WO2007054724A2

WO2007054724A2 - Location information system

Info

Publication number: WO2007054724A2
Application number: PCT/GB2006/004223
Authority: WO
Inventors: Kevin Lamacraft; Robert Gerwyn Lloyd; Paul Victor Brennan; Stuart Robson; Georges François GYORY
Original assignee: Innovision Research & Technology Plc; University College London
Priority date: 2005-11-11
Filing date: 2006-11-13
Publication date: 2007-05-18
Also published as: GB0523025D0; WO2007054724A3

Abstract

There is described a receiver, comprising: a radio -frequency receiver including frequency converter circuitry, and a frequency estimator configured to analyse a radio -frequency signal received by said radio frequency receiver to provide an estimated value for the carrier frequency of said received signal, and provide said estimated value to said frequency converter circuitry. The frequency converter circuitry is operative in dependence on said estimated value to convert said received signal to a predetermined frequency.

Description

LOCATION INFORMATION SYSTEM

Field

Location information system utilising radio- frequency (RF) signalling.

Background

It is always important that an airport runs as smoothly as possible and is as secure as possible. Early identification of any potential delays to flights or security threats is essential to minimise ongoing impact on flights and costs.

One of the factors which can affect operational efficiency of the airport is the location of passengers . Information on passengers can be used to ascertain where a passenger is within the airport, identify the location of late passengers, provide additional information as to passenger flow through the airport and potentially identify any security threats, such as passengers entering restricted areas. Location information on specific passengers may also be of potential use to the police or other public authorities .

Systems exist for radio frequency tagging of individuals, for example radio-tagging of prisoners has been proposed. Such systems tend to be closed systems and use alarms or warning systems to detect unwanted movement of such tagged individuals. Systems also exist for identifying individuals through the use of camera or other visual technologies, the amount of information obtainable depends on the use of the camera technology, orientation and positioning of such technology and the resolution achievable .

Similar concerns may also apply to other environments in which there is a requirement to track individuals or to obtain location information or individual flow information.

Summary

In one aspect the present invention provides for an RF apparatus comprising

At least one RF receiving means in the form of an antenna;

At least one RF signal strength detection means for detecting the strength or relative strength of a received RF signal;

Preamble identification means for detecting whether an incoming RF signal is from a valid RF transmitter;

Demodulation means for demodulating a received modulated RF signal; Characterised in that the RF apparatus has means for identifying and/or detecting the frequency of a received RF signal during receipt of the preamble.

In a preferred embodiment such RF apparatus comprises multiple RF receiving means and each antenna forms part of a multiple antenna array. In a further preferred embodiment such antenna array comprises four antennas .

In a second aspect the present invention provides for an RF apparatus comprising at least one RF receiver and at least one RF transmitter wherein: the at least one RF receiver comprises: receiving means in the form of an antenna; at least one RF signal strength detection means for detecting the strength or relative strength of a received RF signal ; preamble identification means for detecting whether an incoming RF signal is from a valid RF transmitter; demodulation means for demodulating a received modulated RF signal; and the at least one RF transmitter comprises, transmitting means for transmitting an RF signal which encodes a preamble identification means, a data store and control means operable to control transmission of the RF signal at random time intervals characterised in that the RF apparatus has means for identifying and/or detecting the frequency of a received RF signal during receipt of the said preamble identification means. In a preferred embodiment the RF transmitter is operable to transmit RF signals only. In an alternative embodiment the RF transmitter may be operable to receive RF signals and respond to such RF signals, for example by writing data into its data store or by transmitting a reply. In a further preferred embodiment the RF transmitter comprises a low cost oscillator resulting in frequency diversity in the transmitted RF signal.

In a third aspect the present invention provides for an information system for use in an airport environment comprising:

An RF transmitter, wherein such RF transmitter is operable to transmit a unique identifier and a preamble identification means,- An RF receiver, operable to receive an RF signal from said RF transmitter, to ascertain the signal strength or relative signal strength of the received RF signal, to ascertain the carrier frequency of the received RF signal during receipt of the preamble identification means and to demodulate said received RF signal to obtain the unique^' identifier, An antenna array, each antenna being connected to an RF receiver,-

At least one base station comprising at least one camera; and At least one control station for controlling the operation of the information system and for providing location data and/or visual data to a user;

In a preferred embodiment the camera or lens provides a field of view of up to 360 degrees. In one embodiment multiple cameras will be provided within the same base station. In a preferred embodiment the RF receiver will additionally be comprised within the base station.

In a fourth aspect of the invention an information system for use in an airport environment is provided comprising

An RF transmitter, wherein such RF transmitter is operable to transmit a unique identifier and a preamble identification means ;

An RF receiver, operable to receive an RF signal from said RF transmitter, to ascertain the signal strength or relative signal strength of the received RF signal, to ascertain the carrier frequency of the received RF signal during receipt of the preamble identification means and to demodulate said received RF signal to obtain the unique identifier,

An antenna array, each antenna being connected to an RF receiver; At least one base station comprising at least one camera;

At least one control station for controlling the operation of the information system and for providing location data and/or visual data to a user; and An initialisation unit operable to receive a unique identifier from the RF transmitter and to supply such a unique identifier to the control station and/or to program a unique identifier into the RF transmitter.

In a preferred embodiment such unique identifier is coupled with passenger specific information in the control station enabling users to identify and/or access a particular passenger location.

In a fifth aspect of the invention the RF receiver described in the above aspects may also additionally comprise RF transceiver functionality for interaction with other RF based systems within the airport or other system environment. For example such RF transceiver could be used to program or interact with RF transponders . In a sixth aspect of the invention there is provided a receiver, comprising: a radio-frequency receiver including frequency converter circuitry; a frequency estimator configured to analyse a radio- frequency signal received by said radio frequency receiver to provide an estimated value for the carrier frequency of said received signal, and provide said estimated value to said frequency converter circuitry; and wherein said frequency converter circuitry is operative in dependence on said estimated value to convert said received signal to a predetermined frequency. In practical terms, the frequency estimator provides an estimated value for the carrier frequency which is within manufacturing or operational tolerances, and does not have to be exactly accurate. The estimated value merely has to be sufficiently accurate sacks that the received signal may be frequency converted to within the bandwidth of a desired predetermined frequency.

The frequency converter circuitry may include a frequency synthesiser ^'and frequency mixer circuitry, said frequency synthesiser operative to generate a local oscillator signal in dependence on said estimated value for providing to said frequency mixer circuitry to convert said received signal to said predetermined frequency. Suitably, the frequency synthesiser is a direct digital synthesiser which can generate a desired frequency almost instantaneously.

Optionally, the frequency converter circuitry is frequency down-converter circuitry operative in dependence on said estimated value to convert said received signal to a predetermined intermediate frequency, as is usual in a receiver such as a superheterodyne receiver.

The frequency estimator may comprise fast fourier transform circuitry, and optionally may comprise SAW filter circuitry.

Additionally, the frequency estimator is configured to analyse a preamble of said received signal comprising a predetermined code to determine said estimated value, which provides for a quick analysis and estimate of the carrier frequency value.

The receiver may also include signal verification circuitry operative to utilise said preamble to verify said received signal as a signal suitable for said receiver. The signal verification circuitry may comprise fast fourier transform circuitry or SAW filter circuitry.

The receiver may further comprise demodulator circuitry configured to demodulate said converted signal to recover an identifier code from said received signal, which allows the receiver to distinguish between many signals it may receive. Additionally, the receiver may further comprise received signal strength indicator circuitry for providing an indication of the signal strength of said received signal, and/or the receiver may be configured to provide a phase indication for radio-frequency signals received at each of the one or more antennas, and/or comprise time of arrival circuitry for providing an indication of the time of arrival of said received signal.

In a particular arrangement, the receiver is operatively coupled to one or more antennas for receiving a radio-frequency signal and configured to provide a received signal strength indication, and/or phase indication, and/or time of arrival indication for radio-frequency signals received at each of said one or more antennas .

The receiver may comprise one or more of the foregoing described antennas . In a seventh aspect of the present invention there is provided direction location apparatus configured to receive two or more received signal strength indications for received signals having the same identifier code as each other from one or more receivers according to claim 12, and/or to receive two or more phase indications for received signals having the same identifier code as each other from one or more receivers according to claim 14, and/or to receive two or more indications of the time of arrival for received signals having the same identifier code as each other from one or more receivers according to claim 16, and to determine a bearing of a source of said received signals relative to said one or more antennas .

The direction location apparatus may be further configured to determine a range of said source of said received signals from said one or more antennas, which provides better location information.

Suitably, the direction location apparatus is included within or as part of a receiver.

In accordance with an eighth aspect of the present invention there is provided location information system, comprising: one or more transmitters each operative to transmit a radio-frequency signal modulated with an identifier code corresponding to respective transmitters; one or more receivers for receiving signals transmitted by said plurality of transmitters and operative to determine said identifier code for each received signal; direction location apparatus configured to determine a bearing of the source of a received signal relative to a reference point ; and a controller configured to utilise two or more bearings for received signals having the same identifier code to determine the location of a source of said received signals within said location information system.

Suitably, the two or more receivers and said direction location apparatus are configured as set out above.

The location information system typically comprises direction location apparatus as set out above wherein said controller is configured to utilise two or more bearings and/or ranges for received signals having the same identifier code to determine the location of a source of said received signal within said location information system.

In a particularly useful embodiment the location information system includes one or more cameras controllable by said controller to be directed to the said location of a source of said received signals. Advantageously, the location information system is configured to control said one or more cameras to track the movement of a source of said received signals within said system.

The location information may also include a data store of data items corresponding to one or more identifier codes, and wherein said controller is configured to retrieve one or more data items corresponding to an identifier code of a source of said received signals, and maybe further configured to receive a data item corresponding to a said identifier code, look said data item up in said data store to identify a corresponding identifier code and determine the location of a source of a received signal comprising said identifier code.

Viewed from a ninth aspect of the present invention provides a transmitter for use in a location information system as set out above, comprising: a radio-frequency signal generator; a modulator for modulating a radio-frequency signal from said generator with an identifier code associated with said transmitter; and an antenna for radiating a modulated radio-frequency signal from said transmitter .

Suitably, the radio-frequency signal generator utilises a free-running oscillator, which is a low-cost oscillator and suitable for disposable transmitters.

The transmitter comprises a local power supply for supplying power to transmitter circuitry, thereby making it independent and portable and suitable to be wearable and to be attachable to clothing and/or baggage . Such a transmitter may be configured to be disposable. The transmitter further comprises a controller configured to provide said identifier code to said modulator, there may be configured to generate said identifier code. Optionally, the identifier code is provided by a source external to said transmitter.

Suitably, said modulator is configured to modulate said radio-frequency signal with a preamble code.

Brief description of figures

Figure 1 shows an embodiment of an RF receiver

Figure 2 shows an embodiment of one part of an RF receiver

Figure 3 shows an embodiment of an RF transmitter Figure 4 shows an embodiment of an apparatus according to an aspect of the present invention

Figure 5 shows a flow diagram illustrating operation of one embodiment of the invention

Figure 6 shows a flow diagram.

Detailed Description

RF apparatus in accordance with one aspect of the invention comprise at least one RF receiver and at least one RF transmitter. In one embodiment the RF apparatus is arranged as a location information system having a number of transmitters, although the system is capable of operation with just one transmitter, and an RF receiver. The output from the RF receivers are used by processing means, for example a controller, within the RF apparatus to determine a bearing or location for the received RF signal and therefore the relative location of an individual carrying the relevant RF transmitter.

An example RF receiver in accordance with one aspect of the invention is shown in Figure 1. The RF receiver 400 comprises a power supply 401 which is used to power operation of the RF receiver. The power supply may be specific to the RF receiver, alternatively the power supply may be contained within a separate system or larger device (for example a base station used to house cameras at an airport) . Operation of the RF receiver will be controlled by the controller 402. The extent of such control will vary depending on the functionality of the RF receiver, and whether the RF receiver is linked to a control station or other processing means, for example a central processor within the RF apparatus. The controller may be a state machine, micro-controller or microprocessor.

An RF signal will be received at antenna 404. The antenna 404 forms part of a multiple antenna array. The antenna array is comprised, for example of 4 separate antennas set at 90 degree intervals. In this example each antenna within the antenna array is connected to its own RF receiver. Alternatively all the antennas may be connected to a central RF receiver or the RF receivers may share certain functionality, for example processing power. Signal reception circuitry 405 will filter and down-convert the receiver signal to a suitable IF

("intermediate frequency") frequency. The resulting IF signal will be fed to the demodulator 407 for demodulation. The resulting demodulated data will be fed to the controller 402 for processing. Signal' level detection means 406 (for example automatic gain control circuitry) will be used to detect the strength of the received RF signal. The resulting strength will be supplied to the controller 402. the strength detected may be actual signal strength or a relative signal strength, for example as compared to an expected or preset level.

The RF receiver utilizes the signal reception circuitry to quickly detect valid RF transmission signals and then to lock on to the carrier frequency being used by the RF transmitter. This enables receipt and analysis of multiple signals, allowing the RF transmitters to be less specific on frequency used. For example, where a low cost oscillator is used there will be frequency diversity in any transmitted RF signal. It is important that the relevant carrier frequency be detected quickly. That is to say, there is a relaxed frequency tolerance for the carrier frequency of the received signals (those transmitted by the RF transmitters) , as the receiver is configured to identify the carrier signal of the received signal quickly and therefore it is not necessary to know the carrier frequency in advance. The RF receiver utilizes a preamble i.e. initial part of the RF signal to lock on to the carrier frequency being used. Figure 2 illustrates the signal reception circuitry (405 from Figure 1) in more detail.

The signal 208 may be the received RF signal or a prior down-converted IF frequency. The signal is then sampled using, for example, a band-pass sampler 201 and 202. A real-time processor 203 (which may be the same or different to the processor 402 in figure 1) then analyses part of the preamble, for instance using FFT

("Fast Fourier Transform") or SAW ("Surface Acoustic

Wave" ) filter techniques , and determines whether the received preamble matches the required characteristics for such a preamble. For example the processor 203 may look for a particular spectral signature data sequence, series of pulses, series of gaps between received pulses. When the preamble has been verified, the frequency of the received RF signal is estimated and used to set the frequency of a DDS ( "Direct Digital Synthesiser") 204 - a device that can almost immediately generate a given frequency. This frequency is maintained for the duration of the received RF signal and acts to down-convert the signal to a given final IF frequency (using mixer 205 and bandpass filter 206) , within a very narrow frequency error, at which demodulation is performed.

Figure 3 provides an embodiment of an RF transmitter in accordance with one aspect of the invention. RF transmitter 300 comprises a controller 301. The controller may be a microprocessor, state machine or microcontroller. The controller controls operation of the RF transmitter including the frequency of transmission, data supplied, response to any data received (for example from an external programming source) . On activation the power supply 306, which may be a battery or similar power supply, will supply power to the controller. Activation may be through the removal of an isolation strip or through the combination of two contacts. On supply of power the controller will control generation of the RF signal by signal generator 308. The signal generator 308 may generate the RF signal in a variety of ways . For example the RF signal may be generated by a phase-locked loop frequency synthesiser. Such a system is capable of generating a desired frequency, and if it is used the receiver does not need to estimate the carrier frequency since it is reliably generated by transmitter. Optionally, a free-running oscillator may be used, which is simple, low-cost and suitable for disposable RF transmitters. The RF signal may be generated by use of a pre-configured algorithm or direct digital synthesis. The RF signal generated by the signal generator 308 is fed into the differential driver

307 which outputs complementary pulses to the antenna

(304) . The controller 301 will provide modulation control signals to the differential driver 307. These control signals will control at least one of the signal level and the modulation depth in accordance with the data being transmitted and the communication protocols under which the RF transmitter 300 is operating. The modulation pattern will represent a series of binary ones and zeros reflecting the data to be transmitted. In a preferred embodiment such modulation pattern will reflect both the unique identifier for the transmitter and the preamble used by the RF receiver to validate the RF transmitter and lock-on to the carrier frequency being used by the RF transmitter if necessary.

The antenna 304 is shown in figure 3 as a non-tuned circuit comprising a coil. Additional capacitors and resisters may be provided to minimise any unwanted harmonics and prevent the circuit exceeding emissions regulations . The circuit may also comprise a tuned circuit or a resonant printed (patch) antenna.

In a preferred embodiment the RF transmitter will transmit its preamble and unique identifier (and any other applicable data) at certain time intervals. The time intervals may be pre-set, for example every 1 second or may alternatively be at random intervals, for example through the use of a psuedo random number generator which adjusts the delay between each transmission. In a preferred embodiment a random delay is used with such delay being between 0 and 1 seconds. The advantages of a random delay period is that such a delay assists with collision avoidance between RF transmitters within range of the same RF receiver. The RF band used by the RF transmitter will depend on the RF apparatus and range required. In a preferred embodiment use of 5.8GHz is used with a 30MHz bandwidth for all RF transmitters operable within the same RF system or RF apparatus. For example, the RF transmitter may use BPSK ("Binary Phase Shift Keying") modulation at a 1 MBit/s data rate and have a 16-bit preamble of the form 1010101010101010. Other modulation schemes may be used such as Phase Shift Keying (PSK) , and embodiments of the invention are not limited to any particular modulation scheme. An FFT window of 8 ?s is sufficient for an RF receiver of the type described above (see Figures 2 and 4) to analyse the spectrum of this transmitted signal to a resolution of 125 kHz. The RF transmitter signal contains two dominant components with a 1 MHz separation - equivalent to 4 FFT resolution cells. A simple peak search algorithm is able to detect any signal of this form and distinguish it from even high-level noise or other interference, thus estimating its frequency to a precision of ±62.5 kHz. The DDS (204 in figure 2) is set to this frequency but with an offset equal to the desired final IF frequency and then down-converts the signal to its final IF frequency. Since the signal bandwidth is around 1 MHz it is now an easy matter to demodulate by standard techniques, such as a Costas loop, which will acquire lock within a further couple of bit periods, well before the end of the preamble. Realtime FFTs can be performed at around 80 MSamples/s, allowing a detection bandwidth of around 30 MHz.

The location of an RF transmitter is determined by the RF apparatus with the aid of a direction-finding antenna array. RF receivers attached to each antenna within the array either themselves or via a central processor, process the relative strength of signals received. The relative strength is then used by a central processor within the RF apparatus to provide a bearing for the RF transmitter concerned. Where the RF apparatus is part of a larger system or is combined with other RF apparatus, the bearings obtained from two or more spatially-separate RF readers can then be used by a central control station to estimate or provide further details on the location of the RF transmitter. Obviously the more antenna arrays (and therefore the more bearings fed into a central control station) in any given area the more detail which can be obtained on location.

In one embodiment of the invention, the RF apparatus described above can be used to locate passengers in an airport in a cost-effective manner, thereby providing enhanced security and reduced delays . Figure 4 shows an embodiment of an apparatus according to an aspect of the present invention. The system comprises an RF transmitter 101, an initialisation unit 105, a central control station 110 and a base station 102. The base station 102 comprises a camera 103, an antenna array 104 and at least one RF receiver (not shown) connected to the antenna array 104. The central control station is connected to the initialisation unit via a network link 108. The base station 102 is connected to the central control station through a second network link 107. Such network links 107 and 108 may for example be a wire link, a wireless link and an infra red link or an RF link. Multiple initialisation units 105 may be connected to the central control station 110 either through the same network link 108 or through separate network links 109. _, Likewise multiple base stations 102 may be connected to the central control station through network link 107 or through separate network links 106. Depending on the pre-existing systems present in the airport environment, a single central control station may be provided. Alternatively multiple control stations may be provided corresponding to different areas of the airport. Such separate control stations may themselves interface to other control stations or central systems.

Figure 5 shows a flow diagram illustrating the way in which one embodiment of the invention may operate. At S501 the RF transmitter is initialised. The initialisation process will involve activating the RF transmitter and reading its unique identifier ("ID") . In this example the ID is programmed into the RF transmitter on manufacture . For example where the RF transmitter is an integrated circuit, the ID may be programmed at wafer level. Optionally, the ID may be programmed at the time of utilisation, for example for an aircraft passenger baggage label when the passenger checks in and linked to the passengers personal information at that stage. Activation of the RF transmitter may, for example, be by the connection of a power supply to the RF transmitter, for example a battery or other power supply. At S502, the ID of the RF transmitter is read by the initialisation unit. Such reading may be by contact or non-contact means. For example the initialisation unit may comprise an RF receiver operable to receive an RF transmission from the RF transmitter once such RF transmitter is powered. At S503, the ID and associated passenger information (for example a photograph) is sent to a central control station via a network link. The control station may be a computer or other similar control station. Such control station may have direct user access (for example a keyboard, joystick, other user control means together with a display) or user access may be provided by slave or separate units connected to the control station. Optionally, the passenger information is stored in a database accessible by the central control station and associated with the ID. The passenger information and research by ID, or an ID can be searched for by way of passenger information.

The RF transmitter is then issued to every passenger (S504) . For example the RF transmitter may be provided within a clip-on or stick-on label, within a security tag, to be attached to an item of clothing or with other documentation provided to such passengers or to baggage (hold or carry-on baggage) . The RF transmitter may be provided at check-in, on entry to the airport environment, at a security gate or alternatively at some passenger control desk.. The RF transmitter may also be provided to other personnel within the airport, in fact where the RF transmitter is being used to study flow characteristics or is being used for security purposes, everyone within particular areas of the airport may need to be provided with an RF transmitter.

As a passenger moves around the airport, the RF transmitter will transmit its data (including identification data and the unique ID and the preamble) as described above (see Figure 3) .

As the RF transmitter comes within range of an antenna array, the transmitted RF signal will be received by the antenna array and at the same time by the receiver or multiple receivers attached to the array

(S505) . The RF transmission will include at least a preamble and unique identifier. The preamble is used by the RF receiver to validate the incoming RF signal. As soon as the RF signal is validated the RF receiver detects the RF frequency being used by the RF transmitter and locks on to such RF frequency. (S505a) The receiver will then detect the RF signal strength being received (S506) . The RF receiver will also demodulate the received signal to obtain the unique identifier (S507) . In one embodiment each antenna within the antenna array will be connected to a separate receiver unit with each separate receiver unit then being connected to the central control station or processing unit. Each receiver unit will independently determine the received signal strength and demodulate the received RF signal . The resulting data will then be fed to a central processor or alternatively the central control station. The central control station or central processor will then compare the signal strength data (bearings) received from each RF receiver and from other receivers connected to other arrays in order to determine relevant location data. In the alternative a single receiver unit may be provided for each antenna array, such receiver unit will comprise a processor capable of interpreting the signal strength received from each antenna and of demodulating the received signal. Such processor may also carry out a comparison of the received signal strengths and supply a single data value consistent with the relative signal strengths from each antenna within the array to the central control station.

Examples of direction finding techniques and circuits may be found in the book "Radio Direction Finding and Super Resolution" (IEEE Electromagnetic Waves Series) by P. J. D. Ge thing. Both amplitude and phase comparison direction finding are well-known and date from the 1950s. Time of arrival techniques are also well known, and are the basis of GPS, but have not been established quite so long. The book "Understanding GPS: Principles and Applications", second edition by Elliot D. Kaplan (editor), Christopher Hegarty, provides examples for time of arrival techniques .

The RF receivers may be on and capable of receiving transmission all of the time. Alternatively such receipt may be turned on at random time intervals or at certain pre-set time intervals. As a further alternative, reception may be activated by a user, for example when location data is required on a particular passenger.

In a preferred embodiment and as shown in Figure 4 , the RF apparatus (comprising RF receivers and RF transmitters) is combined with a system of cameras.

The visual information, together with RF transmitter tag IDs and direction data, is transmitted to the central control station 106 via a network link 107. In some implementations, link 107 may be combined with link 108. Additional base stations 102 may be connect to the control station 106 via network link 107 or additional base stations 102 may be connected using additional network links 110. The central control unit 106 will provide a user interface and processing capability such that some of the following functions are provided: locate a particular RF transmitter (and therefore person) , follow a particular RF transmitter as a person moves around, identify which passengers are in particular areas .

Figure S illustrates in a flow diagram what happens when location data is required.

The user will request details from the central control station (or a separate slave unit able to interface with the central control station) in relation to, for example the location of a particular passenger (S601) . The central control station will link the passenger details or requirements to a particular unique identifier (S602) . The identifier corresponds to the RF transmitter that the passenger was provided with. The central control station will then identify the location of the relevant RF transmitter using the location information provided by the multiple antenna array and RF receiver i.e. by comparing the relative signal strengths from each antenna in the array (S603) . This may be sufficient to identify a general area. The same location information is then used by the central control station to retrieve image data from cameras located in the relevant area (S604) . Passengers or locations can then be visually tracked to assist security personnel or other airport personnel to locate the passenger (s) concerned. The location information provided by the RF transmitters could also be used to identify passengers within a particular area covered by a camera. For example if a security guard identifies an individual trying to access a restricted area, the location details from the camera can be used by the central control station to identify all identifiers in that same area and as a result relevant individual details.

Each camera within the system (103 in figure 1) is comprised a lens, optical sensor and interface electronics. Any suitable camera may be used. The camera or collection of cameras should be chosen to meet the image requirements of the system. For example, where only a low resolution image is required the determination of the camera used may be different from where a high resolution image is required or where a full 360 degree view is required. Different types or forms of camera may be combined within the same base station to provide increased user information. For example the cameras may provide both a continuous 360 degree view plus several local targeted views which are either selected automatically by a central control station or selected by a relevant operator. The camera system may also permit individual operators to select and zoom to separate views simultaneously. In one embodiment the camera system should be sensor based, permit scalable processing and have networking capability.

In a preferred embodiment the cameras are used in groups of 8, each group forming an optical cluster. There is one optical cluster per base station. The cameras are positioned with an angular separation of 45 degrees such that eight cameras provide a full 360 degrees view. Since each camera has an angle of view greater than 45 degrees the set of eight cameras provides a full 360 degrees view with no gaps. Software is used to combine the eight individual images into a single panoramic view with the overlaps removed. The base station additionally comprises a digital signal processor (DSP) and is linked to an ethernet capable host computer which controls either directly or via a central control station the operation of the camera system.

Each camera provides an angle of view 29.25 degrees left of centre, 29.25 degrees right of centre, 40 degrees below horizon, 0 degrees above horizon. The asymmetric vertical view is achieved by offsetting the centre of the lens relative to the centre of the sensor. Optical distortions introduced by this arrangement are removed using software. The sensor has a resolution of 2 million pixels . The camera provides a colour image using a colour filter array and Bayer reconstruction.

The DSP is operable to handle bayer interpolation, geometric image correction, stitching of images and compression.

Once the camera has captured the image (either as part of continuous operation or through operator selection) the image will be transmitted over the provided ethernet channel as required. A central control station may capture all transmitted images and integrate such images and/or data into a form presentable to an operator. For example where the central control station relays a request for images relating to a particular location identified via the RF receivers, the central control station will then resolve the images received from the selected cameras and present the end image to the operator. The images may be presented in a display screen within the central control station or at one or more slave units connected to the central control station.

To achieve greater location information or individual information the cameras and associated software may be operable to use pattern recognition and motion detection to identify individuals . In a further example the cameras are spatially referenced to a model of the environment being monitored and may be operable to track individuals or follow certain individuals through that environment. A tracking function would have the additional advantage of enabling an individual to be located in one camera and then automatically be found as the individual moves to the next camera .

In a further example a single camera or group of cameras are moved, either manually or mechanically within the environment, and may spatially reference themselves to each other and the environment on demand. Mobile RF receivers may also be moved and relocated in this network. In this mode of operation the mobile camera units and RF receivers are able to provide a local surveillance services suited, for example, to monitor a particular departure gate, an at risk area or even the inside of an aircraft.

Other embodiments of the RF apparatus and of the system described above will be apparent to the skilled man. For example the RF apparatus may be used wherever there is a need to obtain relative location information on an individual carrying an RF transmitter or to track such an individual through a defined environment .

Insofar as embodiments of the invention described above are implementable, at least in part, using a software-controlled programmable processing device such as a digital signal processor, microprocessor, or other processing device, data processing apparatus or computer system, it will be appreciated that a set of machine- implementable instructions, for example a computer program, for configuring a programmable device, apparatus or system to implement the foregoing described methods , apparatus and system is envisaged as an aspect of the present invention, the computer program may be embodied as source code and undergo compilation for implementation on a processing device, apparatus or system, or may be embodied as object code, for example. A skilled person would readily understand that the term "computer" in its most general sense encompasses programmable devices such as referred to above, and data processing apparatus and computer systems.

Suitably, the set of instructions or computer program is stored on a carrier medium in machine readable form, for example in solid-state memory or magnetic memory such as disk or tape, in particular CD- ROMs and DVDs. The computer program may be supplied from a remote source embodied in the communications medium such as an electronic signal, radio frequency carrier wave or optical carrier waves . Such carrier media are also envisaged as aspects of the present invention. In the view of the foregoing description it will be evident to a person of ordinary skill in the art that various modifications may be made within the scope of the invention. For example, although the foregoing embodiments have been described with reference to monitoring passengers or individuals within an airport or other environment, embodiments of the present invention may be used to monitor the location of objects such as document files in office, books in a library or goods in a warehouse or store.

Claims

1. A receiver, comprising: a radio- frequency receiver including frequency converter circuitry; a frequency estimator configured to analyse a radio- frequency signal received by said radio frequency receiver to provide an estimated value for the carrier frequency of said received signal, and provide said estimated value to said frequency converter circuitry; and wherein said frequency converter circuitry is operative in dependence on said estimated value to convert said received signal to a predetermined frequency.

2. A receiver according to claim 1, wherein said frequency converter circuitry includes a frequency synthesiser and frequency mixer circuitry, said frequency synthesiser operative to generate a local oscillator signal in dependence on said estimated value for providing to said frequency mixer circuitry to convert said received signal to said predetermined frequency.

3. A receiver according to claim 1 or claim 2, wherein said frequency converter circuitry is frequency down-converter circuitry operative in dependence on said estimated value to convert said received signal to a predetermined intermediate frequency.

4. A receiver according to any preceding claim, wherein said frequency estimator comprises fast fourier transform circuitry.

5. A receiver according to any preceding claim, wherein said frequency estimator comprises SAW filter circuitry.

6. A receiver according to any preceding claim, wherein said frequency estimator is configured to analyse a preamble of said received signal comprising a predetermined code to determine said estimated value .

7. A receiver according to claim 6, further comprising signal verification circuitry operative to utilise said preamble to verify said received signal as a signal suitable for said receiver.

8. A receiver according to claim 7, wherein said signal verification circuitry comprises fast fourier transform circuitry.

9. A receiver according to claim 7, wherein said signal verification circuitry comprises SAW filter circuitry.

10. A receiver according to any preceding claim, further comprising demodulator circuitry configured to demodulate said converted signal to recover an identifier code from said received signal.

11. A receiver according to any preceding claim, further comprising received signal strength indicator circuitry for providing an indication of the signal strength of said received signal.

12. A receiver according to claim 11, operatively coupled to one or more antennas for receiving a radio- frequency signal and configured to provide a received signal strength indication for radio-frequency signals received at each of said one or more antennas .

13. A receiver according to any one of claims 1 to 10, further comprising phase measurement circuitry for providing an indication of the phase of said received signal .

14. A receiver according to claim 13 , operatively coupled to one or more antennas for receiving a radio- frequency signal and configured to provide a phase indication for radio- frequency signals received at each of said one or more antennas .

15. A receiver according to any one of claims 1 to 10, further comprising time of arrival circuitry for providing an indication of the time of arrival of said received signal .

16. A receiver according to claim 15, operatively coupled to one or more antennas for receiving a radio- frequency signal and configured to provide a time of arrival indication for radio-frequency signals received at each of said one or more antennas.

17. A receiver according to claim 12, 14 or 16 comprising said one or more antennas .

18. Direction location apparatus configured to receive two or more received. signal strength, indications for received signals having the same identifier code as each other from one or more receivers according to claim 12, and/or to receive two or more phase indications for received signals having the same identifier code as each other from one or more receivers according to claim 14 , and/or to receive two or more indications of the time of arrival for received signals having the same identifier code as each other from one or more receivers according to claim 16, and to determine a bearing of a source of said received signals relative to said one or more antennas .

19. Direction location apparatus according to claim 18, further configured to determine a range of said source of said received signals from said one or more antennas :

20. A receiver according to any one of claims 1 to 17, further comprising direction location apparatus according to claim 18 or claim 19.

21. A location information system, comprising: one or more transmitters each operative to transmit a radio-frequency signal modulated with an identifier code corresponding to respective transmitters ; one or more receivers for receiving signals transmitted by said plurality of transmitters and operative to determine said identifier code for each received signal; direction location apparatus configured to determine a bearing of the source of a received signal relative to a reference point; and a controller configured to utilise two or more bearings for received signals having the same identifier code to determine the location of a source of said received signals within said location information system.

22. A location information system according to claim

21, wherein said two or more receivers are configured in accordance with any one of claims 1 to 17 or 20, and said direction location apparatus is configured in accordance with claim 18.

23. A location information system according to claim

22, further comprising direction location apparatus according to claim 19 and wherein said controller is configured to utilise two or more bearings and/or ranges for received signals having the same identifier code to determine the location of a source of said received signal within said location information system.

24. A location information system according to any one of claims 21 to 23 including one or more cameras controllable by said controller to be directed to the said location of a source of said received signals.

25. A location information system according to claim 24, wherein said controller is configured to control said one or more cameras to track the movement of a source of said received signals within said system.

26. A location information system according to any one of claims 21 to 25, further comprising a data store of data items corresponding to one or more identifier codes, and wherein said controller is configured to retrieve one or more data items corresponding to an identifier code of a source of said received signals.

27. A location information system according to claim 26, configured to receive a data item corresponding to a said identifier code, look said data item up in said data store to identify a corresponding identifier code and determine the location of a source of a received signal comprising said identifier code.

28. A transmitter for use in a location information system according to any one of claims 21 to 27, comprising: a radio-frequency signal generator; a modulator for modulating a radio-frequency signal from said generator with an identifier code associated with said transmitter; and an antenna for radiating a modulated radio-frequency signal from said transmitter .

29. A transmitter according to claim 28, wherein said radio-frequency signal generator utilises a free- running oscillator.

30. A transmitter according to claim 28 or 29, further comprising a local power supply for supplying power to transmitter circuitry.

31. A transmitter according to any one of claims 28 to 30, configured to be wearable.

32. A transmitter according to any one of claims 28 to 31, configured to be attachable to clothing and/or baggage .

33. A transmitter according to any one of claims 28 to 32, configured to be disposable.

34. A transmitter according to any one of claims 28 to 33, further comprising a controller configured to provide said identifier code to said modulator.

35. A transmitter according to claim 34, wherein said controller is further configured to generate said identifier code.

36. A transmitter according to claim 34, wherein said identifier code is provided by a source external to said transmitter .

37. A transmitter according to any one of claims 28 to 36, wherein said modulator is configured to modulate said radio-frequency signal with a preamble code.

38. A set of machine-readable instructions and/or parameters operative in a data processing apparatus to configure said data processing apparatus to implement at least a part of a receiver according to any one of claims 1 to 17 or 20.

39. A set of machine-readable instructions and/or parameters operative in a data processing apparatus to configure said data processing apparatus to implement at least a part of direction location apparatus according to claim 18 or 19.

40. A set of machine-readable instructions and/or parameters operative in a data processing apparatus to configure said data processing apparatus to implement said controller of the location information system of any one of claims 21 to 27.

41. A set of machine-readable instructions and/or parameters operative in a data processing apparatus to configure said data processing apparatus to implement at least a part of said transmitter of any one of claims 28 to 37.

42. A receiver substantially as hereinbefore described and with reference to figures 1, 2 and 4 of the drawings .

43. A location information system substantially is hereinbefore described and with reference to the drawings .

44. A transmitter substantially as hereinbefore described and with reference to figure 3 of the drawings .