U.S. patent application number 11/485190 was filed with the patent office on 2008-01-24 for perimeter security system.
Invention is credited to Sendil Rangaswamy, Eric van Doorn.
Application Number | 20080018464 11/485190 |
Document ID | / |
Family ID | 38970899 |
Filed Date | 2008-01-24 |
United States Patent
Application |
20080018464 |
Kind Code |
A1 |
van Doorn; Eric ; et
al. |
January 24, 2008 |
Perimeter security system
Abstract
A security system for detecting physical intrusion in a
monitored area including a plurality of radio units arranged in a
network around the monitored area to determine received signal
strength and pass variations thereof through the radio units to a
base station.
Inventors: |
van Doorn; Eric; (Frederick,
MD) ; Rangaswamy; Sendil; (Gaithersburg, MD) |
Correspondence
Address: |
Epstein & Gerken
Suite 340, 1901 Research Boulevard
Rockville
MD
20850
US
|
Family ID: |
38970899 |
Appl. No.: |
11/485190 |
Filed: |
July 12, 2006 |
Current U.S.
Class: |
340/553 |
Current CPC
Class: |
G08B 13/2491 20130101;
G08B 13/187 20130101; G01S 7/003 20130101; G08B 13/126 20130101;
G01S 13/003 20130101 |
Class at
Publication: |
340/553 |
International
Class: |
G08B 13/18 20060101
G08B013/18 |
Claims
1. A security system for detecting physical intrusion in a
monitored area comprising a plurality of radio units arranged in a
network, each of said radio units having a signal transmitter, a
signal receiver, a circuit coupled with the receiver to measure the
signal strength of signals received by the receiver and produce an
output representative of received signal strength, a controller
responsive to said circuit output to cause said transmitter to
transmit a signal representative of the strength of the signal
received by said receiver and to provide said radio unit with a
receive mode and a transmit mode such that said receiver and said
transmitter do not operate simultaneously; and a base station
positioned to receive the transmitted signal from one of said radio
units and to provide an indication of intrusion into the monitored
area, said radio units being positioned such that each radio is
within communication range of at least one other radio.
2. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein said transmitter
signals are frequency hopped.
3. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein each of said radio
units includes a memory coupled with said controller for storing
radio unit control algorithms for operating the transmitter of each
radio unit.
4. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein said circuit
establishes a nominal threshold for received signal strength and
produces a signal representative of intrusion in the monitored area
when the received signal strength exceeds said threshold.
5. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein said nominal threshold
is adjusted continually to compensate for environmental
changes.
6. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein said radio units are
arranged such that alternate radio units have an amplifier and no
amplifier.
7. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein said radio units are
arranged in a triangular pattern.
8. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein said radio units are
arranged to form an inner ring and an outer ring around the
monitored area.
9. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein said radio units
include narrow band, low data rate, low power radios.
10. A security system for detecting physical intrusion in a
monitored area as recited in claim 1 wherein the same transmissions
from the transmitters are used to detect intrusions and to transmit
detection status to the base station.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to wireless security systems
and, more particularly, to wireless security systems for detecting
physical intrusions or movements in a monitored area or perimeter
and reporting any intrusions and/or movements.
[0003] 2. Description of the Prior Art
[0004] There is a great need for wireless security systems to
detect physical intrusions into monitored areas by human or other
intruders and report the intrusion and its nature. In the past,
wireless security or intruder detection systems have had the
disadvantages of being complicated with respect to tracking an
intrusion, of providing inaccurate readings in the presence of
noise or interference and of utilizing expensive equipment not
easily arranged to form a perimeter around an area to be monitored.
U.S. Pat. No. 4,213,122 to Rotman et al, U.S. Pat. No. 4,224,607 to
Poirier et al, U.S. Pat. No. 6,424,259 to Gagnon, U.S. Pat. No.
6,614,384 to Hall et al and U.S. Pat. No. 6,822,604 to Hall et al
and U.S. Published Patent Applications No. 2004/0080415 to
Sorensen, No. 2005/0055568 to Agrawala et al and No. 2005/0083199
to Hall et al are representative of efforts to provide such
wireless security systems.
SUMMARY OF THE INVENTION
[0005] One aspect of the present invention is to provide a
multi-purpose security system utilizing narrow-band, low-data rate,
low power (approximately 10 megawatts) radio units in a frequency
range between 800 MHz and several GHz. The radio units are arranged
in a network with each radio unit having a signal transmitter, a
signal receiver, a circuit coupled with the receiver to measure the
signal strength of signals received thereby and produce an output
representative of received signal strength and a controller
responsive to the circuit output to cause the transmitter to
transmit a signal representative of the strength of the signal
received by the receiver and to provide each radio with a receive
mode and a transmit mode such that the receiver and the transmitter
of each radio do not operate simultaneously. The security system
includes a base station/user positioned to receive the transmitted
signal from one of the radio units and providing an indication of
intrusion into the monitored area. The radio units are positioned
such that each radio unit is within communication range of at least
one other radio units, and the radio units can be capable of
frequency hopping.
[0006] In a further aspect, the present invention uses a network of
radio units to detect physical intrusions into a monitored area and
report detected intrusions wherein transmissions between the radio
units, which are affected by intruders, are also used to transfer
detection notification to a base station.
[0007] In another aspect, the present invention utilizes
half-duplex radio units arranged in a network where each radio unit
is within communication range of at least one other radio unit with
the radios using digital modulation of a carrier frequency to
encode data with one of the radio units connected by wireless link
or by wire, to a base station such as a computer or a PDA, referred
to herein in some cases as a user, which displays the status of the
perimeter security system.
[0008] In a further aspect, the present invention provides a
perimeter security system for detecting physical intrusion in a
monitored area utilizing a network of radio units which transmit
signals periodically or, at other times, are either in a receiving
mode or a sleeping mode. The transmissions occur according to a
preset schedule established in a manner to prevent a receiver in a
radio unit from simultaneously receiving signals from more than one
transmitter. The transmitted signals are packet-based with each
packet carrying the ID of the transmitter, the ID of the intended
receiver(s), a CRC bit, payload and end-of-packets bits.
[0009] The security system of the present invention can monitor
physical intrusions into an area, either indoors or outdoors, by
human or other intruders and report the intrusion and its nature to
a user. Some of the uses for the security system of the present
invention, due to its flexible and adaptable nature, include
perimeter sensing for detecting humans crossing a particular
perimeter, bread crumbs functioning, retracing the path of a human
such as in a cave, secure transportation of containers and cartons,
detecting human movement behind a wall, detecting humans caught in
rubble, alarm systems for animals, such as pets, tripwire fencing
for military applications, swimming pool safety, work site safety,
work site theft prevention, traffic monitoring, and detection of
illegal border (perimeter) crossing.
[0010] Inasmuch as the present invention is subject to many
variations, modifications and changes in detail, it is intended
that all subject matter discussed above or shown in the
accompanying drawings be interpreted as illustrative only and now
be taken in a limiting sense.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIGS. 1 and 2 are schematic diagrams of the security system
of the present invention using a triangular arrangement of radio
units.
[0012] FIG. 3 is a block diagram of the security system of the
present invention establishing a linear link between a transmitter
and a base station.
[0013] FIGS. 4 and 5 are block diagrams of radio units for use with
the security system of the present invention.
[0014] FIG. 6 is a schematic representation of a multiple perimeter
security system according to the present invention.
[0015] FIGS. 7 and 8 are representative of operation of the
security system of the present invention relative to intrusion
detection.
[0016] FIG. 9 is a block diagram illustrating an example of the
manner in which radio units of the security system of the present
invention can be controlled.
[0017] FIG. 10 includes graphs showing signal strength versus
time.
[0018] FIG. 11 is a schematic/block diagram representation of the
security system of the present invention used with a PDA.
[0019] FIG. 12 is a block diagram of another embodiment of a
perimeter formed by the security system of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] An exemplary embodiment of the present invention is shown in
FIGS. 1 and 2 with FIG. 1 illustrating a simple relaying network 10
of radio units 12 disposed at nodes in a triangular arrangement as
illustrated in FIG. 2 to form the "backbone" for relaying
information while acting as sensors arranged to form a perimeter
for a monitored area 14. The radio units 12 shown in FIG. 1 are
essentially arranged in triangular relationships as shown in FIG. 2
where the radio units of a triangle are illustrated as 12a, 12b and
12c. As shown simplistically in FIG. 3, a simple perimeter, as
opposed to the triangular arrangement shown in FIGS. 1 and 2, is
formed of a transmitter Tx, relay links or nodes RT and a receiver
base Rx such as a PDA or computer. An intrusion, such as a human
crossing in the line of sight between the relay links and the
receiver base would be detected and sent to a monitoring or base
station. The security system includes a network of narrow band
radio units interfaced to produce the transmitter radio (TX) the
relay nodes (RT), the receiver (RX) and a base unit coupled with a
radio unit.
[0021] Each of the radio units 12 or RT is formed of a transmitter,
a receiver, a received signal strength indicator (RSSI), a
microcontroller, an analog-to-digital converter (ADC) and a memory.
As previously noted, the radio units are half-duplex, i.e. each
radio unit can transmit and receive but not transmit and receive
simultaneously. When receiving an analog signal is generated to
indicate the strength of the signal received by the receiver in
each radio (RSSI), and the RSSI signal is converted to a digital
signal and forwarded to the microcontroller for storage in the
memory. The radio units include narrow-band, low-data rate, low
power (.apprxeq.10 mW) radios operating in the frequency range
between 800 MHz and several GHz. Each radio is half-duplex and,
preferably, is capable of frequency hopping. The radio units use
digital modulation of the carrier frequency to encode data and
frequency shift keying in some cases. One of the radio units is
connected by a wireless link, or by wire, to the base station, i.e.
computer/PDA/user. The computer/PDA displays the status of the
security system to an individual user. The same packet transmission
that is used to detect intruders is also used to transfer detection
notification and network status and control around the network and
to the user.
[0022] The signals sent by the radio units are packet-based with a
first part indicating whether the signal should be received and
checking security (counting zeros or ones) such that only accepted
packets are received thereby eliminating interference. Corrupted
signals are dropped; and, therefore, the security system can
operate in unregulated bands. The radio units operate with very low
bits per second such that communications take a long time reducing
bit error and corruption while causing increased signal stress.
[0023] Operation of two of the radio units 12 will be explained
with respect to FIGS. 4 and 5 which show identical radio units 1400
and 1400-2, respectively, having components as described above.
When transmitter 1410 of radio unit 1400 is in the transmit mode, a
narrow band signal, which may be frequency hopped, is transmitted
from radio unit 1400 and is received by radio unit 1400-2 which is
in the receive mode. Receiver 1420-2 receives the signal
transmitted from radio unit 1400, and an RSSI signal indicative of
received signal strength is generated at 1430-2, converted to a
digital signal by ADC 1450-2 and is supplied to the microcontroller
1440-2 which executes an intrusion detection function and provides
radio unit control algorithms which are read from memory 1460-2.
The intruder detection algorithms are based on RSSI levels, and a
criterion for detection of an intruder is based on the received
signal being significantly above or significantly below a nominal
threshold established by the memory. Sudden changes that affect all
radios simultaneously, such as a sudden rainstorm, are not
misinterpreted as an intruder because no intruder would affect all
radios simultaneously.
[0024] When an intruder is detected, the corresponding information
is added to the next set of packets (signals) transmitted by radio
unit 1400-2 to be received by a neighboring radio unit which will
be in the receive mode. The receiving units will add the detection
information to their outgoing packets (signals) such that the
information will reach the user or base via the network of radio
units. An advantageous feature of the security system of the
present invention is that the same transmissions that are used to
detect intruders are also used to transmit the detection and node
status data to the user or base.
[0025] A modification of the present invention is shown in FIG. 6
wherein radio units are arranged in a more complex geometry such
that multiple radio units receive each transmitted signal/packet.
Radio units 1101, 1102, 1103, 1104 and 1105 form an outer ring
around the area to be monitored, and an inner ring is formed of
radio units 1106, 1107, 1108, 1109 and 1110, the inner ring
providing additional security. The sequence of radio units
1101-1105 transmitting can be in the manner described above, that
is in numerical sequence, but each transmission is detected by five
other radio units. For example, the signal transmitted by radio
unit 1101 is received by at least radio units 1105, 1102, 1110,
1106 and 1107. If the signals received at any of these radio units
are indicative of detection of an intruder, the radio unit
temporarily stores that information until that radio unit is placed
in transmit mode. After radio units 1101-1105 transmit, radio units
1106-1110 transmit again in sequence. If any of these radio units
had detected an intruder in the previous cycle, that information is
added to their transmitted signals/packets, and radio units
1101-1105 will forward this information sequentially to the user.
During the transmitting mode of radio units 1106-1110, each
transmission is detected by at least five radio units. For example,
the signal transmitted by radio unit 1106 will be detected by radio
units 1101, 1102, 1107, 1110 and 1105, and each of these radio
units is thus able to detect intruders. The multiple rings add
robustness to the system and prevent false alarms through
redundancy. For most paths, any intruder must affect eight
direction sensitive paths traversing from outside to inside the
monitored area. If a single transmission time from a radio unit is
ten milliseconds, all ten transmissions will occur at ten
transmissions per second from each radio unit. With reference to
FIGS. 7 and 8, it will be noted that intruders near the line of
sight of any link between radio units will affect the strength of
the signals therebetween as indicated by the RSSI. If the intruder
is on the line of sight (LOS), the received signal is weaker due to
absorption. If the intruder is close to the line of sight, the
signal strength increases due to constructive interference between
the line of sight signal and the signal that is reflected from the
intruder. For larger distances from the line of sight, the received
signal strength may become stronger or weaker, depending on the
phase shift between the line of sight signal and the signal
reflected from the intruder. These fluctuations in signal strength
are measured by the RSSI in the receiving radio unit, converted to
a digital signal and processed by the receiver's microcontroller.
In the example shown in FIG. 7, an intruder represented as motion
orthogonal to the line of sight between radio units 1101 and 1102
and in the center between the radio units, it being noted that
other geometries will generate similar results. The radio unit in
transmit mode is radio unit 1101, and the radio unit in receive
mode is radio unit 1102. Four positions are shown labeled t.sub.1
through t.sub.4 indicating the times at which the intruder passes
each point. An intruder will be detected by either an increase or a
decrease in the received signal strength as compared with the
normal signal strength as shown in FIG. 8 with the normal signal
strength level being adjusted at a slow rate to accommodate for
environmental changes.
[0026] In operation, after the radio units are arranged around the
area to be monitored and turned on, each radio unit transmits
periodically. At other times, the radio units are either in
receiving or sleeping mode. The transmissions occur according to a
schedule as shown in FIG. 9, the schedule being established in a
manner such that collisions due to two or more transmitters
affecting a receiver simultaneously are minimized. The schedule can
be established before the radio units are deployed or may be
established after deployment during an automatic setup period.
[0027] FIG. 9 illustrates an example of radio units transmitting
according to a schedule that avoids two transmitters simultaneously
transmitting within communication range of the same receiver. T1,
T2 and T3 indicate radio units that are transmitting, and R1, R2
and R3 indicate radio units that are receiving. C indicates the
computer or PDA (base) for monitoring the security system, and
T=0,1, 2 indicates time steps. The communications between radio
units is packet-based with each packet carrying the ID
(identification) of the transmitter, the ID of the intended
receiver, CRC bit, payload and end-of-packet bits. When a receiver
receives a packet intended for that receiver, the RSSI measures the
signal strength.
[0028] After the radio units of the security system are initially
deployed, or established in a network, around an area to be
monitored, the radio units measure RSSI values of many packets
transmitted between all radio units that are within communication
range with each other. The user ascertains that, during this
initial setup period, no intruders are present in the area to be
monitored. The measured RSSI values are processed by each radio
unit individually, or relayed to a central processing node.
Specifically, for each link between a pair of radio units, the
mean, standard deviation and other characteristics of the RSSI
values are computed. In one embodiment, a user-specified
"probability of false alarm" (PFA) with the statistical parameters
of RSSI values are used to compute thresholds for the RSSI values
for each radio unit to detect an intruder. The upper graph in FIG.
10 illustrates raw signal strength data vs. time for a 70 ft link
and illustrates noise from automobile traffic as well as an
intruder crossing at t t.sub.(s)=600 s. The bottom graph shows
processed signal strength vs. time with the signal-to-noise ratio
for the intruder detection at 600 s improved by more than 10
dB.
[0029] Once the thresholds are established, the RSSI value for each
radio unit is evaluated against the threshold for that link. If the
threshold is exceeded, a counter in the microcontroller of each
radio unit is incremented. If the RSSI value does not exceed the
threshold, the counter is decremented. If the counter reaches a
predetermined value, a message containing the time, details of the
RSSI value and a message that an intruder is detected is added to
the payload of the packet transmitted by that radio unit. If the
RSSI value at a particular radio unit does not exceed the
threshold, a message is added to the next packet transmitted
indicating that no intruder was detected and that the link was
operational. Each radio unit passes on or relays the status of each
link as indicated by the payload of the packets the radio unit
receives, including the status of the links of which that radio
unit is part. In this manner, messages containing the status of
each link will periodically be received by all radio units in the
network including the radio unit that communicates with the user. A
graphical user interface (GUI) is provided at the user's
computer/PDA indicating the status of each radio link, and the GUI
can also indicate the location of each radio unit if the location
of radio units is noted or recorded during placement. An example of
a PDA with such a GUI is illustrated in FIG. 11 wherein the
numbers, 1-8, on the GUI correspond with the radio units 1-8
deployed around an area to be monitored (not shown).
[0030] Transmitters external to the security system of the present
invention that transmit using the same carrier frequency will cause
the RSSI to fluctuate, as do intruders. However, since the data
rate of the radio units is low, the modulation frequency of the
carrier wave is low and, thus, each occurrence lasts many
microseconds. For any intruders located within a few wavelengths
from the line of sight, the path difference between the line of
sight signal and the signal reflected from the intruder is at most
a few periods of the carrier signal. That means that inter-symbol
interference (overlapping of two symbols in time in a receiver) is
negligible for a frequency above 100 megahertz and that signal
strength fluctuations caused by the intruder will not cause bit
errors. This represents a key difference between signal strength
fluctuations due to intruders and signal strength fluctuations due
to external transmitters. Transmitters external to the security
system of the present invention that transmit the same carrier
frequency will not be in phase with the radio unit transmitters.
For sufficiently strong signals, the interference will cause bit
errors in the packets sent by the radio units and cause a receiver
to drop a packet. In this way, a strong external transmitter could
jam the security system of the present invention. To reduce
vulnerability to jamming, the transmitters and receivers of the
radio units are capable of frequency hopping. Since each packet
only lasts a few milliseconds, the radio units, transmitters and
receivers can hop through a predetermined list of frequencies. If
any particular frequency is jammed by external transmitters, the
jamming will occur for only a few milliseconds.
[0031] Another embodiment of the security system of the present
invention is illustrated in FIG. 12 and includes radio units with
amplifiers, denoted as A, and radio units without amplifiers
denoted as R, the radio units being connected in series with
alternating distances in between, for example, a 40 ft distance
between a transmitter T and a first radio unit with amplifier A. In
the embodiment shown, initially the security system will be set up
using the radio units with amplifiers A and the radio units without
amplifiers R as shown; and, after noting the location using a GPS
system, the location of each of the radio units is provided to the
base/GUI. The transmitter T is a radio with an amplifier but
configured to operate only as a transmitter to transmit a data
packet to the first radio unit with amplifier A.sub.1 which
receives the packet, measures the RSSI, analyzes the RSSI to
determine the presence or lack of presence of an intruder near the
T-A.sub.1 link and sends a data packet to the first radio without
amplifier R.sub.1 with a message of "yes" or "no" (a 0 or a 1)
indicating that there either is or is not an intruder in the
segment of the system between A.sub.1 and R.sub.1. The next radio
unit with amplifier in the security system A.sub.2 detects the
message from radio unit R.sub.1 due to its close proximity to radio
unit R.sub.1. Radio unit A.sub.2 then sends a data packet on to
radio unit R.sub.2 with a message indicating a 0 or a 1 for the
segment between A.sub.1 and R.sub.1 and a 0 or a 1 indicating
either that there is or there is not an intruder in the segment
between A.sub.2 and R.sub.2. The data packet is sent through each
radio unit with amplifier with each successive radio unit with
amplifier transmitting data indicating the presence or absence of
an intruder in the segment of the security system directly adjacent
thereto and in the preceding segments or links of the security
system. The last radio unit is connected to a modem M.sub.1 which
transmits all of the information to a second modem M.sub.2 located
a substantial distance from the first modem (indicated as 1/2
mile). The second modem M.sub.2 is connected to a GUI/base at which
a user can observe the system from a safe distance and report any
detection of intruders. By utilizing triangular links as described
above with respect to FIGS. 1 and 2, the security system of FIG. 12
can provide redundancy to compensate for any disruption of any of
the radio units and will allow continuous operating of the security
system in the event of a disruption in one link. An additional
advantage of the use of the triangular pattern is to determine the
direction of travel in addition to detecting the intrusion across a
perimeter or perimeter link. Bi-directional amplifiers/receivers
can be utilized to increase the distance between the radio units,
and the GPS can be integrated into the security system such that
location information does not need to be input manually into the
GUI/base.
[0032] Inasmuch as the present invention is subject to many
variations, modifications and changes in detail, it is intended
that all subject matter discussed above or shown in the
accompanying drawings be interpreted as illustrative only and not
be taken in a limiting sense.
* * * * *