FR2730111A1 - RDS transceiving method e.g. for short wave radio programme - Google Patents

Abstract

The method involves transmitting audio data coded in baseband as a two-phase signal according to the RDS standard. The transmitted audio signal is interrupted during a predetermined time interval and the two-phase signal is transmitted across the channel during the predetermined time interval in place of the audio signal. The channel is preferably a radio transmission channel using short wave frequencies. The frequency used for data transmission can be switched to a different, predetermined frequency, with the switching operation having a predetermined duration. The transmission interruptions accompany the switching operations and the time intervals are equal to the predetermined interval.

Description

The invention relates to a method of transmitting and receiving information data, in particular in radio. It relates more particularly to a process using the technology called "RDS" (from the Anglo-Saxon "Radio Data
System ").

 The invention also relates to a transceiver system for implementing such a method.

It is known to broadcast auxiliary data, in particular digital data, in conjunction with radio or television programs. For example, for television, we have offered the teletext service
ANTIOPE. The line blanking interval of a television signal is used to transmit data.

 In broadcasting, many systems using auxiliary channels to transmit data are also known.

 One of the main applications targeted by the invention is, within the framework of radio program transmissions, the transmission of data concerning the programming of such transmissions, in particular shortwave (called OC in the following) intended for appropriate receivers .

 More specifically, for communications in the OC band, it is necessary to use specific frequencies according to the hours of the day or the seasons of the year, the propagation conditions, etc. It is known to transmit frequency programming data to be used during a given period of time. Most often, during a transmission, the listener is obliged to carry out several switching of reception frequencies. Also, it seems desirable that these switches can be made, as far as possible, as automatically as possible.

 Another constraint is as follows: the broadcasting of this programming data being audible, the corresponding signal must be as discreet as possible and of relatively short duration so as not to disturb the listener.

 In the known art, radio amateurs use links based on radio modems to transmit the aforementioned data, which may be called frequency switching assistance data. This technique is similar to data transmission by telephone and it is applicable to the broadcasting of data by radio.

 However, this technique has a significant drawback. Indeed, the digital raw bit rate is low, around 300 bits / s, which is not enough for many applications and, in any case, incompatible with the application mentioned above. For this type of application, it would be necessary to achieve a flow approximately three times higher, or approximately 1 kbits / s. In addition, it is necessary to transmit the signal at a low level so that it remains discreet, which does not promote good reception and correct decoding of the data thus transmitted.

 In what follows, without limiting its scope in any way, we will place ourselves within the framework of the preferred application of the invention, unless otherwise stated.

 The invention aims to overcome the drawbacks of known art methods.

 To do this, the method according to the invention consists in replacing the normal audio signal, for a short period, with a two-phase signal conforming to the "RDS" standard, for transmitting data in the soundtrack of a radio broadcast.

 In a preferred embodiment of the method of the invention, the time interval between two switching operations is used, typically a time interval of 10 seconds for the abovementioned OC transmissions.

 The method is also compatible with data communication by telephone.

 The subject of the invention is therefore a method of transmitting and receiving information data to be broadcast during the transmission of audio signals by a determined communication channel, characterized in that, on transmission, said data are coded under form of baseband biphase signals according to the "RDS" standard, in that said transmission of audio signals is interrupted during determined time intervals and in that biphase signals are transmitted by said channel during these determined time intervals, in place of audio signals.

 The invention also relates to a transmission-reception system for the implementation of such a method.

The invention will be better understood and other characteristics and advantages will appear on reading the description which follows with reference to the appended figures, and among which:
- Figure 1 schematically illustrates an example system
transmission-reception for the implementation of such a method;
- Figure 2 is a block diagram of part of the transmitter;
- Figures 3a and 3b are diagrams relating to the properties of
two-phase signals according to the "RDS"standard;
- Figure 4 is a timing diagram illustrating different periods
resignation;
- Figure 5 is a detail figure of the circuits of Figure 2;
- Figure 6 is a block diagram of the receiver;
- Figure 7 schematically illustrates the architecture of a
transmission comprising a telephone channel and a voice answering machine.

 The method according to the invention will be described on the basis of an exemplary embodiment of a transceiver system for broadcasting OC audio programs, as illustrated in FIG. 1.

Conventionally, the transmitter part 1 of the system comprises an actual transmitter 13, transmitting, for example, in the range of OCs, in amplitude modulation kM. Such a transmitter, in itself, is well known and there is no need to describe it further
Likewise, the receiver part of the system comprises one or more receivers 2, for example portable receivers as illustrated in FIG. 1.

This also includes, in a conventional manner, means for receiving (not shown) the electromagnetic signals emitted by the transmitter 13 (high frequency carrier in the OC range) and for demodulating the audio and biphase coded signals, an electroacoustic transducer 22 ( loudspeaker for example) for the reproduction of audio signals after demodulation and interactive display means 20 (liquid crystal display, for example) and data input 21 (keyboard). In addition to use for functions common to Known Art, these interactive means, 20 and 21, will be used in the context of the invention, in the manner which will be explained below.

If we return to the transmission part 1, this comprises means more specific to the invention
It comprises, first of all, data processing means 1, for example a conventional microcomputer, making it possible to prepare the data for the broadcaster, data in particular relating to frequencies and frequency switching times, intended for users of the broadcasting service (receivers 2). These data processing means 10 are connected to an encoder 11 of digital signals according to the "RDS" standard. The signals, at the output of the latter, are of the so-called "biphase" type and are transmitted to a recorder-reader 12, the output of which is connected to the transmitter 13. It has been assumed that the latter also includes the "sound chain"; it being understood that the functions "sound chain" and emission, being, in themselves known and common to Known Art.

 The data to be broadcast can be entered into the data processing means 10 by any suitable method, for example by means of a keyboard 100, as illustrated in FIG. 1. They can also be generated automatically by calculations from different parameters: hours, etc.

 Finally, the data processing means can control the operation of the various elements of the transmission chain, "RDS" encoder 11, recorder-reader 12 and transmitter 13 using digital control signals transmitted over a serial link or parallel (bus) referenced Sc.

 FIG. 3 illustrates in more detail, the circuits of the “RDS” coder 11 and of the transmitter 13, in the form of block diagrams, and the way in which they are interconnected, for carrying out the method according to the invention.

 The "RDS" encoder 1 1 is an encoder, per se, conventional and conforms, for example to the CENELEC standard EN 50067. I1 comprises a differential encoder 110 receiving binary data with a diffuser, after coding according to the aforementioned standard.

In the example described, the data to be coded comes from the data processing means 10 and is presented on the input "e" of the differential encoder 10. The output of the latter is connected to a two-phase symbol generator 111.

 Both the differential encoder 110 and the two-phase symbol generator 111 receive a clock signal H of frequency 1187.5 Hz.

 Such biphase signals, in accordance with the aforementioned standard, are illustrated in FIG. 3b.

 This figure is a chronogram representing the relative amplitude of two biphase symbols, Syl and Syg, as a function of time t (horizontal axis). More precisely, the curve in solid line illustrates the evolution as a function of time of a biphase symbol, Syl, generated when the data bit presented on the input "e" is at logic "1", and the curve in lines discontinuous, illustrates the evolution as a function of time of a biphase symbol, Syg, generated when the data bit presented on the input "e" is at logical "0". These two curves go through zero for t = 0. The Syl curve takes positive values between the instant (-5/8) td and 0 and negative values between 0 and (+5/8) td; td being equal to the period of the above-mentioned clock H, that is [1 / 1187.5] seconds. It goes back to zero for these values. For values lower than (-5/8) td and higher than (+5/8) td, the curve oscillates around the horizontal axis, being more and more damped. As a first approximation, we can estimate that the amplitude of the signal is significant between -td2 and + td2, that is to say a total time interval equal to td.

 The curve Sy0, in broken lines, is symmetrical with the curve Syl with respect to the time axis t, which makes it possible to discriminate the two symbols, one representing a logical "1", the other a "0" logic.

 The clock signal H is usually generated by an oscillator 114 at 57 kHz (output signal H57K) followed by a divider by twenty-four producing an intermediate frequency of 2375 Hz and a divider by two producing the frequency of 1187 , 5 Hz above. The whole has been grouped together under the unique reference 112.

In general, oscillator 114 receives a pilot clock signal, referenced
HR in FIG. 2. This HR signal is advantageously produced by the "sound chain" of the transmitter 13, in particular when it is a broadcast in stereophony. The frequency of this clock signal is then 19 kHz.

 The output signal Ssy of the biphase symbol generator 111 is applied to a band corrector 113 raising the level of the bottom of the spectrum.

 For a more detailed description of the circuits entering an "RDS" type encoder, reference may be made to the CENELEC EN 50067 standard mentioned above.

 The transmitter 13 comprises a chain 130, receiving 5audio I1 audio signals as an input and outputting the audio signal Sst to be transmitted. Advantageously, as has been indicated, these circuits 130 also generate a clock pilot signal HR, in particular when the transmission is in stereophony. In the latter case, the "sound system" 130 comprises a stereophonic coder and the audio signals of Studio inputs are split into a left channel and a right channel, in the usual way. The HR pilot signal is transmitted as a reference to the oscillator 114.

 According to an important aspect of the invention, an electronic switch 131 is provided between the actual transmitter stage 132 and the stereophonic coder 130. The latter is under the control of a switching control signal Sol3. As previously indicated, this control signal SC13 can be one of the signals conveyed by the link Sc and produced by the data processing means 10.

 In normal times, the output signals SSt of the "sound chain" 130 are transmitted to the transmitter 132, that transmitting the broadcast program and received by the receivers 2.

When the transmission frequency used by the transmitter 13 is switched, for the various reasons previously indicated (daily timetable, etc.), the signal Sc3 causes the switching between the signal Sst and the output signal Ss of the modulator 113 From now on, these are biphase type signals which will be transmitted to the transmitter stage 132, signals which will replace the "normal" audio signals. This substitution of signals lasts over time
T necessary for frequency switching, typically for 10 seconds. Then, the signal Sc commands the reverse switching and the emission of the "normal" sound signals resumes.

 Figure 4 is a timing diagram illustrating the evolution of the signal Sol3.

It was assumed to be a binary signal. In the logic "0" state, the switch 131 transmits the audio program to the transmitter stage 132, and in the logic "1" state, it is the biphase type signals Ss which are transmitted to this transmitter stage 132. They are therefore broadcast as if it were a normal radio program. Two switching operations have been shown, referenced "switching 1" and "switching 2". Naturally, the time interval separating two successive switching operations is much greater than the time intervals T during which the signal Sci3 is in the logic state "1".

 Since the two-phase "RDS" signal has a frequency spectrum between 0 and 2400 Hz, it is included in the radio frequency bands, notably the OCs for which the bandwidth is 4500 Hz, with very low frequency correction .

FIG. 3a represents the relative amplitude of broadcast signals coded in biphase as a function of the modulation frequency, in Hz. In reality,
The energy of the spectrum is concentrated between the frequencies 350 and 1700 Hz, as also illustrated in FIG. 3a: frequencies for a relative amplitude equal to 0.5.

This advantageous characteristic allows use of the method according to the invention in telephony, as will be shown below.

As indicated, the data coded in the form of biphase signals are not normally broadcast in real time but previously recorded in the recorder-reader 12. Control signals SCl2 as illustrated in FIG. 5, conveyed by the link Sc , can control the operation of the recorder-player 12, whether recording or playing. When data is transmitted for coding to the "RDS" coder 11, the recorder-reader is switched to recording mode. The signals Ssy at the output of the two-phase symbol generator 111 are then recorded in the recorder-reader 12 and remain there. Before switching transmission frequency,
The recorder-player 12 is switched to playback mode and the recording medium (tape, disc, etc., not shown in the figure) included in that positioned at the start of the recording if necessary (in the case of a tape-type sequential recording, for example). During the time intervals T (see FIG. 4), the reading of the recording is authorized. The signals read SISJT are then transmitted to the band corrector 113. During these same time intervals T, the signal SC13 causes the switching of the switch 131 and the signals Ss are transmitted to the transmitter stage 132, in place of the signals Sst , as described above.

 The data disseminated, as indicated, concerns, in particular, the frequency switching schedules and, of course, the frequencies associated with these schedules. Additional information of various kinds can also be transmitted through this.

 The receiver, as illustrated in more detail in FIG. 6, comprises a conventional reception part 23, that is to say HF stages 230 for receiving the electromagnetic signals transmitted by the transmitter 1, for example in OC band, and a "sound chain" 231. The output signals from this stage 231 are transmitted to an electroacoustic transducer 22 for restoring sound information, for example a loudspeaker. This reception part 23, quite common to Known Art, does not need to be described further.

 On the other hand, the signal Sr at the output of the H.F. stages 230 is transmitted, not only to the "sound chain" stage 231, but according to an additional aspect of the method of the invention, to a "RDS" decoder 24.

 The output of the demodulator is transmitted to a 2.4 ItHz filter 242 so as to supply a biphase symbol decoder 243. The output of the filter 242 is also transmitted to a clock 245, of bit rate recovery. The latter also receives the Hi output of an internal clock 241 at 38 kHz. The clock signals Hb (bit frequency) generated by the circuit 245 are transmitted to a differential decoder 244 which receives the output signals from the biphase symbol decoder 243. These arrangements make it possible to reconstruct the data broadcast in digital form SD at the output of the symbol decoder 244. The reverse process of coding on transmission was therefore carried out.

The circuits 24, per se, are of a known type and meet the standard
CENELEC EN 50067 mentioned above. Reference will be made with advantage to this standard for a more complete description of the various circuits making up the decoder 24, as well as for the precise synchronization processes implemented.

 The SD data is transmitted to a data processor 25, advantageously a microprocessor or microcontroller, which receives timing information in the form of the clock signals Ht ,. The latter receives command data from a keyboard 21 or from a similar data input member, advantageously arranged on the front face of the receiver 2, if it is a pocket receiver. It also advantageously includes a display screen 20 controlled by the data processor.

 The organs, 20, 21 and 25 can naturally be used for various routine operations relating to receiver 2: operating mode, search for a transmitting station, etc. These operations are common to Art Known.

 According to one aspect of the invention, these members, in particular the data processor 25 also and above all make it possible to use the data transmitted during the periods T (see FIG. 4) to carry out the necessary frequency switches, at the desired times. To do this, the data processor 25, in a preferred embodiment of the invention, is associated with a volatile random access memory 26 ("RAM" according to English terminology), via a data bus / addresses 260.

 Still in a preferred embodiment, the hourly programming data are broadcast in advance by the transmitter 1 for a determined period of time. The same information can be re-transmitted at each period T, or on the contrary be "refreshed" to take account of possible modifications in the programming of the planned frequency switches.

The "RDS" decoder 24 being connected as a probe on the output of the stages
HF 230, this permanently receives the signals Sr. It is only when these signals $ are biphase coded signals that the signals Sr will be decoded so as to reconstruct the broadcast data, data recorded in the memory 26.

 The data received can be organized according to a predetermined configuration by the processor 25, under the guidance of program instructions, before being recorded in the memory 26. These instructions can themselves be recorded in a non-represented fixed memory (" ROM "according to English terminology) or loaded into volatile memory 26 by any appropriate means. They can, in particular, be sorted by time slot and / or by transmitters.

 These recorded data constitute an hourly database of radio programs, this base being able to be updated periodically according to the process recalled above.

 The raw data transmission rate, which is enabled by "RDS" coding, is approximately 1200 bits / s, ie a useful rate of around 730 bits / s. This speed allows the transmission of a relatively large amount of data for short periods of time, typically of the order of 10 seconds.

 The exploitation of the database can be carried out using the interactivity means that constitute the keyboard 21 and the display screen 20. In fact, the user, in possession of the receiver 2, can interrogate the contents of the base by scrolling on the screen 20 the successive memory positions. Depending on the information displayed, it can enter, in clear or coded form, one or more instructions transmitted to the processor 25, in the form of binary words.

 The latter can generate, on receipt of these instructions, a Soeni control signal transmitted to the H.F. 230 stages to calibrate the reception frequency on the operating frequency to be used, as it emerges from the database.

 In a preferred variant, the user enters data relating directly to a given station whose emissions he wishes to receive. The data processor 25 then searches the memory 26 for the hourly data and the frequencies corresponding to this station. A data processing device 25, such as a microprocessor, is usually provided with an internal clock. It is therefore possible to load a real-time program triggering time-stamped actions, and more precisely to generate command signals SCom triggering the different frequency switches required, as a function of the time database recorded in memory 26. At the head data, are transmitted the time and the identification of the transmitting station.

 Naturally, the user can at any time, using the keyboard 21, interrupt the process in progress, make manual adjustments (for example on the reception frequency) or change the transmitting station.

 It should be clear that the method offers the possibility of recording programming data relating to several transmitting stations. It suffices to associate, with each station, an identification code recorded in the memory 26, concurrently with the data characterizing the emissions of this station. The name of the station, by decoding the identification code, can moreover be displayed in plain text on the screen 20. For this purpose, a correspondence table "codes - station names" can be saved in a memory, in the memory 26 or in a fixed memory (not shown).

 As indicated, the method according to the invention is also compatible with transmissions in the telephone band. The latter is between the frequencies 300 and 3400 Hz The means of transmission usually used cause an attenuation of the low part of the spectrum without however significantly interfering with reception and decoding, if on transmission, a correction is made to the low end of the spectrum. Indeed, the examination of Figure 3a has shown that the signal energy is mainly concentrated in a band between 350 and 1700 Hz. This signal is audible but more discreet than that produced by a FSK type modem, like those used in Known Art, by radio amateurs.

 We can therefore provide the possibility of connecting the receiver 2 to a telephone network. FIG. 7 schematically illustrates the hardware architecture of such a system.

 To establish the connection with the telephone network (generally referred to as 4), a voice server 3 having access to the switched network 4 can be used to transmit data and a simple telephone set 27, the handset 270 of which is brought closer to a microphone 280 incorporated in the receiver 2. This also includes an amplifier receiving the output signals from the microphone 280. The output of the amplifier is connected to the RDS decoder 24 of the receiver.

In themselves, these operations are conventional and are within the reach of as of
Job.

 The information captured is advantageously provided by a dedicated voice server unit 3, which can be interrogated remotely by telephone. This includes, in particular, the actual voice server 30, an "RDS" encoder 31 and a database 32.

 It would naturally be possible not to transmit the programming data over the air and acquire the data necessary for programming the switching operations only through the voice server 3.

However, this method takes away a lot of flexibility from the process, since it is necessary, in particular, to have access to a telephone line. Quite the contrary, the reception of information by decoding the data broadcast over the air allows complete freedom as to the location of the receiver 2. Also, according to a preferred embodiment of the method, the possibility of data acquisition by advantage is advantageously used. telephone only in addition to the acquisition by hertzian way. It is indeed necessary that the receiver 2 is active at the time of the transmission of the programming data in order to be able to save the database or update the database. In a preferred embodiment, the data is broadcast during the switching of the frequencies and not permanently. One can think of increasing the frequency of occurrence of the periods of transmission of the programming data (FIG. 4: T). However, this method involves temporarily stopping the "normal" radio program and these periods cannot be multiplied. Also, if the user has not been able to register the database by this route, he has the option of interrogating the voice server to perform this operation. Then, it receives the update information by the usual channel, that is to say the radio channel, as it has been explained with reference to FIG. 6.

 On reading the above, it is easy to see that the invention achieves the goals it has set for itself.

 It also has the advantage of allowing the use, without significant modification, of circuits and components known from the "RDS" technology, whether in the transmitter (encoder) or in the receiver (decoder). As indicated, these technologies are moreover standardized, which allows great ease of realization and production, taking advantage of the scale factor of the aforementioned components.

 It should be clear that the invention is not limited to the only examples of embodiments precisely described, in particular in relation to FIGS. 1 to 7.

 It is in particular not limited to the only frequency band OC, when it is a question of transmission by radio relay.

 It should also be clear that, although particularly suitable for the application described in detail, namely the aid for automatic tuning in OC connections, the invention cannot be confined to this single application.

Claims (14)

 1. A method of transmitting and receiving information data to be broadcast during the transmission of audio signals (Sst) by a determined communication channel, characterized in that, on transmission (1), said data are coded in the form of baseband biphase signals (Ss) according to the "RDS" standard, in that said transmission of audio signals (sot) is interrupted for determined time intervals (T) and in that biphase signals are transmitted by said channel during these determined time intervals (T), instead of audio signals (5sot)  2. Method according to claim 1, characterized in that said channel is a radio transmission channel.  3. Method according to claim 2, characterized in that the frequency band used for the transmission is the short wave band.  4. Method according to claim 3, characterized in that, the frequency used for the transmission being switched over time according to a determined set of frequencies, the switching operations having a determined duration, the transmission interruptions are concomitant with these switching operations and the said switching operations time intervals (T) are equal to this determined duration.  5. Method according to claim 4, characterized in that said information data constitutes an hourly database for forecasting said switching operations and the frequencies used for the transmission during these switching operations.  6. Method according to claim 5, characterized in that said data further comprises an identifier of a determined transmitter (1).  7. Method according to claim 1, characterized in that said channel is a telephone transmission channel (4).  8. Method according to any one of the preceding claims, characterized in that, on reception (2), said biphase signals according to the "RDS" standard (Ss) are decoded to reconstitute said data and recorded in storage means ( 26).  9. Method according to claim 8, characterized in that, said audio signal transmission channel being a radio transmission channel, the data is stored forms a time-stamped database and in that this data is used to control (SCOm) the operating frequency of the receiver (2).  10. Transmission-reception system for implementing such a method comprising a transmission part and a reception part, characterized in that it comprises:  - for the transmission part, a transmitter (1) comprising, at least, means (132) for modulating said audio signals (fool) and for transmitting electromagnetic signals in a determined frequency band, an "RDS" encoder (11 ) said information data to be broadcast in coded signals in the form of two-phase baseband signals according to the "RDS" standard (Ss), data processing means (10) generating this information data as well as additional commands (sol3) and switching means (131) reacting to these command signals (sol3) for selectively transmitting said audio signals (Sst) to the modulation and transmission means (132) during first periods of time and said signals coded in the form of biphase signals according to the "RDS" standard (Ss) for second periods of time, these second periods of time being confused with said determined time intervals (T) ;;  - for the reception part, a receiver (2) comprising, at least, means (23) for receiving said emitted electromagnetic signals and for demodulating said audio signals and said coded signals in the form of biphase signals according to the "RDS" standard, a "RDS" decoder (24) receiving the demodulated signals (on) and reconstructing said information data (SD) during the detection of said coded signals in the form of biphase signals according to the "RDS" standard, means for processing data information (25) and storage of this data (26), in a determined configuration.  11. System according to claim 10, characterized in that said transmitter (1) further comprises a data recorder-reader (12) temporarily storing, for transmission during said second periods (T), said data to be broadcast .  12. System according to claim 10, characterized in that said data processing means (25) of the receiver (1) are provided with interactive means constituted by a keyboard (21) and a display screen (20) so as to interrogate the means for storing (26) data and entering into said means for processing data (25) instructions for adjusting the operating frequency of the receiver (1) used for the reception of said electromagnetic signals.  13. System according to claim 12, characterized in that, the frequency used for the transmission being switched over time according to a set of determined frequencies, said information data constitute a time-stamped database recorded in said storage means ( 26) and in that the instructions are processed by said data processing means (25) so as to automatically carry out a succession of adjustments to the operating frequency of the receiver (1) so as to calibrate according to a program preset on the frequencies of said game.  14. System according to any one of claims 10 to 13, characterized in that it further comprises a voice server (30) interrogable remotely by telephone, this server delivering said information data and being coupled to a "RDS" encoder (31), and in that the output signals picked up by a microphone (270) from a telephone handset are transmitted to the decoder  "RDS" (24) of the receiver (2).