CN102064853A - Method for simulating frequency dynamic of radio frequency signal at intermediate frequency by using two DDSs - Google Patents

Abstract

The invention relates to a method for simulating the frequency dynamic of a radio frequency signal at an intermediate frequency by using two direct digital synthesizers (DDSs). The method comprises the following steps of: simplifying the Doppler frequency characteristics of a pseudo code and a carrier in a satellite transmitted signal to form a linear proportional relationship between the output signal frequency of a first DDS for producing a clock signal of a code clock of the pseudo code and the output signal frequency of a second DDS for producing a clock signal of a modulated carrier; performing synchronization control on the output signal frequency of the first DDS and the output signal frequency of the second DDS through frequency control words to dynamically simulate the frequency Doppler of the code clock of the pseudo code and the carrier of an application object; sending an output signal of the first DDS to a spread spectrum transmitter to produce a transmitted pseudo code, and performing spread spectrum modulation on information data by using the transmitted pseudo code to acquire a baseband spread spectrum signal; performing frequency multiplication on an output signal of the second DDS to produce an intermediate frequency carrier signal; and directly modulating the baseband spread spectrum signal by using the intermediate frequency carrier signal to acquire an intermediate frequency signal which contains the required pseudo code and carrier frequency dynamic.

Description

A kind of method that adopts two DDS in intermediate frequency analog radio-frequency signal frequency dynamic

Technical field

The invention belongs to the space flight measurement and control communications field, relate to the method that the two DDS of a kind of usefulness simulate pseudo-code sign indicating number clock and carrier doppler frequency deviation simultaneously.

Background technology

Visual plant based on the space flight measurement and control communication system of spread spectrum is the intermediate frequency digital receiver.The radiofrequency signal of satellite is received by antenna, through low-noise preamplifier, is down-converted to intermediate frequency by the comprehensive local oscillation signal that produces of local oscillator.The Doppler frequency deviation and the pseudo-code information that after optical mixing process, have kept signal, just carrier frequency has reduced, and Doppler frequency deviation still is as the criterion with the Doppler frequency deviation on the original radiofrequency signal.Intermediate-freuqncy signal enters the digital receiver passage and handles after analog-to-digital conversion.The intermediate frequency digital receiver need be finished the catching and following the tracks of of satellite emission signal, and promptly finishes the recovery to pseudo-code and carrier wave.Relative motion meeting between satellite and the receiver makes the carrier frequency of received signal and pseudo-bit rate all have Doppler frequency deviation, in order to test and assess receiver catching and follow-up control signal under Doppler's current intelligence, must manage to make the signal of input receiver to have doppler characterization (comprising pseudo-code and carrier wave), dynamic environment that is virtually reality like reality.

At present, mainly be divided into three major types about Doppler's dynamic Simulation Techniques.

The one, by transmitter and receiver is loaded on the actual vector, carry out the frequency dynamic simulation with the relative motion between carrier.The method needs special place and motion carrier, and is subjected to the influence of actual vector motion control precision, can't simulate the various motion states in the true dynamic environment.

The 2nd, with channel simulator transmitter and receiver is linked to each other and to carry out frequency dynamic simulation.The method is subjected to the restriction of channel simulator simulation precision, can't accurately simulate truly dynamically, and the cost height.

The 3rd, publication number is the Chinese patent application (being disclosed on August 27th, 2008) of CN101252398A, and name is called " spread-spectrum signal source with Doppler analogue function " disclosed a kind of Doppler's Dynamic Simulation Method.This spread-spectrum signal source comprises Doppler's dynamic analog, the layout of data set frame format and intermediate-freuqncy signal modulate emission three parts.Doppler's dynamic analog is partly realized the dynamic analog of processor motion state, from the carrier phase increment derivation carrier wave NCO frequency control word of adjacent moment, generates the carrier wave that comprises Doppler through tabling look-up in conjunction with D/A; From the derive frequency control word of sign indicating number NCO of the pseudo-code phase increment of adjacent moment, produce the sign indicating number clock signal that comprises Doppler in conjunction with D/A through tabling look-up.Intermediate-freuqncy signal frequency in this equipment and pseudo-bit rate all are fixed values, can't produce the pseudo-code signal and the modulated intermediate frequency signal of other frequency flexibly, frequency dynamic that also can't any rf frequency of simulation application object/pseudo-bit rate combination condition.

Summary of the invention

Technology of the present invention is dealt with problems and is: overcome the deficiencies in the prior art, provide a kind of only according to the radio frequency carrier frequency of application and the proportionate relationship of intermediate frequency carrier frequency, just can be by output frequency control, in the method for intermediate frequency analog radio-frequency signal frequency dynamic to two DDS.

Technical solution of the present invention is: a kind of method that adopts two DDS in intermediate frequency analog radio-frequency signal frequency dynamic, and step is as follows:

(1) adopt first Direct Digital Frequency Synthesizers to produce the clock signal that comprises the pseudo-code Doppler frequency deviation, the frequency control word of described first Direct Digital Frequency Synthesizers is

F wherein ₀Be input reference frequency,

f _DcBe the Doppler frequency deviation of pseudo-code, R _cBe pseudo-bit rate, N is the figure place of frequency control word, f _sIt is the sampling clock frequency in first Direct Digital Frequency Synthesizers;

(2) adopt second Direct Digital Frequency Synthesizers to produce the clock signal that comprises the radio-frequency carrier Doppler frequency deviation, the frequency control word of described second Direct Digital Frequency Synthesizers is

F wherein _rBe radio frequency carrier frequency, f _iBe the intermediate frequency Modulation carrier frequency;

(3) output signal of first Direct Digital Frequency Synthesizers is delivered to spread spectrum transmitter and produced the emission pseudo-code, and obtain base-band spread-spectrum signal after utilizing described emission pseudo-code to the information data band spectrum modulation;

(4) produce intercarrier signal after the output signal frequency multiplication with second Direct Digital Frequency Synthesizers;

(5) adopt the intercarrier signal of step (4) that the base-band spread-spectrum signal of step (4) is directly modulated, obtain the dynamic intermediate-freuqncy signal of desired pseudo-code and carrier frequency.

The input parameter of the frequency control word of the frequency control word of described first Direct Digital Frequency Synthesizers or second Direct Digital Frequency Synthesizers comprises control frequency f and FREQUENCY CONTROL precision S, and satisfies relational expression Δ F _Dmax=f * S, wherein Δ F _DmaxIt is the peak frequency doppler changing rate of first Direct Digital Frequency Synthesizers or the second Direct Digital Frequency Synthesizers output signal.

The present invention's advantage compared with prior art is: the present invention adopts the method for two DDS in intermediate frequency analog radio-frequency signal frequency dynamic, the Doppler frequency characteristic of pseudo-code in the satellite emission signal and carrier wave is reduced to the DDS output signal of the clock signal that is used to produce pseudo-code sign indicating number clock and is used to produce the linear ratio relation of DDS output signal frequency of the clock signal of modulated carrier.Simulation precision depends on the FREQUENCY CONTROL precision of DDS, does height easily, and it is easy that parameter is set, use flexibly, cooperate spread spectrum transmitter and intermediate frequency modulator, just can be according to the application requirement, generation has desired pseudo-code and the dynamic modulated intermediate frequency signal of carrier frequency.

Description of drawings

Fig. 1 is the theory diagram of the inventive method;

Fig. 2 is a radio frequency carrier frequency Doppler simulation of the present invention;

Fig. 3 is dynamic by the radio frequency carrier frequency that the ranging receiver tracking receives for the present invention;

Fig. 4 is the radio frequency carrier frequency of the present invention by ranging receiver distance measurement value reflection poor dynamically and between the radio frequency carrier frequency Doppler simulation value;

Fig. 5 is for producing the block diagram of system of the 140MHz intermediate-freuqncy signal that has the carrier doppler frequency deviation in the embodiment of the invention.

Embodiment

The present invention is reduced to a DDS (Direct Digital Synthesizer Direct Digital Frequency Synthesizers) of the clock signal that is used to produce pseudo-code sign indicating number clock with the Doppler frequency characteristic of pseudo-code in the satellite emission signal and carrier wave and is used to produce the linear ratio relation of frequency control word between the 2nd DDS of clock signal of modulated carrier, adopt two DDS to simulate pseudo-code sign indicating number clock and carrier doppler frequency deviation simultaneously, in conjunction with spread-spectrum signal transmitter and intermediate frequency Modulation, just can produce the intermediate-freuqncy signal of analog satellite radiofrequency signal doppler characterization.Principle as shown in Figure 1.By the inventive method, can realize the Doppler simulation of pseudo-code sign indicating number clock frequency and intermediate frequency carrier frequency simultaneously according to concrete application requirements.

Because the Doppler effect that the relative motion between satellite and the receiver causes can be expressed as:

$f_{\mathrm{dr}}=\frac{f_{r}v\left(t\right)}{c}---\left(1\right)$

$f_{\mathrm{dc}}=\frac{R_{c}v\left(t\right)}{c}---\left(2\right)$

In the formula: f _DrAnd f _DcBe respectively the Doppler frequency deviation of radio-frequency carrier and the Doppler frequency deviation of pseudo-code, c is the light velocity, and v (t) is the radially relative velocity between satellite and the receiver, f _rAnd R _cBe respectively the frequency and the pseudo-bit rate of radio-frequency carrier.In same sampling instant, get by formula (1) and formula (2)

$\frac{f_{\mathrm{dr}}}{f_{\mathrm{dc}}}=\frac{f_r}{R_c}---\left(3\right)$

By (3) as can be known, frequency Doppler is directly proportional with signal frequency,

$\frac{f_{d1}}{f_{\mathrm{dc}}}=\frac{f_0}{R_c}$

Promptly the Doppler frequency deviation of a DDS output signal should be:

$f_{d1}=\frac{f_0{f}_{\mathrm{dc}}}{R_c}---\left(4\right)$

In the formula: f ₀Centre frequency for DDS output.

In like manner, the Doppler frequency deviation of the 2nd DDS output signal should be:

${\mathrm{<figure-callout\; id="2"\; label="f\; d"\; filenames="HSA00000328373100021.png"\; state="\{\{state\}\}">f</figure-callout>}}_d=\frac{f_0{f}_{\mathrm{dr}}}{f_i}---\left(5\right)$

Wushu (3) and formula (4) substitution formula (5):

${\mathrm{<figure-callout\; id="2"\; label="f\; d"\; filenames="HSA00000328373100021.png"\; state="\{\{state\}\}">f</figure-callout>}}_d=\frac{f_r{f}_{d1}}{f_i}$

In the formula: f _iBe the intermediate frequency Modulation carrier frequency.This shows that the Doppler frequency deviation of two DDS output signals is the linear ratio relation, and only relevant with the ratio of radio frequency carrier frequency and intermediate frequency carrier frequency.

So a DDS and the 2nd DDS output signal frequency are respectively:

f ₁＝f ₀+f _d1

$f_2=f_0+{\mathrm{<figure-callout\; id="2"\; label="f\; d"\; filenames="HSA00000328373100021.png"\; state="\{\{state\}\}">f</figure-callout>}}_d=f_0+f_{d1}\frac{f_r}{f_i}$

Like this, just can be by in the frequency deviation controlled quentity controlled variable that the superior coefficient of the frequency deviation controlled quentity controlled variable of a DDS is obtained to the 2nd DDS.

In each updated time, the frequency control word FCW1 (n) of a DDS and the frequency control word FCW2 (n) of the 2nd DDS are respectively:

$\mathrm{FCW}1\left(n\right)=f_1\left(n\right)\&times;\frac{2^N}{f_s}=({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HSA00000328373100012.png,HSA00000328373100013.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+f_{d1})\&times;\frac{2^N}{f_s}$

$\mathrm{FCW}2\left(n\right)=f_2\left(n\right)\&times;\frac{2^N}{f_s}=({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HSA00000328373100012.png,HSA00000328373100013.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+f_{d1}\frac{f_r}{f_i})\&times;\frac{2^N}{f_s}$

N is the figure place of DDS frequency control word in the formula, f _sBe the sampling clock frequency in the DDS.

According to the frequency dynamic requirement, the frequency computation part of corresponding each updated time obtains the pseudo-code frequency control word of each updated time and imports a DDS like this, and a DDS is reference with the reference clock signal, and control produces the clock signal that comprises the pseudo-code Doppler frequency deviation.Obtain each updated time carrier frequency control word according to the scale factor between rf frequency and the IF-FRE and import the 2nd DDS, the 2nd DDS is reference with the reference clock signal, and control produces the clock signal that comprises the carrier doppler frequency deviation.

The clock signal input spread spectrum transmitter that comprises the pseudo-code Doppler frequency deviation of the one DDS output, mode by frequency division produces the sign indicating number clock that comprises the pseudo-code Doppler frequency deviation, the sign indicating number clock produces the emission pseudo-code by the mode that drives the sign indicating number generator polynomial or look into code table, and the emission pseudo-code obtains base-band spread-spectrum signal after to the information data band spectrum modulation.Produce intercarrier signal after the clock signal frequency multiplication that comprises the carrier doppler frequency deviation with DDS2 output, the base-band spread-spectrum signal after the spread spectrum transmitter band spectrum modulation is directly modulated, finally obtain the intermediate-freuqncy signal that pseudo-code and carrier wave all have doppler characterization.

The simulation of frequency dynamic should satisfied under the situation of simulation precision, guarantees the continuity that output signal frequency changes, avoid owing to the signal frequency sudden change that produces causes the receiver losing lock, the control frequency of DDS is wanted high, and frequency step is little, and it is high that FREQUENCY CONTROL resolution is wanted.According to the centre frequency of rf frequency and the IF-FRE and the DDS of application, the dynamic analog of radio-frequency carrier is required (to comprise frequency Doppler excursion F _MaxWith peak frequency doppler changing rate Δ F _Max) the dynamic analog characteristic that is converted to the DDS output signal frequency (comprises frequency Doppler excursion F _DmaxWith peak frequency doppler changing rate Δ F _Dmax), the dynamic analog characteristic will satisfy

ΔF _Dmax＝f×S

Wherein f is the control frequency, and S is the frequency step (the FREQUENCY CONTROL precision is generally got less than 1mHz) of DDS, so the FREQUENCY CONTROL frequency

$f=\frac{\mathrm{\&Delta;}{F}_{D\max }}{S}$

Need consider the performance of DDS device during actual the use.

Based on the actual application requirements, based on FREQUENCY CONTROL to two DDS, the inventive method has realized comprising uniform rectilinear motion model, and (Doppler frequency is fixed, can be provided with as required), the uniformly accelrated rectilinear motion model (fix by the Doppler frequency rate of change, can be provided with as required) and become the simulation of quickening rectilinear motion model (Doppler frequency sinusoidal variations, frequency range and cycle can be provided with).Fig. 2, Fig. 3, Fig. 4 have provided radio-frequency carrier Doppler frequency sinusoidal variations in ± 5kHz respectively, the radio frequency carrier frequency Doppler simulation curve the when cycle is 70 seconds, follow the tracks of the radio-frequency carrier Doppler that receives and between the two poor with ranging receiver.Doppler frequency that transmits and the actual dynamic frequency value of resolving of following the tracks of of receiver that simulation produces are compared.Sine wave curve amplitude among Fig. 2 is 5kHz, cycle is 70 seconds, be the dynamic theoretical modeling of radio frequency carrier frequency, curve among Fig. 3 is for receiving the intermediate-freuqncy signal that this method produces with ranging receiver, and find range, extrapolating the radio-frequency carrier Doppler who traces into from the variation of distance measurement value and change, Fig. 4 is the poor of dynamic analog value and actual tracking results, as can be seen from Figure 4, radio frequency carrier frequency Doppler tracking error is in 10Hz.This shows that the dynamic characteristic that transmits that produces based on the FREQUENCY CONTROL to two DDS is consistent with the Doppler frequency deviation of Theoretical Calculation.

Embodiment

The 140MHz intermediate-freuqncy signal that has a carrier doppler frequency deviation with generation is that example describes below.

As shown in Figure 5, related system is made up of man-machine interface unit, DDS1, DDS2, spread spectrum transmitter and intermediate frequency modulator.According to dynamic analog requirement and radio frequency/intermediate frequency frequency frequency parameter and DDS proportionality coefficient are set in the man-machine interface unit, produce corresponding frequency dynamic model, calculate the frequency control word of 10MHz frequency, the frequency control word 1 control DDS1 that the man-machine interface unit produces is reference with input 10MHz signal, the comprehensive 10MHz signal that has the pseudo-code Doppler frequency deviation that produces.While is according to the linear relationship of carrier frequency and pseudo-bit rate, carry out carrier frequency Doppler's simulation process: the frequency control word that calculates the 10MHz frequency, the frequency control word 2 control DDS2 that the man-machine interface unit produces are reference with input 10MHz signal, the comprehensive 10MHz signal that has the carrier doppler frequency deviation that produces.

DDS adopts the digital frequency synthesizer AD9852 filter joint of AD company to realize.Filter is determined bandwidth according to the output signal frequency scope.

In the present embodiment, the control frequency of DDS is no less than 20000 times/second, minimum step is less than 1mHz, and FREQUENCY CONTROL resolution is better than 0.1mHz.The little dynamic change of analog frequency, 10MHz signal frequency rate of change is less than 1mHz/ second; The big dynamic change of analog frequency, simulation 10MHz signal frequency rate of change that can be level and smooth is greater than 20Hz/s.The frequency word quantified precision is up to 48 bits and quantizes.

Aspect circuit design, the circuit design unanimity of two DDS.In addition, for guaranteeing the corresponding relation of pseudo-code Doppler and carrier doppler, control two DDS simultaneously.

The 10MHz signal input spread spectrum transmitter that comprises pseudo-code Doppler of DDS1 output produces the 5MHz sign indicating number clock that comprises Doppler, is used for producing the emission pseudo-code, and the emission pseudo-code obtains base-band spread-spectrum signal after to the data band spectrum modulation.With producing the 140MHz intercarrier signal after 10MHz signal 14 frequencys multiplication that comprise carrier doppler of DDS2 output, base-band spread-spectrum signal is directly modulated, finally obtain the 140MHz intermediate-freuqncy signal that pseudo-code and carrier wave all have doppler characterization.

The content that is not described in detail in the specification of the present invention belongs to those skilled in the art's known technology.

Claims (2)

1. method that adopts two DDS in intermediate frequency analog radio-frequency signal frequency dynamic is characterized in that step is as follows:

(1) adopt first Direct Digital Frequency Synthesizers to produce the clock signal that comprises the pseudo-code Doppler frequency deviation, the frequency control word of described first Direct Digital Frequency Synthesizers is

F wherein ₀Be input reference frequency,

f _DcBe the Doppler frequency deviation of pseudo-code, R _cBe pseudo-bit rate, N is the figure place of frequency control word, f _sIt is the sampling clock frequency in first Direct Digital Frequency Synthesizers;

(2) adopt second Direct Digital Frequency Synthesizers to produce the clock signal that comprises the radio-frequency carrier Doppler frequency deviation, the frequency control word of described second Direct Digital Frequency Synthesizers is

F wherein _rBe radio frequency carrier frequency, f _iBe the intermediate frequency Modulation carrier frequency;

(3) output signal of first Direct Digital Frequency Synthesizers is delivered to spread spectrum transmitter and produced the emission pseudo-code, and obtain base-band spread-spectrum signal after utilizing described emission pseudo-code to the information data band spectrum modulation;

(4) produce intercarrier signal after the output signal frequency multiplication with second Direct Digital Frequency Synthesizers;

(5) adopt the intercarrier signal of step (4) that the base-band spread-spectrum signal of step (4) is directly modulated, obtain the dynamic intermediate-freuqncy signal of desired pseudo-code and carrier frequency.

2. a kind of method that adopts two DDS in intermediate frequency analog radio-frequency signal frequency dynamic according to claim 1, it is characterized in that: the input parameter of the frequency control word of the frequency control word of described first Direct Digital Frequency Synthesizers or second Direct Digital Frequency Synthesizers comprises control frequency f and FREQUENCY CONTROL precision S, and satisfies relational expression Δ F _Dmax=f * S, wherein Δ F _DmaxIt is the peak frequency doppler changing rate of first Direct Digital Frequency Synthesizers or the second Direct Digital Frequency Synthesizers output signal.

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