GB2318671A - Radiotelephone proximity detector - Google Patents

Abstract

A radiotelephone proximity detector comprises of a telephone proximity unit 16 associated with a mobile telephone and a belt clip proximity unit 46 associated with a user, both containing transceivers 74, 54 respectively. Transmitter 76 produces a master signal S2 to be received and demodulated by a receiver 58 which communicates the strength of the signal to a controller 52. If the receiver does not receive a signal within a predetermined time interval or the magnitude of the signal received is less than a given value, an alarm is actuated indicating that the two units are separated by more than an acceptable distance, and normal operation of the telephone becomes inhibited. If an appropriate signal is received, the slave unit responds by sending a response signal S1 which is received and analysed in similar fashion by receiver 78. Both units can be coupled via contacts 62, 82 which places the units in a standby mode.

Description

RADIOTELEPHONE PROXIMITY DETECTOR The present invention relates to a radiotelephone proximity detector.

It is known that portable radiotelephones by virtue of their mobility are easily misplaced, abandoned or stolen. The present invention aims generally to tackle these problems.

With this in mind, the present invention provides a radiotelephone proximity detector comprising a first proximity unit associated with a radiotelephone and including a first transceiver and a second proximity unit associated with a user and including a second transceiver, wherein the first and second transceivers can provide a two-way communication link therebetween and the units include analysis means for analysing the output of the receiver in the first or second transceivers to estimate the proximity of the first and second proximity units.

The present invention provides a proximity detector having an architecture which is able to respond as required at either end of the link, if the estimated proximity of the two proximity units fall outside acceptable limits when viewed from the perspective of either of the first or second proximity units. In this way, the proximity detector of the present invention provides a platform which supports a wide variety of possible operational modes for the detector and hence provides flexibility to the user.

For example, in one embodiment the second proximity unit estimates the proximity of the first and second proximity units by comparing the received signal strength of a proximity signal transmitted by the first proximity unit with a threshold. If this received signal strength falls below the threshold, then the second proximity unit estimates that the first proximity unit is too far away from the second proximity unit and causes an alarm to be sounded. Similarly, the first proximity unit estimates the proximity of the first and second proximity units by comparing the received signal strength of a proximity signal transmitted by the second proximity unit with a threshold, which need not be the same as the threshold in the second proximity unit. If this received signal strength falls below the threshold, then the first proximity unit estimates that the second proximity unit is too far away. In response to this estimation, the first proximity unit may cause an alarm to be sounded, but it need not. Instead, or additionally, the first proximity unit may cause the radiotelephone to change into an operating mode in which its normal use is prevented. For example, in one such mode, the radiotelephone may require that a correct personal identification or so-called PIN number is entered before any further use can be made of the phone. In another such mode, the call placing capability of the radiotelephone may be inhibited but other functions such as the capability to receive a call may be available.

In accordance with the invention, similar flexibility of response can be provided in the second proximity unit.

This flexibility is not possible in a proximity detector in which a one way communication link is established between two proximity units (one associated with the user and one associated with the radiotelephone) as by definition the transmitting unit will never receive a return signal from the other receiving unit confirming the presence of the receiving unit. The receiving unit must sound an alarm and the transmitting unit does not 'know' when to take action.

In other embodiments, the proximity of the first and second proximity units is estimated by the time taken for the proximity signals to travel between the first and second proximity units. Preferably, the first proximity unit is located within the casing of the radiotelephone and is powered by the battery of the radiotelephone. The first transceiver is preferably dedicated to the task of providing the two-way communication link. In other embodiments, the main transceiver of the radiotelephone which transmits and receives signals to and from the cellular network can perform the role of the first transceiver of the first proximity unit in providing the two-way communication link. Preferably, the second proximity unit is associated with the user by being integrated with means which are ordinarily worn or carried by the user, for example, a belt clip assembly, a hearing aid, a brief case or a case for carrying the radiotelephone.

The communication link is preferably established using radio wave transmission, but other techniques such as ultrasonic wave transmission can also be used.

Exemplary embodiments of the invention are hereinafter described with reference to the accompanying drawings, in which: Figure 1 is a perspective of a cellular mobile telephone; Figure 2 is a schematic diagram of the main features in the telephone of Figure 1; Figure 3 is a side view of the telephone of Figure 1 together with a belt clip assembly; Figure 4 is a front view of the body of the belt clip assembly of Figure 3 attached to a belt; Figure 5 is a perspective view of the clip member of the belt clip assembly of Figure 3 in isolation; Figure 6 is a schematic showing the interaction between the proximity unit of the belt clip assembly and the telephone; Figure 7 is a flow diagram showing the operation of the proximity units in the separated or away position; Figures 8(a) and 8(b) show diagrams of the control field set up by the telephone proximity unit; and Figures 9(a) and 9(b) show diagrams of the control field set up by the belt clip assembly proximity unit.

The telephone apparatus shown in Figure 1 is a cellular mobile telephone having an A or front cover 3a and a B or rear cover 3b powered by a rechargeable battery pack 2. The telephone 1 includes a transceiver 9 for transmitting and receiving signals to and from the cellular network and all the other features conventionally found in a cellular telephone, as shown schematically in Figure 2. Since these aspects of the telephone are not directly relevant to the instant invention no further details will be given here, except to say that a microprocessor 4 (see Figure 2) is employed to control all the basic functions of the telephone 1 and to control the keypad, display functions and a tone generator 12. Additionally, a memory 14 is provided for storing third party subscriber telephone records. The user-interface of telephone 1 comprises a display, e.g. a liquid crystal display 5 and a keypad 6 on the front of the telephone 1. The display is coupled to and regulated by the microprocessor 4.

The keypad 6 essentially comprises two main sets of keys, namely alphanumeric keys 6a associated with alphanumeric data especially for dialling telephone numbers, but also for entering alphanumeric data into the telephone number store 14; and a set of function keys 6b for enabling various predetermined functions or operations.

The telephone also includes a microphone 7, a loudspeaker 8, and a proximity unit 1 6 which will be described in greater detail later.

The mobile telephone is equipped with a belt clip assembly 20 which enables a user to attach the telephone 1 to his belt for convenient transportation when the telephone is not in use. The belt clip assembly 20 is in its mechanical aspects largely known in the art. Full details of its mechanical construction can be found in EP-A1-683587, but for the sake of completeness the following brief description is included.

The belt clip assembly 20 comprises a clip member 22 as shown in Figure 5.

The clip member 22 removably snap-fits onto the rear of the telephone casing.

The clip member 22 includes a planar member 24 having bent ends which serve as arms 25 to removably grasp in a snap-fit manner the telephone casing as shown in Figure 3. A first fastening element 26 upstands from the planar member 24. The belt clip assembly 20 further comprises a body portion 28 which attaches to a belt 30 of a user. The body portion 28 comprises a back member 32 from which rearwardly projects a j-shaped member 34 and a protrusion 36. The j-shaped member 34 and the protrusion 36 define a channel 38 as shown in Figure 3 within which the belt 30 can be slid and retained.

Guide flanges 40 project forwardly from the back member 32 and define a region 41 into which the first fastening element 26 of the clip member 22 can be slid. A second fastening element 42 projects forwardly into the region 41 and can co-operate with the first fastening element 26 to secure the clip member 22 and hence the telephone in place.

The belt clip assembly 20 further comprises a proximity unit 46 mounted to the rear of the back member 32.

The telephone proximity unit 16 and the belt clip assembly proximity unit 46 are shown in Figure 6.

The belt clip assembly proximity unit 46 is powered by a low power supply 50 including a replaceable battery. The proximity unit 46 also comprises a controller 52 which controls the operation of a transceiver 54. The controller 52 can be implemented as dedicated combinational logic or as a microprocessor. The transceiver 54 comprises a transmitter 56 and a receiver 58 for transmitting and receiving a lower power ultra high frequency (UHF) signals to and from the telephone proximity unit 16, respectively. The transceiver 54, under control of the controller 52, can be switched into a reduced power mode in which the transmitter 56 is non-operational. The controller 52 also controls a loudspeaker 57, the output volume of which is controllable by the user via a potentiometer 59. A slideable control member of the potentiometer 59 is denoted in Figure 3 by reference numeral 59a. The controller 52 is also responsive to the state of a depressable key 60.

The telephone proximity unit 1 6 is powered by the battery 2 of the telephone.

The proximity unit 1 6 also comprises a controller 72 which controls the operation of a transceiver 74. The controller 72 can be implemented as dedicated combinational logic or as a microprocessor. The transceiver 74 comprises a transmitter 76 and a receiver 78 for transmitting and receiving lower power ultra high frequency (UHF) signals to and from the proximity unit 46, respectively. The transceiver 74, under the control of the controller 72, can be switched into a reduced power mode in which the transmitter 76 is nonoperational. The controller 72 is controlled by the microprocessor 4 of the telephone 1.

The belt clip proximity unit 46 further comprises detection circuitry 61 having a detecting contact 62. The detecting contact 62 is located, as can be seen in Figure 4, in the second fastening element 42. The telephone proximity unit 16 further comprises detection circuitry 81 having a detecting contact 82. The detecting contact 82 projects through the rear casing or cover 3b so as to be located, as can be seen in Figure 3, in the first fastening element 26. When the telephone 1 is mounted to the belt clip assembly 20 in a so-called 'home position', the detecting contacts 62, 82 electrically contact each other. The presence of the telephone 1 is thereby electrically signalled to the detection circuitry 61 and hence the controller 52, and the presence of the belt clip assembly is likewise electrically signalled to the controller 72.

As can be seen in Figure 6, the transmitter 56 is operable to transmit a signal S1 comprising a carrier signal at a frequency F1 having identification coding C1, indicating the belt clip proximity unit 46 as the origin of the signal, modulated into it. The receiver 78 is operable to receive and demodulate the identification coding from the signal S1 and communicates this and also the power or strength of the received signal to the controller 72. Similarly, the transmitter 76 is operable to transmit a signal S2 comprising a carrier signal at frequency F2 having identification coding C2, indicating the telephone proximity unit 16 as the origin of the signal, modulated into it. The receiver 58 is operable to receive and demodulate the identification coding from the signal S2 and communicates this and also the power or strength of the received signal to the controller 52. The belt clip proximity unit 46 and the telephone proximity unit 16 are a 'matched pair' in that the belt clip proximity unit 46 is preprogrammed to recognise the identification coding C2 of the telephone proximity unit 1 6 and vice versa.

In operation, when the telephone 1 is in its home position, this is detected, as a result of the electrical contact between detecting contacts 62, 82, by the detection circuitries 61, 81 which place the proximity units 16, 46 into a sleep or standby mode. In the sleep mode, only the detection circuitries 61, 81 consume energy, albeit a very small amount the rest of the units 16, 46 being switched off. When the telephone is removed from the belt clip proximity unit 46 it is in a so-called 'away position' in which there is no electrical contact between the detecting contacts 62, 82. The absence of electrical contact between the detecting contacts 62, 82 triggers the detection circuitries 61, 81 which switch on the proximity units 46, 16.

In the away position, the proximity units 16, 46 switch on and operate as shown in the flow diagram of Figure 7. The telephone proximity units 16 acts as master and the belt clip proximity unit 46 acts as slave. Referring first to the operation of the telephone proximity unit 16, its transmitter 76 transmits master proximity signal S2 at step 102. After this transmission, the transmitter is switched into reduced power mode at step 104. Next, at step 106, its receiver 78 waits to receive the slave acknowledgement proximity signal S1 from the 'matched' belt clip proximity unit 46. If no signal is received within a predetermined interval, say T, or within this interval a signal is received but the identification coding does not match or equal C1, step 108 is executed by which an alarm is sounded for a brief interval. Similarly, should the correct signal S1 bearing the correct identification coding be received but the received signal strength is of a magnitude less than a first threshold because the belt clip assembly proximity unit 46 is too far away, then step 108 is again executed.

Figure 8(a) shows this situation with the boundary B, indicating the region where the received signal strength of S1 equals the first threshold. The region within the boundary B1 is referred to as the telephone control field TCF. In all the above circumstances, the telephone proximity unit 1 6 sounds the alarm at step 108 as a result of having failed to receive an acceptable acknowledgement to the proximity signal S2 transmitted in step 102. At step 108, the alarm is sounded at the main loudspeaker 8 of the telephone by the microprocessor 4 via the tone generator 1 2 under the instruction of the controller 72. The out-ofrange alarm sound is selected to be very distinct from any of the ringing tones with which the telephone may be ordinarily provided. After the alarm has been sounded for a brief interval at step 108, the controller 72 of the radiotelephone proximity unit 16, at step 109, sends instructions to the microprocessor 4 which switches the telephone from its normal mode into a mode in which it waits to have a PIN number entered and all other functions of the telephone, such as the capability to receive or place a call, are unavailable to the user. At step 111, the controller 72 waits to receive instructions from the microprocessor 4 which indicate that the correct PIN number has been entered.

Once the correct PIN number has been entered the alarm can be re-enabled via a menu option on the telephone to operate from step 11 2. On the other hand, the telephone proximity unit 1 6 can be reset into sleep mode by returning it to the home position in which it is mounted on the belt clip assembly 20.

However, should, within interval T, a signal bearing the correct identification coding C1 and within a greater than predetermined magnitude be received, then the telephone proximity unit 1 6 presumes that the belt clip proximity unit 46 is within range, i.e. within the telephone control field TCF as shown in Figure 8(b), and a delay is executed at step 110. After the delay, the transmitter 76 is switched back into full power mode at step 112 and proceeds step 102 to repeat the above steps.

Meanwhile, after the belt clip proximity unit 46 is switched on, the transmitter 56 is placed into reduced power mode at step 122. Next at step 124, its receiver 58 waits to receive the master proximity signal S2 from the 'matched' telephone proximity unit. If no signal is received within a predetermined interval, say again T, or within this interval a signal is received but the identification coding does not match or equal C2, step 1 26 is performed by which an alarm is sounded for a brief interval. Similarly, should the correct signal S2 bearing the correct identification coding be received but the signal is magnitude less than a second threshold because the telephone proximity unit 1 6 is too far away, then step 1 26 is executed. Figure 9(a) shows this situation with the boundary B2 indicating the region where the signal strength of S2 equals the second threshold. The region within the boundary B2 is referred to as the belt clip control field BCCF. In all the above circumstances, the belt clip proximity unit 46 as a result of having failed to properly receive the master proximity signal S2, sounds an alarm for a brief interval (step 126) via the loudspeaker 57 accordingly and enters the sleep mode at step 127. The operation of the belt clip proximity unit 46 can be resumed at step 122 by pressing the switch 60. However, should, within interval T, a signal bearing the correct identification coding C2 and with a greater than predetermined magnitude be received, then the belt clip proximity unit 46 presumes that the telephone proximity unit 1 6 is within range, i.e. within the belt clip control field BCCF as shown in Figure 9(b), and the transmitter 56 is switched into full power mode at step 1 28. Next, at step 130, the transmitter 56 transmits the slave acknowledgement signal S1 and proceeds to step 1 22 to repeat the above steps.

If at any time during operation in the away position as described in relation to Figure 7, the proximity units 16, 46 are returned to the home position, this is detected by the detection circuitries 61, 81 and the proximity units 16, 46 return to the sleep mode.

As a variant to the described method of operation, the proximity units 16, 46 can, at steps 106, 124, defer taking action in response to having failed to receive a valid proximity signal or a proximity signal of acceptable signal strength for a predetermined number of executions of the respective steps.

This will assist in preventing false alarms caused by spurious and transient events in the environment. As a refinement of this approach when the telephone proximity unit 1 6 is receiving a valid proximity signal S1 but the signal strength is repeatedly below the first threshold, the telephone proximity unit 1 6 can monitor the trend in the received signal strength and this trend can be used to govern the action which is taken, should that be necessary (i.e. after the predetermined number of executions of step 106). For example, if after the predetermined numbers of executions of step 106, the controller 72 determines that the telephone and belt clip proximity units 16, 46 are moving apart very rapidly, then the telephone can be completely disabled as described above. On the other hand, if the telephone and belt clip proximity units 16, 46 are not moving apart rapidly or are stationary, then only an alarm need be sounded.

It will be appreciated that the size of the telephone control field TCF is determined by the transmitting power of the transmitter 56 of the belt clip assembly proximity unit 46 and the first threshold. Likewise, the size of belt clip control field BCCF is determined by the power of the transmitter 76 of the telephone proximity unit 16 and the second threshold. The size of the control fields TCF and BCCF are selected such that when the user makes use of the telephone 1 in the normal way, the telephone 1 remains within the control fields. A typical suitable size for the control fields TCF and BCCF is 2-3 metres.

The controller 52 is also responsive to the remaining charge available from the power supply 50 and, when the remaining charge is below a predetermined threshold, the controller 50 sounds a brief alarm, from time to time, via the loudspeaker 58 to indicate this. The alarm which is signalled in these circumstances is distinct from the out-of-range alarm mentioned above.

In other embodiments of the invention, the telephone proximity unit 16 need not act as the master, but can perform the role of the slave. In other embodiments, either one of the proximity units can act as a 'passive relay' for the proximity signal transmitted by the other proximity unit. The passive relay can comprise a simple resonance circuit and an antenna, and is operable to reflect the proximity signal, modified by the characteristics of the resonance circuit, back to the other proximity unit.

When it is stated in the described embodiments that the telephone 1 sounds an alarm because the telephone and belt clip proximity units 16, 46 are outside acceptable range of each other, in other embodiments, this audio alarm can be accompanied or replaced by other forms of alarm. Other forms of alarm include a visual alarm displayed on the display 5. The visual alarm comprises an indication, based on text or an icon/symbol, that the out-of-range condition exists, and/or the name of the authorised user of the telephone 1. The display of the name of the authorised user can be useful in ensuring that a similar telephone belonging to a third party is not mistakenly picked up. Another alarm takes the form of the telephone automatically sending a message to a predetermined number.

Claims (8)

1. A radio telephone proximity detector, comprising: a first proximity unit associated with a radiotelephone and including a first transceiver; and a second proximity unit associated with a user and including a second transceiver; wherein the first and second transceivers can provide a two-way communication link therebetween and the units include analysis means for analysing the output of the receiver in the first or second transceivers to estimate the proximity of the first and second proximity units.

2. A detector as in Claim 1, wherein the analysis means comprises a first analysis unit for analysing the output of the receiver of the first proximity unit to estimate the proximity of the first and second proximity units.

3. A detector as in Claims 1 or 2, wherein the analysis means comprises a second analysis unit for analysing the output of the receiver of the second proximity unit to estimate the proximity of the first and second proximity units.

4. A detector as in Claims 2 or 3, wherein a said proximity unit is responsive to the estimated proximity of the first and second proximity units exceeding a threshold to cause an alarm to be sounded.

5. A detector as in Claims 2 to 4, wherein the first proximity unit is responsive to the estimated proximity of the first and second proximity units exceeding a first threshold to cause the radiotelephone to change into an operating mode in which its normal use is prevented.

6. A detector as in any preceding claim, wherein the second proximity unit is associated with the user by being mounted in a belt clip assembly, which the user can wear.

7. A detector as in any of Claims 2 to 6, wherein a said transceiver includes a reduced power mode in which its transmitter is deactivated.

8. A proximity detector constructed, arranged and adapted to operate substantially as hereindescribed with reference to the accompanying drawings.