PERSONNEL LOCATION MONITORING SYSTEMThis invention relates to a location monitoring system.
In sensitive environments, such as prisons or nuclear establishments, there is a need to be able to track personnel so that, in the event of an emergency, at least their approximate location can be determined. Because this needs to be done at least partly indoors, conventional range and direction finding equipment is unsuitable.
In accordance with one aspect of the present invention, there is provided a location monitoring system, comprising a plurality of mutually spaced-apart fixed units each capable of transmitting a wire tess fixed unit signal (preferably a microwave and/or infra-red signal, but alternatively a magnetic 01. radio signal for example), at least one mobile unit to be carried by a person (for example in, or- clipped to, their breast pocket) and capable of detecting such a fixed-unit signal when in a limited region (such as within 3 metres) with respect to the fixed unit transmitting the signal, a central unit, and means for' transmitting a location signal from the or- each mobile unit to the central unit indicating which fixed unit was last detected by that mobile unit.
Preferably, the fixed unit signal of each fixed unit is indicative of the identity of that fixed unlit, and the location signal.
transmitting means is operable t.o transmit from the mobile on it. to the central unit such a location signal indicative of the identity of the detected fixed unit. @ In the case wtoer'e there is a plul-ality of such mohile units, preferably the location signal is also indicative of the identity of the respective mobile till it In one embodiment, the location signal is transmitted as a wi.re- less signal (for example a radio signal) directly from the, or the respective, mobile unit to the central unit. In this case, the or each mobile unit is preferably operabLe l.o store the identity of aL least the last detected fixed unit and optionally also the time of detection.
The or each mobile unil. preferably further comprises means operable by the person to cause the location signal. to be transmitted. This may be used to contact Lhe central unit in an emergency. In this case, the central unit may include means to transmit an acknowledgement signal in response to receipt of the location signal, and the or- each mobile unit may include means to receive the acknowledgement signal caused by it location signal and indicate the acknowledgement signal to the person.
Additionally or- alternatively, the or each mobile unit may comprise means to cause the location signal to be transmitted periodically.
Also, additionally or alternatively, the central unit may be operable to transmit an interrogation signal, anti the or each mobile unit may be operable to detect such an interrogation signal and to transmit the location signal in response thereto.
In another embodiment, the location signal may be transmitted as a wire-less signal (for example of the same type as the fixed unit signal) from the, or the respective, mobile unit to the fixed unit and relayed to the central unit, the location signal being indicative of detected fixed unit. by virtue of which fixed unit r-clays the location signal. In this case, such a location signal may he transmitted each time a fixed unil. is detected.
In accordance with another aspect oi' the present invention, there is provided a system for monitoring the location of a portable transmitting anti receiving module in a given space, comprising a plurality of separated and fixed units (for example microwave units) each adapted to emit a beam limited to a specific region in space, and the portable nodule being adapted to be cats vied l)y a person and to detect the beam when in the region to cause the region to be identified and recorded.
A specific embodiment of the present invention and some modifications thereto will now be described by way of example with reí'erence to the accompanying drawings, in whirl: Figure 1 is a block diagram il lustr-ating one of the @ fixed units; Figure 2 is a block diagram illustrating a mobile unit; andFigure 3 is a block diagram illustrating a central unit.Referring to Figure 1, each fixed unit comprises a secure housing 10 having an external connection 12 to mains electricity which supplies a power supply unit 14 which may also include a back-up rechargeable battery. The power supply unit 14 ener-gises a microwave or infra-red transmitter 16 and also a code gener-ator- 18.The code generator 18 produces a coded signal which is unique to the fixed unit in question and which modulates the transmitter 16, so that the signal FUS transmitted thereby is specific to that fixed unit.
A respective fixed unit is installed at each point to be monitored. In a prison environment, fixed units would be installed, for- example, above external doorways, above entrances to corridors, in narrow gaps between buildings, at a gate to a r-ecreation field, and so on.
Each person to be monitored, for example each prison officer, is provided with a mobile unit, as shown in Figure 2, which is normally carried in or clipped to the breast pocket. Each mobile unit comprises a housing 20 containing a rechargeable battery 22, microwave or infrå- red (as appropriate) receiver 24, radio transmitter 26 and receiver 28, switch 30, indicator 32, such as a light, and microprocessor comprising an MPU 34, with associated RAN 36, ROM 38 and I/O 40.
The MPU 34 is programmed by the ROM 38 to operate in part as follows. The output of the microwave/infra-red receiver 24 is monitored and when a fixed unit signal FUS is detected the identity code of the fixed unit generating the signal is stor-ed in the RAM 36.
Either the KAM 36 may store the identity code of the last detected fixed unit, or alternatively it may store the Identity codes of the last two or more detected fixed units in the order in which they were detected. The mobile unit may also include a r-eal time clock, and the time of detection of the fixed tini I. can then also be stored.
The power of the transmitters 16 in the fixed units and the sensitivity of the receivers 24 in the mobile units are selected so that each mobile unit only responds to a fixed unit when it is a predetermined distance therefrom, such as 3 metres.
Referring to Figur-e 3 the central unit comprises a micro- computer- 50 comprising a CPti 52 with associated ROM 54, RAM 56 and I/O 58, a display 60, a keyboard 62, a radio receiver 64 antl a radio transmitter 66.
The MPU 34 of each mobile unit is programmed by its ROM 38, andMPU 52 of the central unit is programmed by its KOM 54, to operate as follows. The state of the switch 30 of the mobile unit. is monitored, and when depressed the radio transmitter 26 is enabled to transmit a location signal LS which includes a code (stored in the RON 38) specific to the mobile unit in question and the identity code or codes (stored in the KAM 36) of the last detected fixed unit(s) and optionally also the time(s) of detection. In the central unit, the output oE the receiver 64 is monitored, and when a location signal LS is detected, the codes contained therein are decoded and displayed on the display 60 so as Lo identify the generating mobile unit and the last: detected fixed units. Furthermore, an acknowledgement signal AS is transmitted by the transmitter 66 of the central station including the identity code of the generating mobile unit. Also, an alarm signal may be generated at the central station.The mobile units monitor the outputs of the receivers 28, and upon detection of an acknowledgement signal AS containing the code of the mobile unit in question, the indicator lighL 32 of that mobile unit is illuminated, thus indicating acknowledgement by the central unit.
In the case of a prison environment, it will be appreciated that as each prison officer passes a fixed unit, his mobile unit will he updated with the code of that fixed unit. In the event of an emergency, sucti as an attack on the officer, upon pressing the switch of his mobile unit, the central unit will be informed of the identity of the officer and at least the last fixed unit which the officer passed. Assistance can then be summoned by the operator of the central unit, and also the indicator- light on the officer's mobile unit will be lit, assuming successful transmission, to reassure him that assistance should be on the way.
Variolls modi f icat ions, developments and refinements may be made to the system described above. For example, the fixed unit signals FtiS may be other wire-less signals, such as radio signals or magnetic field signals. Al so, instead of the identity code for- each mobile unit being stored in it S ROM 38, it may be stor-ed in a personal identifi(::atior key, such as a smart-card, which is specific to a particular user, and the personal identification key may be then @nser@ed into any mobile unit and program that unit with the user-'s identity. in this case, rather I hari the alarm being raised by pressing a switch 30, the mobile units may operate such that r-emoval of the per-sondl identification key from the mobile unit serves the same purpose.Furthermore, instead of, or in addition to, the location signal LS being transmitted only upon operation of the switch 30 (or- removal of the personal identification key), it. may be transmitted periodically, or each Lime a fixed unit is detected, or in response to a coded interrogation signal sent from the central unit to the mobile unit. In this way, the central unit can be kepl: op to date as regards the approximate locations of all of the mobile units.Additionally, instead of the location signals being transmitted directly from the mobile urn its to the central unit, they may be relayed via fixed relay units or the fixed units mentioned above. In the latter case, iL may be unnecessary for the location signal transmitted from the mobile unit to the fixed unit to include the code of the fixed unit, provided that the central unit is able to determine from which fixed unit it is receiving a location signal.It will also be appreciated that, if the system described above is used with only one mobile unit, or if it is unnecessary to be able to distinguish one mobile unit from another, then the location signal need not include the code identifying the mobile unit. The fixed units may l)e anli-tamper protected arid include a rad C) transmitter so that if a fixer unit is tampered with it can send ari appropriat:e signal to the central unit. Although the central unit has been described above as a single unit, it will be appreciated that the receiver and transmitter may be near the area being ng monitored, whereas the remainder of the central unit may be at a r-ernote location.