CN1674450A - Analog modulation carrier interference eliminating method in on-band co-channel digital audio frequency broadcasting - Google Patents

Abstract

The present invention relates to an analog modulation carrier interference removing method in in-band co-channel digital audio-frequency broadcast. Said method includes the following steps: 1). receiving compound signal, said compound signal is formed from analog-modulated single-carrier signal and several digitally-modulated subcarrier signals; 2). amplitude normalization of received compound signal, 3). multiplying received compound signal by conjugate of normalized compound signal to obtain module value of received actual signal; 4). low-pass filtering received actual signal module value to obtain carrier amplitude estimation signal, delaying said module value to produce delayed actual signal module value, and extracting the difference value of delayed actual signal module value and carrier amplitude estimation signal; and 5). multiplying the above-mentioned module value, difference value and normalized compound signal to obtain digitally-modulated subcarrier signal whose signal interference is removed.

Description

Analog-modulated ici cancellation methods in the in-band on-channel digital audio broadcasting

Technical field

The present invention relates to analog-modulated ici cancellation methods in the interior a kind of in-band on-channel digital audio broadcasting of digital processing field.

Background technology

Digital audio broadcasting (DAB) is a kind of digital mode multiple carrier wireless transmission system, and it has adopted advanced digital processing new technology to realize the transmission of wireless channel signal.Compare the advantage that DAB has extremely strong multipath fading inhibition ability, advanced person's error-correcting performance, class compact disc (CD) tonequality, power system capacity is big and wide coverage etc. given prominence to traditional analog broadcasting.Because broadcasting only takies limited frequency resource, DAB has caused the different standard of DAB to the different occupancy modes of frequency resource: with the European Eureka-147 DAB dedicated frequency standard that is representative with American I BOCDAB is in-band on-channel (IBOC) standard of representative.

Same carrier frequencies is used in IBOC DAB and current analog broadcasting radio station of using, and relies on the different of frequency separation and modulation system, with broadcasting analog-and digital-two kinds of programs.The employed frequency range of FM audio broadcasting is to realize the desirable frequency range of DAB.As shown in Figure 1, FM IBOC DAB system is placed on digital signal (comprising audio service and data service) in the frequency band identical with simulating the FM signal, realizes that the analog signal of same FM broadcast program and digital signal mix with broadcasting.

A large amount of simulation and the analysis showed that works in digital sidebands DAB signal among the FM IBOC DAB of mixing (Hybrid) pattern when the main FM centre frequency 129kHz of simulation is between 197kHz, and it is simulated main FM performance impact minimum.But the interference between the adjacent channel but always exists, especially first interference of facing channel, as shown in Figure 2.

Studies show that, cut apart and the geographic layout optimization that then can not occur simultaneously ± interference of 200KHz first adjacent channel, this just can guarantee to have at least a sideband not disturbed by it in the frequency diversity transmission if guarantee the channel in radio station.

In the FM IBOCDAB receiver system as shown in Figure 3, after the signal (comprising analog-modulated carrier wave and digital side frequency signal) that receives is handled through radio-frequency front-end processing, Frequency mixing processing, intermediate frequency filtering and separator, produce analog-modulated carrier wave and digital band signal (after A/D conversion and Digital Down Convert), enter corresponding analog circuitry processes module and digital signal circuit processing module then respectively and handle accordingly, still have the interference of analog-modulated carrier wave in the digital band signal after still separating.

Summary of the invention

The object of the present invention is to provide analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting, it is mainly used in the analog-modulated carrier signal of eliminating in the in-band on-channel digital audio broadcasting and disturbs.

Analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting of the present invention, at in-band on-channel digital audio broadcasting receiving terminal, the composite signal that receives is handled through radio-frequency front-end, Frequency mixing processing, after intermediate frequency filtering and separator are handled, produce analog-modulated carrier wave and digital band signal after A/D conversion and Digital Down Convert, entering corresponding analog circuitry processes module and digital signal circuit processing module then respectively handles accordingly, but still there is the interference of analog-modulated carrier wave in the digital band signal after separating, it is characterized in that, comprise the steps:

1) receives composite signal, receive composite signal and form by analog-modulated single-carrier signal and a plurality of digital modulation subcarrier signal;

2) butt joint is recovered and to be closed signal and carry out amplitude normalization and handle, and normalized composite signal equals to receive the value that composite signal and the absolute value that receives composite signal are divided by;

3) will receive the conjugate multiplication of composite signal and normalized composite signal, obtain receiving the mould value of real signal;

4) the mould value that will receive real signal is carried out low-pass filtering, produces the carrier amplitude estimated signal; The mould value of real signal is postponed, produce the real signal mould value that postpones; Ask for the real signal mould value of delay and the difference of carrier amplitude estimated signal;

5) with the difference of the real signal mould value that postpones and carrier amplitude estimated signal and delayed after the normalization composite signal multiply each other, eliminated the digital modulation subcarrier signal of analog carrier signal interference.

Wherein receiving composite signal is made up of analog-modulated single-carrier signal and a plurality of digital modulation subcarrier signal.

The value that the absolute value that wherein normalized composite signal equals to receive composite signal and receive composite signal is divided by.

Wherein will receive the conjugate multiplication of composite signal and normalized composite signal, obtain receiving the mould value of real signal.

The difference of wherein asking for the two comprises the steps:

A) the mould value that receives real signal is carried out low-pass filtering, produces the carrier amplitude estimated signal;

B) the mould value with real signal postpones, and produces the real signal mould value that postpones;

C) ask for the real signal mould value of delay and the difference of carrier amplitude estimated signal.

Wherein with the difference of the real signal mould value that postpones and carrier amplitude estimated signal and delayed after the normalization composite signal multiply each other, eliminated the digital modulation subcarrier signal of analog carrier signal interference.

Description of drawings

For further specifying technology contents of the present invention, below in conjunction with first facing that channel analog-modulated carrier-in-interference is eliminated (FAC) embodiment and accompanying drawing is described in detail as follows among the FM IBOC DAB, wherein:

Fig. 1 is the power spectrum of mixed mode in-band on-channel digital audio broadcasting signal.Wherein, the triangle that dotted line is represented is the frequency spectrum of simulation FM signal, and the solid-line rectangle on FM both sides is represented DAB numeral side frequency.

Fig. 2 is based on the disturbed condition of first adjacent channel that channel spacing is the 200kHz system (apart from main FM centre frequency+200kHz place, dotted portion) for main FM channel (solid line);

Fig. 3 is an in-band on-channel digital audio broadcast receiver theory diagram;

Fig. 4 is an analog-modulated ici cancellation methods flow chart in the in-band on-channel digital audio broadcasting of the present invention.

Embodiment

See also Fig. 4, the present invention relates to analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting, at in-band on-channel digital audio broadcasting receiving terminal, the composite signal (comprising analog-modulated carrier wave and digital side frequency signal) that receives is handled through radio-frequency front-end, Frequency mixing processing, after intermediate frequency filtering and separator are handled, produce analog-modulated carrier wave and digital band signal (after A/D conversion and Digital Down Convert), entering corresponding analog circuitry processes module and digital signal circuit processing module then respectively handles accordingly, but still have the interference of analog-modulated carrier wave in the digital band signal after separating, the present invention is mainly used in and eliminates the analog-modulated carrier-in-interference in this co-channel digital audio broadcasting in the band.

Analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting is characterized in that, comprises the steps:

1) receives composite signal, receive composite signal and form by analog-modulated single-carrier signal and a plurality of digital modulation subcarrier signal; Wherein receiving composite signal is made up of analog-modulated single-carrier signal and a plurality of digital modulation subcarrier signal;

2) butt joint is recovered and to be closed signal and carry out amplitude normalization and handle, and normalized composite signal equals to receive the value that composite signal and the absolute value that receives composite signal are divided by; The value that the absolute value that wherein normalized composite signal equals to receive composite signal and receive composite signal is divided by.

3) will receive the conjugate multiplication of composite signal and normalized composite signal, obtain receiving the mould value of real signal; Wherein will receive the conjugate multiplication of composite signal and normalized composite signal, obtain receiving the mould value of real signal.

4) the mould value that will receive real signal is carried out low-pass filtering, produces the carrier amplitude estimated signal; The mould value of real signal is postponed, produce the real signal mould value that postpones; Ask for the two poor of the real signal mould value of delay and carrier amplitude estimated signal; The difference of wherein asking for the two comprises the steps:

A) the mould value that receives real signal is carried out low-pass filtering, produces the carrier amplitude estimated signal;

B) the mould value with real signal postpones, and produces the real signal mould value that postpones;

C) ask for the real signal mould value of delay and the difference of carrier amplitude estimated signal;

5) with the difference of the real signal mould value that postpones and carrier amplitude estimated signal and delayed after the normalization composite signal multiply each other, eliminated the digital modulation subcarrier signal of analog carrier signal interference; Wherein with the difference of the real signal mould value that postpones and carrier amplitude estimated signal and delayed after the normalization composite signal multiply each other, eliminated the digital modulation subcarrier signal of analog carrier signal interference.

In the power spectrum of FM Hybrid IBOC signal shown in Figure 1, the triangle that dotted line is represented is the frequency spectrum of simulation FM signal, and the solid-line rectangle on FM both sides is represented DAB numeral side frequency.

The FM triangle power spectral density that with the G-bar is 0.36dB/kHz is an example, the gross power P of FM _TotalFor:

$P_{\mathrm{total}}={\∫}_{-\∞}^{+\∞}{P}_{\mathrm{peak}}\·{10}^{-0.36\·\left|f\right|/10}\·\mathrm{df}=24.1275P_{\mathrm{peak}}$

Then have: 10lg (P _Peak)=10lg (P _Total)-10lg (24.1275)=10lg (P _Total)-13.8 (dB)

This shows that FM power spectral density peak is lower than total carrier power reference value (0dB) 13.8dB place, as shown in fig. 1-position of 13.8dB.

Suppose that the bilateral digital band of DAB has ± 95 subcarriers, effectively Nyquist Bandwidth is 726.75Hz, and then the DAB power spectral density in the 1kHz bandwidth is:

$10\log \left({\mathrm{PSD}}_{\mathrm{DAB}}\right)=10\log \left(\frac{{10}^{-25/10}}{95\×0.72675}\right)=-43.4(\mathrm{dB}/\mathrm{kHz})$

What Fig. 2 showed is the disturbed condition of first adjacent channel (apart from main FM centre frequency+200kHz place, dotted portion) of 200kHz for main FM channel (solid line) based on channel spacing.Do not expect that or not (is that D 〉=6dB), first adjacent channel is destructive for the interference of digital sidebands in the main FM channel that control station that the adjacent channel performance number is lower than reception at least covers edge expectation performance number 6dB although the distribution in the geographical position in regulation FM radio station should guarantee to receive.Broken line triangle has all covered the last digital sidebands part (it is mutual disturbing in fact: the solid line triangle among the main FM has covered the following digital sidebands of dotted line too) of main FM among Fig. 2; Equally, if consider apart from the adjacent channel at FM centre frequency-200kHz place and disturb, also whole disturbed flooding of digital sidebands part down in the then main FM channel.

Under the situation that decline is not disturbed, the composite signal of reception can be expressed as:

S(t)＝a·e ^jθ(t)+d(t) (1)

Wherein a represents the amplitude of FM modulated-analog signal, the instantaneous phase of θ (t) expression FM modulated-analog signal; D (t) represents digital modulation signals.

The average power of supposing d (t) is 1; Because simulate the DAB numeral side frequency signal power high approximately 25dB of main FM total power signal, so the condition of a＞＞1 is always set up than FM both sides.

Simultaneously, because hypothesis does not exist decline to disturb, so that signal amplitude can keep is constant, the model shown in the expression formula (1) is based upon on this hypothesis basis.Otherwise, when the decline interference exists, can adopt the following model of thanksing for your hospitality:

S(t)＝[a+f(t)]·e ^jθ(t)+d(t) (2)

Wherein f (t) is dynamic decline, can produce the amplitude modulation effect of simulation FM carrier wave.If the slow fading that is caused by Raleigh decline in the scope of analyzing, can be ignored this decline and disturb so, promptly still can be similar to and think that signal amplitude keeps constant.But if selectivity decline, then Fu Jia interference f (t) is just more serious, will produce image signal in the treatment step of the present invention's proposition and can not eliminate.

Specifically handling process is as shown in Figure 4:

In receiving the composite signal module, receive the composite signal that comprises analog-modulated carrier wave and digital side frequency signal shown in expression formula (1) (not having decline disturbs ideally) or (2) (having under the situation about disturbing that declines).This signal enters into the amplitude normalization processing module, after the absolute value signal of itself and self is divided by, obtains following approximate normalized composite signal expression formula (having considered to have this moment decline to disturb, so calculate with the model of expression formula (2)):

$\frac{S\left(t\right)}{\left|S\left(t\right)\right|}\≈e^{\mathrm{j\θ}\left(t\right)}+\frac{d\left(t\right)}{[a+f\left(t\right)|}---\left(3\right)$

Normalized composite signal get complex conjugate after, multiply each other with the composite signal that receives:

$\frac{S^{*}\left(t\right)}{\left|S\left(t\right)\right|}\·S\left(t\right)\≈(e^{-\mathrm{j\θ}\left(t\right)}+\frac{d^{*}\left(t\right)}{[a+f\left(t\right)]})\·\left\{\right[a+f\left(t\right)]\·e^{\mathrm{j\θ}\left(t\right)}+d\left(t\right)\}---\left(4\right)$

$=a+f\left(t\right)+d^{*}\left(t\right)\·e^{\mathrm{j\θ}\left(t\right)}+d\left(t\right)\·e^{-\mathrm{j\θ}\left(t\right)}+\frac{{\left|d\left(t\right)\right|}^2}{[a+f\left(t\right)]}$

Above-mentioned signal is postponed respectively to handle and low-pass filtering treatment, and asks for the poor of the two:

$\frac{S^{*}\left(t\right)}{\left|S\left(t\right)\right|}\·S\left(t\right)-a=f\left(t\right)+d^{*}\left(t\right)\·e^{\mathrm{j\θ}\left(t\right)}+d\left(t\right)\·e^{-\mathrm{j\θ}\left(t\right)}+\frac{{\left|d\left(t\right)\right|}^2}{[a+f\left(t\right)]}---\left(5\right)$

At last with difference signal and delayed after the normalization composite signal multiply each other:

$(\frac{S^{*}\left(t\right)}{|S\left(t\right)}\·S\left(t\right)-a)\·\frac{s\left(t\right)}{\left|S\left(t\right)\right|}=(f\left(t\right)+d^{*}\left(t\right)\·e^{\mathrm{j\θ}\left(t\right)}+d\left(t\right)\·e^{-\mathrm{j\θ}\left(t\right)}+\frac{{\left|d\left(t\right)\right|}^2}{[a+f\left(t\right)]})\·\frac{S\left(t\right)}{\left|S\left(t\right)\right|}$

$=d\left(t\right)+d^{*}\left(t\right)\·e^{j\·2\mathrm{\θ}\left(t\right)}+f\left(t\right)\·e^{\mathrm{j\θ}\left(t\right)}+\frac{f\left(t\right)\·d\left(t\right)}{[a+f\left(t\right)]}+\frac{d^2\left(t\right)\·e^{-\mathrm{j\θ}\left(t\right)}}{[a+f\left(t\right)]}$

$+2\·\frac{{\left|d\left(t\right)\right|}^2\·e^{\mathrm{j\θ}\left(t\right)}}{[a+f\left(t\right)]}+\frac{{\left|d\left(t\right)\right|}^2\·d\left(t\right)}{{[a+f\left(t\right)]}^2}$

Because FM analog carrier signal power is much larger than DAB numeral side frequency signal power, so following formula can be approximated to be:

$(\frac{S^{*}\left(t\right)}{\left|S\left(t\right)\right|}\·S\left(t\right)-a)\·\frac{s\left(t\right)}{\left|S\left(t\right)\right|}---\left(6\right)$

$\≈d\left(t\right)+d^{*}\left(t\right)\·e^{j\·2\mathrm{\θ}\left(t\right)}+f\left(t\right)\·(e^{\mathrm{j\θ}\left(t\right)}+\frac{f\left(t\right)\·d\left(t\right)}{[a+f\left(t\right)]})$

Following formula shows, if the f (t)=0 that causes is disturbed in the selectivity decline, then can obtain:

$(\frac{S^{*}\left(t\right)}{\left|S\left(t\right)\right|}\·S\left(t\right)-a)\·\frac{s\left(t\right)}{\left|S\left(t\right)\right|}---\left(7\right)$

$\≈d\left(t\right)+d^{*}\left(t\right)\·e^{j\·2\mathrm{\θ}\left(t\right)}$

Here it is, and modulated-analog signal disturbs the required DAB numeral side frequency signal of having eliminated.

Even exist the selectivity decline to disturb, if satisfy:

$e^{\mathrm{j\&theta;}\left(t\right)}+\frac{d\left(t\right)}{[a+f\left(t\right)]}<\frac{1}{a^2}\&CenterDot;\left\{\begin{array}{c}[4a+2f\left(t\right)]\&CenterDot;d\left(t\right)+[a+f\left(t\right)]\&CenterDot;[2a+f\left(t\right)\&CenterDot;e^{\mathrm{j\&theta;}\left(t\right)}\\ +[2a+f\left(t\right)]\&CenterDot;e^{j\&CenterDot;2\mathrm{\&theta;}\left(t\right)}\&CenterDot;d^{*}\left(t\right)\end{array}\right\}---\left(8\right)$

So, self disturbing of being produced in this method processing procedure will be very little also, and promptly the 3rd in the expression formula (6) is smaller.(3) are further approximate, can get:

e ^jθ(t)＜2·e ^jθ(t) (9)

This shows that this method interference eliminated that decline causes for selectivity also has the raising of 6dB potential gain.

Claims (6)

1, analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting, at in-band on-channel digital audio broadcasting receiving terminal, the composite signal that receives is handled through radio-frequency front-end, Frequency mixing processing, after intermediate frequency filtering and separator are handled, produce analog-modulated carrier wave and digital band signal after A/D conversion and Digital Down Convert, entering corresponding analog circuitry processes module and digital signal circuit processing module then respectively handles accordingly, but still there is the interference of analog-modulated carrier wave in the digital band signal after separating, it is characterized in that, comprise the steps:

1) receives composite signal, receive composite signal and form by analog-modulated single-carrier signal and a plurality of digital modulation subcarrier signal;

2) butt joint is recovered and to be closed signal and carry out amplitude normalization and handle, and normalized composite signal equals to receive the value that composite signal and the absolute value that receives composite signal are divided by;

3) will receive the conjugate multiplication of composite signal and normalized composite signal, obtain receiving the mould value of real signal;

4) the mould value that will receive real signal is carried out low-pass filtering, produces the carrier amplitude estimated signal; The mould value of real signal is postponed, produce the real signal mould value that postpones; Ask for the two poor of the real signal mould value of delay and carrier amplitude estimated signal;

5) with the difference of the real signal mould value that postpones and carrier amplitude estimated signal and delayed after the normalization composite signal multiply each other, eliminated the digital modulation subcarrier signal of analog carrier signal interference.

2, analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting according to claim 1 is characterized in that, wherein receives composite signal and is made up of analog-modulated single-carrier signal and a plurality of digital modulation subcarrier signal.

3, analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting according to claim 1 is characterized in that, the value that the absolute value that wherein normalized composite signal equals to receive composite signal and receive composite signal is divided by.

4, analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting according to claim 1 is characterized in that, wherein will receive the conjugate multiplication of composite signal and normalized composite signal, obtains receiving the mould value of real signal.

5, analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting according to claim 1 is characterized in that the difference of wherein asking for the two comprises the steps:

A) the mould value that receives real signal is carried out low-pass filtering, produces the carrier amplitude estimated signal;

B) the mould value with real signal postpones, and produces the real signal mould value that postpones;

C) ask for the real signal mould value of delay and the difference of carrier amplitude estimated signal.

6, analog-modulated ici cancellation methods in a kind of in-band on-channel digital audio broadcasting according to claim 1, it is characterized in that, wherein with the difference of the real signal mould value that postpones and carrier amplitude estimated signal and delayed after the normalization composite signal multiply each other, eliminated the digital modulation subcarrier signal of analog carrier signal interference.

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