WO2003096482A1

WO2003096482A1 - Method and system for functional control of an active antenna

Info

Publication number: WO2003096482A1
Application number: PCT/SE2003/000727
Authority: WO
Inventors: Tony Westman
Original assignee: Tony Westman
Priority date: 2002-05-07
Filing date: 2003-05-06
Publication date: 2003-11-20
Also published as: AU2003230524A1; SE524607C2; SE0201385L; SE0201385D0; EP1506596A1

Abstract

The present invention discloses a system for a simultaneous surveillance of an active antenna including an RF amplifier, the device being a portion of a positioning system for instance for dedicated surveillance and tracking system anti-theft system forming a transponder system communicating with a main controller. Any break of a short-circuit in the active antenna or its feeder connecting the antenna, for instance, to a GPS receiver or corresponding localization device of the surveillance and tracking system is noticed and generates an interrupt to a system control. Such an interrupt generates for instance a SMS message being sent generally via built-in device for mobile telephone access to predefined address informing a main remote control unit that the performance of the active antenna/feeder cable of the surveillance and tracking system has degraded. Such a message tells that the localizing system no longer can deliver proper coordinate information and has to rely in other facilities of a main system. A secondary microprocessor (9) of a detector unit (5) using a sensing resistor (7) evaluates the voltage fed to the active antenna (1) of a positioning system. The detector unit may at any time be provided with new parameters regarding the voltage range to be accepted for a proper function of the guarded active antenna.

Description

Method and system for functional control of an active antenna

TECHNICAL FIELD The present invention relates to antennas, and more particularly to a method and a device for supervision and surveillance of the functioning of an external antenna.

BACKGROUND

Modern technologies offer many different methods of surveillance of for instance merchandize, transported goods or even vehicles. The general manner of such surveillance is that whenever the guarded item leaves a defined area an alarm will be triggered. In many cases it is also essential to be able, after such a triggered alarm to be able track the item in a way such that it may easily be recovered.

In our initial U.S. Patent No. 6,236,836 a transponder system is provided, which presents a portable or mobile system for localization of movable objects, e.g. for surveillance of valuable transports and the like. The system is controllable by a radio system and control information may be sent to the transponder for defining for instance the basic functions of a built-in marker transmitter used for localizing the moving object. Furthermore, the system may utilize different localization systems, for instance the well established GPS (Global Positioning System). GPS is able to with a high accuracy present the coordinates of such a transponder supplied with a GPS receiver, and coordinates obtained may be further transferred over a suitable network, e.g. a mobile telephone network like GSM, WDMA or similar systems for tracking purposes.

Such a system can be very efficient for tracking valuable merchandize like an expensive automobile, which will simply be able to carry such equipment well hidden. A stolen car may quickly be moved over large distances and will even in a short time be brought abroad. Therefore such a surveillance and tracking system for protection must be able to operate at least for an entire continent. To be able to communicate the equipment among other things will have to rely on an antenna device, which has to be mounted such that it is not electrically or magnetically shielded to be able to radiate and receive radio waves. Therefore such a communication antenna is the first object to be chosen for disconnection or destruction for preventing communication with the surveillance system. Just disconnecting power supply to the surveillance system, or the entire surveillance system itself, will simply effect the total function of for instance a vehicle making it immobile, besides such a system will generally also have an internal powering lasting for at least a limited period of time.

To further increase function of such a surveillance automatically tracking system there is a desire of a further functional system for preventing the communicating antenna of the surveillance system from being incapable of operating in a way which would prevent further tracking and surveillance of for instance a stolen vehicle.

SUMMARY The present invention solves the problem of a simultaneous surveillance of a passive reception antenna device being a portion of a dedicated surveillance and tracking system forming a transponder system communicating with a main unit. Any break or a short-circuit in the antenna itself or in a feeder connecting the active antenna, for instance, to a GPS receiver or corresponding device serving the surveillance and tracking system is noticed and generates an interrupt to the system controller of the system. This will occur whenever the efficiency of the passive reception antenna is seriously affected. This interrupt in turn generates a message over the Short Message Service (SMS), which is sent generally via a mobile telephone access to a predefined address informing a main remote controller unit that the performance of the GPS antenna/ feeder cable in the surveillance and tracking system has degraded. Such a message tells that the localizing system no longer can deliver proper coordinate information and the system may be provided with new parameters regarding the system function. SHORT DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, may best be understood by referring to the following detailed description taken together with the accompanying drawings, in which:

FIG. 1 illustrates a system for securing operation of active antenna according to the present invention; and

FIG. 2 illustrates in a flow diagram the method according to the present invention.

DETAILED DESCRIPTION

A surveillance and tracking system for protection of for instance an expensive vehicle or a suitcase for transport of money generally operates such that is utilizes a communication to a remote controller which can register different events occurring regarding the object. In a typical embodiment of such a system the remote controller can access the mobile autonomous system and control a number of defined parameters by transfer of a request over its communication line. The communication line includes in a typical case a mobile phone operating in a defined data mode. In a typical embodiment messages like SMS may be utilized. The mobile network may be any system utilizing for instance Time Division Multiple Access

(TDMA), Global System for Mobile Communication (GSM), Code Division Multiple Access 2000 (CDMA2000) or Wide Band Code Division Multiple

Access (WDCMA) or any corresponding mobile network.

An essential part of such a surveillance and tracking system (here also referred to as C-TRACK) will generally use an orientation system for instance the Global Positioning Satellite System (GPS) to obtain a positioning of the vehicle at any desired moment. Positioning information is also to some extent available by means of the mobile network used. However this orientation portion by satellite uses a passive receiver, which monitors a number of navigation satellites above horizon at any given instant. The number of observable satellites should be at least three, but will at most places around the earth be of the order 6 to 10 out of the available 24 satellites forming the GPS positioning system. From the signals received from the satellite system this very compact receiver system will be able calculate its present position with accuracy at present down to the order of meters. This information is passed to the surveillance and tracking system, for instance a C-TRACK, which then simply can decide any motion of the object under surveillance. The information will further be transferred to a controller, which then will decide from give parameters if it is a motion permitted or an unauthorized motion of the object.

It should also be noted that in a case when the surveillance and tracking system no longer will be able to communicate with any base station in the utilized communication system this will result in other defined actions of the system for announcing the faulty situation. Typically such a system will start acting as a beacon which may be localized by a dedicated direction finding system. Such situations are more easily handled by the systems according to the state of the art, as that part of the system forms an active system, while the GPS monitoring portion is a passive receiving system. A situation when the GPS receiver no longer can receive localization information can only be sensed by the surveillance system itself, but can be the result of several causes, some natural but also some deliberate.

In the general case the GPS receiver in order to increase its sensitivity will need to use an antenna separated form the receiver, which may be integrated in the hidden surveillance and tracking system. Such an antenna unit is often made as an active device, in other words it also contains a built- in amplifier for the GPS operation frequency band. However the system should be able to judge if absence of signal reception is due to technical reasons, for instance that the antenna has been removed or there is a short- circuit in the feeding cable or the amplifier is no longer operating and hence drawing current from its supply. In other cases reception of GPS signals may cease due to that the carrier of the surveillance and tracking system is temporally shielded from the satellites. However such situations may also clearly be recognized by the main system and its communication links.

In an illustrative embodiment of the system according to the present invention the GPS receiver of the surveillance and tracking system 15 utilizes a compact active antenna 1 connected via a coaxial cable 2 from the active receiver antenna via a sensing resistor 7 to a GPS receiver input terminal 20. The amplifier 3 of the active antenna is also DC supplied by for instance 3 volts fed over the inner conductor of the coaxial cable 2. In series with this coaxial cable, generally close to the GPS receiver a detection unit 5 is positioned for detecting a break-up or a short-circuit in the feeding of supply voltage to the active antenna 1. Thus the antenna functional control operates using only one resistor and a simple microprocessor incorporating a A/D converter.

In the illustrative embodiment the detection unit 5 comprises a sensing resistor 7 of low resistance and high tolerance in series with the inner conductor of the coaxial cable 2. A secondary microprocessor 9 having for instance analog/ digital converter inputs 10 and 12 is cooperating with the sensing resistor 7. In a preferred embodiment of the detector unit the microprocessor is a small RISC processor of type 16LF87X from Microchip Corporation. However any low current microprocessor in combination with a suitable low power A/D converter could be used to achieve the desired function. The microprocessor 9 of the embodiment contains itself two A/D input terminals and takes its power directly from the 3 volts supply VDD for the active antenna from a main unit 15 (in this case a C-TRACK). A reference voltage (V_I ) input of the microprocessor is also obtained from the 3 volts supply and fed to the A/D converter input 10 of the secondary microprocessor. The A/D converter input 12 measures voltage level after the sensing resistor. A break-up of the supply of power or an amplifier no longer taking any current is indicated by NR_ef being close or equal to the voltage measured at the A/D converter input 12. The microprocessor 9 then generates an active low pulse on its I/O-line 16 to the interrupt system of a primary CPU of the surveillance and tracking system in the main unit 15. To separate the feed of RF from the antenna to the receiver and the DC voltage supply typically small RF-chokes 4 are inserted in the supply of DC voltage to the amplifier and the microprocessor 9 not to load the RF output of the active antenna.

A short-circuit will similarly be detected by the secondary microprocessor 9 in that the voltage drop over the sensing resistor becomes too high. The resistance of the sensing resistor 7 is adapted such that in spite of a direct short-circuit the total current drawn still must allow a sufficient voltage supply to still be feeding the microprocessor 9, which also in this case then generates an active low pulse transferred to the surveillance and tracking system. It is at any time possible to set voltage levels/ limits, which are deciding if an interrupt should be triggered for indicating a break or short in the supply of power to the amplifier of the active antenna 1.

An interrupt to the microprocessor 9 may also be generated from the CPU of the surveillance and tracking system, which then will be able to start up a communication protocol via the I/O port 16 whereby for instance voltage levels may be set in the microprocessor 9 programming, or read from the microprocessor of the detection unit 5. Furthermore this means that programming of the microprocessor 9 may even be performed from the remote controller via the main unit 15.

The processor 9 of the detector unit 5 is generally always in a state for a continuous measurement of the voltage VAMP fed to the amplifier 3 of the antenna unit 1. This voltage VAMP is sensed by the analog- to-digital input 12 of the processor 9, which is this state always has its I/O-line 16 set as an input from the main processor. The interrupt system of the processor 9 is active and an active low pulse in to IRQ-line 14 from the main processor makes the processor interrupt the measurement of the voltage VAMP and start a communication protocol with the main processor of the C-TRACK. After ending the communication protocol the processor 9 resumes monitoring

VAMP.

A change of the voltage VAMP due to a change of current through resistor 7 will be detected. A short in the feeding of voltage to the amplifier 3 results in a too low VAMP measured and a disconnection of amplifier 3 results in a measurement where VAMP is equal to VDD. In the processor 9 threshold values are set for defining a permitted range of variation of V_AMP. If a voltage out of this permitted voltage range is detected the interrupt system of the processor 9 is deactivated and the I/O-line 16 is set to output, and an active low pulse on the I/O-line to alert the main processor of the C-TRACK. The I/O-line of the C-TRACK is always set as input in the normal state. After being alerted the main processor can request measured value from the processor 9 if desired. An interrupt from the processor 9 will immediately result in a message generated to the remote controller over any of communication possibilities of the surveillance and tracking system C- TRACK.

Thus, any attempt to disturb the reception of GPS signals by shorting or disconnecting the active antenna will result in defined actions performed by the surveillance and tracking system. This will add an important factor in the protection of for instance a vehicle or a suitcase equipped with this surveillance and protection device.

The surveillance and tracking system can in turn control the possibility to move for instance a protected vehicle by its own engine by not permitting a start-up of its engine. Still moving it by means of other vehicles will also be noted and reported. This is also applicable to any object provided with the autonomous system surveillance and tracking system. If the object is moved unauthorized, it will be possible to detect and track this motion at once and the autonomous surveillance and tracking system will continue for at least a limited time to operate even if the battery of a guarded vehicle should deliberately be disconnected, but which event will also immediately be reported by its communication system. A detection of a change in current consumption of the amplifier 3 which comes above or below a defined threshold defined by the processor 9 will immediately result in a message being sent. It is important that such a message is generated instantaneously as this may indicate an ongoing theft, which tries to sabotage the GPS reception and thereby the continuous tracking of the object.

In a second embodiment of the present invention the detector unit will be an integrated part of a satellite positioning receiver, for instance a GPS receiver system. In this embodiment the controlling microprocessor system of the positioning receiver will by means of A/D converters also control the voltage drop over a sensing resistor in series with an antenna jack for an external active antenna provided with an RF pre-amplifier, to be used for improving signal quality from the navigational satellite system utilized.

In a further' embodiment of the active antenna guarding system a small capacitance may easily be connected parallel to the sensing resistor in order not to unnecessary lower the RF signal from the active antenna fed to the receiver portion.

It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.

Claims

1. A system for functional control of an active antenna unit of a receiver arrangement, characterized in a primary microprocessor controlled positioning and tracking anti- theft system (15), an active antenna unit utilizing an RF amplifier (3) powered by a detector unit (5) and operating via a connecting cable as a separated arrangement for reception of radio frequency signals, the detector unit (5) including a sensing resistor (7) and a secondary microprocessor (9) for communicating with the primary microprocessor controlled positioning and tracking anti-theft unit, the secondary microprocessor unit providing at least one input for measurement of a voltage drop over the sensing resistor (7) connected in series with the connecting cable supplying driving voltage to the RF amplifier of the active antenna.

2. The system according to claim 1, characterized in that the secondary microprocessor (9) is powered by the same voltage supply as the RF amplifier (3), the voltage supply to the secondary microprocessor also serving as a reference for the measurement of the voltage drop over the sensing resistor (7).

3. The system according to claim 2, characterized in that the voltage drop over the sensing resistor (7) is evaluated by the secondary microprocessor (9) to be within a specified range, and whenever the voltage drop over the sensing resistor (7) falls outside the specified range an interrupt will be generated by the secondary microprocessor (9) to the primary microprocessor controlled positioning and tracking anti-theft system (15) for indicating a situation of no possible reception of positioning information by the active antenna (1).

4. The system according to claim 3, characterized in that the active antenna (1) containing the RF amplifier (3) is tuned for receiving simultaneous satellite positioning signals from a number of positioning satellites positioned over the horizon.

5. The system according to claim 3, characterized in that the secondary microprocessor is a low power processor offering at least one input/ output terminal and one interrupt terminal for communication with the primary microprocessor controlled positioning and tracking anti-theft system the primary microprocessor controlling further communication, positioning and direction finding facilities.

6. The system according to claim 3, characterized in that the secondary microprocessor (9) is programmable over a single I/O-line (16).

7. A method for functional control of an external active antenna unit of a satellite receiving positioning arrangement, characterized by the steps of utilizing for the external active antenna an RF amplifier powered by a voltage supplied via a connecting cable to the external active antenna for amplification of received of radio frequency signals; measuring a voltage drop over a sensing resistor (7) inserted in series with the connecting cable supplying power to the active antenna in order to monitor a current consumption via the connecting cable in order to detect changes resulting, for instance, from a broken or a shorted connecting cable.

8. The method according to claim 7, characterized by the further step of using as measuring step a microprocessor including an A/D converter for evaluation of the voltage drop over the sensing resistor (7).

9. The method according to claim 8, characterized by the further step of defining for the microprocessor a lower and an upper value for the voltage drop over the sensing resistor (7) to be accepted.