CN100586116C - Multielement positional phase shift keying modulation and demodulation method - Google Patents

Abstract

The method comprises: using M-scale notation information symbols to directly control the location of sinusoidal carrier phase jump moment in each code element cycle, and inserting a certain guard gap to implement the modulation of M-element signals so as to realize the higher rate transmission in case of the symbol rate same with the EBPSK (extended binary phase shift keying) and same bandwidth occupation.

Description

Multielement positional phase shift keying modulation and demodulation method

Technical field

The present invention relates to the information modulation and demodulation in the digital communication, particularly a kind of multielement positional phase shift keying modulation and demodulation method belongs to the technical field of high-efficiency digital message transmission.

Background technology

In the digital communication system, the process of binary data 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 applicant's patent application formerly " unified binary phase modulation and demodulation method " (application number: 200610040767.2, publication number: CN1889550A), proposed a kind of unified description and digital implementation method, obtained a class " binary phase shift keying of expansion " (EBPSK:Extended Binary Phase Shift Keying) modulation system the binary phase modulation system.EBPSK utilizes data bit directly to control the phase hit and the duty ratio of time thereof of sinusoidal carrier: when transmission binary element " 0 ", transmission is the sine wave of N carrier cycle; And at the transmission binary element when " 1 ",, thereby realized that main peak gives prominence to the extremely low spectrum structure of sideband to the carrier wave interpolation phase hit in preceding K cycle of this N carrier cycle.But EBPSK generally can only transmit binary element, is not easy to high system modulation.Therefore, under the almost constant condition of spectrum structure and transmitting power, above-mentioned patent application expanded be used for polynary modulation and demodulation, necessary.

In the pulse modulation system of classics, adopt pulsion phase to transmit different symbolic information usually, as pulse position modulation (PPM:Pulse Position Modulation) for the difference of carrier position." multielement positional phase shift modulated and the demodulation method " that the present invention proposes also is to realize the multi-system transmission by changing the position; have necessarily similar to PPM; but the method for its control sinusoidal carrier phase jump position, protection at interval insertion and based on the demodulation structure of phase-locked loop, all have more different with PPM.

Summary of the invention

The present invention seeks to propose a kind of multielement positional phase shift keying modulation and demodulation method, be desirable to provide a kind of can be in a code-element period diverse location of offset of sinusoidal carrier wave carry out phase shift keying (PSK:Phase Shift Keying) modulation and corresponding demodulation method, so that on the basis of previous application EBPSK modulation, further utilize the carrier phase saltus step difference of position to occur, characterize the modulation symbol of multi-system, make with N same carrier cycle of EBPSK in can transmit the more information data.When being reception, key need carry out position probing and integration judgement according to the amplitude difference of phase-locked loop phase discriminator output level.

Technical scheme of the present invention is: multielement positional phase shift keying modulation and demodulation method, the sudden change phase place that directly changes sinusoidal carrier with the binary message code element realizes modulation, realize that with phase-locked loop demodulation method is the basis, be engraved in the position in each code-element period during the phase hit that it is characterized in that adopting M binary information symbol directly to control sinusoidal carrier, realize the modulation of signal, it can specifically be expressed as in a code-element period NT:

$f_k\left(t\right)=\left\{\begin{array}{ccc}\sin {\mathrm{\&omega;}}_{c}t,& 0\&le;t<\mathrm{NT},& k=0\\ \left\{\begin{array}{ccc}\sin {\mathrm{\&omega;}}_{c}t& 0\&le;t\&le;(k-1)\mathrm{KT}& \\ \sin ({\mathrm{\&omega;}}_{c}t+\mathrm{\&theta;})& (k-1)\mathrm{KT}<t<(k-r_g)\mathrm{KT},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}& 1\&le;k\&le;M-1\\ \sin {\mathrm{\&omega;}}_{c}t& (k-r_g)\mathrm{KT}\&le;t<\mathrm{NT}& \end{array}\right.& & \end{array}\right.$

Wherein, k=0,1 ..., M-1 is the symbol of actual transmission, and M＞2 kind of different value is arranged; $T=\frac{2\mathrm{\&pi;}}{{\mathrm{\&omega;}}_c}$ Be carrier cycle; 0≤r _g＜1 for symbol protection interval controlling elements, by M, K, N, θ and r _gConstituted " modulation parameter " that change signal bandwidth, efficiency of transmission and demodulation performance; In addition, after the carrier phase saltus step, can insert guardtime at interval.

Adopt phase-locked loop to realize separating timing, utilize phase discriminator output to judge the position of phase hit, realize the demodulation of multi-system symbol, both can adopt during judgement and simply put sampling value method relatively by turn, also can export phase discriminator according to the saltus step duration earlier and put coherent accumulation by turn, reconvict after making signal to noise ratio improve, to guarantee better demodulation performance.

Advantage of the present invention and beneficial effect:

1) band efficiency height.Because adopt the transmission technology of multi-system, under identical chip rate, information rate can significantly improve, and maintenance transmitting power and transmission bandwidth are almost constant.Therefore, has the very high availability of frequency spectrum.

2) the performance adjustment is flexible.By " modulation parameter " M, K, θ and r _gAnd N, can change signal bandwidth, transmission code rate and demodulation performance arbitrarily, make that the performance design of communication system and index adjustment are more flexible.

3) receiver structure is simple.With the digital PLL is the receiver of core, has not only realized the coherent demodulation of signal, and is used for frequency synthesis, bit synchronization, carrier frequency tracking etc.Improved PD structure can accurately be extracted modulation intelligence, alleviates the design difficulty of subsequent detection and judging module.

Description of drawings

Fig. 1 is the MPPSK modulating system block diagram that the present patent application proposes;

Fig. 2 is the MPPSK demodulating system block diagram that the present patent application proposes;

Fig. 3 be the MPPSK that proposes of the present patent application when M=4, the modulation signal waveform that produces by quaternary symbol sebolic addressing [0,3,1,2] and the corresponding output result of receiver phase discriminator ideally.

Embodiment

At first, the inventive method is remake in detail and further specifies.

1, the EBPSK modulator approach is looked back

The EBPSK modulator approach that we propose in No. 200610040767.2 patent applications is that directly to change frequency with the binary message code element be ω _cThe sudden change phase place of sinusoidal carrier realize modulation, make the modulated signal f of corresponding digital " 0 " _o(t) be the sine wave of N carrier cycle, and the f of corresponding numeral " 1 " _x(t) then be to be ω in frequency _cThe sine wave of N carrier cycle in, the phase hit in a preceding K cycle θ angle.Promptly

f ₀(t)＝Asinω _ct，0≤t＜NT

$f_1\left(t\right)=\left\{\begin{array}{cc}B\sin ({\mathrm{\&omega;}}_{c}t+\mathrm{\&theta;}),& 0\&le;\mathrm{tKT},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}\\ A\sin {\mathrm{\&omega;}}_{c}t,& \mathrm{KT}\&le;t<\end{array}\right.----\left(1\right)$

Wherein, T=2 π/ω _cBe carrier cycle, then NT is the symbol period of data message, and promptly information symbol has continued N 〉=1 carrier cycle; Phase hit has then continued K≤N carrier cycle.

If the amplitude of EBPSK modulation change signal then makes A=B=1, and uses k=0, the actual information symbol that sends of 1 expression, then (1) formula can be unified to be simplified shown as

$f_k\left(t\right)=\left\{\begin{array}{ccc}\sin {\mathrm{\&omega;}}_{c}t,& 0\&le;t<\mathrm{NT},& k=0\\ \left\{\begin{array}{cc}\sin ({\mathrm{\&omega;}}_{c}t+\mathrm{\&theta;}),& (k-1)\mathrm{NT}\&le;t<\mathrm{kKT},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&theta;}\\ \sin {\mathrm{\&omega;}}_{c}t,& \mathrm{kKT}\&le;t<\mathrm{NT}\end{array}\right.& k=1& \end{array}\right.---\left(2\right)$

2, introduce position modulation information

Be not difficult to find out by EBPSK expression formula (2): the position of phase hit corresponding to numeral " 1 " is fixed, thereby EBPSK is modulated in the symbol period and can only transmits 1bit.If the phase hit of EBPSK can be staggered in time, just can in a symbol period, represent more information.Suppose in a symbol period, can hold M-1 different phase jump position, then together with pure sine wave corresponding to the no phase hit of digital " 0 ", can represent M 〉=2 kind of different information value, thereby EBPSK from having only this one-dimensional modulation of fixing phase shift keying, expand to a kind of and can on phase shift and position, all carry out the two-dimensional modulation of keying, we are referred to as multielement positional phase shift keying (MPPSK:M-ary PositionPhase Shift Keying) modulation, can be expressed as follows in the one symbol period:

$f_k\left(t\right)=\left\{\begin{array}{ccc}\sin {\mathrm{\&omega;}}_{c}t& 0\&le;t<\mathrm{NT}& k=0\\ \left\{\begin{array}{ccc}\sin {\mathrm{\&omega;}}_{c}t& 0\&le;t\&le;(k-1)\mathrm{KT}& \\ \sin ({\mathrm{\&omega;}}_{c}t+\mathrm{\&theta;})& (k-1)\mathrm{KT}<t<(k-r_g)\mathrm{KT},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}& 1\&le;k\&le;M-1\\ \sin {\mathrm{\&omega;}}_{c}t& (k-r_g)\mathrm{KT}\&le;t<\mathrm{NT}& \end{array}\right.& & ---\left(3\right)\end{array}\right.$

Wherein, k=0,1 ..., M-1 is the symbol of actual transmission, and the different value of M kind is arranged; 0≤r _g＜1 is symbol protection interval controlling elements.By M, K, θ, r _gAnd N, constituted " modulation parameter " that change signal bandwidth, efficiency of transmission and demodulation performance.Obviously, as M=2 and r _g=0, (3) formula deteriorates to (2) formula, and visible EBPSK is modulated to a special case of MPPSK modulation.

Thereby the transmission signals of actual MPPSK modulation is:

$S\left(t\right)=\underset{n}{\mathrm{\&Sigma;}}f(t-\mathrm{nNT})---\left(4\right)$

3, the symbol protection at interval

Because the demodulation of signal is directly relevant with the output of phase-locked loop (PLL) phase discriminator (PD), so the quality of PD output waveform will directly influence demodulation performance.Ideally, require the PD output pulse width to be limited in the carrier cycle, at this moment put sampling by turn and can obtain the optimal judgement effect; And the output pulse of actual PD tends to broadening, and difference is not obvious when causing putting by turn sampling, thereby causes erroneous judgement; Therefore, take all factors into consideration factors such as the exponent number of loop bandwidth, damping coefficient and PD low pass filter of PLL and cut-off frequency, can effectively tightly restraint the width of PD output pulse, improve demodulation performance; And on the other hand,, can also directly dwindle the width of PD output pulse if can after the carrier phase saltus step, insert the protection interval of certain hour, avoid erroneous judgement.Created symbol that Here it is in the MPPSK expression formula of (3) formula protection is controlling elements r at interval _gPurpose.

In addition, when actual channel is transmitted, because the temporal extension and the frequency expansion of channel can cause intersymbol interference, and pass through r _gInsert protection and not only can alleviate intersymbol interference at interval, also offset the influence of multipath transmission to a certain extent.

4, code check, carrier frequency and system number

1) information symbol of MPPSK modulation can have M kind value, so be M system (or M unit) modulation, every symbol can transmit r=log ₂The M bit, only from this on the one hand, the M value is big more, and efficiency of transmission is high more.

2) owing to the structure of receiver, so to reserve certain stabilization time between twice phase hit of carrier wave, so that make PLL return to tracking mode based on phase-locked loop.From (3) formula as can be known, it is " M-1 " that twice phase hit of carrier wave minimum value at interval occurs in previous information symbol, and a back information symbol is " 1 ", and this interval minimum value is:

g _min＝NT-[(M-1)-rx]KT＝NT-(M-1-r _g)KT＜NT-(M-2)KT (5)

By g _Min〉=0, can obtain

N＞(M-2)K (6)

By (6) formula and (3) formula as can be known, if N is certain, then K=1 helps M and gets bigger value, increase and make the transmission code rate and the availability of frequency spectrum all can promote thereupon because system is counted M, but input will be more difficult also.Then this moment, (6) formula became

N＞M-2 (7)

3) as carrier cycle T (or carrier frequency ω _c) and M one regularly, the more little then symbol width of N (NT) is narrow more, and transmission code rate is also high more, but the transmission bandwidth that takies is also wide more.

4) if N and M are certain, short more (or the carrier frequency ω of carrier cycle T then _cHigh more), transmission code rate is high more, and the absolute bandwidth that takies is wide more, but relative bandwidth then remains unchanged.

Therefore, choosing of code check, carrier frequency and system number will be considered according to the concrete condition of actual MPPSK communication system comprehensively, and the parameter group of above-mentioned MPPSK modulation just in time provides the flexibility of multiple choices.

Embodiment: system parameters: get carrier frequency f _c=465kHz, N=10, phase place deflection

Sample rate f _s=10f _c=4.65MHz, r _g=0, carrier cycle T=1/f then _c, character rate=1/ (10T)=46.5kHz.

As shown in Figure 1, the sampled value of modulation symbol basic waveform is stored in the waveform table, tables look-up and send corresponding M PPSK modulated signal waveform by digital to analog converter (D/A) by the value of symbol of input symbols sequence.Utilize the implementation of this hardware consulting table, even insert non-vanishing protection r at interval _g, can not increase extra operand and expense yet.

As shown in Figure 2, adopt the demodulator of PM signal PM structure based on phase-locked loop, when realizing carrier synchronization and sign synchronization, position probing and integration judgement are carried out in output to PD, realize the demodulation of signal.

Fig. 3 is " 0,3,1; 2 for one section symbol sebolic addressing of receiving terminal intercepting " 4PPSK waveform and corresponding PD output waveform, be not difficult to find, constantly at each phase hit, phase-locked loop PD has a bigger amplitude output, can determine positional information thus and demodulate the quaternary code element of transmission.Actual measurement finds, phase hit duration even can be less than a carrier cycle, and remainder as the protection interval;

Generally speaking, adopt, can select optimum value, simplified receiver structure greatly according to maximum a posteriori probability to PD output direct sample judgement.When interchannel noise is serious, also can put integration by turn to PD output, by accumulation with amplify and adjudicate again after improving signal to noise ratio, thereby effectively improve the demodulation performance of signal.

Claims (1)

1, multielement positional phase shift keying modulation and demodulation method, the sudden change phase place that directly changes sinusoidal carrier with the binary message code element realizes modulation, realizes demodulation with phase-locked loop, be engraved in the position in each code-element period during the phase hit that it is characterized in that adopting M binary information symbol directly to control sinusoidal carrier, realize the modulation of signal, this method can specifically be expressed as in a code-element period NT:

$f_k\left(t\right)=\left\{\begin{array}{ccc}\sin {\mathrm{\&omega;}}_{c}t& 0\&le;t<\mathrm{NT}& k=0\\ \left\{\begin{array}{c}\sin {\mathrm{\&omega;}}_{c}t\\ \sin ({\mathrm{\&omega;}}_{c}t+\mathrm{\&theta;})\\ \sin {\mathrm{\&omega;}}_{c}t\end{array}\right.& \begin{array}{c}0\&le;t\&le;(k-1)\mathrm{KT}\\ (k-1)\mathrm{KT}<t<(k-r_g)\mathrm{KT},0\&le;\mathrm{\&theta;}\&le;\mathrm{\&pi;}\\ (k-r_g)\mathrm{KT}\&le;t<\mathrm{NT}\end{array}& \begin{array}{c}\\ 1\&le;k\&le;M-1\\ \end{array}\end{array}\right.$

Wherein, k=0,1 ..., M-1 is the symbol of actual transmission, and M＞2 kind of different value is arranged; $T=\frac{2\mathrm{\&pi;}}{{\mathrm{\&omega;}}_c}$ Be carrier cycle; 0≤r _g＜1 for symbol protection interval controlling elements, by M, K, N, θ and r _gConstituted " modulation parameter " that change signal bandwidth, efficiency of transmission and demodulation performance, N is the quantity of carrier cycle, and K is preceding K cycle in the sine wave of N carrier cycle;

Adopt phase-locked loop to realize separating timing, utilize phase discriminator output to judge the position of phase hit, realize the demodulation of multi-system symbol.