CN102255632B

CN102255632B - Adaptive pulse position modulation signal demodulation method

Info

Publication number: CN102255632B
Application number: CN 201110201500
Authority: CN
Inventors: 敖珺; 朱勇; 邓洪高; 马春波
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2011-07-19
Filing date: 2011-07-19
Publication date: 2013-09-18
Anticipated expiration: 2031-07-19
Also published as: CN102255632A

Abstract

The invention discloses an adaptive pulse position modulation signal demodulation method, which comprises sampling and judgment. One is added to a pulse timeslot counter every time when sampling points are recorded for N times when the sampling points are recorded, and a sampling point counter is cleared. The method specifically comprises the steps of: sampling, sum computing, judgment made in whether an adaptive range L is finished or not, starting of adaptive processing, synchronous position control and the next adaptive processing. The method is a maximum-comparison-based judgment algorithm; and by the method, besides functions the same as that of the conventional methods are realized, the pulse position module (PPM) signal can be effectively demodulated under the condition of not setting a judgment threshold value and shortening program running time, demodulation performance is greatly improved, and theoretically, signals with energy higher than noise energy all can be accurately decoded.

Description

The adaptive demodulation method of pulse position modulation signal

Technical field

The present invention relates to optical communication or super broad band radio communication system, specifically is the demodulation of pulse position modulation signal.

Background technology

Adopt the PPM(pulse position modulation at present) in the communication system of scheme, what its demodulation method adopted is threshold value judgement method, namely set a fixing signal decision threshold value at receiving terminal, the sampled signal energy that only receives just can be judged to signal greater than this threshold level, otherwise then is judged to no signal.Like this for fear of erroneous judgement, just the requirement of threshold level to received signal is very high, but this method very easily produces failing to judge of signal, and when channel condition changes, threshold value judgement demodulation method can't carry out adaptive adjustment to preset threshold level, thus correctly demodulation.

Existing PPM demodulating algorithm scheme based on the threshold value judgement is as follows: set a decision threshold, the PPM signal is sampled, each time slot of demodulating end is adopted the individual sampling point of n (n is the odd number greater than 3), if the sampled level sum of n sampled point of certain PPM signal slot is greater than this threshold value, then judge and occurred a pulse on this time slot, and recording this pulse place time slot position in signal frame, this time slot position is the information data of emission.

Be specially:

It is a fixed value that decision threshold sum1 at first is set;

A) the PPM signal is sampled, whenever adopt sampling point one time, Pin=Pin+1 preserves sampling point value;

B) ask sum, sum=x (0)+x (1)+...+x (n-1);

C) relatively judgement: if sum 〉=sum1, illustrate and find pulse, carry out step d); Otherwise rebound step a);

D) ask Pk according to the value of current Pin, M;

Pk=int[Pin/n]; The current time slots number equals the merchant of current hits after divided by n and rounds

M=mod[Pin/n]; The bit synchronization of current time slots is adjusted parameter and is equaled current hits divided by the remainder of n.

E) bit synchronization adjustment, if M≤((n-1)/2), Pk=Pk+1; When being M≤((n-1)/2), then the current time slots number adds 1, otherwise that current time slots is counted Pk is constant.

F) note the Pk value, while Pin, Pk, the equal zero clearing of sum, the rebound step a) is carried out the judgement of next round threshold value.

Like this, after taking turns the threshold value judgement through one, if satisfy sum 〉=sum1, namely think and find a pulse, and through step d) and e), just can decode needed information.

The problem that prior art exists:

There is the defective of a maximum in threshold value judgement: in case threshold value setting then can't adjust, if the sampled level sum that produces on incorrect position then can produce the demodulates information mistake greater than this threshold value.Find in the experiment that current communication condition is depended in the setting of threshold value, and in fact communication condition is uncertain often, and changes in time, so just make that the setting of threshold value is more complicated, and have very big restricted.

Summary of the invention

In view of two problems of existing in prior technology, the objective of the invention is to propose a kind of adaptive threshold judgement PPM demodulating algorithm.This method can not need to set under the situation of decision threshold, effectively demodulation PPM signal.

The adaptive demodulation method of pulse position modulation signal of the present invention comprises sampling, judgement, takes N sampled point pulse slot of every record counter just to add 1 in the record sampled point, then with the sampled point counter O reset; Concrete steps are as follows:

A) the paired pulses position modulation signal is sampled, and whenever adopts sampling point one time, Pin=Pin+1, when Pin=N, then:

Pk=Pk+1；

temp_Pk=?temp_Pk+1；

Pin=0；

B) ask sum, sum=x (0)+x (1)+... + x (N-1);

C) judge whether an adaptive range L finishes, if temp_Pk＜L skips to step d), carry out self-adaptive processing; Otherwise skip to step e);

D) begin self-adaptive processing, compare the size of sum and temp_sum, if sum=temp_sum, then: sum=temp_sum, and note current Pk and Pin, a=Pk, M=Pin continues to skip to step a); If temp_sum〉sum, be left intact, skip to step a);

E): the bit synchronization adjustment, if Pk=Pk+1 during M≤((N-1)/2), namely during M≤((N-1)/2), then the current time slots number adds 1, otherwise current time slots is counted Pk and is remained unchanged;

F): note Pk, while sum, temp_sum, the temp_Pk zero clearing continues the rebound step a) and carries out self-adaptive processing next time;

Above-mentioned:

Pk: time slot counter, initial value are 0;

Pin: sampled point counter, initial value are 0;

M: bit synchronization is adjusted parameter, and initial value is 0;

N: each time slot sampling number, get the odd number greater than 3;

A: the i.e. value of Pk;

X; Current sampling numerical value, initial value are 0;

Sum: a current sampled value and preceding N-1 sampled value sum, namely sum=x (0)+x (1)+... + x (N-1);

L: adaptive range, be made as a fixed integer, in L, only there is a signal pulse;

Temp_sum: deposit the sum value of previous moment, initial value is 0;

Temp_Pk: adaptive range counter.

During concrete enforcement, determine L according to the frame structure of PPM signal.

In practical application, with a) to f) the step compiled program, write the pulse position modulation signal dash receiver.

The present invention compares all collected on frame time sum values, and wherein a Zui Da corresponding time slot position of sum value is represented the signal location on this frame.As long as fact proved to meet the following conditions, the present invention is correctly demodulation all:

(a). signal energy is greater than noise energy, and this condition is all set up generally speaking;

(b). set a fixing adaptive range L, and in L, only have a signal pulse, can determine L according to the frame structure of PPM signal.

The present invention has following advantage with respect to traditional threshold value judgement method:

The present invention carries out maximum relatively between each position sum value, do not need to set fixing threshold value, is the decoding judgement that produces the minimum demodulating error probability.

Description of drawings

Fig. 1 self-adapting threshold judgement PPM demodulating algorithm flow chart;

Fig. 2 PPM modulation demodulation system block diagram;

Reception oscillogram when Fig. 3 PPM signal pulse level is 1.5 v;

Reception oscillogram when Fig. 4 PPM signal pulse level is 1v;

Reception oscillogram when Fig. 5 PPM signal pulse level is 0.5 v;

The figure as a result of Fig. 6 conventional P PM demodulating algorithm;

The figure as a result of Fig. 7 Adaptive PPM demodulating algorithm.

Embodiment

See Fig. 1 based on self-adapting threshold judgement PPM demodulating algorithm flow process.Concrete steps are as follows:

S1-1: a fixing adaptive range L is set;

S1-2: the PPM signal is sampled, whenever adopt sampling point one time, Pin=Pin+1 preserves sampling point value;

S1-3: judge whether Pin equals N-1, if equal, then carry out step S1-4; Otherwise, skip to step S1-5;

S1-4:Pk adds 1, temp_Pk and adds 1, Pin zero clearing;

S1-5: ask sum, sum=sum=x (0)+x (1)+... + x (N-1);

S1-6: judge whether adaptive range finishes, if temp_Pk＜L then skips to step S1-7; Otherwise skip to step S1-9;

S1-7: relatively judgement, if temp_sum is less than or equal to sum, then carry out step S1-8; Otherwise skip to step S1-2;

S1-8: preserve value bigger among sum and the temp_sum, namely temp_sum=sum notes current Pk value and Pin value, a=Pk, M=Pin simultaneously;

S1-9: the bit synchronization adjustment, if M=3 or M=4 then carry out step S1-10; Otherwise skip to step S1-11;

S1-10: note the value of a, i.e. the value of Pk;

S1-11: the bit synchronization adjustment, a adds 1, skips to step S1-10;

S1-12:sum, temp_sum, the equal zero clearing of temp_Pk skips to step S1-2, carries out next round adaptive threshold decision algorithm.

A complete PPM modulation demodulation system as shown in Figure 2.The PPM transmission board is used for producing the PPM modulation signal, by the laser external modulation, converts electric PPM signal to light PPM signal and launches then; Optical attenuator is decayed to the light PPM signal strength signal intensity that receives, by regulating the light PPM signal that optical attenuator obtains varying strength; The light PPM signal that photoelectric detector will receive converts electric PPM signal again to, is sent to the PPM dash receiver and carries out demodulation; The PPM dash receiver carries out demodulation to the electric PPM signal of photoelectric detector output, and the character that demodulation is come out is sent to PC by serial ports and shows.Wherein the PPM transmission board sends character string " hold ".

Respectively the program of two kinds of schemes is write in the PPM dash receiver now, come more above-mentioned two kinds of methods by concrete PPM modulating and demodulating signal example.

If in the conventional P PM demodulating algorithm, decision threshold sum1 is made as 1v.

It is 1.5 v that the adjusting optical attenuator makes the PPM signal pulse level of photoelectric detector output, satisfies sum 〉=sum1.Receive waveform as shown in Figure 3.

Regulate the PPM signal pulse electricity 1v that optical attenuator makes photoelectric detector output, satisfy sum=sum1.Receive waveform as shown in Figure 4.

It is 0.5v that the adjusting optical attenuator makes the PPM signal pulse level of photoelectric detector output, does not satisfy sum 〉=sum1.Receive waveform as shown in Figure 5.The demodulation result of above-mentioned two kinds of schemes is seen Fig. 6, Fig. 7.PPM transmission board transmission character string " hold " had only two when PC showed conventional P PM demodulating algorithm among Fig. 6.Proof conventional P PM demodulating algorithm, a PPM signal pulse level in output are that the situation of 1.5 v and 1v can be correctly decoded.When the PPM signal pulse level of output is 0.5v, do not satisfy sum 〉=sum1 the time, can not decode.PC shows that Adaptive PPM demodulating algorithm PPM transmission board sends character string " hold " and has three among Fig. 7.The proof and Adaptive PPM demodulating algorithm of the present invention then all can be correctly decoded under above-mentioned three kinds of situations.

Hence one can see that, and the decoding performance of the adaptive demodulation method of pulse position modulation signal of the present invention obviously is better than conventional P PM demodulation method.

Claims

1. the adaptive demodulation method of pulse position modulation signal comprises sampling, judgement, it is characterized in that: N sampled point of every record in the record sampled point, and the pulse slot counter just adds 1, then with the sampled point counter O reset; Concrete steps are as follows:

Pk=Pk+1；

temp_Pk=?temp_Pk+1；

Pin=0；

B) ask sum, sum=x (0)+x (1)+... + x (N-1);

Above-mentioned:

Pk: pulse slot counter, initial value are 0;

Pin: sampled point counter, initial value are 0;

M: bit synchronization is adjusted parameter, and initial value is 0;

N: each time slot sampling number, get the odd number greater than 3;

A: the i.e. value of Pk;

X: current sampling numerical value, initial value are 0;

L: adaptive range is a fixed value, only has a signal pulse in L;

Temp_sum: deposit the sum value of previous moment, initial value is 0;

Temp_Pk: adaptive range counter.

2. the adaptive demodulation method of pulse position modulation signal according to claim 1, it is characterized in that: the frame structure according to the PPM signal is determined L.

3. the adaptive demodulation method of pulse position modulation signal according to claim 1 is characterized in that: with a) to f) the step compiled program, write the pulse position modulation signal dash receiver.