KR950012822B1 - Initial synchronization loop in spread-spectrum receiver - Google Patents

Abstract

a first signal mixer for mixing a reference frequency of a local oscillator and a PN code; a second signal mixer for mixing the shifted reference frequency by 90≰and the PN code; a first analog matching filter for mixing the output signal of the first signal mixer and a received input signal and for integrating the mixed signal; a second analog matching filter for mixing the output signal of the second signal mixer and the received input signal and for integrating the mixed signal; first and second multipliers for obtaining absolute values of the output signals from the first and second matching filters; an adder for adding the output signals from the first and second multipliers; a comparator for comparing the added signal of the adder with an auto-correlation threshold value of the PN code to output the compared result; and a PN code generator for producing the PN code corresponding to the output of the comparator to supply the PN code to the first and second signal mixers.

Description

Early Synchronous Loop for Receivers in Spread Spectrum Systems

1 is an initial synchronization loop of a receiver of a conventional spread spectrum system.

2 is an autocorrelation characteristic curve of a PN code by an initial synchronization loop in a receiver of a conventional spread spectrum system.

3 is a block diagram of an initial synchronization loop in a receiver of a spread spectrum system of the present invention.

4 is an autocorrelation characteristic curve of a PN code by an initial synchronization loop in a receiver of a spread spectrum system of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a caustic spectrum system, and more particularly, to an initial synchronization loop in a receiver of a spread spectrum system for maintaining an ECCM (Electromagnetic Counter Counter Measure) function by despreading a PN code carried on a frequency using an analog matching filter. It is about.

The communication sensation operated in the spread spectrum method transmits digital data, and the general spread spectrum modulation method uses an exclusive OR gate to convert a relatively high frequency signal and a pseudo-noise code (PN code). Intra-building communications to remove or reduce CW and jamming signals by using a mixer or by forming and transmitting spread signals with very high bandwidth and low spectral density. The low spectral density is useful for reducing interference of various jammers.

In general, in order to demodulate data at the receiving end of the spread spectrum system, an initial synchronization and synchronization tracking process for matching the system clock of the transmitting and receiving end is required.

When the initial-locked loop according to the prior art for this purpose described in the claim 1 as a reference, the received signal (f _1f A first signal mixer 11 for mixing DATAπPN and a signal f _c supplied from a local oscillator, and a second signal mixer 12 for mixing a signal supplied from the first signal mixer 11 with a PN code. ) And a matching filter 14 composed of an integrator 13 for integrating the signal supplied from the second signal mixer 12, and a squarer for obtaining an absolute value of the signal supplied from the matching filter 14; 15) comparing the absolute value of the signal supplied from the multiplier 15 with the autocorrelation threshold value V _TH of the PN code and outputting "0" if the threshold value V _TR is greater than the absolute value. If smaller, the comparator 16 for outputting "1", the PN code controller 17 by removing the PN code corresponding to the output of the comparator 16, and the PN code according to the result of the PN code controller 17. A PN code generator 18 configured to form and output a signal, and the received input No. (f _1f DATA PN is a spread signal and is input to the signal mixer 11 to output the local signal PN. When the PN code in DATA) and the PN code supplied from the PN code generator 18 are in a synchronous state, the output of the matching filter 14 returns the maximum value of the autocorrelation characteristic curve of the PN code shown in FIG. If it is twisted more than one chip (one bit value of PN code), it has the minimum value of the autocorrelation characteristic curve. The absolute value of the signal detected through the power supply 15 is supplied to the comparator 16 and the comparator 16 is compared with the absolute value of the signal in comparison with the autocorrelation threshold V _TH of the PN code. If the threshold is large, "0" is output. If the threshold is small, "1" is output. According to the output value of the comparator, the PN code controller 17 controls to shift the PN code by 1/2 chip when the output of the comparator 16 is "0" and recognizes that initial synchronization is made when the output is "1". The PN code generator 18 implements initial synchronization by forming and outputting a PN code corresponding thereto.

Here, the initial synchronization process can be seen as a process of finding the maximum peak value 21 of the autocorrelation characteristic curve of the PN code shown in FIG. 2 of the output. After performing the code period iterative integration, the peak detection is performed, and after performing the iterative integration for the various PN periods, the output becomes "1" and the initial synchronization is considered to be completed.

In the conventional spread spectrum system receiver according to the above method, the initial synchronization loop consists of a method of extracting autocorrelation, that is, a signal f _{1f in} synchronization, by first removing a frequency component from an input signal and then removing a PN code. When multiple frequencies are simultaneously input to the same output, the carrier signal f _c is impossible to recover, and thus, there is a problem in that it is impossible to implement a jammer defense function which is an original purpose of the spread spectrum communication system.

In order to solve the above problems, in the receiver of the spread spectrum system of the present invention, the initial synchronization loop performs initial synchronization by a method of simultaneously removing a frequency component and a PN code by using an analog matched filter in the process of despreading the PN code. By despreading the spread data, an object of the present invention is to implement a jamming defense function of a spread spectrum communication system.

In order to achieve the above object, an initial synchronization loop in a receiver of a spread spectrum system of the present invention includes a first signal mixer 304 for mixing a reference frequency and a PN code of a local oscillator in a receiver of a spread spectrum communication system. A second signal mixer 305 and a first signal mixer 304 for mixing a PN code and a signal whose phase of the reference frequency of the local oscillator is shifted by 90 ° (π / 2) through a signal shifting means; The signal formed by and the received input signal (f _1f DATA A first analog matched filter 309, the first reception signal and the signal formed by the second mixer 305, the signal (f _1f of mixing and integrating and outputting the mixed signals PN) DATA A second analog matched filter 313 for mixing PN) and integrating the mixed signal and outputting the first analogue filter 314 for obtaining an absolute value of an output signal of the first analog matched filter 309; An adder 316 for adding two signals output from the second and third power generators 315 and 314 and 315 for obtaining an absolute value of the output signal of the second analog matched filter 313. said threshold value (V _TH) is "If the output is small, the 0" is greater than the absolute value by comparing the auto-correlation threshold value (V _TH) of the signal and the PN code to be supplied is added by the adder 316 is 1, " A comparator 317 for outputting a PN code, a PN code controller 318 for controlling a PN code in response to an output of the comparator 317, and a PN code corresponding to the PN code controller 318; And a PN code generator 303 for supplying to the second signal mixers 304 and 305.

Hereinafter, an initial synchronization loop in the receiver of the spread spectrum system of the present invention will be described in detail with reference to the accompanying drawings.

3 is a block diagram of an initial synchronization loop in a receiver of a spread spectrum system of the present invention.

4 is an autocorrelation characteristic curve of a PN code by an initial synchronization loop in a receiver of a spread spectrum system of the present invention.

In the receiver of the spread spectrum system of the present invention shown in FIG. 3, the initial synchronization loop sets the phase of the reference frequency of the local oscillator 310 and the local oscillator 301 to form a reference frequency of 90 degrees (π / 2). PN code generator 303 for forming and outputting the signal shifting means 302 for PN code, and for mixing the reference frequency of the local oscillator 301 and the PN code of the PN code generator 303. The first signal mixer 304 and the second signal mixer 305 for mixing the PN code of the PN code generator 303 with the signal shifted by 90 ° (π / 2) in the signal shifting means 302. And the signal formed by the first signal mixer 304 and the received signal f _1f. DATA A first analog matched filter composed of a third signal mixer 306 for mixing PN, a first low pass filter 307, and a first integrator 308 for integrating the output signal of the filter 307; 309), a signal formed by the first multiplier 314 and the second signal mixer 305 for obtaining an absolute value of the output signal of the first analog matched filter 309 and the received signal f _1f. DATA A second analog matched filter comprising a fourth signal mixer 310 for mixing PN, a second low pass filter 311 and a second integrator 312 for integrating the output signal of the filter 311 313), and outputs two output signals from the second and third substituents 315 and 314 and 3l5 for obtaining the absolute value of the output signal of the second analog matched filter 3l3. The adder 316 and the adder 316 are compared with the next correlation threshold value V _TH of the PN code, and when the threshold value V _TH is greater than the absolute value, " 0 " And a PN code controller 318 for controlling the PN code corresponding to the output of the comparator 317 if the output is small.

In more detail describing the spread spectrum communication system according to the above configuration, the received signal DATA (t) PN (t) COS2πft} is input to the first and second analog matching filters 309 and 313, and the The received signal DATA (t) PN (t) COS2πft input to the first analog match filter 309 is a signal {PN (t + τ) COS (2πft) formed by the first signal mixer 304. + Ψ)} and the third signal mixer 306. In this case, the signal {PN (t + τ) COS (2πft + Ψ)} is a reference signal (COS (2πft + Ψ)) of the local oscillator 301 and the PN code supplied from the PN code generator 303 { PN (t + τ)} is formed by the first signal mixer 304. The signal {PN (t + τ) COS (2πft + Ψ)} formed by the third signal mixer 306 is output through the first low pass filter 307 and the first integrator 308, wherein the process The output signal of the first analog matching filter 309 outputted by the input signal of the received signal {DATA (t) PN (t) COS2πft} and the signal {PN (t + τ) COS (2πft + Ψ)} The magnitude of the autocorrelation value varies according to the COSΨ according to the phase difference between the PN codes, Τ, and the first square 314 is removed to remove the +1 or -1 component of the signal and the signal phase difference (Ψ). The signal of the I-channel is formed by passing.

In the same manner, the received signal {DATA (t) PN (t) COS2πft} input to the second analog matched filter 310 is a signal {PN (t + τ) formed by the second signal mixer 305. SIN (2πft + Ψ)} and the fourth signal mixer 310, where the signal {(N (t + τ) SIN (2πft + Ψ)) is the reference signal CONS of the local oscillator 30l. The signal {SIN (2πft + Ψ)} whose phase of (2πft + Ψ) is shifted by 90 ° (π / 2) and the PN code {PN (t + τ)} supplied from the PN code generator 303 The signal {PN (t + τ) SIN (2πft + Ψ) formed by the second signal mixer 305 and formed by the fourth signal mixer 310 is the second low pass filter 311 and the second. The output signal of the second analog matching filter 313 output through the integrator 312 and output by the process is the received signal {DATA (t) PN (t) COS2πft} and the signal {PN ( The phase difference between the PN codes of t + τ) SIN (2πft + Ψ}, the magnitude of the autocorrelation value according to the value of Τ And a Q channel signal by passing through the second squarer 315 to remove the +1 or -1 component of the signal and the signal phase difference Ψ.

The two signals output from the first and second multipliers 314 and 315 are added by the adder 316 and the added value is the autocorrelation threshold of the PN code input to the comparator 317 by the method. Compared to (V _TH ), "1" is output when the threshold is larger than the absolute value of the signal, and "0" is output when the threshold is smaller. In accordance with the output value of the comparator 317, the output is "1", the PN code (PN (t + τ)), τ is recognized that the initial synchronization made by _c existing between -T _{/ 2} and T _{c / 2} of If the output is " 0 ", since τ exists out of -T _c / 2 and T _c / 2, the PN code controller 318 controls to shift the phase of the PN code by π / 2. The control is repeated until the output of the comparator 317 becomes "1".

In the above description, the output of the third signal mixer 306 is expressed by a formula.

Output of the first low pass filter 307

At this time, when integrating for one period (NT _c ) of the PN code, the DATA (t) is +1 or -1 and COSΨ is independent of t, and the self-payment value of the PN code is R _PN (τ). Denotes the output of the first integrator 309

Output of the first multiplier 314

In addition, the output of the fourth signal mixer 310

Output of the second low pass filter 311

At this time, the output of the second integrator 313

Output of the second squarer 315

Two signals supplied from the first and second squarers 314 and 315,

Signal added and added by the adder 317

This is represented by the PN code autocorrelation characteristic curve by the spread spectrum communication system of the present invention of FIG.

Therefore, in the spread spectrum communication system of the present invention, by using an analog matched filter to simultaneously remove the frequency component and the PN code, the input signal is initially synchronized to despread the spread data, thereby eliminating the carrier signal reproducing means. There is a remarkable effect that simplifies the configuration and makes it possible to extract an undistorted original signal from the disturbing electromagnetic waves.

Claims (4)

A receiving apparatus of a spread spectrum communication system, comprising: a first signal mixer for mixing a reference frequency of a local oscillator and a PN code; A second signal mixer for mixing a PN code and a signal whose phase of the reference frequency of the local oscillator is shifted by 90 ° (π / 2) through a signal shifting means; A first analog matched filter for mixing the signal formed by the first signal mixer and the received input signal and integrating and outputting the mixed signal; A second analog matched filter for mixing the signal formed by the second signal mixer and the received input signal and integrating and outputting the mixed signal; First and second square multipliers for obtaining absolute values of output signals of the first and second analog matching filters; An adder for adding two signals output from the first and second squares; A comparator for comparing and outputting the signal added and supplied from the adder with the autocorrelation threshold value V _TH of the PN code; And a PN code generator for forming a PN code corresponding to the output of the comparator and supplying the PN code to the first and second signal mixers. 2. The apparatus of claim 1, wherein the first analog matched filter comprises: a third signal mixer for mixing a signal formed by the first signal mixer and a received signal; A first low pass filter for filtering the mixed signal; And a first integrator for integrating the output signal of the filter. Here, the output signal of the first analog matched filter is the starch during one period (NT _c ) of the PN code, and the data (t) is +1 or -1 and COSΨ is independent of t. When the autocorrelation value is R _PN (τ), it is represented as 1 / 2DATA (t) COSΨ (τ). 2. The apparatus of claim 1, wherein the second analog matched filter comprises: a fourth signal mixer for mixing a signal formed by the second signal combiner and a received signal; A second low pass filter for filtering the mixed signal; And a second integrator for integrating the output signal of the filter. Here, the output signal of the second analog matched filter is the DATA (t) +1 or -1 at the time of integration for one period (NT _c ) of the PN code, and SINΨ is independent of t. When the correlation value is referred to as R _PN (τ), it is represented by 1 / 2DATA (t) COSΨR _PN (τ). The spread spectrum system of claim 1, wherein the comparator outputs "0" if the signal added and supplied from the adder is larger than the autocorrelation threshold of the PN code, and outputs "1" if the signal is smaller. Initial sync loop for the receiver. Here, the signal output from the adder is represented by 1/4 R _PN ² (τ) when the autocorrelation value of the PN code is R _PN (τ).