Pulse or digital communications – Repeaters – Testing
Patent
1988-10-13
1991-04-02
Safourek, Benedict V.
Pulse or digital communications
Repeaters
Testing
375 39, 329304, H04L 2706, H04L 512
Patent
active
050051865
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention is related to a digital demodulator apparatus, more particularly to a demodulator apparatus which receives transmission signals modulated by the multivalue quadrature amplitude modulation method, having a honeycomb structure signal point arrangement, and reproduces the original code data.
Digitalization by the modulation method is effective for improving the efficiency of frequency utilization, a fundamental point in radio systems. Therefore, use has been made of the QAM (quadrature amplitude modification) system, which enables digitalization relatively easily. As to the modulation level, there tendency is to use of multivalues from 4-value to 16-value and 16-value to 64-value and further 256-value.
However, the use of multivalues has been accompanied by a remarkable increase in the transmission power for ensuring the necessary signal reception level. Further, this increase in the transmission power causes interference with neighboring transmission lines and new problems in the area of ensurement of power at the radio offices.
FIG. 1 shows the signal point arrangement of a general QAM system, wherein the horizontal axis shows the I (In-phase) channel and the vertical axis the Q (Quadrature phase) channel. Note that in this figure, an example is shown of 64 value QAM. The signal points include three bits of the I channel (2.sup.3 =8 level) and three bits of the Q channel (2.sup.3 =8 level), for a total of 64 (=8.times.8). As shown in the figure, the general QAM system is a so-called orthogonal grid structure.
To reduce the transmission power with a modulation system having a signal point arrangement having such an orthogonal grid structure, at least two conditions are necessary (1) the ratio of the average power (power required in the case where 64 values occur at the same probability as random occurrence) to the signal point pitch be made smaller and (2) the ratio of the average power and the peak power (generated at four corners of square signal point arrangement) be made smaller. The honeycomb structure has been proposed with this concept in mind.
FIG. 2 shows a signal point arrangement in a modulation system having a honeycomb structure. The horizontal axis and vertical axis have the same meanings as in FIG. 1. Further, there are also 64 signal points. With such a honeycomb structure, the distance between neighbouring signal points becomes completely the same and the conditions of the above-mentioned (1) are satisfied. Further, the outer periphery of the honeycomb structure becomes close to that of a circle (in the figure, a hexagon), so the above-mentioned condition (2) is satisfied. As shown, the honeycomb structure is an effective means for suppressing the increase in the transmission power along with conversion to multivalues.
FIG. 3 shows the basic construction of a digital demodulation apparatus of the present invention. The digital demodulation apparatus 10 is provided with a detector 11 which receives the transmission signal S.sub.in modulated by the multivalue QAM method with a honeycomb structure signal point arrangement and performs quadrature detection, a filter 12 which performs wave reshaping on the output, and a discrimination 13 which produces a digital demodulation signal by A/D conversion of the output. Further, it is provided with a code decision unit which decodes and reproduces the honeycomb structure modulated signal and, using the same, reproduces the original code data D.sub.I and D.sub.Q.
With the above-mentioned QAM method, on the demodulation side the digital demodulation signal output from the discriminator, which comprises the A/D converter, matches the orthogonal grid structure signal point arrangement as it is, so the hardware for reproducing the code data, that is, the code decision unit (14 in FIG. 3), is extremely simple in construction.
With a modulation method with a honeycomb structure signal point arrangement, however, the original code data cannot be reproduced without passing the digital demodulation signal from the A/D conve
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Aono Yoshihito
Daidoh Yoshimasa
Fujino Nobutsugu
Iwamatsu Takanori
Minowa Morihiko
Fujitsu Limited
Safourek Benedict V.
Smith Ralph
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