listed frequencies of 210 Hz, 230 Hz, 270 Hz and 290 Hz, with the scanner operating at a fixed 250 Hz signal. In operation, system initialization proceeds in usual fashion, in a full-duplex mode. During this period, specific initialization codes (data) are exchanged between the scanner 18' and the subscriber terminal unit 30' which is being addressed, to create encryption keys for the transfer of data and to provide a reference for detecting attempts to compromise the system. Data packets are then echoed back to the scanner 18' by the addressed subscriber terminal unit 30' (during initialization) to verify that data is being transferred properly. To provide a simplex mode of operation, the subscriber terminal unit 30' is then caused to revert to a mode which is responsive to communications received from the scanner 18', as previously described.

To provide a half-duplex or a full-duplex mode of operation, the subscriber terminal unit 30' is enabled to "request" the scanner 18' to echo back a unique, encrypted data packet (on a periodic or a random basis). Failure of the subscriber terminal unit 30' to detect the requested packet then constitutes a "loss of communications" condition. An alternative is for the scanner 18' to send a continuous stream of encrypted packets, and for the subscriber terminal unit 30' to declare a loss of communications upon a loss of properly encrypted packets for a preselected period of time (e.g., 30 seconds). For use in conjunction with operations in a half-duplex mode or a full-duplex mode, the subscriber terminal unit 30' is advantageously provided with a "back-up" communications port 87, for use in situations where primary communications (i.e., the telephone network 31) are found to be inoperative (e.g., due to a cut line, noise or some other impairment). The back-up port 87 is preferably implemented with a wireless system (e.g., using cellular or other radio-based transmissions) to minimize the potential for a compromise of the primary system to also compromise the back-up system, in turn increasing the security offered by such a system. Full-duplex or half-duplex operation of the supervisory signal is necessary for the subscriber terminal unit to be able to detect a failure of the primary communicating channel, and to switch to the back-up channel for further operations to continue. Such functionality is not offered in a simplex mode of operation since the subscriber terminal unit is then unable to detect a loss of communications with the scanner (i.e., only polled responses, using BPSK, FSK or MLT communications, will indicate a loss of communications in the simplex mode of operation).

The previously described derived channel systems are generally implemented in such a way that only one subscriber terminal unit (e.g., one of the subscriber terminal units 22, 23, 24) is capable of communicating with any given telephone line (e.g., one of the telephone loops 14, 15, 16). However, and refening to Figure 6A, there are also applications which would benefit from an ability to place multiple subscriber terminal units 22', 23', 24' in communication with a single telephone loop 14'. For example, this would permit multiple applications to be supported by a single telephone loop 14' (e.g., to provide alarm reporting 22', meter reading 23' and/or home automation 24' functions at a single subscriber's premises). Referring to Figure 6B, this would also permit multiple subscriber terminal units 22", 23", 24" to be supported within the environment of a single switchboard grouping 88, such as a "Centrex" grouping (which can result in calls to other phone lines within the same group that are connected by the switch without the benefit of any signal conditioning or intra-office trunks). In either case, there is a potential for conflicting signals (including the potential for conflicting supervisory signals and/or the potential for conflicting poll/response signals) to be present on a single telephone line, resulting in interference that could effectively prevent such installations from being implemented.

Such multiple use applications can be implemented by using different signals to supervise those subscriber terminal units that are capable of communicating with a given telephone line. This permits the multiple subscriber terminal units to share the same telephone line, in turn supporting the multiple applications that are desired. This can be accomplished by causing each of the several subscriber terminal units (e.g., the subscriber terminal units 22', 23', 24' of Figure 6A, or the subscriber terminal units 22", 23", 24" of Figure 6B) to be associated with a given telephone line (e.g., the loop 14' of Figure 6 A, or the grouping 88 of Figure 6B) to operate on a separate carrier frequency, primarily through selection of the frequency for the supervisory signal (e.g., by selecting between the previously mentioned frequencies of 210 Hz, 230 Hz, 270 Hz and 290 Hz). Such frequency selection can be implemented by programming the subscriber terminal units with the appropriate frequencies, during set-up, or by downloading commands from the scanner that services the telephone line, to any or all of the multiple subscriber terminal units in communication with that telephone line. Alternatively, such programming can be accomplished automatically (by the scanner or by the subscriber terminal units), by detecting a conflicting signal and by causing one of the supervisory signals to change to another, non-conflicting frequency (using frequency detection and switching techniques that are themselves known).

The remaining operating parameters (e.g., the bit rate, modulation technique, etc.), as well as the overall operations of the resulting derived channel system, are the same as those which were previously described for a derived channel system having a single subscriber terminal unit in communication with a given telephone line, with each of the multiple subscriber terminal units operating at their assigned (unique) operating frequency. Encryption of the signals sent from the scanner to each of the subscriber terminal units can be used to further ensure that only one of the subscriber terminal units in communication with a given telephone line will respond with a data message.

The supervisory signal of the present invention is capable of being implemented as a basic tone, providing operations similar to those of the previously used 36 Hz supervisory tone. However, there are also applications that can benefit from the availability of a secure, low-speed telemetry signal, either with or without the security features and the data throughput requirements of a derived channel system. This can include applications such as the automatic reading of utility (e.g., water, gas and electric) meters, energy management, home automation, remote machine monitoring (e.g., photocopying machines, vending machines, etc.) and signal routing (e.g., the routing of telephone calls or e-mail messaging).

Such applications can be implemented by using the supervisory signal as a primary, data carrying signal. Any audible signals (e.g., the audible BPSK, FSK or MLT signals ordinarily associated with a derived channel system) are preferably eliminated for such applications so that all communications between the scanner 18 and the subscriber terminal units 30 serviced by the scanner 18 are accomplished with the data carrying supervisory signal. Hook status detection can also be eliminated for such applications, if desired, since different modes of operation responsive to hook status conditions are no longer required for such applications. Any of a variety of known signal communicating techniques may be used to implement such a data canying supervisory signal, responsive to the type of communications employed (including BPSK, FSK or MLT techniques, or some other equivalent signal communicating technique).

The foregoing data communicating systems (including implementations for purposes of supervisory signaling) can be implemented either as separate components which are capable of being coupled with existing telephone equipment, or as an integral part of such equipment.

Implementing the data communicating system as an integral part of the existing telephone equipment is readily accomplished by "embedding" the previously described system components and capabilities (in the combinations desired) into such equipment (e.g., in telephone switch equipment such as a central office switch, private branch exchange (PBX), digital loop carrier system, router, access multiplexer or the like, and customer premises equipment such as a telephone, modem, alarm panel, parameter monitoring device, etc.). This can be accomplished, for example, by appropriately combining the previously described digital signal processing (DSP) operations, including any necessary software and/or chips and the associated interfacing circuits, with the desired piece of equipment.

In implementing the foregoing data communicating systems as separate components coupled with existing telephone equipment (for example, as in prior implementations for purposes of supervisory signaling), such systems were generally deployed using a bridged (parallel) connection at each end of the (local) telephone loop. For local loops served by an integrated digital loop carrier system, there was typically no option for providing a bridged connection at the telephone central office, leading to the difficulties described previously. Embedding the data communicating system (signal) into the telephone switching system eliminates the need for a bridged connection, in turn eliminating the labor and cost associated with running the necessary "jumper" connections and significantly reducing installation time and costs.

Such improvements can serve to facilitate any of a variety of practical applications which would benefit from continuous low speed telemetry /data communications (i.e., with bit rates of 10 to 80 bps) and bi-directional, inaudible operations which will not interfere with normal telephone use (either supervised or unsupervised).

As an example, individuals having chronic medical conditions often require regular monitoring of vital statistics (e.g., temperature, blood pressure, blood sugar level, heart rate, respiratory rate, etc.), but are not always sufficiently ill to require hospitalization. Such individuals may in such cases need to make frequent trips to an outpatient clinic for routine testing. Implementing the supervisory signal as a primary, data carrying signal can provide a cost-effective communications link between monitoring equipment at the subscriber's premises and a doctor's office or a medical monitoring facility. A "panic alarm" could be included as part of this application, if desired. Such a capability would also be particularly useful in a prison environment, where it is neither desirable nor practical to transport patients outside the prison.

Such an application is readily implemented by placing a subscriber terminal unit in communication with the monitoring equipment to be employed, for example, via a serial data port. Such an application is also readily implemented by embedding the elements of the subscriber terminal unit into the monitoring equipment, if desired. As an additional feature, a back-up port associated with the subscriber terminal unit could be used to provide wireless back-up communications in the event that the communicating telephone line is in some way compromised.

For the more seriously ill patients, desired medical telemetry can be deployed with different architectures, tailored to the particular needs of a given patient, with no need for direct connection to "outside" telephone lines.

In a hospital, nursing home or other assisted living facility served by a PBX system, the in-house wiring from the patient's room to the PBX system would operate to carry the desired telemetry signals. If desired, the PBX system could route the data to a local area network (LAN) or a local or remote monitoring facility. Such an application is best implemented by embedding the necessary elements of the data communicating system in the PBX system and programming the PBX system to route the telemetry data to a local area network, which then interfaces with the appropriate monitoring station. Alternatively, a scanner could be bridged to the telephone lines at the PBX system to route the data to the desired monitoring station. In the patients' rooms, the subscriber terminal units could either be embedded in the monitoring equipment, or implemented as separate components. Another application is presented for situations where an individual would like to be notified of the receipt of "e-mail" without necessarily having to log onto the Internet. This would be particularly useful in cases where the receipt of e-mail is the user's primary Internet application, and a dial-up modem is the means of access. Such an application is readily implemented by coupling a subscriber terminal unit with an indicator device located at the subscriber's premises. The indicator device would then be used to receive a signal via the subscriber terminal unit (e.g., by decoding a personal code) upon the subscriber's receipt of an e-mail message. Such a system could also be implemented by embedding the subscriber terminal unit and the indicator device in the subscriber's modem or personal computer, if desired.

In addition to the notification of an individual that e-mail has been received, similar applications can be developed to allow the Internet service provider, the telephone company, or some other service provider, to report billing problems, urgent messages or other conditions without requiring the subscriber to log onto or otherwise check in with the system. Again, such a system could be implemented by embedding the components of the system in the subscriber's modem or personal computer, in the local switch and/or in the service provider's router, as prefened.

Other applications are presented in connection with high speed modems (e.g., technology supporting data rates to 56 kbps on a copper loop), which suffer from the bandwidth-limiting effects of digital loop carrier systems and digital switching systems. An additional shortcoming that exists with available dial-up modems is that the time required to access an Internet service provider can be very time- consuming during busy hours.

Such problems can be solved by coupling a subscriber terminal unit with the modem (or embedding a subscriber terminal unit in the modem) and by providing the telephone switch (and the remote terminal) with an appropriately placed (or embedded) scanner, to form a "control channel". This control channel (preferably encrypted with proper account codes, etc.) would then operate to signal the switch that the call being made is an Internet access call. Since Internet access calls can be rather lengthy and can tie up switch resources for an extended period of time, the switch could divert the call directly to the Internet service provider's router without tying up a touch tone receiver, an outgoing trunk, etc. In such case, there would be no dial-up and re-dial delays to contend with, and toll calling charges would not apply (although other charges might then apply instead). Other (non-Intemet) modem/fax calls would go through the switch in the usual way. In digital loop carrier installations, the remote terminal could divert the call to a "DS0" channel to bypass the bandwidth limiting A/D and D/A functions, permitting full 56 kbps operation for V.90 modems. Another application which is presented is the remote monitoring of telephone company equipment such as pay telephones. Vandalism, coin box tampering and cut telephone lines have long plagued coin telephone operations. This application is met by providing the pay telephones with subscriber terminal units for reporting adverse operating conditions to the telephone company. For such applications, the subscriber terminal units are preferably incorporated into the pay telephone equipment, and a scanner is correspondingly made part of the line card in the central switch. The resulting signals can continuously send information regarding coin box status and tampering, give an indication that the coin box is full, and/or supervise the communicating telephone line.

Any of a number of other possible applications will occur to the person of ordinary skill.

Two-way communications containing data (including any of a variety of parameters such as identification codes, status conditions, an indication of telephone hook status condition, or some other equivalent parameter) are particularly preferred for use in implementing the foregoing applications. For applications in which the subscriber terminal units are to continuously transmit a signal, for purposes of line supervision, full-duplex operations are required for messages (i.e., "polls") initiated from the scanner and for the message acknowledgements provided by the subscriber terminal units.

In addition to the increased information exchangeable with such a system, tampering with the resulting system is also minimized. For example, attempts have been made to tamper with such systems by substituting a circuit for a subscriber terminal unit, and by causing the substituted circuit to emit a signal simulating an absence of any alarm conditions. Such substitution would be precluded by the change in the associated identification codes which would then result. Still further increases in security would be achievable by encrypting such transmissions.

The data is preferably transmitted between the scanner 18 and a subscriber terminal unit 30 as time-varying, encrypted data packets to permit the detection of attempts to compromise the data canying (or alarm reporting) function of the system, in addition to the fundamental purpose of verifying the integrity of the communicating channel. For applications employing polled responses, upon detecting that the supervisory signal has been disabled or by generating an appropriate (encrypted) message, the scanner 18 is then caused to issue a polling request, to which the affected subscriber terminal unit 30 will then respond. Such communications are typically performed in a half-duplex mode of operation. For other applications, the scanner 18 would be placed in continuous communication with the subscriber terminal unit 30, eliminating the need for polled responses.

To transmit increased amounts of data (either as an alarm supervising signal or as a data-carrying signal) in the low-frequency bands that are useful in accordance with the present invention, it is desirable to increase the bit rate of the communicating signal to the extent possible. Preferably, this is accomplished using modulation techniques that can yield two, three, or more bits per baud, yielding a conesponding bit rate of 20, 30 or more bits per second (bps) while maintaining a channel baud rate that is as low as possible (e.g., 10 or 20 baud).

Modulation techniques such as quaternary phase shift keying (QPSK) and 8-phase shift keying are preferably used for such purposes because these techniques are well adapted to the system components that have previously been described. The reason for this is that as distinguished from biphase (BPSK) modulation, which uses 180-degree phase shifts to yield one bit per baud, QPSK modulation uses multiples of 90-degree phase shifts to provide two bits per baud, and 8-phase modulation uses multiples of 45 -degree phase shifts to provide three bits per baud, which is readily implemented with reference to the description which follows. However, it is also possible to use discrete multi-tone (DMT) modulation techniques, if desired for a particular application.

As previously described, Figure 3A shows a block diagram for a BPSK transmitter 35. In the configuration described (for BPSK modulation), the NCO 36 uses a sine table look-up to produce the phase shifted versions of the carrier frequency. This circuit can similarly be used to develop either QPSK or 8-phase modulation by changing these 180-degree increments to either 90-degree or 45-degree increments, respectively, which is readily accomplished by changing the offset value from a position for BPSK operation to the new position which is appropriate for either QPSK or 8-phase operation. For example, using a 256-sample table, a jump of 128 samples will conespond to a 180-degree phase shift, a jump of 64 samples will conespond to a 90-degree phase shift, and a jump of 32 samples will conespond to a 45-degree phase shift. The following tables show the relationships between the transmitted phase shifts and the conesponding data bit patterns. QPSK 8-phase

Bits Phase Shift Bits Phase Shift

00 0 degrees 000 0 degrees

01 90 degrees 001 45 degrees

10 180 degrees 010 90 degrees

11 270 degrees Oil 135 degrees

100 180 degrees

101 225 degrees

110 270 degrees

111 315 degrees

For QPSK and 8-phase modulation, the data timer 37 of the transmitter 35 of Figure 3 A will operate at the symbol rate (baud rate) and not at the transmitted bit rate. Figure 7 shows a prefened receiver 90 for use with the

BPSK, QPSK or 8-phase transmitter 35 of Figure 3A. A numerically controlled oscillator 91 and a splitter 92 are used to generate in-phase (cosine) and quadrature (sine) components of the carrier frequency, which are then multiplied with the received input signal 93 (in multiplexers 94, 95, respectively) to produce in-phase and quadrature representations of the received signal. These signals are then summed over multiple periods of the canier frequency by the summers 96, 97. Phase calculator 98 determines the phase shifts in the received samples by dividing the in-phase component into the quadrature component to determine the phase angle of the received vector, at 99. The symbol rate recovery function 100 then converts the phase shift information into the appropriate (1-bit, 2-bit or 3 -bit) pattern. The bit rate converter function 101 then performs a parallel-to-serial conversion, to yield the output bit string 102. It will be understood that various changes in the details, materials and anangement of parts which have been herein described and illustrated in order to explain the nature of this invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the following claims.

Claims

ClaimsWhat is claimed is:

1. A system for providing communication between a central location and instrumentalities other than a conventional telephone located at premises of telephone network subscribers using a telephone signal communicating network, comprising: a transmitter, and a receiver in combination with the transmitter, for communicating a data containing signal between the subscriber premises and the central location, wherein the data containing signal has a frequency which is transmitted by telephone signal communicating networks including digital transmission equipment having band pass filtration means which pass signals limited to the audible telephone frequency range, and wherein the data containing signal is transmitted at an attenuated level.

2. The system of claim 1 wherein the telephone signal communicating network includes digital transmission equipment having band pass filtration means associated therewith.

3. The system of claim 2 wherein the band pass filtration means associated with the digital transmission equipment of the telephone signal communicating network passes frequencies in a range from 300 to 3200 Hz.

4. The system of claim 1 wherein the data containing signal is transmitted during both on-hook and off-hook conditions of the telephone at the subscriber premises.

5. The system of claim 1 wherein the data containing signal has a frequency of from 200 Hz to 300 Hz.

6. The system of claim 5 wherein the frequency is selected from the group of frequencies consisting of 210 Hz, 230 Hz, 250

Hz, 270 Hz and 290 Hz.

7. The system of claim 1 wherein a modem is in communication with the telephone signal communicating network, and wherein the data containing signal has a frequency at or below 150 Hz.

8. The system of claim 7 wherein the data containing signal operates at a single frequency of about 80 Hz.

9. The system of claim 7 wherein the data containing signal operates at plural frequencies selected from the group of frequencies consisting of 80 Hz, 90 Hz and 100 Hz.

10. The system of claim 1 wherein the transmitter operates to transmit the data containing signal when the instrumentalities at the subscriber premises are in a first predetermined state, and to interrupt transmission of the data containing signal when one of the instrumentalities at the subscriber premises assumes a second predetermined state different from the first predetermined state.

11. The system of claim 10 wherein the transmitter is associated with the instrumentalities at the subscriber premises and the receiver is associated with the central location.

12. The system of claim 10 wherein a first transmitter is associated with the instrumentalities at the subscriber premises and a first receiver is associated with the central location, and a second transmitter is associated with the central location and a second receiver is associated with the instrumentalities at the subscriber premises.

13. The system of claim 12 wherein the subscriber premises and the central location communicate with each other one at a time.

14. The system of claim 12 wherein the subscriber premises and the central location simultaneously communicate with each other.

15. The system of claim 14 wherein communications from the subscriber premises to the central location operate at a first frequency, and communications from the central location to the subscriber premises operate at a second frequency different from the first frequency.

16. The system of claim 15 wherein the first frequency is selected from the group of frequencies consisting of 210 Hz, 230 Hz, 270 Hz and 290 Hz.

17. The system of claim 16 wherein the second frequency is about 250 Hz.

18. The system of claim 12 which further includes a back- up communications port coupled with the first transmitter, and means for transferring communications from the first transmitter to the back-up communications port responsive to a loss of signal at the second receiver.

19. The system of claim 1 wherein a plurality of transmitters are simultaneously in communication with a single telephone signal communicating network, and wherein each of the transmitters operates at a different frequency.

20. The system of claim 19 wherein the operating frequency for each of the transmitters is selected from the group of frequencies consisting of 210 Hz, 230 Hz, 270 Hz and 290 Hz.

21. The system of claim 19 which further includes means for selecting the frequency from a location remote from the subscriber premises.

22. The system of claim 19 which further includes means for automatically detecting when more than one of the plurality of transmitters are operating at the same frequency, and means for automatically switching the operating frequency of one of the plurality of transmitters that are operating at the same frequency to a different frequency.

23. The system of claim 1 wherein the transmitted signals are biphase modulated signals.

24. The system of claim 1 wherein the transmitted signals are frequency shift keyed signals.

25. The system of claim 1 wherein the transmitted signals are multi-tone modulated signals.

26. The system of claim 1 wherein the transmitted signals are quaternary phase shift keyed signals.

27. The system of claim 1 wherein the transmitted signals are 8-phase shift keyed signals.

28. The system of claim 1 which further includes means for sensing signals communicated between the central location and the subscriber premises, wherein the communicated signals have a level which is continuously variable between a minimum level and a maximum level, and means for dynamically adjusting the level of the data containing signal responsive to increases and decreases in the sensed level of the communicated signals.

29. The system of claim 1 which further includes means for sensing signals communicated between the central location and the subscriber premises, wherein the communicated signals have a level which is continuously variable between a minimum level and a maximum level, and means for dynamically adjusting the frequency of the data containing signal responsive to increases and decreases in the sensed level of the communicated signals.

30. The system of claim 1 which further includes means for sensing signals communicated between the central location and the subscriber premises, wherein the communicated signals have a level which is continuously variable between a minimum level and a maximum level, and means for dynamically adjusting the level and frequency of the data containing signal responsive to increases and decreases in the sensed level of the communicated signals.

31. The system of claim 1 which further includes means for sensing activation of telephone equipment other than the telephone at the subscriber premises, and means responsive to the activation sensing means for temporarily interrupting communications between the central location and the subscriber premises.

32. The system of claim 1 wherein the data containing signal is comprised of a series of bits.

33. The system of claim 32 wherein the data containing signal is an encrypted signal.

34. The system of claim 32 wherein the data containing series of bits includes an identification code corresponding to the subscriber premises.

35. The system of claim 32 which further includes means located at the subscriber premises for advising the central location of hook status conditions of the telephone at the subscriber premises, and wherein the data containing series of bits communicates the hook status

5 conditions of the telephone at the subscriber premises to the central location.

36. The system of claim 32 which further includes means located at the subscriber premises for remotely monitoring equipment at o the subscriber premises, and wherein the data containing series of bits communicates data associated with the remotely monitored equipment between the subscriber premises and the central location.

37. The system of claim 32 wherein the data containing 5 series of bits establishes two-way communications between the central location and the subscriber premises.

38. The system of claim 1 wherein the data containing signal is a supervisory signal associated with means for monitoring the 0 instrumentalities at the subscriber premises, and wherein the system further includes: means for selectively transmitting signals from the central location to different subscriber premises using the telephone signal communicating network; and 5 means located at the subscriber premises, connected to the telephone and responsive to the transmitted signals, for retransmitting signals from the subscriber premises to the central location in an audible telephone frequency range and indicative of states of the instrumentalities, using the telephone signal communicating network. 0

39. The system of claim 38 which further includes means for taking an event-responsive action at the central location responsive to interruption of the supervisory signal.

40. The system of claim 38 wherein each of the subscriber premises are separately connected to the central location, and which further includes multiplexing means for selectively applying the transmitted signals to different subscriber premises, individually and in predetermined sequence, and for selectively receiving the responsive signals from the instrumentalities at the subscriber premises, in the same predetermined sequence.

41. The system of claim 38 which further includes means for sensing discontinuance of the supervisory signal, and means responsive to the means for sensing the discontinuance of the supervisory signal, for transmitting the signals from the central location to the subscriber premises.

42. The system of claim 41 wherein the means for sensing the discontinuance of the supervisory signal is located at the subscriber premises.

43. The system of claim 38 which further includes means located at the subscriber premises for advising the central location of hook status conditions of the telephone at the subscriber premises.

44. The system of claim 43 wherein the advising means is a carrier signal, separate from and in addition to the supervisory signal, at a frequency transmitted by the telephone signal communicating network.

45. The system of claim 38 which further includes means for sensing off-hook conditions of the telephone at the subscriber premises, and means responsive to the sensing means for inhibiting transmissions of the signals from the central location to the subscriber premises.

46. The system of claim 45 wherein the supervisory signal is transmitted from the subscriber premises during the off-hook conditions of the telephone at the subscriber premises.

47. The system of claim 45 wherein the supervisory signal is transmitted from the subscriber premises during both on-hook and the off-hook conditions of the telephone at the subscriber premises.

5 48. The system of claim 45 which further includes means for sensing discontinuance of the supervisory signal during the sensing of the off-hook condition at the subscriber premises, and means responsive to the means for sensing the discontinuance of the supervisory signal, for transmitting the signals from the central location to the subscriber o premises.

49. The system of claim 45 which further includes means for sensing discontinuance of the off-hook condition of the telephone at the subscriber premises, and means responsive to the means for sensing 5 the discontinuance of the off-hook condition, for transmitting the signals from the central location to the subscriber premises.

50. A method for communicating between a central location and instrumentalities other than a conventional telephone located at premises of telephone network subscribers using a telephone signal communicating network, comprising the steps of: transmitting a data containing signal between the subscriber premises and the central location, communicating data contained by the data containing signal between the subscriber premises and the central location, wherein the data containing signal has a frequency which is transmitted by telephone signal communicating networks including digital transmission equipment having band pass filtering which passes signals limited to the audible telephone frequency range, and an attenuated level.

51. The method of claim 50 wherein the telephone signal communicating network includes digital transmission equipment having band pass filtration means associated therewith.

52. The method of claim 51 wherein the band pass filtration means associated with the digital transmission equipment of the telephone signal communicating network passes frequencies in a range from 300 to 3200 Hz.

53. The method of claim 50 which further includes the step of transmitting the data containing signal during both on-hook and off-hook conditions of the telephone at the subscriber premises.

54. The method of claim 50 wherein the data containing signal has a frequency of from 200 Hz to 300 Hz.

55. The method of claim 54 wherein the frequency is selected from the group of frequencies consisting of 210 Hz, 230 Hz, 250 Hz, 270 Hz and 290 Hz.

56. The method of claim 50 wherein a modem is in communication with the telephone signal communicating network, and wherein the data containing signal has a frequency at or below 150 Hz.

57. The method of claim 56 wherein the data containing signal operates at a single frequency of about 80 Hz.

58. The method of claim 56 wherein the data containing signal operates at plural frequencies selected from the group of frequencies consisting of 80 Hz, 90 Hz and 100 Hz.

59. The method of claim 50 which further includes the steps of transmitting the data containing signal when the instrumentalities at the subscriber premises are in a first predetermined state, and intenupting transmission of the data containing signal when one of the instrumentalities at the subscriber premises assumes a second predetermined state different from the first predetermined state.

60. The method of claim 59 wherein the transmitting is associated with the instrumentalities at the subscriber premises and the receiving is associated with the central location.

61. The method of claim 59 which further includes the steps of transmitting signals between a first transmitter associated with the instrumentalities at the subscriber premises and a first receiver associated with the central location, and transmitting signals between a second transmitter associated with the central location and a second receiver associated with the instrumentalities at the subscriber premises.

62. The method of claim 61 wherein the subscriber premises and the central location communicate with each other one at a time.

63. The method of claim 61 wherein the subscriber premises and the central location simultaneously communicate with each other.

64. The method of claim 63 which further includes the steps of operating communications from the subscriber premises to the central location at a first frequency, and operating communications from the central location to the subscriber premises at a second frequency different from the first frequency.

65. The method of claim 64 wherein the first frequency is selected from the group of frequencies consisting of 210 Hz, 230 Hz, 270 Hz and 290 Hz.

66. The method of claim 65 wherein the second frequency is about 250 Hz.

67. The method of claim 61 which further includes a back-up communications port coupled with the first transmitter, and which further includes the step of transferring communications from the first transmitter to the back-up communications port responsive to a loss of signal at the second receiver.

68. The method of claim 50 which further includes the steps of simultaneously placing a plurality of transmitters in communication with a single telephone signal communicating network, and operating each of the transmitters at a different frequency.

69. The method of claim 68 wherein the operating frequency for each of the transmitters is selected from the group of frequencies consisting of 210 Hz, 230 Hz, 270 Hz and 290 Hz.

70. The method of claim 68 which further includes the step of selecting the frequency from a location remote from the subscriber premises.

71. The method of claim 68 which further includes the steps of automatically detecting when more than one of the plurality of transmitters are operating at the same frequency, and automatically switching the operating frequency of one of the plurality of transmitters that are operating at the same frequency to a different frequency.

72. The method of claim 50 wherein the signals are transmitted as biphase modulated signals.

73. The method of claim 50 wherein the signals are transmitted as frequency shift keyed signals.

74. The method of claim 50 wherein the signals are transmitted as multi-tone modulated signals.

75. The method of claim 50 wherein the signals are transmitted as quaternary phase shift keyed signals.

76. The method of claim 50 wherein the signals are transmitted as 8-phase shift keyed signals.

77. The method of claim 50 which further includes the steps of sensing signals communicated between the central location and the subscriber premises, wherein the communicated signals have a level which is continuously variable between a minimum level and a maximum level, and dynamically adjusting the level of the data containing signal responsive to increases and decreases in the sensed level of the communicated signals.

78. The method of claim 50 which further includes the steps of sensing signals communicated between the central location and the subscriber premises, wherein the communicated signals have a level which is continuously variable between a minimum level and a maximum level, and dynamically adjusting the frequency of the data containing signal responsive to increases and decreases in the sensed level of the communicated signals.

79. The method of claim 50 which further includes the steps of sensing signals communicated between the central location and the subscriber premises, wherein the communicated signals have a level which is continuously variable between a minimum level and a maximum level, and dynamically adjusting the level and frequency of the data containing signal responsive to increases and decreases in the sensed level of the communicated signals.

80. The method of claim 50 which further includes the steps of sensing activation of telephone equipment other than the telephone at the subscriber premises, and temporarily interrupting communications between the central location and the subscriber premises responsive to the activation sensing.

81. The method of claim 50 which further includes the step of transmitting the data containing signal as a series of bits.

82. The method of claim 81 which further includes the step of encrypting the data containing signal.

83. The method of claim 81 which further includes the step of including an identification code conesponding to the subscriber premises in the data containing series of bits.

84. The method of claim 81 which further includes the step of communicating hook status conditions of the telephone at the subscriber premises to the central location using the data containing series of bits.

85. The method of claim 81 which further includes the steps of remotely monitoring equipment at the subscriber premises, and communicating data associated with the remotely monitored equipment between the subscriber premises and the central location using the data containing series of bits.

86. The method of claim 81 which further includes the step of establishing two-way communications between the central location and the subscriber premises using the data containing series of bits.

5

87. The method of claim 50 wherein the data containing signal is a supervisory signal associated with monitoring of the instrumentalities at the subscriber premises, and wherein the method further includes the steps of: o selectively transmitting signals from the central location to different subscriber premises using the telephone signal communicating network; and retransmitting signals indicative of states of the instrumentalities at the subscriber premises, from the subscriber premises 5 to the central location and in an audible telephone frequency range, responsive to the transmitted signals and using the telephone signal communicating network.

88. The method of claim 87 which further includes the 0 step of taking an event-responsive action at the central location responsive to interruption of the supervisory signal.

89. The method of claim 87 wherein each of the subscriber premises are separately connected to the central location, and 5 which further includes the steps of selectively applying the transmitted signals to different subscriber premises, individually and in predetermined sequence, and selectively receiving the responsive signals from the instrumentalities at the subscriber premises, in the same predetermined sequence. 0

90. The method of claim 87 which further includes the steps of sensing discontinuance of the supervisory signal, and transmitting the signals from the central location to the subscriber premises responsive to sensing of the discontinuance of the supervisory 5 signal.

91. The method of claim 90 wherein the sensing of the discontinuance of the supervisory signal is performed at the subscriber premises.

92. The method of claim 87 which further includes the step of advising the central location of hook status conditions of the telephone at the subscriber premises.

93. The method of claim 92 wherein the advising is performed using a carrier signal, separate from and in addition to the supervisory signal, and at a frequency transmitted by the telephone signal communicating network.

94. The method of claim 87 which further includes the steps of sensing off-hook conditions of the telephone at the subscriber premises, and inhibiting transmissions of the signals from the central location to the subscriber premises responsive to the sensing.

95. The method of claim 94 which further includes the step of transmitting the supervisory signal from the subscriber premises during the off-hook conditions of the telephone at the subscriber premises.

96. The method of claim 94 which further includes the step of transmitting the supervisory signal from the subscriber premises during both on-hook and the off-hook conditions of the telephone at the subscriber premises.

97. The method of claim 94 which further includes the steps of sensing discontinuance of the supervisory signal during the sensing of the off-hook condition of the telephone at the subscriber premises, and transmitting the signals from the central location to the subscriber premises responsive to sensing of the discontinuance of the supervisory signal.

98. The method of claim 94 which further includes the steps of sensing discontinuance of the off-hook condition of the telephone at the subscriber premises, and transmitting the signals from the central location to the subscriber premises responsive to sensing of the discontinuance of the off-hook condition.