CN101729470A - Constant amplitude and period digital signal modulation and demodulation method - Google Patents

Abstract

The invention discloses a constant amplitude and period digital signal modulation and demodulation method which directly changes wave forms of carrier waves by utilizing binary information code elements. The method specifically comprises the following steps of: respectively sampling two basic wave forms of f0(t) of characteristic information 0 and f1(t) of characteristic information 1 within a period, controlling a selective switch by binary information to be transmitted, and respectively selecting a corresponding storage area of any one of f0(t) or f1(t) within a wave form period; and under the control of a synchronous clock, converting the wave forms in the storage areas into modulated high-frequency analog signals by using a digital-to-analogue converter and outputting the analog signals through a band-pass filter. Demodulation can be finished only by carrying out a sampling decision at a middle point namely a 1/2 period part of a received signal wave form so as to restore originally sent binary information. A constant amplitude and period high-efficiency modulation system realized through the method further improves the utilization rate of frequency bands, guarantees the constant of the amplitudes of modulated wave forms, and enhances the capacities of resisting channel distortion and noise interference of the system, thereby having wide application prospect.

Description

Modulation of constant amplitude and period digital signal and demodulation method

Technical field

The present invention is a kind of method that is used for digital signal is carried out modulation and demodulation, belongs to digital communicating field.Be a kind of constant amplitude and period digital signal modulation and demodulation method specifically.

Background technology

Modulation and demodulation is a crucial link in the electronic communication field, and different modulation means is to the various performance parameters decisive role of a communication system.At the transmitting terminal of communication system, employing is modulated to the binary radix band signal of low frequency on the high frequency and conveniently transmits usually, by receiving terminal the baseband signal demodulation on the high frequency carrier is come out, and restores original transmission signal.In recent years, various new type of modulation demodulation techniques continue to bring out, in order to reach high as far as possible band efficiency, the i.e. higher numeric code rate (is dimension with bps/Hz) of transmission in the unit frequency band is that the super arrowband technical development of main bright spot is particularly swift and violent with high bandwidth transmission efficient and upper sideband inhibition level.Domestic a series of relevant patent is application one after another also, and (application number: 03152978.X), its invention key is to make the modulated signal g of characterization logic " 0 " such as a kind of being called " the information modulation and demodulation method of operating factor of highband " ₀(t) and the modulated signal g of characterization logic " 1 " ₁(t) all and the different wave shape minimum between the sinusoidal signal, shown in Fig. 1 (a), but the amplitude difference of two halves before and after its waveform is unfavorable for being applied in the complex modulated.In order to overcome this shortcoming, " the information modulation and demodulation method of the operating factor of highband of constant amplitude " (application number: 200410064681.4) also invented, shown in Fig. 1 (b).

But above-mentioned two patents still have place not fully up to expectations.The waveform of " the information modulation and demodulation method of operating factor of highband " as previously mentioned, the amplitude difference of front and back two halves, in some amplitude occasions with limited, will influence its demodulation performance, there is the occasion of unified amplitude requirement inapplicable at some to waveform, and fixing because of the amplitude in its each code-element period, this technology also is difficult to combine with traditional amplitude modulation/frequency modulation technology, can transmit the digital information of one tunnel high speed when being implemented in transmission of analogue signal again.Observe its power spectrum such as Fig. 2 (a) and can find that the high order harmonic component of this waveform is more and amplitude is bigger, this not only can waste the further lifting that energy also can limiting bandwidth efficient." the information modulation and demodulation method of the operating factor of highband of constant amplitude " though waveform carried out some amplitude limiting processing, but if under the low signal-to-noise ratio condition in order further to increase the discrimination of two kinds of basic waveforms, the accuracy of guaranteeing message transmission just needs by increasing the otherness that parameter A (the waveform regulation and control parameter in this patent) strengthens two kinds of basic waveforms, but from Fig. 3 (b), can clearly find out, further increase along with parameter A, the amplitude of two kinds of basic waveforms begins to occur disunity gradually, particularly increase to 0.5 when above as A, two kinds of waveform separation degree are higher, but the saltus step of the amplitude of waveform is quite obvious, the basic waveform amplitude is unified these sharpest edges and will do not existed in this patent, under requiring than higher occasion to the waveform separation degree, can't combine with broadcast system preferably, because the method that adopts in the middle of this patent is the parasitic waveform that superposes on sine wave, can not fundamentally address the aforementioned drawbacks.

Summary of the invention

Technical problem: the purpose of this invention is to provide a kind of constant amplitude and period digital signal modulation and demodulation method, make the bandwidth availability ratio of communication system be further improved, the amplitude of modulation waveform has constant uniformity simultaneously, can apply to all kinds of need carrying out in the communication system for modulation the amplitude of carrier wave, the ability of opposing noise has also obtained further enhancing.

Technical scheme: the present invention divides digital signal modulation and demodulation method two parts, and is as follows respectively:

1) constant amplitude and period digital signal modulating method

This method utilizes the binary message code element directly to change the waveform of carrier wave, the modulation waveform f that produces when information bit is " 1 " ₁(t) the modulation waveform f that produces and when information bit is " 0 " ₀(t) compare with standard sine wave and have adjustable fine difference.This modulation system can be expressed as:

$f(t,\mathrm{\&tau;})=\left\{\begin{array}{cc}\sin \mathrm{<figure-callout\; id="0"\; label="t"\; filenames="H2008101548554E0000011.png,H2008101548554E0000021.png"\; state="\{\{state\}\}">t</figure-callout>}& 0\&le;t\&le;\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\\ \sin (\frac{t-\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}}{\mathrm{\&tau;}-\frac{T}{4}}\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}+\frac{T}{4})& \frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\&le;t\&le;\mathrm{\&tau;}\\ \sin (\frac{t-\mathrm{\&tau;}}{\frac{3T}{4}-\mathrm{\&tau;}}\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}+\frac{T}{2})& \mathrm{\&tau;}\&le;t\&le;\frac{3\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\\ \sin t& \frac{3\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\&le;t\&le;T\end{array}\right..---\left(1\right)$

Wherein: T is the cycle of modulation waveform, also is the symbol intervals of code-element period and information simultaneously; F=1/T is the frequency of carrier wave, numerically also equals the transmission rate of code element; When information bit was " 1 ", waveform generator produced

The time f (t) (remember into f ₁(t)); When information bit was " 0 ", waveform generator produced

The time f (t) (remember into f ₀(t)), wherein α (0＜α＜1) is waveform regulation and control parameters.

This modulation system has following technical characterictic:

The difference of a, two kinds of basic waveforms reaches maximum at t=T/2.

B, two kinds of basic waveform amplitude A are invariable, and peak value lays respectively at t=T/4 and t=3T/4 place, and can any change not take place along with the increase of basic waveform difference.

C, waveform satisfy f ₁(t)=-f ₀(T-t), f ₀(t) and f ₁(t) be the sine wave of standard in the time period in [0, T/4] and [3T/4, T], its frequency spectrum has obtained better compression.

The frequency of d, this modulation waveform is invariable all the time and is numerically equal to bit rate.

E, can control the difference size of two kinds of basic waveforms by the selection of waveform regulation and control parameter alpha (0＜α＜1), when being in the discrimination that can weaken different wave under the big signal to noise ratio environment by increase α, can be under the little signal to noise ratio environment when being in by reducing the discrimination that α strengthens different wave.

2) realization of constant amplitude and period digital signal modulation

According to (1) formula respectively to the f of characterization information " 0 " ₀(t) and the f of " 1 " ₁(t) two kinds of basic waveforms are sampled in one-period, and the waveform sample in the complete cycle that obtains after the sampling is stored in two storage areas.Selector switch of binary message control waiting for transmission in a wave period, is selected f respectively ₀(t) or f ₁(t) road corresponding memory block in.Waveform sample in the memory block converts modulated high frequency analog signals to and exports behind band pass filter by digital to analog converter under the control of synchronised clock.Complete theory diagram as shown in Figure 4, this digital scheme characteristics are that the signal frequency that produces is accurate, amplitude stabilization, the upper limiting frequency of the modulation waveform that produces is directly determined by the performance of DAC, both be convenient to the production of integrated circuits in later stage, and also helped utilizing digital filtering accurately to control bandwidth and the spectral shape that sends signal.

3) constant amplitude and period digital signal demodulating method

In demodulation method, only need be two/one-period to locate once to sample to adjudicate just can finish demodulation at the mid point of received signal waveform based on small phase difference.As shown in Figure 5, the modulated signal that receives is removed through band pass filter earlier and is disturbed, enter sampler then, formed sampling pulse and sent into sampler by system clock, sampler is sent the phase place that obtains into the binary message that small phase difference detector restores original transmission by half place of code-element period is sampled.The characteristics of this method are that operand is low, and equipment is simple, and processing speed is fast, compared with the employed coherent detection method of " 03152978.X " number patent application, greatly reduce sample rate, have improved system effectiveness.

, can also adopt the demodulation method of another kind based on the zero crossing detection here, same only need be two/one-period to locate once to sample to adjudicate just can finish demodulation at the mid point of received signal waveform.By Fig. 1 (c) as can be known, the midpoint at code-element period has f ₀(T/2)＞0, f ₁(T/2)＜0.So sample by the received signal to this moment, just the binary element that can adjudicate transmission according to the polarity of sampled value is " 1 " or " 0 ".

4) raising of band efficiency

Can certainly adopt the demodulation method of same small phase difference to the VWDK waveform after original VWDK waveform among Fig. 1 (a) and Fig. 1 (b) and the improvement, if equally the sampling judgement is taken at the mid point of code-element period constantly, compare with Fig. 1 (c), the ability that the latter resists wave distortion and noise jamming is stronger, this waveform is expected to by the narrower channel of bandwidth, can drop to the influence that limited bandwidth caused minimumly, obtain band efficiency more efficiently.

To Fig. 1 (a), waveform among Fig. 1 (b) and this method Fig. 1 (c) carries out small phase difference detection by the mid point at code-element period behind the band pass filter respectively, under the prerequisite that keeps identical no code check, the frequency spectrum of more several signals after, corresponding diagram 6 (a) (b) (c) respectively through band pass filter separately.As can be seen, Fig. 6 (c) (b) compares with Fig. 6 (a), though kept two line spectrums, main lobe width reduces greatly, and therefore required bandwidth is narrower.Fig. 7 is the error rate analyzer of this method.The regulation and control parameter gets 0.9 and 0.85 respectively, and has carried out further contrast with MPSK (minimum phase shift keying).

The inventive method has kept the advantage of prior art, and as total digitalization, system regulation (only needs to change a regulation and control parameter) flexibly, also has the following advantages in addition:

1) band efficiency is higher.

By among formula (1) and Fig. 1 more as can be known, the waveform of Fig. 1 (c) is more near sinusoidal wave, Fig. 6 shows under demodulation performance prerequisite about the same, in three kinds of methods, the frequency bandwidth minimum that this patent is required, spectrum energy is also more concentrated.

2) stable constant amplitude.

As shown in Figure 3, three kinds of modulator approaches are when separately regulation and control parameter changes, have only this patent truly realizing the amplitude unification of modulation waveform, and can distortion or jump take place along with the variation of regulation and control parameter unlike basic waveform in other two patents.

3) ability of opposing channel distortion and noise jamming is stronger.

The modulation waveform of amplitudes such as output of the present invention is, it can pass through the narrower bandpass filtering of frequency band, can stand the influence of system's amplitude limit again to a certain extent, along with of the regulatable enhancing of two kinds of basic waveforms in half place's difference of code-element period, the noise robustness of system has also obtained further enhancing, and as seen this waveform has all obtained enhancing in the linear distortion (limited as frequency band) of opposing transmission channel and the ability aspect the nonlinear distortion (limited as amplitude).

4) more wide application prospect.

Exactly because characterizing the difference of two kinds of basic waveforms of different information can change along with the change of regulation and control parameter, and in the process that changes, the amplitude of waveform is constant, make the method for this invention both can use with big signal to noise ratio condition under, equally also be suitable for little signal to noise ratio condition under, can also be used in the system that to modulate the amplitude of carrier wave, by carrier wave also transmission of one line high speed digital information, as transmitting digital information by the carrier wave in traditional broadcasting system, be implemented in and read newspaper on the broadcast receiver, see picture, see TV etc., thereby realize the compound of analog communication and digital communication.

Description of drawings

Fig. 1 (a) is the output signal (α=0.9) of " 03152978.X " number patent application original VWDK modulator approach of inventing; Fig. 1 (b) is the output signal (A=0.2) of " 200410064681.4 " number improved VWDK modulator approach that patent application proposed; Fig. 1 (c) is the output signal (α=0.9) of the inventive method.

Fig. 2 (a) is the logarithmic table diagrammatic sketch (α=0.9) of the power spectrum amplitude of the original VWDK modulation signal invented of " 03152978.X " number patent application; Fig. 2 (b) is the logarithmic table diagrammatic sketch (A=0.2) of the power spectrum amplitude of " 200410064681.4 " number improved VWDK modulation signal that patent application proposed; Fig. 2 (c) is the logarithmic table diagrammatic sketch (α=0.9) of power spectrum amplitude of the output signal of the inventive method.

Fig. 3 (a) is the output signal (value of α is from 0.2～0.9) of " 03152978.X " number patent application original VWDK modulator approach of inventing; Fig. 3 (b) is the output signal (value of A is from 0.2～0.9) of " 200410064681.4 " number improved VWDK modulator approach that patent application proposed.Fig. 3 (c) is the output signal (value of α is from 0.2～0.9) of the inventive method.

Fig. 4 is the modulating system block diagram of the cycle waveforms such as constant amplitude of constant amplitude and period digital signal modulating method of the present invention.

Fig. 5 is the demodulating system block diagram of the cycle waveforms such as constant amplitude of constant amplitude and period digital signal demodulating method of the present invention (based on the demodulation method of small phase difference).

Fig. 6 is the demodulating system block diagram of the cycle waveforms such as constant amplitude of constant amplitude and period digital signal demodulating method of the present invention (based on the demodulation method of zero crossing detection).

Fig. 7 is " 03152978.X " number patent, " 200410064681.4 " number patent and the inventive method through-put power spectrum when keeping demodulation performance identical.

Fig. 8 is the bit error rate performance tracing analysis figure of constant amplitude and period digital signal demodulating method of the present invention.

Embodiment

Below in conjunction with accompanying drawing, the present invention is described in further detail.

The present invention utilizes cycle information modulation system such as novel constant amplitude directly to change the waveform of sinusoidal carrier, the modulation waveform f that produces when making the corresponding informance bit for " 1 " with binary element ₁(t) the modulation waveform f that produces and when information bit is " 0 " ₀(t) compare with standard sine wave and have adjustable fine difference.By can among bandwidth efficiency and demodulation performance, seeking a balance point to a waveform regulation and control parameter control.The regulation and control parameter obtains more little, and the basic waveform difference of characterization logic " 0 " and logical one is big more, and the difficulty of demodulation is more little, but the also corresponding reduction of bandwidth efficiency; The regulation and control parameter obtains big more, and the basic waveform difference of characterization logic " 0 " and logical one is more little, and band efficiency is high more, but demodulation performance can be worse and worse.This modulation system is expressed as:

$f(t,\mathrm{\&tau;})=\left\{\begin{array}{cc}\sin \mathrm{<figure-callout\; id="0"\; label="t"\; filenames="H2008101548554E0000011.png,H2008101548554E0000021.png"\; state="\{\{state\}\}">t</figure-callout>}& 0\&le;t\&le;\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\\ \sin (\frac{t-\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}}{\mathrm{\&tau;}-\frac{T}{4}}\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}+\frac{T}{4})& \frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\&le;t\&le;\mathrm{\&tau;}\\ \sin (\frac{t-\mathrm{\&tau;}}{\frac{3T}{4}-\mathrm{\&tau;}}\frac{\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}+\frac{T}{2})& \mathrm{\&tau;}\&le;t\&le;\frac{3\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\\ \sin t& \frac{3\mathrm{<figure-callout\; id="4"\; label="T"\; filenames="H2008101548554E0000052.png"\; state="\{\{state\}\}">T</figure-callout>}}{4}\&le;t\&le;T\end{array}\right..---\left(1\right)$

The T here is the cycle of modulation waveform, also is the symbol intervals of code-element period and information simultaneously; F=1/T is the frequency of carrier wave, numerically also equals the transmission rate of code element; When information bit was " 1 ", waveform generator produced

The time f (t) (remember into f ₁(t)); When information bit was " 0 ", waveform generator produced

The time f (t) (remember into f ₀(t)), wherein α (0＜α＜1) is waveform regulation and control parameters.

F (t) is four sections functions shown in Fig. 1 (c).Two sections functions and Fig. 1 (a) that itself and " 03152978.X " number patent are invented compare, in a code-element period, no one overlaps two kinds of basic code unit waveforms of the characterization logic " 0 " of g (t) and logical one in time domain, even two kinds of waveforms have greater difference, the performance in frequency domain just can not be very good like this.For super narrowband modulation technology, key point is need can embody the difference that characterizes two kinds of basic logic signals at half place of code-element period to get final product, specific (special) requirements is not done in other positions, in order to realize the super arrowband in the frequency domain, the basic waveform difference of wishing other positions certainly is the smaller the better, and the sine wave that is near the mark more is good more.Contrast first section and the 4th section sine wave that belongs to standard of four sections function f (t), middle two sections [T/4, τ] and [τ, 3T/4] two kinds of basic waveforms locating (supposing that a code-element period is T) characterization logic " 0 " and logical one begin to occur difference, and reach maximum at T/2, be beneficial to separate the small phase difference detection that timing carries out a half period place.This modulation system also has following technical characterictic:

The difference of a, two kinds of basic waveforms reaches maximum at t=T/2.

B, two kinds of basic waveform amplitude A are invariable, and peak value lays respectively at t=T/4 and t=3T/4 place, and can any change not take place along with the increase of basic waveform difference.

C, waveform satisfy f ₁(t)=-f ₀(T-t), f ₀(t) and f ₁(t) be the sine wave of standard in the time period in [0, T/4] and [3T/4, T], its frequency spectrum has obtained better compression.

The frequency of d, this modulation waveform is to be invariable all the time and to be numerically equal to bit rate.

E, can control the difference size of two kinds of basic waveforms by the selection of waveform regulation and control parameter alpha (0＜α＜1), when being in the discrimination that can weaken different wave under the big signal to noise ratio environment by increase α, can be under the little signal to noise ratio environment when being in by reducing the discrimination that α strengthens different wave.

In addition, in each code-element period, no matter be to select any waveform, transmitting power is almost constant.

Get T=1ms, the time domain waveform that obtains three kinds of different modulating modes as shown in Figure 1.Fig. 2 is the logarithm map of magnitudes of the power spectrum of three kinds of different modulating mode correspondences, wherein ordinate be power spectrum amplitude with carrier frequency 1kHz place as 0dB, abscissa is relative frequency f/f _cAs can be seen from the figure, in the output signal power spectrum of this patent less higher harmonic components is arranged, but its amplitude is all than more than the low 40dB at least of first-harmonic (be about ten thousand of first-harmonic/), only need less bandwidth just can keep wave character preferably after by band pass filter, the waveform of output is also comparatively near sinusoidal wave.Fig. 2 (c) is compared and can find with Fig. 2 (a), and spectrum energy is concentrated to the fundamental frequency place more, and the overall attenuation speed of spectrum envelope is also faster.Though the frequency spectrum main lobe has been widened, this can suppress by band pass filter.Continue comparison diagram 2 (c) and Fig. 2 (b), the higher harmonic components of Fig. 2 (c) is more than Fig. 2 (b) as can be seen, and the width of main lobe also slightly increases, and these can suppress by band pass filter too.

Fig. 3 has provided the time domain waveform of three kinds of distinct methods correspondences when regulation and control parameter is separately got different value, can find obviously that the performance of Fig. 3 (c) is better than other two kinds of methods.At the waveform among Fig. 3 (a), when the regulation and control parameter alpha was got different values, the difference of two kinds of basic wave modes was generally bigger, and the amplitude disunity; Waveform among Fig. 3 (b), when regulating and control parameter A (similarly regulating and control parameter) when getting less value with α, two kinds of basic waveforms have less difference, and amplitude is unified, when being under the little signal to noise ratio environment, when needing increase regulation and control parameter A to strengthen the discrimination of basic waveform, problem has just occurred, can find to increase to after 0.5 as A, it is no longer unified that the amplitude of two kinds of basic waveforms just becomes, saltus step can take place in amplitude maximum and minimum value place in two kinds of waveforms, and this can badly influence various performance parameters and further use.Waveform among Fig. 3 (c) can be controlled the output bandwidth and the signal to noise ratio of modulation signal by changing the regulation and control parameter alpha, this modulation signal can obtain higher band efficiency again behind filter, in regulation and control parameter alpha change process, modulation waveform is continuous everywhere, and wave-shape amplitude is unified all the time, be constant amplitude modulation waveform truly, satisfy f ₁(t)=-f ₀(T-t), simultaneously at time period [0, T/4] and [3T/4, T] be exactly the sine wave of standard, this waveform is just because of kept the constant of modulated signal amplitude, so can not be subjected to the influence of amplitude limit, help the synchronous of signal simultaneously, also make things convenient for the reception of demodulating end, its practicality has also obtained promoting greatly.

The example of modulator of the present invention as shown in Figure 4, being kept in the memory is by the defined f of (1) formula ₀(t) and f ₁(t) sampled value of waveform in one-period (promptly characterizes " 0 ", " 1 ") waveform sample, the quantity of sample value can be set as required, also can be according to the requirement of bandwidth, storage is through the filtered waveform sample of digital band pass, utilize then by selector switch of the Digital Signals that will transmit, under the control of clock signal, select corresponding waveform sample, selected waveform sample is directly changed into the modulated signal of simulation by digital to analog converter, export through after the band-pass filter, whole modulating system is that total digitalization realizes again.

The demodulation method of constant amplitude and period digital signal of the present invention is based on the demodulates information mode of small phase difference, only need just can finish demodulation in the i.e. two/one-period place's judgement of once sampling of the mid point of received signal waveform.Its characteristics have operand low, and equipment is simple, and processing speed is fast.Fig. 5 is the example of demodulator of the present invention, have interchannel noise and distortion and the modulated signal of distortion through behind the bandpass filtering, be divided into two-way, the carrier frequency of leading up to extracts synchronizing signal, forms sampling pulse; Another road is in half place's sampling of code-element period, and waveform phase information and standard sine wave phase that sampling is obtained compare, if waveform phase is more leading than standard sine wave phase, the binary message that can judge transmission is " 1 ", otherwise is " 0 ".Here also can adopt the demodulation method of another kind based on the zero crossing detection, same only need be two/one-period to locate once to sample to adjudicate just can finish demodulation at the mid point of received signal waveform.By Fig. 1 (c) as can be known, the midpoint at code-element period has f ₀(T/2)＞0, f ₁(T/2)＜0.So by sampling to received signal in this moment, the binary element that can adjudicate transmission according to the polarity of sampled value is " 1 " or " 0 ".As shown in Figure 6, the modulated signal that receives is removed through band pass filter earlier and is disturbed, enter sampler then, form sampling pulse and send into sampler by system clock, sampler is sent signal sampling value into zero-crossing detector at half place of code-element period, if sampled value is a positive number, the binary message that can judge transmission is " 0 ", otherwise be " 1 ", thereby restore the digital information of original transmission.

For native system, can in the signal bandwidth of 200Hz, realize the transmission code rate of 20kb/s, modulation efficiency reaches 100bps/Hz, and might further improve.

Claims (3)

1. constant amplitude and period digital signal modulating method utilizes the binary message code element directly to change the waveform of carrier wave, the modulation waveform f that produces when information bit is " 1 " ₁(t) the modulation waveform f that produces and when information bit is " 0 " ₀(t) compare with standard sine wave and have adjustable fine difference; This modulation system can be expressed as:

$f(t,\mathrm{\&tau;})=\left\{\begin{array}{cc}\sin t& 0\&le;t\&le;\frac{T}{4}\\ \sin (\frac{t-\frac{T}{4}}{\mathrm{\&tau;}-\frac{T}{4}}\frac{T}{4}+\frac{T}{4})& \frac{T}{4}\&le;t\&le;\mathrm{\&tau;}\\ \sin (\frac{t-\mathrm{\&tau;}}{\frac{3T}{4}-\mathrm{\&tau;}}\frac{T}{4}+\frac{T}{2})& \mathrm{\&tau;}\&le;t\&le;\frac{3T}{4}\\ \sin t& \frac{3T}{4}\&le;t\&le;T\end{array}\right..---\left(1\right)$

Wherein: T is the cycle of modulation waveform, also is the symbol intervals of code-element period and information simultaneously; F=1/T is the frequency of carrier wave, numerically also equals the transmission rate of code element; When information bit was " 1 ", waveform generator produced

The time f (t) (remember into f ₁(t)); When information bit was " 0 ", waveform generator produced

The time f (t) (remember into f ₀(t)), wherein α (0＜α＜1) is waveform regulation and control parameters;

This method has following technical characterictic:

The difference of a, two kinds of basic waveforms reaches maximum at t=T/2;

B, two kinds of basic waveform amplitude A are invariable, and peak value lays respectively at t=T/4 and t=3T/4 place, and can any change not take place along with the increase of basic waveform difference;

C, waveform satisfy f ₁(t)=-f ₀(T-t), f ₀(t) and f ₁(t) be the sine wave of standard in the time period in [0, T/4] and [3T/4, T], its frequency spectrum has obtained better compression;

The frequency of d, this modulation waveform is invariable all the time and is numerically equal to bit rate;

E, can control the difference size of two kinds of basic waveforms by the selection of waveform regulation and control parameter alpha (0＜α＜1), when being in the discrimination that can weaken different wave under the big signal to noise ratio environment by increase α, can be under the little signal to noise ratio environment when being in by reducing the discrimination that α strengthens different wave.

2. one kind is used for the described constant amplitude and period digital signal modulating method of claim 1, it is characterized in that:

According to (1) formula respectively to the f of characterization information " 0 " ₀(t) and the f of " 1 " ₁(t) two kinds of basic waveforms are sampled in one-period, and the waveform sample in the complete cycle that obtains after the sampling is stored in two storage areas; Selector switch of binary message control waiting for transmission in a wave period, is selected f respectively ₀(t) or f ₁(t) road corresponding memory block in; Waveform sample in the memory block converts modulated high frequency analog signals to and exports behind band pass filter by digital to analog converter under the control of synchronised clock.

3. demodulation method that is used for the constant amplitude and period digital signal of claim 1 or 2 described constant amplitude and period digital signal modulating methods is divided into two kinds of the demodulation methods that detect based on the demodulation method of small phase difference with based on zero crossing; It is characterized in that:

Based on the demodulation method of small phase difference, only need be two/one-period to locate once to sample to adjudicate just can finish demodulation at the mid point of received signal waveform; That is: the modulated signal of reception is removed through band pass filter earlier and is disturbed, enter sampler then, formed sampling pulse and sent into sampler by system clock, sampler is sent the phase place that obtains into the binary message that small phase difference detector restores original transmission by half place of code-element period is sampled.

Based on the demodulation method that zero crossing detects, only need be two/one-period to locate once to sample to adjudicate just can finish demodulation at the mid point of received signal waveform; That is: in the midpoint of code-element period, f is arranged ₀(T/2)＞0, f ₁(T/2)＜0, sample by the received signal to this moment, the binary element of adjudicating transmission according to the polarity of sampled value is " 1 " or " 0 ".

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