Mobile radio apparatus, such as a car radio or the like, in particular a vhf receiver

The invention relates to a portable radio, such as a car radio or the like. In particular, an FM receiver, the genus defined in the preamble of claim 1.

In a known radio receiver of this type (DE-A-32 14 155), a complete second receiver part with a transmitter setting device is provided for checking the reception quality of the alternative transmitters, in which the alternative transmitters are set in succession to the transmitter currently being heard and their reception quality, here the reception field strength, is compared with that of the station currently being listened to. As soon as an alternative transmitter has a better reception quality, here a higher reception field strength, than the transmitter currently being listened to, the latter is replaced by this alternative transmitter, which is then switched to audible and represents the new transmitter being heard.

Such a radio receiver is relatively complex because of the required complete second receiver train and can only be found as a car radio in the upper price category. Although it has already been proposed in the aforementioned DE-A to dispense with the second reception train and to carry out the checking of the alternative transmitters in the transmission pauses of the station currently being listened to, this gives the alternative transmitters tuning and the determination of their field strength as a result of the relatively short pause times any faults that are currently occurring make a less reliable statement about their reception quality, so that there is sometimes a frequent change of the station being listened to. In addition, pause detection circuits are relatively complex.

Document DE-A-3130864 shows a test device for the reception quality which checks both the transmitter currently being heard and the alternative transmitter. The test device of the radio has a circuit which samples the reception quality of the transmitter currently being heard and the reception quality of the alternative transmitters received briefly in short mute times, a circuit for averaging the sample values ​​associated with a transmitter, a memory for storing the average values ​​and a comparison circuit which makes the best selection based on the comparison of the current sample values ​​and the mean values.

The invention has for its object to improve a mobile radio receiver of the type mentioned in such a way that in the presence of only one receiver train without disturbing the auditory impression of the station currently being heard a reliable check of the reception quality of the transmitter and alternative transmitter is achieved and a switch only to better stations in the long term, whereby the current samples are rated higher and the older samples are taken into account adjustable with a lower rating.

This object is achieved in a radio receiver, the type specified in the preamble of claim 1 according to the invention by the features in the characterizing part of claim 1.

The radio receiver according to the invention has the advantage that in the best selection of the transmitters, in addition to the current measured values ​​of the reception quality, a large number of individual measured values ​​of the reception quality recorded at different points in time are taken into account, the relevance of the individual values ​​for the test result also being taken into account. The recording of the individual values ​​of the reception quality takes place in extremely short mute times of approx. 20 ms which are not perceived by the listener if the frequency is not too high. The station currently owned - hereinafter referred to as G transmitter - will only be replaced by an alternative transmitter - hereinafter referred to as A transmitter - if it has better reception quality in the long term.

By averaging the samples or measured values ​​of the reception quality, which corresponds to the filtering by means of a digital recursive low-pass filter of the first order or approximately the filtering by means of an analog RC low-pass filter, an evaluation of the reception quality is achieved which takes into account an optimal auditory impression. It is sufficient to check the reception quality, which is dependent on the modulation and has a static character, only relatively rarely, ie at intervals of 5 s - 30 s, depending on the quality of the reception quality. The setting of the linkage factor k is adapted to the circumstances. For the first sample value, k is close to 0, since this measured value is highly relevant, while it is close to 1 with a relatively constant, ie little fluctuating, or increasing reception quality, which strongly averages. If the instantaneous reception quality is significantly poorer than the averaged one, then k is again close to 0, so that the sample or measurement value influences the mean value very strongly. The latter makes sense insofar as, for example, individual strong and short-term disturbances are perceived subjectively much more strongly than their weight and thus impair the auditory impression very strongly. This change in the linkage factor k can be carried out in a simple manner after a predefined definition as a function of the comparison result, for example the difference, from the instantaneous sample or measurement value and mean value.

An advantageous embodiment of the invention also results from claim 2. This measure avoids unnecessary muting. However, the reception quality of the G transmitter is continuously checked and the test result is continuously improved by averaging over a constantly growing number of samples.

An advantageous embodiment of the invention also results from claim 3. These measures optimize the reception quality check; because reception quality testing by checking the field strength alone is only sufficient if there are ideal, ie undisturbed reception conditions. In this case the reception quality is proportional to the reception field strength. In the case of the mobile radio receiver, the car radio, the multi-path reception or the so-called picket fence effect that occurs during the journey, which is caused by reflections, considerably reduces the reception quality despite sufficient field strength. The interference-free measure obtained by means of a circuit arrangement described in DE-A-31 26 224, referred to there as the measure of quality, takes account of such influences which impair the reception quality. The level of the interference-free measure is a measure of the size and frequency of such interference and is inversely proportional.

An advantageous further development of the invention also results from claim 4. This measure gives priority to the field strength when selecting the best; because only a sufficiently large field strength ensures acceptable reception. However, if this is present, the evaluation of the reception quality is determined by the measure of freedom from interference.

An advantageous embodiment of the invention also results from claim 5. This ensures that with less satisfactory current reception field strength of both the G transmitter and the checked A transmitter, the A transmitter is only switched to be audible if its field strength is long-term and with respect the auditory impression is the better.

An advantageous embodiment of the invention results from claim 6. This ensures that the tested A transmitter is then switched to inaudible and its further check is terminated if its current reception field strength is already smaller than that of the G transmitter.

An advantageous embodiment of the invention also results from claim 7. This has the effect that the A transmitter is not switched to audible and its checking is stopped when, in contrast to the G transmitter, its current reception field strength is below the predetermined field strength minimum.

An advantageous embodiment of the invention also results from claim 8, in particular in connection with claim 9. These measures ensure that with sufficient reception field strength of the A transmitter, it is only switched to audible if not only is its current interference-free measure greater than that of the G-transmitter, but it also has an interference-free measure that gives the better auditory impression in the long term. If, on the other hand, its current interference-free measure sample value is smaller than that of the G transmitter, its further check is terminated and the G transmitter is used.

An advantageous embodiment of the invention also results from claim 10. These measures control the frequency of the required best selection depending on the reception quality of the G transmitter in order to require as few mute times as possible for the transmitter check. If the interference-free measure sample value of the G transmitter drops below a first threshold, which corresponds to an average reception quality when the field strength sample value is above the minimum field strength value, a trigger signal is emitted after, for example, 30 s to initiate a new best selection. If, on the other hand, the interference-free measure sample value drops below a second threshold, which corresponds to poor reception quality, a trigger signal is output after only 5 s. If the interference-free measure sample value of the G transmitter drops below a third threshold, which corresponds to a very poor reception quality, the trigger signal is output after 0.5 s. In all cases, the output of further trigger signals is repeated in this time grid, unless an A transmitter with better reception quality has not been switched in the meantime. In the latter case of very poor reception quality, the trigger signal repetition is limited to seven times because of the mute times which can be noticed over a longer time interval and a switching rhythm of 0.5 s. If no alternative transmitter with better reception quality is found afterwards and switched to audible, the system switches to a test cycle of 5 s.

An advantageous embodiment of the invention results from claim 11. This measure ensures that a check process of the available A transmitters for better reception quality is triggered in any case if the field strength is insufficient.

An advantageous development of the invention results from claim 12. This measure accelerates the checking mode, since the A transmitters are selected according to the probability of a better reception quality. The greater the field strength of an A transmitter, the more likely it is that it has good reception quality.

An advantageous embodiment of the invention results from claim 14. Through this A-transmitter update, in the event of poor reception quality of all A-transmitters, those new A-transmitters are automatically determined which can now be received due to the change of location of the radio and which may have better reception quality. Since this identification of new A transmitters requires a check of the entire main memory and the tuning of possible A transmitters, the loudspeaker must be muted for a long time (range of seconds).

An advantageous embodiment of the invention results from claim 15. This measure means that an update and thus a muting is not unnecessarily carried out, ie with little chance of success; because the more A transmitters have already been determined, the less likely it is that there will be more A transmitters and vice versa.

An advantageous embodiment of the invention also results from claim 16. In this way, an update circuit is not only implemented in a simple manner, but also the field strength and the interference-free measure are taken into account in the frequency of the update. If both are very good, there is no need to update. The down counter is not decremented. Is the field strength e.g. continuously very small, so by continuously decrementing the down counter an update takes place very early. Since the field strength at a location is usually the same for all transmitters, it is advisable to only start the update attempt when the field strength increases again. The waiting time is limited in time, for example to 3 minutes, and then an update is started even when the field strength is very small.

The invention is described below with reference to an embodiment shown in the drawing. The drawing shows a block diagram of an FM receiver designed as a car radio.

The FM receiver has a receiving part 10, which in a known manner comprises an FM tuning part or tuner 11 with a transmitter setting device 12 for station search or station preselection, an FM demodulator 13 and a low-frequency amplifier 14. 15 denotes the antenna and 16 the loudspeaker. Between the FM demodulator 13 and the low-frequency amplifier 14, a mute circuit 17 is also switched on here, by means of which the transmitter tuned in the tuner 11 can be audibly or muted. A control panel 18 is connected to the transmitter setting device 12, by means of which the desired program of a desired broadcaster can be preselected or a search of the transmitter setting device 12 can be triggered by pressing the SA button for the automatic search function.

In the VHF receiver there is also a known transmitter identification device 19 which identifies a station set by means of a search or by key selection according to the broadcaster, program, transmission frequency, station location and station range. For this purpose, the transmitter identification device 19 accesses a main memory 20, in which all transmitters receivable within the possible radius of action of the VHF receiver are stored with their transmission frequencies, transmitter locations, broadcast programs, their associated broadcasters and with their transmitter ranges. A possible structure of the transmitter identification device 19 is described in DE-A-2850733. In addition to the functions specified there, the transmitter identification device 19 determines so-called alternative transmitters for a received and identified transmitter - hereinafter referred to as A transmitters for short - ie receivable transmitters which emit the same program from the same broadcaster as the received transmitter. These A transmitters are stored in an alternative transmitter memory, which is combined with the main memory 20. For this purpose, only the marks identifying the A transmitters are expediently set in the main memory. A possible expansion of the transmitter identification device 19 to achieve this mode of operation is described in DE-A-32 14 155. After identification of a transmitter tuned in the tuner 11, all transmitters receivable at the current location of the FM receiver are available with the same transmission program as the received transmitter for selection in the main memory 20 or in the alternative transmitter memory integrated in this. The transmitter identification device 19 and its interaction with the control panel 18 and the transmitter setting device 12 is controlled by a control device 21, which carries out further control functions described below.

The VHF receiver also has a test device 22, which checks the reception quality of the currently audible transmitter - hereinafter referred to as G transmitter for short - and which the A transmitter tests and specifies the transmitter with the better reception quality of the control device 21, which then transmits the transmitter setting device 12 effects the setting of the best transmitter. In this test device 22, the reception quality check is carried out according to two criteria: on the one hand by checking and comparing the reception field strengths and on the other hand by checking and comparing a so-called interference-free measure that takes interference in reception into account. To determine the interference-free measure of a transmitter, an S-circuit 23 is connected to the demodulator 13, at the output of which an output voltage proportional to the interference-free measure can be removed. The letter S of the S circuit 23 stands for interference-free measure in the following. The structure and mode of operation of the S circuit is described in DE-A-31 26 224. In the S-circuit 23, interference in reception, such as that caused, for example, by multipath reception or by the so-called picket effect, is detected. The measure of freedom from interference S is inversely proportional to the frequency and size of the disturbances that occur.

The received field strength F and the interference-free measure S of the G transmitter are taken as analog sample values ​​by means of a sample and hold circuit 24 or 25 from the tuner 11 or from the output of the S circuit 23. After analog / digital conversion in the A / D converters 26, 27 there are digital F or. S-samples are available that form the current F or S values ​​of the G transmitter. The reception field strength F and the interference-free measure S of the A transmitters are again reduced by the sample and hold circuits 24, 25 in extremely short mute times of 20 ms. In these short mute times, the G transmitter is switched off by the mute circuit 17 and the tuner 11 is tuned to a predetermined A transmitter. The analog F- or from the sample and hold circuits 24, 25 After conversion in the A / D converters 26, 27, S sampled values ​​form the digital current F and S values ​​of the A transmitter. The scanning sequence of the sample and hold circuits 24, 25 and the activation of the mute circuit 17 are controlled by the control device 21.

For each individual transmitter, that is to say for the G transmitter and for each of the available A transmitters, the F values ​​on the one hand and the S values ​​on the other hand are subjected to averaging in a computing circuit 28 or 29. The arithmetic circuit 28 or 29 calculates with the nth sample value A._n the mean <o ostyle="single">A</o>_n according to the following equation:<maths id="math0001" num=""><math display="inline"><mrow><msub><mrow><mover accent="true"><mrow><mtext>A</mtext></mrow><mo>¯</mo></mover></mrow><mrow><mtext>n</mtext></mrow></msub><mtext> = </mtext><msub><mrow><mover accent="true"><mrow><mtext>A</mtext></mrow><mo>¯</mo></mover></mrow><mrow><mtext>n-1</mtext></mrow></msub><msub><mrow><mtext> K + (1 - k) A</mtext></mrow><mrow><mtext>n</mtext></mrow></msub></mrow></math><img file="EP0211366B1_D0001.tif" /></maths>

A stands for the respective F or S value. <maths id="math0002" num=""><math display="inline"><mrow><mover accent="true"><mrow><mtext>A</mtext></mrow><mo>¯</mo></mover></mrow></math><img file="EP0211366B1_D0002.tif" /></maths>_n-1 is the mean value formed from n-1 samples. The linking factor k is set according to the relevance of the F or S value between the end values ​​"0" and "1" which is used for the averaging. At compared to the mean<o ostyle="single">A</o>_n-1 larger sample value A_n the factor becomes "1" and compared to the mean <o ostyle="single">A</o>_n-1 smaller value A_n the factor is shifted to "0". In addition, the factor for the first sample value A 1 to be taken into account when averaging is close to "0", since this first sample value A 1 is of great relevance. This setting of the linkage factor k can be carried out, for example, by a difference former 30 or 31, which determines the current sample value A_n and the mean <o ostyle="single">A</o>_n-1 compares and gives a value corresponding to the size of the difference to the computing circuit 28 or 29. The averages<o ostyle="single">F</o> or. <o ostyle="single">S</o> are for each transmitter in one <o ostyle="single">F</o>Memory 32 and one <o ostyle="single">S</o>- Memory 33 stored at the same address. This address corresponds in each case to the address at which the G transmitter or the individual A transmitters can be called up in the main memory 20.

The current F and S values ​​and the mean values <o ostyle="single">F</o> and <o ostyle="single">S</o> of the G transmitter and a selected A transmitter are now compared in a comparison circuit 34 according to certain comparison criteria and the transmitter with the best reception quality (best selection) of the control device 21 is specified. In this case, only the reception field strength F is taken into account if the current, ie the just sampled and digitized F value of the A transmitter is below a predetermined field strength minimum value F_min , and only the interference-free measure S is taken into account if the current F value of the A transmitter is above the minimum field strength value F_min lies.

The comparison circuit 34 has a large number of comparators and a test logic 35, which is expediently part of the control device 21. A first comparator 36 is successively supplied with the current F values ​​from the G transmitter and an A transmitter to be compared via a switch 39 controlled by the test logic 35, for which purpose the two F values ​​are temporarily stored in a 2-bit shift register 37. The comparator 36 compares the two F values ​​in succession with a minimum field strength value F_min. The two F values ​​are compared with one another in a second comparator 38. In a third comparator 40, the<o ostyle="single">F</o>-Values ​​of the G transmitter and the A transmitter compared, for which the from <o ostyle="single">F</o>Memory 32 read out successively <o ostyle="single">F</o>-Value the comparator 40 once directly (<o ostyle="single">F</o>Value of the A transmitter) and once via a 1-bit shift register 41 (<o ostyle="single">F</o>Value of the G transmitter). The outputs of the three comparators 36, 38 and 40 are connected to the test logic 35.

In a fourth comparator 42, the current S values ​​from the G transmitter and the A transmitter are compared with one another, for which purpose they are temporarily stored in a 2-bit shift register 43. The mean values ​​are compared in a fifth comparator 44<o ostyle="single">S</o> A transmitter and G transmitter compared. This too<o ostyle="single">S</o>-Values ​​are addressed by addressing the <o ostyle="single">S</o>Memory 33 successively read out from this, the <o ostyle="single">S</o>Value of the G transmitter is temporarily stored in a 1-bit shift register 45. The outputs of the two comparators 42 and 44 are also connected to the test logic 35.

The comparison which takes place in the comparators 36, 38, 40, 42, 44 to determine the best transmitter is carried out by the test logic 35 in the following manner: First, the current F value of the A transmitter is compared with the field strength minimum value F_min compared. If this is below the predefined threshold, then the switch 39 compares the F value of the G transmitter with the field strength minimum value. If this is greater than the predetermined threshold, the test logic 35 of the control device 21 specifies the G transmitter as the best transmitter. If the F value of the G transmitter is also below this threshold F_min, the second comparator 38 is activated and the two F values ​​of the A transmitter and the G transmitter are compared. If the F value of the G transmitter is greater than the F value of the A transmitter, the test logic 35 of the control device 21 specifies the G transmitter as the best transmitter. If the F value of the A transmitter is greater than that of the G transmitter, the third comparator 40 is activated, which compares the field strength averages of the two transmitters with one another and the transmitter with the largest<o ostyle="single">F</o>-Value identifies as the best sender. This is communicated to the control device 21 by the test logic 35.

If the comparison in the comparator 36 reveals that the F value of the A transmitter is greater than the predetermined field strength minimum value, the fourth comparator 42 is activated, which compares the current S values ​​of the G and A transmitters with one another. If the S value of the A transmitter is smaller than that of the G transmitter, the test logic reports the G transmitter as the best transmitter to the control device 21. If the S value of the A transmitter is greater than that of the G transmitter, the test logic 35 activates the fifth comparator 44, which is now the mean value <o ostyle="single">S</o> compares the two transmitters with each other and the transmitter with the larger one <o ostyle="single">S</o>Value of the test logic 35 as the best transmitter, which in turn communicates this to the control device 21.

In order to initiate the above-described test process of an alternative transmitter, which comprises the comparison process described above on the one hand and the determination of the values ​​required for the comparison on the other hand, the test device 22 has a test start circuit 46 which has a time-delayed trigger signal for reading an A transmitter from the main memory 20 and tuning the read A transmitter in the tuner 11 outputs. The time delay of the output of the trigger signal can be set depending on the size of the current S value of the G transmitter, here in steps. If the S value is below an upper threshold S_Max, but in their vicinity, a trigger signal is issued every 30 s. If the S value is close to a lower threshold S_min, a trigger signal is output after 5 s. If the S value is below the lower threshold S_min, a trigger signal is already given to the control device 21 after 0.5 s. Such a test start circuit 46 can be formed, for example, by a presettable down counter 47, the presetting of which is carried out by a comparison circuit 48 which has a plurality of threshold value stages and is assigned the current S value in each case. The down counter 47 is decremented at a predetermined clock frequency and, when reaching its zero position, it issues a trigger signal to the control device 21.

A comparison unit 49 is also connected to the test start circuit 46, in which the current F value of the G transmitter with the field strength minimum value F_min is compared. If this is below this minimum value F_min, the test start circuit 46 is activated, which in turn sends a trigger signal to the control device 21. This can in turn be brought about by the comparison unit 49 immediately setting the down counter 47 to zero.

The mode of operation of the radio as described above is summarized below using an example: By pressing the button SA in the control panel 18, a station search is carried out in the transmitter setting device 12 when the loudspeaker 16 is muted. The transmitter found first is identified on the basis of its transmission frequency in the transmitter identification device 19 and all A transmitters for this identified transmitter are marked in the main memory 20. Then the muting 17 is deactivated and the set transmitter can be heard as a G transmitter. Through the sample and hold circuits 24, 25, the reception field strength F and the interference-free measure S are continuously sampled, digitized, the mean values ​​formed and the mean values ​​at the address at which the G transmitter can be called up in the main memory 20 in the G transmitter Average value memories 32 and 33 are written. As long as the current F value of the G transmitter is above the minimum field strength value F_min lies (comparison unit 49) and the current S value of the G transmitter is not below the predetermined upper threshold S._Max decreases (comparison circuit 48) only this continuous check of the G transmitter is carried out.

The reception quality of the G transmitter now deteriorates in such a way that the current S value is slightly below the upper threshold S._Max decreases, after a time delay of 30 s the test start circuit 46 sends a trigger signal to the control device 21. This searches the main memory 20 for an alternative transmitter, in the order of the falling reception field strength, activates the muting 17 for 20 ms and causes the transmitter setting device 12 to tune the tuner 11 to the new transmission frequency of the A transmitter. From the sample and hold circuits 24, 25, the received field strength F and the interference-free measure S of the A transmitter provided are sampled, the sample value is digitized and the mean values ​​are formed which are available at the same address in which the A transmitter can be called in the main memory 20 , are stored in the two mean value memories 32, 33. The test logic 35 of the comparison circuit 34 now carries out the comparison of the F-, S-,<o ostyle="single">F</o>- and <o ostyle="single">S</o>Values ​​of the A transmitter and the G transmitter. If the G transmitter is recognized as the best transmitter, then the control device 21 causes the transmitter setting device 12 to tune the tuner 11 to the transmission frequency of the G transmitter. The activation of the muting 17 is canceled. This process, carried out in a silent phase of 20 ms, is not perceived by the listener. He will still hear the G transmitter during this process.

After a further 30 s - or when the S value of the G transmitter has now reached the lower threshold S_min has already deteriorated after 5 s - the test start circuit 46 sends a new trigger signal to the control device 21. This activates the muting 17 and calls up the transmission frequency of a new A transmitter from the main memory 20 and causes the transmitter setting device 12 to tuner 11 to tune to this transmission frequency. Again, the reception field strength F and the interference-free measure S of the new A transmitter are sampled, the samples are digitized, the mean values ​​are formed and the mean values ​​at the next address, under which the new A transmitter can also be called up in the main memory 20, in the mean value memories 32.33 filed. The described comparison process is carried out again. As long as the G transmitter is output as the best transmitter, the test mode described is repeated with another A transmitter. However, if the checked A transmitter is identified as the best transmitter, then the control device 21 only cancels the activation of the muting 17 and the A transmitter tuned in the tuner 11 is switched audibly. It now forms the new G transmitter.

If the reception quality of the G transmitter and all available A transmitters is continuously poor, which means that either the F value of all transmitters is below the minimum field strength value F_min lies or the <o ostyle="single">S</o>-Value of all transmitters continuously below a specified minimum value <o ostyle="single">S</o>_min of the mean value of the interference-free measure or both occurs, the A transmitters are updated, ie an attempt is made to identify alternative transmitters that can be received at the current new receiving location of the radio and to insert them into the table of the A transmitters. For this purpose, an A transmitter update circuit 50 is provided, which generates a start signal which triggers a renewed determination of A transmitters by the transmitter identification device 19 when the F value and the <o ostyle="single">S</o>-Value of the G transmitter continuously below the respective minimum value F_min or. <o ostyle="single">S</o>_min lies. The frequency of the start signal generation is inversely dependent on the number of A transmitters in the table, that is to say on the number of A transmitters marked in the main memory 20.

Such an update circuit 50 can be implemented by a presettable down counter 51 in conjunction with two comparators 52 and 53. The F comparator 52 compares the current F value with the predetermined field strength minimum value F_min and the <o ostyle="single">S</o>-Comparator 53 compares the mean <o ostyle="single">S</o> of the G transmitter with the specified minimum interference level <o ostyle="single">S</o>_min. The outputs of the two comparators 52, 53 are connected to the counting input of the down counter 51. Via the control device 21, the down counter 51 is preset to a number which is inversely proportional to the number of A transmitters marked in the main memory 20. With each output signal from the comparators 52, 53, the down counter 51 is now decremented until it gives a start signal to the control device 21 when the counter reading is zero. In response to this start signal, the control device 21 activates the muting device 17 and the transmitter identification device 19. The latter identifies a new table of the A transmitters received at the current location of the radio or supplements the existing A transmitter table with newly added A transmitters. The muting is activated for a longer time (seconds).

The invention is not restricted to the exemplary embodiment described above. The control device 21, the transmitter identification device 19 and the test circuit 22 with the comparison circuit 34 and the test start circuit 46 and the alternative update circuit 50 are expediently implemented by a microprocessor.