GB2240677A

GB2240677A - Automatic retuning in RDS receiver with means for reselecting original signal

Info

Publication number: GB2240677A
Application number: GB9101595A
Authority: GB
Inventors: Kasa Koichi; Reisuke Sato; Kiyoshi Izumi; Akira Hayama; Yoshiro Kunugi; Hitoshi Kawabata
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1990-01-31
Filing date: 1991-01-24
Publication date: 1991-08-07
Anticipated expiration: 2011-01-24
Also published as: DE4102735C2; GB9101595D0; GB2240677B; DE4102735A1; JPH03227131A

Abstract

A method of selecting a reception frequency in a radio data system receiver capable of receiving a radio data system broadcast signal which comprises a plurality of station frequency data of a station group network and program identification data including an area code and capable of changing the reception frequency from a current frequency to a frequency of another station in the same network in accordance with one of the station frequency data, the method comprising, holding station frequency data and program identification data obtained from a first broadcast signal having a first frequency and received from a first station, sensing the presence of a second station broadcasting with a signal of a frequency different from the first frequency, tuning the reception frequency to that of the second station if program identification data received from the second station and the held program identification data from the first station correspond to one another except for area code, and retuning, the reception frequency to that of the frequency indicated by the held station frequency data, in response to a command. <IMAGE>

Description

-d 2! -l 0 65 -7 -7 NETHM OF SELECTW A PM=ON F1WIENCY IN AN 1RDS RECEIVER

The present invention relates to a method ot selecting the receiving frequency in an RDS receiver.

The RDS (Radio Data System) broadcasting Is a broadcasting service in which, in the program broadcasting of general broadcasting stations. Information relating to the broadcast such as information regarding the program content or the like is transmitted as data by a multiplex modulation. The transmitted data Is demodulated on the reception side. so that a desired program content can be selected on the basis of the demodulated data. thereby services are offered to a radio listener.

In the RDS.broadcasting,, a signal of 57 kHz as a third harmonic of a stereo pilot signal of 19 kHz in a range out of a frequency band of an FM modulation wave is used as a subcarrier. The subcarrIer is amplitude modulated Into a radio data signal by a data signal. which Is treated by filtering and Biphase codingy carrying information regarding the broadcasting such as 1 program content and the like, and the amplitude modulated subcarrier is frequency modulated into the main carrier for the broadcasting. Standards of the above broadcasting scheme were proposed by the European Broadcasting Union (EBU).

As will be clearly understood from Fig. 1 showing a base band coding structure of a radio data signal, in the radio data signal, data of 104 bits are processed as one group and are repetitively transmitted through a multiplex transmission. One group comprises four blocks each having 26 bits. Each block comprises an information word of 16 bits and a check word of 10 bits. Each group is classified into sixteen types, that is, Type 0 through Type 15 indicated by four bits according to the information content. Furthermore. two versions A and B are defined for each of the types (0 to 15).

rigs. 2A and 2B show the format of groups of the types OA and OB, respectively. In the type OA group, program identification data (referred to as PI data hereinafter) of 16 bits consisting of a country code, an area code, and a program code is arranged in a block 1. Various codes such as group type code, version code (B0), traffic information broadcasting station identification (TP) code, program content identification (PTY) code, and the like are arranged in a block 2. Station frequency data (hereinafter, abbreviated as AF data) of network stations broadcasting the same program is arranged in a block 3. Broadcasting station name data (hereinafter. abbreviated as PS data) is arranged in a block 4. On the other hand, in the type OB group (shown in Fig. 2B), only the content of the block 3 differs from that in the type OA group. Specifically, the PI code is arranged in the block 3. That is, the AF data of the network stations is transmitted by only the type OA group. The PS data is transmitted by the type OA and OB groups.

As mentioned above, the AF data of the network stations which broadcast the same program as the program of the broadcasting station which is currently being received is also included in the radio data signal of the type OA group. Therefore, a network follow function described below can be performed. At the time of the reception, the AF data and PI code which are obtained by the demodulation are retrieved and stored as an AF list. For instance, in the case where a receiving strength of the broadcasting station of the program which is currently being received is decreased due to a disturbance such as the multipath interference or the like, another station in the same network station group is selected on the basis of the AF list which has previously been stored. Further, a check is made to see 3 if the program which was received in accordance with the AF list is correct or not by comparing the PI codes. Thus. the same program can be listened always in a good receiving state by the network follow function without being influenced by,external disturbances.

Since stations having different area codes in the PI data are included in the same network station group. a Regional OFF mode in which the area code is ignored in the PI check operation and a Regional ON mode in which the area code is included in the PI check are defined in the network follow function. In the Regional OFF mode, a station of the same network station group located outside the area in which the first receiving station is located may be received.

On the other hand, there may by a case that the Regional OFF mode is erroneously designated by a mistake in the operation and a station outside a desired area is received when the user wishes to limit the network follow function to the same network stations in the area in which the first receiving station is located. In such a case, even though the user wishes to limit stations to be received to stations in the desired area. it was not possible to return the receiving station to a station in the desired area by means of the conventional network follow function 4 The present invention is based on the recognition of the inconvenience described above and it is an object of the invention to provide a receiving frequency selecting method in an RDS receiver in which. when a same network station outside the desired area is received in the Regional OFF mode. the receiving station can be returned to a station in the desired area.

According to the present invention there is provided a method of selecting a receiving frequency, in an RDS receiver capable of receiving an RDS broadcasting wave on which a plurality of AF data of a same network station group and PI data including an area code are superimposed. the selecting method for changing the receiving frequency from the current receiving frequency to the frequency of another same network station given by one of the plurality of AF data, comprising: a first step of holding AF data and PI data obtained by a broadcast wave of the presently selected receiving frequency; a second step of sensing the presence of a receiving station; a third step of setting a new receiving frequency to the frequency of the receiving station sensed in the second step If PI data obtained by the broadcast wave of the receiving station sensed in the second step and the PI data held in the first step 6 coincide with each other except the area code, and a fourth step of returning, in response to a command, the receiving frequency to the receiving frequency given by the AF data held in the first step.

In the receiving frequency selecting method according to the invention, AP data of the first receiving station is held previously and, when a station outside the area in which the first receiving station is located is received in the Regional OFF mode, the receiving frequency is returned, in response to a command, to the former receiving frequency given by the AF data being held.

The invention will now be described by way of a preferred embodiment and with reference to the accompanying drawings in which:- Fig. 1 is a diagram showing a base band coding structure of radio data; Figs. 2A and 2B are diagrams showing formats of group types OA and OB, respectively; Fig. 3 is a block diagram showing a fundamental construction of an RDS receiver to which the receiving frequency selecting method according to the present invention is applied; and Fig. 4 is a flowchart showing an example of processing steps of the network follow function as an embodiment of the receiving frequency selecting method of the present invention.

An embodiment of the present invention will be described in detail hereinafter with reference to the drawings.

Fig. 3 is a block diagram generally showing an example of a fundamental construction of an RDS receiver to which the receiving frequency selecting method according to the present invention is applied. In the diagram, an FM multiplexed broadcasting wave received by an antenna 1 is supplied to a front-end 2, by which a desired station is selected and the signal of the selected station is converted into an intermediate frequency (IF). After that, the signal is supplied through an IF amplifier 3 to an FM detector 4. For instance, the front-end 2 employs a PLL synthesizer system using a PLL circuit including a programmable frequency divider. A frequency dividing ratio of the programmable frequency divider is controlled by a controller 13 which will be explained later, so that a station selecting operation is performed. A detection output of the FM detector 4 is supplied to an MPX (multiplex) demodulating circuit 5 and is separated into audio signals of the L (left) and R (right) channels in the case of a stereophonic broadcasting. The signals of the L and R channels are provided as reproduced audio 7 output signals through a muting circuit 18. The muting circuit 18 is on- off controlled by means of the controller 13.

On the other hand, by the transmission of the detection output of the FM detector 4 through a filter 6, a subcarrier of 57 kHz, which is amplitude modulated by a biphase coded data signal, that is a radio data signal, is extracted and is demodulated by a PLL circuit 7. The demodulated output is supplied to a digital the PLI, circuit 8 and a decoder 9. In the D-PLL circuit 8, clocks for data demodulation are produced on the basis of the demodulated output of the PLL circuit 7. In the decoder 9, the biphase coded data signal as the demodulated output of the PLL circuit 7 is decoded synchronously with the clocks produced by the D-PLL circuit 8. A locking state detecting circuit 10 detects locking and unlocking states of the D-PLL circuit 8. Locking ranges of the PLL circuit 7 and D-PLL circuit 8 are switch controlled by a detection output of the detecting circuit 10.

Output data of the decoder 9 has the group unit of 104 bits comprising four blocks each consisting of 26 bits as shown in Fig. 1 and is sequentially supplied to a group. block sync & error detecting circuit 11. In the detecting circuit 11, synchronization of the group and block is performed on the basis of an offset word of 10 8 bits which are respectively assigned to the check word of 10 bits of each block. Further, errors in the information word of 16 bits are detected on the basis of the check word. The error detected data is error corrected by an error correcting circuit 12 at the next stage. Thereafter, the error corrected data is supplied to the controller 13.

The controller 13 is constituted by a microcomputer and adapted to execute the network follow function in the following manner. At first the controller 13 retrieves code information of each block in the radio data which is sequentially input on a group unit basis, that is, radio information regarding the program content of the broadcasting station which is at present being received and stores the information into the RAM 14. In response to a station selection command from an operation section 15, the controller 13 controls a frequency dividing ratio of the programmable frequency divider (not shown) of the PLL circuit constituting a part of the front-end 2, thereby executing the network follow function. As mentioned before. the network follow function has the Regional OFF mode in which the area code is ignored in the PI check and the Regional ON mode in which the PI check is performed including the area.code. One of these modes is designated by the user through the operation 9 section 15.

A level detection circuit 16 is provided to detect a receiving signal level (field intensity) on the basis of the IF signal level in the IF amplifier 3. Furthermore, there is provided a station detection circuit 17 which detects the presence of a receiving station thereby to produce a station detection signal when the IF signal level in the IF amplifier 3 is higher than a predetermined level and at the same time the detection output signal of the so-called S-curve characteristic in the FM detector 4 is in a predetermined level range. The receiving signal level detected by the level detection circuit 16 and the station detection signal produced by the station detection circuit 17 are supplied to the controller 13.

A processing steps of the network follow function which are executed by the processor of the controller 13 will now be described with reference to a flowchart of Fig. 4. It is assumed, in this example, that the Regional OFF mode has been designated previously in the operation section 15, and a regional ON flag has been reset by this designation. It is further assumed that AF data obtained by the demodulation of the received broadcast wave has been already retrieved and the AF list of the network stations the same as the station being received has 1 already been produced in the memory 14.

The processor first retrieves the AF data and PI data of the broadcast wave currently being received and stores those data into predetermined regions of the memory 14 (step S1). According to the AP list mentioned above, the processor reads out one of the AF data in the AF list from the memory 14 (step S2). Then the processor turns the muting circuit 18 on, to effect the audio muting (step S3), and supplies the read-out AF data to the PLL circuit (not shown) in the front-end 2 (step S4). At the same time, the processor 13 sets a PLL timer for measuring a time period T1 required for the PLL circuit to be locked (step S5). The AF data supplied to the PLL circuit is set to the programmable frequency divider in the PLI, circuit, so that the receiving frequency changes from the current receiving frequency to another frequency of a network station within the period timed by the PLL timer.

After the time-out of the PLL timer (step S6), the processor 13 judges the presence or absence of a receiving station by monitoring the station detection signal from the station detection circuit 17 (step S7). If a receiving station exists, the processor 13 retrieves from the level detection circuit 16 the receiving signal level of the network station being received (step S8).

11 Then the processor 13 judges whether or not the receiving signal level is equal to or hither than a predetermined setting level Vs (step S9). If the receiving signal level is higher than the setting level Vs, the processor retrieves the PI data of the receiving station (step S10). Then the processor 13 judges whether or not the regional ON flag is set (step S11). Since the Regional OFF mode has been designate previously, the regional ON flag has been reset. Therefore, the processor 13 judges whether or not the retrieved PI data and the PI data held in step S1 coincide with each other except the area code (step S12a). If the PI data coincide with each other, the processor 13 turns the muting circuit 18 off, to cancel the audio muting (step S13). Through these operations, the frequency of the network station being received currently is set as a new receiving frequency.

On the other hand, in the Regional ON mode in which the regional ON flag is set, the processor 13 judges whether or not the retrieved PI data and the PI data held in step S1 coincide with each other (step S12b), and proceeds to step S19, to cancel the audio muting if the PI data coincide with each other.

When it is judged in step S7 that no receiving station exists, it is detected in step S9 that the receiving signal level is below the setting level, or 12 when it is detected in step S12a or S12b that the PI data do not coincide with each other, the processor judges whether or not the processes of checking the existence of the receiving station, checking the receiving signal level, and determining the coincidence of the PI data are completed for all of data in the AF list (step S14). If the processes are not completed, the processor 13 goes back to step S2 to repeat the procedure described above. If the processes are completed for all of the data in the AF list, the processor 13 reads-out the former AF data stored in step S1 (step S15), and effects the audio muting (step S16), and supplies the read-out AF data to the PLL circuit subsequently (step S16). At the same time, the processor sets the PLI, circuit (step S17). After the time-out of the PLL timer (step S18), the processor cancels the audio muting (step S19). Through these operations. the receiving frequency is returned to the frequency of the former receiving station.

The normal network follow function has been described above. According to the present invention. the functions described as follows are added to the operations described above. After the cancellation of the audio muting in step S13, the processor sets a return timer for measuring a certain constant time period T2 (step S20). Within a constant time period T2 before the 13 time-out of the return timer, processor 13 monitors the generation of a return command by the user through the operation section 15 (steps S21 and S22). If the return command is not generated before the time-out of the return timer, the process of this routine will be finished without performing any further operation. If the return command is generated, the processor cancels the audio muting (step S23), sets the Regional on flag (step S24), and proceeds to step S15 subsequently.

In other words. if a station outside the area of the first receiving station is received by the network follow function in the Regional OFF mode, the receiving frequency can be returned to the first receiving frequency within the constant time period T2 in response to the generation of the return command by the user through the operation section since the AF data of the receiving station tuned before the network follow operation is retrieved by the return command.

By the addition of the function described above, when the Regional OFF mode is erroneously designated by a mistake in the operation and a station outside a desired area is received although the user wishes to limit the network follow function to the same network stations in the area in which the first receiving station is located, the receiving station can be automatically returned to 14 the former station by the generation of the return command if the user wishes to return the receiving station to a station in the former area. In this case, since the Regional ON flag is set in step S24, the Regional ON mode is designated automatically. Thereafter, the network follow function will be limited to the same network stations in the area in which the former receiving station is located.

As described specifically in the foregoing, in the receiving frequency selecting method according to the present invention, the AF data of the first station is held previously. When a station outside the area in which the first station is located is received by the network follow function in the Regional OFF mode, the receiving frequency can be returned to the former receiving frequency given by the AF data being held in response to the command. By this feature, the receiving station can be returned to a station in the desired area even though a same network station outside the desired area is received in the Regional OFF mode.

16

Claims

1. A method of selecting a reception frequency in a radio data system receiver capable of receiving a radio data system broadcast signal which comprises a plurality of station frequency data of a station group network and program identification data including an area code and capable of changing the reception frequency from a current frequency to a frequency of another station In the same network in accordance with one of the station frequency data, the method comprising:

holding station frequency data and program identification data obtained from a first broadcast signal having a first frequency and received from a first station; sensing the presence of a second station broadcasting with a signal of a frequency different from the first frequency; tuning the reception frequency to that of the second station if program identification data received from the second station and the held program identification data from the first station correspond to one another except for area code; and retuning, the reception frequency to that of the frequency indicated by the held station frequency data, in response to a command.

2. A method according to claim 1, wherein the retuning is only executable during a fixed time period after the tuning to the second station.

3. A method according to either preceding claim, wherein the determination of correspondence between the program information data is performed after the retuning.

4. Apparatus for selecting a reception frequency in a radio data system receiver capable of receiving a,radio 1 17 data system broadcast signal which comprises a plurality of station frequency data of a station group network and program identification data including an area code and capable of changing a reception frequency from a current frequency to a frequency of another station in the same network in accordance with one of the station frequency data, the apparatus comprising: means for holding station frequency data and program Identification data obtained from a first broadcast signal having a first frequency and received from a first station; means for sensing the presence of a second station broadcasting with a signal of a frequency different from the first frequency; means for tuning the reception frequency to that of the second station if program identification data received from the second station and the held program identification data from the first station correspond to one another except for an area code; and means for retuning the reception frequency to that of the frequency indicated by the held station frequency data, in response to a command.

5. A method of selecting a receiving frequency, in an RDS receiver capable of receiving an RDS broadcasting wave on which a plurality of AF data of a same network station group and PI data including an area code are superimposed, for changing the receiving frequency from a current receiving frequency to the frequency of another same network station given by one of the plurality of AF data, comprising: a first step of holding AP data and PI data obtained by a broadcast wave of a currently selected receiving frequency; a second step of sensing the presence of a receiving station; 18 a third step of setting a new receiving frequency to the frequency of the receiving station sensed in the second step if PI data obtained by the broadcast wave of the receiving station sensed in the second step and the PI data held in the first step coincide with each other except the area code; and a fourth step of returning, in response to a command, the receiving frequency to the receiving frequency given by the AF data held in the first step.

!v

6. A method of selecting a reception frequency in a radio data system receiver, the method being substantially as hereinbefore described with reference to the accompanying drawings.

7. An apparatus for selecting a reception frequency in a radio data system receiver, the apparatus being substantially as hereinbefore described with reference to the accompanying drawings.

I 1 Published 1991 atThe Patent Office. State House. 66171 High Holborn. UndonWC1R47?. Further copies may be obtained from Sales Branch. Unit 6, Nine Mile Point C-wmfelinfach. Cross Keys. Newport, NPI 7HZ. Printed by Multiplex techniques ltd, St Mary Cray, Kent.