KR950013441B1 - Symbol discernment digital regeneration device using gaussian minimum shift keying - Google Patents

Abstract

a digital comparing unit(1-2) for comparing a threshold value of a frequency detected signal of a GMSK modulating wave received with a threshold value of a digital input signal and if greater than that of the digital input signal, for outputting a digital value "1", but if lower than that of the digital input signal, for outputting a digital value "0"; a maintaining unit(2) for receiving an output of the digital comparing unit to maintain the output for 1 time slot and for outputting a reproduction signal to an output terminal; and a threshold value supplying unit(3) for receiving the reproduction signal from the maintaining unit and if the reproduction signal is "1", for selecting a higher threshold value, but if the reproduction signal is "0", for selecting a lower threshold value, to output the selected threshold value to the digital comparing unit.

Description

Code Recognition Digital Playback Device using Gaussian Minimum Transition Method

1 is a block diagram of a conventional code identification reproduction apparatus of a Gaussian minimum transition method.

2 is a block diagram of a code identification digital reproduction apparatus of a Gaussian minimum transition method according to the present invention.

3 is an eye pattern diagram of a detection output of a Gaussian minimum transition modulated wave of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a code identifying and reproducing apparatus of a Gaussian minimum shift keying (GMSK) method. In particular, a GMSK code and a digital reproducing apparatus which detects a received GMSK signal, converts it into a digital signal, and compares and reproduces the digital signal. It is about.

In the conventional technique of converting and demodulating to analog to transmit a digital signal in a form suitable for a characteristic of a transmission line, in order to reduce the interference between communication lines caused by a wide spectrum of modulated signals, There are various ways to reduce it. In other words, since the digital signal contains a lot of high frequency components, the spectrum is very wide, and in the process of being multiplied with the carrier, its shape does not change and causes the modulated wave to have a wide spectrum. Therefore, when the baseband signal is used through the low pass filter, interference between communication paths can be reduced. However, such filtering increases the time range of the baseband bit waveforms, so that neighboring bit sections are overlapped and thus intersymbolic interference. Will be produced. The Minumum Shift Keying (MSK) method has a modulation index of 0.5 so that the baseband multiplied by the carrier becomes a smooth waveform, thereby reducing interference between communication lines and having a phase continuity. Interference between codes due to amplifiers can also be avoided. In order to reduce the frequency occupied bandwidth of the GMSK method, the GMSK method of MSK modulation after band limiting the digital data with a Gaussian low pass filter (Gaussian LPF) occurs as described above. As a result, inter-code interference occurs, eye pattern deterioration occurs, and code identification is difficult on the receiving side, resulting in poor transmission quality. Therefore, a code identification and reproducing means having a very small code error is desired on the receiving side of the GMSK method. The most commonly used method is to track the center of a data section in a clock reproducing circuit as shown in FIG. The threshold value is determined by averaging the energy of the GMSK detection signal at this time, and comparing the threshold signal with the input GMSK detection signal, and comparing the threshold signal with the input GMSK detection signal to " 1 " Although it is determined, accurate determination is difficult in an environment where the eye pattern is narrow or noisy.

Accordingly, an object of the present invention is to provide a digital type code reproducing apparatus having excellent bit error rate (BER) characteristics for reproducing the original signal transmitted in spite of poor conditions in a communication system using the GMSK scheme. To provide.

In order to achieve the above object, the GMSK code identification digital reproducing apparatus of the present invention provides digital signals from an A / D converter and an A / D converter for outputting an analog signal obtained by frequency detection of a GMSK modulated wave as a digital signal in a threshold supply means. Compared with the digital reference value, the comparison means for comparing and determining as "0" when it is smaller than the threshold value, and storing the binary value from the comparison means for one time slot and outputting the reproduced signal to the output terminal. Holding means for supplying a high threshold value THh when the value of the holding means is "1", and supplying a low threshold value THi to improve the accuracy of the determination to improve the BER characteristic. Characterized in that provided.

Next, the GMSK code identification and playback apparatus of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram of a conventional GMSK code identification / reproducing apparatus, when the analog GMSK detection signal inputted through the input terminal 10 is compared with the threshold provided by the threshold supply means 3, the value is " 1 " Analogue comparison means (1) for comparing and judging with " 0 ", holding means (2) for retaining the binary value from the comparison means (1) for one time slot and outputting the reproduced output to the output terminal (20); And threshold adjusting means (3) for providing the average value of energy of the GMSK code as a single threshold. This method uses the clock reproducing circuit to track the center of the data section as the decision point for the accuracy of the data judgment. The regeneration clock input terminal 30 is supplied to a holding means 2 that requires a regeneration clock.

2 is a block diagram of a digital code reproducing apparatus according to the present invention, which includes a digital comparing means (1) comprising an A / D converter (1-1) and a digital comparator (1-2), and a high threshold value TH _h . Generator 3-1, low threshold TH _l generator 3-2, first end gate 3-3, inverter 3-4, second end gate 3-5 and oragate ( It consists of the threshold supply means 3 and the holding means 2 which consist of 3-6).

The operation according to the configuration of FIG. 2 is as follows.

The analog signal obtained by detecting the signal transmitted by GMSK modulation from the transmitting side enters into the A / D converter 1-1 through the input terminal 10, and once converted into a digital signal, enters the digital comparator 1-2. The digital comparator 1-2 compares the digital signal output from the A / D converter 1-1 with the digital threshold provided by the threshold supply means 3, and determines that it is "0" if it is lower than the threshold. To print.

The holding means 2 delays the signal output from the comparing means 1 for one time slot and then outputs it to the threshold supply means 3 and the reproduction code output terminal 20.

According to the threshold supplying means (3), a first AND gate (3-3) is reproduced to be outputted from the high threshold (TH _h) generator (3-1) high threshold (TH _h) and the holding means (2) that is output from the performing logical multiplication with respect to the sign, and a second aND gate (3-5) are inverted is output from the low threshold value (TH _l) and the inverter (3-4) output from the low threshold value (TH _l) generator (3-2) The AND is performed on the reproduced code, and the OR gate 3-6 performs an OR on the output signal of the first AND gate 3-3 and the output signal of the second AND gate 3-5. Therefore, in the threshold supply means 3, the reproduction code outputted from the holding means 2 is inputted, and if the data preceding the value is "1" in accordance with the data value one time slot earlier than the determination scheduled (n + 1), the value is high. The threshold TH _h is output to the digital comparator 1-2, and if " 0 ", the low threshold TH ₁ is output to the digital comparator 1-2.

On the other hand, the regeneration clock input through the regeneration clock input terminal 30 is supplied to the holding means 2 and the digital comparing means 1 which require a clock.

3 is an eye pattern diagram of a GMSK detection output showing the present invention in an eye pattern. The threshold value output from the threshold supply means 3 has an appropriate value near the center of two eye regions h1 and h2 occurring at the sign adjacency point on the eye pattern, and the detection output at decision point n, n + 1. One point is concentrated in each of the allowable areas 1, 2 and 3. That is, if the sign in the center of the eye pattern is "0", the detection output value at the previous decision point n thereof may be 2,3, and if the next sign is "1", the detection output value at decision point n + 1 is region 3 Only exists.

According to the present invention, the code adjacent point can be determined as a determination point even when the band is strictly limited in order to eliminate interference between communication paths at the transmitting side, compared to the method of determining at the center of the code by a conventional simple circuit configuration. Since the signal can be reproduced, the BER characteristic is excellent, and if the logical conversion means is made on the transmitting side in comparison with the conventional method of converting the code logic to determine at the code adjacent point, the error rate can be improved only for the transmitting side. There is an advantage in that the circuit configuration is simplified and accurately reproduced, rather than a method of determining a code in a result of discriminating a plurality of consecutive code adjacent points. In addition, there is an effect of reproducing the original signal more accurately by using a digital comparator compared to a conventional analog comparator.

Claims (1)

A GMSK digital code identification device for recognizing a signal obtained by frequency-detecting a GMSK modulated wave and reproducing an original signal, wherein the frequency-detected signal of the received GMSK modulated wave is compared with a digital input signal obtained by A / D conversion and compared with a threshold. Digital comparison means for outputting "1" when the input signal is larger than the threshold and outputting "0" when the input signal is smaller; Holding means for receiving the output of the digital comparing means and holding it for one time slot and outputting the reproduced code to the output terminal; And a threshold supply means for inputting the code reproduced from the holding means, if it is " 1 ", and if it is " 0 ", the lower threshold value is selected and outputted to the digital comparison means. GM-SS code identification digital playback device characterized in that.