EP0445885B1 - 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 present invention relates to a radio receiver with means for acquiring binary signals, and for comparing between the binary signals of a first channel called the current channel and of a second channel called the alternative channel, the signals of at least the current channel comprising a repetitive group of N binary data (N positive integer) comprising in particular its own coded identification and at least one tuning indication for searching for an alternative channel. An example of such a channel is known from the publication "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 "EBU" 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 issuer whose hearing is in progress.

Thus, a receiver intended to implement this possibility is known from DE-OS-38 32 455. This document describes how to find out whether other channels of the same network are capable of providing better reception than the current channel. The method used presupposes a priori that the frequency information of the other channels of the same network is sufficient.

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 of which some only are equipped, on transmission, with the RDS system.

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 on page 12 of the document " EBU "cited), and with at least one indication of alternative frequency (AF code in an OA type group as indicated on page 16 of the document" EBU "cited).

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 received alternating signal for the current channel, it is necessary to make sure that this received signal corresponds well 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 current program, and without interfering with it.

On page 29 of the cited "EBU" document, 3 solutions are proposed, but none is satisfactory for a receiving device having 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 silence 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.

• de moyens "A" pour, alors que le récepteur a été syntonisé sur le canal en cours dont le code d'identification a été mémorisé, le syntoniser sur le canal alternatif pendant une durée "d1" avant de le syntoniser à nouveau sur le canal en cours, la dite durée "d1" étant plus courte que la durée d'émission d'un groupe de N données, et pour acquérir et mémoriser les données binaires dites alternatives éventuellement émises par le dit canal alternatif pendant la dite durée "d1",
• de moyens "B" pour comparer les codes d'identification acquis du canal alternatif par les moyens "A" et ceux mémorisés du canal en cours et pour :
  • en cas d'égalité, positionner un signal d'égalité indiquant que le canal alternatif diffuse bien le même programme que le canal en cours,
  • en cas d'inégalité, comparer le nombre des dites données alternatives mémorisées avec le nombre N de données d'un groupe et :
    • dans le cas "inférieur à", attendre une durée "d2" avant de réactiver les moyens "A",
    • dans le cas "supérieur ou égal", positionner un signal de non-égalité indiquant que le canal alternatif ne diffuse pas le même programme que le canal en cours.

According to the present invention, a receiver is provided with:

• means "A" for, while the receiver has been tuned to the current channel whose identification code has been memorized, tune it to the alternative channel for a period "d1" before tuning it again to the channel in progress, said duration "d1" being shorter than the duration of emission of a group of N data, and for acquiring and memorizing the so-called alternative binary data possibly transmitted by said alternative channel during said duration "d1" ,
• means "B" to compare the identification codes acquired from the alternative channel by means "A" and those stored in the current channel and for:
  • in the event of a tie, set an equality signal indicating that the alternative channel is broadcasting the same program as the current channel,
  • in the event of inequality, compare the number of said alternative stored data with the number N of group data and:
    • in the case "less than", wait for a period "d2" before reactivating the means "A",
    • in the case "greater than or equal", set a non-equality signal indicating that the alternative channel is not broadcasting the same program as the current channel.

The invention takes advantage of the fact that the listener's ear does not realize 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 decoder for decoding the binary messages and a controller for supervising all the functions of the receiver, the decoder comprises test means for testing an identification code of another program than the one being heard, and that a connection is provided between the decoder and the controller for, as the case may be, activating or not the means for testing the decoder identification code and a connection for indicating or not the equal identification codes for the current program and the alternative program.

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 d'une part la modulation audio (SON) qui est acheminée vers un amplificateur (BF) puis à un haut-parleur (HP), 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 shares on the one hand the audio modulation (SOUND) which is routed to an amplifier (BF) then to a speaker (HP), on the other share a 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 beginning 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 parallel and clear (DATAR) packets, 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 CKPI connection 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 what are the frequency (s), that is to say the alternative channels, of the transmitters geographically neighboring and transmitting the same program.

At any time, 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 the European patent application EP-A-0 098 634 of June 14, 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 identification 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 having positioned 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 causes the hearing of the current channel to resume by indicating to the tuner the initial frequency and resetting 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 correctly 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 manner that is inaudible to the listener.

For this purpose, the duration 'd1' is short enough so that the listener 'does not hear the 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' can notably depend 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 would always be the same; in practice d2 must be different from 81,185,289, ....

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 providing 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), et
• 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), and
• 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 (4)

1. A radio receiver comprising means for acquisition of binary signals (DEC) and for comparison (TPI) between the binary signals from a first channel, referred to as the current channel, and a second channel, referred to as the alternative channel, the signals from at least the current channel comprising a repetitive group (BITA) of N binary data (N being a positive integer), particularly having its own identification code (PI) and at least a tuning indication for searching an alternative channel, characterised in that it comprises:

   - means "A" (CTR, TD1) for tuning the receiver, while it is tuned to the current channel whose identification code has been stored, to the alternative channel during a period "d1" before it is again tuned to the current channel, said period "d1" being shorter than the transmission period of one group of N data, and for acquiring and storing the binary data (BITA) referred to as alternative data transmitted by said alternative channel during said period "d1",

   - means "B" (TPI) for comparing the identification codes of the alternative channel acquired by the means "A" and those stored for the current channel and for:

   - setting, in the case of equality (OKPI), an equality signal (EQ) which indicates that the alternative channel transmits the same program as the current channel,

   - comparing (TAF), in the case of inequality, the number of said stored alternative data with the number N of data of a group, and:

   - waiting for a period "d2" before reactivating the means "A" in the case of "less than",

   - setting an inequality signal, in the case of "greater than or equal to", which inequality signal indicates that the alternative channel does not transmit the same program as the current channel.
2. A receiver as claimed in Claim 1, characterised in that the signals from the channel are modulated in accordance with the RDS system, i.e. comprise binary sequences of N = 104 bits transmitted at a rate of 1,187.5 bits/second with an identification code comprising 16 bits, the period "dl" being substantially smaller than or equal to 0.02 second (in which 23 bits can be acquired) and the period "d2" being equal to 104+n.104 bits ('n' being a positive integer or zero) in such a manner that the alternative bits stored upon each processing by the means "A" can be concatenated in the memory.
3. A receiver as claimed in Claim 1, characterised in that the signals from the channel are modulated in accordance with the RDS system, i.e. N = 104 bits transmitted at a rate of 1,187.5 bits/second and said identification code comprises 16 bits, the period "d1" being substantially smaller than or equal to 0.02 second (in which 23 bits can be acquired) and the period "d2" being equal to 58+m.104 bits ('m' being a positive integer or zero) in such a manner that the alternative bits stored upon each processing by the means "A" can be concatenated in the memory.
4. A receiver as claimed in Claim 2 or 3, characterised in that it comprises a decoder (DEC) for decoding the binary messages and a control unit (CTR) for controlling all the functions of the receiver, the decoder (DEC) comprising test means (TPI) for testing an identification code (PI) of another program than the program being listened to, and comprising between the decoder and the control unit a connection (CKPI) for activating or not activating, as the case may be, the means for testing the identification code (PI) of the decoder and a connection (EQ) for indicating, as the case may be, the equality or inequality of the identification codes of the current program and of the alternative program.

Images