WO2010081539A1

WO2010081539A1 - Antenna input adaptor device, communications system, portable electronic communications apparatus and method of communicating a radio frequency signal

Info

Publication number: WO2010081539A1
Application number: PCT/EP2009/050366
Authority: WO
Inventors: Theo Kamalski; Henny Verweij
Original assignee: Tomtom International B.V.
Priority date: 2009-01-14
Filing date: 2009-01-14
Publication date: 2010-07-22
Also published as: WO2010081564A1; CN102187584A; TW201027037A

Abstract

An antenna input adaptor device (306) comprises a first Radio Frequency (RF) input (316) for coupling to an antenna (318). The device also comprises a second RF input (322) for coupling to a portable electronic apparatus (200) capable of transmitting an RF signal, and an RF output (326) for coupling to an input of an RF tuner (302). A control unit (340) is also provided and arranged to couple the first RF input (316) to the RF output (326) and decouple the second RF input (322) from the RF output (326) in a first state and to decouple the first RF input (316) from the RF output (326) and couple the second RF input (322) to the RF output (326) in a second state, transition between the first and second states being responsive to the control unit (340).

Description

ANTENNA INPUT ADAPTOR DEVICE. COMMUNICATIONS SYSTEM. PORTABLE

ELECTRONIC COMMUNICATIONS APPARATUS AND METHOD OF

COMMUNICATING A RADIO FREQUENCY SIGNAL

Field of the Invention

The present invention relates to an antenna input adaptor apparatus of the type that, for example, is capable of being located in-line between an antenna and a Radio Frequency tuner, such as a Frequency Modulation radio in a vehicle. The present invention also relates to a communication system of the type that, for example, comprises a Radio Data System communications unit to communicate an audio signal to a Radio Frequency tuner, such as a Frequency Modulation radio in a vehicle. The present invention also relates to a portable electronic communications apparatus of the type that, for example, comprises a Radio Data System communications unit for communicating an audio signal to a Radio Frequency tuner, such as a Frequency Modulation radio in a vehicle. The present invention further relates to a method of communicating a Radio Frequency signal, the method being of the type that, for example, communicates the Radio Frequency signal from a portable electronic apparatus to an external RF tuner, such as a Frequency Modulation radio in a vehicle.

Background to the Invention

Portable computing devices, for example Portable Navigation Devices (PNDs) that include GPS (Global Positioning System) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems. In general terms, a modern PND comprises a processor, memory and map data stored within said memory. The processor and memory cooperate to provide an execution environment in which a software operating system is typically established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the PND to be controlled, and to provide various other functions.

Typically, these devices further comprise one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by means of which information may be relayed to the user. Illustrative examples of output interfaces include a visual display and a speaker for audible output. Illustrative examples of input interfaces include one or more physical buttons to control on/off operation or other features of the device (which buttons need not necessarily be on the device itself but can be on a steering wheel if the device is built into a vehicle), and a microphone for detecting user speech. In one particular arrangement, the output interface display may be configured as a touch sensitive display (by means of a touch sensitive overlay or otherwise) additionally to provide an input interface by means of which a user can operate the device by touch.

Devices of this type will also often include one or more physical connector interfaces by means of which power and optionally data signals can be transmitted to and received from the device, and optionally one or more wireless transmitters/receivers to allow communication over cellular telecommunications and other signal and data networks, for example Bluetooth, Wi-Fi, Wi-Max, GSM, UMTS and the like.

PNDs of this type also include a GPS antenna by means of which satellite- broadcast signals, including location data, can be received and subsequently processed to determine a current location of the device.

The PND may also include electronic gyroscopes and accelerometers which produce signals that can be processed to determine the current angular and linear acceleration, and in turn, and in conjunction with location information derived from the GPS signal, velocity and relative displacement of the device and thus the vehicle in which it is mounted. Typically, such features are most commonly provided in in-vehicle navigation systems, but may also be provided in PNDs if it is expedient to do so. The utility of such PNDs is manifested primarily in their ability to determine a route between a first location (typically a start or current location) and a second location (typically a destination). These locations can be input by a user of the device, by any of a wide variety of different methods, for example by postcode, street name and house number, previously stored "well known" destinations (such as famous locations, municipal locations (such as sports grounds or swimming baths) or other points of interest), and favourite or recently visited destinations.

Typically, the PND is enabled by software for computing a "best" or "optimum" route between the start and destination address locations from the map data. A "best" or "optimum" route is determined on the basis of predetermined criteria and need not necessarily be the fastest or shortest route. The selection of the route along which to guide the driver can be very sophisticated, and the selected route may take into account existing, predicted and dynamically and/or wirelessly received traffic and road information, historical information about road speeds, and the driver's own preferences for the factors determining road choice (for example the driver may specify that the route should not include motorways or toll roads).

The device may continually monitor road and traffic conditions, and offer to or choose to change the route over which the remainder of the journey is to be made due to changed conditions. Real time traffic monitoring systems, based on various technologies (e.g. mobile phone data exchanges, fixed cameras, GPS fleet tracking), are being used to identify traffic delays and to feed the information into notification systems. PNDs of this type may typically be mounted on the dashboard or windscreen of a vehicle, but may also be formed as part of an on-board computer of the vehicle radio or indeed as part of the control system of the vehicle itself. The navigation device may also be part of a hand-held system, such as a PDA (Portable Digital Assistant), a media player, a mobile telephone or the like, and in these cases, the normal functionality of the hand-held system is extended by means of the installation of software on the device to perform both route calculation and navigation along a calculated route.

Route planning and navigation functionality may also be provided by a desktop or mobile computing resource running appropriate software. For example, the Royal Automobile Club (RAC) provides an on-line route planning and navigation facility at http://www.rac.co.uk, which facility allows a user to enter a start point and a destination whereupon the server with which the user's computing resource is communicating calculates a route (aspects of which may be user specified), generates a map, and generates a set of exhaustive navigation instructions for guiding the user from the selected start point to the selected destination. The facility also provides for pseudo three-dimensional rendering of a calculated route, and route preview functionality which simulates a user travelling along the route and thereby provides the user with a preview of the calculated route.

In the context of a PND, once a route has been calculated, the user interacts with the navigation device to select the desired calculated route, optionally from a list of proposed routes. Optionally, the user may intervene in, or guide the route selection process, for example by specifying that certain routes, roads, locations or criteria are to be avoided or are mandatory for a particular journey. The route calculation aspect of the PND forms one primary function, and navigation along such a route is another primary function. During navigation along a calculated route, it is usual for such PNDs to provide visual and/or audible instructions to guide the user along a chosen route to the end of that route, i.e. the desired destination. It is also usual for PNDs to display map information on-screen during the navigation, such information regularly being updated on-screen so that the map information displayed is representative of the current location of the device, and thus of the user or user's vehicle if the device is being used for in- vehicle navigation. An icon displayed on-screen typically denotes the current device location, and is centred with the map information of current and surrounding roads in the vicinity of the current device location and other map features also being displayed. Additionally, navigation information may be displayed, optionally in a status bar above, below or to one side of the displayed map information, examples of navigation information include a distance to the next deviation from the current road required to be taken by the user, the nature of that deviation possibly being represented by a further icon suggestive of the particular type of deviation, for example a left or right turn. The navigation function also determines the content, duration and timing of audible instructions by means of which the user can be guided along the route. As can be appreciated, a simple instruction such as "turn left in 100 m" requires significant processing and analysis. As previously mentioned, user interaction with the device may be by a touch screen, or additionally or alternately by steering column mounted remote control, by voice activation or by any other suitable method. A further important function provided by the device is automatic route recalculation in the event that: a user deviates from the previously calculated route during navigation (either by accident or intentionally); real-time traffic conditions dictate that an alternative route would be more expedient and the device is suitably enabled to recognize such conditions automatically, or if a user actively causes the device to perform route re-calculation for any reason.

As mentioned above, it is also known to allow a route to be calculated with user defined criteria; for example, the user may prefer a scenic route to be calculated by the device, or may wish to avoid any roads on which traffic congestion is likely, expected or currently prevailing. The device software would then calculate various routes and weigh more favourably those that include along their route the highest number of points of interest (known as POIs) tagged as being for example of scenic beauty, or, using stored information indicative of prevailing traffic conditions on particular roads, order the calculated routes in terms of a level of likely congestion or delay on account thereof. Other POI-based and traffic information-based route calculation and navigation criteria are also possible.

Although the route calculation and navigation functions are fundamental to the overall utility of PNDs, it is possible to use the device purely for information display, or "free-driving", in which only map information relevant to the current device location is displayed, and in which no route has been calculated and no navigation is currently being performed by the device. Such a mode of operation is often applicable when the user already knows the route along which it is desired to travel and does not require navigation assistance.

Devices of the type described above, for example the GO 920 Traffic model manufactured and supplied by TomTom International B. V., provide a reliable means for enabling users to navigate from one position to another. Such devices are of great utility when the user is not familiar with the route to the destination to which they are navigating.

In order to facilitate in-vehicle use of the PND, some PNDs are equipped with a Frequency Modulation (FM) transmitter, for example the GO 920 model PND. Instead of amplified audio signals being reproduced by a loudspeaker of the PND, the FM transmitter frequency modulates and transmits the audio signals on a user-selectable frequency. When in a vehicle, a user of the PND tunes an FM radio located in the vehicle to the user-selected frequency so that the FM radio receives the frequency modulated audio signal, demodulates the frequency modulated audio signal and reproduces the audio signal through loudspeakers coupled to the FM radio. Of course, the FM radio can be part of an in-vehicle entertainment system capable of FM reception and including a Compact Disc (CD) multi-changer and other facilities.

It should be noted that it is desirable to use the loudspeakers of in-vehicle entertainment systems via FM transmission for other types of portable device, for example so-called MP3 players and/or mobile telephones. Indeed, it is known for such other portable devices to possess so-called Short-Range Radio (SRR) FM transmitters to transmit audio to FM receivers.

However, transmission of audio using the SRR transmitter suffers from a number of disadvantages. One disadvantage is the limited transmission power of the SRR FM transmitter that can sometimes result in poor audio quality being experienced by a user. The poor audio quality is exacerbated by a so-called Faraday cage effect created by metallic vehicle bodywork and metal coatings used in relation to vehicle windows. Indeed, the poor audio quality can, in part, manifest itself as poor stereo reproduction. In this respect, a poor received field intensity of an RF signal leads to low channel separation and hence only monophonic or low-quality stereo sound reproduction. Additionally, the number of available FM channels that are free at any given time for use by the SRR is limited and location dependent. The FM channel "landscape", i.e. those FM channels in an FM spectrum that are in use and available for use, changes with location as different frequencies are used for broadcasts in different geographic locations. Hence, when the SRR is moving from one geographic area to another geographic area, for example when the SRR is disposed within a vehicle that is travelling between cities, some of the relatively small number of available FM channels cease to be remain available and other unavailable FM channels, previously in use, become available. This is a function of FM spectrum usage in different the geographic areas. Consequently, the SRR has to be re-tuned regularly as the frequency landscape changes. A further problem encountered in relation to the SRR is when one SRR is located in relatively close proximity to another SRR, for example when two PNDs actively employing respective SRRs are waiting in respective vehicles at a set of traffic lights. In such circumstances, the SRRs can serve as sources of interference for one another. In a particularly disadvantageous situation, audio navigation instructions transmitted by an SRR of one PND in a first vehicle is received by an FM tuner in a neighbouring vehicle, resulting in the driver of the neighbouring vehicle following navigation instructions of a neighbouring PND and not the PND located in the vehicle where the instructions are heard. In this respect, such interference can easily occur when two vehicles are waiting at traffic lights as mentioned above, the incorrect instructions leading to, for example, one vehicle taking a turn at the traffic lights instead of proceeding ahead. This type of problem is partly due to the restricted number of available FM channels as mentioned above, leading to a higher probability of two neighbouring SRRs transmitting on the same FM channel. Furthermore, the problem use of the same FM channel only increases as the number of devices employing SRRs increases. In order to mitigate such problems, it is known for the portable device to employ an additional tuner to search for available FM channels. Advantage is taken of Radio Data System (RDS) capabilities possessed by many in-vehicle entertainment systems, for example RDS FM radios. On an available channel, a portable device equipped with an RDS encoder transmits, inter alia, a Programme Identification (Pl) code, a Programme Service (PS) name (for example, "TomTom") and a list of Alternative Frequencies (AFs), the available channel and the list of AFs being selected from free channels detected amongst the FM landscape of channels in which the portable device is operating. The portable device also typically transmits an audio test message on the same available channel. The formation and transmission of the Pl code, the PS name and the list of AFs are in accordance with the RDS technical specification set out by the International Electrotechnical Commission (IEC).

AFs are usually used by broadcasters to identify their respective broadcast networks. A transmitted list of AFs indicates frequencies of adjacent transmitters associated with a same radio programme as a transmitter currently being received. FM radios in vehicles use the list of AFs to select and remain tuned to a transmitter with a best signal strength associated with the same network. The FM radios store the list of AFs received from the transmitter and update the list of AFs each time the FM radios tune to a different transmitter in the network. However, in the context of SRR transmitters, the AF feature can be used by the PND to enable use of different frequencies so as to avoid interference both with mainstream broadcasters and other SRR transmissions.

In the vehicle, for example, the user sets the FM radio to scan for an FM transmission from the portable device and identified by the RDS information transmitted by the portable device. When the transmission by the portable device has been found by the FM radio, the frequency modulated audio signal transmitted by the portable device, typically the audio test message, is reproduced by the loudspeakers of the FM radio and a display of the FM radio displays the PS name, namely "TomTom" in this example.

Whilst employing RDS functionality in conjunction with the SRR can reduce coincidence of FM channel usage, the basic problem of poor audio quality reproduction is not necessarily solved. Indeed, it can be argued that use of the RDS in relation to SRR transmission actually reduces system performance, because the RDS implementation described above typically requires the provision of an integrated transmitter and receiver that cannot be simultaneously active. In this regard, when frequency band scans or signal strength measurements are performed, the transmitter does not transmit whilst the receiver is active. Hence, a communications link between the SRR and the FM radio is interrupted, which can result in strong audio "noise" being heard by the user of the FM radio and disruption of listening, for example music and/or navigation instructions.

Unfortunately, regular frequency band scans need to be performed in order for the PND or other portable device to operate properly in a continuously changing FM channel landscape without intervention from the user. Furthermore, shortening the frequency band scans and performing multiple shorter band scans that, together, cover the FM spectrum of frequencies so as to avoid the noticeable interruption caused by a single long band scan of the FM spectrum has, in fact, an opposite effect, because switching times of current SRR chipsets are too slow, resulting in the mere act of deactivating the transmitter and activating the receiver being noticeable and this is before any measurements even take place.

Summary of the Invention

According to a first aspect of the present invention, there is provided an antenna input adaptor device comprising: a first Radio Frequency (RF) input for coupling to an antenna; a second RF input for coupling to a portable electronic apparatus capable of transmitting an RF signal; an RF output for coupling to an input of an RF tuner; and a control unit; wherein the control unit is arranged to couple the first RF input to the RF output and decouple the second RF input from the RF output in a first state and to decouple the first RF input from the RF output and couple the second RF input to the RF output in a second state, transition between the first and second states being responsive to the control unit.

The control unit may be arranged to couple the first RF input to ground potential in the second state. Coupling the first RF input to the ground potential may attenuate, when in use, RF signals received via the antenna. The control unit may be arranged to receive, when in use, a control signal and to execute a transition between the first and second states in response to the control signal.

The control signal may be received from the portable electronic apparatus. The

RF signal transmitted by the portable electronic apparatus may constitute the control signal. The control unit may be arranged to detect the RF signal from the portable electronic apparatus.

A plurality of RF signals within a range of frequencies associated with a

Frequency Modulation (FM) spectrum received, when in use, at the first RF input may be received by the RF tuner in attenuated form when in the second state. The device may further comprise: a first switching unit coupled between the first

RF input and the RF output; and a second switching unit may be coupled between the second RF input and the RF output.

The device may further comprise: an antenna switching unit coupled between the first RF input and the ground potential. The second RF input may be arranged to receive a wired connection for receiving the RF signal from the portable electronic apparatus.

According to a second aspect of the present invention, there is provided a communications system comprising: an antenna; an antenna input adaptor device as set forth above in relation to the first aspect of the invention, the antenna being coupled to the first RF input of the antenna input adaptor device; wherein the portable electronic apparatus comprises an RDS communications unit, the RDS communications unit being coupled to the second RF input of the antenna input adaptor device.

The RDS communications unit may be coupled to the second RF input by a wired connection. The portable electronic apparatus may be arranged to store a plurality of

Alternative Frequency (AF) frequencies; the AF frequencies may be substantially uniformly spaced across a Frequency Modulation (FM) spectrum range of frequencies.

The portable electronic apparatus may be arranged to store a plurality of Alternative Frequency (AF) frequencies; the AF frequencies may be substantially randomly spaced across a Frequency Modulation (FM) spectrum range of frequencies. The RDS communications unit may be arranged to perform scans in respect of each of the plurality of AF frequencies. Each scan in respect of an AF frequency of the plurality of AF frequencies may comprise sweeping a range of frequencies about the AF frequency.

The RDS communications unit may be arranged to identify any AF frequencies already in use and to prevent use of the any AF frequencies identified in respect of future re-tuning.

The FM communications unit may be arranged to re-tune to another frequency from a tuned frequency in response to detection of the tuned frequency being used by a transmission source other than the portable electronic apparatus; the another frequency may be one of the plurality of AF frequencies.

The tuned frequency may be used by a radio broadcast station.

The one of the plurality of AF frequencies may be an available AF frequency not prevented from being used by the RDS communications unit.

According to a third aspect of the present invention, there is provided a portable electronic communications apparatus comprising: a Radio Data System (RDS) communication unit for communicating an audio signal to an external RF tuner; wherein the RDS communications unit is arranged to generate, when in use, a Radio Frequency (RF) antenna switching signal for triggering attenuation of RF signals wirelessly received by the external RF tuner via an antenna. The RDS communication unit may be arranged to communicate the audio signal to the external RF tuner following triggering of attenuation of the RF signals. The RDS communications unit may be arranged communicate the audio signal via a wired communications port thereof for coupling a connecting lead thereto.

The apparatus may further comprise a data store arranged to store a plurality of Alternative Frequency (AF) frequencies and to initiate a scan in respect of each of the plurality of AF frequencies in order to determine availability of the each of the plurality of AF frequencies.

The plurality of AF frequencies may be substantially uniformly spaced across a Frequency Modulation (FM) spectrum range of frequencies. The plurality of AF frequencies may be substantially randomly spaced across a

Frequency Modulation (FM) spectrum range of frequencies. Each scan in respect of an AF frequency of the plurality of AF frequencies may comprise sweeping a range of frequencies about the AF frequency in order to determine whether the AF frequency is available for transmission thereon.

The RDS Communications unit may be arranged to select one of the AF frequencies of the plurality of AF frequencies determined as available for transmission thereon.

The RDS Communications unit may be arranged to identify an AF frequency already in use and to prevent use of the AF frequency identified in respect of future re- tuning. The RDS Communications unit may comprise a Traffic Message Channel (TMC) receiver; the TMC receiver may be arranged to perform the scan in respect of the each of the plurality of AF frequencies in order to determine availability of the each of the plurality of AF frequencies.

The TMC receiver may be arranged to perform the scan during empty time slots of a TMC broadcast, for example when a time slot may not comprise TMC content.

According to a fourth aspect of the present invention, there is provided a portable navigation device comprising the portable electronic communications apparatus as set forth above in relation to the third aspect of the invention.

According to a fifth aspect of the present invention, there is provided a method of communicating a Radio Frequency (RF) signal from a portable electronic apparatus to an external RF tuner, the method comprising: the portable electronic apparatus issuing an RF antenna switching signal; attenuating any RF signals to be wirelessly received by the RF tuner via an antenna in response to the RF antenna switching signal.

According to a sixth aspect of the present invention, there is provided a computer program element comprising computer program code means to make a computer execute the method as set forth above in relation to the fifth aspect of the invention.

The computer program element may be embodied on a computer readable medium.

It is thus possible to provide an antenna input adaptor device, communications system, portable electronic communications apparatus and method of communicating a radio frequency signal that enable audio information to be reproduced by a Frequency

Modulation (FM) tuner, for example disposed in a vehicle, with improved quality as a result of suppression of other external sources of RF signals received via an antenna otherwise coupled to the FM tuner. Consistent stereo reproduction can therefore be achieved. Indeed, due to a difference in signal strength difference between the RF signal of the portable electronic communications apparatus and the attenuated RF signals, an Automatic Gain Control (AGC) of the FM tuner serves to further attenuate the RF signals already attenuated by the antenna input adaptor device to an even lower level. Additionally, the need to re-tune is reduced and a greater number of FM channels are available when re-tuning is necessary. Hence less manual re-tuning is required, thereby reducing driver workload and hence improving safe use of the portable electronic communications apparatus and/or the FM tuner. Furthermore, when frequency band scans are required, the frequency band scan is faster and thus reduces interruption time during scanning. Consequently, the user experience is improved as potentially annoying interruptions to listening are reduced in frequency and duration and the possibility of missing, for example, audible navigation instructions is thus also minimised. Hence, the user is less likely to deviate from a calculated route being followed. The ability to prevent deviation by a driver from the route being followed not only reduces inconvenience to the user, but also improves safety whilst driving.

Other advantages of these embodiments are set out hereafter, and further details and features of each of these embodiments are defined in the accompanying dependent claims and elsewhere in the following detailed description.

Brief Description of the Drawings

At least one embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic illustration of an exemplary part of a Global Positioning System (GPS) usable by a navigation apparatus;

Figure 2 is a schematic diagram of electronic components of a navigation apparatus constituting an embodiment of the invention; Figure 3 is a schematic diagram of a part of Figure 2 coupled to a communications unit;

Figure 4 is a schematic representation of an architectural stack employed by the navigation apparatus of Figure 2;

Figure 5 is a schematic diagram of the navigation apparatus of Figure 2 when located in a vehicle;

Figure 6 is a schematic diagram of a docking arrangement for optional use in the vehicle of Figure 5;

Figure 7 is a schematic diagram of connectivity between an FM tuner, the navigation apparatus and an antenna input adaptor of Figure 5; Figure 8 is a schematic diagram of the antenna input adaptor of Figures 5 and 7 in greater detail; Figure 9 is a flow diagram of a method of communicating a radio-frequency signal using the navigation apparatus of Figure 2;

Figures 10 to 15 are screen shots from a display of the navigation apparatus following the method of Figure 9; Figure 16 is a graph of FM spectrum usage when employing the antenna input adaptor of Figures 5, 7, and 8;

Figure 17 is a flow diagram of a method of re-tuning a receiver;

Figure 18 is a graph of Frequency Modulation (FM) spectrum usage when employing the antenna input adaptor of Figures 5, 7, and 8 in the vicinity of an FM transmitter tower; and

Figure 19 is a flow diagram of a response by the receiver to the method of Figure 17

Detailed Description of Preferred Embodiments Throughout the following description identical reference numerals will be used to identify like parts.

One or more embodiments of the present invention will now be described with particular reference to a PND. It should be remembered, however, that the teachings herein are not limited to PNDs but are instead universally applicable to any type of processing device, for example but not essentially those configured to execute navigation software in a portable and/or mobile manner so as to provide route planning and navigation functionality. It follows therefore that in the context of the embodiments set forth herein, a navigation apparatus is intended to include (without limitation) any type of route planning and navigation apparatus, irrespective of whether that device is embodied as a PND, a vehicle such as an automobile, or indeed a portable computing resource, for example a portable personal computer (PC), a mobile telephone or a Personal Digital Assistant (PDA) executing, for example, route planning and navigation software. Indeed, a mobile telephone, smartphone, a music player, such as an MP3 player, or the like can simply be employed in respect of some embodiments without the benefit of route planning or navigation software.

With the above provisos in mind, the Global Positioning System (GPS) of Figure 1 and the like are used for a variety of purposes. In general, the GPS is a satellite-radio based navigation system capable of determining continuous position, velocity, time, and in some instances direction information for an unlimited number of users. Formerly known as NAVSTAR, the GPS incorporates a plurality of satellites which orbit the earth in extremely precise orbits. Based on these precise orbits, GPS satellites can relay their location to any number of receiving units.

The GPS system is implemented when a device, specially equipped to receive GPS data, begins scanning radio frequencies for GPS satellite signals. Upon receiving a radio signal from a GPS satellite, the device determines the precise location of that satellite via one of a plurality of different conventional methods. The device will continue scanning, in most instances, for signals until it has acquired at least three different satellite signals (noting that position is not normally, but can be determined, with only two signals using other triangulation techniques). Implementing geometric triangulation, the receiver utilizes the three known positions to determine its own two-dimensional position relative to the satellites. This can be done in a known manner. Additionally, acquiring a fourth satellite signal allows the receiving device to calculate its three dimensional position by the same geometrical calculation in a known manner. The position and velocity data can be updated in real time on a continuous basis by an unlimited number of users. As shown in Figure 1 , the GPS system 100 comprises a plurality of satellites 102 orbiting about the earth 104. A GPS receiver 106 receives spread spectrum GPS satellite data signals 108 from a number of the plurality of satellites 102. The spread spectrum data signals 108 are continuously transmitted from each satellite 102, the spread spectrum data signals 108 transmitted each comprise a data stream including information identifying a particular satellite 102 from which the data stream originates. The GPS receiver 106 generally requires spread spectrum data signals 108 from at least three satellites 102 in order to be able to calculate a two-dimensional position. Receipt of a fourth spread spectrum data signal enables the GPS receiver 106 to calculate, using a known technique, a three-dimensional position. Referring to Figure 2, it should be noted that the block diagram of the navigation apparatus 200 is not inclusive of all components of the navigation apparatus, but is only representative of many example components. The navigation apparatus 200 is located within a housing (not shown). The navigation apparatus 200 includes a processor 202, the processor 202 being coupled to an input device 204 and a display device, for example a display screen 206. Although reference is made here to the input device 204 in the singular, the skilled person should appreciate that the input device 204 represents any number of input devices, including a keyboard device, voice input device, touch panel and/or any other known input device utilised to input information. Likewise, the display screen 206 can include any type of display screen such as a Liquid Crystal Display (LCD), for example.

In one arrangement, one aspect of the input device 204, the touch panel, and the display screen 206 are integrated so as to provide an integrated input and display device, including a touchpad or touchscreen input 310 (Figure 6) to enable both input of information (via direct input, menu selection, etc.) and display of information through the touch panel screen so that a user need only touch a portion of the display screen 206 to select one of a plurality of display choices or to activate one of a plurality of virtual or "soft" buttons. In this respect, the processor 202 supports a Graphical User Interface (GUI) that operates in conjunction with the touchscreen.

In the navigation apparatus 200, the processor 202 is operatively connected to and capable of receiving input information from input device 204 via a connection 210, and operatively connected to at least one of the display screen 206 and an output device 208, via respective output connections 212, to output information thereto. The output device 208 is, for example, an audible output device (e.g. including a loudspeaker). As the output device 208 can produce audible information for a user of the navigation apparatus 200, it should equally be understood that input device 204 can include a microphone and software for receiving input voice commands as well. Further, the navigation apparatus 200 can also include any additional input device 204 and/or any additional output device, such as audio input/output devices for example. The processor 202 is operably coupled to a memory resource 214 via connection 216 and is further adapted to receive/send information from/to input/output (I/O) ports 218 via connection 220, wherein the I/O port 218 is connectible to an I/O device 222 external to the navigation apparatus 200. The memory resource 214 comprises, for example, a volatile memory, such as a Random Access Memory (RAM) and a non-volatile memory, for example a digital memory, such as a flash memory. The external I/O device 222 may include, but is not limited to an external listening device, such as an earpiece for example. The connection to I/O device 222 can further be a wired or wireless connection to any other external device such as a car stereo unit for hands-free operation and/or for voice activated operation for example, for connection to an earpiece or headphones.

Figure 2 further illustrates an operative connection between the processor 202 and an antenna/receiver 224 via connection 226, wherein the antenna/receiver 224 can be a GPS antenna/receiver for example. It should be understood that the antenna and receiver designated by reference numeral 224 are combined schematically for illustration, but that the antenna and receiver may be separately located components, and that the antenna may be a GPS patch antenna or helical antenna for example. In order to support the functionality described herein, the processor 202 is also coupled to a Frequency Modulation (FM) port 228. It will, of course, be understood by one of ordinary skill in the art that the electronic components shown in Figure 2 are powered by one or more power sources (not shown) in a conventional manner. As will be understood by one of ordinary skill in the art, different configurations of the components shown in Figure 2 are contemplated. For example, the components shown in Figure 2 may be in communication with one another via wired and/or wireless connections and the like. Thus, the navigation apparatus 200 described herein can be a portable or handheld navigation apparatus 200.

Turning to Figure 3, the processor 202 is capable of communicating via the FM port 228 with a Radio Data System (RDS) communications unit 254. The RDS communications unit 254 comprises an RDS encoder 256 and communications circuitry to transmit both audio and RDS data in accordance with the RDS technical specification, for example as described in the IEC/CENELEC EN 62106 specification for RDS. As RDS communications units are know in the art, further detailed description of the structure of the RDS communications unit 254 will not be provided herein for the sake of clarity and conciseness of description. However, it should be appreciated that the RDS communications unit 254 includes an FM transmitter (not shown), an FM receiver (not shown) and a Traffic Message Channel (TMC) receiver (not shown) coupled to an RDS output port 258 that supports a wired connection to the RDS communications unit 254. Turning to Figure 4, the memory resource 214 stores a boot loader program (not shown) that is executed by the processor 202 in order to load an operating system 262 from the memory resource 214 for execution by functional hardware components 260, which provides an environment in which application software 264 can run. The operating system 262 serves to control the functional hardware components 260 and resides between the application software 264 and the functional hardware components 260. The application software 264 provides an operational environment including the GUI that supports core functions of the navigation apparatus 200, for example map viewing, route planning, navigation functions and any other functions associated therewith. Referring to Figure 5, in the following examples, the navigation apparatus 200 is to be used in a vehicle, for example an automobile 300 having an in-vehicle entertainment system, for example an audio entertainment system, such as an FM radio 302 or tuner having an FM receiver (not shown) therein and a display 303. The FM radio 302 is coupled to a loudspeaker system 304. However, the skilled person should appreciate that the navigation apparatus 200 can be deployed in other environments where an RDS capable FM receiver exists that is coupled to one or more loudspeakers, the use of the loudspeakers being desired for audio output of audio signals originating from another device or apparatus. The navigation apparatus 200 is, in this example, coupled to an antenna input adaptor device 306, the antenna input adaptor 306 being coupled in-line between the FM tuner 302 and an antenna (not shown). To facilitate use thereof, the portable or handheld navigation apparatus 200 of Figure 2 can be connected or "docked" in a known manner to the automobile 300, or any other suitable vehicle, for example a bicycle, a motorbike, a car or a boat. The navigation apparatus 200 is then removable from the docked location for portable or handheld navigation use. In this respect (Figure 6), the navigation apparatus 200 may be a unit that includes the integrated input and display device 310 and the other components of Figure 2 (including, but not limited to, the internal GPS receiver 224, the microprocessor 202, a power supply (not shown), memory resource 214, etc.).

The navigation apparatus 200 may sit on an arm 312, which itself may be secured to a vehicle dashboard/window/etc, using a suction cup 314. This arm 312 is one example of a docking station to which the navigation apparatus 200 can be docked. The navigation apparatus 200 can be docked or otherwise connected to the arm 312 of the docking station by snap connecting the navigation apparatus 200 to the arm 312 for example. The navigation apparatus 200 may then be rotatable on the arm 312. To release the connection between the navigation apparatus 200 and the docking station, a button (not shown) on the navigation apparatus 200 may be pressed, for example. Other equally suitable arrangements for coupling and decoupling the navigation apparatus 200 to a docking station are well known to persons of ordinary skill in the art.

Turning to Figure 7, a first input port 316 of the antenna input adaptor 306 is coupled to the antenna 318 by an antenna cable 320. A second input port 322 of the antenna input adaptor 306 is coupled to the RDS output port 258 of the navigation apparatus 200 by a wired connection, for example, a first antenna patch lead 324. An output port 326 of the antenna input adaptor 306 is coupled to an antenna input port 328 of the FM tuner 302 by a second antenna patch lead 330.

Referring to Figure 8, the first input port 316 of the antenna input adaptor 306 is coupled to the output port 326 thereof via a first switching unit 332. The first input port 316 is also coupled to a ground potential 334 an antenna switching unit 336. The output port 326 of the antenna input adaptor 306 is also coupled to the second input port 322 thereof via a second switching unit 338. The antenna input adaptor 306 also comprises a control unit 340, the control unit 340 being coupled to the second input port 322 of the antenna input adaptor 306. In this example, the control unit 340 is also coupled to the first switching unit 336, the antenna switching unit 336 and the second switching unit 338 in order to be able to operate selectively the first switching unit 332, the antenna switching unit 336 and the second switching unit 338.

In this example, the first switching unit 332, the antenna switching unit 336 and the second switching unit 338 are any suitable switching devices, for example RF attenuators, Field Effect Transistors (FETs) or any other compatible solid state switching device. Indeed, the types of devices employed for the first switching unit 332, the antenna switching unit 336 and the second switching unit 338 can be a combination of different types of switching devices if it is expedient to make such a combination for a given application. Although, in this example, the antenna input adaptor 306 is described as an external device, the skilled person should appreciate that the antenna input adaptor 306 can be provided as an internal module in, for example, the FM tuner 302 or the navigation apparatus 200. In such embodiments, it should be understood that the antenna input adaptor module nevertheless still serves to adapt an antenna input port of an FM tuner that would, otherwise, be directly coupled to the antenna 318 without an ability to selectively decouple the antenna 318 from the FM tuner 302 in an automated manner.

In operation (Figure 9), it is assumed, for the sake of conciseness of description, that the antenna input adaptor 306 is already disposed in the automobile 300 and the first input port 316 of the antenna input adaptor 306 is coupled to the antenna 318 and the output port 326 is coupled to the FM tuner 302 in the manner already described above. Furthermore, in a default first state, the control unit 340 sets the first switching unit 332 to permit electrical coupling of the first input port 316 to the output port 326 of the antenna input adaptor 306. In the first state, the control unit 340 also sets the antenna switching unit 336 to decouple the first input port 316 and hence the antenna 318 from the ground potential 334 and sets the second switching unit 338 to decouple the second input port 322 and hence the navigation apparatus 200 from the output port 326 of the antenna input adaptor 306.

In this example, a user of the navigation apparatus 200 wishes to drive to an office from home using traffic avoidance functionality of the navigation apparatus 200. After entering the automobile 300, the user couples the RDS output port 258 of the navigation apparatus 200 to the second input port 322 of the antenna input adaptor 306 using the first antenna patch lead 324 to complete the configuration already described above in relation to Figure 7. The user then powers-up (Step 400) the navigation apparatus 200 (Figure 10) and touches the touchscreen display 310 in order to access a menu structure supported by the GUI (Step 402). The user then selects (Step 404) the "Change preferences" menu option 350 (Figure 1 1 ) and then negotiates the menu structure (Step 406) to reach a "Speaker preferences" menu option 352 (Figure 12). Upon selecting the speaker preferences menu option 352, the GUI displays a first screen of speaker preference options 354 (Figure 13) in respect of audible instructions provided by the navigation apparatus 200. In this example, the user wishes the audible instructions to be played through the loudspeakers 304 in the automobile 300 and so selects (Step 408) an "FM to your car radio" option 356. The user then presses a "Done" soft button 358 to indicate that a final selection has been made and the GUI then displays a second screen of speaker preference options 360 (Figure 14) in respect of music provided by or via the navigation apparatus 200. In this example, it is possible to couple an electronic music player to the navigation apparatus 200 in order to permit play of music through the navigation apparatus 200, either through an internal speaker of the navigation apparatus 200 or another external output device. For the sake of simplicity, this example assumes that no music player or other source of audio signals is coupled to the navigation apparatus 200. However, the skilled person will appreciate that the principles described herein in relation to play of the navigation instructions through the loudspeakers 304 of the FM radio 302 are applicable to the option of use of the loudspeakers 304 in relation to other sources of audio signals. As a consequence of the above assumption, the user does not modify any options presented on the second screen of speaker preference options 360 in respect of music and simply presses another "Done" soft key 362.

Thereafter, the RDS communications unit 254 can generate (Step 409) a trigger or control signal that is communicated to the antenna input adaptor 306 via the first antenna patch lead 324 and detected by the control unit 340 by virtue of the coupling of the control unit 340 to the second input port 322. However, in this example an RF signal used to communicate the audio information constitutes the control signal. In response to receipt of the trigger signal, circuitry of the control unit 340 transitions the antenna input adaptor 306 into a second state by setting the first switching unit 332 so as to decouple the first input port 316 from the output port 326 of the antenna input adaptor 306. In the second state, the control unit 340 also sets the antenna switching unit 336 to couple the first input port 316, and thus the antenna 318, to the ground potential 334 and sets the second switching unit 338 to couple the second input port 322 to the output port 326 of the antenna input adaptor 306 in place of the first input port 316.

The processor 202 in cooperation with the RDS communications unit 254 then scans (Step 410) a frequency band or range allocated for FM radio broadcast and identifies a plurality of available frequencies that are not occupied by other broadcasters and so can serve as a frequency to which the FM receiver or the radio 302 can be tuned and a respective plurality of Alternative Frequencies (AFs). The processor 202 then selects (Step 412) a number of AFs from the plurality of AFs, the selected number of the AFs being stored by the memory resource 214 (although a memory resource of the RDS communications unit 254 can be used). In this respect, it is known that a typically memory allocation made in respect of FM receivers is for storage of 25 AFs, which is consistent with the number of Alternative Frequencies that can be transmitted relating to the Pl code using the type OA message set out in the RDS technical specification. Optionally, in order to avoid filling the memories of receivers, for example of the FM radio 302, the processor 202 caps the number of AFs selected to a predetermined maximum quantity of AFs that is less than the capacity of the typical memory capacity of receivers, for example by a margin of entries. For example, the number of AFs selected can be less than 25, such as about 20. Once the number of AFs has been selected from the plurality of AFs identified, the RDS communications unit 254 of the navigation apparatus 200 tunes to the tuned frequency selected above and transmits (Step 414) first RDS data, for example type OA groups, comprising a list of the selected AFs. Of course, the RDS communications unit 254 transmits other RDS data, for example a Programme Identification code and the Programme Service name ("TomTom") associated with the tuned frequency. In this example, the Programme Identification code can be generated in accordance with the technique proposed by the RDS Forum for portable electronic apparatus known to those skilled in the art. Furthermore, the list of AFs is usually communicated over a series of messages or groups.

The GUI then passes to an instruction screen (Figure 15), which instructs the user to tune the FM radio 302, in the present example located in the automobile 300, to a channel identified by the Programme Service name "TomTom". The user therefore sets the FM radio 302 to scan for stations (Step 416), RDS capabilities of the FM radio 302 enabling the name of each station detected to be presented by the display 303 of the FM radio 302.

The scanning procedure therefore eventually results in the FM radio 302 being tuned to the TomTom "channel", the frequency associated with the TomTom channel being the tuned frequency. The first RDS data, for example the type OA group comprising the list of selected AFs, is also received in respect of the tuned frequency. As part of the tuning process, the FM radio 302 stores the selected AFs received in a respective space allocated in the memory (not shown) thereof reserved for a channel being received.

Once the FM radio 302 has acquired the "TomTom" broadcast, the user presses a further "Done" soft key 364 (Figure 15) and the GUI responds by returning (Step 418) to a map display screen (Figure 10).

Once the FM radio 302 has been tuned to the TomTom channel, audio signals transmitted by the navigation apparatus 200, for example navigation instructions, are reproduced by the loudspeakers 304 once, for example, a route has been set or an instruction provided to avoid traffic by a user of the navigation apparatus 200. In this respect, the RF signal associated with the audio information is communicated from the navigation apparatus 200 to the FM radio 312 via a wired connection formatted by the first and second antenna patch leads 324, 330 and the antenna input adaptor 306. Whilst, in the above example, the RDS communications unit 254 has searched for the plurality of available frequencies, for example all available frequencies, the skilled person should appreciate that only the number of AFs required can be identified for communication during the scanning process carried out by the navigation apparatus 200 without identifying all available frequencies or more than are required. For example, the processor 202 can simply select the first AFs encountered whilst scanning and stop once sufficient AFs have been found to comply with the cap implemented.

Turning to Figure 16, it can be seen that the coupling of the antenna 318 to the ground potential 334 serves to suppress or attenuate RF signals received by the FM radio 302 via the antenna 318. Indeed, attenuation can be achieved by simply decoupling the antenna 318 from the output port 326 of the antenna input adaptor 306 and hence the FM radio 302 without coupling to the ground potential 334. However, the degree of attenuation is improved when the antenna 318 is coupled to the ground potential 334. As can be seen from Figure 16, RF signals usually received on FM channels with associated strong signal strengths are attenuated, thereby providing channel "headroom", i.e. FM channels are "cleared" of RF signals from the receiving perspective of the navigation apparatus 200 and the FM radio 302, thus providing a greater number of available channels for use in the process of communicating audio information from the navigation apparatus 200 to the FM radio 302. In this respect, usually RF signals of strong signal strengths are attenuated to a level whereby they are no longer significant interference sources. Furthermore, due to the wired connection between the navigation apparatus 200 and the FM radio 302, the received signal strength associated with the TomTom channel 372 is high and a substantial margin exists between the received signal strengths of the TomTom channel 372 and the other FM channels received via the antenna 318. Indeed, further attenuation is also achieved where the FM radio 302 employs Automatic Gain Control (AGC) in order to attenuate the RF signal associated with the TomTom channel 372, thereby also attenuating the usually good, but unwanted, received RF signals mentioned above further still. Of course, even better attenuation can be achieved where the AGC is selective.

Turning to Figure 17, the navigation apparatus 200, via the RDS communications unit 254, transmits (Step 420) RDS data including the number of AFs as mentioned above, the AFs being stored in the allocated memory space of the FM radio 302. Whilst the navigation apparatus 200 is travelling, the FM spectrum landscape changes, because signals originating from some FM signal transmitters become more dominant as the automobile 300 travels towards these FM signal transmitters, and signals originating form some other FM signal transmitters become less dominant as the automobile 300 travels away from these FM signal transmitters. In consequence, the received signal strength measured at the FM tuner in respect of some FM channels increases and the received signal strength decreases in respect of other FM channels. Hence, as the navigation apparatus 200 and the FM radio 302 approach a given FM signal transmitter that broadcasts on the tuned frequency of the FM radio 302, interference will increase and received signal strength falls. The RDS communications unit 254 monitors, via the FM receiver thereof, the interference and once the level of the interference reaches a level that is deemed detrimental to the quality of reproduction by the FM radio 302 of the audio information transmitted by the navigation apparatus 200, it is deemed necessary to re-tune the RDS communication unit 254 to another frequency. In this respect, the another frequency is selected (Step 424) from the number of AFs previously selected. Typically, the another frequency is a first AF in the list of AFs that is the number of AFs. Once the FM transmitter has selected the another frequency, the RDS communications unit 254 then proceeds to perform a search (Step 426) for AFs followed by generation (Step 428) of RDS data comprising the new AFs. The new AFs found are stored in the memory 214 in place of the previously selected number of AFs. The RDS communications unit 254 then re-tunes (Step 430) to the another frequency and transmits (Step 432) the second RDS data, for example the type OA groups identifying the new AFs. Hence, account is taken of the changing FM spectrum landscape as the automobile 300 travels and hence the location of the navigation apparatus 200 and the FM radio 302 changes.

At the FM radio 302 (Figure 18), the receiver thereof monitors (Step 450) receive signal strength. Whilst the receive signal strength associated with the tuned frequency is sufficiently strong, the receiver of the FM radio 302 continues to receive on the tuned frequency in accordance with the RDS technical specification. However, when the receive signal strength falls below a threshold value, the FM radio 302 accesses the memory thereof to identify a first AF from the number of AFs stored in the memory of the FM radio 302 and re-tunes (Step 452) to the first AF selected. The FM radio 302 then monitors (Step 454) the receive signal strength associated with the first AF retrieved from the memory of the FM radio 302. If the signal strength associated with the first AF is inadequate, the FM radio 302 accesses the memory thereof again to identify a second AF from the number of AFs stored in the memory of the FM radio 302 and re-tunes (Step 456) to the second AF selected. The above procedure (Steps 454 and 456) is repeated until another AF has been found that has an adequate signal strength associated therewith.

Once the FM receiver 302 has tuned to an AF having adequate signal strength associated therewith and a correct Programme Identification code, the FM radio 302 proceeds to receive the second RDS data transmitted by the navigation apparatus 200 as described above. In particular, the FM radio 302 receives (Step 458) the type OA group identifying the new AFs and records (Step 460) the new AFs in place of the number of AFs currently stored in the memory of the FM radio 302. Hence, the number of AFs previously stored in the memory of the FM radio 302 are replaced by the new AFs received from the navigation apparatus 200 on the another frequency and thus the memory of the FM radio 302 is purged.

Once the user has finished using the navigation apparatus 200 and the navigation apparatus 200 is either powered-down or the first antenna patch lead 324 is disconnected from the navigation apparatus 200 and/or the antenna input adaptor 306, the control unit 340 operates the first switching device 332, the antenna switching device 336 and the third switching device 338 such that antenna input adaptor 306 transitions back to the first state described above. Indeed, the navigation apparatus 200 can be arranged to specifically issue a control signal to the antenna input adaptor 306 to implement the transition back to the first state, although in this example the response by the control unit 340 is automatic by virtue of the control unit 340 monitoring the first antenna patch lead 324. In this respect, in this embodiment the control unit 340 uses the presence or absence of the RF signal received at the second input port 332 as the control signal. Of course, the skilled person should appreciate that, if desired, a separate, dedicated, control line can be provided between the navigation apparatus 200 and the antenna input adaptor 306 to provide the control signal to influence the control logic of the control unit 340.

In the above embodiment, the RDS communications unit 254 of the navigation apparatus 200 scans the FM spectrum of frequencies in order to find the AFs. The above embodiment assumes that due to the attenuation provided by the antenna input adaptor 306, the need to re-tune is infrequent as FM signals received via the antenna 318 are suppressed. However, in some instances (Figure 18), the automobile 300 and hence the navigation apparatus 200 and the FM radio 302 travel close to or pass close by strong transmission sources. In this respect, if the FM radio 302 sufficiently near to a transmitter of, for example, broadcast radio channels, the received signal strengths of the FM channels 374 are, unsurprisingly, still sufficiently high to be received by the FM radio 302, typically with sufficient channel separation, even when attenuation of the received RF signals of other FM channels 376 is being performed. Typically, the transmitter transmits between 3 and 8 FM channels and so if any of these transmitted FM channels coincide with the tuned frequency or any of the selected AFs, then the navigation apparatus 200 and the FM radio 302 need to re-tune to an available frequency. In some geographic areas, it can be necessary to trigger re-tuning more often than in other geographic areas and so an increased need will exist to re-tune on a more frequent basis. In such circumstances, more frequent re-tuning and the need to scan for AFs in the face of a changed FM spectrum landscape, as stated initially above, can be disruptive to the listening enjoyment of the user or other listeners in the automobile 300. Consequently, in order to reduce the amount of time necessary to scan the FM spectrum range of frequencies, the following technique can optionally be adopted.

In another embodiment (Figure 18), instead of scanning the entire FM spectrum of frequencies, the RDS communications unit 254 can select a number of candidate alternative frequency points in the FM spectrum. In this example, the number of candidate alternative frequency points, for example 25 frequency points, is uniformly spaced across the FM spectrum of frequencies. However, if desired, the number of candidate alternative frequency points can be randomly distributed across the FM spectrum of alternative frequencies. The above-described scan for AFs is modified so that the RDS communications unit 254 simply scans in respect of the number of candidate alternative frequencies, for example by sweeping a respective range of frequencies about, and including, each of the number of candidate alternative frequencies instead of the entire FM spectrum range of frequencies. The size of the range of frequencies swept corresponds to, for example, the bandwidth of an FM "channel". In this respect, the RDS communications unit 254 identifies a set of frequencies from the number of candidate alternative frequencies that are available, for example not subject to interference, and the set of frequencies identified are permitted by the RDS communications unit 254 to be used as AFs and communicated as such, whereas the remaining unavailable frequencies from the number of alternative frequencies are precluded for use as AFs in respect of future re-tuning.

Hence, instead of having to scan the entire FM spectrum range of frequencies, the RDS Communications unit 254 only has to scan a proportion of the FM spectrum range of frequencies and so the scanning process takes less time. If required, multiple FM receivers can be employed by the RDS communications unit 254 in order to scan different sets of the candidate alternative frequencies. When the attenuation capability of the antenna input adaptor 306 is used in combination with the above improved scanning technique, a sufficiently large number of frequencies amongst the number of candidate alternative frequencies exist to avoid interference with FM channels broadcast by nearby transmitters and any possible interference from other devices equipped with SRRs within sufficient proximity to the FM radio 302. In a further embodiment, instead of using the FM receiver as described above, the TMC receiver of the RDS communications unit 254 can be used to perform the scans in respect of the number of candidate alternative frequencies. Typically, a TMC broadcast provides a sufficient number of small time slots containing no TMC data to permit performance of each scan, for example respectively during an empty time slot, without loss of receipt of TMC messages during measurement of the candidate alternative frequencies. An empty time slot can be a time slot that does not comprise TMC content.

It should be understood that the antenna input adaptor 306, the FM radio 302 and the navigation apparatus 200 constitute, in the above examples, a communication system.

Whilst the above examples have been predominantly described in the context the RDS, the skilled person will appreciate the above embodiments can be employed in relation to the different technical specification implemented in North America, for example in the United States of America, known as the Radio Broadcast Data System (RBDS). Hence, for the avoidance of doubt, references herein to the RDS should be construed to embrace the RBDS as well.

It should be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims.

For example, it should be noted that although the RDS communications unit 254 described herein is internal to the navigation apparatus 200, the FM port 228 can be provided for coupling an external RDS communications unit to the navigation apparatus 200 or any other suitable portable electronic apparatus.

As another example, whilst embodiments described in the foregoing detailed description refer to GPS, it should be noted that the navigation apparatus may utilise any kind of position sensing technology as an alternative to (or indeed in addition to) the GPS. For example the navigation apparatus may utilise other global navigation satellite systems (GNSS) such as the proposed European Galileo system when available. Equally, it is not limited to satellite based but could readily function using ground based beacons or any other kind of system that enables the device to determine its geographic location, for example the long range navigation (LORAN)-C system.

By way of further example, it should be appreciated that although the above embodiments have been described in the context of a navigation apparatus, the techniques described herein are not only applicable to navigation apparatus, but also to any other electronic communications apparatus in respect of which it is desirable to transmit RDS or RDBS data on an FM channel for receipt by an FM receiver, for example mobile telephones or media players, such as music players, in particular but not exclusively MP3 players or accessories therefor. Alternative embodiments of the invention can be implemented as a computer program product for use with a computer system, the computer program product being, for example, a series of computer instructions stored on a tangible data recording medium, such as a diskette, CD-ROM, ROM, or fixed disk, or embodied in a computer data signal, the signal being transmitted over a tangible medium or a wireless medium, for example, microwave or infrared. The series of computer instructions can constitute all or part of the functionality described above, and can also be stored in any memory device, volatile or non-volatile, such as semiconductor, magnetic, optical or other memory device.

It will also be well understood by persons of ordinary skill in the art that whilst the preferred embodiment implements certain functionality by means of software, that functionality could equally be implemented solely in hardware (for example by means of one or more ASICs (application specific integrated circuit)) or indeed by a mix of hardware and software. As such, the scope of the present invention should not be interpreted as being limited only to being implemented in software. Lastly, it should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features or embodiments herein disclosed irrespective of whether or not that particular combination has been specifically enumerated in the accompanying claims at this time.

Claims

1 . An antenna input adaptor device comprising: a first Radio Frequency (RF) input for coupling to an antenna; a second RF input for coupling to a portable electronic apparatus capable of transmitting an RF signal; an RF output for coupling to an input of an RF tuner; and a control unit; wherein the control unit is arranged to couple the first RF input to the RF output and decouple the second RF input from the RF output in a first state and to decouple the first

RF input from the RF output and couple the second RF input to the RF output in a second state, transition between the first and second states being responsive to the control unit.

2. A device as claimed in Claim 1 , wherein the control unit is arranged to couple the first RF input to ground potential in the second state.

3. A device as claimed in Claim 2, wherein coupling the first RF input to the ground potential attenuates, when in use, RF signals received via the antenna.

4. A device as claimed in any one of the preceding claims, wherein the control unit is arranged to receive, when in use, a control signal and to execute a transition between the first and second states in response to the control signal.

5. A device as claimed in any one of the preceding claims, wherein a plurality of RF signals within a range of frequencies associated with a Frequency Modulation (FM) spectrum received, when in use, at the first RF input are received by the RF tuner in attenuated form when in the second state.

6. A device as claimed in any one of the preceding claims, further comprising: a first switching unit coupled between the first RF input and the RF output; and a second switching unit coupled between the second RF input and the RF output.

7. A device as claimed in any one of the preceding claims, further comprising: an antenna switching unit coupled between the first RF input and the ground potential.

8. A device as claimed in any one of the preceding claims, wherein the second RF input is arranged to receive a wired connection for receiving the RF signal from the portable electronic apparatus.

9. A communications system comprising: an antenna; an antenna input adaptor device as claimed in any one of the preceding claims, the antenna being coupled to the first RF input of the antenna input adaptor device; wherein the portable electronic apparatus comprises an RDS communications unit, the RDS communications unit being coupled to the second RF input of the antenna input adaptor device.

10. A system as claimed in Claim 9, wherein the portable electronic apparatus is arranged to store a plurality of Alternative Frequency (AF) frequencies, the AF frequencies being substantially uniformly spaced across a Frequency Modulation (FM) spectrum range of frequencies.

1 1 . A system as claimed in Claim 9, wherein the portable electronic apparatus is arranged to store a plurality of Alternative Frequency (AF) frequencies, the AF frequencies being substantially randomly spaced across a Frequency Modulation (FM) spectrum range of frequencies.

12. A system as claimed in Claim 10 or Claim 1 1 , wherein the RDS communications unit is arranged to perform scans in respect of each of the plurality of AF frequencies.

13. A system as claimed in Claim 12, wherein each scan in respect of an AF frequency of the plurality of AF frequencies comprises sweeping a range of frequencies about the AF frequency.

14. A system as claimed in Claim 12 or Claim 13, wherein the RDS communications unit is arranged to identify any AF frequencies already in use and to prevent use of the any AF frequencies identified in respect of future re-tuning.

15. A system as claimed in Claim 9, wherein the FM communications unit is arranged to re-tune to another frequency from a tuned frequency in response to detection of the tuned frequency being used by a transmission source other than the portable electronic apparatus, the another frequency being one of the plurality of AF frequencies.

16. A portable electronic communications apparatus comprising: a Radio Data System (RDS) communication unit for communicating an audio signal to an external RF tuner; wherein the RDS communications unit is arranged to generate, when in use, a Radio Frequency (RF) antenna switching signal for triggering attenuation of RF signals wirelessly received by the external RF tuner via an antenna.

17. An apparatus as claimed in Claim 16, further comprising a data store arranged to store a plurality of Alternative Frequency (AF) frequencies and to initiate a scan in respect of each of the plurality of AF frequencies in order to determine availability of the each of the plurality of AF frequencies.

18. An apparatus as claimed in Claim 17, wherein the plurality of AF frequencies are substantially uniformly spaced across a Frequency Modulation (FM) spectrum range of frequencies.

19. An apparatus as claimed in Claim 17, wherein the plurality of AF frequencies are substantially randomly spaced across a Frequency Modulation (FM) spectrum range of frequencies.

20. An apparatus as claimed in Claim 17 or Claim 18, wherein each scan in respect of an AF frequency of the plurality of AF frequencies comprises sweeping a range of frequencies about the AF frequency in order to determine whether the AF frequency is available for transmission thereon.

21 . An apparatus as claimed in any one of Claims 17 to 20, wherein the RDS communications unit is arranged to select one of the AF frequencies of the plurality of AF frequencies determined as available for transmission thereon.

22. An apparatus as claimed in any one of Claims 17 to 21 , wherein the RDS communications unit is arranged to identify an AF frequency already in use and to prevent use of the AF frequency identified in respect of future re-tuning.

23. An apparatus as claimed in Claims 17 to 22, wherein the RDS communications unit comprises a Traffic Message Channel (TMC) receiver, the TMC receiver being arranged to perform the scan in respect of the each of the plurality of AF frequencies in order to determine availability of the each of the plurality of AF frequencies.

24. A portable navigation device comprising the portable electronic communications apparatus as claimed in any one Claims 17 to 23.

25. A method of communicating a Radio Frequency (RF) signal from a portable electronic apparatus to an external RF tuner, the method comprising: the portable electronic apparatus issuing an RF antenna switching signal; attenuating any RF signals to be wirelessly received by the RF tuner via an antenna in response to the RF antenna switching signal.

26. A computer program element comprising computer program code means to make a computer execute the method as claimed in Claim 25.

27. A computer program element as claimed in Claim 26, embodied on a computer readable medium.