NAVIGATION SYSTEM
The presented invention relates to a navigation system and in particular relates to a navigation system which uses low frequency signalling in combination with satellite navigation.
Whilst aircraft, ships and military vehicles have been provided with navigation systems for many years, recent technological development have meant that such navigation systems have become more user friendly and widely available. As a result, the use of personal navigation systems has become more commonplace over the past few years.
Currently, many navigation systems use satellite navigation such as Global Positioning System (GPS) or Galileo. GPS is a space-based global satellite system that provides three dimensional location and time information to a personal navigation system receiver anywhere on the Earth providing the receiver has an unobstructed line of sight to four or more GPS satellites. Galileo operates on the same basis as GPS. GPS navigation systems are widely used in private vehicles to help with road navigation. GPS navigation systems are also used by, for example, outdoor sports enthusiasts as an aid to navigation in conjunction with a detailed map and are of particular use in poor weather. However, whilst GPS navigation aids are useful and reliable, they have two significant limitations. The first limitation is that the GPS satellite system provides the receiver with a location position having an accuracy of between 1 to 10 meters. Whilst such accuracy is acceptable in most instances, for some users, such as a visually impaired pedestrian a higher precision of pinpointing location would be necessary for the pedestrian to navigate safely. The second limitation of the UPS system is the need for the navigation system receiver to have a clear line of sight to at least four satellites. In many circumstances this is not always possible, for example if the user is underground, inside or surrounded by tall buildings. Again, whilst this is not an
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issue for many users, in the case of a visually impaired user, a more reliable and consistent provision of navigation information is required as they wilt still require navigation aid when walking, for example, within an underground shopping mall.
Alternative navigation systems are available which utilise mobile phone network cell transmission terminals to provide location information, The mobile phone navigation systems are limited in their reliability by the requirement of a connection to a cell terminal to obtain a reliable high quality signal in order for a location position to be obtained, As many mobile phone users are aware, a high quality connection is not possible in all environments, with poor quality signal reception common in both rural and urban areas, Navigation aids which rely on the mobile phone network also have limited utility in a multi-path environment, such as a densely routed area of a city, or within an office block, as it becomes difficult for the navigation system to accurately measure and pinpoint the exact location.
The determining of the location currently requires a complex algorithm which includes pre-rneasured positions. In view of this, while mobile phone navigation systems are useful as a general navigation tool, in the case of a visually impaired user, a more reliable and accurate provision of navigation information would be required.
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The third type of navigation system, which is more commonly used in an enclosed environment such as an office building, is a locally implemented navigation system, for example one which uses fingerprinting based locations and/or other technology including Zigbee. A system relying on fingerprinting based location requires the use of a distributed network of sensor modules capable of recognising the characteristic unique features present in each individual's finger prints. Each sensor module can communicate with each other module, and a base unit, using a wired or wireless network and any appropriate protocol. The dynamics of the users as they move within the environment, checking their fingerprint through the sensors as they go, are therefore monitored. This type of navigation system has the benefit of not requiring connection with an external source and is of particular use in meeting the challenge posed with multi-path environments such as office environments. However, the system is limited by the need to be able to determine the uscr's position as they move into different environments as sensor modules are required in each environment to enable continued navigation assistance.
Therefore, none of the navigational systems detailed can operate consistently and reliably in all environments. The currently available navigation systems which use GPS and mobile terminals for position location must be able to communicate with one or several reference points to enable a position to be located. As has been described above, this is not always possible. In addition, whilst locally implemented navigation systems can be more accurate, they are limited by their local nature. As a result, a user of these navigation systems needs alternative means, such as for example, a map, to support navigation which, if the user is congenitally or environmentally visually impaired, is not always possible.
Therefore, there is a need for a navigation system which can provide reliable and accurate location and navigation information to a user throughout all types of environments.
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It is an object of the present invention to obviate or mitigate at least one of the aforementioned problems.
According to a first aspect of the invention there is provided a personal guidance system, the system comprising a plurality of fixed transmitters each having a fixed location, and each being operable to transmit a unique fixed identification signal, and a plurality of mobile transmitters each being operable to transmit a unique mobile identification signal; a receiver module comprising a fixed identification signal receiver operable to receive fixed identification signals and a mobile identification signal receiver operable to receive mobile identification signals, the receiver module operable to determine a relative position of the receiver module with respect to the plurality of fixed transmitters and/or the plurality of mobile transmitters and to generate relative position information; and a guidance unit associated with the receiver, and operable to receive relative position information from the receiver, and to output direction information derived from such relative position information in combination with stored mapping information.
The provision of a navigation system for a pedestrian which is operable to use transmission of signals from a plurality of fixed transmitters and/or mobile transmitters, enables the receiver module to provide a guidance unit with precise position information and thus act as a navigation aid throughout a range of different environments and spaces, including underground.
Each fixed transmitter may be operable to transmit a fixed transmitting signal having a frequency and phase combination unique to the transmitter concerned, the frequency being less than 300kHz.
With each fixed transmitter operating at a frequency of less than 300kHz the signals received by the receiver module provide the guidance unit with precise position information in a variety of environments.
Conveniently, the frequency may be less than 30kHz or may be less than 3kHz.
Use of a frequency of less than 30kHz will enable the navigation system increased signal penetration and navigation aid coverage across a wider range of environments and spaces. Use of a frequency of less than 3kHz will enable the navigation system increased signal penetration and navigation aid coverage across a yet larger range of environments and spaces.
Each fixed transmitter may be operable to transmit its fixed identification signal at predefined intervals, for example. between one and five times per second.
Each fixed transmitter may further be operable to transmit a fixed identification signal at a predetermined signal frequency different from the predetermined signal frequency of each other fixed transmitter.
Preferably, the receiver and the fixed transmitters may include respective clock signal generators, which are operable to synchronise with one another.
The provision of clock signal generators in the receiver and fixed transmitters which are operable to synchronise with one another facilitates accurate location determination by the receiver using the fixed identification signals transmitted by the fixed transmitters, The mobile transmitters may be satellite navigation system transmitters.
Preferably the receiver, the fixed transmitters and mobile transmitters may include respective clock signal generators which are operable to synchronise with one another.
According to a second aspect of the invention there is provided a personal guidance device, the device comprising: a receiver operable to receive respective identification signals from a plurality of fixed transmitters each having a fixed location, and each of which is operable to transmit a unique fixed identification signal, the receiver further operable to receive respective identification signals from a plurality of mobile transmitters each of which is operable to transmit a unique mobile identification signal, the receiver also being operable to determine a relative position of the receiver with respect to the plurality of fixed transmitters and/or the plurality of mobile transmitters and to generate relative position information; and a guidance unit operable to receive relative position information from the receiver, and to output direction information derived from such relative position information in combination with stored mapping information.
The provision of a personal guidance device operable to receive signals from fixed and/or mobile transmitters enables the personal guidance device to provide location and direction information in a wide range of environments.
Preferably, the fixed transmitters may transmit a fixed identification signal having a frequency and phase combination unique to the transmitter concerned, the frequency being less than 300kHz The provision of a personal guidance device which uses fixed identification signals from a plurality of fixed transmitters. each of which operates at a frequency of less than 300kHz enables a receiver to provide a guidance unit with precise position information and thus act as a navigation aid throughout different environments and spaces including underground.
Conveniently, the frequency may be less than 30kHz or may be less than 3kHz.
Use of a frequency of less than 30kHz will enable the guidance device increased signal penetration and navigation aid coverage across a wider range of environments and spaces. Use of a frequency of less than 3kHz will enable the guidance device increased signal penetration and utility as a guide across a yet larger range of environments and spaces. r)
Preferably, the receiver is operable to receive identification signals at predefined intervals, for example, between one and five times per second.
The receiver may further comprise a clock signal generator operable to synchronise with clock signal generators in such fixed transmitters.
The receiver may further comprise a clock signal generator operable to synchronise with clock signal generators in such mobile transmitters.
The provision of clock signal generators in the receiver and fixed and mobile transmitters which are operable to synchronise with one another facilitates accurate location determination by the receiver using the signals transmitted by the fixed and mobile transmitters.
The receiver may be further provided with a compass such as, but not limited to an n-axis magnetometer, to determine directional information.
The position and direction information available to the system may be stored, for example, at the receiver unit, such that in the event of loss of fixed and non-fixed identification signals, the apparatus is operable to output destination information derived from the stored position and direction information in combination with the stored mapping information to guide a user to a defined location despite the absence of identification signals.
The defined location may comprise a location already encountered during the course of the journey or may comprise, for example, the nearest example of a selected group of locations such as, but not limited to, police stations, hospitals.
government offices or other predefined safe location.
Furthermore, the buffer of stored position information and direction information may comprise any desired size, but may typically include information and/or data stored during the five to ten minutes immediately preceding identification signal loss.
A further safety feature of the system may comprise the ability to send, on request, an alert to a predefined address, such as but not limited to, a police station or security center or to a carer, to notify the recipient of the alert that the user of the system requires assistance. It will be understood that the alert may also be sent to a mobile location e.g. to a carer via a mobile device such as a mobile handset, pager or the like.
Embodiments of the present invention will now be provided, by way of example only, and with reference to the following figures, in which: Figure 1 is a schematic diagram of a navigation system according to a first embodiment of the present invention; and Figure 2 is a schematic diagram of navigation system receiver unit of the navigation system of Figure 1.
With reference to Figure 1 there is shown a navigation system 10 having three Low Frequency (LF) transmitters 12a, 12b, 12c each of which has a corresponding transmitting signal range 13a, 13b, 13c. The transmitters 12a-c are located in fixed positions such as to surround a geographic area 1 so that the transmitting signal range 13a-c includes the geographic area 16 which the navigation system 10 is to cover. The navigation system 10 is also provided with three mobile transmitters i4a, 14b, 14c which are, in this case, satellite transmitters which are part of a UPS satellite navigation system (not shown). The system 10 is further provided with a navigation unit 18 which is operable to receive the signals 5ac generated by each fixed transmitter l2a-c when it is within the signal range 13 a-c of the fixed transrnittersi2a-c and operable to receive the signals Za< generated by each mobile transmitter 14a-c when it is within the signal range (not shown) of the mobile transmitters 14a-c. The fixed transmitters l2a-c are synchronised by means of a synchronous clock signal 20 and in this case they are synchronised with the mobile transmitters 14a-c of which mobile transmitter 14c generates the clock signals 20.
The navigation unit 18 is also synchronised by means of the same clock signal 20 resutting in the fixed transmitters 12a-c, the mobile transmitters 14a-c and the navigation unit 18 being synchronous.
Each of fixed transmitters 12a-c transmits a periodic signal s with duration T and phase q, with i=1,2,...,n corresponding to a frequency v belonging to the LF band frequency being less than 300kHz. The frequency may be within the Very Low Frequency band (VLF) of less than 30kHz or the Ultra Low Frequency (ULF) band of less than 3kHz depending on the environment of the location of the navigation system 10, with the frequency chosen as to be appropriate to provide a reasonable accuracy of location. Each fixed transmitter l2i generates its own transmitted signal s of phase Qi which corresponds to a precise location point of the fixed transmitter i2 with geographic co-ordinates latitude lat1 and longitude long1.
An embodiment of the navigation unit 18, is shown in more detail with reference to Figure 2. The navigation unit 18 comprises a LF receiver unit 30, a satellite navigation receiver unit 32, a microprocessor 34, Flash RUM 36 connected to the microprocessor 34 via memory controller 38 and RAM 40 connected to the microprocessor 34 via memory controller 42. The navigation unit 18 further includes a wireless module, in this case Bluetooth module 44 and a digital compass, in this case an n-axis magnetometer 46, both of which arc connected to the microprocessor 34. The navigation unit 18 is also provided with a connection unit 48, in this case serial bus 48 and a power unit 50. The navigation unit 18 is further provided with an input unit 52 which provides input to microprocessor 34; output module 54 with its provided data output from microprocessor 34; motion detection module 56; and plug in module 58, each of which provide data input to the microprocessor 34. In this embodiment, the satellite navigation receiver unit 32 is operable to receive signals transmitted by space-based global navigation satellite transmitters, in this case mobile transmitters 14a-c which form part of GPS, to provide location and time information to the microprocessor 34. The input unit 52 is, in this case, an input pad with an alphanumeric input pad which is integrally formed within the navigation unit 18. The motion detecting module 56 incorporates sensors (not shown) which provide the microprocessor 34 with data confirming if the navigation unit 18 is in motion and thus if an iterative process of route detection and provision should be implemented. It will be understood that the navigation unit 18 may function effectively without the inclusion of a motion detection module 56. The plug-in module 58 is, in this embodiment, a secure digital card which is inserted in a secure digital card slot (not shown) provided in the navigation unit 18 whereby the plug in module 58 is removably attachable to the navigation unit 18. The removably attachable plug in module 58 provides means for downloading data to the navigation unit 18.
In this embodiment, the Flash ROM 36 stores control software which in this case is the firmware of the navigation unit 18. In addition, in this case, the Flash ROM 36 stores suitable software so as to provide navigation capability including, but not limited to, databases with geographic coordinates such as latitude, longitude, altitude and the like. It will be appreciated that whilst the firmware is in this case stored within the same Flash ROM 36 modules as the other navigation software, and it may, for example, be stored in a separate ROM module, such as, but not limited to, a dedicated EEPROM module.
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The navigation unit 18 receives signals Zac broadcast by mobile transmitters 14a-c via satellite navigation receiver unit 32 which provides them to the microprocessor 34. The microprocessor uses the latitude and longitude data from these signals to determine the position of the navigation unit 18. The microprocessor also determines the direction in which the unit IBis pointing by means of the data received from the digital compass 46 and the motion detection module 56.
The navigation unit 18 also receives fixed transmitted signals s, in this case signals 5a 5h and s which are captured by antenna 31, through receiver unit 30. The waveform of each signal s captured is compared by a signal analyser (not ii shown) which in this case is embedded in the microprocessor 34 and which compares the received signals 5a s. by computing the phase difference APah between the signal 5a received from transmitter 12a and the signal 5b received from transmitter 2b This process is repeated for each of the signals 5a-c received. From the phase difference Aab between pair of transmitters 12a and 12b along with the remaining phase differences Ap11 for each remaining combination of pairs of transmitters from transmitters 12a-c, it is possible to obtain the relative distance Dab. Dac, and D of the navigation unit 18 from each of the transmitters 12a-c. The computed distance Dac will identify a plane perpendicular to the line of sight between transmitter 12a and transmitter 12c and the navigation unit 18 lies within this plane. The plane is established for each pair of transmitters 12a, 12b and 12c.
Intersection between these planes will identify a single point which identifies the location of the navigation unit 18. This process is carried out on an ongoing iterative basis. The navigation unit 18 must be in the signal range of three or more transmitters T1 in order to allow for triangulation.
The microprocessor 34 of navigation unit 18 then compares the co-ordinates of the latitude lat and longitude longs of the location determined by the signals received from fixed transmitters i2a-c to the coordinates of latitude lat and longitude longa detennined from the signals received from mobile transmitters 14a-c.
To achieve navigation using the navigation unit 18, the Flash ROM 36 is provided with digital mapping information which enables a journey start point, a journey end point and a route between the two to be selected. The route selection is, in this case. input into the navigation unit 18 using keypad 52 which is removably connected temporarily to the navigation unit 18 via serial bus 48. Although in this embodiment the keypad 52 is separate to the navigation unit 18, it is to be appreciated that the keypad 52 may alternatively be located within navigation unit 18. * fl
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The receiver 30 receives the signals 5a-c from each fixed transmitter 12a-c and signals Zac from each mobile transmitter 14a-c and using the process detailed above, the microprocessor 34 extracts the location point for the navigation unit 18.
The microprocessor 34 also determines which direction the navigation unit 18 is pointing by means of the data received from the digital compass 46. The latitude and longitude of the extracted location point is compared to the selected route which is intended to be followed; the selected route makes use of the digital map stored in the Flash ROM 36. As the user of the navigation unit 18 moves along the selected route, the extracted location point for the navigation unit 18 identified from the received transmitter signals 5a-c is compared with the previous point on the mapped route generated for the navigation unit 18 and with the current direction in which the navigation unit 18 is facing which is provided by the output of digital compass 46. The output from the microprocessor 34 as a result of these features being compared generates the next location point. The navigation unit 18 then compares the next location point with the next predicted point in the mapped route.
The microprocessor 34 within the navigation unit 18 will then send the user. by way of an output unit (not shown) a signal indicating the direction in which to travel to reach the next point on the intended route. if, as the user starts to travel, the angle between the direction from the current point and the next point, and the direction from the current point to the expected point is higher than a certain predetermined critical value, the navigation unit 18 sends a correction signal to the user by way of an output unit (not shown). If, as the user starts to travel, the angle between the direction from the current point and the next point, and the direction from the current point to the expected point is within a predetermined acceptable range, the navigation unit 18 sends a reassurance signal, by way of output unit (not shown) to the user that the correct navigation direction is being taken.
In the event that navigation unit 18 moves out of range of the signal Zac, or the signals z is lost for some other reason, the navigation unit 18 is able to autonomously switch to using the fixed transmitter signals ac to provide navigation until the reception of the mobile transmission signals z is restored.
When the navigation unit 18 is able to receive signals from the fixed transmitters 12a-c and mobile transmitters 14a-c the navigation system 10 can operate as a mobile transmitter based navigation augmented by the fixed transmitter navigation capability. It will be understood that the system 10 can also operate as a mobile transmitter based navigation system and use the fixed transmitter location information only to check for positioning errors.
The use of low frequency radio signals by the navigation system 10 means that the transmitted signals 5a-c are able to penetrate most materials and thus are able to penetrate through structures or geographical features which the user may encounter during travel such as pedestrian travel. The increased penetration of the transmitted signals 5a-c enables the receiver 30 to receive the transmitted signals 5a-c even when the user is in an environment such as an underground shopping mall thus providing the navigation unit 18 with a reliable signal s on which to establish precise location information relating to the navigation unit 18 The navigation unit 18, can further utilise the data provided by the digital compass 46 and the motion detection module 56 to continually assess and monitor the direction of and the speed of travel of the navigation unit 18. Determining the direction of and speed of travel of the navigation unit 18 provides an additional reference measure when determining the position of the navigation unit 18. The reference measure can be established as the starting point of the navigation unit 18 is known and the motion progress can be determined and tracked using the direction of and speed of travel data thus enabling location points after a period of travel to be determined by extrapolation. The navigation unit can utilize this data further to predict the subsequent position based upon the data received by the microprocessor 34 which augments the accuracy of the navigation.
The navigation unit 18 can also constantly calculate the distance of the user to the closest safe point in the determined route which is being navigated. The calculation of this safe point provides a buffer to allow navigation in the event that connection to the mobile identification signal z is lost. Re-acquisition of the mobile identification signal z may then require a process of re-routing the user to the intended destination; this process may or may not be preceded by a request from the navigation unit 18 to the user.
The combination of the low frequency signal transmission with additional monitoring carried out by the assessment unit (not shown) enables navigation unit 18 to determine location points with high precision In use the navigation unit 18 may be provided as a portable or handheld device which can be carried or worn by a user. The user may be a pedestrian. The user may be further helped in the guidance process by the device via motion sensors which are in contact with the user or via an audio command which can be provided directly or via one or two headphones. The user may be a pedestrian. The navigation unit 18 may alternatively be formed integrally within mobility equipment such as wheelchairs or scooters.
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In an alternative embodiment of the navigation unit 18, a reference synchronised signal is made available to compare to the waveforms. The reference synchronised signal is made available, for example, by means of an internally synthesised signal.
The comparison carried out by the signal analyser 32 in this case examines phase shift between the reference waveform and signal s.
In a further embodiment of the navigation system 10, each of the transmitters i2a-c transmit periodic signals s of different frequencies v1, i=l,2,...,n, Each of the signals s are, when the navigation unit iS is within range, received by the navigation unit 18 and compared, using signal analysis, to establish a single point of location for the navigation unit 18 within the navigation system 10 on an ongoing iterative basis.
LF signals by their nature can be susceptible to several sources of disturbing noises including, but not limited to, noise from electronic devices, motors and computer systems each of which can cause interference in the LF signal. However, in a further embodiment of the navigation unit 18. the navigation unit is provided with high selectivity filters (not shown) which filter with relative accuracy any such disturbing noises thus reducing the interference in the LF signal.
It is also noted that the low transmission speed associated with LF signals does not adversely affect the operation of the navigation system 10 as transmitters 12a-c are not, in the embodiments detailed above, required to send specific data instead sending periodic signals 5a s having a predetermined frequency and phase and with the determination of the location point being performed on the navigation unit.
Various modifications may be made to the embodiments hereinbefore described without departing from the scope of the invention. For example, it will be clearly understood that whilst the navigation system illustrate in Figure 1 comprises three fixed transmitters 12a, 12b and i2c, the navigation system may include any number of fixed transmitters l2a -l2n. Furthermore, it will be clearly understood that the mobile navigation transmitters 14a-c are satellite navigation transmitters which as part of the GPS network they may be part of any similar system including but not limited to Galileo. Also, it will be clearly understood that whilst the clock signal which synchronises the fixed transmitters 12a-n, mobile transmitters 14a-c and receiver unit 18 is described as being provided by GPS receivers linked to the transmitters 12a-n and receiver unit 18, the synchronous clock signal could be generated by any suitable means including, but not limited to, a radio generated clock.
The route selection process has been detailed as being carried out using input from an input keypad included in input module 52 provided integrally with the navigation unit 18. However route selection may be carried out using any one of a variety of methods including, but not limited to a temporary or permanent keypad (not shown); a temporary or permanent input pad (not shown); vocal command, whereby the vocal commands are captured by a speech recognition module (not shown) which is in communication with the microprocessor of the navigation unit or by using a touch pad screen (not shown). In another embodiment the input module 52 may incorporate a speech recognition module used either in addition to, or instead of, the keypad. The speech recognition module and the keypad unit may optionally coexist within the same embodiment. Data may also be input into the navigation unit 18 via the wireless module 44 from any compatible wireless device as desired. The microprocessor 34 has also been detailed as determining which direction the input unit 18 is pointing by means of the data received from the digital compass 46. However, it will be understood that the input unit 18 may also include an n-axis accelerometer (not shown) and data from the accelerometer may also be used in helping to determine the direction in which the input unit 18a is facing.
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It will be understood that whilst the RAM memory 40 is detailed as being connected to the microprocessor 34 it could, alternatively, be embedded within the microprocessor 34, with further external RAM memory (not shown) being interfaced to extend the capabilities of the microprocessor 34 in order to support more resource-intensive operations, such as for example speech recognition The amount of RAM required by the navigation unit 10 will depend upon the maximum addressable memory capacity of the microprocessor 34. The microprocessor 34 is complimented by read-only memory (ROM) 36 of a suitable amount, which in this case is Flash RUM but may alternatively be EEPRUM or any suitable RUM type.
The Flash memory RUM 36 can be organised in one or more modules of adequate capacity and whilst details as being connected to the microprocessor 34 via memory controller 38, it may alternatively be formed integrally with the microprocessor 34. The Flash ROM 36 is described as storing relevant navigation software data modules and it will be appreciated that these can be operable to make use of stored or otherwise accessible databases including geographic coordinates such as latitude, longitude, altitude; additional information on locations, points of interest, and other information which may be utilised by the unit and the user to refine the navigation.
Furthermore, whilst the navigation unit 10 is detailed as including a serial bus 48, the navigation unit 18 may usefully be provided with more than one communication interface including, but not limited to, a serial link such as an RS- 232; an USB, mini-USB or micro-USB port or any other suitable communication port, to enable communication and data exchange between the navigation unit 18 and any other suitable device. Such connection capability will provide the navigation unit with a mechanism for expanding the capability of the navigation unit 18, updating the firmware of the navigation unit 18 or performing other navigation system maintenance operations to the navigation unit 18; as well as to provide updates to the software, provide new additional software modules or provide updated maps to the navigation unit 10.
The output unit 54 may be a tactile unit, however, it may alternatively provide an output to a user in any other suitable way, including but not limited to, audio commands and visual commands. Furthermore, the output unit 52 may be provided in the same housing as the other components of the navigation unit 18.
Alternatively, it may be provided in a separate housing which is in communication with the main body of the navigation unit 18, for example, using wire connections or using wireless communications.
In addition, plug-in module 159 has been detailed as a secure digital card which is inserted in a secure digital card slot (not shown). However, it is to be appreciated that the plug in module may be any suitable additional module including, but not limited to, a multi-standard, in which case navigation unit 18 would require an appropriate multi format memory slot.