Title: 3-Way call detection system and method
Abstract: Disclosed herein is a three-way call detection system and method for detecting the addition of a third party to a pre-existing telephonic connection between a first party and a second party. The system comprises a meter for measuring the amplitude of a line voltage of a telephonic connection between a first party and a second party.
Patent Number: 6,895,086 Issued on 05/17/2005 to Martin
| Inventors:
|
Martin; Thomas J. (State College, PA)
|
| Assignee:
|
Inmate Telephone, Inc. (Altoona, PA)
|
| Appl. No.:
|
291659 |
| Filed:
|
November 12, 2002 |
| Current U.S. Class: |
379/189; 379/207.01; 379/406.14 |
| Intern'l Class: |
H04M 003/00 |
| Field of Search: |
379/189,207.01,406.01,406.14
|
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Other References
Coherent Announces Industry's First Remote Management System for Echo Canceller,
Business Wire, Mar. 3, 1997.
Audioconferencing options. (Teleconference Units, Conference Bridges and Sevice
Bureaus) (Includes related articles on speech processing and new conferencing technology),
Frankel, Elana, Teleconnect, v 14, n 5, p131(3), May 1996.
Digital on Call, Silberg, Lurie, HFN The Weekly Newspaper for the Home Furnishing
Network, p. 97, Mar. 17, 1997.
Inmate Telephone Services: Large Business: Voice, Oct. 2, 2001.
|
Primary Examiner: Isen; Forester W.
Assistant Examiner: Harold; Jefferey F.
Attorney, Agent or Firm: Wiley, Rein & Fielding, LLP
Parent Case Text
RELATED APPLICATIONS
This application claims priority to U.S. Provisional Application No. 60/331,258,
filed Nov. 13, 2001, which is incorporated by reference in its entirety.
Claims
1. A three way call detection system for detecting the addition of a third party
to an pre-existing telephonic connection between a first party and a second party,
said system comprising:
a meter for measuring the amplitude of a line voltage of a telephonic connection
between a first party and a second party, said line voltage having a frequency
band F
1,
a first filter to remove a frequency band F
2 from said line voltage and
output a filtered signal, said frequency band F
2 being a subset of F
1;
a white noise generator for generating a low level white noise signal with a
frequency band that corresponds to F
2 and with an amplitude that is at least
3 db below an amplitude level of the measured line voltage for frequency band F
2,
a coupler for combining the low level white noise signal with the filtered signal,
thereby outputting an additive line voltage;
a second filter that passes only a portion of the additive line voltage, said
signal that passes being referred to as the band-passed signal, said band-passed
signal having a frequency range F
3, said frequency band F
3 being
a subset of F
1 and being inclusive of F
2; and
a processor for processing the band-passed signal and determining a baseline
amplitude level associated with a two-way call;
wherein said processor monitors the band-passed signal in the time domain for
a shift in baseline amplitude level, which shift is associated with the addition
of a third party to the telephonic connection.
2. The three way call detection system of claim 1, wherein the coupler is selected
from the group consisting of: a voltage adder, a summer, a signal combiner, and
a processor preprogrammed with a function that adds two signals to form a combined signal.
3. The three way call detection system of claim 1, wherein the coupler is a signal combiner.
4. The three way call detection system of claim 1, wherein the coupler is a processor
preprogrammed with a function that adds two signals to form a combined signal.
5. The three way call detection system of claim 1, wherein the amplitude of the
line voltage is measured at a location selected from the group consisting of: the
location of the first party, a telephone switching station, and a telephone central office.
6. The three way call detection system of claim 1, wherein the amplitude of the
line voltage is measured at a telephone switching station.
7. The three way call detection system of claim 1, wherein the amplitude of the
line voltage is measured at a telephone central office.
8. The three way call detection system of claim 1, wherein the first filter is
selected from the group consisting of: a notch filter, a band reject filter, a
processor preprogrammed with a function that cancels any amplitude signal within
frequency band F
2, and a circuit that subtracts the amplitude signal in
frequency band F
2 from the amplitude of the line voltage in frequency band F
1.
9. The three way call detection system of claim 1, wherein the first filter is
selected from the group consisting of a band reject filter.
10. The three way call detection system of claim 1, wherein the first filter
is a processor preprogrammed with a function that cancels any amplitude signal
within frequency band F
2.
11. The three way call detection system of claim 1, wherein the first filter
is a circuit that subtracts the amplitude signal in frequency band F
2 from
the amplitude of the line voltage in frequency band F
1.
12. The three way call detection system of claim 1, wherein the second filter
is selected from the group consisting of: a band pass filter, a processor preprogrammed
with a function that cancels any amplitude signal not within frequency band F
3,
and a circuit that subtracts the amplitude signal not in frequency band F
3
from the amplitude of the line voltage in frequency band F
1.
13. The three way call detection system of claim 1, wherein the second filter
is a band pass filter.
14. The three way call detection system of claim 1, wherein the second filter
is a processor preprogrammed with a function that cancels any amplitude signal
not within frequency band F
3.
15. The three way call detection system of claim 1, wherein the second filter
is a circuit that subtracts the amplitude signal not in frequency band F
3
from the amplitude of the line voltage in frequency band F
1.
16. The three way call detection system of claim 1, wherein the white noise generator
is selected from the group consisting of: a white noise source coupled to a bandpass
filter and a processor preprogrammed to generate a random noise signal with a frequency
band corresponding to F
2.
17. The three way call detection system of claim 1, wherein the white noise generator
is a white noise source coupled to a bandpass filter.
18. The three way call detection system of claim 1, wherein the white noise generator
is a processor preprogrammed to generate a random noise signal with a frequency
band corresponding to F
2.
19. The three way call detection system of claim 1, wherein the meter is selected
from the group consisting of: a voltmeter, a multimeter, and a measuring circuit.
20. A method of detecting the addition of a third party to an pre-existing telephonic
connection between a first party and a second party, said method comprising:
measuring a line voltage for amplitude, said measured line voltage having a frequency
band F
1;
filtering the measured line voltage to remove a frequency band F
2 to create
a filtered signal, said frequency band F
2 being a subset of frequency band
F
1;
generating a low level white noise signal with a frequency band that corresponds
to F
2 and with an amplitude that is at least 3 db below an amplitude level
of the measured line voltage for frequency band F
2,
adding the low level white noise signal to the filtered signal to create an additive
line voltage;
filtering the additive line voltage to pass only a portion of the additive line
voltage, said signal that passes being referred to as the band-passed signal, said
band-passed signal having a frequency range F
3, said frequency band F
3
being a subset of F
1 and being inclusive of F
2;
processing the band-passed signal to determine a baseline amplitude level associated
with the characteristics of a two-way call;
monitoring the band-passed signal in the time domain for a shift in baseline
amplitude level, which shift is associated with the addition of a third party to
the previous two-party call.
Description
FIELD OF INVENTION
This invention relates generally to telephony, and more particularly to a method
and a system for detecting when a party has been added to a pre-existing telephone call.
BACKGROUND OF INVENTION
Generally, there is a need for systems that detect three way calls. There
is a great need for such systems in telephone systems for jails, prisons, and other
correctional institutes, where the calls of inmates are closed monitored for unauthorized activity.
Conventional systems exist for detecting three way calls, but such conventional
systems do not reliably and accurately detect when new parties have been added
to an existing call. Accordingly, a need exists for improved three way call detection
methods and systems.
SUMMARY OF THE INVENTION
Particular implementations of the present invention, which have yielded
reliable and accurate three-way call detection systems and methods, will now be
described. These present inventions use computers and software to create efficiencies
and improve reliability of three-way call detection.
Disclosed herein is a method of detecting the addition of a third party
to an pre-existing telephonic connection between a first party and a second party.
The method comprises the steps of: measuring a line voltage for amplitude, said
measured line voltage having a frequency band F1; filtering the measured
line voltage to remove a frequency band F2 to create a filtered signal,
said frequency band F2 being a subset of frequency band F1; generating
a low level white noise signal with a frequency band that corresponds to F2
and with an amplitude that is significantly below an amplitude level of the measured
line voltage for frequency band F2; adding the low level white noise signal
to the filtered signal to create an additive line voltage; filtering the additive
line voltage to pass only a portion of the additive line voltage, said signal that
passes being referred to as the band-passed signal, said band-passed signal having
a frequency range F3, said frequency band F3 being a subset of F1
and being inclusive of F2; processing the band-passed signal to determine
a baseline amplitude level associated with the characteristics of a two-way call;
monitoring the band-passed signal in the time domain for a shift in baseline amplitude
level, which shift is associated with the addition of a third party to the previous
two-party call. The white noise being added is preferably at least 3 dB below the
amplitude level of the measured line voltage, more preferably at least 10 dB, more
preferably at least 20 db, and most preferably 40 db below. The frequency band
F2 is selected from F1 to be significantly large enough to permit
more reliable detection, and yet small enough to be barely perceptible to the listener.
For example, F2 may comprise the frequencies from 1-2 KHz. An F2
of 1-1.3 KHz. also functions well.
Also disclosed herein is a three way call detection system for detecting the
addition of a third party to an pre-existing telephonic connection between a first
party and a second party. The system comprises: a meter for measuring the amplitude
of a line voltage of a telephonic connection between a first party and a second
party, said line voltage having a frequency band F1; a first filter to remove
a frequency band F2 from said line voltage and output a filtered signal,
said frequency band F2 being a subset of F1; a white noise generator
for generating a low level white noise signal with a frequency band that corresponds
to F2 and with an amplitude that is significantly below an amplitude level
of the measured line voltage for frequency band F2; a coupler for combining
the low level white noise signal to the filtered signal, thereby outputting an
additive line voltage; a second filter that passes only a portion of the additive
line voltage, said signal that passes being referred to as the band-passed signal,
said band-passed signal having a frequency range F3, said frequency band
F3 being a subset of F1 and being inclusive of F2; and a processor
for processing the band-passed signal and determining a baseline amplitude level
associated with a two-way call. The processor monitors the band-passed signal in
the time domain for a shift in baseline amplitude level, which shift is associated
with the addition of a third party to the telephonic connection. The white noise
being added is preferably at least 3 dB below the amplitude level of the measured
line voltage, more preferably at least 10 dB, more preferably at least 20 db, and
most preferably 40 db below. The frequency band F2 is selected from F1
to be significantly large enough to permit more reliable detection, and yet small
enough to be barely perceptible to the listener. For example, F2 may comprise
the frequencies from 1-2 KHz. An F2 of 1-1.3 KHz. also functions well.
The present invention overcomes the problems and disadvantages associated with
conventional methods and systems, and provides improved systems and methods whereby
the additions of new parties to a telephone call may be detected.
Other embodiments and advantages of the invention are set forth in part in
the description that follows, and in part, will be obvious from this description,
or may be learned from the practice of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the invention and some advantages thereof,
reference is now made to the following descriptions taken in connection with the
accompanying drawings in which:
FIG. 1 is the block diagram for an type of codec chip that is used in some phone systems
FIG. 2 is the block diagram for a more modern codec chip.
FIG. 3 is a block diagram for a system set up that monitors for three-way calls.
FIG. 4 is are spectral plots that show how one embodiment of the present system
may be implemented.
FIG. 5 is an amplitude vs. time plot that shows how a three way call may be
detected in one embodiment of the present invention.
FIG. 6 is a amplitude vs. time plot, which shows how a three way call may be
detected in another embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The following is a sequence of events that may occur when a caller adds a third-party
call using a 3-way calling service.
1. First, the prisoner (or similar person) may call a telephone number that is
not blocked or otherwise restricted. The recipient of the call answers the phone.
2. Once the initial call is established, a communication path with fairly constant
electrical characteristics is formed.
3. At some point, the party that has been called (and who is not subject to the
correctional institutes calling restrictions) decides to add a third party. The
called party may use a hook flash sequence to put the caller on hold or he/she
may have a more modern phone or PBX that does not use a hook flash. Even in the
latter case of no hook flash, one or more periods of silence will occur, along
with a release pulse, when the 3-way call becomes active.
4. Once the 3-way call is established, since another section of phone line has
effectively been added to the circuit, the characteristics of the overall noise
level have changed, which can be detected by the present invention.
A technical advantage of the present invention is that it may be used to significantly
reduce the number of unauthorized calls that go undetected by conventional systems.
Another technical advantage is that the present invention may be used to
more closely monitor for unauthorized uses of inmate telephone systems.
Another technical advantage of the present invention is that it may be easily
adjusted for any given telephone system with which it is installed for improved
three-way call detection.
Many people in the US have a telephone that's part of what called the ‘POTS’
network, or the Plain Old Telephone System. This system consists of pairs of wires
that carry analog telephone signals along with DC power to and from customers and
one of many Central Offices (COs) all over the country. Other people have new,
modem digital phones or fiber optics connecting their houses with the Central Offices
as well. So, when a call is placed across town, or across the country, the paths
which sound must travel often cross a plurality of different systems, different
connections, and different mediums. Each such system, connection and medium result
in mismatches in impedance as well as the introduction of noise. These mismatches
result in echos that add noise and degrade call quality. With the addition of each
new party to a telephone call, the result is an increase in echos, noise and signal degradation.
Another cause of echoes that appear on three-way calls has to do with the
imperfect electrical characteristics of what's called a ‘two-wire-to-four
wire hybrid’ or simply a ‘hybrid’ present at each POTS telephone.
POTS phone lines consist of only two wires, and these wires carry incoming signals
(what we hear on the phone), outgoing signals (what we say on the phone) and DC
power. Remember that our telephones have two wires for a microphone and two wires
for a speaker, for a total of four. Accordingly, such phones must include a ‘two-wire-to-four
wire hybrid’ circuit to process the electric connection between a POTS phone
line (the 2-wire side) and a microphone/speaker pair (on the 4-wire side). For
a more detailed discussion of echos that occur in connection with three-way calls
and echo cancellers that are used to remove such echos, see U.S. Pat. Nos. 5,535,194,
and 6,035,034, which patents are hereby incorporated by reference in their entireties.
To send a spoken message out onto the phone line, the hybrid must place the signal
on the phone line, and at the same time, the hybrid must also retrieve an incoming
signal and pass it through the hybrid to the speaker. For a number of reasons (including,
for example, imperfect transformers) a portion of the spoken speech gets passed
through the hybrid, onto the phone line, back off the phone line, back into the
hybrid and sent to the speaker. The result is an echo, one that we usually don't
notice because it's barely delayed in time from our own speech. Our brains unconsciously
filter this echo.
When a long-distance call is placed, the outgoing speech goes over the phone
line to the called party, and due to the mismatches along the way, a small portion
of it comes back over the line from the called-party's hybrid and results in an
echo on the originating side. Only this time, there may be a considerable time
delay due to the round-trip travel of the signal, so these echoes can be very noticeable.
Calling Europe, for example, can result in very long, annoying echoes.
During three-way phone calls, a similar effect happens. Assume speaker A is
an original caller who makes a call to Speaker B; and while on the line, either
A or B then makes a three-way call to Speaker C who then joins the call as a third-party.
The signal from speaker A goes both to speaker B and speaker C, so the overall
signal travel time is longer than when speaker A just calls speaker B or C alone.
Furthermore, the signals from the other callers (B and C in this case) are traveling
and reflecting back from the other callers so that all three parties potentially
hear echoes. As the distance between callers increases, the echoes may become more
noticeable. In addition, the ability of the hybrid circuits to function properly
on either end of a connection directly affects the perceptibility of such echoes.
The phone companies, in their attempts to produce very good-quality phone calls,
have circuitry built in to their systems that detect and remove echoes. This circuitry
implements a number of electronic functions in an attempt to reduce echoes.
FIG. 1 below is the block diagram for an example chip that's used in some phone
systems as part of the Central Office circuitry. This part is called a ‘codec’,
and is a fundamental circuit in the phone system, as every POTS line has one. In
particular, FIG. 1 is a block diagram for Agere Systems T8532 Codec.
The signals on the left side of the diagram represent those on the POTS phone
line; the signals on the right side represent the signals within a digital Central
Office. VTX/VTRX represent signals coming into the CO which are spoken by a speaker;
VRP/VRN represent signals going out from a CO to a customer (the signals that one
hears on a phone call).
Notice the various blocks marked ‘Gain’. Gain means a change
in amplitude, either making the signal louder or softer, depending on what's needed
at the time. A principal use of the Gain blocks is to maintain reasonable volume
levels for all calls passed though a codec. Much more signal amplitude (volume)
will have to added to a call that's made over 100 miles of POTS wiring than one
that's made over 10 miles of POTS wiring. The Gain of phone calls is handled automatically
by the phone system so we don't realize all this is actually happening.
FIG. 2 below is the block diagram for another, more modem codec, namely, the
Agere Systems T8535B Codec. As with FIG. 1, the signals on the left side of the
diagram represent those going to and from a POTS phone line, and those on the right
are the signals inside a digital Central Office. The VfxIn are signals coming from
a caller into the CO; VfxOPn/Onn are signals going out of a CO to a customer. In
this diagram that there are two very important blocks—one marked ‘Termination
Impedance’ and the one marked ‘Hybrid Balance Network’.
These two blocks taken together form an electronic version of a hybrid circuit,
one with electrical characteristics far superior to old-time transformer-based
hybrids. The two triangular blocks marked ‘Digital Gain’ provide
gain functions similar to those shown in FIG.
1. They increase or decrease
signal volume as needed.
Now that a general description of the overall phone systems has been provided,
the particulars of the present invention can be better appreciated.
It is known that phone systems monitor the signals on phone lines and adjusts
their amplitudes (volumes) continually in an effort to provide the best possible
call quality. The ability of a phone system to monitor and adjust amplitudes varies
from system to system and from path to path. The ability to make adjustments is
further complicated because older phone line circuits have transformer-based hybrid
circuits while newer ones tend to have electronic hybrids. Accordingly, phone systems
have to constantly make adjustments based on the interaction of new and old systems.
When three-way calls are established, echoes are created due to the hybrid circuits
and due to new signal paths being added to the mix. Because of these changes, phone
company circuits must detect these echoes and try to cancel them using a number
of techniques. These techniques are designed to improve the overall quality of
the call.
Because the addition of parties to a preexisting phone call results in the
phone companies making adjustments to the line volume on the call, one can monitor
the line volume for such adjustments in an effort to detect a three way call. The
challenge is to design a detection technique that is reliable and accurate. Reliability
and accuracy are complicated by the fact that any given phone call can have a path
across any number of different phone systems and different kinds of circuitry.
The techniques employed by the present invention have achieved an unexpected
result, namely, a much improved level of accuracy and reliability.
FIG. 3 shows a block diagram of a setup for one embodiment of the present invention.
The following is a detailed description of the steps involved in the three-way
call detection shown in FIG.
3:
- The microphone signal coming from a telephone handset is received.
- Its amplitude is adjusted as needed (not implemented yet in my software)
for a decent call.
- A certain block of frequencies is filtered out of the received speech
to prevent higher and lower signal amplitudes in the given frequencies from falsely
triggering the three-way call detector.
- In the frequency bands that were filtered out, spectral bins constituting
random noise are added to the received and filtered speech. The amplitude of the
random noise is carefully generated and held constant. The new speech+noise signal
is then passed to the phone to go through the hybrid and get passed out onto the
phone line.
- The signal out on the phone line is measured and the signal levels in
the frequency bands of the test signal are measured and compared to what was sent.
Their relative amplitudes in decibels are calculated.
- This process happens continually, and whenever a three-way call of sufficient
characteristics happens, the phone company adjusts the gain of the signals on the
line and/or the line impedance, and that difference can be measured. Since the
test signal put out on the line has constant volume, a non-three-way call will
settle out in a few seconds such that the amplitude of the test signal on the line
is also constant. Three-way calls have the gain of the signals on the line decreased,
as discussed earlier, and thus the test signal's amplitude will be lower and can
be measured.
- It may be sufficient to simply measure the amplitude of the speech received
from the microphone and compare this to the amplitude of the same speech on the
line, but detection is very tough when the original caller doesn't speak, since
outgoing signal amplitude will be extremely low. The addition of the test signal
solves this problem.
FIG. 4 contains four spectral plots that help to illustrate a further embodiment
of the present invention.
FIG. 4A is the spectral plot for a 16-second block of speech samples. The X
axis is frequency (0 Hz at the left and 4 kHz at the right) and the Y axis is decibels (dB).
FIG. 4B shows how a portion of the frequency spectrum of the signal in FIG.
4A may be removed (for example, using DSP or a notch filter). In this case, the
frequency band of 1000-1300 Hz. has been removed. The filtered signal is shown
here. Depending on which frequencies are removed, the resulting audio speech may
be almost indistinguishable from the original. In a preferred embodiment, a small
group of frequencies (e.g., having a bandwidth of 300 Hz or less) are removed.
Ideally, the bandwidth can be adjusted for each system in order to minimize the
perceptibility of such frequencies that are removed.
FIG. 4C shows a band of white noise that corresponds to the frequencies removed
earlier. The amplitude of the noise should be far enough down from the speech signal
to remain undetected on the phone line. Preferably, the signal is at least 3 dB
below the speech signal, and more preferably, 20 dB, and most preferably 40 dB.
FIG. 4D shows the resulting signal when the noise has been added to the filtered
speech to produce a composite signal. One skilled in the art can adjust the width
(bandwidth) of the removed spectrum and added noise based on conditions on the
line and other conditions to provide the highest 3-way call detection rate.
FIGS. 5 and 6 show examples of three-way call detection using the above techniques
for a call made between State College, Pa. and a small town in Northeast Ohio:
FIG.
1. As can be seen, an initial baseline is established and then monitored
for a significant change that is the result of the addition of a new party to the
call. In FIG. 5, the signals being monitored are in the 1 kHz-2 kHz band, and in
FIG. 6, the signals being monitored are in the 1 kHz-1.3 kHz band
While the invention has been particularly shown and described in the foregoing
detailed description, it will be understood by those skilled in the art that various
other changes in form and detail may be made without departing from the spirit
and scope of the invention. It is intended that the specification and examples
be considered exemplary only, with the true scope and spirit of the invention indicated
by the claims below.
*
