Assisted determination of free and blocked channels

The present invention is related to the determination of channels for radio transmissions. It is particularly concerned with an assisted determination of free channels for unlicensed FM radio transmissions.

Prior art

Mobile electronic devices which are capable of music and/or video playback have become very popular recently, with the iPod ™ by Apple® Computer Inc. being one of the most prominent examples. These media players are mainly intended for being used in conjunction with head- or earphones. For a typical mobile use of such devices, this is a preferable listening manner. However these players have become rather sophisticated recently, many of them comprise hard disks capable of storing e.g. gigabytes of music. Therefore, it seems logical that a user would want to use his player, on which a big amount or all of his own music/videos, games etc. is stored, as the source of media data also in other environments, and also for playing back music with normal speakers.

The user could use the earphone or line-out output to connect his player device with his hi-fi equipment or the like. However, cable connections are inconvenient, particularly in conjunction with small mobile player devices. Because of the wide variety of used plug/socket connector systems, this is also likely to cause incompatibilities between devices.

Another example would be to use such a player as a replacement for a CD-changer in a vehicle. However, many existing car radio systems still do not comprise any input interface to connect a mobile player. As one of the main advantages of mobile music players is the possibility to easily carry it along, it would be desirable if it could be coupled with other equipment in a standardized way, with some kind of common interface.

Therefore, wireless transmission of music or other media data from a player device would be useful. As many audio playback devices like stereo systems and car radios comprise an FM tuner or receiver, a known implementation of such wireless transmission is to "mimic" the music player as a conventional FM radio station and to send the audio data encoded as a standard FM radio transmission.

In the United States of America (and also other countries, including the European Union) the usage of unlicensed (i.e. personal/private) FM-radio transmitters is allowed. In the U.S. the FCC (Federal Communications Commission) allows such devices according to FCC rule 15 (see section 15.239). Such a transmitter can thus be used for conveniently transmitting sound or music and in principle also other media content like video or data from any device wirelessly to an FM radio operating in the 88 - 108 MHz band, e.g. from a CD-player or an MP3-ρlayer. An example is the iTrip™ add-on accessory for the iPod™ by Apple®. This allows listening to music from such a device e.g. through a car FM radio. Due to the restricted transmission power with field strengths of about 250 μV/m in a distance of 3 meters, the transmission range of such private transmitters is small. Interference is therefore expected to be low. However, interference with licensed FM transmitters, e.g. a radio station, is not allowed. Regulations in other countries may be similar.

Conventional transmitters for that purpose simply transmit on a fixed frequency or frequency that can manually be chosen. This requires manually setting the corresponding transmission frequency on both the transmitter connected with the player device and the FM radio receiver. Furthermore, if the mobile device is being used in a vehicle that is moving or if the user is in an area where the surroundings change (e.g. when the user is surrounded by moving traffic), the user may experience regular interference and general poor quality of the received signal due to other much larger signals breaking through either on the same channel or perhaps even on adjacent channels.

Each time this happens the user will need to retune his FM receiver to another clear channel and set his FM transmitter to the same frequency. During the course of a long journey this

may have to be done many times, and if the user is the driver of a vehicle, then this is of course extremely distracting and hence a danger to her / him and other road users.

That is, currently the transmission of information (e.g. music) from devices such as the iPod™ via the iTrip™ accessory using frequency modulation radio transmission (FMTx) technology requires intervention from the user on a regular basis to maintain a good and acceptable reception of the signal transmitted from the device. This includes that the user first has to locate an available channel via an FM receiver and then has to set the same frequency on the transmitting device.

Therefore, it was suggested to automate the search for available frequencies in conjunction with making use of the Alternate Frequency feature (AF) of the Radio Data System (RDS). Available frequencies are determined automatically and at least one available alternative frequency is provided to the FM receiver as AF of RDS, in order to enable it to switch to the new frequency.

Even when using a method to listen for available channels such as utilizing an FM receiver or a basic received signal strength indicator (RSSI) scanning technique, potential problems still exist that need to be addressed.

In the prior art methods, the required available frequencies are detected by scanning the frequency range in order to find frequencies having a signal level to be considered as representing a free channel. On the one hand this procedure can take considerable time, which is apparently undesirable, inter alia in view of restricted power supply of mobile devices. Powering on the receiver and the required logic for evaluating signal levels can decrease the runtime of battery powered mobile devices.

On the other hand this cannot prevent erroneously determining a certain frequency as available that only appears to be free due to some only local circumstances. For example the device performing the scan might be located in an area where a building or other structure is blocking a transmission on a certain frequency. The device might now use this frequency for

transmission, as it appears to be available. When the user leaves the area in which the frequency is blocked he might encounter a strong interference on this frequency and the device will finally be forced to switch to yet another frequency.

The invention thus suggests means for avoiding or at least minimizing these problems.

Summary of the invention

According to a first aspect a method is provided for providing broadcast frequencies to a transmitter device, comprising: determining the geographical area where said transmitter device is currently located; accessing a database comprising associations between geographical areas and available frequencies in said geographical areas; selecting at least one frequency from said database that is available in said determined geographical area; and transmitting an indication of said at least one selected frequency to said transmitter device.

The use of external sources for determining available broadcast frequencies enables the transmitter device to operate more reliable, with less power consumption, and also react faster, e.g. at start-up in finding an initial free frequency. The operation is made more reliable due to the fact that more reliable sources can be used for the determination of a plurality of alternate frequencies, without relying solely on the limited frequency scanning capacity (if this is present anyway) of the transmitter device. Furthermore, this can help to avoid shutting down the transmitter for checking the currently used frequency and thus provide uninterrupted listening to a user. The invention can both be an addition to performing active frequency scans in the transmitter device as well as represent a replacement for such scans at all.

It is to be noted that the term "available frequency" is to be understood as designating a frequency being free for use that is, not occupied by any strong interfering signal like a

licensed radio station. It is not to be understood as a frequency just being technically available and / or legally allowed to be used. Also the consideration if a frequency is free of interfering signals is based on a signal level threshold, as there will always be a remaining signal level of noise etc. Frequencies having a signal level below that threshold are considered free. In turn frequencies having a signal level above the threshold are considered as being unavailable.

In an exemplary embodiment the determining the geographical area of said device comprises: receiving an indication of the geographical area from said device.

For example the transmitter device can be equipped with a GPS or other locating component, or determine its position via location based services. This is an alternative solution compared to a location determination solely from the device providing the external sources.

In an exemplary embodiment the database further comprises associations between at least one geographical area and an indicator for frequencies in said geographical area, said indicator being indicative of a probability to encounter interference on a frequency, the method further comprising: transmitting the indicator associated with said at least one selected frequency to said transmitter device.

While there may be a plurality of frequencies that are in principle available, it is still possible that there are frequencies which are more likely to cause interference when used for transmission. This embodiment enables to provide a more detailed indication about the "quality" of certain frequencies, thus enabling the receiving transmitter device to make a better choice of a suitable transmission frequency.

In an exemplary embodiment said database further comprises associations between geographical areas and unavailable frequencies in said geographical areas, the method further comprising: selecting frequencies from said database that are unavailable in said determined

geographical area; and transmitting an indication of said selected unavailable frequencies to said transmitter device.

Since it is possible to use the invention also in conjunction with mobile devices that can perform frequency scans on their own, it may be advantageous to provide a list of "blocked" frequencies, e.g. such that are unavailable due to legal restrictions or local reception conditions, in order to accelerate the scan by not wasting time for scanning such blocked frequencies.

In an exemplary embodiment said indication is transmitted using one of: a cellular network connection; a Multimedia Message Service; a Short Message Service; - a General Packet Radio Service connection; an Internet connection; a Bluetooth connection; an infra-red IrDA connection; and a Wireless Local Area Network connection.

Any other suitable connection method can also be applied in the present invention.

In an exemplary embodiment the method further comprises: receiving an indication of at least one available or unavailable frequency from said transmitter device; and updating said database based on said indication.

This embodiment is particularly useful when the mobile devices or transmitter devices include a scanning capability. When information about free/blocked frequencies from the transmitter devices is taken into account for updating the central database, a more refined image of the actual frequency situation may be derived. Weighting can be applied to any

reported free/blocked frequency. For example if a frequency is reported as blocked by at least three different devices it may be regarded as actually being blocked. Also the weighting might take into account the accuracy of the position determination in conjunction with such a report. While devices that are precisely locatable might be treated as reliable sources, such with a less precise location may be treated less reliable as well.

In an exemplary embodiment each geographical area in said database has an associated area identifier, the method further comprising: transmitting the identifier of the determined geographical area to said transmitter device.

This enables the transmitter device to base AF selection on for example the country it is currently located in, or generally its geographical location. As low power RF transmission might be subject to different legal regulations in different countries, this embodiment can ensure that only "allowed" frequencies are actually used by the device. An association of legally or otherwise "forbidden" frequencies may for example be included in the firmware of the device. A more detailed description of the country code feature will be given below. This feature is particularly useful due to the provision of an easy way to indicate blocked frequencies with very low data throughput, e.g. a two-digit country code. Also, frequencies that could otherwise be considered useable by the device can be excluded in this manner.

In an exemplary embodiment the method further comprises: detecting if said transmitter device changes from a first geographical area into a second geographical area; and - determining if available frequencies are different in said first and said second geographical area; wherein transmitting said indication to said transmitter device is triggered if available frequencies are different.

This can reduce the data volume and/or amount of transmissions necessary to indicate AF 's to the transmitter device.

According to yet another aspect of the invention a method is provided for obtaining broadcast frequencies for a transmitter device, comprising: transmitting a request for available frequencies, said request comprising an indication of the current location of the transmitter device; receiving an indication of at least one available frequency; storing said at least one available frequency; and selecting a transmission frequency based on said at least one available frequency.

In an exemplary embodiment the method further comprises: receiving an indicator of a probability to encounter interference on said at least one available frequency; wherein said selecting of a transmission frequency is based also on said indicator.

The indicator can for example be implemented as a percentage value, wherein 10% indicates that interference is unlikely to occur on a frequency, while 50% or more indicate that interference is to be expected rather likely, etc. This can also be utilized to indicate unavailable frequencies, which would then have an associated percentage value of substantially 100%. The selection of the transmission frequency can take into account this value, such that frequencies having lower values are preferred over others.

In an exemplary embodiment said indication is received via one of: a cellular network connection; a Multimedia Message Service; - a Short Message Service; a General Packet Radio Service connection; an Internet connection; a Bluetooth connection; an infra-red IrDA connection; and - a Wireless Local Area Network connection.

In an exemplary embodiment the method further comprises: receiving an indication of at least one unavailable frequency; and excluding said at least one unavailable frequency from further use for transmission.

In an exemplary embodiment the method further comprises: maintaining a list of frequencies and storing an indication of the availability of each listed frequency; wherein said availability indication is derived from one of or a combination of: said received indication of at least one available frequency; - said received indication of at least one unavailable frequency; and said received indicator of a probability to encounter interference.

In the context of this invention the term "availability" is to be understood as both indicating if the frequency is available at all (e.g. due to legal restrictions or frequencies that are technically unavailable due to some electrical device properties) as well as indicating how reliable the transmission on the frequency is to be expected. The "availability" indication can be a value ranging from zero availability, which indicates unavailable frequencies, to low or medium availability wherein it will depend on the evaluation if a corresponding frequency is still considered unavailable or already considered available, to higher availability, which indicates available frequencies. The availability indicator can be considered as a kind of "fuzzy" value from which the absolute value can be derived which indicates if a frequency is considered to be available or not, depending on the threshold used to evaluate the fuzzy availability value.

In an exemplary embodiment the method further comprises: sorting the list of frequencies according to their availability indications.

This enables to have the frequencies first on the list which are likely to provide the best transmission. Depending on the hardware and / or software implementation it can be advantageous to store all frequencies that are technically possible, e.g. the very high frequency VHF range of 88-108 MHz ₅ together with availability indications, instead of just

storing frequencies that are considered being available. Sorting frequencies can be applied to both use cases.

In an exemplary embodiment the indication of the availability is based on the measured or received signal strength on a frequency. That is, frequencies having a lower signal (or noise) level are given a higher availability.

In an exemplary embodiment the method further comprises: storing an indication of the usage history of each stored frequency, wherein the usage history comprises one or more of: the number of times the frequency has been used; the time span the frequency has been used; the number of times the frequency has been left during operation; the number of times the frequency has been unavailable; and the geographical location(s) where the frequency has been used.

These parameters can also be used to determine the availability of certain frequencies. For example, if a certain frequency has been manually left by a user this indicates that this frequency has a low availability. On the other hand frequencies that have been used often and/or for long periods of time should be treated with high availability.

In an exemplary embodiment the method further comprises: maintaining a list of frequencies and storing an indication of the availability of each listed frequency; wherein said availability indication is derived from one of or a combination of: said received indication of at least one available frequency; said received indication of at least one unavailable frequency; and said received indicator of a probability to encounter interference.

This embodiment also includes to "mark" unavailable frequencies as such or to remove them from the list, and keeping already present available frequency or newly storing ones that are

not stored yet.

In an exemplary embodiment the method further comprises: scanning a plurality of frequencies; wherein frequencies on which no signal levels above a pre-determined threshold are currently received are stored in said list as available frequencies; and frequencies on which signal levels above the pre-determined threshold are currently received are removed from said list or marked as being unavailable.

Although the invention enables to omit any scans to be performed by the device itself, doing so can help to supplement the AF's provided to the device. As not all "micro" local conditions can be taken into account by a centralized approach using external sources, it can be advantageous to perform the scans in addition to the use of more or less reliable external sources.

In an exemplary embodiment the method further comprises: transmitting said list to another transmitter device.

In another exemplary embodiment the method further comprises: receiving a list from another transmitter device; and updating said list according to said received list.

The AF list(s) can even be passed on to other devices, that is, can be shared between them. This embodiment can help to reduce the time for determining a suitable AF list even further. Also, if some of the devices the list is shared with are located such that they cannot receive the external AF lists (e.g. due to some local building structure blocking cellular network access), they can still benefit from AF lists shared via some local connectivity like WLAN, Bluetooth or like.

In an exemplary embodiment said transmitter device comprises a memory storing

associations between identifiers of geographical areas and frequencies unavailable in said geographical areas, the method further comprising: receiving an identifier of a geographical area; and removing unavailable frequencies associated with said identifier from said list.

This has already been shortly described above in connection with the "country" or generally area code feature of the invention. More detailed information will be given below.

According to another aspect of the invention a computer program product is provided, comprising instructions stored on computer-readable medium, for instructing a computer to perform the method steps as explained above when run on the computer.

According to a further aspect of the invention a device for obtaining broadcast frequencies for a transmitter device is provided, comprising: - a radio transceiver; a memory; and a controller, adapted for transmitting a request for available frequencies, said request comprising an indication of the current location of the transmitter device, and for receiving an indication of at least one available frequency, using said transceiver, storing said at least one available frequency in said memory, and selecting a transmission frequency based on said at least one available frequency.

In an exemplary embodiment the transceiver is adapted for operating according to one of: a cellular network protocol; - a Multimedia Message Service protocol; a Short Message Service protocol; a General Packet Radio Service protocol; the Internet protocol; a Bluetooth protocol; - an infra-red IrDA protocol; and a Wireless Local Area Network protocol.

In an exemplary embodiment the device further comprises: a location component adapted for determining the geographical location of the device. For example a Global Positioning System receiver can be used, or in case the device has a cellular network interface location based services can be employed.

In an exemplary embodiment the controller is further adapted for receiving an indication of at least one unavailable frequency, using said transceiver, and for excluding said at least one unavailable frequency from use for transmission.

In an exemplary embodiment the controller is further adapted for storing an indication of the usage history of each stored frequency, wherein the usage history comprises one or more of: the number of times the frequency has been used; the time span the frequency has been used; the number of times the frequency has been left during operation; the number of times the frequency has been unavailable; and the geographical location(s) where the frequency has been used.

According to still another aspect of the invention a system for radio transmissions is provided, comprising: a wireless network; at least one transmitter device comprising a radio transmitter; a processor; - a memory; and a wireless interface adapted for operation within said wireless network; a server comprising a database comprising associations between geographical areas and available radio frequencies in said geographical areas; - an interface connected to said wireless network; a controller;

wherein said server is adapted for determining the geographical area where said transmitter device is currently located, wherein said controller is adapted for selecting at least one frequency from said database that is available in said determined geographical area, and for transmitting an indication of said at least one selected frequency to said transmitter device via said wireless network; and said transmitter device is adapted for receiving said indication of at least one available frequency, storing said at least one available frequency in said memory, and wherein said processor is adapted for selecting a transmission frequency from frequencies stored in said memory.

In an exemplary embodiment said wireless network comprises location based services, wherein said server is adapted for determining the geographical area where said at least one transmitter device is currently located using said location based services.

In an exemplary embodiment said at least one transmitter device comprises a locating component adapted for determining the geographical area of said transmitter device, and wherein said processor is adapted for transmitting an indication of said geographical area to said server using said wireless interface.

In an exemplary embodiment said server is adapted for selecting all frequencies from said database that are unavailable in said determined geographical area, and transmitting an indication of said unavailable frequencies to said transmitter device via said wireless network; and said transmitter device is adapted for receiving an indication of at least one unavailable frequency, and excluding said at least one unavailable frequency from further use for transmission.

In an exemplary embodiment said transmitter device is adapted for maintaining a list of available frequencies in said memory by storing new available frequencies and removing already stored unavailable frequencies.

In an exemplary embodiment said transmitter device comprises a radio receiver adapted for scanning a plurality of frequencies, wherein said processor is adapted for storing frequencies in said list on which no signal levels above a pre-determined threshold are currently received and removing frequencies from said list on which signal levels above the pre-determined threshold are currently received.

In an exemplary embodiment said processor is adapted for sharing available frequencies stored in said memory with another transmitter device using said wireless interface.

In an exemplary embodiment said processor is adapted for receiving a list from another transmitter device via said wireless interface and for updating stored available frequencies according to said received list.

In an exemplary embodiment said wireless interface is one of: - a cellular network interface; an Internet interface; a Bluetooth connection; an infra-red IrDA connection; and a Wireless Local Area Network connection.

Brief description of the drawings

The invention can be more fully understood by the following detailed description of exemplary embodiments, when also referring to the drawings, which are provided in an exemplary manner only and are not intended to limit the invention to any particular embodiment illustrated therein. In the drawings

Figure 1 presents a first typical use case scenario;

Figure 2 presents a second typical use case scenario;

Figure 3 presents a block diagram of the current art;

Figure 4 presents scan and channel selection according to the invention;

Figure 5 presents the band as in fig. 4 after a threshold has been applied in accordance with the invention;

Figure 6 presents the band after external AF list data have been applied in accordance with the invention;

Figure 7 presents blocked channels as used in product profiling according to the invention;

Figure 8 presents an exemplary embodiment of the system of the invention in form of a block diagram;

Figure 9 presents an exemplary embodiment of an embodiment of channel status information and AF list selection in form of a block diagram;

Figure 10 depicts an exemplary embodiment of a device according to the present invention;

Figure 11 is a flow diagram of an embodiment of the method of the invention, as implemented on the sending side; and

Figure 12 is another flow diagram of an embodiment of the method of the invention, as implemented on the receiving side.

Detailed description of the invention

It is to be noted that due to the partitioning and allocation of the VHF FM radio band, the terms "channel" and "frequency" are used interchangeably throughout this document.

In earlier solutions, the system relied on performing real-time measurements of signals in a frequency band and deciding if the channel is free or not. The problem with relying only on this method is that radio frequency RF reception is dependant on the environment. E.g. at the time of performing a scan to obtain an AF list the user may be shielded by buildings, trees or hills or may even be inside a tunnel or a concrete structure like a car park. Another possibility is that the mobile devices Tx/Rx antenna may not be very efficient. AU of these cases will impair the reception of signals. Under these conditions the system may conclude it has found acceptable quiet channels and hence assign them to the AF list to use. When reception conditions get clear of such obstructions the apparently quiet channels stored within the AF list may now carry strong signals, so that any attempt to use them as an AF will probably fail or impair the user's listening experience and generally experience of the whole system.

This invention helps to prevent the above situation arising due to the use of information that could be made available via various sources. The system would make use of as many of these sources of information as required and provide a very accurate and up to date representation of which channels are free in a particular geographical area. The information would be dynamic in the sense that the mobile device would be regularly updated either automatically or on request from the user. The user may also choose by which means the information is obtained, thus allowing the user to control the methods by which the system is updated. This is required to give the user control since various services are chargeable by the operators. Alternatively, the system defines the rules by which means the information is obtained according to predefined rules or rules derived from the user behavior. Automatic updates may be triggered by moving between cells or perhaps based on GPS location.

To improve the current art, i.e. making use of the existing AF list feature provided by the RDS system, the invention suggests to use other, e.g. external sources of information to assist in the use of the AF feature and then allow the transmitting device to make a better judgment of which available channels (frequencies) are to be used in the AF list that is then transmitted to the FM receiver using RDS. Any mixture and hence any number of alternative sources of information can be utilized to improved the AF selection. There may be of course more than one AF list that the system can use.

By using other potential sources of AF list information it is possible to enhance and improve the real-time scan for available channels and also to improve the mobile devices power consumption and the user's listening experience by allowing accurate selective band scanning to take place.

Figure 1 shows a typical urban scenario. Signals from radio stations may vary in strength due to surrounding obstacles from e.g. buildings and trees which cause signal attenuation, deflection or reflection. Possible (location dependent) mixing products from or with other signals may add to signal strength variations. This may cause any channel scan to return quite different results as a vehicle moves around the area (i.e. from position Pl to position P2). A measurement may result that some usually strong signals appear weak and may erroneously be considered as free/quiet channels by the system upon a scan. This problem is amplified if the mobile device enters a region where the terrain is very hilly or even mountainous and the worst case can be considered if the mobile device enters a tunnel. This last case is described in Figure 2.

In figure 2 a situation is depicted wherein the vehicle is traveling from position Pl to position P3 via position P2, i.e. traveling through a tunnel. If a scan is performed when the vehicle is inside the tunnel (position P2) then the majority (if not all) frequencies of the very high frequency, VHF spectrum will appear quiet and it is possible that the AF list could then contain channels (frequencies) that are not quiet outside the tunnel. The transmitter will then begin to transmit on what it believes to be a clear channel but when the vehicle emerges from the tunnel (position P3), the signal from the FMTx device may be interfered with by a much stronger signal being transmitted by a licensed radio station such as that being transmitted from FS3. It is to be noted that an FM transmitter or FMTx device can be a kind of accessory device, e.g. for a mobile phone or mp3 player or like, or it can also be integrated in a mobile phone or player device.

A control software in the system could analyze the scan results and determine in this case that the vehicle has probably entered an area with no radio coverage and could then decide not to

make any changes to the last known good AF list and discard the scan that took place whilst in the tunnel. However, in a very hilly or mountainous region or more likely in a built-up urban area such as that described in figure 1, the free channel scan results are more likely to be inconsistent and the system is then more likely to make a poor decision about which channels are actually quiet.

Figure 3 shows the current art and illustrates the corresponding basic system. This consists of a mobile FM receiver such as an in-car stereo that is RDS capable, a mobile device capable of FMTx and performing a method for listening for clear channels within the VHF FM radio band. FS 1-3 are licensed broadcasting radio stations that the FMTx device has to compete with and it is these radio stations that the FMTx system must remain clear of in terms of transmitting frequencies and PI codes.

The mobile device will also comprise a processor and memory to control the FMTx device and the scanning method. It is this memory that may be used to maintain the status of the VHF FM radio band to allow the system to decide which channels are free to be used by the FMTx device. These free channels are maintained in one or more AF lists that are sent to the FM receiver using of the AF feature of RDS.

Alternatively, a list is kept with all blocked channels. As a third alternative, a list is kept with all channels of the FM radio system. For each channel, an indication can be given to mark the channel as free or blocked. E.g. a "1" can mean that the channel is free and a "0" can mean that the channel is blocked. A more graded rating of the channels can be given as well, e.g. depending on different thresholds used to classify the channel measurement results. E.g. a "00" can mean that there is a very strong signal (above a high threshold), a "01" can mean that there is a strong signal (between a medium threshold and the high threshold), a "10" can mean that there is a medium signal (between a low threshold and the medium threshold) and a "11" can mean that there is a weak or no signal (below the low threshold). Alternatively, the measurement results can be given for every threshold. In addition, an indication can be given for a preferred channel, e.g. a channel that was used in the past and never or rarely experienced any interference.

Figure 4 is an example of how the VHF FM band scan may appear to the system after scan of the band is complete. THl is the threshold that the system has set which marks the level at which any signals detected above are unable to be overcome by the FMTx transmitter and as such should not be considered as valid clear/quiet regions of the band.

Figure 5 shows how the band may look to the system once the THl threshold has been applied. FSl and FS2 are clearly strong signals from a nearby radio station transmitter and are unlikely to cause any problems since the system will simply bar these channels from use by the FMTx system. AU other signal peaks above THl are also safely barred from use by the system. However, FSa, FSb and FSc are signals that fluctuate to at least a level such that interference is noticed if the system operates on any of the frequencies used by FSa, FSb or FSc, depending on the position of the receiver device. This may be due to buildings in the vicinity, trees, hills, intermodulation, fading and/or reflections.

The amount of variation in these signals is such that they may fall below or rise above the threshold set by the system. In a system that only relies on the scan of the VHF FM radio band it is highly possible that these signals will be monitored at a time when they are at their lowest power level as seen by the RSSI scan or FM receiver scan. If this is the case, then these apparently quiet channels may be added to the AF list and sent to the FM receiver via RDS. If this happens the mobile device may begin to transmit its audio data on one of the apparent free/quiet channels (here assumed to be FSb) due to the previous channel becoming noisy or weak in signal strength and the FM receiver (in this case a car stereo) will tune to this transmission frequency.

At some point during this transmission the original signal FSb may suddenly appear much stronger due to the vehicle moving to an area where reception of this signal is better. At this point the FMTx system has to perform yet another AF jump. This scenario leads to a number of problems:

a) The fluctuation in signal FSb may be so rapid that the user will again be subject to a poor

FMTx experience due to interference from that signal. b) The user may also have a poor FMTx experience since the system will likely be performing lots of AF jumps in a short period of time. c) The system may not get a chance to successfully perform another scan and update the AF list in time before another AF jump is required.

Figure 6 explains how the present invention can help prevent this problem. This figure shows how the use of externally provided region-based AF list information via other means (i.e. over various media types and system infrastructures) can be used to back up and aid the AF list selection process of the FMTx system. Data obtained over a period of time or simply knowledge of the transmissions within this area can be used to ensure that channels FSa, FSb and FSc are marked as not being suitable for FMTx. By including these channels in a blocked channel list or by excluding these channels from the available quiet/free channel list the apparent availability of free/quiet channels is reduced. This has a number of benefits:

1) The system will appear more reliable and AF jumps will be required less frequently, thus improving the user's experience.

2) In a system that uses a crude RSSI scanning technique and does not have a separate FM receiver to perform any background scanning the user's listening experience will be improved since the transmitter will be switched off for less time while a scan takes place, and interference with the audio transmission is therefore much less likely.

3) The RF scanning technique employed has the potential to take less time since it will be unnecessary to scan the whole band and therefore this will reduce the power consumed from batteries in mobile devices.

Figure 7 shows how product profiling may be used to bar channels that and inherently noisy due to internal components and clocks within the mobile device. Each mobile device will effectively have its own 'signature' and this can be measured and the data can then be used to filter out these noisy channels. In the example in figure 7 it can be seen that the high frequencies are noisy and should thus be excluded from the AF list entirely. This will help prevent to waste time scanning channels that are always going to be noisy and hence to speed

up the detection of quiet/free channels and at the same time help reduce power consumption. THl is the threshold at which the FMTx device is unable to overcome signals above this level.

Figure 8 shows an exemplary embodiment of the invention. It must be noted that it is feasible to apply only part of or a combination of parts depicted in this figure to provide a significant enhancement to the FMTx AF selection process. A wireless network is shown here, indicated by the network masts 6. A server 8 is connected with the wireless network, and comprises a database about geographical areas and associated available frequencies to be used for a list of alternate frequencies AF. In advanced embodiments the server 8 may also store frequencies that are unavailable in certain areas, or even all areas, and indicated them to any mobile device provided with AF lists by the server 8. An exemplary use of this feature will be described later on in conjunction with the "country code" feature of the invention.

Three users are depicted, wherein user 1 is located in his vehicle, and uses a personal transmitter device, e.g. a mobile device 12, to supply music to his in-car FM radio 10. Radio stations 4 are located within the area, thus blocking certain frequencies for licensed broadcasts. The user's mobile device 12 has to take into account these blocked frequencies when choosing a transmission frequency and determining alternate frequencies for ensuring connectivity. The mobile device 12 comprises a memory 14 for storing an (or a plurality of) AF list(s) AF1...AF3. For example each such AF list # might represent a personal profile, like "home", "work" or others. The use of profiles associated to AF lists will be explained in more detail later on in this description.

The mobile device 12 further comprises a processor 16 and an FM radio transmitter 18, having an optional capability of FM frequency scans, that is, a limited reception capability. The processor 16 is adapted to control the selection of AF's and their transmission to a RDS capable FM receiver (like in this figure, receiver 10). The mobile device 12 may, in exemplary embodiments, further comprise a (not shown) locating component, e.g. a GPS receiver, which is enabled to determine the device's current geographical location by using the GPS satellites 2. The position can then be indicated to the server 8 via the wireless

network.

Another embodiment uses the wireless network to determine the position, for example by known cell-based locating methods. It is not required that the mobile device 12 determines the position and transmits it to the server 8. It is also possible to have the server 8 determine the position of mobile device 12, e.g. also via location based services of the wireless network, without active participance of the mobile device 12.

Users 2 and 3 may also have mobile devices 12 capable of FM transmission and the use of the AF feature. As is indicated by the dashed lines, these three users may share the AF list(s) of one mobile device, e.g. the one belonging to user 1. Using local wireless connectivity like WLAN, Bluetooth or IrDA the users could share their respective AF lists. A detailed description of the use of this feature of the present invention will be given below.

Figure 9 shows an exemplary embodiment of how the AF list (channel list) information may be organized in memory of a mobile device and how the data is then processed to generate an accurate and concise AF list that may be used to control the AF jump of an RDS capable FM receiver. The mobile device will use one or more of the filtered AF lists and pass this information on to the FM receiver via the RDS feature. Any of the schemes described in this specification may be used to gather and then filter and / or process the information in order to obtain the final AF list.

In figure 10 a mobile device 12 according to an embodiment of the present invention is depicted. The device 12 comprises an FMTx unit 18 connected with an antenna. A controller 16 is provided for controlling the device 12. A memory 14 is provided for storing, exclusively or among other data, available frequencies, unavailable frequencies, a usage history of frequencies or other transmission related information as described above. An external interface 20 is provided for communicating with an external data source for obtaining information on the availability/unavailability of frequencies. This interface 20 can be wireless as well as wire-based. Possible implementations include cellular interfaces like GSM, CDMA or UMTS, further wireless interfaces like WLAN, Bluetooth and infra-red,

wired interfaces like USB and other suitable data interfaces.

The controller 16 enables the device to manage a list of frequencies to use for transmission and/or a list of "blacklisted" frequencies which are excluded from use. The list can be updated based on information received via the interface 20, either by passively receiving the information (e.g. from a cellular network) or by requesting it from an external source.

The mobile device 12 can either have an integrated source for the data to be transmitted via the FMTx unit 18, e.g. be a mobile phone having an mp3 player, or have an interface (not shown) for receiving the data to be transmitted, e.g. a 3.5mm stereo jack for plugging into the earphone socket of an mρ3 player.

In figure 11 the steps of an embodiment of the inventive method as implemented on the sending side are depicted. In step 102 the geographical area of a transmitter device is determined. This can be achieved using location based services, in case the transmitter device has a cellular network connection, or by having the transmitter device indicate its location, e.g. determined via GPS. In step 104 a database is accessed comprising associations between (a) geographical area(s) and frequencies available therein.

It is to be noted that the invention includes using a central database, e.g. located at the cellular network operator, or using a plurality of decentralized databases. For example in a cellular network each base station can be equipped with a local database of frequencies available in the cell.

In step 106 at least one available frequency is selected from the database. It has to be noted that this step can similarly be performed for selecting frequencies unavailable in the respective area. Both available as well as unavailable frequencies can be indicated to a transmitter device. In step 108 an indication of the selected frequency is transmitted to the transmitter device, in order to enable it to choose a suitable transmission frequency for an FM transmission, e.g. audio data.

In figure 12 the steps of an embodiment of the inventive method as implemented on the receiving side, i.e. a device having FM transmission capabilities, are depicted. In step 202 a request for available frequencies is transmitted, the request including the current location of the device. Transmission can be achieved using cellular protocols, messaging services or wireless or wire-based links. It is to be noted that the interface used for this transmission does not have to be identical to the FM transmission interface, although this is in principle also possible.

In step 204 an indication of at least one frequency is received. This at least one frequency is stored in step 206. In step 208 a transmission frequency is chosen based on the stored frequency or frequencies, in order to enable the FM enabled device to reliably transmit data, e.g. audio, via the chosen frequency.

It is possible that the mobile device may utilize more than one AF list in memory. The weighting method employed in the example exemplary embodiment uses "Low", "Medium", and "High", to indicate the preferred channels (frequencies). A "High" weighting indicates that this is the preferred choice. A "Low" weighting implies that it can be used but may prove unreliable and another AF jump may need to take place as this signal has the possibility of degrading to a point that it becomes unusable.

In it's simplest form a "True" or "False" method could be employed which would indicate that channels are either "free" for use or "blocked" from use, respectively. This may reduce the amount of memory being used due to a reduction in size of the data structures; e.g. for every channel only one bit will be required to represent True or False (1 or 0). By adding another bit, i.e. two bits per channel, the possibilities can be increased to allow that a "weighted" method is used. The bit combinations could then be as follows:

0O = BLOCKED 0I = LOW 10 = MEDIUM H = HIGH

Of course, more bits can be utilized at the expense of using more memory to provide even more precise weighting.

The invention includes several schemes for improving obtaining and providing alternative frequencies to be used by radio transmitter devices, by using further sources and criteria to compile an up-to-date list of reliable alternative frequencies to the system. It is also possible to combine more than one scheme for obtaining/providing the AF data.

A first example is a network assisted scheme, performed via a cellular network. In this scheme access to a central database is required which contains up to date information on available (and possibly as well unavailable) frequencies for different geographical areas. An example of geographical areas that could be used is the cells of the cellular network. However, there is no restriction in choosing the positions and/or sizes of the areas. The database maintains data associations between the geographical areas and frequencies available therein (and optionally frequencies unavailable therein). It might happen that in some areas there are no frequencies available at all, although this is to be expected to be rare.

Depending on the location of the user and his transmission device, this scheme will provide the user with location-dependent information about at least one available frequency (unless there is no such frequency at all). It is also possible to provide the user's device with a list comprising more than one frequency. This is advantageous because there may be varying transmission situations even within the geographical areas that can only be assessed on site.

That is, the user might be located in a region within such a geographical area where transmission is not possible on a frequency indicated as available, due to some "micro" local conditions the database can not take into account. Just as an example the user might be located within range of a building structure blocking some frequencies. In this case the user's device has to select between other available frequencies provided to it in an unassisted manner.

In an embodiment location based services of the cellular network are employed. Here, the

mobile device will know which cell location the user is in as the user roams the country. Based on this information the mobile device can obtain the latest AF list information for that area from the network. This information can then be used by the mobile device to help determining the best channels to use for the AF list. It may be possible to transport this information using existing cellular protocols. In an exemplary embodiment this can be achieved by the use of SMS, MMS or other messages that may automatically be triggered when the device is entering a new area, or generally when available frequencies change due to a change in the location.

In an alternative embodiment an internet connection, e.g. via the General Packet Radio Service GPRS, can be utilized to obtain the AF information rather than via the cellular system itself. An advantage thereof is that this will not require any updates to the cellular system infrastructure and protocol which may be necessary otherwise.

The location of the device may be determined also by other means, e.g. employing a Global Positioning System GPS receiver included in the device. This may be used as a replacement of or an addition to cellular based location. That is, both cell locating via location based services LBS and/or GPS can be used as input into the database in order to extract the latest most accurate AF data.

In addition to or in other embodiments even in replacement of cellular and/or Internet connectivity, Bluetooth, WLAN or other local connectivity methods can be used in the present invention. For example this might be used when a user is traveling on foot and is walking around a city. AF list information can be passed to the mobile device via local connectivity means and could be used when the user returns to his vehicle and begins to use the FMTx feature with his in-car stereo. Alternatively, this would be useful if the user wants to broadcast audio data to another user, as it enables sharing AF lists via Bluetooth, WLAN or like. Such sharing can then be used to set up the involved users' transmitter/receiver devices accordingly.

Other users may benefit from the AF list of another user using Bluetooth, WLAN, SMS,

MMS, IrDA or any other wireless or even wire-based connection. Users may thus exchange AF list information using various methods. An example of where this would be useful is when a user wishes to broadcast audio data to (a) fellow user(s) and the transmitting handset is provided with the capability of passing on it's AF list to other potential listeners. These listeners will then be able to benefit from the shared AF list information. In other words, AF lists might also be exchanged via peer to peer connections among a plurality of users.

According to the present invention not only available frequencies may be obtained and provided to transmitter devices. It is also possible to indicate frequencies that are unavailable due to different reasons.

For example a mobile device user may travel to different countries and may wish to use the FMTx feature within those countries. Depending on the country being visited, the legal requirements for the use of low power FM transmitters are likely to vary and this may affect the allowable maximum effective radiated power ERP and also the frequency band/channels that the device is allowed to transmit on.

Therefore the invention also includes the use of "country" profiles that will configure the various parameters for FMTx automatically. This may e.g. be based on country code information obtained either from a cellular network or via RDS. Any other method for identifying where the user currently is located may be used as well. Depending on the country it is possible to restrict the use of frequencies to those allowed in the particular country. In an exemplary embodiment this may be achieved by providing a "blacklist" of frequencies that are not allowed. Such blacklists can be pre-programmed into a device associated with different countries, or in association with other region-based restrictions.

While in certain embodiments the transmitter device can change an AF list itself, including updating an "inverse AF list" containing frequencies which are blocked by transmissions or other interfering signals, such a black list of forbidden frequencies is implemented so that it cannot be changed by the device. That is, the frequencies that are prohibited in certain countries are effectively "blacklisted" and therefore are barred from selection by the user/the

device for as long as the user remains within that country. Unless the blacklist itself is updated, it will only be possible to add frequencies which are unavailable (due to other reasons than legal requirements), but not to remove a barred frequency from the blacklist.

The concept of the invention of using country profiles can in general also be applied to any situation where certain circumstances require that certain frequencies are to be excluded from use. The default country profile may be stored within the factory defaults for the mobile device which will be selected when the device is reset to the factory defaults. In another embodiment there are no country profiles located on the device itself, instead the provider of the AF list can take into account the local legal requirements or like when compiling the AF lists.

The use of profiles can be generalized even more; it can also be used for performing a "product profiling". Due to having differing hardware components, running at different clock frequencies, due to supporting other wireless or galvanic interfaces (e.g. product version with/without WLAN transceiver) and also due to varying mechanical and antenna design different mobile devices will all have their own "signature" in terms of RF interference and performance. In other words, depending on aforementioned features of the device there may be certain frequencies which will always be noisy, caused by the device itself in an intrinsic manner. By using frequency blacklists or frequency exclusion profiles, each product could be profiled and any noisy channel could be marked as blocked.

Using such exclusion profiles can help to accelerate AF allocation since the device does not waste time checking channels which are always noisy for that particular product. Frequencies excluded in this manner are also not to be changed by the device itself or upon user control. They could e.g. be hard-coded into the firmware of the device.

Another possible method to increase the user's experience of FMTx is by ensuring there is a free channel either side of the selected channel i.e. ensuring that the free channel does not have channels having a strong signal level on either side of it that may cause interference; in other words, allowing space around the free channel. This has the potential to ensure that no

interference will break through and impair the user's experience.

Users do generally have certain habits and thus the areas in which the FMTx capable mobile device will be used are likely to be fairly consistent during the ownership of the mobile device. Therefore the invention further includes to employ a neural based or other adaptive learning system that is able to learn the user's daily routine and hence apply the most commonly used available channels at the right time and in the right location. Generally, an average user lives in the same location from day to day and also works at the same location from day to day and gets to and from those locations by the same route. Although this of course is not necessarily true for every day of the user's life, the neural system could match this with a calendar. E.g. at weekends it is more likely that the user will be frequenting public amenities. A neural system or other adaptive learning system is beneficial in areas where poor network coverage is experienced and utilizing other methods to obtain AF list information is limited.

As the neural system learns the user's FMTx use habits, the user may wish to assign labels or tags to learnt data such that a user could select and effectively force a profile to be used. These profiles might have tags such as "work", "weekend", "home" etc. to describe the type of profile that the system should use. This would be useful since a user may take a day off from work and would want the FMTx system to make use of perhaps the "home" profile instead of the assumed automatically selected "work" profile. Although the system would be more than capable of selecting the correct profile automatically (perhaps by detecting cell location information), allowing the user to force the mobile device to only use a particular profile would allow more efficient selection of alternate frequencies.

The device can thus use the external resources to build a dynamic history based on individual behavior such that the user would be provided with a faster and more precise way of finding/selecting a valid free channel/frequency. Particularly in cases of built-up-areas this can represent a valid and very useful feature.

As the user changes his movement habits, the system will adapt over time as different

information is presented to the system based on differing geographical locations. It may also be provided that the user is enabled to save typical movements and therefore AF list profiles into presets that the user may recall at any time.

Providing a central database holding all of the AF list information would mean that all users have access to the same AF data no matter where they are in the country. Each country would have its own database. To allow the database information to remain current and therefore accurate, data from individual's handsets could (if allowed by the user) be uploaded to the database to enhance and also to verify the accuracy of the information stored on the database. Over time the database becomes more accurate with respect to the AF data it provides. AF list data can also be shared directly between users.

In FMTx system implementations where a user is able to initiate an AF jump, the system could learn which channels are often discarded by a user, that is, which channels are most likely to be manually left by user input. In this manner the system can determine channels which may be considered as blocked or blacklisted channels, as they are likely to show bad Tx performance. It is to be noted that the user will usually not specify the frequency to tune to, instead the transmitter device will automatically chose one. Therefore usually no conclusions about the quality of the new frequency can be derived from the jump alone. A weighting system can be applied based on this data such that when the system is working in an automatic manner, this information could also be taken into account when creating the AF list and selecting an AF.

The origin of AF list information would also affect the apparent reliability and hence the apparent integrity of the data. E.g. if the data was obtained from Location Based Services

(LBS) from the cellular network, then this would carry a stronger weighting since the data has a higher probability of being accurate. However, if the data is obtained from another user in a peer-to-peer exchange then the data may not be that accurate for the area in which the user currently is. This data would therefore hold a weaker weighting. The FMTx system within the mobile device can use the weighted AF list information to build as accurate a picture of the current state of the VHF FM band for that location as is possible and hence

improve the overall user experience and also help to reduce the power consumed by the mobile device due to not having to scan the whole band for available channels.

The present invention also includes providing a user interface for enabling users to edit the list of available and/or blocked frequencies. In further embodiments also any weighting settings with respect to the frequencies can be changed using the interface. Certain restrictions can be applied to control access to such an interface. For example certain frequencies that are blocked due to legal and/or technical reasons will be excluded from editing.

Legal fixed radio stations are allocated their own program identification (PI) code. This is utilized by the RDS system such that when a user is roaming the country and the radio signal of the current station gets weaker, the RDS capable FM receiver will then scan the VHF band for a stronger good signal that has the same PI code thus allowing the user to always listen to his chosen radio station when on the move.

Because allocating a fixed PI code per mobile device would be impractical and could potentially be in conflict with a legal station having the same PI code, a dynamically allocated PI code would be beneficial. A dynamic list of PI codes will have to be maintained by the mobile device and the PI code may need to change should the user move into an area where a legal radio station's signal becomes strong enough such that the currently allocated PI code can no longer be used.

A PI code usually has a section indicating the country related to the respective radio broadcast. In order to avoid any conflict with licensed (national) radio broadcasts, it is possible in the invention to use a PI code having a different country code on purpose. Just as an example, when using the transmitter device in Germany, the country code of Great Britain might be used. In even more advanced embodiments it is possible to query a database in order to select a country code to be used that is neither used in the current country nor in any adjacent country (in the above example the one of Spain or like, while avoiding Netherlands,

Belgium, France, Poland etc.).

A country code to be used as a default can be programmed into a device "according" to the country it is intended to be sold in, as has been detailed above. Thus it can be ensured that a transmitter device will most certainly not be subject to PI code conflicts at least as long as it is used in a country where it is sold.

The part of the PI code indicating the actual radio station can be adjusted based on the usage of PI codes in the current reception area. However, it can also be derived in a pseudo-random manner, e.g. it can be derived from some unique device property. In case of FMTx enabled mobile phones the International Mobile Equipment Identifier IMEI can be used to derive a PI code part for this purpose. This can be used alone or be combined with the above mentioned "false" country code.

The mobile device will update the FM receiver via RDS with the new information. This will have to be done as soon as possible to avoid the legal station AF list being used instead of the mobile devices AF list. In order to make use of the dynamic PI code feature the mobile device will need access to an RDS capable FM receiver to allow the mobile device to obtain the PI code for each valid and legal FM radio station that is detected.

In summary, the invention is making use of various external resources to obtain an updated and thus "personalized" AF list. The advantages should be apparent; a more accurate AF selection means that the user will have the best experience when using the FMTx feature in conjunction with AF. Faster AF selection, improved reliability resulting in less user intervention and hence improved safety when being used in a vehicle are obtained. By providing the FMTx system with a more accurate and concise AF list, power consumption is also reduced due to the system not having to scan the whole VHF FM radio band. This is an important aspect for mobile devices.

In essence, this invention offers the user an enhanced listening experience generated from a mobile data source by creating and dynamically managing the internal generation and use of

AF lists from historic and numerous current data inputs, and to maintain an optimal

connection to the listening receiver from which the user is obtaining the direct listening experience.