EP0902564B1 - Method for evaluating digital signals, specially radio data signals - Google Patents

Description

State of the art

The invention is based on a method for evaluating digital signals, which are transmitted via a transmission frequency other than a transmission frequency set on a radio receiver, according to the preamble of the main claim.

It is known from the European Broadcasting Union's "Specifications of the Radio Data System (RDS) for VHF / FM Sound Broadcasting" of March 1984, in addition to the radio programs in the context of the Radio Data System, RDS for short, about broadcasting frequencies Information in the form of digital signals, grouped together in groups, which are in turn divided into blocks. Part of this information is the program frequencies identifiers (Program Identification Code PI) assigned to the transmission frequencies or the programs transmitted via the transmission frequencies, which indicate which program is transmitted via the respective transmission frequency. Other particularly important information is a Program Type Code (PTY), which indicates what kind of program content, e.g. As pop music, Klossische music, sports, etc., is broadcast on the received program and finally a traffic information (Traffic Program TP) indicating whether the received program is a traffic program.

According to the o. G. Specification is provided that in the context of the radio-data system groups of various information content can be broadcast in any order on the transmission frequencies, but the aforementioned, considered particularly important information (PI, PTY, TP) are common to all group types and in of the respective group also occupy a fixed assigned position.

From DE-A-41 03 061 radio receivers are known in which the program chain identifiers are used to find receivable transmission frequencies over which the same program as over the current transmission frequency is transmitted. In order to test such alternative frequencies, the receiving frequency of the radio receiver for the duration of the test of an alternative frequency, i. H. to check their reception field strength and their associated program chain identifier PI switched to the alternative transmission frequency. The resulting signal interruptions in the range of 20 to 30 msec. or 150 to 300 msec. make themselves felt in the form of crackling noises and information loss. It is therefore proposed to insert substitute signals into the signal gaps which are obtained from the audio signal section immediately preceding the interruption by buffering and thus to mask the signal interruptions.

To avoid the costs associated with the recording of the interruption preceding audio signal portion and simultaneous inaudible evaluation of next to a broadcast program on a different than a currently set at a receiver transmission frequency digital signals is in the non-prepublished patent application DE-A-197 01 042 of the applicant a procedure in which the receiver is switched back and forth again by means of a high-speed phase-locked loop (PLL) from the original to an alternative frequency within the duration of one bit of the digital signal transmitted via the alternative frequency. The bits of the digital signal received during the period of residence of the receiver on the alternative frequency are read into a buffer, so that when repeated switching of the receiver during successive bits of the digital signal finally in the memory, the entire transmitted over the alternative frequency digital signal for evaluation ready.

EP-A-0 497 116 A2 discloses an RDS receiver in which data samples are taken from their radio data signal for testing the program identification code (PI) of an alternative transmission frequency by short-term transitions to the alternative transmission frequency stored PI are compared to the originally set transmission frequency. It can also be sampled data from different groups of the radio data signal of the alternative transmission frequency.

Advantages of the invention

The inventive method with the features of the main claim has over the known from DE-A-41 03 061 radio receiver has the advantage that is not audible due to the brevity of switching from the current to the test transmission frequency, the audio signal interruption during the switching. In addition, the effort to record the interruption preceding audio signal section, as already in the latter prior art, saved.

Compared to the teaching of DE-A-197 01 042, the inventive method has the advantage that the switchover to the alternative frequency and from this back to the mother frequency is less time-critical and thus the phase locked loop for frequency switching must meet less stringent requirements.

It is also advantageous to interrupt the playback of the audio signal during the switching of the receiver to an alternative frequency, so as to disturbing pops that z. B. may result from the fact that a different modulation is transmitted to the alternative frequency than on the original frequency, avoided.

drawing

• Figur 2 beispielhaft den Aufbau eines mittels des Radio-Daten-Systems übertragenen digitalen Signals,
• Figur 3 eine schematische Darstellung zur Verdeutlichung des Ablaufs des erfindungsgemäßen Verfahrens,
• Figur 4a und b beispielhaft eine resultierende Gruppe, die durch Mittelung aus mehreren empfangenen Gruppen gebildet ist und
• Figur 5a und b den Ablauf des erfindungsgemäßen Verfahrens anhand des Ablaufplans der in der Steuerung des Rundfunkempfängers implementierten Software.

Embodiments of the invention are illustrated in the drawings and will be explained in more detail below. FIG. 1 schematically shows the part of a radio receiver essential for the invention for carrying out the method according to the invention,

• FIG. 2 shows, by way of example, the structure of a digital signal transmitted by means of the radio-data system,
• FIG. 3 shows a schematic representation to clarify the sequence of the method according to the invention,
• FIGS. 4a and 4b exemplarily show a resulting group formed by averaging a plurality of received groups and FIG
• 5a and b show the sequence of the method according to the invention with reference to the flow chart of the software implemented in the control of the radio receiver.

Description of an embodiment

The inventive method is described below with reference to a radio receiver for receiving information transmitted by the Radio Data System (RDS), but in principle also applicable to other digitally transmitted information that is transmitted in structured structured bit groups.

In the radio receiver shown in Figure 1 for carrying out the method according to the invention a pending on a receiving antenna 1 broadcast signal is forwarded to a receiving part 2, the means required for the reception and demodulation of broadcast signals, such as an antenna signal amplifier, an adjustable phase-locked loop (PLL) Tuning of the receiving part 2 to a certain transmission frequency, an intermediate frequency part and a demodulator for demodulating the received broadcast signal has. The phase locked loop for switching the receiving part from a first to a second transmission frequency is controlled by a controller 5 explained in more detail later. The pending at the output of the receiving part 2 stereo multiplex signal with which the received transmission frequency is modulated, on the one hand via a mute circuit 6 for interrupting the reproduced audio signal to a playback unit 7 forwarded in the known manner on the for playback of the in the Stereo multiplex signal contained audio signal such as stereo decoder, amplifier and speakers features. The controlled by the controller 5 mute circuit 6 is designed in the present case as a controllable switch whose output to a memory, in the simplest case a capacitor connected is. In this way, the coupling capacitors of the subsequent stages are held at interruption of the audio signal to the last applied value, so that cracking noises are effectively avoided as a result of transients on the coupling capacitors when opening and closing the switch.

Alternatively, the Mute circuit may be configured such that the audio signal is off in the context of an interruption after a predetermined time function and after the temporary frequency switching is displayed again. In this way, a suppression of unpleasant clicks is also possible.

The stereo multiplex signal is further supplied to the input of an RDS demodulator 3 connected to the controller 5 for demodulating the 57 kHz subcarrier of the stereo multiplex signal (MPX) modulated by the RDS signal. The output of the RDS demodulator 3 is connected to a memory 4 for storing the bits of the RDS signal in turn, which in turn is connected to the controller 5. The memory 4 in this case comprises a number o, in the present case o = 4 registers, each 104 bits in length, so that a total of four groups of the RDS signal can be stored here. In addition, the memory 4 comprises a result register for recording a resulting bit group of the RDS signal, which can be fed to a further evaluation in the controller 5.

FIG. 2 shows, by way of example, a section of a radio data (RDS) signal 20 which is transmitted by a broadcast program via a transmission frequency. The RDS signal 20 is composed of bit groups 21, 22, 23, hereinafter referred to as groups, as the largest contiguous unit, each group having a length of 104 bits. Each group of the RDS signal is in turn divided into blocks 25, 26, 27, 28 of 26 bits each. Each block consists of an information word comprising the first 16 bits, the actual information to be transmitted and an overlay 35, 36, 37, 38 of a control word formed from the information word and an offset word indicating the position of the respective block within the group.

According to the RDS specification mentioned above, it is provided that various information is transmitted by means of the RDS signal by means of different group types which are sent in an order not determined by the protocol. In FIG. 2, two different group types are shown by way of example. In the first group 21 of the type 0A of the RDS specification, in addition to information discussed later in block C (27) in the sections marked 43, information about alternative frequencies (AF) to the currently received transmission frequency and in block D (28) the program name (PS) 44 transmitted over the currently received transmission frequency program. On the other hand, in the blocks C and D (27, 28) of the type-22 group 22, radio-text data (RT) 45 is transmitted.

In contrast to these different types of information, depending on the group type, it is provided according to the RDS specification that information regarded as particularly important, such as the program chain identifier (PI), the indicates which program is received via the currently received transmission frequency, the program type identifier (PTY) which indicates which program type is being transmitted over the current transmission frequency and the traffic information (TP) which indicates whether it is the currently received one Program is a traffic messaging program, each at the same position within each group, regardless of group type. For example, the program chain identifier (PI) 40 in block A 25 of each group takes the first 16 bits each, the traffic identification (TP) 41 in block B 26 the sixth bit and the program type identifier (PTY) 42 in block B 26 the bit positions 7 to 11 on.

The present invention now makes use of the fact that the particularly important information, and these are to be detected by the method according to the invention, are transmitted at fixed positions within the groups of the digital signal, in the present case the RDS signal. The relevant data of a currently set transmission frequency, hereinafter also called mother frequency (MF), alternative transmission frequency (AF) are now not collected in a continuous stream. Rather, the set mother frequency (MF) is only in the range of a few msec for a very short time. and set an alternative frequency to make the interruption in receiving the mother frequency inaudible to a listener. During the short-term switching to the alternative frequency, a short bit sample is taken from the data stream 20 transmitted via the alternative frequency. Subsequently, the mother frequency is set again and taken again after an interval time a data sample. To the interruption to make it as inaudible as possible in the reception of the mother frequency, a data sample should not exceed 5 to 8 bits.

mit p = 17 oder $$26\times 4\mathrm{\hspace{0.17em}}\mathrm{Bit},$$

mit p = 26 oder $$13\times 8\mathrm{\hspace{0.17em}}\mathrm{Bit},$$

mit p = 13.In order to capture all the relevant data of the alternative frequency, since synchronization of the receiver to the frames of the alternative frequency digital signal can not be assumed, it is necessary to repeat at least a full 104 bits by repeating data samples from the alternative frequency Length with a total time of 87.6 msec. capture. The data samples are tuned so that in each case after p samples 104 bits result, so for example $$15\times 6\mathrm{}\mathrm{bit}+2\times 7\mathrm{}\mathrm{bit}=104\mathrm{}\mathrm{bit}.$$

with p = 17 or $$26\times 4\mathrm{}\mathrm{bit}.$$

with p = 26 or $$13\times \mathrm{8th}\mathrm{}\mathrm{bit}.$$

with p = 13.

To ensure the detection of a complete group, the interval time T _I = nx T _G + T _V between two data samples must be an integer multiple of the group duration T _G = 87.6 ms (milliseconds). A suitable choice of the residence time T _V on the alternative frequency for taking a data sample at a fixed interval time T _I ensures that for each data sample, the successive BitPositionen within the jumped groups of the alternative frequency are detected.

The group of the digital signal emitted via the alternative frequency, which is composed of the p data samples, now contains signal sections of p groups of the digital signal which, with a certain probability, have a different group type. The information content of the thus detected group is thus low, a Group or block synchronization is therefore just as impossible as a Syndromberechnung. To obtain meaningful information, it is proposed to collect several groups, ie an integer multiple of 104 bits, and to determine a resulting bit group by averaging. For the purpose of averaging, the evaluation of the autocorrelation, the formation of a moving average or a summation followed by a threshold value decision come into question.

For the purpose of averaging collect z. B. 4, 6 or 8 x 104 bits and links the currently read bit sequence with the values of the previous to a resulting bit sequence. As a result, assuming that each group from which a data sample was taken has a different content, that is, a different group type, then in the resulting extrema bit group only at those locations where information consistent for all group types, such as the Program chain identifier in block A, the program type identifier and the traffic identifier at bit positions 7 to 11 and 6 of block B, as these data are then repeated 4, 6 or 8 times and added up, as opposed to other signal portions having statistically different values and thus have a medium value. At the same time as a result of the averaging over a large number of groups, possibly data or reading errors are suppressed since these are statistically evenly distributed in a large number of groups.

The method according to the invention will now be explained in more detail with reference to FIG. 3 using the example of a radio data signal transmitted in addition to a broadcast program via a broadcasting transmission frequency.

FIG. 3 shows by way of example a detail of an RDS signal 20 which is transmitted via an alternative frequency 19. The receiving frequency of the receiving part is or is at successive times t _i , which are designated in the figure by the reference numerals 56, 57, 58, 59 and 60, switched from the mother frequency 18 to the alternative frequency 19. From the points of time t _l, which in the present example, the switching times t coincide _i, data samples 65, 66, 67, 68 taken from 20 of the Alternative Frequency 19-72 from the RDS signal and latched the functioning according to the inventive method, the radio receiver in the memory 4 ,

As shown in Figure 3 it can be seen in the present example the switching instants ti and the reading times t _l, at which a data sampling begins at the alternative frequency 19, are selected so that the data samples are taken 65 and 72 from directly successive groups of the RDS signal , In the present case, the distance between two groups jumped to the data sampling is one and thus n = 1. The residence time T _V , designated by reference numeral 50 in FIG. 3, is chosen so that m = 8 bits are read during each data sampling operation. Thus, the data samples 65 to 72 according to FIG. 3 comprise
65: bit 25, block A - bit 6, block B; Group 1,
66: bit 7, block B - bit 15, block B; Group 2,
67: bit 16, block B - bit 24, block B; Group 3,
...
72: Bit 16, Block A - Bit 24, Block A, Group 13.

The interval duration T _I , designated 54 in FIG. 3, between the beginning of two consecutive data sampling (eg 58 and 59) corresponds in the present case to the group duration T _G approximately equal to 87.6 ms = 104 × T _B with T _B the duration of one bit, plus the duration of a data sampling, ie the residence time T _V = mx T _B on the alternative frequency. The time taken to acquire a complete group from time 56 of a first sample then becomes $${\mathrm{T}}_{\mathrm{R}}=\left(\mathrm{p}-1\right)\times {\mathrm{T}}_{\mathrm{I}}+{\mathrm{T}}_{\mathrm{V}}\mathrm{}\mathrm{With}\mathrm{}\mathrm{p}={\mathrm{T}}_{\mathrm{G}}/{\mathrm{T}}_{\mathrm{V}}\mathrm{}\mathrm{and}\mathrm{}{\mathrm{T}}_{\mathrm{I}}=\mathrm{n}\times {\mathrm{T}}_{\mathrm{G}}+{\mathrm{T}}_{\mathrm{V}}$$

As already mentioned, the acquisition of a single complete group of the RDS signal 20 is not sufficient for obtaining meaningful data, since the data sections that make up this group can be taken from groups of different types and thus different data contents. Thus, it is necessary to form a resultant group of a plurality o of groups. The total duration T _tot , which is required for reading in o groups from the time of the first data sample, is then $${\mathrm{T}}_{\mathrm{ges}}=\mathrm{O}\times \left((\mathrm{p}-1)\times {\mathrm{T}}_{\mathrm{I}}+{\mathrm{T}}_{\mathrm{V}}\right)\mathrm{,}$$

In the example according to FIG. 3 with the parameters n = 1, m = 8 and o = 4, one thus obtains T _tot ≈ 4.5-5 ms for the total _{evaluation duration} T.

Of course, the above formulas apply only in the event that the number m of bits read per data sample is the same for all data samples, not, for example, for the aforementioned example with p = 17, with 6 during each of the first 15 data samples and 6 during the last one both data samples are read 7 bits each.

So far, it was assumed in the description of Figure 3, that the switching times t _i , to which the receiving frequency of the receiving part 2 are switched from the mother frequency 18 to the alternative frequency 19 coincide with the times t _l , to each of which the removal of a data sample of the alternative frequency begins. However, this assumption would only be fulfilled with an infinitely fast phase locked loop (PLL) that would be able to switch back and forth between two receive frequencies. In reality, however, it can be assumed that the PLL used has a finite settling time when switching from a first to a second reception frequency. This must be taken into account in the calculation of the switching times ti such that the PLL at the times t _{l is} already settled on the alternative frequency, and thus the reading of a data sample at time t _l can be started punctually. Thus, the switching times t _i from the mother frequency 18 to the alternative frequency 19 with respect to the reading times t _l by at least the settling time of the PLL, which is indicated in Figure 3 by the reference numeral 51, vorzuverlegen. The total duration T _U , indicated by the reference numeral 53 in FIG. 5, the interruption of the reception of the mother frequency then results according to FIG. 3 as T _U = 2 × T _E + T _V , with T _E the settling time of the PLL.

In a first embodiment of the method according to the invention, it is provided that the frequency switching is advanced from the mother frequency 18 to the alternative frequency 19 with respect to the times t _l by a flat assumed transient time T _E. The flat-rate settling time of the PLL corresponds to the maximum settling time, which results in a frequency hopping over the largest possible frequency range, ie between two lying at the opposite ends of the FM frequency band transmission frequencies. If the switching times t _i are advanced by this maximum settling time T _E , the PLL is already set to the alternative frequency 19 for smaller than the maximum frequency jumps before the corresponding read time t ₁ . In order to ensure that the data sample is read in at the time t ₁ in this situation, it is also necessary to monitor the achievement of the times t ₁ .

In a second embodiment of the method according to the invention, it is provided that the settling time T _E , which, as already indicated, is dependent on the width of the skipped frequency range, is calculated from the difference of the values of the parent and the alternative frequency, and the switching times t _i compared to the reading times t ₁ are advanced by this individually calculated settling time T _{E of} the PLL. This ensures that the PLL has timed to the alternative frequency in time for the beginning of a data sample acquisition and at the same time reaches the interruption 53 when receiving the mother frequency their smallest possible value.

FIGS. 4a, b each show an example of the content of the resulting memory contents or of the result register. The content of the result register, which has a length of 104 bits like the intermediate registers, results in the present case by adding the contents of the intermediate register contents, in this case the value o, ie the number of bit groups to be evaluated and thus also the number of intermediate registers in the Memory 4 to four was chosen. In the following considerations, it is assumed that the logic 1 value of the digital signal has been mapped to the value "1" and the logical value "0" has been mapped to the value "0".

Due to the fact that different groups from which data samples were taken have at least partially different group types and thus different contents (FIG. 4a), extremes, ie maxima and minima, result only at those places in the result register where information is stored, firstly secondly, regardless of group type, in each group in the same position. These are, as shown in FIG. 4a, firstly the PI 40 which is transmitted in block A of each group and in the present case has been detected with the data samples 70 and 71, furthermore the TP 41 and the PTY 42 as part of the block B 26 that were read in with data samples 65 and 66. In addition, maxima and minima in the area of data samples 72 and 65 can be seen in the form of the superimposition of control and offset word of block A 25. These are due to the fact that with identical content of the block A for each group, the control word calculated from the information word has the same value from group to group and further the PI in each group is transmitted in block A, so that the superposition from control and offset word for block A has the same value for each group. Furthermore, it can be seen in FIG. 4 a that values which fluctuate around the arithmetic mean value of the extreme values occur in the area of the blocks B 26 and D 28. This is due to the fact that data was collected from different group types and thus from a statistical one Distribution of the bit positions of the signal on which different information is transmitted from group to group can be assumed.

FIG. 4 b shows the content of the result register in the event that all data samples have been taken from groups of the same type. In this case, the other data of the group, which have different information contents for different group types, are also usable. In addition to the extreme values, intermediate values 80, 81 and 82, which result, for example, from errors in the transmission of the digital signal, are also shown in FIG. 4b.

The decision as to whether individual bit values are to be regarded as extreme values or as outliers from the statistical mean is, for example, B. by combinatorial consideration of the respective value and the frequency of deviations from the extremes in the environment of the considered value possible.

FIGS. 5 a and b show the sequence of the method according to the invention, which is implemented, for example, in the form of software in the controller 5 of a radio receiver according to the invention. The process begins with step 100. In step 110, the RDS demodulator 3 of the radio receiver according to the invention is synchronized to the digital signal of the alternative frequency. This is done according to Figure 5 b, characterized in that in a step 112, the receiving part 2 is tuned by means of the PLL of the mother frequency to the alternative frequency, in step 113, the detection of a bit is checked, after detection of a bit beginning in step 114, the time of the detected Bitanfangs stored as the basis for the calculation of the other switching times t _i and the times t _l for the removal of the data samples and finally in a step 115, the receiving part 2 is tuned by means of the PLL from the alternative frequency back to the mother frequency. In step 120, after bit synchronization of the RDS demodulator, along with further calculations, the dwell time T _V on the alternative frequency is obtained from the quantities m and p, the next read time t _l from the group duration T _G and the values n, m, p, the next Switching time ti calculated from the mother frequency to the alternative frequency taking into account the settling time T _{E of} the PLL. After reaching the switching time ti, which is checked in block 130, the receiving part 2 of the radio receiver is tuned in block 140 from the mother frequency to the alternative frequency. In block 160, if, as checked in block 150, the read time t ₁ calculated in block 120 is reached, one bit is read, in step 170 it is checked whether the dwell time T _V on the alternative frequency has already elapsed, and if so is not the case, the next bit of the digital signal is read in step 160. If, according to the check in step 170, the dwell time T _{V has} expired on the alternative frequency, ie if all the bits of the current data sample have been detected, in step 180 the receiver 2 of the radio receiver is tuned back to the mother frequency by the alternative frequency. Subsequently, in step 190 it is checked whether sufficient data samples are already available for an evaluation, ie whether a limit oxm has been reached. If this is not the case, the method is calculated with the step 120, ie the calculation of a new dwell time T _V the next reading time t _i for taking the next data sample. Is, however, the reached the aforementioned barrier, so all the intermediate registers of the memory 4 are occupied with newly detected data, so in step 200, the evaluation in such a way that, as in the example of Figures 4a and 4b, the contents of the intermediate registers added, the result register contents supplied to a threshold decision and the data taken from the Schwellwertentscheider useful for further processing, for. B. the PI evaluation are supplied. The method finally ends in step 210.

In a further embodiment of the method according to the invention, an evaluation of the read signal sections can also be such that the new data is collected in a second register, linked to the contents of the first register and then the result is written back into the same register.

Claims (4)

1. Method for evaluating digital signals (20), particularly radio data signals, which are transmitted in bit groups (21, 22, 23) of prescribed length (52) in addition to a broadcast radio programme on a transmission frequency (19) other than a transmission frequency (18) which is currently selected on a receiver, where the reception frequency of the receiver is repeatedly temporarily changed over from the originally selected frequency (18) to the other frequency (19), with the bits from the digital signal (20) transmitted via the other frequency (19) which are received while the receiver is tuned (50) to the other frequency (19) being read and buffer-stored,
   characterized,
   in that the repeated temporary changeover operations (56, 57, 58, 59, 60) take place at intervals of time (54) which correspond to an integer multiple of the group length (52) plus the time tuned (50) to the other frequency (19),
   in that the temporary changeover operations (56, 57, 58, 59, 60) are repeated until an integer multiple (O) of bit groups has been buffer-stored,
   in that the bits of the digital signal (20) which have been read during the temporary changeover operations (56, 57, 58, 59, 60) are evaluated in an evaluation cycle (200), and
   in that the bits in a resultant bit group provided for evaluation are formed by averaging the bits in the buffer-stored bit groups.
2. Method according to Claim 1, characterized in that only those blocks in the resultant bit group whose bits are received as identical in a plurality of incidents on account of the averaging and are thus reliably identified are supplied to an evaluation stage.
3. Method according to one of the preceding claims, characterized in that while the receiver is being changed over to the other transmission frequency (19) the reproduction of a received program is interrupted.
4. Broadcast radio receiver for evaluating digital signals which are transmitted in bit groups (21, 22, 23) of prescribed length (52) in addition to a broadcast radio programme on a transmission frequency (19) other than a transmission frequency (18) which is currently selected on a reception part (2) in the apparatus, having a controller (5), which repeatedly temporarily changes over the reception frequency on the reception part (2) from the originally selected frequency (18) to the other frequency (19), and having a memory (4) for buffer-storing the bits of the digital signal (20) transmitted via the other frequency (19) which are received while the reception part (2) is tuned (50) to the other frequency (19), characterized by the controller (5) being in a form such
   that the repeated temporary changeover operations (56, 57, 58, 59, 60) take place at intervals of time (54) which correspond to an integer multiple of the group length (52) plus the time tuned (50) to the other frequency (19),
   that the temporary changeover operations (56, 57, 58, 59, 60) are repeated until an integer multiple (o) of bit groups has been buffer-stored,
   that the bits of the digital signal (20) which have been read during the temporary changeover operations (56, 57, 58, 59, 60) are evaluated in an evaluation cycle (200), and
   that the bits of a resultant bit group provided for evaluation are formed by averaging the bits in the buffer-stored bit groups.

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