CN103457892A - Novel carrier extraction method for binary frequency shift keying signals - Google Patents

Abstract

The invention belongs to the communication technical field in the electronic information technical field, and relates to communication principles and signal processing subjects, in particular to a novel carrier extraction method for binary frequency shift keying (2FSK for short) signals. Input signals of a module comprise a 2FSK modulating signal which is received, and a bit synchronization signal. An output signal of the module is a continuous center carrier signal. The novel carrier extraction method has the advantages of being capable of realizing continuous carrier error detection, thereby obtaining coherent carriers with higher accuracy.

Description

A New Carrier Extraction Method for Binary Frequency Shift Keying Signal

technical field

The invention belongs to the field of communication technology in the field of electronic information technology, relates to communication principles and signal processing disciplines, and specifically relates to a new carrier extraction method for Binary Frequency Shift Keying (2FSK) signals.

Background technique

和

），目前针对2FSK信号使用的相干解调方法中，对于载波提取通常采用平方环法，这种方法的原理是分别经过两个滤波器获得两个不同的载波频点，这种方法的缺点是：得到的两路载波信号是不连续的。将会增加信噪比门限和误码率，从而降低解码性能。因此，研究一种连续跟踪的载波提取技术对于针对2FSK调制信号实现更优的解码性能有着十分现实的意义。 In a communication system, if the receiving end wants to recover the original digital baseband signal from the modulated high-frequency signal, it needs to demodulate the received signal. At present, the main demodulation methods are divided into two categories: coherent demodulation and non-coherent demodulation; among them, the decoding performance of the coherent demodulation method is better. Under normal circumstances, coherent demodulation has a gain of 3dB compared with non-coherent demodulation. , but coherent demodulation needs to restore the coherent carrier. For 2FSK signals, since there are different carriers for different digital baseband codes (corresponding to

and

), in the coherent demodulation method currently used for 2FSK signals, the square loop method is usually used for carrier extraction. The principle of this method is to obtain two different carrier frequency points through two filters respectively. The disadvantage of this method is : The obtained two carrier signals are discontinuous. Will increase the SNR threshold and BER, thereby degrading decoding performance. Therefore, it is of great practical significance to study a continuous tracking carrier extraction technique to achieve better decoding performance for 2FSK modulated signals.

Contents of the invention

The present invention provides a new carrier extraction method for coherent demodulation of 2FSK modulated signals, which can realize continuous coherent carrier reproduction.

In order to achieve the above object, the technical scheme of the present invention is as follows:

。 A new carrier extraction method for 2FSK signals is implemented by the carrier extraction module, which has two input signals, one is the received 2FSK modulation signal, the other is the bit synchronization signal, and the output is the continuous center carrier signal, the center carrier signal

.

The numerically controlled oscillator in the carrier extraction module first generates a center carrier signal with a certain phase error, and divides the signal into two channels, one of which passes through the 90° phase shifting module to obtain two orthogonal center carrier signals, which are then combined with the receiving The obtained 2FSK modulation signal is multiplied, and the obtained results are respectively passed through a band-pass filter to filter out the high-frequency components obtained by the multiplication operation, and two quadrature signals containing the center carrier frequency phase error information are obtained, and then passed through a The phase detector module can obtain the error information between the center carrier frequency generated by the numerical control oscillator and the corresponding center carrier frequency in the 2FSK modulation signal. The mathematical model of this information is shown in formula (a).

                              （a）

(a)

 为鉴相器输出的相位误差信号；

 为数字基带信号对应的两个频点与中心载波频率之间的频率差值，即

；

 为数控振荡器产生的中心载频与2FSK调制信号中对应的中心载频之间的相位误差；

 为当时的数字基带信号取值。 in,

is the phase error signal output by the phase detector;

is the frequency difference between the two frequency points corresponding to the digital baseband signal and the center carrier frequency, that is

;

is the phase error between the center carrier frequency generated by the numerically controlled oscillator and the corresponding center carrier frequency in the 2FSK modulation signal;

Get the value for the digital baseband signal at that time.

，将相位误差信号分成两路，其中一路通过一个延时器，该延时器的延时时常由输入的位同步信号控制，之后，将这两路信号通过一个乘法器，接着再经过一个环路滤波器滤除高频分量，就得到只包含相位误差信息的控制信号，该信号的数学模型如公式（b）所示。 In order to eliminate the frequency difference information contained in formula (a)

, the phase error signal is divided into two paths, one of which passes through a delayer, the delay of which is often controlled by the input bit synchronization signal, after that, the two paths of signals pass through a multiplier, and then pass through a loop The high-frequency component is filtered out by a circuit filter, and a control signal containing only phase error information is obtained. The mathematical model of the signal is shown in formula (b).

                                           （b）

(b)

in, As the final phase error control signal, it can be seen that the signal only contains the phase error information between the center carrier frequency generated by the numerical control oscillator and the corresponding center carrier frequency in the 2FSK modulation signal .

Finally, the phase error control signal is used to control the numerically controlled oscillator, so that the center carrier signal output by the carrier extraction module and the center carrier signal in the received 2FSK modulation signal achieve the same frequency and phase.

The beneficial effect of the present invention is that the continuous carrier error detection can be realized by using the present invention, so that a coherent carrier with higher precision can be obtained.

Description of drawings

Fig. 1 is the input-output interface diagram of the carrier extraction module diagram of the present invention;

Fig. 2 is the implementation structure block diagram of the carrier extraction extraction method of the present invention;

Fig. 3 is a logical block diagram of a 2FSK coherent receiver using the present invention.

Reference signs are as follows: 1. carrier extraction module, 2. 2FSK modulation signal, 3. bit synchronization signal, 4. center carrier signal, 5. multiplier, 6. 90° phase shifting module, 7. bandpass filter, 8 . Numerical control oscillator, 9. Phase detector, 10. Delay device, 11. Loop filter, 12. Coherent demodulation module, 13. Sampling judgment module.

Detailed ways

The 2FSK carrier extraction module of the present invention is a functional module in the 2FSK signal receiver, and needs to be matched with the back-end coherent demodulation module and the sampling decision module to jointly realize the demodulation output of the digital baseband signal of the 2FSK modulation signal. The specific composition structure is as follows Figure 3 shows.

Use a vector signal generator to generate a 2FSK modulation signal in which the digital baseband signal is 0 code and 1 code appearing alternately. The center frequency is set to 455KHz, and the frequency deviation is ±1.2KHz.

The 2FSK modulation signal used for the test is divided into two paths, one path is connected to the input of the carrier extraction module, and the other path is connected to the input terminal of the coherent demodulation module (12).

The bit synchronization signal output by the sampling decision module (13) is connected to the data interface of the carrier extraction module.

The output interface of the carrier extraction module of the present invention is connected to the coherent demodulation module.

Using an oscilloscope to observe the output interface of the sampling decision module, we can get code 0 and code 1 that appear alternately.

Use an oscilloscope to observe the output interface of the carrier extraction module of the present invention, and you can see the center frequency of the carrier carrier that is stably tracked. After testing, the carrier frequency is 455KHz, and it is the same frequency and phase as the center frequency point of the frequency generated by the vector signal generator. the

Claims (1)

1. the new method of the carrier extract for binary frequency shift keying signal, is characterized in that concrete grammar is as follows: 1) use digital baseband signal of vector signal generator generation to be 0 yard and 1 yard and replace the 2FSK modulation signal occurred; 2) test signal is divided into to two-way, the input interface of a road access carrier extraction module, the input of a road access coherent demodulator; 3) data-interface of the bit synchronization signal access carrier extraction module of sampling decision device output; The output interface of 4) carrier extract module is linked into coherent demodulator; 5) adopt oscilloscope to observe the output interface of sampling judging module, obtain 0 yard and 1 yard of alternately appearance; 6) adopt oscilloscope to observe the output interface of carrier extract module, obtain producing the centre carrier frequency of the center frequency point of frequency with frequency homophase tenacious tracking with vector signal generator.

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