EP0874483A2 - Method and apparatus for simultaneous transmission of analog and digital broadcast programmes on AM frequency bands - Google Patents

Abstract

The simultaneous transmission method involves using a carrier for the analogue modulation and a frequency-offset auxiliary carrier for the digital modulation. The analogue modulation is provided by a double sideband modulation. The AM transmitter (1) may be supplied with a carrier which is modulated by a sum signal. The sum signal is obtained by summation of the analogue signal to be transmitted and the digitally modulated signal.

Description

The invention relates to a method and an arrangement for an analog-digital simultaneous transmission of radio broadcasts in the AM frequency bands, especially in the Application for long, medium and short wave broadcasting, according to the generic terms of claims 1 and 5.

The well-known transmission of radio broadcasts in the frequency ranges of long, Medium and short waves using amplitude modulation (AM) have a low transmission quality on. This lack leads to a decreasing acceptance on the part of the Broadcast listeners, because with other available modulation methods the broadcast transmission done with better quality. To the quality of the broadcast for transmission to improve radio broadcasts in the aforementioned AM frequency bands, it has been proposed to carry out the transmission by means of digital modulation (DE-A1-19535030).

For a changeover from AM modulation to digital modulation is for the transition period to be expected that initially only relatively few radio receivers on the market that can be used to receive digital modulation. Because of this expected low number of recipients, a transmission of Broadcasts using digital modulation based on the number of listeners very much be elaborate. This high effort will introduce the new transmission method hinder because on the one hand the program providers themselves because of the high effort per listener will shy away from sending out a sufficient number of programs, on the other hand, because of the initially low demand for receivers for digital Modulation due to the small number of radio programs that manufacturers of Radio receivers are hesitant to start producing receivers.

The system "Skywave 2000" from Thomcast is a simultaneous transmission analog single sideband modulation and digital modulation in a shortwave channel have been presented ("worldwide listening", 4/97, pages 6 to 8), the digital Transmission is offset in frequency such that the two transmissions are frequency selective can be received. The principle of simultaneous transmission of analog and digital modulation offers an approach to overcoming the above Difficulty launching digital AM broadcasting. A disadvantage of that the aforementioned system is the single sideband transmission of the analog modulation, since this with standard AM receivers can only receive distorted and of it It can be assumed that there will be no nationwide coverage of the audience with single-sideband receivers is given or can be reached in the future.

Furthermore, for the simultaneous transmission of an analog single-sideband signal and one digital additional transmission a single-sideband transmitter is necessary. The one for broadcasts used high-performance transmitter, which is suitable for single sideband operation are characterized in that the envelope of the single sideband signal by means of a Amplifier is amplified and this amplified envelope signal for envelope modulation the phase-modulated high frequency amplified by means of high-frequency amplifiers is used in the power amplifier of the transmitter

On the envelope amplifier of the high-power transmitters described above special requirements when using the described separate reinforcement put. Since the envelope signal of a single sideband oscillation interacts with the modulation contains a changing DC component, although the low-frequency message to be transmitted contains no DC component, the envelope amplifier must be designed such that the DC component of the envelope can be amplified. This requirement is met by modern Switching amplifiers fulfilled, based on the principle of pulse duration amplification (PDM) or work according to the principle of pulse stage amplification (PSM). With older stations whose High-frequency output stages are modulated via modulation transformers is the gain of the direct component of the envelope signal is not possible because the modulation transformers cannot transfer the DC component.

In addition to the demand for the reinforcement of the DC component, the bandwidth of the Envelope amplifier to make the requirement that he is able to at least the second harmonic of the highest low frequency to be transmitted with as little distortion as possible to be able to transfer. The reason for the increased bandwidth requirement is the fact that the actual low-frequency message is not amplified in the envelope amplifier is, but the envelope of the high-frequency emission, which in turn despite Bandwidth limitation of the low-frequency signal to be transmitted is in principle not limited.

When a single-sideband signal is transmitted, as explained above, to place increased demands on the transmitter. Therefore, with the known Process only a part of the AM transmitters in operation worldwide on the presented simultaneous processes can be converted.

The invention has for its object a method for an analog-digital simultaneous transmission to create a broadcast in the AM frequency bands that is fully applicable to conventional AM transmitters and receivers Task also includes the creation of an arrangement for performing the above Procedure.

This object is solved by the features of claims 1 and 4. Training the invention are specified in the subclaims.

The solution according to the invention only requires an AM transmitter to be sufficient Bandwidth; a transfer of a DC voltage component is not necessary, since the envelope signal with pure amplitude modulation in contrast to a single sideband transmission corresponds to the input signal and contains no DC component.

The required bandwidth of the modulation amplifier corresponds to the sum of the Frequency offset between the "analog" and the "digital" carrier and half Bandwidth of the digital modulation signal.

Advantageous developments of the invention for transmission are in the subclaims of different information on the sidebands of digital modulation and limiting the digital modulation to a sideband.

Fig.1

zeigt eine Anordnung zur Aussendung einer simultanen analog-digitalen Rundfünkübertragung,

Fig.2

zeigt das Spektrum der Aussendung der in Fig. 1 gezeigten Anordnung,

Fig.3

zeigt eine Anordnung zur simultanen analog-digitalen Rundfunkübertragung mit einer Seitenbandunterdrückung bei der digitalen Modulation,

Fig.4

zeigt das Spektrum der resultierenden Aussendung des in Fig.3 gezeigten Verfahrens,

Fig.5

zeigt eine Ausbildung eines Signalaufbereitungsmodules für das in Fig.3 gezeigte Verfahren und

Fig.6

zeigt eine Anordung zur simultanen Aussendung von einer analogen und zwei unterschiedlichen digitalen Modulationen.

Exemplary embodiments of the invention are explained in more detail with reference to the drawing.

Fig. 1

shows an arrangement for the transmission of a simultaneous analog-digital broadcast transmission,

Fig. 2

shows the spectrum of the transmission of the arrangement shown in Fig. 1,

Fig. 3

shows an arrangement for simultaneous analog-digital radio transmission with a sideband suppression in digital modulation,

Fig. 4

shows the spectrum of the resulting emission of the method shown in FIG. 3,

Fig. 5

shows an embodiment of a signal conditioning module for the method shown in Fig.3 and

Fig. 6

shows an arrangement for the simultaneous transmission of one analog and two different digital modulations.

The arrangement shown in Fig.1 for sending a silicon analog-digital Broadcast transmission consists of a standard AM transmitter 1, two Oscillators 2 and 3, from a digital modulator 4 and from a summing element 5.

The AM transmitter 1 receives its carrier f _T from the oscillator 2 and is driven with a sum signal U _GES , which consists of the analog NF signal NF to be transmitted and a digitally modulated signal U _DIG . The digitally modulated signal U _DIG is formed in the digital modulator 4 by means of a signal DS, which is designed as a digital data stream, and an auxiliary carrier f _H. The sum signal U _GES is formed in the summer 5. The signal DS is, for example, the output signal of an audio source encoder.

For the solution according to the invention it is irrelevant whether the digital modulation is a single-carrier or a multi-carrier method with several frequency-shifted subcarriers f _H. If there is only a limited modulation range for the digital modulation signal, it can be advantageous to use one To use digital modulation, the ratio between peak value and effective value (crest factor) is as low as possible in order to use the available modulation range as effectively as possible. Consequently, it then appears to be advantageous to carry out the digital modulation in the form of a single-carrier method instead of a multi-carrier method, since it is known that the crest factor of a multi-carrier method is greater in distortion-free transmission than in a comparable single-carrier method.

The solution according to the invention is not based on the simultaneous transmission of a radio broadcast limited. One can on the analog and on the digital channel Many types of information, including information that deviates from one another on the channels, be transmitted. So instead of radio broadcasts, radio broadcasts, Embassy radio broadcasts and data broadcasts on the digital channel, Time broadcasts ... etc. with appropriate hardware adaptation and training of the analog NF signal NF and the signal DS are transmitted. The one Hardware adaptations required do not require the person skilled in the art to invent them Activities.

The subcarrier f _H generated in a single-carrier method with the oscillator 3 should preferably correspond to the channel grid frequency of the frequency range used, or an integral multiple of this frequency. As is known, a channel raster frequency of 9 kHz is used in the long and medium wave range, while a channel raster frequency of 5 kHz is used in the short wave range.

2 shows the spectrum of a transmission that is transmitted with an arrangement according to FIG. For the frequency-shifted digital modulation, a single-carrier method with the auxiliary frequency f _{H is} used in the example shown. The upper and lower sidebands of the analog modulation OSB _AN and USB _AN occur directly adjacent to the carrier f _T. The upper and lower sidebands of the digital modulation OSB _DI and USB _DI appear at a distance of +/- f _H from the carrier f _T.

If the digital modulation U _DIG and the analog NF signal NF are band-limited with suitable means before the application to the summer 5, no overlap of the spectra occurs during transmission and interference-free transmission of the signals can be expected. According to the invention, a conventional AM receiver is required to receive the analog signal and a corresponding digital receiver is required to receive the digitized information.

The conventional AM receiver is tuned to the frequency of the carrier f _T and, due to its design, has a bandwidth that filters out the AM signal, consisting of the upper and lower sidebands of the analog modulation OSB _AN and USB _AN, and thus the sidebands the digital modulation OSB _DI and USB _DI suppressed.

The digital receiver is tuned according to the frequency of the subcarrier f _H to the offset subcarriers f _T - f _H or f _{T +} f _H if only one digital sideband is to be received. If the digital receiver is to evaluate both digital sidebands, it is tuned to the frequency of the carrier f _T. A filter contained in the receiver then suppresses the AM transmission. This signal processing makes it possible to evaluate the two digital sidebands. If the digital sidebands were derived from coupled digital data streams, both partial data streams can be received and combined again at the same time.

In order to keep the mutual influence of the analog and digital channels low, it is advantageous to limit the amplitude of the analog LF signal NF before it is fed into the summer 5 such that the amplitude of the sum signal U _{GES is} less than the maximum permissible modulation of the AM transmitter 1. With this measure, the band extensions indicated in FIG. 2 at the foot of the analogue sidebands, which are due to a non-linear amplification of an AM transmitter 1, can be avoided.

The required bandwidth of the AM transmitter 1 can be read from FIG. For the exemplary embodiment according to FIG. 1, it corresponds to the sum of the offset of the subcarrier f _H and half the bandwidth of the digital modulation signal.

In Fig3. An arrangement for carrying out the invention is shown, in which, in contrast to the embodiment described above in relation to FIG. 1, the AM transmitter 1 is driven with a phase-modulated carrier-frequency oscillation. The phase modulation is selected such that the upper or the lower sideband of the digital modulation OSB _DI or USB _DI is suppressed in the resulting transmission.

The arrangement shown in FIG. 3 for transmitting a standard analog-digital radio transmission consists of a standard AM transmitter 1, two oscillators 2 and 3, from a digital modulator 4 and a signal conditioning module 6.

The AM transmitter 1 receives its phase-modulated carrier f _PH from the signal processing module 6, to which a carrier f _T generated by the oscillator 2 is fed. The AM transmitter 1 is controlled with an envelope signal U _HÜLL , which is _generated in the signal _{conditioning module} 6 from the analog LF signal NF to be transmitted and from a digitally modulated signal U _DIG . The digitally modulated signal U _DIG is formed in the digital modulator 4 by means of a signal DS and an auxiliary carrier f _H.

The phase modulation of the carrier f _T and the associated envelope signal for the AM transmitter 1 required to suppress one of the digital sidebands is carried out in the signal processing module 6 in a manner known to the person skilled in the art.

At the same time, this phase modulation ensures that the amplitudes of the remaining digital sideband are increased. This measure improves the utilization of the transmitted spectrum. The demands on the AM transmitter increase, since an overall signal is now transmitted which contains a single sideband component, the digitally modulated component. If the amplitude of the subcarrier f _{H is} small compared to the amplitude of the carrier f _T , it can be expected that a broadband transmission of the envelope signal will not be necessary, since the harmonic content of the envelope curve becomes disproportionately lower as the subcarrier becomes smaller and consequently incorrect transmission the low envelope harmonics will only cause a negligible error in the modulation process. It can be shown that with a modulation of 10%, the portion of the upper part of the envelope is approx. 30 dB smaller than the amplitude of the fundamental wave.

5 is an example of the configuration of the signal conditioning module 6 Arrangement shown in Figure 3. The AM transmitter 1 thus actuated consists of an envelope amplifier 1.1, a high-frequency amplifier 1.2 and an output stage 1.3, which is equipped with a tube, for example.

The signal DS digitally modulated onto the subcarrier f _H arrives as signal U _DIG via an input stage 6.1 on the one hand to a Hilber transformer 6.3 and on the other hand to the input of a delay element 6.2 which compensates for the delay time of the Hilber transformer 6.3. The output signals from the runtime and Hilber transformers correspond to the in-phase and quadrature components of the output signal of the AM transmitter 1. The analog NF signal NF is superimposed on the in-phase component by addition in a summer 6.4. The envelope _signal U _{HÜLL is} formed from this in-phase component, modified by the analog modulation, and the quadrature component calculated in the Hilbert transformer in an absolute value generator 6.5. The magnitude signal thus formed is used to control the envelope amplifier 1.1. The amount is formed, for example, by forming the square root from the sum of the squared in-phase and quadrature components and a carrier additive T. This carrier additive T is added via a summer 6.14 to the analog NF signal NF on the input side.

When using an AM transmitter in which the modulation transformer low frequency amplified in the modulator superimposed on a constant anode voltage this constant carrier additive T is omitted in the signal processing module 6.

The in-phase and quadrature components also become dividers 6.6 and 6.7 guided. Here are the signals by the amount determined in the amount generator 6.5 divided to have a phase-modulated carrier at the output of the preparation alone to get constant amplitude. The signals standardized by the amount are in Delay elements 6.8 and 6.9 are delayed in such a way that the envelope amplifier's delay time 1.1 is compensated so that when merging the signals in the power amplifier Runtime difference occurs.

In modulators 6.10 and 6.11, the signal components are modulated onto two carrier-frequency oscillations of the same amplitude that are shifted by 90 ° relative to one another by multiplication. In a phase shifter 6.12, two oscillations phase-shifted by 90 ° are formed from the supplied carrier f _T. The signal suitable for carrier-frequency control of the AM transmitter 1 is then generated from these modulated carrier-frequency vibrations in a summer 6.13. This signal is amplified in the high-frequency amplifier 1.2 of the AM transmitter 1 to the power level required to control the output stage. In the final stage 1.3, the phase-modulated carrier-frequency oscillation is amplified to its final value, the amplitude of the transmission being determined by the output voltage of the envelope amplifier 1.1, which serves as the supply voltage for the final stage.

Both a transistorized amplifier and a tube amplifier are used as the output stage suitable. With transistorized amplifiers, the output amplitude of the transmission determined via the collector or drain voltage serving as supply voltage, while with the tube transmitter, the anode voltage is the one working in overvoltage mode Tube determines the amplitude of the output voltage.

An arrangement is shown in FIG. 6 which allows simultaneous analog modulation to send two digital modulation signals with different information.

Here, the digital modulation signals can contain two digital data streams from a common data source by dividing the common data stream arise. This division enables larger data rates to be transmitted, because only part of the total data stream is transmitted in each digital sideband. In the receiver, these two separate partial data streams can then return to the original data stream.

The two different _{pieces of} information are each modulated in a known manner in a digital modulator on at least one subcarrier f _H and, as digitally modulated signals U _DIG1 and U _DIG2, input _stages 6.1 and 6.15 are fed to the arrangement shown in FIG. Via input stages 6.1 and 6.15, they arrive at Hilbert transformers 6.3 and 6.17 and in parallel to runtime elements 6.2 and 6.16, which compensate for the runtime of the Hilbert transformers.

The in-phase components of the digitally modulated signals U _DIG1 and U _DIG2 are available at the outputs of the delay _elements and the quadrature components of the digitally modulated signals U _DIG1 and U _{DIG2 are available} for further processing at the outputs of the Hilbert transformers. The in-phase signals are added in phase in a summer 6.4, while the quadrature components are only added in a summer 6.19 after inverting one of the quadrature components, which takes place in an inverter 6.18. As a result of the inversion, the corresponding digitally modulated signal - for example the signal U _{DIG2 is} selected here - is _shifted into the other side band.

The analog NF signal NF, on which the carrier additive T is superimposed in the summer 6.14 is given on the totalizer 6.4 for the in-phase components. For the further Processing of the signal processing module in the input area described above 6 summed up signals, the arrangement shown in FIG. 6 is identical 5 with the arrangement shown in FIG. 5, so that the description the function blocks downstream of the entrance area to the previous ones Fig.5 made statements can be removed.

The arrangements shown in FIG. 5 and in FIG. 6 can be implemented using digital signal processing modules or in the form of analog modules.

Claims (9)

Process for analog-digital simultaneous transmission of radio broadcasts in the AM frequency bands with a carrier for analog modulation and at least a frequency-shifted subcarrier for digital modulation, thereby characterized in that the analog modulation takes place as double sideband modulation. A method according to claim 1, characterized in that by suitable phase and Amplitude modulation of the high-frequency carrier a digital sideband is suppressed. Method according to claims 1, characterized in that by suitable phase and Amplitude modulation two digital sidebands with different modulation contents are transferred. A method according to claim 3, characterized in that the digital sidebands arise from coupled data streams. Arrangement for analog-digital simultaneous transmission of a radio broadcast in the AM frequency bands with a carrier for analog modulation and at least one frequency-shifted subcarrier for digital modulation, characterized in that the simultaneous transmission is transmitted with an AM transmitter (1), the carrier (f _T ) is modulated with a sum signal (U _GES ), which is composed of the analog LF signal (NF) to be transmitted and a digitally modulated signal (U _DIG ), the latter by digital modulation of at least one frequency-shifted subcarrier (f _H ) with a signal (DS) and the frequency offset of the subcarrier (f _H ) - or the subcarrier (f _H ) - is selected so that the spectra of the analog and digital modulation are separated from one another. Arrangement according to claim 5, characterized in that in a signal _{processing module} (6) from the analog LF signal (NF) and from the digitally modulated signal (U _DIG ) the amount of an envelope signal (U _HÜLL ) and the associated high-frequency phase-modulated carrier (f _PH ) are derived and that the derived low and high frequency control of the AM transmitter (1) is carried out with these derived signals. Arrangement according to claim 6, characterized in that the envelope _signal (U _HÜLL ) and the phase-modulated carrier (f _PH ) in the signal _{processing module} (6) are derived such that either only the upper or the lower sideband of the digital modulation (OSB _DI , USB _DI ) arises. Arrangement according to claim 6, characterized in that the envelope _signal (U _HÜLL ) and the phase-modulated carrier (f _PH ) are derived such that the upper and lower sidebands of the digital modulation (OSB _DI , USB _DI ) contain different modulation contents, the Modulation contents are derived from a common data stream source by dividing the data stream generated thereby. Arrangement according to claim 6, characterized in that the envelope _signal (U _HÜLL ) and the phase-modulated carrier (f _PH ) are derived such that the upper and lower sidebands of the digital modulation (OSB _DI , USB _DI ) contain different modulation contents, the Modulation contents are derived from two data stream sources.

Images