Abstract:
There is disclosed an antenna diversity system for relatively broadband broadcast reception in vehicles such as motor vehicles. The device can include a diversity processor having numerous components including a microprocessor for controlling a signal selection switch. In alternative embodiments the processor can be incorporated into a receiver or into a multi-antenna system. One advantage of these designs is that it is able to exist with one reception tuner and being able to select one signal from a plurality of antenna signals A 1 , A 2 , . . . AN, with great probability, whose signal components lie above the level necessary for interference-free reception, over the entire channel bandwidth B.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application hereby claims priority from German Application DE 10 2007 032 048.7 filed on Jul. 10, 2007, the disclosure of which is hereby incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    At least one embodiment of the invention relates to an antenna diversity system for relatively broadband broadcast reception in vehicles such as motor vehicles. The term Broad band such as mobile broadband can be used to describe various types of wireless high-speed internet access through a portable modem, telephone or other device. Examples of different broadband network standards that may be used, include EV-DO, WiMAX, UMTS/HSPA, or some portable satellite-based systems. 
         [0003]    In this case, multi-path propagation leads to narrowing of the bandwidth of the channel from the transmitter antenna to the mobile receiver if the path differences of the electromagnetic wave bundles that arrive at the reception location are not small enough to be ignored. Therefore, there is a dependence in frequency at a reception location that is similar to the one observed at a fixed frequency over the driving path. This dependence is illustrated in  FIG. 2   a , in a wave field with Rayleigh distribution, in a two-dimensional representation. 
         [0004]    Particularly in the case of relatively broadband broadcast reception, whose channel width is greater than the bandwidth of the transmission channel as a result of multi-path reception, this phenomenon leads to interference that is known from television reception in vehicles.  FIG. 2   c  shows the level distribution at a location, plotted above the frequency, and shows that a reception minimum exists at a frequency deviation of about 5.5 MHz from the video carrier, for example. In the case of a diversity system according to the scanning method, an antenna that is selected for good reception of the video carrier therefore cannot receive the audio carrier equally well. For this reason, the signals of a multi-antenna system are separated, in the European patent EP 0521 123 B1 which is also published in corresponding U.S. Pat. No. 5,313,660, to Lindenmeier et al which issued on May 17, 1994 the disclosure of which is hereby incorporated herein by reference in its entirety. This patent disclosure shows the signals of the multi-antenna system are separated by means of separate use of a diversity system for video and audio reception, in each instance. 
         [0005]    Nevertheless, the disadvantage remains that the video signal components that lie far away from the video carrier are reproduced only deficiently. In the case of digitally modulated, relatively broadband transmission methods, in particular—such as the DVBT method (Digital Video Broadcasting Terrestrial) and the DAB method (Digital Audio Broadcasting)—the loss due to non-detectable symbols at elevated bit error rates frequently has such an effect that the broadcast connection breaks off. 
         [0006]    Thus, one benefit of the invention is that it creates a particularly efficient antenna diversity system, which avoids the disadvantages connected with an overly low bandwidth of the transmission channel, to a great extent. 
       SUMMARY 
       [0007]    The particular advantage of an antenna diversity system according to one embodiment of the invention comprises in making do with only one reception tuner and being able to select one signal from a plurality of antenna signals A 1 , A 2 , . . . AN, with great probability, whose signal components lie above the level necessary for interference-free reception, over the entire channel bandwidth B. This advantage is particularly decisive for transmission according to the modern OFDM methods (orthogonal frequency division multiplexing), such as in the case of television transmissions according to the DVBT method and radio transmissions according to the DAB method. In both cases, the signals are transmitted by means of a plurality of sub-carriers disposed equidistantly in frequency and MPSK-modulated (i.e. BPSK, QPSK, 8PSK, etc.), in each instance. In this connection, modulated sub-carriers according to the QPSK method (quadrature phase shift keying) or also according to the QAM method (quadrature amplitude modulation) are primarily used. In this connection, the channel bandwidth B of a DVBT signal with approximately 6700 sub-carriers, for example, comes to approximately 7.5 MHz. The channel bandwidth B for a DAB signal with approximately 1500 sub-carriers having a distance of lkHz comes to approximately 1.5 MHz. 
         [0008]    It turns out that the assured bandwidth of the transmission channel from the transmission antenna to the mobile receiver, in the case of Rayleigh distribution, is not less than 0.6 MHz if the running path differences are not greater than 100 m. However, this bandwidth is very small as compared with the requirements for mobile digital TV reception, and also for digital radio reception. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings. It is to be understood, however, that the drawings are designed as an illustration only and not as a definition of the limits of the invention. 
           [0010]    In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
           [0011]      FIG. 1  is a schematic block diagram of one embodiment of an antenna diversity system; 
           [0012]      FIG. 2  is a representation of the reception signal levels in the case of Rayleigh multi-path reception, with running path differences, over location and frequency 
           [0013]      FIG. 3  is a Level distribution over the reception frequency channel of the antenna signals A 1  . . . A 4  over the frequency of the pilot carriers of a DVBT system at a first reception location wherein the pilot carriers of the antenna signals A 3  and A 4  are all received above the detectability threshold; 
           [0014]      FIG. 4  is a level distribution as in  FIG. 3  but at a different reception location, there, the pilot carriers of the antenna signals A 1  and A 2  are all received above the detectability threshold; 
           [0015]      FIG. 5  is an interference probability in the case of propagation profile 100 m/300 m as a function of the signal level threshold for error-free detection without and with antenna diversity with four partially correlated antennas 
           [0016]      FIG. 6  is an interference probability graph as in  FIG. 5  but with a propagation profile 200 m/600 m; 
           [0017]      FIG. 7  is an interference probability graph as in  FIG. 5  but with a propagation profile 400 m/1200 m; 
           [0018]      FIG. 8  is a schematic block diagram of another embodiment of the invention; 
           [0019]      FIG. 9  is a schematic block diagram of another embodiment of the antenna diversity system, with slightly expanded receiver; and 
           [0020]      FIG. 10  is another embodiment of an antenna diversity system similar to that as in  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Referring to the drawings,  FIG. 1  shows an antenna diversity system comprising a multi-antenna system  1 , having its output passed to a signal selection switch  2 . Signal selection switch has its output passed to an input of receiver  3 . Receiver  3  passes its output to a diversity processor  4 . In addition, there is a clock generator  15  which also has its output passed to diversity processor  4 . Diversity processor  4  comprises a frequency-interval-selective level detection circuit  5  of reception signal  17 . In this case, the output signals of circuit  5  are compared with the signal level threshold  7  in a frequency-interval-selective level evaluation circuit  6 . Circuit  6  passes its output to determination circuit  8  which determines an interference rate of reception signal  17 , from the deviations. Circuit  8  passes this rate to interference rate memory  9 . Memory  9  has address signal generation, in which an address signal is generated and sent to signal selection switch  2  to set signal selection switch  2 . 
         [0022]    Thus, with this design it is possible with great likelihood, in each instance, to select an antenna signal from a plurality of available antenna signals A 1 , A 2 , . . . AN, in terms of diversity, in such a manner that none of the received sub-carriers goes below the detectability threshold or to select that antenna signal with a minimum detect ability—errors respectively. 
         [0023]    This is achieved, in that reception signal  17  that is present in receiver  3  is passed to diversity processor  4 , at a relatively great frequency bandwidth B, preferably in the IF frequency plane, to determine the signal quality of reception signal  17 , whose frequency bandwidth B is divided up into frequency intervals Δf. An example of signal quality is explained in greater detail in U.S. Pat. No. 6,236,372 to Lindenmeier et al, which issued on May 22, 2001, the disclosure of which is hereby incorporated herein by reference in its entirety. 
         [0024]    In this connection, the frequency bandwidth of the frequency intervals Δf can be as large as necessary, but must be selected to be smaller than the expected bandwidth of the transmission channel. In this way, the levels of the frequency components of reception signal  17  are essentially constant within the frequency intervals Δf, at given reflection conditions, in each instance. A frequency-interval-selective level detection  5  is present in diversity processor  4 , which detection separately detects the components of reception signal  17  that occur in the frequency intervals, as frequency-interval-specific level values  11 . These components of reception signal  17  are separately compared with a signal level threshold  7  that is required for interference-free reception, in a frequency-interval-selective level evaluation  6 , and the interference rate  13  of broadband reception signal  17  is determined by means of evaluation of these measurements over all the frequency intervals Δf. If errors occur, a different reception signal  17 , in terms of diversity, is passed to receiver  3 , by means of a signal to signal selection switch  2 . There is then the possibility of selecting a HF signal  24  having the lowest interference rate  13  in diversity processor  4 , by means of selectively switching on all the available antenna signals. 
         [0025]    In the case of TV signals according to the DVBT method, for phase-correct detection of the sub-carriers of the system, for example 489 pilot carriers P are transmitted at a frequency distance of 16 kHz over the entire channel bandwidth. This frequency distance of Δf=16 kHz is particularly suitable for establishing the frequency intervals according to at least one embodiment of the present invention, whereby the level of each received pilot carrier P is treated as a frequency-interval-specific level value  11  according to at least one embodiment of the invention.  FIG. 3  shows the level distribution of the pilot carriers over the reception frequency channel for the antennas A 1  . . . A 4 . In this connection, a propagation profile for the received wave bundles was assumed, in such a manner that the intensity of the wave bundles decrease with running path differences that become greater. The diagram shown clearly shows, for an instantaneous reception situation at a location, that the antenna signals A 1  and A 2  lose the corresponding pilot carriers in the range 125 . . . 140 and in the range between 225 . . . 245, respectively, but that the antenna signals A 3  and A 4  receive all the pilot carriers without interference. In this way, the sub-carriers, which are situated in the frequency between the pilot carriers, are also received without interference. At a different location, the instantaneous record in  FIG. 4  shows a strong frequency dependence of the antenna signal A 4 , with a loss of the pilot carriers in the range between 180 and 200, and also strong frequency dependencies of the antenna signal A 3 , while both the antenna signal A 2 , which previously had interference, and the antenna signal A 1  receive all the pilot carriers without interference. For quantification of the reduction in interference probability brought about with the antenna diversity system, the bit error rates are shown in  FIGS. 5 to 7  over the required signal level threshold, in dB, for error-free detection of the sub-carriers. The upper curve shows the bit error rate p e  during operation without antenna diversity, in each instance; the lower curve (p d ) with antenna diversity, in each instance. Different propagation profiles are assumed in the figures, whereby the first length indication describes the running path difference after which the wave bundles have decreased to 1/e-multiple in intensity, and the second length indication means that wave bundles having a greater running path difference than this value are not relevant. The diversity efficiency is only slightly dependent on the propagation profile, and shows a good value of n=2.1, particularly for the case of 100 m/300 m that frequently occurs in urban areas, and taking into consideration the partial correlation of the antenna signals A 1  . . . A 4 . The relationship between the interference probability p e  without antenna diversity and the interference probability p d  with antenna diversity is: 
         [0000]      P d =(p e ) n    
         [0000]    In a manner analogous to this, in the case of reception of DAB radio signals, the frequency intervals Δf are formed by the plurality of sub-carriers, and the frequency-interval-specific level values  11  of the frequency intervals Δf=approximately 1 kHz defined in this manner are detected by means of the level values of the sub-carriers. 
         [0026]    A particular advantage of an antenna diversity system according to at least one embodiment of the invention results from the fact that the diversity efficiency can be further increased, in extremely cost-advantageous manner, by means of formation of linear combinations of the reception signals of the antennas. In this connection, means for phase rotation and amplitude configuration can advantageously be used. 
         [0027]    In another advantageous embodiment, the output signals of the frequency-interval-selective level evaluation  6  can be configured as binary signals, and passed to the interference rate determination of the reception signal  17 . There, the number of sub-carriers with interference in the case of digital modulation can be determined, for example, in the simplest embodiment. From this, the interference rate  13  of the reception signal  17  can therefore be indicated directly by means of evaluation of the binary signals. 
         [0028]    The determination of the interference rate  13  in combination with updating of an advantageously switched-through reception signal  17  can take place, in steps that follow one another closely in time, whereby the time intervals must be selected to be short enough so that the driving path traveled within such an interval does not exceed the length λ/10, if at all possible. The steps that follow one another within a short time are repeatedly initiated, in simple manner, by means of a clock generator  15 , by means of the cycle signal  16  of which the determination of the interference rate  13  repeatedly takes place. In order to prevent the cycle signal  16  from occurring during the symbol duration, it is advantageous, to derive the cycle signal  16  from the symbol cycle of the OFDM signal. The DVBT symbol duration, including the guard interval, amounts to approximately 1 ms, depending on the design of the system, for example in 8k mode. It is particularly advantageous, to set up switchover of the antenna signal during the guard interval. 
         [0029]    With the goal of establishing a ranking list with regard to the reception quality of the reception signals  17 , an interference rate memory with address signal generation  9  is present in the diversity processor  4 , in an advantageous embodiment of the invention. The interference rate  13  is stored in it, in each instance, and the current interference rate  13 , in each instance, is compared with the interference rates  13  that preceded it in time. The most advantageous antenna signal  17  indicated in the ranking list is passed to the signal selection switch  2  using a correspondingly generated address signal  14 , so that of the available reception signals  17 , i.e. of the corresponding reception signals  17   a  in the IF plane, the one having the smallest interference  13  is switched through. 
         [0030]    One embodiment of the present invention can be used in particularly advantageous manner for the reception of DVBT-modulated signals. For reliable transmission of such a signal, every tenth sub-carrier, for example, is configured as a pilot carrier, whose phase provides the reference phase for phase detection of the sub-carriers that are adjacent in terms of frequency. The frequency distance between two pilot carriers therefore amounts to approximately 10 kHz, and is small enough to make it possible to consider the transmission channel as being constant over this small frequency bandwidth. The sub-carriers that are situated between the pilot carriers in terms of frequency, whose phase contain the data to be transmitted in the case of QPSK modulation—i.e. also in combination with their amplitude in the case of QAM modulation—can be correctly detected, in this connection, even in a reception field in which interference is caused by multi-path propagation, as long as the pilot carriers are received at a sufficiently great level. A processor for evaluation of these signals is present in every DVBT receiver, which processor can be configured, in advantageous manner, to produce a diversity processor  4  according to at least one embodiment of the present invention, by making some additions that are not very complicated. In this connection, the frequency intervals Δf are formed by the plurality of the pilot carriers disposed at the frequency interval Δf, and the frequency-interval-specific level values  11  of the frequency intervals Δf are determined by means of the level values of the pilot carriers P. The I and Q components are present for evaluating the phase of the pilot carriers P; for example, the amplitude values of the pilot carriers are determined from them, and used to assess the interference rate  13 , according to at least one embodiment of the invention. 
         [0031]    The amplitude value of a pilot carrier that is determined at reception can be put into relation, in simple manner, with the minimum value that is required for error-free detection of the signal content of the sub-carriers positioned between two pilot carriers, in each instance, in the frequency interval Δf of 10 kHz frequency bandwidth, for example. The interference rate  13  determined for the pilot carriers therefore corresponds to the interference rate of the entire digital reception signal in the reception channel B. 
         [0032]    The digital evaluation of the amplitudes of the pilot carriers is, of course, connected with a waiting time (latency), which generally increases with the number of pilot carriers to be detected. In the interests of the least possible circuitry expenditure in connection with the smallest possible waiting time, it is therefore advantageous to select the bandwidth of the frequency intervals Δf to be greater—for example 50 kHz—and to use the amplitude of only every fifth pilot carrier, for example, as the frequency-interval-specific level value  11  to determine the interference rate  13  of the reception signal  17 . 
         [0033]    In  FIG. 8 , diversity processor  4  shown in  FIG. 1  is divided up, in terms of its functions, into an expanded receiver  39  and multi-antenna system  1 , which are connected with one another by way of high-frequency line  10 . This embodiment evaluates the pilot amplitudes P in a pilot amplitude detection unit  20  and determines the reception power in the reception channel B by means of evaluation of an IF signal  36  for formation of the ranking list. This device is for current selection of one of the reception signals of the antennas A 1  . . . AN (with HF amplifier  23  connected, if necessary), by means of microcontroller  21 , in which a coded address signal  14   a  for turning on an address signal generator  22  is generated. These signals are to be passed on by way of high-frequency line  10 , and for setting signal selection switch  2 , using address signal  14 . 
         [0034]    Receiver  3  for the OFDM broadcasting systems described above, is generally configured as a superimposition receiver with oscillator signal  27  (See  FIG. 9 ) and IF signal  36 , in its basic structure without diversity function, and contains switching units for passing the pilot carriers P on to the pilot amplitude detection unit  20  in  FIG. 8 . The determination of the interference rate  13  of reception signal  17  takes place in microcontroller  21 , with the interference rate determination component  8  contained in it, by means of comparing the pilot amplitudes with a signal level threshold  7 . In an expansion of the diversity function described in connection with  FIG. 1 , in the arrangement in  FIG. 8 , the signal power within the reception channel B is determined as rough, but very quickly available early data concerning the quality of the antenna signal A 1  . . . AN that is currently applied. On the basis of the early data obtained in this manner, the ranking list can be effectively supplemented, in advantageous manner, whereby an antenna signal A 1  . . . AN can already be eliminated from the selection, for example, before the determination of the interference rate  13 —which is connected with the waiting time that was described, but provides more information—has taken place using the pilot amplitude detection unit  20 . Obtaining these early data can take place, for example, in advantageously simple manner, by means of evaluating the IF signal  36  of the receiver  3 , using IF broadband band-pass filter  18   a  with subsequent level detector  19 , whose HF-channel-specific level value  11   a , available at the output, is used accordingly in microcontroller  21 , to form the coded address signal  14   a . Address signal  14   a  is passed to multi-antenna system  1  by way of high-frequency line  10 , and an address signal generator  22  generates the address signal  14  to turn on signal selection switch  2  in this system. 
         [0035]      FIG. 9  shows receiver  39  and a set-off multi-antenna system  1  having a signal pre-selection switch  2   a  for cycled determination, which takes place parallel in time to the reception, of a reception-worthy HF signal  24 , controlled by microcontroller  21 . In this case, the interference rate  13  is determined on the basis of the oscillator signal provided by receiver  39 , and the address signal  14  is generated, with which signal the selection of the reception signal  24  takes place, using the cycle signal  16 , which is also available in microcontroller  21 , correctly in terms of time. In addition, the signal power in the reception channel B is determined as an HF-channel-specific level value  11   a , for the purpose of advance information concerning the signal quality of the HF signal  24  in question, by way of the IF broadband band-pass filter  18   a.    
         [0036]    In the antenna diversity system in  FIG. 9 , the majority of the diversity functions are accommodated in a separate unit in the multi-antenna system  1 , in advantageous manner. This results in the possibility of expanding a receiver  3  that functions according to the basic principle of broadcast reception, with little effort, so that the reception system can optionally be equipped with the diversity function. In the expanded receiver  39 , only selection devices  30 ,  29 ,  31 , are present for this purpose, by way of which the oscillator signal  27 , in the form of the oscillator signal of twice the frequency  28 , and the cycle signal  16 , are passed to the multi-antenna system  1  by way of the high-frequency line  10 . There, the address signal  14  for selecting the antenna signal is generated by means of turning on the signal selection switch  2  by a microcontroller  21 , in such a manner that a signal pre-selection switch  2   a , also controlled by the microcontroller  21 . Signal pre-selection switch  2   a  receives antenna signals A 1 , A 2 , . . . AN which are passed on to the input side of signal pre-selection switch  2   a . These antenna signals A 1 , A 2 , . . . AN are alternately passed to an IF narrowband band-pass  18   b  having the bandwidth of a frequency interval Δf, by way of a frequency converter  34   b -which, for frequency conversion, is turned on by a frequency interval selection signal  35  for step-by-step detection of the bandwidth of the reception channel B, controlled by microcontroller  21 , offset relative to the oscillator signal  27 , in terms of frequency, in steps of a multiple of the frequency interval Δf. At the output of the IF narrowband band-pass  18   b , a frequency-interval-specific level value  11  of the antenna signal in question is present in the microcontroller  21 , in each instance, from which the current address signal  14  and the ranking list are formed. The cycle signal  16  of the digitally modulated HF signals  24  are also passed to the microcontroller  21 , so that change-over of signal selection switch  2  can take place at the proper time. This arrangement is connected with the advantage that during reception, it is possible to determine the frequency-interval-specific level values  11  and the interference rate  13  that results from them, as well as the early data concerning the signal quality, with little delay, using fast testing processes of the antenna signals A 1  . . . AN, which are carried out parallel in terms of time, and control of signal selection switch  2  can take place with great accuracy, with regard to the most advantageous available HF signal  24 . 
         [0037]    In an exemplary embodiment of such a system, the oscillator signal  27  is passed to multi-antenna system  1  by way of a frequency doubler  25 , an oscillator frequency high-pass  29 , and by way of high-frequency line  10 , and in the system, it is passed to a frequency converter  34   a  for superimposition with the VCO signal  37  by way of frequency divider  26 , in the original frequency position. The microcontroller  21  controls the voltage-controlled oscillator  33  with reference oscillator  32  step by step, in such a manner that the superimposition with the oscillator signal  27  in the frequency converter  34   a  results in the frequency interval selection signal  35 , which—again superimposed with the antenna signal at the output of the signal pre-selection switch  2   a  in the frequency converter  34   b -yields the frequency-interval-specific IF signal  36 . At the output of the IF narrowband band-pass  18   b , the frequency-interval-specific level values  11  can be determined by the microcontroller  21 , in each instance. The greater the bandwidth of the frequency interval Δf is selected to be, the faster the frequency-interval-specific level values  11  can be determined, and the diversity system can be used at an all the greater driving speed and smaller wavelength of the HF reception signals. On the other hand, the criterion for the selection of an advantageous antenna signal A 1  . . . AN, derived from the frequency-level-specific level values  11 , becomes less accurate with an increasing bandwidth of the frequency intervals Δf. In practice, it has been shown that the bandwidth of the IF narrowband band-pass  18   b  should therefore not be selected to be greater than 1.5 MHz for a DVBT system. For the diversity system described in connection with  FIG. 8 , with pilot amplitude detection  20 , this accordingly means that the frequency distance between the pilot carriers whose amplitudes are used for determining the frequency-interval-specific level values  11  should not be greater than 1.5 MHz. 
         [0038]    To obtain the early data concerning the signal quality of an antenna signal A 1 , A 2 , . . . AN, as described above, the frequency-interval-specific IF signal  36  is passed to an IF broadband band-pass  18   a  having the frequency bandwidth of the reception channel B. In order to determine the signal power in the reception channel B, the frequency interval selection signal  35  is adjusted to the frequency of the oscillator signal  27 , over the duration of the measurement process, so that the HF-channel-specific level value  11   a  is present at the output of the IF broadband band-pass  18   a , for an evaluation in the microcontroller  21 . 
         [0039]    The antenna diversity system in  FIG. 10  functions in a manner similar to the system in  FIG. 9 , but is advantageously simplified in that the frequency of the oscillator signal  27  is passed to the microcontroller  21  in the receiver  3 , as a digitally coded oscillator frequency signal  38 , by way of the high-frequency line  10 . Signal  38  is for controlling the digitally controllable voltage-controlled oscillator  33  that generates the corresponding frequency interval selection signal  35 , in each instance, and which is controlled by the microcontroller  21 . 
         [0040]    Accordingly while only a few embodiments of the present invention have been shown and described, it is obvious that many changes and modifications may be made thereunto without departing from the spirit and scope of the invention. 
       List of Reference Symbols 
       [0000]    
       
         Multi-antenna system  1   
         Signal selection switch  2   
         Signal pre-selection switch  2   a    
         Receiver  3   
         Diversity processor  4   
         Frequency-interval-selective level detection component  5   
         Frequency-interval-selective level evaluation component  6   
         Signal level threshold  7   
         Interference rate determination  8  of the reception signal  17   
         Interference rate memory with address signal generation  9   
         High-frequency line  10   
         Frequency-interval-specific level values  11   
         HF-channel-specific level value  11   a    
         Interference rate  13  of the reception signal  17   
         Address signal  14   
         Coded address signal  14   a    
         Pre-selection address signal  14   b    
         Clock generator  15   
         Cycle signal  16   
         Reception signal  17 ,  17   a    
         IF broadband band-pass filter  18   a    
         IF narrowband band-pass filter  18   b    
         Level detector  19   
         Pilot amplitude detection  20   
         Microcontroller  21   
         Address signal generator  22   
         HF amplifier  23   
         HF signal  24   
         Frequency doubler  25   
         Frequency divider  26   
         Oscillator signal  27   
         Oscillator signal having twice the frequency  28   
         Oscillator frequency high-pass  29   
         Cycle frequency low-pass  30   
         HF band-pass filter  31   
         Reference oscillator  32   
         Voltage-controlled oscillator  33   
         Frequency converter  34   a    
         Frequency converter  34   b    
         Frequency interval selection signal  35   
         Frequency-interval-specific IF signal  36   
         VCO signal  37   
         Coded oscillator frequency signal  38   
         Expanded receiver  39   
         Antenna signals A 1 , A 2 , . . . A N    
         Bandwidth of the reception channel B 
         Frequency interval Δf 
         Pilot carrier P