WO2004086327A1

WO2004086327A1 - Swimming safety system

Info

Publication number: WO2004086327A1
Application number: PCT/GB2004/001327
Authority: WO
Inventors: Stephen Ralph Takel; Richard Douglas Orme
Original assignee: Qinetiq Limited
Priority date: 2003-03-27
Filing date: 2004-03-29
Publication date: 2004-10-07
Also published as: GB0307073D0; GB2399967A

Abstract

This invention relates to swimming safety systems. Existing systems either do not discriminate between normal and abnormal swimmer behaviour or require complicated devices to be worn by a user of the system. This invention provides an improved swimming safety system comprising a simple user worn RF tag (1) and a series of receiving aerials (3a, 3b, ...3n) located around the swimming area (11).

Description

SWIMMING SAFETY SYSTEM

This invention relates to swimming and specifically to safety systems capable of identifying persons in danger of drowning in pools or other water bodies.

Every year thousands of people world-wide are involved in drowning incidents. In the UK alone there is an average of 691 incidents per annum and drowning is the third largest cause of accidental death in the home for children under five years of age. A significant number of these incidents occur in swimming pools - both private and public.

Furthermore, a larger number of people are involved in non-fatal drowning incidents which result in permanent injury, e.g. brain damage.

A number of swimming safety systems exist which monitor people in swimming pools. For example, the "safety turtle" is a device that sounds an alarm when a child falls into water. It comprises a wristband that is worn by a child and a base station that sounds an alarm when the wristband contacts water. A drawback of this system is that the alarm is sounded as soon as water contacts the wristband. The system is not capable of monitoring a swimmer and sounding an alarm only when trouble is encountered.

A further system is described in US 6154140 which comprises a device which is worn by the swimmer which senses water pressure and transmits a signal when a pre-determined depth is passed. A neural network processes received signals and determines whether a swimmer is in trouble. This system involves the use of a sophisticated "intelligent" tag to be worn by the swimmer. The tag worn in this system only transmits once the wearer exceeds a certain depth. The system therefore relies on the correct functioning of the swimmer's tag to be able to identify when trouble is encountered. In the case of tag failure or mis-calibration the system will not detect the swimmer's tag and therefore will not be able to recognise a swimmer in difficulty.

It is therefore an object of the present invention to provide a swimming safety system which substantially mitigates the above' mentioned problems with prior art systems. Accordingly to a first aspect of the present invention there is now proposed a swimming safety system comprising

a transmitter arranged in use to transmit an identification signal,

a plurality of receiving aerials for receiving the identification signal from the transmitter,

and signal processing means for determining the location of the transmitter relative to the aerials,

wherein the signal processing means measures the timing of signals received at each aerial in order to determine the location of the transmitter.

The safety system according to the invention comprises a transmitter which is preferably housed in a substantially waterproof tag device worn by the swimmer. The transmitter sends an identification signal which is picked up by the receiving aerials which are located either above the pool or on the pool bottom.

By timing the received signal at each aerial a general location of the swimmer can be determined.

Preferably, the signal processing means further measures the strength of the signals received at each aerial in order to determine the location of the transmitter. The signal processing means may calculate transmitter depth by measuring the attenuation of the identification signal strength at each receiving aerial.

The received signal strength will depend on the attenuation encountered in the pool, and if the receiver aerials are mounted on the ceiling above the pool, or in the air above the pool. Because attenuation in water is much greater than in air the air phase can be neglected and the signal strength becomes a function of the water path length. As readings of the signal strength are made at several receiver aerial locations, unique determination of depth can be made.

The transmission power of the transmitter is preferably arranged such that, in use, the identification signal transmitted therefrom is measurably attenuated by passage through the water, whilst remaining receivable by a plurality of the receiver aerials. Preferably, the transmission power is arranged such that, in use, the identification signal is receivable by all of the receiver aerials within the system.

The invention has the advantages that it is capable of uniquely determining the depth and location of a swimmer at any time. The processing system can be programmed to monitor the movements of each user of the system and alert unusual motion via an alarm or other notification means.

A further advantage over the prior art is that the tag is not required to carry out any processing itself - it merely repeats an identification signal. No conditions have to be met/measured by the tag before it begins to transmit. All the required processing is done by the signal processing means and so the system is less prone to equipment malfunction.

Preferably the identification signal is short in duration and is transmitted repeatedly. If the signal is short compared to the time between successive transmissions then a number of tags can be operated simultaneously in the same pool.

Either a synchronous (time delay between successive transmissions is the same for each tag) or asynchronous (each tag transmits with different time delays) transmission scheme can be used for multiple tag systems.

Preferably the transmitter is multi-band and transmits the identification signal at at least two different frequencies. Signal attenuation is affected by the distance the signal travels through a medium and also the frequency of the signal. Given the output of the transmitter the path length through the medium in question (water in this case) can be determined by the measured signal strength. However, variations in the output signal strength from the transmitter, caused for example by poor battery condition, could result in erroneous depth measurements. The use of two or more frequencies enables the depth to be determined without a need to know the transmit signal strength. Signal propagation speed also varies with frequency when travelling through a conducting medium.

Alternative to measuring the strength of the signals received at each aerial, or in addition thereto, the signal processing means may measure the dispersion of the signals received at each aerial in order to determine the location of the transmitter. The time difference (dispersion) gives a measure of the path length through water and hence unique determination of transmitter depth can be made.

In a preferred embodiment, the system further comprises means for generating an alarm signal if the signal processing means indicates that the swimmer behaviour is not normal, for example if the swimmer remains submerged for an extended period of time and / or substantially stationary in the water.

According to second aspect of the present invention there s now proposed a receiver, having a plurality of aerials responsive to an identification signal transmitted from at least one transmitter, and comprising signal processing means adapted, in use, to measure the time of receipt of the identification signal at each aerial and to determine therefrom the location of the transmitter relative to the aerials.

Preferably, the signal processing means is further adapted, in use, to measure the strength of the identification signal received at each aerial and to determine therefrom the location of the transmitter relative to the aerials.

In a preferred embodiment, the aerials are responsive to an identification signal transmitted at a plurality of frequencies and the signal processing means is adapted, in use, to measure the dispersion of the identification signal received at each aerial and to determine therefrom the location of the transmitter relative to the aerials.

Advantageously, the receiver further comprises means for generating an alarm signal if the signal processing means indicates that the transmitter is at least one of located at a predefined position for a predefined period of time and substantially stationary for a predefined period of time.

According to a third aspect of the present invention, there is now proposed a method for monitoring the position of a swimmer comprising the steps of

(i) providing a transmitter capable of being worn by a swimmer and adapted in use to transmit an identification signal,

(ii) monitoring the transmitted identification signal using a plurality of aerials, and (iii) measuring the time of receipt of the identification signal at each aerial and determining therefrom the location of the transmitter relative to the aerials.

In a preferred embodiment, the method comprises the further steps of measuring the strength of the identification signal received at each aerial and determining therefrom the location of the transmitter relative to the aerials.

In another embodiment, the method comprises the further step of calculating transmitter depth by measuring the attenuation of the identification signal strength at each receiving aerial.

Advantageously, the aerials are responsive to an identification signal transmitted at a plurality of frequencies and the method comprises the further steps of measuring the dispersion of the identification signal received at each aerial and determining therefrom the location of the transmitter relative to the aerials.

Conveniently, the method further comprises the step of generating an alarm signal if the transmitter is at least one of located at a predefined position for a predefined period of time and substantially stationary for a predefined period of time.

Embodiments of the invention are described below by way of example only and in reference to the accompanying drawings in which:

Figure 1 shows a diagrammatic representation of a swimming pool and swimming safety system according to the invention,

Figure 2 shows a timing scheme for transmitting devices according to the present invention,

Figure 3 shows an alternative transmission timing scheme.

Turning to Figure 1 a swimming safety system according to the invention comprises a tag 1 and a series of aerials 3a, 3b...3n connected to a computer 5. The tag 1 contains an RF aerial 7 and a battery 9 arid in use is worn by a user in the swimming pool 11.

The receiving aerials 3 are shown mounted above the pool 11. Alternatively the aerials could be located at the bottom of the pool.

In use the tag repeatedly emits an identification signal. The transmission may only last of the order a few milliseconds and is repeated every second or so. Further tags may be used which transmit in the period between successive emissions of the identification signal thereby allowing simultaneous multiple use of the safety system.

Each of the receiving aerials 3 detect the timing and signal strength of the identification pulses. The location of a swimmer can generally be determined from these timings by the use of a look up table which is tailored individually to a specific swimming pool.

The signal strength of the identification signal at each of the aerials is also measured. This signal is attenuated as it passes through the water and the air to the receiving aerial. The water attenuation far outweighs the attenuation experienced in the air phase and so the reduction in signal strength gives an indication of the distance travelled through the water in the pool. The computer 11 can therefore determine the depth of the swimmer from an analysis of the signal strength at several of the receiver locations.

Signal attenuation and speed of propagation are affected by the frequency of the signal and so in order to combat incorrect depth measurements caused by poor battery condition on the tag 1 the tag transmits at at least two frequencies (e.g. two discrete frequencies may be used, alternatively the transmitter may be adapted to transmit a spectrum of frequencies or a frequency chirp).

Figure 2 shows an asynchronous timing scheme wherein a number of tags can be used simultaneously by different users. In this case each tag has a different time delay between successive transmissions of its identification signal.

Figure 3 shows a synchronous timing scheme. In this case the time delay is the same for each tag.

Claims

1. A swimming safety system comprising

a transmitter (1 ) arranged in use to transmit an identification signal, a plurality of receiving aerials (3a, 3b, ...3n) for receiving the identification signal from the transmitter (1), and signal processing means (5) for determining the location of the transmitter (1) relative to the aerials (3a, 3b, ...3n), wherein the signal processing means (5) measures the timing of the signal received at each aerial (3a, 3b, ...3n) in order to determine the location of the transmitter (1).

2. A swimming safety system as claimed in claim 1 wherein the signal processing means (5) further measures the strength of the signals received at each aerial (3a, 3b, ...3n) in order to determine the location of the transmitter (1 ).

3. A swimming safety system as claimed in claim 2 wherein the signal processing means (5) calculates transmitter depth by measuring the attenuation of the identification signal strength at each receiving aerial (3a, 3b, ...3n).

4. A swimming safety system as claimed in any of the preceding claims wherein the transmitter (1) is a multi-band transmitter.

5. A swimming safety system as claimed in claim 4 wherein the signal processing means (5) further measures the dispersion of the signals received at each aerial (3a, 3b, ...3n) in order to determine the location of the transmitter (1).

6. A swimming safety system as claimed in any of the preceding claims wherein the system further comprises means for generating an alarm signal if the signal processing means (5) indicates that the swimmer behaviour is not normal.

7. A receiver, having a plurality of aerials (3a, 3b, ...3n) responsive to an identification signal transmitted from at least one transmitter (1), comprising signal processing means (5) adapted, in use, to measure the time of receipt of the identification signal at each aerial (3a, 3b, ...3n) and to determine therefrom the location of the transmitter (1 ) relative to the aerials (3a, 3b, ...3n).

8. A receiver as claimed in claim 7 wherein the signal processing means (5) is further adapted, in use, to measure the strength of the identification signal received at each aerial (3a, 3b, ...3n) and to determine therefrom the location of the transmitter (1) relative to the aerials (3a, 3b, ...3n).

9. A receiver as claimed in claim 7 or 8 wherein the aerials (3a, 3b, ...3n) are responsive to an identification signal transmitted at a plurality of frequencies and wherein the signal processing means (5) is adapted, in use, to measure the dispersion of the identification signal received at each aerial (3a, 3b, ...3n) and to determine therefrom the location of the transmitter (1) relative to the aerials (3a, 3b, ...3n).

10. A receiver as claimed in any of claims 7 - 9 further comprising means for generating an alarm signal if the signal processing means (5) indicates that the transmitter is at least one of located at a predefined position for a predefined period of time and substantially stationary for a predefined period of time.

11. A method for monitoring the position of a swimmer comprising the steps of

(i) providing a transmitter (1) capable of being worn by a swimmer and adapted in use to transmit an identification signal,

(ii) monitoring the transmitted identification signal using a plurality of aerials (3a, 3b, ...3n),

(iii) measuring the time of receipt of the identification signal at each aerial (3a, 3b, ...3n) and determining therefrom the location of the transmitter (1 ) relative to the aerials (3a, 3b, ...3n).

12. A method as claimed in claim 11 comprising the further steps of measuring the strength of the identification signal received at each aerial (3a, 3b, ...3n) and determining therefrom the location of the transmitter (1) relative to the aerials (3a, 3b, ...3n).

13. A method as claimed in claim 12 comprising the further step of calculating transmitter depth by measuring the attenuation of the identification signal strength at each receiving aerial (3a, 3b, ...3n).

14. A method as claimed in any of claims 11 - 13 wherein the aerials (3a, 3b, ...3n) are responsive to an identification signal transmitted at a plurality of frequencies, the method comprising the further steps of measuring the dispersion of the identification signal received at each aerial (3a, 3b, ...3n) and determining therefrom the location of the transmitter (1) relative to the aerials (3a, 3b, ...3n).

15. A method as claimed in any of claims 11 - 14 further comprising the step of generating an alarm signal if the transmitter (1) is at least one of located at a predefined position for a predefined period of time and substantially stationary for a predefined period of time.