KR950003667B1 - Minimum shift keying modulator and demodulator using bfsk demodulating method - Google Patents

Abstract

The device provides the MSK modulation/demodulation method using the BPSK. It is simple to hardware implement and doesn't require the accurate phase difference maintainenance between the signal. The device includes; (a) reverse direction differential coder (41) which processes the transmitting data; (b) a modulator which produces the MSK modulated signal by modulating the mixers (3,9) output with a sinusoidal generator (6) output and phase shifted signal; (c) a mid-frequency reproduction circuit (29) produces the sinusoidal signal which is synchronized with the mid-frequency of MSK modulated signal; and (d) low-pass filters (24,25) which process the mixer output.

Description

Modulation Demodulation Device for MSK (minimum shift keying) using BFSK demodulation method

1 is a block diagram of a transmitter using a general MSK modulation scheme.

2 is an exemplary configuration diagram of an MSK demodulator using the BFSK demodulation method of the present invention.

3 is an exemplary configuration diagram of an MSK modulator with reverse differential coding according to the present invention.

4 is an exemplary configuration diagram of an MSK demodulator with reverse differential decoding according to the present invention.

5 illustrates one embodiment of the differential encoder / decoder of the present invention.

6 is a signal waveform diagram of the modulation and demodulation process of the present invention.

* Explanation of symbols for main parts of the drawings

21: discriminator 22, 23: integrator

24,25: low filter 26,27: mixer

28: bit clock player 29: intermediate frequency playback circuit

30,34: Band filter 32: Local oscillator

33: amplifier 34: antenna

41: backward differential encoder 51: backward differential encoder

The present invention relates to an MSK demodulation device for performing MSK reception and differential encoding of data capable of recovering an MSK modulated signal in a BFSK method by using characteristics of an MSK modulation waveform among digital modulation and demodulation methods.

The demodulation method of the conventional MSK modulation and demodulation system detects signals by separating them into the same in-phase channel and quadrature-phase channel. In this conventional method, a phase difference between an in-phase signal and an orthogonal signal is exactly 90 ° to accurately detect a signal. If the phase difference between the two channels is not maintained at exactly 90 ° due to hardware factors, the performance of the ideal MSK modulation / demodulation system will be lower than that of the ideal MSK modulation system. There was a problem that there are many technical difficulties.

Therefore, the present invention devised to solve the problems caused by the conventional scheme is simple in terms of hardware, and MSK using BFSK demodulation scheme (synchronous or asynchronous) that does not need to accurately maintain a phase difference between signals between two channels. It is an object of the present invention to provide an MSK demodulation device for demodulating and demodulating modulation data in order to demodulate a modulated signal and to improve the performance of the proposed scheme.

In order to achieve the above object, the present invention provides a backward differential encoding means for automatically encoding data to be transmitted and a reverse differential encoding means for separating the output of the reverse differential encoding means into in-phase and orthogonal channels through a parallel-to-parallel converter, To delay orthogonal data with respect to in-phase data through the device, and to modulate the signal with the in-phase data and the orthogonal data, the output of the sinusoidal wave generator and the signal of phase shifting the sinusoidal wave are respectively modulated through a mixer. Modulating means including transmission means for modulating the output of the mixer with the output of a sinusoidal wave generator of a carrier frequency and a phase shifted signal and combining the outputs with a combiner to generate an MSK modulated signal; Intermediate frequency regeneration means for generating cos (wift) and sin (sift) signals synchronized to the intermediate frequency to the MSK modulated signal input and processed in the intermediate frequency band, and a mixture for locally inputting the output signals of the intermediate frequency regeneration means, respectively. A matched filter comprising a means, a low pass filtering means for filtering the output signal of the mixing means, and an integrating means, and a signal level of the matched filter being received, and the signal level is compared and determined as 1 or -1. And a modulation receiving means including a discriminating means for outputting a signal and a clock regenerating means for receiving the output of the intermediate frequency reproducing means as an input, extracting a clock, and providing the integrating means and the discriminating means.

In addition, the demodulation device according to another embodiment, the intermediate frequency reproduction for generating a cos (wift) and sin (wift) signal synchronized to the intermediate frequency in the MSK modulation signal of the intermediate frequency band input and processed to the final output terminal of the demodulation means Further means is configured.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

1 is a configuration diagram of an MSK transmitter using a general MSK modulation scheme, in which 1 is a serial to parallel converter, 2 is a delay element (consisting of D flip-flops), and 3, 4, 9, and 10 are shown in FIG. A mixer, 5 and 6, is a sinusoidal oscillator, 7, 8 is a 90 ° phase shift, 11 is a combiner, 12 is a band filter, 13 is a power amplifier, and 14 is an antenna.

The input data are separated into in-phase and orthogonal channels through the serial-to-parallel converter (1), and at this time, when the data transmission rate of the input data is R _b = 1 / T _b, the data transmission rate of the in-phase data and the orthogonal data is R _s = 0.5. Let R _b . In the orthogonal channel, the orthogonal data is delayed by T _b with respect to the in-phase data through the delay element 2, and the generated in-phase data and the orthogonal data are cos (nt / 2T _b ), that is, 1 to shape the signal. The output of the sinusoidal wave generator 5 having a frequency of / 4T _b and the signal (output of 7) in which the sinusoid is 90 ° out of phase are modulated by the mixer 3 and the mixer 9, respectively. Then, the outputs of the other mixers 3 and 9 are modulated by the output of the sine wave generator 6 of the carrier frequency and the signal (output of 8) which has been phase shifted by 90 degrees. 7,8 is a 90 ° phase shifter that delays each input signal by 90 °. The MSK modulated signal is generated by combining the in-phase signal m ₁ (t) (output of 4) and the quadrature signal m _q (t) (output of 10) output through the above process with the combiner 11, and In the final stage, the MSK modulated signal is limited to the band filter 12, and the power amplifier 13 amplifies the signal to a desired output to propagate the radio wave through the antenna 14.

2 is an exemplary view according to the configuration of the MSK demodulation receiver using the BFSK demodulation method according to the present invention, 21 is a discriminator, 22, 23 is an integrator, 24, 25 is a low-pass filter, 26, 27, 31 A mixer, 28 a data sampling clock regeneration circuit, 29 an intermediate frequency or carrier regeneration circuit, 30 and 34 a bandpass filter, 32 a local oscillator, 33 an amplifier and 35 an antenna.

The MSK modulated signal received by the antenna 35 outputs a signal of a desired band only through the band filter 34, and is amplified by the amplifier 33 to the input signal level at the next stage. The mixer 31 drops to the intermediate frequency through the output signal of the local oscillator 32. The signal is filtered and amplified again and output as an input signal of the BFSK demodulator. At this time, cos (wift) and sin (wift) signals are synchronized with the intermediate frequency through the intermediate frequency regeneration circuit 29 from the MSK modulated signal of the intermediate frequency band, and these signals are locally input signals of the mixers 26 and 27, respectively. To the output. The output signal of each stage generated in this way is compared with the discriminator 1 by a matched filter composed of low-pass filters 24 and 25 and integrators 22 and 23, and discriminated as 1 or -1. Output the data.

At this time, the integral section of the integrators 22 and 23 and the discrimination timing clock of the discriminator 21 are generated by the data clock regeneration circuit DRC 28 which receives the output of the intermediate frequency regeneration circuit ICRC 29 as an input.

The signal waveform of each stage generated by FIG. 1 and the data detected by FIG. 2 are shown in FIG.

In the form of a = f _c -1 / 2T _b of BFSK modulated signals _- FIG. 6, as shown at 78 the MSK modulated waveform _{f + = f c + 1 /} 2T b and f. Thus f ₊ . f _- It can be seen that the signal can be detected by BFSK demodulation with two frequencies. This will be described in more detail the signal waveform of each stage of FIG.

In FIG. 6, 71 denotes data to be transmitted, and 72 and 73 show in-phase data and quadrature data output by the serial-to-parallel converter 1 together with timing. 74 is a sine wave shaping the in-phase data, 75 is a shaping wave orthogonal data. 76 denotes signal waveforms m _f (t) and m _q (t) obtained by modulating the in-phase signal a _q (t) and 77, the orthogonal signal a _q (t). 78 is an MSK modulation waveform obtained by analog-combining the in-phase signal m _f (t) and the quadrature signal m _q (t). 79 is an MSK modulation waveform and the MSK modulation waveform as indicated, separated by a frequency component _{f + = f c + 1 /} 2T b f - a signal waveform of the BFSK having two frequency components in = f _c -1 / 2T _b It can be seen that. 80 demodulates the MSK modulated signal by using the BFSK demodulation method according to FIG. 4 according to the frequency component indicated in 79, and shows reverse differentially decoded data.

Referring to 80 of FIG. 6, it can be seen that the signal detected by the BFSK demodulation method coincides with the data obtained by performing the differentially decoded decoding. Therefore, the receiver at this time should be configured as shown in FIG.

4 is a configuration diagram of another embodiment of the receiver required when the transmitter of the present invention is configured as shown in FIG. 1. The data is processed by the reverse differential decoder 51 with the output data of the discriminator of FIG. It is.

Therefore, when there is no error on the channel, it can be seen that the data demodulated by the BFSK demodulation method is a form of forward differential encoding of the transmitted data. Therefore, before the data is output from the receiver, the differential differential coding must be performed to recover the data transmitted from the transmitter. In this case, the system performance is reduced by 3 dB.

In order to improve this, as shown in FIG. 3, the transmitter of FIG. 1 is improved, and a receiver coupled to the receiver may be applied by the BFSK demodulation method shown in FIG.

3 is a diagram of encoding data to be transmitted with a reverse differential encoder 41, and then inputs input data of FIG. 1 and modulates the data according to the process already described with reference to FIG. When the MSK modulated signal generated by the receiver configuration of FIG. 3 is demodulated by the receiver configuration of FIG. 2, the recovered data is detected in the same manner as the data string of FIG. Accordingly, the MSK modulated signal transmitted by FIG. 3 can recover data in the same manner as the data originally transmitted (71 in FIG. 6) in the configuration of FIG.

5 is a diagram illustrating an embodiment of a backward differential encoder / decoder, in which 61 is an exclusive OR gate and 62 is a delayed flip-flop.

The input data is connected to one input terminal of the exclusive OR gate, and the other data is inputted by delaying the output data by T _b, and the output data is generated by processing the exclusive OR.

Therefore, the present invention configured and operated as described above is configured through a simple modification of the conventional circuit, so that the implementation is simple and economically effective in increasing competitiveness.

Claims (4)

In the MSK demodulation device using the BFSK demodulation method, a reverse differential encoding means (41) for performing reverse differential encoding of data to be transmitted, and an output of the reverse differential encoding means (41) through a serial-to-parallel converter (1) And orthogonal channels, and in orthogonal channels, delay orthogonal data with respect to synchronizing data through delay element 2, and in-phase data and orthogonal data are each separated from the sinusoidal wave generator 5 in order to shape the signal. The output and the phase shifted signal of the sine wave are modulated by the mixers 3 and 9, respectively, and the output of the mixers 3 and 9 is modulated by the output of the sinusoidal wave generator 6 of the carrier frequency and the phase shifted signal. Modulating means for transmitting to combiner 11 to generate an MSK modulated signal; An intermediate frequency reproducing means 29 for generating a cos (wift) and sin (wift) signal synchronized with the intermediate frequency from the MSK modulated signal input and processed in the intermediate frequency band, and an output signal of the intermediate frequency reproducing means 29 Matching means composed of mixing means 26 and 27 input locally, low filtering means 24 and 25 and integral means 22 and 23 filtering the output signal of the mixing means 26 and 27, respectively. matched) filter and the output of the discrimination means 21 and the intermediate frequency reproducing means (ICRC) 29 for inputting the signal of the matched filter and comparing the signal level to determine 1 or -1 to output data. Receiving and extracting a clock and including a modulation receiving means having a clock reproducing means (DRC) 28 which is provided to the integrating means 22 and 23 and the discriminating means 21. Modulation demodulation device. The reverse differential encoding means (41) of claim 1, wherein the exclusive differential sum processing means (61) for receiving input data from one input terminal and the output of the exclusive OR processing means (61) are delayed and fed back. And a delay means (62) for providing it as another input of said exclusive-OR processing means (61). An MSK demodulation device using the BFSK demodulation method, comprising: an intermediate frequency reproducing means 29 for generating a cos (wift) and sin (wift) signal synchronized to an intermediate frequency from an MSK modulated signal input and processed in an intermediate frequency band, Mixing means 26 and 27 for locally inputting the output signal of the intermediate frequency reproducing means 29, low-pass filtering means 24 and 25 for filtering the output signal of the mixing means 26 and 27, and integration A matched filter composed of means 22 and 23, a discrimination means 21 for receiving the signal of the matched filter and comparing the signal level and discriminating 1 or -1 to output data; A reverse differential decoding means 51 for reverse differential decoding of the output of the means 21 and an output of an intermediate frequency reproducing means (ICRC) 29 as an input to extract a clock, thereby integrating the integration means 22 and 23 and the discriminating means. And clock reproducing means (DRC) 28 provided to 21. Demodulator of the MSK using BFSK demodulation method. The reverse differential decoding means (51) according to claim 3, wherein the reverse differential decoding means (51) delays the output of the exclusive-OR processing means (61), which receives input data from one input terminal, and the output of the exclusive-OR processing means (61). And a delay means (62) provided to another input of the OR processing means (61). The MSK demodulation device using the BFSK demodulation method.