CN1889550A - Unified binary phase modulating and demodulating method - Google Patents

Abstract

A information modulating and demodulating method used on digital communication includes realizing modulation by utilizing binary information code element to directly vary abrupt phase of sine carrier wave, utilizing lock phase ring to realize demodulation, making modulated signal g0(t) corresponding to number zero be sine wave of N carrier wave period and making g1(t) corresponding to number one be in sine wave of N carrier wave period with frequency of fc, applying phase jump off angle theta and parameter tau as modulation index for varying signal bandwidth and transmission code rate as well as demodulation property.

Description

Unified binary phase modulating and demodulating method

Technical field

The present invention is a kind of information modulation and demodulation method that is used for digital communication, belongs to the technical field of digital information transmission.

Background technology

In the digital communication system, the process of the baseband signal of representing binary data upwards being moved given transmission frequency range is called modulation, and opposite process then is referred to as demodulation.In the practicality, both pursued high as far as possible band efficiency, i.e. the higher numeric code rate (is dimension with bps/Hz) of transmission in the unit frequency band; Also wish and more effectively to utilize emitted energy, obtain better laser propagation effect.

The strong control of traditional binary phase shift (BPSK) modulation is by ° realizing its anti-phase θ=180 conversion of logical zero and " 1 " at the zero phase place of sinusoidal carrier, wherein the periodicity that continues of the anti-phase sine wave of the sine wave of representative " 0 " and representative " 1 " is identical.Dui Cheng result suppressed carrier fully like this, but the frequency spectrum of modulated signal is expanded very widely, and band efficiency has only 1bps/Hz in theory.

2002, the H.R.Walker of the U.S. has applied for that core is two United States Patent (USP)s that are referred to as phasing back keying (PRK:PhaseReversal Keying) modulating/demodulating technology, i.e. " Pulse Position PhaseReversal Keying/Missing Cycle Modulation " (United States Patent 6445737) and " Digital modulation device in a system and method for using the same " (United States Patent 6445738).Its way is: when " 1 " (being " 0 " to occur originally) appears in the input data, one or several cycle of sinusoidal carrier phase hit (being PRK) occurs or loses (being so-called MCM:Missing Cycle Modulation), and is then constant when " 0 " (being " 1 " to occur originally) occurring.When time of phase change enough in short-term, then the power spectrum of the high-frequency signal after the modulation just presents outstanding and extremely low " super arrowband " situation of sideband of main peak, particularly for the PRK modulation system.

But, PRK modulation in the above-mentioned United States Patent (USP) is to trigger the modulation circuit that control is made up of comparator and gate with data message, the modulation signal that only produces several specific phase is exported through behind the simulation forming filter based on quartz crystal, and just assert just that according to the output effect of this specific quartz-crystal filter duty ratio is so-called 3PRK the best of 1: 4 and has provided corresponding circuit realization.

Summary of the invention

Technical problem: the purpose of this invention is to provide a kind of unified binary phase modulating and demodulating method, this method finds the unified expression of the binary phase modulation that can select arbitrary phase θ and any duty ratio, adopt digital filter to replace and be not easy to extensive integrated quartz crystal simulation forming filter, obtain the more general Digital Modulation and the implementation method of demodulation.

Technical scheme: unified binary phase modulation and demodulation method of the present invention realizes modulation with the sudden change phase place that the binary message code element directly changes sinusoidal carrier, realizes demodulation with phase-locked loop, makes the modulated signal g of corresponding digital " 0 " ₀(t) be the sine wave of N carrier cycle, and the g of corresponding numeral " 1 " ₁(t) then be to be f in frequency _cThe sine wave of N carrier cycle in, the phase hit in a preceding K cycle θ angle; Promptly

f ₀(t)＝Asin2πf _ct，0≤t＜T

$f_1\left(t\right)=\left\{\begin{array}{cc}B\sin (2\mathrm{\&pi;}{f}_{c}t+\mathrm{\&theta;}),& 0\&le;t<\mathrm{\&tau;},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}\\ A\sin 2\mathrm{\&pi;}{f}_{c}t,& \mathrm{\&tau;}\&le;t<T\end{array}\right.$

T=N/f wherein _c, τ=K/f _c, K≤N, and these 2 parameters of θ and τ constitute " modulation index " that changes signal bandwidth, transmission code rate and demodulation performance.Realize separating timing with phase-locked loop, utilize the phase discriminator output of phase-locked loop is carried out coherent accumulation according to time τ earlier, the method for reconvict after making signal to noise ratio improve " 0 " and " 1 " guarantees better demodulation performance; And also can adopt liftering to come to be complementary with signal waveform at the phase discriminator input.This method is specific as follows:

1. the unified expression way of the binary phase shift keying modulation of expanding

Communication enineer is all known, for continuous sinusoidal carrier f (t)=Asin2 π f _cT, if wherein have only the sine wave phase in one, two cycle that the saltus step of θ angle takes place, then its spectrum energy still high concentration at carrier frequency f _cOn the pairing spectral line, the both sides also corresponding sideband can occur, i.e. spread spectrum has appearred in the saltus step owing to phase place.Obviously, when θ=180 °, the sideband expansion is maximum; Along with θ → 0, whole waveform is near sinusoidal wave, and more high concentration is at the carrier frequency place for its spectrum energy, and the width and the amplitude of corresponding sideband expansion all can level off to 0.Limiting case, θ=0, whole carrier wave is a pure sine wave, is exactly a spectral line at frequency domain, and energy height is concentrated, and bandwidth is zero in theory, also can't transmit any Useful Information certainly.Allow it keep the saltus step angle very little now, almost near sinusoidal wave, then its spectrum energy high concentration is at the carrier frequency place for the waveform after the modulation so.If the saltus step angle θ of carrier waveform is controlled by Useful Information, can realize the modulation that the availability of frequency spectrum is very high, and " super arrowband " frequency spectrum of so-called " flagpole formula ".

If:

1) symbol intervals of data message (being the time span of code element) T has continued N 〉=1 carrier cycle, i.e. T=N/f _c

2) the time span τ of saltus step waveform has continued K carrier cycle, i.e. τ=K/f _c, and K≤N;

3) " 0 " and " 1 " institute modulated waveform is respectively f ₀(t) and f ₁(t);

Then the present invention is defined as the uniform expression of any binary phase modulation signal

f ₀(t)＝Asin2πf _ct，0≤t＜T

$f_1\left(t\right)=\left\{\begin{array}{cc}B\sin (2\mathrm{\&pi;}{f}_{c}t+\mathrm{\&theta;}),& 0\&le;t<\mathrm{\&tau;},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}\\ \mathrm{<figure-callout\; id="2"\; label="A\; sin"\; filenames="A20061004076700111.png"\; state="\{\{state\}\}">A</figure-callout>}\sin 2\mathrm{\&pi;}{f}_{c}t,& \mathrm{\&tau;}\&le;t<T\end{array}\right.---\left(1\right)$

(1) modulation waveform of formula itself has following characteristics:

1. for data " 0 ", be that N cycle is 1/f in the whole symbol intervals T _cSine wave, amplitude is A;

2. for data " 1 ", in the whole symbol intervals T, be that K cycle is 1/f the last period _c, first phase is the sine wave of θ, amplitude is B; The back then is that N-K cycle is 1/f for one section _cSine wave, amplitude is A;

3. except that the section start in data " 1 " had in short-term phase hit (θ is saltus step angle or modulation angle) or amplitude saltus step (hop value is B-A), all the other all were continuous sine waves, and the broadening that this helps to suppress the modulated wave frequency spectrum makes its concentration of energy at carrier frequency f _cThe place, and the saltus step angle is more little, and the modulated wave frequency spectrum is concentrated more;

4. in a symbol intervals T, the mean value of modulated wave is zero, thereby does not contain DC component in its frequency spectrum;

5. as if B=0, then (1) formula is the MCM modulation in the above-mentioned United States Patent (USP).In fact, in fact so-called MCM is exactly a kind of long-term pulse modulation, and is unfavorable for the contraction of modulation spectrum and the raising of demodulation performance, therefore, if do not consider the MCM mode, need only make B=A in (1) formula.Then if this moment is θ=π: (1) formula classical BPSK of expression just when τ=T, when τ=T/4 just represents 3PRK in the above-mentioned United States Patent (USP); And so-called 3PSK modulation system in the United States Patent (USP) then is again a special case when θ=pi/2 and τ=T/4 in (1) formula;

6. the modulated degree of carrier wave is different because of θ and τ.0≤θ≤π can be used as the bandwidth Control Parameter: when θ → 0, the modulated wave frequency spectrum is the narrowest; And as θ → π, the modulated wave frequency spectrum is the wideest.τ/T=K/N can be described as " modulation duty cycle ".

Choose suitable θ according to (1) formula, the control of τ cooperates forming filter preferably more in addition, can control the bandwidth of modulated signal very narrowly.Therefore, the present invention is the modulation signal form of (1) formula definition, be referred to as " binary phase shift keying of expansion " (Extended Binary Phase Shift Keying, be abbreviated as EBPSK), because of its both contained 3PRK, MCM that classical BPSK and United States Patent (USP) newly put forward, 3PSK, NRZMSB and etc. modulation system, other new modulation system that potential again forefathers do not find or relate to is because have θ and two parameters of τ to make up here.

2. based on the demodulation mode of phase-locked loop and liftering

Celestial your information theory points out that channel capacity C almost is proportional to channel width W, so the super narrowband performance of EBPSK will be a cost with higher demodulation signal to noise ratio (meaning higher transmitting power usually) demand generally.Have higher transmitting power (as radio broadcasting, long wave radio station and subsurface communication etc.) although many limited bandwidth types are used, reduce requirement for the demodulation signal to noise ratio as far as possible and be still and be concerned about very much in the application.

In the analog communication epoch, phase-locked loop (PLL) once was widely used in the demodulation of frequency modulation and phase-modulated signal; And in digital communication, then be widely used in to coherent demodulation extraction reference carrier, set up bit synchronization and frequency synthesizer etc.Consider that phase-locked loop is the desirable tracking filter of sinusoidal signal, strictness has been in close proximity to sine wave after limiting and EBPSK signal proposed by the invention is through transmitting terminal ultra-narrow bandwidth filter (band is logical), and the EBPSK signal itself with certain modulation duty cycle also more helps the locking ratio of pure sine wave (because higher) of PLL, therefore adopts phase-locked loop to carry out the optimal demodulation of EBPSK signal.

But because behind the bandpass filtering of EBPSK signal through transmitting terminal super arrowband, the difference of waveform transition is very little between the representative " 0 " and " 1 ", it is reliable inadequately to utilize phase discriminator among the PLL to carry out the phase-modulated signal demodulation method of SPA sudden phase anomalies detection usually.For this reason, the present invention proposes that coherent accumulation is carried out in the demodulation output of phase discriminator and reconvicts (as Fig. 3), guarantees better transmission property.In case of necessity, the present invention also can (we propose in the application for a patent for invention of " the information modulation and demodulation method of operating factor of highband ": application number: 03152978.X carrying out special digital liftering before the phase discriminator, publication number: 1494284), to promote the high fdrequency component of signal, compensate the influence of super arrowband bandpass filtering.

Beneficial effect:

1. band efficiency height.Owing to have certain modulation duty cycle, the EBPSK carrier wave keeps the pure sinusoidal wave lasting cycle more, thereby its spectrum energy high concentration, occupied bandwidth very narrow (the power spectrum sideband of Fig. 1 carrier frequency both sides all is lower than-60dB), if use restraint through a simple band pass filter again, band efficiency then of the present invention is high, can realize the high speed data transfer of super arrowband.

2. total digitalization realizes.Modulation such as the 3PRK/MCM of the aforementioned U.S., 3PSK will have special polycrystal analog filter, and volume is big, and consistency is poor, and it is integrated to be not easy to hardware; And the present invention has got rid of the polycrystal analog filter that United States Patent (USP) is mainly protected, transmitting terminal can directly be exported the numeral sample (even the sample behind super narrow-band filtering) of modulation waveform and get final product (Fig. 2) through digital to analog converter (DAC), be convenient to the making of integrated circuit (IC), also be convenient to utilize digital filtering accurately to control bandwidth and the spectral shape that sends signal; And receiving terminal also can be realized the total digitalization processing (Fig. 3) of receiver afterwards at analog to digital converter (ADC), thereby helps whole receive-transmit system all is integrated into IC SOC (system on a chip) (SOC:System On Chip).

3. adapt to face width.Principle according to aforementioned EBPSK, as long as change modulation angle θ and/or modulation duty cycle (fixedly T and only change τ), get final product control signal bandwidth and transmission code rate, (being that parameter A is constant) obtains different transmission performances under same transmitting power, to adapt to different channel circumstances.Particularly after modulation system and transmission code rate all change, as long as carrier frequency f _cConstant, then adopt the receiver of Fig. 3 demodulation mode just can interruptedly not automatically identify the isoparametric change value of modulation duty cycle, symbol width and transmission code rate, especially be fit to noncooperative specific communication requirement, be convenient to constitute very flexibly the communication system of programmed settings or online dynamic reorganization in advance.

4. receiver structure is simple.Present patent application is that core constitutes the EBPSK receiver with the digital phase-locked loop, and PLL not only realizes the coherent demodulation of EBPSK signal, and (it is Mf that the frequency with the carrier wave strict synchronism is provided to be used for frequency synthesizer _cSampling pulse), set up bit synchronization, carry out carrier frequency and follow the tracks of (elimination Doppler frequency shift) etc.If do not consider digital filtering, then the whole EBPSK receiver of Fig. 3 also can save ADC, and realizes based on a slice analog PLL.Because EBPSK modulates not suppressed carrier, thereby PLL input signal-to-noise ratio height, the performance of whole system is improved.

5. be that new high-speed transfer system (as mobile communication, radio broadcasting and computer network) and anti-interference method (as military electronic countermeasures) provides possibility.

Description of drawings

Fig. 1 is that θ=π/4 are worked as in the EBPSK modulation that the present patent application proposes, and the logarithm of modulation signal power spectral density was represented when duty ratio was 24dB (1/16).

Fig. 2 is the EBPSK modulating system block diagram that the present patent application proposes.

Fig. 3 is the EBPSK demodulating system block diagram that the present patent application proposes.

Embodiment

Get θ=π/4, f _c=48MHz, the power spectrum that obtains the EBPSK modulation signal as shown in Figure 1, wherein ordinate is that power spectrum amplitude with the carrier frequency place is as 0dB.As seen from the figure, the energy height of EBPSK modulation signal is concentrated, and the carrier frequency amplitude is higher than other sideband 60dB (1,000,000 times) at least, and the time domain waveform of EBPSK modulation signal is similar to sine wave really very much.

This method realizes modulation with the sudden change phase place that the binary message code element directly changes sinusoidal carrier, realizes demodulation with phase-locked loop, makes the modulated signal g of corresponding digital " 0 " ₀(t) be the sine wave of N carrier cycle, and the g of corresponding numeral " 1 " ₁(t) then be to be f in frequency _cThe sine wave of N carrier cycle in, the phase hit in a preceding K cycle θ angle; Promptly

f ₀(t)＝Asin2πf _ct，0≤t＜T

$f_1\left(t\right)=\left\{\begin{array}{cc}B\sin (2\mathrm{\&pi;}{f}_{c}t+\mathrm{\&theta;}),& 0\&le;t<\mathrm{\&tau;},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}\\ A\mathrm{<figure-callout\; id="2"\; label="sin"\; filenames="A20061004076700111.png"\; state="\{\{state\}\}">sin</figure-callout>}2\mathrm{\&pi;}{f}_{c}t,& \mathrm{\&tau;}\&le;t<T\end{array}\right.$

T=N/f wherein _c, τ=K/f _c, K≤N, and these 2 parameters of θ and τ constitute " modulation index " that changes signal bandwidth, transmission code rate and demodulation performance.Realize separating timing with phase-locked loop, utilize the phase discriminator output of phase-locked loop is carried out coherent accumulation according to time τ earlier, the method for reconvict after making signal to noise ratio improve " 0 " and " 1 " guarantees better demodulation performance; And also can adopt liftering to come to be complementary with signal waveform at the phase discriminator input.

Fig. 2 is the totally digitilized embodiment of EBPSK modulating system: transmitting terminal directly will be by the expressed interior modulated waveform f of a symbol width of (1) formula ₀(t) and f ₁(t) discrete sampling value is kept in the memory in advance, selects corresponding f according to the sample frequency that clock generator provided then under the control of the defeated information sequence of tendency to develop ₀(t) waveform sample (if information bit is " 0 ") or f ₁(t) waveform sample (if information bit is " 1 "); The modulation waveform numeral sample of choosing is directly changed into the modulated signal output of simulation through behind the arrowband or super narrow band digital filter filtering of required spectral shape by DAC.In addition, we even all right directly storage f ₀(t) and f ₁(t) waveform sample behind super narrow-band filtering, just can save the higher digital filter of cost at transmitting terminal like this, thereby the EBPSK modulating system that not only makes whole total digitalization realize can be integrated on a slice IC at an easy rate, and can improve the clock frequency (being modulated wave frequency or transmission code rate) of modulating system.

Fig. 3 is the totally digitilized embodiment of EBPSK demodulating system: be converted to digital signal by ADC after having the amplification of EBPSK received signal through necessity because of Channel Transmission noise and distortion distortion deterioration, through behind the digital filtering of inverse filter, send into the digital phase discriminator (PD) of PLL.The essence of this numeral inverse filter frequency response curve, in the effective band of signal, compensate fuzzy (promptly recover and even amplification phase hit angle θ) of (i.e. " contrary " filtering) transmitting terminal exactly, and outside the effective band of signal, still need effective filtering useless noise and interference because of " 0 " " 1 " waveform that super narrowband digital filtering caused.Phase demodulation output is divided into two-way: top one the tunnel has been continuous demodulation output, but in order to reduce the error rate, continue accumulate in the time period at τ carry out " 0 " again after (integration or add up), adjudicate " 1 "; Below one the tunnel be the PLL frequency synthesizer of a standard, its principle is classical and known, this example is directly continued to use.Why giving phase discriminator again behind the output M frequency division with voltage controlled oscillator (VCO), is that frequency is strict to be carrier frequency M sampling pulse and system clock doubly for the enable clock generator produces.

Claims (2)

1, a kind of unified binary phase modulating and demodulating method is characterized in that this method realizes modulation with the sudden change phase place that the binary message code element directly changes sinusoidal carrier, realizes demodulation with phase-locked loop, makes the modulated signal g of corresponding digital " 0 " ₀(t) be the sine wave of N carrier cycle, and the g of corresponding numeral " 1 " ₁(t) then be to be f in frequency _cThe sine wave of N carrier cycle in, the phase hit in a preceding K cycle θ angle; Promptly

f ₀(t)＝Asin2πf _ct，0≤t＜T

$f_1\left(t\right)=\left\{\begin{array}{cc}B\sin (2\mathrm{\&pi;}{f}_{c}t+\mathrm{\&theta;}),& 0\&le;t<\mathrm{\&tau;},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}\\ A\sin 2\mathrm{\&pi;}{f}_{c}t,& \mathrm{\&tau;}\&le;t<T\end{array}\right.$

T=N/f wherein _c, τ=K/f _c, K≤N, and these 2 parameters of θ and τ constitute " modulation index " that changes signal bandwidth, transmission code rate and demodulation performance.

2, unified binary phase modulating and demodulating method according to claim 1, it is characterized in that realizing separating timing with phase-locked loop, utilization is carried out coherent accumulation according to time τ earlier to the phase discriminator output of phase-locked loop, reconvict after making signal to noise ratio the improve method of " 0 " and " 1 " guarantees better demodulation performance; And also can adopt liftering to come to be complementary with signal waveform at the phase discriminator input.

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