GB2120047A - Radio receivers and broadcasting network - Google Patents

Abstract

In order to provide correct automatic tuning of a VHF radio receiver 10 such as a car radio to the correct frequency in any area, an associated Traffic Information Service receiver 15 also detects a code indicating the area where the receiver is located. This code and a code indicating the programme selected on push buttons 13 by the user address a ROM 18 which stores the programme frequencies for all areas. The selected frequency enables an automatic tuning circuit 11 to tune the receiver 10. The ROM can be replaced by a RAM which is automatically updated by transmitting the frequencies or frequency codes (channel numbers) plus the programme labels and area codes on the TIS wavelength. Alternatively the frequency and label information for updating the RAM can be derived from the main receiver 10. <IMAGE>

Description

SPECIFICATION Radio receivers and broadcasting network The present invention relates to radio receivers, particularly car radio receivers, which are used in a variety of different areas where programmes have differentfrquencies.The invention also relates to an improved broadcasting network which enables a particular problem with mobile receivers to be overcome.

The problems oftuning and station identification, particulary on FM VHF radio, are well known. For example, ambiguities can arise when the same programme can be found in more than one place on the dial ofthe receiver and the correct signal may be difficultto identify at first. If the programme is monophonic a signal may appear satisfactory, even though it may be weak. Fading may then occur or a stereophonic programme maybeginandtheweak- ness ofthe signal is then revealed. This would have been avoided if the correct, strong signal had been tuned in the first place.

Several approaches are being studied to assist in tuning to the correct station, first time, One approach uses the fact that signals for a particular programme, in a particular area, will be found on certainfrequen- cies. A receivercan be designed to tune automatically and precisely to these frequencies, provided they can be defined precisely; synthesiser-tuned receivers are particularly suited to this application. If more than one frequency is available (i.e. it is impossibleto define only one correct frequency for a given area) a receiver may be designed to selectthe strongest signal.It is recognized thatthe strongest signal is not necessarily always the best signal butthis is a reasonable first assumption. Some receivers allow the userto select eitherthestrongestorthesecond strongest signal.

Another approach uses radio-data "labelling", whereby each radiated signal carries a special inaudible data signal to enable suitably equipped receivers to identify each received signal by decoding the data label. The data label may besufficientlycomprehen- siveto identify the radiated signal (ie programme and transmitter) unambiguously. On the other hand, it may bethought orfound necessary to identifythe radiated signal only partially andforthe receiverto take the stronger or strongest signal as before. (In addition to enabling the signal to be identified, radio-data may also carry other, changing information such as the kind of programme, clock-time, etc).

In the first method, (and to some extent in the second) itwill be necessary to supply the receiver with information concerning the frequencies whereby particular programmes may be found. For this it is necessaryto knowthe locality in which the receiver is situated in orderto knowthe particular frequencies.

The more precisely the location ofthe receiver is known, the more likely is the correctfrequency to be known. Naturally if the user is in possession ofthe relevant information, this can be used to tune the receiver manually; other methods such as punched or magnetic- cardsfor programming the receiver have also been suggested. All such methods suffer from the disadvantage of requiring special knowledge and/or action on the part of the user.

According to the present invention in one aspect, there is provided a radio broadcasting network wherein a plurality of differentfirst programmes are broadcast on frequencies which are different from area to area served by the system, and wherein a further programme is broadcast from a plurality of transmitters serving respective service areas, characterised in that the transmitters for the further programme are arranged also to broadcast coded signals identifying at leastthe corresponding service areas.

The further programme may be a Traffic Information Service, which employs a large number of well-defined, small, abutting service areas, covering say the United Kingdom and using a common frequency.

For use with such a broadcasting networkthe invention further provides a dual radio receiver comprising a first tunable receiverwith means for automatic tuning to selected programmes, and a second receiver adapted to receive coded signals identifying the area in which the dual receiver is located, and means responsive to the coded signals to suppiy programme identifying information to the automatic tuning means.

The second receiver may, in particular, be a Traffic Information Service (TIS) receiver. For convenience the ensuing description is in terms of thins option.

On a firstform ofthe invention, each TIS transmitter radiates an additional "Area Code" Signal and each receiver incorporates a Read Only Memory (ROM) in which are stored, against each Area Code, the frequency data appropriate to the various broadcast radio services. The receiver, when commanded to tuneto a particular service, tunes to the appropriate frequency, using data found in the ROM against that service and Area Code (already received via the Traffic Information Service). if there is morethan one such frequency, then the receiver can tune to the strongest level.

Because ofthe inflexibility of ROM"s, in modifications of the first form ofthe invention, a non-volatile RAM is used and learning circuitry is provided to enable the RAM to maintain an up-to-date file of frequencies, thus accommodating changes in frequency allocations.

In an alternative form of the invention, each TIS transmitteraiso radiates additional data signals giving the programme codes (labels) ofthevarious broadcast radio services in its own area, together with the frequency (orfrequencies) on which each may be found in that area. As a further alternative, frequencydata applicable to other (perhaps adjacent) areas may also be radiated. The receiver stores the received data and, when commanded to find a particular service, (i.e. to find a particular label) tunes to the appropriate frequency. Again, if more than one frequency is involved it can tune to the strongest.

In both proposais, the additional data signals can convenientlyfollowthe FINISH code signal (used in the Traffic Information Service to deactivate the receivers), in which case the data signal will not be heard by users ofthe Traffic Information Service because their receivers will have been deactivated previously bythe FINISH signal.

It will probably be sufficient to transmit the additional data signals following everyTIS message, so thatthetwo systems can be almost independent. The TIS section ofthe receiver can operate in the normal way butwill also receive the additional data signals and feed these to a store in the main (non-traffic) tunable receiver; this process would be independent of whether or notthe traffic Information Service had been selected by the user.

Area Codes, as used for the first proposal, can be simple numbers, 1 to 80 for example. for the second proposal, the actual values offrequency need not be transmitted; these could be coded (for example as channel numbers). Although the invention has particular application to VHF radio broadcasting, it is also applicableto MF, LF and any otherform of broadcasting. Any system oftransmittersthat have well-defined service areas of appropriate size and location may be used to carry the area-based information, in place of TIS transmitters; for example UHF broadcasttelevisiontransmitters may be suitable forthis purpose.

No specific description of the construction of the broadcasting network is required since it can employ conventional equipment with suitably circuitry for causing the required coded signaisto be broadcast from each TlStransmitter. Automatic read-outfrom a ROM or replay of tape can be triggered every time the FINISH signal occurs and for at regular intervals during thewholetime no Tl message is being transmitted.

Three embodiments of a dual receiver embodying the invention will however be described, by way of example, with referencetotheirblockdiagrams in Figs 1 to 3 ofthe accompanying drawings.

In Fig 1 a VHF receiver loins of the type well known in itself incorporating an automatic tuning stage 11 which tunes the receiver to afrequencystored in a register 12. A push button or keypad unit 13 allows the userto choose his programme by entering a corresponding number in a register 14.

ATIS receiver 15 receives TIS broadcasts and operates in known mannerto mute the receiver 10 and feedtheTlSmessagestoan outputstage 16 common to both receivers. In addition the receiver 15 detects a received Area Code and feeds it into a register 17.

Conventional techniques are used to enable the receiver 1 stro distinguish an Area Code from other received information, in dependence upon a specified dataformatforthe code A ROM 18 stores all the actual programme frequen ciesfor everyTlS area and is addressed by an address decoder 1 9which decodes the numbers in the programme register 14 and the area code register 17.

The corresponding frequency is read out into the register 12 and the receiver 1 Otunes automatically to thatfrequency. Where there is more than one possible frequency, the receiver can automatically select the strongest signal but the circuitry for performing this function is known in itself and is therefore not shown, to avoid unnnecessary complication.

Fig 2 illustrates a modified form of Fig 1 in which the ROM 18 is replaced by a RAM 20 which is non-volatile and may, to this end, be a low-power, permanently energised static RAM.

In this embodiment, according to the alternative form ofthe invention, the memory 22 is loaded with frequency-data associated with the appropriate programme code (label) and area code, all received via the TIS receiver. When a burst of data signals is received, it is detected and de-multiplexed by a circuit 23 into a frequency register 22, an area code register 21 and a received programme code (label) register 26. A 'write' instruction is then generated via a write/read control 24 and the frequency-data iswritten into the RAM 22 using an address formed from the area code and received programme code (label). Thus there will then be stored in the RAM againstthe area code one or morefrequencies for each programme network. This information is built up from bursts of data signals transmitted at regular intervals.

The area code register 17 of Fig 1 is also shown in Fig 2, for storing the code for the currentlyoccupied area, this code also being transmitted at regular intervals. The provision of separate current and updating area code registers 17 and 21 allows updating information to be transmitted for all areas from all TIS transmitters. When commandedto tune to a particular programme (forexample by keying the appropriate programme label into the register 14 by means ofthe buttons 13)the memory 20 is scanned to find againstthat label and the local area code held in the register 17 the appropriatefrequency orfrequen cies to tune the receiver.Thewritelread control 24 responds to push button actuation to cause read-out ofthefrequencyto the frequency register 12.

The data in the memory need not always be erased or overwritten by new data when a different area code is received (as, forexamplewhen the receiver moves or is located in an overlap between two areas) butthe memory can have capacityforseveral areas and can accumulate frequency-data area-by-area, as part of a learning process. Areas could be numbered (for example by a matrix, or row and column, method) so thatthe remoteness of an area could be determined by the difference between its roworcolumn numberand those ofthe local area. Thus the data stored against a particular area code could be classified as 'stale' and overwritten by new data.On this basisthis would enable a memory of modest size to be used, since there would be no point in a receiverstoringfrequen- cy-data for an area hundreds of miles distant because it could easily obtain the necessary information on approaching the new area; the distance atwhich this new information became available would not be critical provided itwas nottoo short. To assist a learning receiver, theTIS transmitterwould carry also the frequency-data applicable to other area codes,for example those applying to adjacent areas, in which case the area code applicable to the actual local area would be specially identified. Thus, in Fig 2, when receiving frequency-data applicable to other areas, the area code register 21 will carry a different code from area code register 17, which will always hold onlythe most recently received actual local area code.

Fig 3 illustrates a further modified form of Fig 1 in which the ROM 18 is replaced by a non-volatile RAM 20,The main receiver includes a label detector 25 of known form.

In this embodiment, the memory 20 is loaded and kept up to date by using off-air labels and the associated area codes and frequencies. Thus, when commanded to tune to a particular programme (by keying-in the appropriate programme label) the memory is scanned to find, against that label and the local area code (from the area code register 17),the appropriate frequencyorfrequencies to tune the receiver. In a receiver of this kind,a standby or 'learning' mode will be used. Thus, wheneverthe receiver was apparently switched off, certain circuits could remain active, atleastfora period of time, when the receiver would scan the band, detecting and storing frequencies against programme labels and the local area code; a new receiver would require a few minutes learning-time before it could work automatically. The detailed implementation is not shown but will follow the principles of Fig 2,exceptthatthe frequency and label data for updating the RAM 20 are derived from the main receiver, rather than the TIS receiver.

Claims (10)

1. A radio broadcasting network wherein a plurality of differentfirst programmes are broadcast on frequencies which are different from area to area served by the system, and wherein a further programme is broadcastfrom a plurality of transmitters serving respective service areas, characterised in that the transmitters for the further programme are arranged also to broadcast coded signals identifying at leastthe corresponding service areas.

2. A radio broadcasting network according to claim 1, wherein the further programme is broadcast on a common frequency from all the transmitters.

3. Aradio broadcasting networkaccordingto claim 1 or 2, wherein the coded signals identify the frequencies ofthe first programmes pertaining to the respective service areas.

4. A radio broadcasting network according to claim 3, wherein the coded signals carry the values of the frequencies ofthe first programmes pertaining to the respective service areas.

5. Aradio broadcasting network according to any of claims 1 to 4, wherein the further programme is a message broadcast programme broadcasting intermittent messages, and the coded signals are broadcast in between the messages.

6. A dual radio receiver comprising a first tunable receiver with means for automatictuning to selected programmes, and a second receiveradaptedto receive coded signals identifying the area in which the dual receiver is located, and means responsive to the coded signals to supply programme identifying information to the automatictuning means.

7. A dual radio receiver according to claim 6, wherin the responsive means comprise a memory storing the identifying information for each of a plurality of areas and means responsive to the coded signals to select corresponding stored information for usebythetunable receiver.

8. A dual radio receiver according to claim 6, wherein the responsive means comprise a read/write memory and means responsive to data received via at least one of the first and second receivers to write the identifying information in the memory.

9. A dual radio receiver according to claim 8, wherein the writing means include means responsive to the second receiver to store area code signals, programme label signals and associated frequency identifying signals.

10. A dual radio receiver according to claim 6,7,8, or 9, wherein the dual receiver is a car radio receiver and the second receiver is a traffic information service receiver.