CN100468989C - Method for adapting single frequency net in digital broadcasting satellite system - Google Patents

Abstract

The method regulates the carrier frequency (CF) of all emitters in the satellite broadcast system (SBS) to the same frequency point. Emitters send the broadcast signal on the same CF. this realizes a large range seamless cover in SBS, i.e. the single frequency net cover. The steps to realize are: according to the hi-precision clock signal generated by the clock source, producing a standard frequency signal; mixing the satellite down-going signal with this standard signal to obtain the baseband signal carrying the frequent difference (FD); the FD estimator estimates FD residing in the baseband signal; according to this estimation, producing the mid-frequency signal (MFS) on suitable frequencies; carrying out RF up-conversion for MFS so as to produce the satellite up-going signal (SUS); The satellite carries out frequency conversion and amplification for SUS to produce the satellite down-going signal. Cycling above steps realizes synchronization of satellite broadcast net frequency.

Description

The method for adapting single frequency net of digital broadcasting satellite system

Technical field

The present invention relates to digital information transmission technical, relate in particular to the method for in the digital satellite broadcasting single frequency network, each carrier of transmitter frequency being adjusted to identical frequency.

Background technology

Digital broadcasting has characteristics such as broad covered area, signal volume are big, and its maximum characteristics are to have broadcasting, and a bit to multiple spot, point-to-area, and what of the cost of broadcast message and number of users have nothing to do.Therefore, digital broadcasting has critical role as an important component part of ICT industry in national information infrastructure construction, realization universal service and national information security strategy.

For digit broadcasting system, owing to have powerful antijamming capability and digital processing ability, single frequency network is the very favorable mode that covers that enlarges.Single frequency network is one of present satellite digital broadcasting system three kinds of main paties of expanding the coverage area, promptly in certain geographic area, with some transmitters simultaneously according to the same broadcast singal of identical transmit frequency, so that realize reliable seamless covering in this zone.Single frequency network allows the overlapping of the area of coverage, has improved the cliff effect that multiple frequency network, MFN covers the edge greatly, helps improving covering quality and expands the coverage area.

Most important technology during single frequency network is used, the signal that requires each transmitter to broadcast exactly all keeps synchronous in frequency with on the time.Frequency Synchronization promptly requires the operating frequency of each single frequency network transmitter all identical.For multi-carrier modulation, also require the frequency of each subcarrier identical.Though Frequency Synchronization can be by realizing with same reference frequency (the general 10MHz reference frequency of using from gps satellite) is phase-locked synchronously.But because the free oscillation frequency of each transmitter is difficult to reach identical, thus need a kind of method of design, in order to each carrier of transmitter frequency is adjusted to identical frequency.

Summary of the invention

For solving the technical problem that prior art proposes, the objective of the invention is to propose a kind of method for adapting single frequency net of digital broadcasting satellite system, be used for each carrier of transmitter frequency is adjusted to identical frequency, this method may further comprise the steps:

Generate the clock signal in clock source; According to the clock source clock signal that is generated, generate reference frequency; Downward signal of satellite and described reference frequency are carried out mixing, obtain having the baseband signal of frequency deviation; According to frequency offset estimating, estimate the frequency departure between downward signal of satellite and the described reference frequency to described baseband signal; Intermediate-freuqncy signal according to described frequency departure generation; Intermediate-freuqncy signal is carried out RF up-converter, generate satellite uplink signal; By satellite described satellite uplink signal is carried out frequency conversion and amplification, generate downward signal of satellite; Above step is carried out in circulation, thus realize to network synchronously.

The method for adapting single frequency net of the digital broadcasting satellite system that the present invention proposes compensates frequency errors at different levels by the output frequency that changes described exciter, and introduces known random signal in satellite-signal, is used for frequency offset estimating.In frequency offset estimating, frequency offset estimator uses relevant mode to realize the mark frequency offset estimating, uses the mode of frequency sweep to realize the integer frequency bias estimation.

Said method of the present invention is by closed-loop fashion control downward signal of satellite frequency, so have higher Frequency Synchronization precision; Simultaneously, the frequency of each transmitter all locks onto on the reference frequency, can guarantee the frequency accuracy of the whole network by the precision that guarantees reference frequency.

The system that is used to realize this method can flexible configuration, single or a plurality of satellites of may command, and inter-satellite is separate, does not have any interference, can flexible Application in single frequency network of only forming by satellite and the single frequency network of forming jointly by satellite and land-based repeaters.

Description of drawings

Fig. 1 is the digital broadcasting satellite system method for adapting single frequency net flow chart of first embodiment of the invention;

Fig. 2 is the mark frequency offset estimating flow chart of the digital broadcasting satellite system method for adapting single frequency net of first embodiment of the invention;

Fig. 3 is that the integer frequency bias of the digital broadcasting satellite system method for adapting single frequency net of first embodiment of the invention is estimated flow chart;

Fig. 4 is the digital broadcasting satellite system method for adapting single frequency net flow chart of being made up of two satellites of second embodiment of the invention.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described in further detail.

Fig. 1 is the digital broadcasting satellite system method for adapting single frequency net flow chart of first embodiment of the invention.The digital broadcasting satellite system of realizing this method comprises satellite and ground transmitter, the carrier signal tranmitting frequency of ground transmitter is locked on the reference frequency 2647.5MHz, the closed-loop control of this method by hereinafter described also is locked in the frequency of downward signal of satellite on the 2647.5MHz.

Adopt atomic clock as the clock source in the present embodiment, the clock signal frequency of its generation is 10MHz, generated frequency is the reference frequency signal of 2647.5MHz after the frequency multiplication that this clock signal process reference frequency maker is 264.75 times, and this signal is a sine wave signal in the present embodiment:

$f_0\left(t\right)=e^{j2\mathrm{\π}{f}_{\mathrm{ST}}t}---\left(1\right)$

F wherein _ST=2647.5MHz.

At this moment, generate satellite baseband signal f by exciter _S(t), wherein comprise the identical time domain random sequence of two neighboring sections signal PN (t), sequence time length is T.Simultaneously, exciter is also with this baseband signal f _S(t) be transformed to intermediate-freuqncy signal:

$f_{\mathrm{IF}}\left(t\right)=f_S\left(t\right)\·e^{j2\mathrm{\π}(f_1-\mathrm{\Δf})t}---\left(2\right)$

F wherein _IBe that nominal value is the intermediate frequency of 70MHz, Δ f is the frequency departure compensation.

Subsequently, by radio-frequency-up-converter to this intermediate-freuqncy signal f _IF(t) carry out up-conversion, obtain the satellite uplink signal that centre frequency is 14000MHz:

$f_{\mathrm{UP}}\left(t\right)=f_{\mathrm{IF}}\left(t\right)\·e^{j2\mathrm{\π}{f}_{U}t}---\left(3\right)$

F wherein _UBe that nominal value is the frequency of the up-conversion of 13930MHz.

Then, this satellite uplink signal f of receiving of satellites coupling _UP(t) carry out frequency conversion and amplification, obtain the downward signal of satellite that nominal frequency is 2647.5MHz:

$f_{\mathrm{DN}}\left(t\right)=f_{\mathrm{UP}}\left(t\right)\·e^{j2\mathrm{\π}{f}_{\mathrm{SAT}}t}---\left(4\right)$

F wherein _SATBe that nominal value is-frequency of the satellite down-conversion of 11352.5MHz.

Owing to each equipment in the system is being made the frequency departure that causes and in use owing to aging and temperature such as float at the frequency departure that reason causes, above-mentioned nominal frequency f _I, f _U, f _SATBe difficult to have accurate nominal value, cause the downstream signal of satellite can not accurately remain on the nominal frequency of 2647.5Mhz, therefore need adjust system.

Earlier downward signal of satellite and reference frequency signal are carried out mixing, obtain by frequency mixer:

$f_{\mathrm{MIX}}\left(t\right)=f_{\mathrm{DN}}\left(t\right)\&CenterDot;{\mathrm{<figure-callout\; id="0"\; label="f"\; filenames="C200610086592E00102.png"\; state="\{\{state\}\}">f</figure-callout>}}_0^{*}\left(t\right)=f_{\mathrm{DN}}\left(t\right)\&CenterDot;e^{-j2\mathrm{\&pi;}{f}_{\mathrm{ST}}t}---\left(5\right)$

Wherein

Be f ₀(t) conjugation.

Because above-mentioned f _I, f _U, f _SATInaccuracy, so f _MIX(t) center frequency point is not 0, but Δ f, just each environment division frequency departure of accumulating out.

Extract two continuous random sequence PN the signal of frequency offset estimator after mixing ₁And PN ₂When the systematic sampling rate is f _PThe time, random sequence comprises M=T/f _PIndividual sampled point.Frequency offset estimation procedure is as follows:

1. mark frequency offset estimating

At first calculate the correlation function of two random sequences:

$\mathrm{Corr}={\mathrm{\&Sigma;}}_{k=0}^{M-1}{\mathrm{PN}}_2\left(k\right)\&CenterDot;{\mathrm{<figure-callout\; id="1"\; label="PN"\; filenames="C200610086592E00101.png,C200610086592E00102.png"\; state="\{\{state\}\}">PN</figure-callout>}}_1^{*}\left(k\right)---\left(6\right)$

Pass through then

Δf _Frac＝arctan(imag(Corr)，real(Corr))×f _P/(2π×M) (7)

Estimate mark frequency deviation Δ f _FracImag (Corr) wherein, real (Corr) is respectively real part and the imaginary part of Corr, arctan () is an arctan function.This mark frequency offset estimating flow process as shown in Figure 2.

2. integer frequency bias is estimated

The scope of mark frequency offset estimating is | Δ f _Frac|≤f _s/ (2 * M), when carrier wave frequency deviation is not within this scope, just need carries out integer frequency bias and estimate.

At first according to the f of Δ as a result of mark frequency offset estimating _Frac, the mark frequency deviation of correcting the random sequence signal:

${\mathrm{<figure-callout\; id="1"\; label="PN"\; filenames="C200610086592E00101.png,C200610086592E00102.png"\; state="\{\{state\}\}">PN</figure-callout>}}_1^{\&prime;}\left(k\right)={\mathrm{PN}}_1\left(k\right)\&times;e^{-j2\mathrm{\&pi;}\frac{\mathrm{\&Delta;}{f}_{\mathrm{Frac}}}{f_P}k},k=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,M-1---\left(8\right)$

Then local PN sequence is carried out the frequency deviation adjustment:

${\mathrm{PN}}_{L,n}\left(k\right)={\mathrm{PN}}_L\left(k\right)*e^{-j2\mathrm{\&pi;}\frac{n{f}_{E}k}{f_P}},k=\mathrm{0,1},\&CenterDot;\&CenterDot;\&CenterDot;,M-1,n=-\max ,-\max +1,......,\max -1,\max ---\left(9\right)$

Wherein, PN _L(k) be local long synchronizing sequence, f _EBe integer frequency bias frequency sweep precision, and f _E=f _P/ M, max are the integer frequency bias swept frequency ranges.

Behind the mark correcting frequency deviation Carry out cross-correlation with the adjusted local PN sequence of integer frequency bias, and ask mould square:

${\left|Q\left(n\right)\right|}^2={\left|{\mathrm{\&Sigma;}}_{k=0}^{M-1}|{\mathrm{<figure-callout\; id="1"\; label="PN"\; filenames="C200610086592E00101.png,C200610086592E00102.png"\; state="\{\{state\}\}">PN</figure-callout>}}_1^{\&prime;}\left(k\right)*{\mathrm{PN}}_{L,n}\left(k\right)|\right|}^2---\left(10\right)$

| Q (n) | ²N correspondence when maximum integer frequency bias:

Δf _Int＝f _E·N (11)

This integer frequency bias is estimated flow process as shown in Figure 3.

Obtain total frequency deviation value by said process

Δf＝Δf _Frac+Δf _Int (12)

At last the above-mentioned frequency deviation value Δ f that estimates is sent into the IF spot of exciter, thereby realize closed-loop control the downward signal of satellite frequency with change output.

Fig. 4 is the digital broadcasting satellite system method for adapting single frequency net flow chart of being made up of two satellites of second embodiment of the invention.The method of second embodiment of the invention realizes that by the digital broadcasting satellite system that two satellites are formed the clock source in this system is a gps clock, and two closed-loop control system structures shown in the figure are identical, and shared same reference frequency.Two loop courses of work are identical with the loop of first embodiment, but work alone separately, are locked on the reference frequency, therefore each other without any interference.

The present invention is not limited to above-mentioned particular implementation example; do not deviating under spirit of the present invention and the real situation thereof; skilled personnel can make various corresponding changes and distortion according to the present invention, but these corresponding changes and distortion all should belong within the claims protection range of the present invention.

Claims (5)

1, a kind of method for adapting single frequency net of digital broadcasting satellite system may further comprise the steps:

Generate the clock signal in clock source;

According to the clock source clock signal that is generated, generate reference frequency signal;

Downward signal of satellite and described reference frequency signal are carried out mixing, obtain having the baseband signal of frequency deviation;

According to frequency offset estimating, estimate the frequency departure between downward signal of satellite and the described reference frequency signal to described baseband signal;

According to described frequency departure, produce the adjusted intermediate-freuqncy signal of frequency departure;

Described intermediate-freuqncy signal is carried out RF up-converter, generate satellite uplink signal;

By satellite described satellite uplink signal is carried out frequency conversion and amplification, generate downward signal of satellite;

Above step is carried out in circulation, thus realize to network synchronously.

2, the method for claim 1 is characterized in that, it compensates frequency errors at different levels by adjustment and the change to described intermediate-freuqncy signal.

3, the method for claim 1 is characterized in that, it introduces known random signal in satellite-signal, be used for frequency offset estimating.

4, the method for claim 1 is characterized in that, realizes the mark frequency offset estimating with relevant mode in frequency offset estimating.

5, the method for claim 1 is characterized in that, the mode with frequency sweep in frequency offset estimating realizes the integer frequency bias estimation.

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