CN102064853B - 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 couple DDS that adopt are in the method for intermediate frequency analog radio-frequency signal frequency dynamic

Technical field

The invention belongs to the Space TT﹠C field, relate to the method that the two DDS of a kind of usefulness simulate pseudo-code code clock and carrier doppler frequency deviation simultaneously.

Background technology

Visual plant based on the TT ﹠ C Telecommunication of spread spectrum is intermediate frequency digital receiver.The radiofrequency signal of satellite through low-noise preamplifier, is down-converted to intermediate frequency by the comprehensive local oscillation signal that produces of local oscillator by antenna reception.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 processes after analog-to-digital conversion.Intermediate frequency digital receiver need to be finished the catching and following the tracks of of satellite emission signal, and namely finishes the recovery to pseudo-code and carrier wave.Relative motion meeting between satellite and the receiver makes the carrier frequency that receives signal and pseudo-bit rate all with 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 impact of actual vector motion control precision, the various motion states in can't the Reality simulation dynamic environment.

The 2nd, with channel simulator transmitter and receiver is linked to each other to carry out the frequency dynamic simulation.The method is subjected to the restriction of channel simulator simulation precision, and accurately Reality simulation is dynamic, and cost is high.

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 framing 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 code NCO of the pseudo-code phase increment of adjacent moment, produce the code clock signal that comprises Doppler through tabling look-up in conjunction with D/A.Intermediate-freuqncy signal frequency in this equipment and pseudo-bit rate all are fixed values, can't produce flexibly pseudo-code signal and the modulated intermediate frequency signal of other frequency, 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 the output frequency control to two DDS, in the method for intermediate frequency analog radio-frequency signal frequency dynamic.

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

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

(2) adopt the 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 the 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 the 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 the 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 the first Direct Digital Frequency Synthesizers or the 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 the 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 two DDS in the method for intermediate frequency analog radio-frequency signal frequency dynamic, is for generation of the DDS output signal of the clock signal of pseudo-code code clock and for generation of the linear ratio relation of the DDS output signal frequency of the clock signal of modulated carrier with the Doppler frequency characteristics simplified of pseudo-code in the satellite emission signal and carrier wave.Simulation precision depends on the FREQUENCY CONTROL precision of DDS, easily does height, and parameters is easy, use flexibly, cooperate spread spectrum transmitter and intermediate frequency modulator, just can according to the application requirement, produce with 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 radio frequency carrier frequency Doppler simulation of the present invention;

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

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

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

Embodiment

The present invention with the Doppler frequency characteristics simplified of pseudo-code in the satellite emission signal and carrier wave be for generation of the clock signal of pseudo-code code clock a DDS (Direct Digital Synthesizer Direct Digital Frequency Synthesizers) and for generation of the linear ratio relation of frequency control word between the 2nd DDS of the clock signal of modulated carrier, adopt two DDS to simulate simultaneously pseudo-code code clock and carrier doppler frequency deviation, 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 simultaneously according to concrete application requirements the Doppler simulation of pseudo-code code clock frequency and intermediate frequency carrier frequency.

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 frequency and the pseudo-bit rate of radio-frequency carrier.In same sampling instant, got 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,

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

Namely 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, 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 the frequency of a DDS and the 2nd DDS output signal is 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:

$\mathrm{FCW}1\left(n\right)=f_1\left(n\right)\&times;\frac{2^N}{f_s}=({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HSA00000328373100013.png,HSA00000328373100021.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+f_{d1})\&times;\frac{2^N}{f_s}$

$\mathrm{FCW}2\left(n\right)=f_2\left(n\right)\&times;\frac{2^N}{f_s}=({\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="HSA00000328373100013.png,HSA00000328373100021.png"\; state="\{\{state\}\}">f</figure-callout>}}_0+f_{d1}\frac{f_r}{f_i})\&times;\frac{2^N}{f_s}$

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 inputs a DDS like this, and a DDS is take reference clock signal as reference, 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 input the 2nd DDS, the 2nd DDS is take reference clock signal as reference, 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 code clock that comprises the pseudo-code Doppler frequency deviation, the code clock produces the emission pseudo-code by the mode that drives the code 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 be in the situation that satisfy simulation precision, the continuity that the assurance 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 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 to consider the DDS performance of devices during actual the use.

Based on the actual application requirements, based on the FREQUENCY CONTROL to two DDS, the inventive method has realized comprising uniform rectilinear motion model, and (Doppler frequency is fixed, can arrange as required), the uniformly accelrated rectilinear motion model (fix by Algorithm for Doppler Frequency Rate-of-Change, can arrange as required) and become the simulation of accelerating rectilinear motion model (Doppler frequency sinusoidal variations, frequency range and cycle can arrange).Fig. 2, Fig. 3, Fig. 4 have provided respectively radio-frequency carrier Doppler frequency sinusoidal variations in ± 5kHz, 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.The 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 to receive the intermediate-freuqncy signal that the 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, the dynamic characteristic that transmits that produces based on the FREQUENCY CONTROL to two DDS is consistent with the theoretical Doppler frequency deviation that calculates.

Embodiment

The below describes as example to produce with the 140MHz intermediate-freuqncy signal of carrier doppler frequency deviation.

As shown in Figure 5, related system is comprised of human-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 human-machine interface unit, produce corresponding frequency dynamic model, calculate the frequency control word of 10MHz frequency, the frequency control word 1 control DDS1 that human-machine interface unit produces is take input 10MHz signal as reference, and comprehensive generation is with the 10MHz signal of pseudo-code Doppler frequency deviation.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 human-machine interface unit produces are take input 10MHz signal as reference, and comprehensive generation is with the 10MHz signal of carrier doppler frequency deviation.

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

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 large 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 of two DDS is consistent.In addition, for guaranteeing the corresponding relation of pseudo-code Doppler and carrier doppler, control simultaneously two DDS.

The 10MHz signal input spread spectrum transmitter that comprises pseudo-code Doppler of DDS1 output produces the 5MHz code clock that comprises Doppler, and for generation of the emission pseudo-code, 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. one kind is adopted two DDS in the method for intermediate frequency analog radio-frequency signal frequency dynamic, it is characterized in that step is as follows:

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

(2) adopt the 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 the 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 the 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 the second Direct Digital Frequency Synthesizers;

(5) adopt the intercarrier signal of step (4) that the base-band spread-spectrum signal of step (3) is directly modulated, obtain the dynamic intermediate-freuqncy signal of desired pseudo-code and carrier frequency.

2. a kind of couple DDS that adopt according to claim 1 are in the method for intermediate frequency analog radio-frequency signal frequency dynamic, it is characterized in that: the input parameter of the frequency control word of the frequency control word of described the first Direct Digital Frequency Synthesizers or the 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 the first Direct Digital Frequency Synthesizers or the second Direct Digital Frequency Synthesizers output signal.

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