EP0445885A1 - Receiver with means for acquisition and comparison of identification data of two transmission channels - Google Patents

Abstract

The invention is in particular adapted to receiving the RDS system in a car radio. <??>The acquisition (BITA) of the identification code of an alternative transmitter, with a view to substituting it for the present transmitter (OKPI), is done by sampling for a fairly short period (TD1) so as to be inaudible. <??>Thus the receiver can include just one tuner. <IMAGE>

Description

The subject of the present invention is a receiver with means of acquisition and comparison, between a first and a second channel of which at least the first channel called the current channel transmits a repetitive group of N data (N positive integer) comprising in particular its own identification code and at least one tuning search indication for searching for said second channel called alternative channel, said receiver being tuned to the current channel whose identification code has been stored.

An example of a channel as mentioned above is known from the publication of "European Broadcasting Union (EBU) techn. 3244 - E page 11", which defines the RDS system. This publication is included here by reference.

The RDS system is designed so that the car radio of a moving listener can automatically and permanently tune in to the best transmitter transmitting the program chosen by the listener.

As it is said on page 29 of the document already cited, various known methods allow the "search for the agreement", that is to say the search for the alternative transmitter whose channel is different from that of the transmitter whose hearing is in progress.

The installation of the RDS system is neither universal, nor compulsory, nor of course immediate so that the manufacturer of a car radio intended for RDS must take into account the fact that there are a multitude of transmitters, some of which only are fitted with the RDS system on transmission.

The invention applies, of course, only if the current transmitter transmits according to the RDS system, that is to say with a program identification code (PI code as indicated in the page 12 of the cited document), and with at least one indication of alternative frequency (AF code in an OA type group as indicated on page 16 of the cited document).

The technical problem posed by the search for an alternative channel, the frequency of which is known, frequency for which the quality of reception, from the point of view of the power of a signal received, is higher than that of the current transmitter , is that, before substituting the alternative signal received for the current channel, it is necessary to make sure that this received signal corresponds to the same program. Indeed, a vehicle which departs simultaneously from the two current and alternative transmitters can hear a third transmitter whose frequency is equal to, or close to, the alternative frequency without transmitting the same program.

The invention aims to carry out an identity check prior to a change in tuning, this checking taking place while the listener listens to the program in progress, and without interfering with it.

On page 29 of the cited document, 3 solutions are proposed, but none is satisfactory for a receiving device comprising only one "RF input stage", that is to say a single tuner.

In fact, during the acquisition of the identification of the alternative channel, it is possible either to mute the LF part and in this case the listener is subjected to unpleasant silences, or to leave the LF part active which amounts to taking the risk of subjecting the listener to incessant program changes and this will indeed be the case in large cities where there are many local radios in a small geographical area.

The object of the present invention is to eliminate this drawback.

• a) syntoniser le dit récepteur sur le dit canal alternatif pendant une durée 'd1' avant de reprendre la réception du canal en cours, la dite durée 'd1' étant plus courte que la durée d'émission d'un seul groupe de N données,
• b) mémoriser les données alternatives éventuellement émises par le dit canal alternatif pendant la dite durée 'd1',
• c) comparer les codes d'identification respectifs du canal alternatif et du canal en cours pour :
  • 1. en cas d'égalité, positionner un signal d'égalité
  • 2. en cas d'inégalité, aller à l'étape d),
• d) comparer le nombre des dites données alternatives mémorisées avec le nombre N de données d'un groupe pour :
  • 1. dans le cas "inférieur à" attendre une durée 'd2' avant de retourner à l'étape a).
  • 2. dans le cas "supérieur ou égal", positionner un signal de non-égalité.

According to the present invention, a method in accordance with the preamble is particularly remarkable in that it comprises the following steps:

• a) tune said receiver to said alternative channel for a duration 'd1' before resuming reception of the current channel, said duration 'd1' being shorter than the duration of transmission of a single group of N data ,
• b) memorize the alternative data possibly transmitted by said alternative channel during said duration 'd1',
• c) compare the respective identification codes of the alternative channel and the current channel to:
  • 1. in the event of a tie, place an equal signal
  • 2. in case of inequality, go to step d),
• d) compare the number of said alternative stored data with the number N of data of a group for:
  • 1. in the case "less than" wait a period 'd2' before returning to step a).
  • 2. in the case "greater than or equal", set a non-equality signal.

The invention takes advantage of the fact that the listener's ear does not notice a very short interruption, for example d1 = 0.02 seconds, even if this interruption is repeated at regular intervals insofar as these intervals are sufficiently large, that is to say that the duration d2 is not chosen to be too short in combination with the duration d1.

With the specifications of the RDS system, a duration d1 of 0.02 sec. corresponds to the acquisition of 23 bits while the repeated group contains 104 (N = 104) and the identification code contains 16.

It is advantageous that the duration d2 corresponds to the duration of the transmission of either 104 + n.104 bits, or 58 + m.104bits ('n' and 'm' positive or zero integers). Thus the bits acquired during two successive time slots d1 are concatenable and the chances of acquiring the 16 identification bits with a number of interruptions less than 5 (5x23> 104) increase.

According to the invention, it is also remarkable that in a receiver comprising a tuner, a controller, a demodulator and a decoder, the implementation of the method is carried out by means of an identification code comparator situated in the decoder which positions a signal intended for the controller.

The present invention will be clearly understood in the light of the description of a nonlimiting exemplary embodiment illustrated by figures.

Figure 1 shows the diagram of a car radio according to the invention.

FIG. 2 represents the steps of the method according to the invention.

• une antenne (ANT) dont les signaux sont fournis à un syntoniseur (TUN),
• le syntoniseur sélectionne les signaux du canal choisi sur une ligne multiplex (MUX) laquelle se partage en d'une part la modulation audio (SON) qui est acheminée vers un amplificateur (BF) puis à un haut-parleur (H.P.), d'autre part une modulation digitale (RDS) qui est acheminée vers un démodulateur (DEM),
• le démodulateur a pour tâche de se synchroniser avec l'émission des signaux binaires RDS et de les mettre en forme sur au moins deux fils à savoir un fil d'horloge (CLK) et un fil de données binaires (DATAK) en série,
• ces deux fils arrivent dans un décodeur (DEC) dont la tâche est de reconnaître le début de chaque groupe de N données RDS et de corriger les erreurs si possible, de sorte qu'il détecte le PI du canal en cours, et qu'il envoie ces données, par exemple par paquets en parallèle et en clair (DATAR), au contrôleur (CTR),
• le contrôleur (CTR) est le "chef d'orchestre" de l'autoradio dont seules les fonctions principales sont maintenant indiquées :
  il reçoit les ordres de l'utilisateur à travers le clavier (CLA) il fournit des informations à l'utilisateur au moyen de l'afficheur (AFI), il indique au syntoniseur quelle est la fréquence sur laquelle se régler, il commande le réglage de l'amplificateur (volume, balance, tonalité,...) et le cas échéant il lui ordonne le silence (MUTE).

The radio in Figure 1 has the following known elements:

• an antenna (ANT) whose signals are supplied to a tuner (TUN),
• the tuner selects the signals of the chosen channel on a multiplex line (MUX) which splits on the one hand the audio modulation (SOUND) which is routed to an amplifier (BF) then to a speaker (HP), on the other hand digital modulation (RDS) which is routed to a demodulator (DEM),
• the demodulator has the task of synchronizing with the transmission of the RDS binary signals and of formatting them on at least two wires, namely a clock wire (CLK) and a binary data wire (DATAK) in series,
• these two wires arrive in a decoder (DEC) whose task is to recognize the start of each group of N RDS data and to correct the errors if possible, so that it detects the PI of the current channel, and that it sends this data, for example in clear and parallel packets (DATAR), to the controller (CTR),
• the controller (CTR) is the "conductor" of the car radio whose only main functions are now indicated:
  it receives user commands through the keyboard (CLA) it provides information to the user by means of the display (AFI), it indicates to the tuner what frequency is to be adjusted, it controls the adjustment of the amplifier (volume, balance, tone ,. ..) and if necessary he orders him to be silent (MUTE).

In current car radios, the controller is a programmed microprocessor as is the demodulator; the connections between the various modules mentioned above, and other modules not mentioned, are numerous but they include neither the connection (CKPI) nor the EQ connection, between the controller and the decoder, which we will talk about later.

In the radio in Figure 1, when the user listens to an RDS transmitter, i.e. a channel in progress, the controller knows, via DATAR, the repeated groups of N (N = 104 = 4 blocks of 26 bits) bits which indicate to it which are the frequency (s), that is to say the alternative channels, of the transmitters geographically neighboring and transmitting the same program.

At all times, the controller knows whether the power received on each alternative frequency is lower or not than the power received on the current channel (to do this, we can proceed as indicated in European patent application N ° 83 200865.0 of 14 June 1983 - 'MCC'). If, at some point, it is planned to change the channel, you must first check that it is the same program.

This verification is carried out according to the process shown diagrammatically in FIG. 2.

When the controller initializes (INIT) the verification procedure, it indicates to the tuner the alternative frequency chosen, it requests silence from the amplifier and it starts a time counter 'd1'.

Reception then takes place on the alternative frequency and the RDS data arrives at the demodulator and the decoder. The decoder also receives, from the controller, a special CKPI command and, at this time, each bit received is stored in a table (BITA) of the decoder; during the time between the reception of two consecutive bits (this time is of the order of a millisecond), the decoder has time to check (TPI) if the table contains a bit configuration identical to that of the identification of program (PI) of the channel that was previously running. The PI has 16 bits which are repeated every 104 bits received, so as soon as one has received 16 bits there is a small chance that these are the bits of the PI; practically we verify two things: 1) equality of the PI or not (TPI), and 2) full table or not (TAF).

In the case of PI equality (OKPI), the verification is completed (END) after positioning an equality signal (EQ).

Otherwise and if the table is full (OKTAF), i.e. at least 104 consecutive bits have been received and stored in the table, the verification is also completed but negatively ( EQ ).

If the table is not full, you must wait for the arrival of the next bit to carry out the same checks again (BITA).

During this wait (TD1), it can happen that the time counter 'd1' arrives at zero, in this case (D10) the controller makes the hearing of the current channel resume by indicating to the tuner the initial frequency and by resuming the amplifier.

At this time a time counter 'd2' is started (TD2) and, when it reaches zero, (TD20K) the above operations (INIT) are executed again until the signal EQ or EQ be positioned.

When the EQ signal, or EQ , has been positioned it is preferable to cause the deletion of the content of the table in order to execute the next PI check to be executed. Alternatively, if an input error (= reception) is to be considered, the content of the table can be kept and updated bit by bit by continuing the input as well as the verification test.

This sequence of operations timed by the down counters 'd1' and 'd2' aims to acquire the RDS data of the alternative channel in a way that is inaudible to the listener.

For this purpose, the duration 'd1' is short enough so that the listener 'does not hear silence ". This is the case for example with' d1 'equal to 2 hundredths of a second while allowing the acquisition of 23 bits stored consecutively in the table since the transmission speed is 1.187.5 bits / sec (23 = 1.187.5x0.02). The duration 'd2' must be measured so that the storage position in the table a second 23-bit train is known. The measurement can be carried out either in the controller, in the decoder, or in both when the durations 'd1' and / or 'd2' are not constant. indeed it seems more economical to work with constant durations, but this is not an obligation and the duration 'd2' may depend in particular on the other tasks of the controller. In the case of RDS, the transmitted bits are repeated every 104 bits and it is clear that the duration 'd2' must imperatively be different from 'N-d1' + iN otherwise the bits entered are always the same; in practice d2 must be different from 81,185,284, ...

Advantageously 'd2' = 104 + nx104 bits (i.e. 104, 208, 312, 415, ...) or even 'd2' = (104-2x23) + mx104 bits (i.e. 58, 162, 266, 370, 474 ,. ..), so in both cases the acquired bits can be concatenated in the table with the bits already stored and the chances of quickly acquiring the PI bits increase.

The values indicated for 'd1' and 'd2' are clearly indicative, the important thing being to manage to acquire the alternative PI by successive samplings without causing hearing impairment to the user although the car radio only has one tuner.

• une table (BITA) avec son indicateur de remplissage
• un décompteur de temps 'd1'
• un décompteur de temps 'd2' (combinable à 'd1' puisqu'ils ne "travaillent" pas simultanément mais alternativement)
• un comparateur de PI pour comparer 16 bits quelconques, mais successifs dans la table, avec le PI du canal en cours.

The execution of the alternative PI verification operations requires, in addition to the elements known in FIG. 1, the following means:

• a table (BITA) with its filling indicator
• a time counter 'd1'
• a time counter 'd2' (combinable with 'd1' since they do not "work" simultaneously but alternately)
• a PI comparator to compare any 16 bits, but successive in the table, with the PI of the current channel.

These means can be assembled in a specialized module suitably connected to the controller and to the demodulator. However, it is advantageous to use the means already existing in the decoder which then becomes a decoder-tester having two functions which it exercises alternately according to the position of an additional binary signal CKPI; the test result is transmitted to the controller via an additional connection (EQ). Depending on the case, the decoder operates in decoder mode or in tester mode; in the tester mode, the DATAR connection can optionally be used to indicate to the controller the position of the EQ test signal or EQ .

Claims (5)

Receiver with acquisition and comparison means, between signals of a first and a second channel of which at least the signals of the first channel called current channel comprise a repetitive group of N data (N positive integer) comprising in particular its own identification code and at least one tuning search indication for searching for said second channel called an alternative channel, said receiver being tuned to the current channel whose identification code has been stored, characterized in that the said means execute the following steps: a) tune said receiver to said alternative channel for a duration 'd1' before resuming reception of the current channel, said duration 'd1' being shorter than the duration of transmission of a single group of N data , b) memorize the alternative data possibly transmitted by said alternative channel during said duration 'd1', c) compare the respective identification codes of the alternative channel and the current channel to: 1. in the event of a tie, place an equal signal 2. in case of inequality, go to step d), d) compare the number of said alternative stored data with the number N of data of a group for: 1. in the case "less than" wait a period 'd2' before returning to step a). 2. in the case "greater than or equal", set a non-equality signal. Receiver according to claim 1, the signals of one of said channels comprising an audio modulation and a digital modulation, characterized in that, the said duration 'd1' is sufficiently short, in combination with a duration 'd2' sufficiently long, for that the interruption (s) of the hearing of the current audio modulation is (are) imperceptible (s) for a listener. Receiver according to claim 2, the signals of the channel being modulated according to the RDS system, that is to say that M = 104 bits transmitted at the speed of 1,187.5 bits / sec and that said identification code comprises 16 bits characterized in that the duration 'd1' is substantially less than or equal to 0.02 seconds (which allows the acquisition of 23 bits) and in that the duration 'd2' is equal to 104 + n.104 bits (' n positive or zero integer) so that the alternative bits stored on each pass by steps a) and b) are concatenated in memory. Receiver according to claim 2, the signals of the channel being modulated according to the RDS system, that is to say that M = 104 bits transmitted at the speed of 1,187.5 bits / sec and that said identification code comprises 16 bits characterized in that the duration 'd1' is substantially less than or equal to 0.02 seconds (which allows the acquisition of 23 bits) and in that the duration 'd2' is equal to 58 + m.104 bits (' m 'positive or zero integer) so that the alternative bits memorized on each pass by steps a) and b) are concatenable in memory. Receiver according to claim 3 or 4, characterized by a decoder comprising test means for testing an alternative PI and in that the connections between the decoder and a controller comprise a connection (CKPI) for, depending on the case, activating or not the PI tester function of the decoder and a connection (EQ) to, as the case may be, indicate or not the equality of current and alternative PIs.

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