WO2008155598A1

WO2008155598A1 - Method and device for transmission of media data to broadcast receivers

Info

Publication number: WO2008155598A1
Application number: PCT/IB2007/001647
Authority: WO
Inventors: Gregor Schneider
Original assignee: Nokia Corporation
Priority date: 2007-06-20
Filing date: 2007-06-20
Publication date: 2008-12-24

Abstract

Methods and devices are described for transmitting media data from a playback device to a broadcast receiver. In order to avoid interference with transmissions in an area, information indicative of an occupation of broadcast channels is received. The received information is evaluated for identifying usable frequencies for a transmission, and a usable frequency is selected for transmitting the media data. Furthermore, in a device information indicative of an occupation of broadcast channels is received on a broadcast transmission. The information may be processed and transmitted on a low power radio link to a further device.

Description

Method and device for transmission of media data to broadcast receivers

Field of the invention

The present invention relates to a method and a device for transmitting media data from a playback device to a broadcast receiver and to a corresponding broadcast receiver for receiving such media data. Particularly, it relates to finding available frequencies for a transmission without causing interference with transmissions in an area.

Background of the invention

Mobile electronic devices which are capable of music playback have become very popular recently, with the IPOD™ by Apple® Computer Inc. being one of the most prominent examples. These music players are mainly intended for being used in conjunction with head- or earphones. For a typical mobile use of such devices this is the most preferable listening manner. However these players have become rather sophisticated recently, many of them even comprise hard disks capable of storing gigabytes of music. Therefore it seems only logical that a user would want to use the player, whereon a big amount or even all of his own music is stored, as a source of music 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 source of music or other stored audio data in a vehicle, for example as a replacement for a CD-changer. However, car radio systems usually 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, a user may want to connect the mobile music player to many different playback devices, preferably without the use of cables.

As many audio playback devices like stereo systems and car radios comprise an FM (frequency modulation) tuner or receiver, a known implementation of such wireless transmission is to "mimic" the music player as a conventional FM radio station and to transmit the audio data encoded as a standard FM radio broadcast transmission.

In the United States of America the FCC (Federal Communications Commission) allows the usage of unlicensed (i.e. personal/private) FM-radio transmitters according to FCC rule 15 (see section 15.239). Similar legislation applies to many other countries. Such a transmitter can thus be used for conveniently transmitting sound or music from any device wirelessly to an FM radio operating in the 88 - 108 MHz band, e.g. from a CD-player or an MP3-player. This allows listening to music from such a device e.g. through a car FM radio. Due to the restricted transmission power with a field strength of 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 usually not allowed.

Conventional transmitters for that purpose simply transmit on a fixed frequency or frequency that can be chosen manually. This requires manually setting the corresponding transmission frequency at both the transmitter connected with the player device and the FM radio receiver, hi order to avoid interference with a licensed transmitter, the user has to perform a manual search for free frequencies before setting the frequency in order not to violate the regulation.

Additionally, when the FM receiver is a car radio and the user is driving, the situation related to free frequencies will change over time. This will require re-tuning from time to time, e.g. because a licensed transmitter (e.g. a radio station) will come in range that is transmitting on the same frequency as the unlicensed private transmitter of the user. On the one hand this is normally prohibited as discussed above and should therefore not occur, and on the other hand such interference will decrease the quality of the signal received from the music player, as the transmission power of the private transmitter is substantially lower than that of licensed transmitters. Manual re-tuning will thus be unavoidable to maintain the quality of the transmission of audio data. An FM transmitter may include a scanning component (e.g. an FM radio receiver) that allows scanning for free frequencies. In addition, the currently used frequency may be scanned for potential interferers, like licensed transmitters. This allows the FM transmitter to construct a list of usable or unusable frequencies and to change transmission to one of the listed usable frequencies when the currently used channel is found to be occupied by another transmitter, especially a licensed broadcast transmitter. However, as one of the main usages of the FM transmitter may be in an automotive environment, the scanning has to be repeated frequently, as the car moves through reception areas of different fixed licensed broadcast transmitters. Consequently, the classification of which frequencies are usable and which are unusable will change accordingly.

Summary

According to a first aspect of the present invention, a method is proposed, comprising receiving on a wireless interface of a device information indicative of an occupation of broadcast channels, identifying usable frequencies for a transmission on the basis of the received information and transmitting on a frequency selected from the identified usable frequencies. This method may be performed in a device, especially a mobile device with stored media data the user wishes to transmit to a second device for media reproduction. In one embodiment of the invention, the device is a mobile communication device, for example a mobile telephone.

The information indicative of an occupation of broadcast channels describes whether broadcast channels are occupied by e.g. transmissions from broadcast transmitters in an area. The area may be the current location or a neighboring area. The indication can be interpreted in that in at least a part of an area a signal on the broadcast channel can be received. The indication may also contain information about the area. The information can be received in several different ways.

Ia one exemplary embodiment, it can be received on a broadcast transmission. This may be a broadcast transmission according to the same standard and using the same broadcast channels or a subset of the same broadcast channels about which the information is received. Alternatively, this may be a different broadcast transmission or a broadcast transmission in a different frequency band. The broadcast transmission may be analog or digital. Examples of analog transmissions are AM (amplitude modulation) transmissions and FM (frequency modulation) transmissions. Further examples of digital transmissions are digital media broadcast transmissions like DAB (digital audio broadcast) DMB (digital media broadcast), DVB (digital video broadcast) which may be terrestrial (DVB-T), terrestrial for handheld devices (DVB-H) or satellite transmission (DVB-S), DRM (digital radio mondiale), MediaFLO™ or the like.

In a further embodiment, the information indicative of an occupation of broadcast channels can be received via a low power radio link. For example, it can be received from another device in the vicinity by Bluetooth™ or WLAN transmission. Further examples of low power radio transmissions comprise UWB (ultra wide band) or W-USB (wireless USB).

m another exemplary embodiment, the information indicative of an occupation of broadcast channels can be received via a cellular transmission, comprising e.g. GSM, CDMA, W-CDMA, UMTS or other cellular radio communication standards.

The broadcast transmitters occupying the broadcast channels may belong to a broadcast network. In an exemplary embodiment, the broadcast network is an analogue network, e.g. an AM or FM radio network. In a further exemplary embodiment the network is a digital network, comprising the standards named above (DAB, DMB, DVB, DRM₃ MediaFLO™ and the like). As these networks allow transmission of audio data, image and video data, application data etc., these networks may be summarized under the term digital media broadcast networks.

According to a further aspect of the invention, the information indicative of an occupation of broadcast channels comprises information indicative of an occupation of broadcast channels in neighboring areas. A neighboring area is an area that is supposed to be covered by transmission of a different transmitter than the area in which the device is currently located (local area or first area). As transmission areas may overlap, a neighboring area may also be defined as an area in which a signal of a different station is received with a stronger signal level than the signal of the transmitter of the local area that belongs to the same network. Receiving information on transmissions in neighboring areas may be helpήil, as the device can find out only about transmission in its local area e.g. by scanning the frequency band of the broadcast network. Transmissions from transmitters in neighboring areas may be too weak to be detected at all at the location of the device, or they maybe too weak to be detected reliably.

In a further exemplary embodiment, the wireless interface is capable of receiving FM radio broadcast transmissions, and the broadcast transmitters are FM broadcast transmitters, i.e. the wireless interface is an FM radio broadcast receiver using the same frequency band as the broadcast transmitters. In a further exemplary embodiment, the transmitter, whose transmission is received at the wireless interface, belongs to the same FM radio network as the FM broadcast transmitters.

hi a further embodiment, the information indicative of an occupation of broadcast channels is received as information of the Radio Data System (RDS). Especially, the Alternate Frequency (AF) data of the Radio Data System is used to derive such information.

These methods may be performed by a device comprising at least a receiver configured to receive information indicative of an occupation of broadcast channels, a processor for identifying usable frequencies for a transmission based on the received information and a transmitter configured to transmit on a frequency selected from the identified usable frequencies. Preferably, the device is a mobile device, as the invention is especially helpful in situations when the user uses the device while moving to such an extent that he / she experiences varying reception of broadcast transmissions, for example when traveling in a car. Thus, the identification of usable frequencies for a local transmission may have to be updated regularly in the device. A list of usable and / or unusable frequencies may be maintained and updated regularly by scanning the frequency band and measuring a received signal strength value on each channel. Using information about transmissions in neighboring areas may reduce the frequency of scanning the frequency band, as the device has already information about transmissions in areas in which the user may travel. By avoiding using the frequencies of transmissions in neighboring areas, the likelihood of transmission on an occupied frequency can be reduced while traveling.

If the mobile device is a mobile communication device, e.g. a mobile phone, it may also use the cellular communication interface(s) for receiving information indicative of an occupation of broadcast channels. For example, it may request the information from certain internet services. Information about the position of the device, e.g. GPS information or information about the cell from the cellular system, may be used to help finding the information suitable for the current location of the device. Location information may be sent to the internet service, which in response sends back a list of broadcast transmitters in the neighborhood of the device.

hi an exemplary embodiment, the receiver of the device is a broadcast receiver, especially a receiver for receiving broadcast information from an analogue or digital network. The receiver may for example be an FM radio receiver or tuner, capable of receiving RDS data and especially capable of evaluating AF data from the RDS. Alternatively, the receiver may be a low power radio receiver or a cellular receiver.

According to a second aspect of the invention, a method is proposed comprising receiving on a broadcast transmission information indicative of an occupation of broadcast channels and transmitting via a low power radio link said information indicative of an occupation of broadcast channels.

This method is performed in a second device and corresponds to the method of the (first) device above for the case that information indicative of an occupation of broadcast channels is received via a low power radio link. The second device comprises a broadcast receiver for receiving information from a broadcast network, extracts the information indicative of an occupation of broadcast channels and transmits the information to the first device via the low power radio link. The second device may further comprise a processor for processing the information in order to alleviate the processing effort in the first device. For example, the information indicative of an occupation of broadcast channels may be compiled in a list, the list may be sorted and duplicate channels may be removed. Furthermore, a frequency for transmission may already be selected.

In an exemplary embodiment, the receiver of the second device is an FM broadcast receiver capable of receiving and decoding data of the Radio Data System, especially AF information from the RDS. The second device may be a car radio.

hi a further aspect of the of the invention, a system is provided, comprising the first device when the receiver is configured to receive the information on occupied channels via a low power radio link, and the second device.

In another aspect of the invention, a computer program product is provided, comprising program code stored on a computer readable medium for carrying out a method comprising receiving on a wireless interface of a device information indicative of an occupation of broadcast channels, identifying on the basis of the received information usable frequencies for a transmission and transmitting on a frequency selected from the identified usable frequencies.

In a still further aspect, a device is proposed, comprising receiving means configured to receive information indicative of an occupation of broadcast channels, processing means for evaluating the information received by the receiving means for identifying usable frequencies for a local transmission and transmitting means configured to transmit on a frequency from the identified usable frequencies.

Brief description of the drawings

The invention may be better understood by referring to the attached drawings, which are solely provided as illustrative examples of possible embodiments of the present invention, and in which:

Fig. 1 shows an embodiment of a local broadcast transmitter;

Fig. 2 shows a block diagram of an embodiment of a first device according to the invention;

Fig. 3 shows a flow diagram of a method of a first device according to the invention;

Fig. 4 shows a usage scenario according to the invention;

Fig. 5 shows a flow diagram of a further method of a first device according to the invention;

Fig. 6a shows a flow diagram of a method of a second device according to the invention; Fig. 6b shows an alternative method of a second device according to the invention;

Fig. 7 shows a block diagram of an embodiment of a second device according to the invention;

Fig. 8 shows a usage scenario in a car according to an aspect of the invention.

Detailed description of the invention

The following description describes exemplary embodiments of the invention using FM transmission, operating in an FM radio environment with one or more radio networks. However, it is to be noted that the invention is not limited to being used for FM radio transmission technology, but can also be used for other analog or digital broadcast transmission technologies.

Fig. 1 shows an audio player with an FM transmitter 100 known in the prior art. A display 102 may show which audio title is currently played (e.g. "Song 4" from the user's collection of audio titles that is stored in the device), and the FM radio transmission frequency that is currently used for transmission (e.g. "104.80 MHz"). A keyboard 104 may be used to start and stop the player, switch FM transmission on or off, or to select a different frequency. An FM transmission signal 106 is sent out for reception by an FM radio device in the vicinity of the device 100.

Fig. 2 shows a block diagram of an embodiment according to the invention. Device 200 may be an audio player with an FM transmitter similar to the device shown in figure 1. Device 200 comprises a wireless interface 201 connected to an antenna 202 for receiving inter alia information about transmissions in neighboring areas. In an embodiment, wireless interface 201 is an FM radio receiver capable of receiving and decoding RDS data. RDS data comprises AF data, which describes alternate frequencies of the same transmission or program that are sent out by transmitters in neighboring areas. The wireless interface 201 is connected to a processor 205 for processing the received RDS data. Preferably, wireless interface 201 is also capable of measuring the received signal strength of frequencies / channels in the frequency band of interest (e.g. the FM radio band). Processor 205 is also connected to a memory 206 for storing a list of usable and / or unusable frequencies in the frequency band of interest. Memory 206 also stores one or more audio files for playback, e.g. MP3-files. Also other audio codecs may be used as a suitable data format for storage and are known in the prior art, like RM (real media), Ogg Vorbis, WMA (Windows media audio) etc. Processor 205 also stores and reads out audio files from memory 206 for transmission by the local transmitter 203, e.g. an FM transmitter that frequency modulates the transmission frequency with an audio signal. The transmitter is connected to antenna 204. In another embodiment, antenna 204 may be the same antenna as antenna 202, if the antenna characteristics match sufficiently and if feedback of the transmitting signal from transmitter 203 into wireless interface 201 can be suppressed to a required level.

Device 200 may contain further interfaces 207 for connection through one or more connectors 210. Similar to the device shown in figure 1, device 200 contains a display 208 and a keyboard 209. If device 200 is a mobile device, it contains a battery 222.

Figure 3 shows a flow diagram of an embodiment of a method, demonstrating how information about transmissions in neighboring areas can be processed by processor 205. hi step 302, the processor 205 instructs the wireless interface 201 to scan for transmissions within the frequency band of interest. The wireless interface may for example start scanning on the lowest frequency and tries to detect a signal. If no signal is found in step 304, then the frequency is increased to the next channel and the scanning process is continued in step 302. If a signal is found, the wireless interface 201 searches for RDS information. If no RDS information is found in step 306, again the scanning frequency is increased to the next channel and the scanning process is continued in step 302. IfRDS information is found, then the information field containing Alternate Frequency (AF) data is decoded in step 308. The found AF data is processed by processor 205, and a list of unusable frequencies is compiled and stored in memory 206. The found alternate frequencies from the RDS information together with the currently received frequency are added to the list of unusable frequencies in step 310. The process continues by checking whether the complete frequency band is scanned in step 312. If not, scanning continues in step 302. If the whole frequency band is scanned, then a frequency for transmission by the local transmitter is selected.

The list of unusable frequencies may contain all frequencies that are judged to be unsuitable for transmission. There may be several different criteria for judging a frequency unsuitable for transmission. For example, a frequency or channel may be judged unsuitable for transmission if a signal level above a threshold is detected on the frequency. A frequency may also be judged unsuitable if a signal level above a threshold was detected frequently in the past. Frequencies which are next to frequencies with high received signal strength may also be judged unsuitable for transmission, as they may experience interference. Furthermore, a frequency may be judged unsuitable if it is found as part of the AF data of a received transmission.

Alternatively, the device 200 may keep a list of usable frequencies in memory 206. hi this case, process 300 may start with a list of all frequencies, denoting all frequencies of the frequency band as usable. While transmissions and alternate frequencies are found during process 300, frequencies are deleted from the list of usable frequencies until the process is finished, i.e. until the complete frequency band is scanned.

As a further alternative, a list of all frequencies of the frequency band is kept in memory 206. As the process 300 continues, frequencies of the list are marked with qualifiers, indicating for example the received signal strength and / or whether the frequency was found to be an alternate frequency. The list may be sorted according to the relevance of the qualifier for selecting the frequency as a suitable frequency for local transmission.

Table 1

Table 1 shows an example table as a result of the scanning procedure of process 300. The table shows the scanned frequencies, the signal level classified from level "0" indicating that no signal or a very weak signal was found to level "3" indicating a strong signal, neighboring frequencies indicating that a frequency is next to a frequency with a strong signal and alternate frequencies indicating that decoded RDS information listed this frequency as an Alternate Frequency. For example, a strong signal level is received on frequency number 4 at 87.8 Mhz. As a result, frequencies number 3 and 5 at 87.7 MHz and 87.9 MHz are marked as neighboring frequencies. In addition, RDS information could be decoded on frequency 4 at 87.7 MHz, listing frequency number 10 (88.4 MHz) and frequency number 204 (107.8 MHz) as alternate frequencies of the same transmission or program that are sent out by transmitters in neighboring areas. These frequencies are marked in the table accordingly. A strong signal was also received on frequency number 10 at 88.4 MHz. RDS information of this signal may indicate that the program received on this frequency is the same as the program received on frequency 4, e.g. by an identical program identification (PI) code. In this case, the AF information of the RDS data may list the same frequencies as the AF information of the signal received at frequency number 4. If however the RDS information on this signal indicates that the transmission contains a different program as the one on frequency 4, the AF information will be different and indicate for example frequency number 6 as alternate frequency of the program received at frequency number 10, as shown in table 1.

Table 2 shows an example of a sorted table of the scanning procedure of process 300.

Table 2

Table 2 lists the frequencies with the strongest received signals first. The second sorting priority is the neighboring frequencies, then the alternate frequencies. At the bottom of the table, those frequencies are listed that have a weak signal, e.g. below a certain threshold, and that are neither neighboring frequencies nor alternate frequencies. These frequencies are the highest priority candidates as usable frequencies for a local transmission by the audio player 100.

Without the invention, frequencies with the same signal level not listed as alternate frequencies could not be distinguished from frequencies listed as alternate frequencies. When traveling e.g. in a car, the user might quickly get into the reception range of one of the listed alternate frequencies. By using the alternate frequency information, the likelihood of getting into the reception range of broadcast transmitters in neighboring areas and then using their broadcast frequencies for local transmission is reduced. In other words, the information on usable and unusable frequencies covers a larger area. Consequently, the frequency of scanning for usable or unusable frequencies can be reduced, or the time until the scanning process needs to be repeated can be enlarged.

Figure 4 illustrates the scenario of a user in a car 402 as he / she drives through a certain area. The user may want to start a local transmission within the car 402 from his audio player (not shown). The wireless interface of the audio player may currently receive transmitters 410 and 420 and be able to decode the RDS information transmitted on their signals. Transmitter 410 belongs to a network A, transmitter 420 belongs to a network B. Also transmitters 412 and 414 belong to network A. Their transmission frequencies are listed in the alternate frequency information of transmitter 410. Similarly, transmitters 422 and 424 belong to network B, and their frequencies are listed in the alternate frequency information of transmitter 420. The wireless interface may for example receive only a weak signal on the frequency used by transmitter 412. No signal is received from transmitters 414, 422 and 424, as these are at a greater distance from car 402 and / or transmit with a lower transmission power. The audio player avoids frequencies used by transmitters 410, 420 and 412 for local transmission because a signal is received on these frequencies. By using the alternate frequency information from transmitters 410 and 420, the audio player also avoids frequencies used by transmitters 414, 422 and 424. Thus, when traveling into reception areas of transmitters 414, 422 and / or 424 the device will not need to retune to a different frequency, as the used frequencies in these areas are already avoided without starting the scanning procedure again.

In a further embodiment, information indicative of an occupation of broadcast channels is received on a low power radio link like Bluetooth or W-USB, as shown in the flow chart 500 of figure 5. An audio player, e.g. the audio player of figure 2, sets up a connection on a low power radio link in step 502. In step 504, it tries to receive AF data on the low power radio link. In case no AF is received, it tries to receive a frequency list. The frequency list may contain information similar to the lists shown in table 1 or 2. If no frequency list is received, the audio player may try to build up a connection to a different device on the low power radio link. Alternatively, the audio player may stop connecting to other devices after a time out. In case either AF data or a frequency list was received, the information is added to the list of usable or unusable frequency stored on the audio player in step 508. As in the process 300, a usable frequency for transmission is selected as the last step (step 510). Receiving AF data or a list of usable or unusable frequencies, or even a single frequency for transmission over a low power radio link from another device may have the advantage that the other device has better capabilities to receive AF data or to build up a reliable list of usable or unusable frequencies. The other device maybe a car radio with a better FM radio receiver or a better antenna. Especially in the in-car scenario, FM reception by the audio player may be poor, as the audio player may not have a good antenna for FM reception or as FM reception quality may be poor due to a low quality FM receiver and / or the proximity to the FM transmitter in the device.

By contrast, the car radio may have a high quality FM receiver and is typically connected to an antenna outside the car (e.g. on the roof of the car) or on the windscreen which provides a higher reception gain. In addition, many car radios process AF data anyway. Also, many car radios have a second FM receiver for background scanning of alternate transmissions. So, while receiving the local transmission from the audio player, they may scan for RDS data from other transmitters. In addition, background scanning doesn't load the battery of the audio player in this scenario.

Figure 6 shows an embodiment of a process 600 used by a car radio. This process is very similar to process 300 of the audio device except for the last step. The car radio starts scanning for transmissions in step 602. If a signal is found in step 604, it is checked whether RDS information can be received in step 606. If either no signal is found or no RDS information is found, the scanning continues in step 602. IfRDS information is found, AF data is decoded in step 608 and added to a list of usable / unusable frequencies in step 610. The list may look like one of the lists shown in tables 1 and 2. Alternatively, only the AF data is compiled. When the complete frequency band has been scanned in step 612, either the pure AF data or the list of usable / unusable frequencies is transmitted on a low power radio link to the audio player in step 614.

In. an alternative embodiment, also the selection process of the transmission frequency is done in the car radio directly before step 614. In this case, shown in figure 6b as a continuation of the process described in figure 6a up to step 612, only data of one frequency which is found suitable for local transmission is selected in step 616 and sent to the audio player via the low power radio link in step 618. The audio player is commanded to tune to this frequency. In this embodiment, the car radio may directly or with a short delay tune to the frequency that was transmitted to the audio player. Or the car radio may wait until transmission on the currently used frequency stops as in step 620, and then tune to the frequency that was transmitted to the audio player in step 624. In this embodiment, the car radio is completely in control of the transmission frequency used for the local FM transmission. If the current transmission hasn't stopped in step 620, the transmitter waits until a time out has expired in step 622. However, before the time out expires, it may transmit the information on the same selected frequency again on the low power radio link. After the time out has expired, it may return to step 616 and select a different frequency for transmission.

In yet another embodiment, the car radio may wait after step 618 for a response from the audio player on the low power radio link. The response may contain either an "accept" or "reject" for the frequency that was sent in step 618. If the frequency is accepted, the process continues to step 620 as described above. If the frequency is rejected, the process may directly return to step 616 and select a different frequency for transmission. The "reject" information from the audio player may contain information on supported frequencies. For example, some FM transmitters may be able to tune only to a sub-range of the whole frequency band, or they may be able to tune only to frequencies of a 200 kHz grid within the frequency range, whereas in many countries a 100 kHz grid is used in FM transmissions.

Figure 7 shows a block diagram of an embodiment of a device 700 performing the process 600, e.g. a car radio. Device 700 contains a broadcast receiver 701, e.g. an FM radio receiver, connected to antenna 702. Antenna 702 may be an antenna outside a car, e.g. on the roof or on the windscreen. Broadcast receiver 701 is capable of receiving information indicative of an occupation of broadcast channels, e.g. in the form of AF data of the RDS. In certain embodiments, receiver 701 may contain 2 separate FM receivers: a first receiver for receiving the active audio program, i.e. the audio program the user is currently listening to, and a second receiver for background scanning of further transmissions in the frequency band. Receiver 701 is connected to processor 705 for processing RDS data and collecting AF data which may be stored in a certain part 720 of memory 706. Alternatively, the RDS data is processed together with further reception information, like received signal strength or neighboring frequencies of strong signals, in order to build up a list of usable or unusable frequencies. The list may be stored in memory 706 in addition to the AF data or as an alternative to the AP data. Processor 705 is also connected to a low power radio transceiver 703 for connecting to other devices in the vicinity of device 700 through a low power radio link. Low power radio transceiver 703 is used to transmit the AF data and / or the list of usable or unusable frequencies to another device in the vicinity through antenna 704. In addition, device 700 may comprise a power regulator 707 connected to a power connector 710 for supplying power to the components of device 700. Furthermore, device 700 may contain a display 708 and a keyboard 709 for user entries.

Figure 8 shows parts of the interior of a car for an embodiment of the invention. For example, a dashboard 802, a steering wheel 804 and a windscreen 806 are shown. A car radio 810 is installed in the dashboard 802. Car radio 802 may have all the components of device 700. Antenna 808 is connected to the broadcast receiver in car radio 810. Thus, antenna 808 corresponds to antenna 702. A local FM transmitter 812 is lying on the passenger seat 814. Local FM transmitter 812 may corresponds to the device 200 of figure 2 and has started playback of an audio file. Using antenna 808, car radio 810 is receiving a local transmission 816 of the audio file from FM transmitter 812 for reproduction on the audio car system.

Furthermore, both the car radio 802 and the FM transmitter 812 are equipped with a low power radio transceiver and have built up a low power radio connection 818. Car radio 802 is also receiving transmission 822 from broadcast transmitter 820 and scans the received signal for AF information of the RDS data. While car radio 802 background scans the FM frequency band, it also receives RDS data from further broadcast transmitters (not shown). The received AF information is compiled in a list and / or processed to a list of usable or unusable frequencies for transmission. The compiled list is sent to the FM transmitter 812 on the low power radio link 818. FM transmitter 812 uses the received information to select a suitable frequency for the local transmission 816.

hi a further embodiment, the compiled list of usable or unusable frequencies for transmission is sent to the FM transmitter 812 before local transmission 816 is started. Thus, the local transmission frequency doesn't need to be changed later, if the currently used frequency is found unsuitable after reception of the list of usable or unusable frequencies.

WMIe the invention has mainly been described in the combination of a mobile music player and a car FM radio receiver, it is not limited to this particular combination. For the artisan many other useful combinations should be apparent. Just as an example a mobile media player could be used to transmit a video on a local DVB-H transmission to a receiver in a car or bus, e.g. for entertainment of the passengers or as a safety instruction video.

Claims

1. A method comprising receiving at a wireless interface information indicative of an occupation of broadcast channels; identifying usable frequencies for a radio transmission on the basis of the received information; transmitting on a frequency selected from identified usable frequencies.

2. The method according to claim 1, wherein said information indicative of an occupation of broadcast channels is received via a broadcast transmission.

3. The method according to anyone of the previous claims, - wherein said information indicative of an occupation of broadcast channels is received in a first geographical area and comprises information indicative of an occupation of broadcast channels in neighboring areas of said first geographical area.

4. The method according to any of the previous claims, wherein the wireless interface is capable of receiving Frequency Modulation, FM, radio broadcast transmissions, and wherein said information indicative of an occupation of broadcast channels indicates broadcast channels that are occupied by FM broadcast transmitters.

5. The method according to claim 4, wherein said information indicative of an occupation of broadcast channels comprises information of the Radio Data System, RDS.

6. The method according to claim 5, wherein said information indicative of an occupation of broadcast channels is decoded from Alternate Frequency, AF, data of RDS.

7. The method according to claim 1 , wherein said information indicative of an occupation of broadcast channels is received via a low power radio link.

8. The method according to claim 2, wherein said information indicative of an occupation of broadcast channels is received via a digital media broadcast transmission.

9. The method according to claim 8, wherein said information indicative of an occupation of broadcast channels comprises information on broadcast transmitters of a digital media broadcast network.

10. The method according to claim 8, wherein said information indicative of an occupation of broadcast channels comprises information on broadcast transmitters of an FM radio network.

11. A method comprising - receiving, via a broadcast transmission, information indicative of an occupation of broadcast channels; transmitting, on a low power radio link, said information indicative of an occupation of broadcast channels.

12. The method according to claim 11, further comprising processing said received information indicative of an occupation of broadcast channels before transmission on the low power radio link.

13. The method according to claim 11 or 12, - wherein said received information indicative of an occupation of broadcast channels comprises Alternate Frequency, AF, data of the Radio Data System, RDS.

14. A device comprising a receiver configured to receive information indicative of an occupation of broadcast channels; - a processor configured for identifying usable frequencies for a transmission on the basis of the received infonnation; and a transmitter configured to transmit on a frequency selected from identified usable frequencies.

15. The device according to claim 14, wherein said receiver is a broadcast receiver.

16. The device according to claim 14 or 15, wherein said information indicative of an occupation of broadcast channels is received in a first geographical area and comprises infonnation indicative of an occupation of broadcast channels in neighboring areas of said first geographical area.

17. The device according to anyone of claims 14 - 16, - wherein said receiver is configured to receive FM radio broadcasts, and wherein said information indicative of an occupation of broadcast channels indicates broadcast channels that are occupied by FM broadcast transmitter.

18. The device according to claim 17, - wherein said receiver is capable of receiving data of the Radio Data System, RDS, and wherein said information indicative of an occupation of broadcast channels is received as infonnation of the Radio Data System, RDS.

19. The device according to claim 18, - wherein said processor is configured to decode said information indicative of an occupation of broadcast channels from Alternate Frequency, AF, data.

20. The device according to claim 14, wherein said receiver is a low power radio receiver.

21. The device according to claim 15, - wherein said receiver is capable of receiving information indicative of an occupation of broadcast channels via a digital media broadcast transmission.

22. The device according to claim 21, wherein said information indicative of an occupation of broadcast channels comprises information on broadcast transmitters of a digital media broadcast network.

23. The device according to claim 21, wherein said information indicative of an occupation of broadcast channels comprises information on broadcast transmitters of an FM radio network.

24. The device according to claim 14, wherein said device is a mobile communication device.

25. The device according to claim 24, wherein said receiver is a cellular receiver.

26. A device comprising a broadcast receiver configured to receive information indicative of an occupation of broadcast channels; a transmitter configured to transmit said information indicative of an occupation of broadcast channels via a low power radio link.

27. The device according to claim 26, further comprising - a processor configured to process said received information indicative of an occupation of broadcast channels before transmission via the low power radio link.

28. The device according to claim 26 or 27, wherein said received information indicative of an occupation of broadcast channels comprises Alternate Frequency, AF, data of RDS.

29. The device according to anyone of claim 26 - 28, wherein said device is a car radio.

30. A system comprising, - a first device comprising a broadcast receiver configured to receive information indicative of an occupation of broadcast channels; a first transmitter configured to transmit said information indicative of an occupation of broadcast channels via a low power radio link; and - a second device comprising a receiver configured to receive via the low power radio link said information indicative of an occupation of broadcast channels; a processor for identifying usable frequencies for a transmission on the basis of the received information; and - a second transmitter configured to transmit on a frequency selected from identified usable frequencies.

31. A computer program product comprising program code stored on a computer readable medium for carrying out the method of anyone of claims 1 to 10 when said program product is run on a computer device.

32. A device comprising means for receiving information indicative of an occupation of broadcast channels; - means for identifying usable frequencies for a transmission on the basis of the received information; and means for transmitting on a frequency selected from identified usable frequencies.