Narrowband QAM transmission

p0001The invention relates to a method and a circuit arrangement for transmitting signals according to the preambles of claims 1 and 6. FIG.

p0002The desire of the radio listeners for better transmission quality were taken into account in the past with the introduction of frequency modulation in the VHF range and currently plans to introduce digital broadcasting (DAB) in the VHF range and L-band. The broadcast programs in the areas of long, medium and short wave are previously transmitted with amplitude modulation and the associated poor quality of the communication channel, whereby these frequency ranges have lost acceptance. Digitizing said frequency ranges will result in an increase in the transmission quality and obtain the benefits of valid for this characteristic frequencies propagation characteristics. It is expected that with higher power transmitters (10 to 100 kW) and digitized transmission will be possible to vesorgen larger parts of a continent by means of a long, medium or short wave transmitter with a high quality signal. In order to ensure a large economic viability of such transmitters, it is necessary to develop channels that have a high efficiency. Furthermore, pay attention to that signal possible having a low bandwidth to operate the existing frequency bands with as many programs can and to interfere as little as possible during a transitional period analog modulated channels.

p0003In order to keep the bandwidth of the transmitted digital signal low, it is necessary to use a high-level digital modulation in addition to a suitable source encoding. The more stages are used, the less bandwidth can be kept.

p0004From the literature (L.Kahn, Single-Sideband Transmission by Envelope Elimination and Restoration, Proceedings of the IRE, 1952, S.803 ff) a high-frequency amplifier is known, which is operated with high efficiency. In the specified reference a station is described, which is characterized by the separate control of the power amplifier with magnitude and phase signal. Here, from the input single sideband signal by envelope detection by the envelope signal and limiting the amplitude of the input signal a signal is derived which contains the phase information is limited in amplitude. The limited high-frequency vibration and the envelope signal are fed to the working in the C-spanned operation amplifier, whereby a gain of a Einseitenbandsignales is achieved with high efficiency.

p0005In EP-0193655 a radio transmitter having a high power and high efficiency is described, is dergeeignet to radiate a single sideband. In this transmitter, the analog low-frequency modulation signal is sampled, digitized, and converted by the signal processor technology into a complex signal consisting of real and imaginary parts. This conversion is effected by means of a Hilbert transformer according to the phase method known from the literature. Then, the magnitude and phase of the signal is determined from these components. the grid of the power tube are then driven with the phase-modulated high-frequency carrier and the anode connected to the magnitude signal corresponding to the envelope signal is driven, as in the circuit mentioned above.

p0006In the above cases, an analog signal is transmitted with high efficiency.

p0007The object of the invention is to provide a transmission method and a system for implementing this method, which allows the transmission of digital signals at high amplifier efficiency and achieve low bandwidths.

p0008This object is achieved by the features mentioned in the Patentannsprüchen 1 and 6. FIG. Advantageous developments of the invention are specified in the subclaims.

p0009The invention enables in an advantageous manner the use of a transmitter amplifier, which splits the signal to be transmitted into a magnitude and phase component, to the transmission of a digital signal taking into account the demands for achieving low bandwidths. The inventive method can therefore advantageously allow a transition to digital broadcasting in the long, medium and short wave.

p0010Claim 3 is an embodiment of the invention, the particularly advantageous supports the use of switching amplifiers to amplify the magnitude component and claim 4 is an embodiment of the invention, the advantageous enables additional transmitting a constant carrier signal, the receiver side by simple means the exact carrier frequency and reference position of is the transmitted signal can be determined.

p0011In Claim 5 an advantageous method of obtaining the reference phase, which does not require special synchronization sequence is described.

p0012Referring to the drawings, embodiments of the invention will be explained in more detail.

p00131 shows an arrangement for generating the magnitude and phase information of a digital modulation signal.

p00142 shows an arrangement for modulating a high-frequency oscillation amplitude and phase by means of a lamp equipped with a tube amplifier stage. 3 shows an arrangement for modulation of a high frequency oscillation magnitude and phase by means of an amplifier stage equipped with transistors.

p00154 shows the constellation of a preferred level signal.

p00165 shows the constellation of a preferred level signal which does not contain a symbol at the origin of the constellation plane.

p00176 shows the constellation of a preferred level signal which contains a targeted asymmetry.

p00187 shows a constellation of a preferred level signal, which is shifted from the zero point.

p0019The digital input signal 2 shown in Fig. 1 digital processing circuit 1 is in the symbol converter 3, converted into a complex signal which is represented in the form of real and imaginary parts. A band limitation of the signal components is done through the filter 4 and 5. From the thus calculated amount of the components of the complex signal is calculated in the absolute-value generator 6, on the one hand the envelope amplifier 20 drives in the figures Fig.2 and Fig.3, and on the other hand the components of the band-limited signals normalized in the dividers 8 and 9. FIG. This thus calculated normalized components are the retarders 10 and 11 supplied to consisting of driver stage 21 to adjust the signal propagation times, one of which is greater in low Hüllkurvenzweig consisting of envelope amplifier 20 with filter 22, generally referred to as the high-frequency phase branch today.

p0020The delayed, normalized signals the carrier or intermediate frequency modulators 12 and 13 supplied to its modulation signal inputs. These modulators are driven at their carrier signal inputs with each other by 90 degrees-shifted components of the carrier or intermediate frequency oscillation and output the modulated output signals to the addition circuit 15. In the case of the use of an intermediate frequency of the adder stage 15 of the frequency converter 16 is connected downstream of the intermediate frequency based on the actual carrier frequency converts.

p0021For the function of the circuit, it is basically the same as if the modulators 12 and 13, the phase division 14 and the addition circuit 15 the necessary operations are carried out in digitized form to work in the form of analog circuits or. When using analog modulators, the retarders 10 and 11 to the respective digital-to-analog converter to complement and the output signal 19 to convert digital to analog in addition, when used in digital form.

p0022The thus-obtained phase-modulated and normalized carrier frequency signal is then supplied for further amplification of the high frequency driver stage 21, which provides sufficient for the output stage 23 or 30 drive voltage available. The amount signal 7 is amplified by the low frequency amplifier 20, which preferably operates as an amplifier with high efficiency. As switching amplifier to amplifier, according to the principle of the step-down converter (pulsdauermodulierender amplifier) ​​or operate on the pulse stage amplifier principle suitable. This amplifier types have in common that they are able to transmit low-frequency signals including the DC components.

p0023As power amplifier is suitable an electron tube 23, which draws its anode voltage from the low Hülkurvenverstärkerzweig, consisting of the amplifier 20 and the downstream filter 22nd The tube is to achieve a high efficiency, spans operated in class C operation (conduction angle less than 90 degrees). Across the anode voltage modulates the tube 23 present at the control grid high-frequency carrier oscillation, which contains the phase modulation in amplitude.

p0024Instead of the electron tube 23 in Figure 2 can be used alternatively 30 a transistorized amplifier. It is advantageous to use the bridge circuit shown in which the transistors are cross-operated in the switching mode. The switching operation used ensures high efficiency.

p0025For digital modulation, in particular those signals whose symbols are within a circle, since it is connected, the possibility of transferring a Maxmium to power at predetermined symbol spacing and symbol Count circuit conditional maximum amplitude swing are. In FIG. 4, an example of a corresponding constellation level is shown.

p0026This type of signal is, in Example .: Bernard Sklar, "Digital Communications, Fundamentals and Applications Prentice-Hall International, Inc, ISBN: 0-13-212713, S.412 f" described.

p0027In Figures 4 to 7 shows constellations to be used are preferably shown. Here is the set of symbols that are characterized by real and imaginary parts or magnitude and phase, as a symbol alphabet, denotes the number of symbols as Stages of the alphabet.

p0028In Figure 5, a further signal in the constellation plane is shown, which is characterized in that the zero point has to be transmitted symbol (corresponding to the zero point of the level) no. Since the above-mentioned amplifier circuit caused signal distortion at very small amplitudes especially when envelope "zero" - generate a signal that omits the center is, especially for the transmission by means of the described amplifier.

p0029In Fig.6 a constellation level is shown having a targeted asymmetry. Due to this asymmetry, it is possible without a special synchronization sequence to determine the reference phase. Example example, so the phase angle zero mark in sending a constantly avoided symbol point on the real axis. Thereby, it is possible at the receiving end, that the phase of the received signal is rotated until the missing symbol like transmitted again is located on the real axis, and thus the reference phase is recovered.

p0030In Figure 7 is a constellation level is shown, the point of symmetry is shifted from the zero point in the plane. This shift is achieved in the symbol converter 3 by an addition of a constant value to the dot-symmetrical symbol points. This type of symbol selection constantly a constant carrier value is also transmitted, which allows the receiving end to determine by simple means from the received signal the exact carrier frequency and the reference phase. If the size of this offset is kept small enough so the desire for an optimum utilization of Amplitudenhubes described above is only slightly injured.