CN105391668B - Phase shift keyed signal demodulation method based on RFID - Google Patents
Phase shift keyed signal demodulation method based on RFID Download PDFInfo
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/22—Demodulator circuits; Receiver circuits
- H04L27/233—Demodulator circuits; Receiver circuits using non-coherent demodulation
- H04L27/2331—Demodulator circuits; Receiver circuits using non-coherent demodulation wherein the received signal is demodulated using one or more delayed versions of itself
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/10—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation
- G06K7/10009—Methods or arrangements for sensing record carriers, e.g. for reading patterns by electromagnetic radiation, e.g. optical sensing; by corpuscular radiation sensing by radiation using wavelengths larger than 0.1 mm, e.g. radio-waves or microwaves
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7073—Synchronisation aspects
- H04B1/7075—Synchronisation aspects with code phase acquisition
- H04B1/70751—Synchronisation aspects with code phase acquisition using partial detection
- H04B1/70752—Partial correlation
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Abstract
The invention discloses a kind of phase shift keyed signal demodulation method based on RFID, it is characterised in that：Include the following steps：The phase difference of the front and back chip of input；Angular dividing line is set, by phase difference is point in reference axis by region division with angular dividing line；After point in reference axis is rotated fixed angle at same direction, then the point in reference axis is mapped as to the decision value without 0；Lead code synchronizes；Sampling judgement；Output conversion；The present invention makes decisions the phase difference of front and back chip by region with angular dividing line, then is rotated to court verdict, and mapping generates the new decision value for being not equal to 0, to improve the correlated performance of spreading code, to improve the noiseproof feature of psk signal demodulation；The present invention is simple to the demodulation method of phase shift keyed signal, unique, can be widely applied in radio-frequency recognition system.
Description
Technical field：
The present invention relates to signal demodulating methods, and in particular to the phase shift keyed signal demodulation method based on RFID.
Technical background：
Radio frequency identification (RFID) system of hyperfrequency (UHF) and microwave frequency band is worked in, it is low compared in having been widely used
Frequency RFID system, have the advantages that operating distance length and read or write speed it is fast, become at present in the world technology and product development
Hot spot.And China is still in the starting stage in the RFID technique of uhf band and microwave band.Although the whole world has existed more
A RFID international standards, but examined in order to which the needs and national information of complying with domestic RFID technique level and industry size are safe
Consider, China has promulgated standard GB/T/T 28925-2012 in 2012《Information technology radio frequency identification 2.45GHz air interfaces
Agreement》.Provide that label and reader support offset quadraphase shift keying (OQPSK) modulation system, and compatible difference two in standard
Phase phase-shift keying (PSK) (DBPSK) modulation system, is transmitted with 2MHz spread-spectrum code chip rates.Since multi-channel operation frequency accuracy is
The deviation of 20ppm, ppm i.e. hundred a ten thousandths, the frequency and local frequency that receive signal is about -100KHz~100KHz, frequency deviation
Range is big.Since the notional phase between chip before and after known frequency expansion sequence is poor, phase-shift keying (PSK) (PSK) non-coherent Differential can be used
Demodulation mode is demodulated.Phase-shift keying (PSK) (PSK) is a kind of modulation technique indicating input signal information with carrier phase.
Existing PSK Non-coherent Demodulations technical solution is：Dot product dot (k) and cross product cross is calculated to I, Q signal
(k), if it is difference PSK, directly demodulation output baseband signalling；If it is PSK, solution difference is carried out to demodulation result, obtains base
Tape symbol.Parallel-serial conversion is carried out to the baseband signalling demodulated again and obtains base band code stream.
Noiseproof feature when de-spreading frequency code with the prior art depends on the auto-correlation function performance of judgement value sequence, works as judgement
Value sequence auto-correlation function autocorrelation value when offset is 0 is higher, and when offset is not 0, autocorrelation value is relatively low, correlation
It can be preferably.Since QPSK/DQPSK modulates the state that lower dot product, difference-product have 0 value, the relevant performance of spreading code is reduced, together
When also reduce signal demodulation noiseproof feature.
Invention content：
Technical problem to be solved by the invention is to provide the phase shift keyed signal demodulation methods based on RFID, to improve
The noiseproof feature of psk signal demodulation.
To solve the above-mentioned problems, the technical scheme is that, the phase shift keyed signal demodulation method based on RFID,
It is characterized in that：Include the following steps：
The phase difference of chip before and after 1st step, input；
Phase difference is point in reference axis by region division with angular dividing line by the 2nd step, setting angular dividing line；
3rd step after the point in reference axis is rotated fixed angle at same direction, then the point in reference axis is mapped as newly
Be free of 0 decision value；
4th step, lead code synchronize：
4.1st step：The shift register that the decision value deposit length that 3rd step is obtained is L × R；L is spreading code the piece number；R
To sample multiple, sampling multiple takes the integer more than or equal to 2, obtains practical judgement value sequence Seqactual；
4.2nd step：The notional phase of known N groups spread-spectrum code chip is poor, and judgement obtains the theoretical decision value sequence of N group spread-spectrum code chips
Arrange { Seqtheory_0,Seqtheory_1…,Seqtheory_ N-1 }, and carry out R samplings；Wherein, under OQPSK modulation, N=16；
Under DBPSK modulation, N=2；
4.3rd step：Respectively by practical judgement value sequence SeqactualThe roads I, the roads Q and lead code 0 theoretical judgement value sequence
SeqtheoryThe roads I, the roads Q after _ 0 progress R samplings carry out cross-correlation, are then overlapped the roads I, the roads Q cross correlation value, obtain
The cross correlation value R of lead code 00；
4.4th step：To the cross correlation value R of lead code 00Judged, works as R0It is obtained more than threshold value Th and when reaching peak value same
Walk enable signal；Threshold value Th=2L × R × gain, gain=0~1；Gain is gain；
5th step, sampling judgement：
5.1st step, sample counter start counting up after synchronous enabled, when reaching next sampling central instant (L × R)
When, export sampling clock；
5.2nd step takes practical judgement value sequence Seq againactualEffective (L-2) × R points and N group spread-spectrum code chips below
Theoretical judgement value sequence { Seqtheory_0,Seqtheory_1…,Seqtheory_ N-1 } carry out the effective (L- in back after R samplings
2) × R points calculate separately the cross-correlation of practical judgement value sequence and the roads I and the roads I, the roads Q and the roads Q of theoretical judgement value sequence；
The roads I of each group, the roads Q cross correlation value are overlapped by the 5.3rd step, obtain N group cross correlation values { R0,R1,…,RN-1}；
5.4th step, when sampling clock is drawn high, export N group cross correlation values in the corresponding index i of maximum value, as solve
The symbol of tune, wherein 0≤i≤N-1；
6th step, output conversion：
To OQPSK modulated signals, carries out parallel data and be converted into serial data, you can obtain base band code stream；
To DBPSK modulated signals, solution difference can be obtained base band code stream.
Angle is arranged in the preferred embodiment of phase shift keyed signal demodulation method according to the present invention based on RFID, the 2nd step
Line of demarcation is spent, by phase difference is point in reference axis by region division with angular dividing line, specifically carries out as follows：
Such as it is that phase difference is divided into the areas Liang Ge by DBPSK modulated signals using n pi/2s (n=± 1) as angular dividing line
Domain, then correspond to by region the point I in reference axisvalue、Qvalue；Calculation formula is：
Such as it is OQPSK modulated signals, angular dividing line is used as with π/4 n (n=± 1, ± 3), phase difference is divided into four
Region, then correspond to by region the point I in reference axisvalue、Qvalue；Calculation formula is：
Wherein diff is phase difference.
The preferred embodiment of phase shift keyed signal demodulation method according to the present invention based on RFID, the 3rd step is by coordinate
After point on axis rotates fixed angle at same direction, then the point in reference axis is mapped as to the decision value without 0；
Specifically carry out as follows：
It is such as DBPSK modulated signals, by the point I in reference axisvalue、QvalueRotation fixed angle counterclockwise(n
For positive odd number), by Ivalue、QvaluePoint is mapped as without 0 decision value Ijudgevalue、Qjudgevalue, calculation formula is：
It is such as OQPSK modulated signals, by the point I in reference axisvalue、QvalueRotation fixed angle counterclockwise(n
For positive odd number), by point Ivalue、QvalueIt is mapped as without 0 decision value Ijudgevalue、Qjudgevalue, calculation formula is：
Wherein A is positive number.
When being modulated due to BPSK/DBPSK, only two-phase, i.e. Ijudgevalue=QjudgevalueOr Ijudgevalue=-
Qjudgevalue, therefore I can be only taken at this timejudgevalueThis decision value all the way.
The advantageous effect of phase shift keyed signal demodulation method of the present invention based on RFID is：Present invention angle point
Boundary line makes decisions the phase difference of front and back chip by region, then is rotated to court verdict, and mapping generates new sentencing not equal to 0
Certainly it is worth, to improve the correlated performance of spreading code, to improve the noiseproof feature of psk signal demodulation；The present invention is to phase shift keyed signal
Demodulation method it is simple, it is unique, OQPSK signals and DBPSK signals when the present invention can be used for known preamble and spreading code
Demodulation, it can also be used to bpsk signal when known preamble and spreading code/QPSK signals demodulation, and only know lead code and without expansion
The lead code of bpsk signal/DBPSK signals/QPSK signals/OQPSK signals when frequency code synchronizes, and can be widely applied to radio frequency knowledge
In other system.
Description of the drawings
Fig. 1 is the phase shift keyed signal demodulation method flow diagram of the present invention based on RFID.
Fig. 2 is the 2nd step schematic diagram that the present invention demodulates DBPSK signals.
Fig. 3 is the 2nd step schematic diagram that the present invention demodulates OQPSK signals.
Fig. 4 is the 3rd step schematic diagram that the present invention demodulates DBPSK signals.
Fig. 5 is the 3rd step schematic diagram that the present invention demodulates OQPSK signals.
Fig. 6 is the structural schematic diagram of data frame.
Fig. 7 is that OQPSK modulates chip offset schematic diagram.
Fig. 8 is the autocorrelator trace using dot product cross product method in background technology.
Fig. 9 is the autocorrelator trace using the phase shift keyed signal demodulation method of the present invention based on RFID.
Figure 10 is pulse-shaping and receiving terminal waveform.
Figure 11 is waveform correlation and synchronized result.
Figure 12 is demodulation result waveform.
Specific implementation mode
Referring to Fig. 1, the phase shift keyed signal demodulation method based on RFID includes the following steps：
The phase difference of chip before and after 1st step, input；
Phase difference is point in reference axis by region division with angular dividing line by the 2nd step, setting angular dividing line；
Due to transmit carrier wave influence, the 0 frequency signal that receiving terminal obtains be not coding when+1, -1 as square wave,
But there are the sine wave of phase delay, thus phase difference be not yet only have as notional phase difference-pi/2,0, pi/2, π
These types of situation, but the curve of consecutive variations, it is therefore desirable to the point being divided into phase difference with line of demarcation in reference axis.
Specifically carry out as follows：
As shown in Fig. 2, to DBPSK modulated signals, using n pi/2s (n=± 1) as angular dividing line, phase difference diff is drawn
It is divided into two regions, then corresponds to the point I in reference axis by regionvalue、Qvalue；Calculation formula is：
As shown in figure 3, to OQPSK modulated signals, angular dividing line is used as with π/4 n (n=± 1, ± 3), by phase difference
Diff is divided into four regions, then the point I in reference axis is corresponded to by regionvalue、Qvalue；Calculation formula is：
3rd step after the point in reference axis is rotated fixed angle at same direction, then the point in reference axis is mapped as not
Containing 0 decision value；
Specifically carry out as follows：
It is such as DBPSK modulated signals, by the point I in reference axisvalue、QvalueRotation fixed angle counterclockwise(n
For positive odd number), by Ivalue、QvaluePoint is mapped as without 0 decision value Ijudgevalue、Qjudgevalue, calculation formula is：
It is such as OQPSK modulated signals, by the point I in reference axisvalue、QvalueRotation fixed angle counterclockwise(n
For positive odd number), by point Ivalue、QvalueIt is mapped as without 0 decision value Ijudgevalue、Qjudgevalue, calculation formula is：
Wherein A is positive number.
Due to the periodicity of phase, if by the point I in reference axisvalue、QvalueIt carries out rotating clockwise angleThen quite
In rotated counterclockwise by angle
In a particular embodiment, referring to Fig. 4, to DBPSK modulated signals, the point in reference axis can be rotated counterclockwise π/
4, if when A=1, (1,0), (- 1,0) point are mapped as (1,1), (- 1, -1), i.e.,：
By the point in reference axis π/4 can be rotated counterclockwise to OQPSK modulated signals referring to Fig. 5, if when A=1, it will
(0, -1), (1,0), (0,1), (- 1,0) point are mapped as (1, -1), (1,1), (- 1,1), (- 1, -1), i.e.,：
When being modulated due to BPSK/DBPSK, only two-phase, i.e. Ijudgevalue=QjudgevalueOr Ijudgevalue=-
Qjudgevalue, therefore I can be only taken at this timejudgevalueThis decision value all the way.
4th step, lead code synchronize：
4.1st step：The shift register for being L × R by decision value deposit length, as practical judgement value sequence Seqactual；
L is spreading code the piece number；R is sampling multiple, takes the integer more than or equal to 2；
4.2nd step：The notional phase of known N groups spread-spectrum code chip is poor, and judgement obtains the theoretical decision value sequence of N group spread-spectrum code chips
Arrange { Seqtheory_0,Seqtheory_1…,Seqtheory_ N-1 }, and carry out R samplings；Wherein, under OQPSK modulation, N=16；
Under DBPSK modulation, N=2；
4.3rd step：Respectively by practical judgement value sequence SeqactualThe roads I, the roads Q and lead code 0 theoretical judgement value sequence
SeqtheoryThe roads I, the roads Q after _ 0 progress R samplings carry out cross-correlation, are then overlapped the roads I, the roads Q cross correlation value, obtain
The cross correlation value R of lead code 00；
4.4th step：To the cross correlation value R of lead code 00Judged, works as R0It is obtained more than threshold value Th and when reaching peak value same
Walk enable signal；Threshold value Th=2L × R × gain, gain=0~1；Gain is gain；
5th step, sampling judgement：
5.1st step, sample counter start counting up after synchronous enabled, when reaching next sampling central instant (L × R)
When, export sampling clock；
5.2nd step takes practical judgement value sequence Seq againactualEffective (L-2) × R points and N group spread-spectrum code chips below
Theoretical judgement value sequence { Seqtheory_0,Seqtheory_1…,Seqtheory_ N-1 } carry out the effective (L- in back after R samplings
2) × R points calculate separately the cross-correlation of practical judgement value sequence and the roads I and the roads I, the roads Q and the roads Q of theoretical judgement value sequence；
The roads I of each group, the roads Q cross correlation value are overlapped by the 5.3rd step, obtain N group cross correlation values { R0,R1,…,RN-1}；
5.4th step, when sampling clock is drawn high, export N group cross correlation values in the corresponding index i of maximum value, as solve
The symbol of tune, wherein 0≤i≤N-1；
6th step, output conversion：
To OQPSK modulated signals, carries out parallel data and be converted into serial data, you can obtain base band code stream；
To DBPSK modulated signals, solution difference can be obtained base band code stream.
In the following, by taking OQPSK modulation /demodulation in 2.45GHz RFID as an example, the present invention will be described in detail.
Carried out data transmission using data frame between reader and label, the structure of data frame is as shown in Figure 6.What agreement used
It is Direct Sequence Spread Spectrum, i.e., indicates an information code element with one section of spreading code, carrier wave is modulated, lead code is 8 data
Symbol 0.The mapping relations of frequency expansion sequence are as shown in table 1, then every 4 information bit maps to a 16 metadata symbols will
Each data symbol is mapped as one in 16 quasi- orthogonal spreading sequences of number of chips L=32.
Mapping of 1 information bit of table to frequency expansion sequence
Frequency expansion sequence is modulated through OQPSK, and even bit chip is modulated onto the roads in-phase branch I, and odd bits chip is modulated
On the road to quadrature branch Q, chip delay half symbol interval of the chip on the roads Q relative to the roads I, wherein TcIt is falling for spreading rate
Number, as shown in Figure 7.
1, computational theory adjudicates value sequence
1.1 calculate the phase difference of front and back chip
Bipolarity transformation is carried out to chip value, according to k-th of chip Ik、QkValue and place quadrant calculate its corresponding phase：
θk=arctan (Qk/Ik) (formula 7)
The then phase difference of k-th of chip：
diffk=θk-θk-1(formula 8)
Phase difference is point in reference axis by region division with angular dividing line by 1.2 setting angular dividing lines
By phase difference it is reference axis by region division with angular dividing line with π/4 n (n=± 1, ± 3) for angular dividing line
On point；I.e.：
After point in reference axis is rotated fixed angle by 1.3 at same direction, then the point in reference axis is mapped as new
Without 0 decision value
Point in reference axis is rotated into π/4 counterclockwise, when taking A=1, by reference axis point (0, -1), (1,0), (0,
1), (- 1,0) is mapped as new decision value (1, -1), (1,1), (- 1,1), (- 1, -1) for being free of 0, i.e.,：
By taking symbol 0 as an example, preceding each stage theory value of 8 chips is as shown in table 2.
The calculated results of 2 symbol of table, 0 preceding 8 chips
Wherein x indicates uncertain, and the chip x that the roads Q are the 1st is related with the chip of the last one of previous symbol.Therefore
To N group spread spectrum code sequences, the roads I, the roads Q decision value Ijudgevalue、QjudgevalueFirst 2 points be uncertain, carry out sampling sentence
It can give up at first 2 points when cross-correlation certainly.
Since lead code is made of 8 data symbols 0, Thus, it is assumed that previous symbol is 0, data symbol 0 is obtained
Theory judgement value sequence Seqtheory_ 0=(Ijudgevalue,Qjudgevalue)=([1-1-1 1,1 11 1,1 1-1-1,1
1 -1 -1,-1 1 1 1,1 -1 -1 1,1 1 -1 1,1 -1 1 1]；[1 1 1 1,-1 -1 -1 -1,-1 1 1 1,1
1 1 1,1 1 1 1,1 1 1 1,-1 1 1 1,1 1 1 -1]).In table 1 data symbol 1-15 also according to this principle according to
Their corresponding spreading codes calculate its corresponding theoretical decision value Ijudgevalue、Qjudgevalue, therefore 16 groups of theories can be obtained and sentenced
Certainly value sequence { Seqtheory_0,Seqtheory_1…,Seqtheory_15}。
2, practical judgement value sequence is calculated
In actual circuit, transmitting terminal is needed to I, Q circuit-switched data pulse shaping, is emitted in re-modulation to carrier wave, and receiving terminal is used
Down coversion and low-pass filtering are carried out with the carrier wave of phase with frequency, obtains corresponding 0 frequency signal.When being sampled by 8MHz, multiple R=is sampled
4, when noiseless, 2 data symbols 0 is taken to be shown, Figure 10 be respectively from top to bottom the roads I forming results, the roads Q forming results,
The waveform of 0 frequency signal of the roads receiving terminal I, 0 frequency signal of the roads receiving terminal Q, wherein there are transmission delays for receiving terminal waveform.It can be with from Fig. 9
Find out, due to the delay in transmission process, even if receiving terminal carries out down coversion with frequency with the carrier wave of phase, 0 obtained frequency signal
Also inconsistent with the waveform of the roads transmitting terminal I, Q pulse shaping, when there are even more so when frequency deviation skew with receiving terminal for transmitting terminal.
To 0 frequency signal of the roads receiving terminal I, 0 frequency signal of the roads Q, similarly according to (formula 7) calculated phase values, (formula 8) calculates phase
Difference, then by (formula 9) with π/4 n (n=± 1, ± 3) for angular dividing line, by phase difference be seat by region division with angular dividing line
Point on parameter rotates the point in reference axis at same direction, and pressing in reference axis (formula 10) is mapped as new to be free of 0
Decision value, the shift register for being 32 × 4 by decision value deposit length, as practical judgement value sequence Seqactual。
3, lead code synchronizes
3.1 autocorrelation performance
Frame synchronization code character requires sharp unimodal autocorrelation performance.The auto-correlation function of sequence x is defined as：
Wherein list entries x, the length of l, autocorrelation value Rxx(τ) is the same sequence x after list entries x and delay τ
Respective coordinates point carries out multiplication, and then l point multiplications result is cumulative, it reflects the same sequence x after list entries x and delay τ
Between degree of correlation.
Fig. 8 calculates separately that auto-correlation is summed again as a result, relevant peaks for dot product, the cross product two-way of preamble data symbol 0
Value only 31.The theoretical judgement value sequence for the data symbol 0 that decision function proposed by the present invention obtains is Seqtheory_ 0=([1
-1 -1 1,1 1 1 1,1 1 -1 -1,1 1 -1 -1,-1 1 1 1,1 -1 -1 1,1 1 -1 1,1 -1 1 1]；[1
1 1 1,-1 -1 -1 -1,-1 1 1 1,1 1 1 1,1 1 1 1,1 1 1 1,-1 1 1 1,1 1 1 -1]).Fig. 9 is
To Seqtheory_ 0 Ijudgevalue、QjudgevalueTwo-way calculates separately that auto-correlation is summed again as a result, correlation peak is 62.It can be with
Find out, correlated performance of the invention is more preferable, has achieved the purpose that the noiseproof feature for promoting demodulation.3.2 cross-correlation test lead codes
Whether synchronize
The cross-correlation function of the sequence of calculation x and y are defined as：
The length of wherein list entries x, y is l, cross correlation value Rxy(τ) is the sequences y pair after list entries x and delay τ
Coordinate points are answered to carry out multiplication, then l point multiplications result is cumulative, it reflects list entries x and postpones the phase between the sequences y after τ
Pass degree.
3.2.1 τ=0 is taken, to the theoretical judgement value sequence Seq of leading code sign 0theoryAfter _ 0 carries out R=4 samplings, root
Itself and practical judgement value sequence Seq are calculated according to (formula 12)actualCross correlation value；
3.2.2 synchronous enabled signal is obtained when cross correlation value is more than threshold value Th and reaches peak value.Th=2L × R ×
Gain, gain=0~1；If Th=200, the cross-correlation waveform and synchronized result when noiseless are as shown in figure 11, divide from top to bottom
It Wei not cross correlation value, synchronous enabled.
4, sampling judgement
4.1 sample counters start counting up after synchronous enabled, when counting to 128, export sampling clock.
4.2 take practical judgement value sequence Seq againactualEffective (32-2) × 4 point and 16 groups of spread-spectrum code chips below
Theory judgement value sequence { Seqtheory_0,Seqtheory_1…,Seqtheory_ 15 } below effective (32-2) × 4 point, count respectively
Calculate the cross-correlation of practical judgement value sequence and the roads I and the roads I, the roads Q and the roads Q of theoretical judgement value sequence；
4.3 are overlapped the roads I of each group, the roads Q cross correlation value, obtain 16 groups of cross correlation value { R0,R1,…,R15}；
4.4 when sampling clock is drawn high, and it is the symbol demodulated to export the corresponding index i of the maximum value in 16 groups of correlations
Number, wherein 0≤i≤15.
5, output conversion
Parallel-serial conversion is carried out to OQPSK signals, parallel 4bit data symbols are converted to serial 1bit information bits, are obtained
To base band code stream.
Demodulation result is as shown in figure 12, from top to bottom respectively sampling clock, the data symbol of demodulation, base band code stream, base
Band clock.
The demodulation of OQPSK signals and DBPSK signals when the method for the present invention can be used for known preamble and spreading code,
BPSK/QPSK signals demodulation when can be used for known preamble and spreading code, and only know lead code and BPSK/ when without spreading code
The lead code of DBPSK signals/QPSK signals/OQPSK signals synchronizes.For BPSK modulated signals, DBPSK in the present invention can be used
Method is demodulated, but need not solve difference.For qpsk modulation signal, can be demodulated with the method for OQPSK in the present invention.
Claims (3)
1. a kind of phase shift keyed signal demodulation method based on RFID, it is characterised in that：Include the following steps：
The phase difference of chip before and after 1st step, input；
Phase difference is point in reference axis by region division with angular dividing line by the 2nd step, setting angular dividing line；
Point in reference axis is rotated fixed angle by the 3rd step at same directionAfter (n is positive odd number), then by reference axis
On point be mapped as it is new be free of 0 decision value；
4th step, lead code synchronize：
4.1st step：The shift register that the decision value deposit length that 3rd step is obtained is L × R, obtains practical judgement value sequence
Seqactual；L is spreading code the piece number, and R is sampling multiple, and sampling multiple takes the integer more than or equal to 2；
4.2nd step：The notional phase of known N groups spread-spectrum code chip is poor, and judgement obtains the theoretical judgement value sequence of N group spread-spectrum code chips
{Seqtheory_0,Seqtheory_1…,Seqtheory_ N-1 }, and carry out R samplings；Under OQPSK modulation, N=16；In DBPSK
Under modulation, N=2；
4.3rd step：Respectively by practical judgement value sequence SeqactualThe roads I, the roads Q and lead code 0 theoretical judgement value sequence
SeqtheoryThe roads I, the roads Q after _ 0 progress R samplings carry out cross-correlation, are then overlapped the roads I, the roads Q cross correlation value, obtain
The cross correlation value R of lead code 00；
4.4th step：To the cross correlation value R of lead code 00Judged, works as R0Obtaining synchronizing more than threshold value Th and when reaching peak value makes
It can signal；Threshold value Th=2L × R × gain, gain=0~1；Gain is gain；
5th step, sampling judgement：
5.1st step, sample counter start counting up after synchronous enabled, reach when reaching next i.e. count value of sampling central instant
When (L × R), sampling clock is exported；
5.2nd step takes practical judgement value sequence Seq againactualThe reason of effective (L-2) × R points and N group spread-spectrum code chips below
By judgement value sequence { Seqtheory_0,Seqtheory_1…,Seqtheory_ N-1 } carry out after R samplings below effective (L-2) ×
R points calculate separately the cross-correlation of practical judgement value sequence and the roads I and the roads I, the roads Q and the roads Q of theoretical judgement value sequence；
The roads I of each group, the roads Q cross correlation value are overlapped by the 5.3rd step, obtain N group cross correlation values { R0,R1,…,RN-1}；
5.4th step, when sampling clock is drawn high, export N group cross correlation values in the corresponding index i of maximum value, as demodulate
Symbol, wherein 0≤i≤N-1；
6th step, output conversion：
Such as it is OQPSK modulated signals, carries out parallel data and be converted into serial data, you can obtain base band code stream；
Such as it is DBPSK modulated signals, solution difference can be obtained base band code stream.
2. the phase shift keyed signal demodulation method according to claim 1 based on RFID, it is characterised in that：2nd step is arranged
Phase difference is point in reference axis by region division with angular dividing line, specifically carried out as follows by angular dividing line：
Phase difference is such as divided into two regions using n pi/2s (n=± 1) as angular dividing line for DBPSK modulated signals, then
The point I in reference axis is corresponded to by regionvalue、Qvalue；Calculation formula is：
Such as it is OQPSK modulated signals, angular dividing line is used as with π/4 n (n=± 1, ± 3), phase difference is divided into four areas
Domain, then correspond to by region the point I in reference axisvalue、Qvalue；Calculation formula is：
Wherein diff is phase difference.
3. the phase shift keyed signal demodulation method according to claim 2 based on RFID, it is characterised in that：3rd step will be sat
After point on parameter rotates fixed angle at same direction, then the point in reference axis is mapped as to the new decision value for being free of 0；
Specifically carry out as follows：
It is such as DBPSK modulated signals, by the point I in reference axisvalue、QvalueRotation counterclockwiseWhen (n is positive odd number),
By Ivalue、QvaluePoint is mapped as Ijudgevalue、Qjudgevalue, calculation formula is：
It is such as OQPSK modulated signals, by the point I in reference axisvalue、QvalueRotation counterclockwiseWhen (n is positive odd number),
It will point Ivalue、QvalueIt is mapped as Ijudgevalue、Qjudgevalue, calculation formula is：
Wherein A is positive number.
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