CN104333525A - GMSK (Gaussian minimum shift keying) modulating system synchronization method - Google Patents
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Abstract
The invention discloses a GMSK (Gaussian minimum shift keying) modulating system synchronization method which includes the steps: performing differential operation for GMSK modulating signals generated by a training sequence of preset numerous burst types to obtain a local reference signal; receiving GMSK data, marking current GMSK data receiving points as sampling points when the length of a received GMSK data segment is as same as that of the local reference signal, and performing differential operation for the current GMSK data segment to obtain a GMSK differential signal; gaining vector space cosine similarity according to the local reference signal and the GMSK differential signal in the same burst type; judging whether the vector space cosine similarity exceeds a threshold or not, continuing to receive the GMSK data if not, and then selecting one synchronization position from alternative synchronization positions to perform system synchronization within preset GMSK data receiving time. If the vector space cosine similarity exceeds the threshold, the burst type is the burst type of the currently received GMSK data, and the current sampling points are the alternative synchronization positions. Reliable synchronization can be realized, and the requirement of engineering application is more effectively met.
Description
Technical field
The present invention relates to digital communication research field, particularly a kind of GMSK modulation system synchronization method.
Background technology
GMSK (Gaussian filtered MSK) signal is the premodulated that have passed through gauss low frequency filter before generating msk signal, and it and MSK belong to permanent envelope digital modulation.Permanent envelope digital modulation can use the nonlinear amplifier that power efficiency is high, avoids non-constant enveloped modulation to use the secondary lobe regeneration of the filtering caused during the high nonlinear amplifier of power efficiency.
Msk signal can regard the continuous phase fsk signal that modulation index is 0.5 as, although it has the advantage such as bandwidth of permanent envelope, Phase Continuation, relative narrower, does not still meet the demands for its out-of-band radiation some communication system.For effective inhibition zone external radiation, therefore before generating msk signal, add the gauss low frequency filter of upper level premodulated.
The waveform of GMSK modulation signal is typically expressed as:
In above formula, f
cit is carrier frequency;
it is carrier phase; E is a code-element period T
binterior signal energy,
for random initial phase, remain unchanged during whole burst modulation, wherein:
In formula, a
k=± 1,
In above formula, g (t) is the response of Gaussian filter to rectangular pulse.
For coherent demodulation, because Crystal Oscillator Errors, Doppler frequency-shift etc. can cause estimating carrier frequencies error and the unknown
initial phase exists, directly carry out related calculation cannot obtain accurately relevant peaks using as synchronization metric.Meanwhile, for a certain specific applied environment, suppose that the energy intensity of noise is relatively stable, the signal energy intensity received for different communication distances is indefinite, can cause the significantly change of correlation, and then dependent threshold also cannot provide definite value, unfavorable Project Realization.The particularly fast-changing application scenario of communication distance.
Such as, a kind of existing adaptive demodulation method is: carry out upset process to the I received, Q signal, relevant method of sliding is adopted to carry out channel estimating to the signal after upset, Delay Synchronization is carried out according to channel estimation value, determine Timing Advance, and according to the energy of channel parameter and the type determining channel, when the channel parameter on maximal correlation position energy and maximum energy and ratio E
ratiowhen exceeding certain threshold value, adopt zero forcing equalization method to carry out demodulation, export soft-decision-value simultaneously, work as E
ratiowhen being less than certain threshold value, Equilized demodulation method is adopted to carry out demodulation.The method does not eliminate the interference that frequency deviation and initial phase cause.
Again such as, a kind of GMSK signal acceptance method is in addition: carried out " precoding " raw information before transmitting terminal carries out GMSK modulation, the two Chirp signals sent for transmitting terminal carry out precoding, frequency difference and experiment is estimated at receiving terminal, then on the basis correcting large frequency-difference, adopt least square method to carry out channel impulse response estimation, finally according to the remaining frequency difference in channel impulse response correction signal and skew, realize the semi-coherent demodulation of GMSK signal.The method can less frequency difference and skew in erasure signal, but the degree of calculating is complicated, and need arrange multiple threshold value, to energy intensity sensitive, and the not actual use of utilizing works.
To sum up, the shortcoming existing for method of existing related synchronization: (1) does not eliminate the interference that frequency deviation and initial phase cause.(2) synchronization metric is to energy intensity sensitive, is unfavorable for Project Realization.
Summary of the invention
Main purpose of the present invention is that the shortcoming overcoming prior art is with not enough, a kind of GMSK modulation system synchronization method is provided, it may be used for the receiving terminal of GMSK modulation system, realize synchronous reliably, particularly be applied in the middle of coherent demodulation, can the interference that causes of frequency offset resistant and initial phase, and to the GMSK signal energy Strength Changes received without specific requirement, make decision threshold comparatively stable, more meet the requirement of engineer applied.
Object of the present invention is realized by following technical scheme: a kind of GMSK modulation system synchronization method, comprises the following steps:
(1) calculus of differences is done to the GMSK modulation signal that the training sequence presetting several outburst types generates, obtain the local reference signal corresponding with outburst type;
(2) GMSK data are received, when the length of the GMSK data segment received is identical with the length of described local reference signal, marking current GMSK data receiver point is sampled point, and calculus of differences is carried out to the GMSK data segment of current reception, obtain the GMSK differential signal corresponding with outburst type;
(3) according to the local reference signal under same outburst type and GMSK differential signal, the vector space cosine similarity that this outburst type is corresponding is asked for;
(4) judge whether described vector space cosine similarity exceedes thresholding corresponding to this outburst type, if exceed described thresholding, this outburst type is the outburst type of the GMSK data of current reception, current sampled point is alternative sync bit, enters step (5); If be no more than described pre-determined threshold, perform step (2);
(5) in the GMSK data receipt time preset, from alternative sync bit, one of them sync bit is selected to carry out system synchronization.
Preferably, in described step (5), the GMSK data receipt time preset is a symbol period, selects the sync bit that wherein vector space cosine similarity is maximum to carry out system synchronization.Symbol period modulates the symbol time interval, alternatively is-symbol length or code-element period exactly.
Concrete, in described step (3), the calculation procedure of vector space cosine similarity is as follows:
If a certain GMSK differential signal and local reference signal are respectively X and Y, data length is n, if i-th data is X (i)=a (i)+jb (i) in GMSK differential signal, in local reference signal, i-th data is Y (i)=c (i)+jd (i), then the vector space cosine similarity computing formula that this outburst type is corresponding is:
Preferably, in described step (4), according to the transmission quality of current outburst type and GMSK data receiver channel, a selected factor alpha, 0.7 < α < 1, threshold value using α n as vector space cosine similarity, wherein n is the length of local reference signal.
Preferably, described step (2), GMSK differential signal adopts the mode of stream process to carry out synchronous process and obtains, step is: establish different outburst types to there being m kind local reference signal, then design m shifting cache district, shifting cache section length is consistent with the local reference signal length of each outburst type, to the calculus of differences that the GMSK data segment of each shifting cache district storage walks abreast; After reception GMSK data segment carries out calculus of differences, last bit data of each shifting cache district is shifted out and is shifted to remaining data, then by first position of new GMSK data stored in each buffer area.
Preferably, described step (1), is solidificated in the receiving terminal of signal by the local reference signal that different outburst type generates.Because once the standard that system adopts is determined, so midamble code is also just determined, the local reference signal of generation is also determined, so directly signal is solidificated in receiving terminal, need not calculate, can shorten the time of signal transacting thereupon at every turn.
Compared with prior art, tool has the following advantages and beneficial effect in the present invention:
1, the GMSK data of the present invention to the GMSK modulation signal generated and reception do calculus of differences, as can be seen from the generation block diagram of GMSK signal, what do that the signals revivification after calculus of differences goes out is by the signal after gauss low frequency filter, before integration, with this signal as the interference asking the local reference signal of synchronization metric can suppress first phase and frequency deviation to cause.
2, the present invention adopts vector space cosine similarity to judge the outburst type of GMSK data, the cosine value of what vector space cosine similarity was asked the is space angle of two complex signals, carry out measuring from the angle of two complex signals, hardly by the impact of energy intensity size, be only subject to the impact of 2 π Δ fT and signal to noise ratio.Thus the present invention can make synchronous thresholding be set to definite value, greatly improves the robustness of thresholding, solves Received signal strength energy intensity and change the problem that the synchronous thresholding caused cannot be set to definite value, be beneficial to Project Realization.
Accompanying drawing explanation
Fig. 1 is the schematic flow sheet of the inventive method.
Fig. 2 is that in the present embodiment, GMSK signal generates schematic diagram.
Embodiment
Below in conjunction with embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited thereto.
Embodiment 1
As shown in Figure 1, a kind of GMSK modulation system synchronization method of the present embodiment, its implementation process specifically comprises the following steps:
(1), according to the midamble code of the different outburst types of the different systems defined of use GMSK modulation, generate corresponding GMSK modulation signal respectively, as shown in Figure 2, its modulated process is classical GMSK orthogonal demodulation signal generating principle to its modulated process, therefore is not repeated herein.Then do calculus of differences to the GMSK modulation signal generated, as can be seen from the generation block diagram of GMSK signal, what do that the signals revivification after calculus of differences goes out is by the signal after gauss low frequency filter, before integration.
In the baseband signal that local carrier carries out after frequency spectrum shift to received signal, there is difference frequency partially and first phase.If do not consider noise, the phase place of baseband signal can simply be expressed as:
Δ f represents frequency deviation,
represent phase noise.After difference processing, the phase place of baseband signal then becomes:
Wherein
T is a code-element period, normally a very little value, therefore when frequency deviation is not very large, 2 π Δ fT are very little on the impact of overall phase place.Therefore, with this signal as the interference asking the local reference signal of synchronization metric can suppress first phase and frequency deviation to cause.Once the standard that system adopts is determined, so midamble code is also just determined, the local reference signal of generation is also determined thereupon.Therefore, the local reference signal that different outburst type generates can be solidificated in the receiving terminal of signal.
(2), GMSK data are received, when the length of the GMSK data segment received is identical with the length of its corresponding local reference signal, marking current GMSK data receiver point is sampled point, and calculus of differences is carried out to current GMSK data segment, obtain the GMSK differential signal corresponding with outburst type.The mode of this example employing parallel processing realizes the calculus of differences to current GMSK data segment, concrete steps are: establish different outburst types to there being m kind local reference signal, then can design m shifting cache district, shifting cache section length is consistent with the local reference signal length of each outburst type.To the calculus of differences that the GMSK data segment of each shifting cache district storage walks abreast.After reception GMSK data segment carries out calculus of differences, last bit data of each shifting cache district is shifted out and is shifted to remaining data, then by first position of new GMSK data stored in each buffer area.
(3), according to the local reference signal under same outburst type and GMSK differential signal, the vector space cosine similarity that this outburst type is corresponding is asked for.
If a certain GMSK differential signal and local reference signal are respectively X and Y, data length is n, if i-th data is that in X (i)=a (i)+jb (i), Y, i-th data is Y (i)=c (i)+jd (i) in X.The vector space cosine similarity computing formula that then this outburst type is corresponding is:
As can be seen from formula, the cosine value of what vector space cosine similarity was asked the is space angle of two complex signals carries out measuring from the angle of two complex signals.If do not consider the impact of noise, if the complex signal direction that I, Q two paths of signals is formed is consistent, then represent that these two complex signal similarities are very large, difference is the size of energy intensity.Now, the vector space cosine similarity of trying to achieve is cos (0)=1.Therefore, vector space cosine similarity value is larger, represents that the similarity of two signals is larger.
(4), judge whether vector space cosine similarity exceedes thresholding corresponding to this outburst type, if cross thresholding, illustrate that this outburst type is the outburst type of the GMSK data of current reception, current sampled point is alternative sync bit, performs step (5); If but thresholding, perform step (2).
Choosing of threshold value will decide according to the length of local reference signal.Do not considering under noise situations, if two complex data directions are consistent, namely angle is 0, and its vector space cosine value reaches maximum 1.Therefore be the burst of n for local reference signal length, the maximum of its ρ is n.Consider the impact of the factor such as void inspection rate, loss index of noise, system requirements, comprehensively a factor alpha can be selected when reality uses, 0.7 < α < 1, the thresholding using α n as vector space cosine similarity.
(5), wait for a symbol period, the sync bit selecting vector space cosine similarity maximum from several the alternative sync bits obtained carries out system synchronization.
Above-described embodiment is the present invention's preferably execution mode; but embodiments of the present invention are not restricted to the described embodiments; change, the modification done under other any does not deviate from Spirit Essence of the present invention and principle, substitute, combine, simplify; all should be the substitute mode of equivalence, be included within protection scope of the present invention.
Claims (5)
1. a GMSK modulation system synchronization method, is characterized in that, comprises the following steps:
(1) calculus of differences is done to the GMSK modulation signal that the training sequence presetting several outburst types generates, obtain the local reference signal corresponding with outburst type;
(2) GMSK data are received, when the length of the GMSK data segment received is identical with the length of described local reference signal, marking current GMSK data receiver point is sampled point, and calculus of differences is carried out to the GMSK data segment of current reception, obtain the GMSK differential signal corresponding with outburst type;
(3) according to the local reference signal under same outburst type and GMSK differential signal, the vector space cosine similarity that this outburst type is corresponding is asked for;
(4) judge whether described vector space cosine similarity exceedes thresholding corresponding to this outburst type, if exceed described thresholding, this outburst type is the outburst type of the GMSK data of current reception, current sampled point is alternative sync bit, enters step (5); If be no more than described pre-determined threshold, perform step (2);
(5) in the GMSK data receipt time preset, from alternative sync bit, one of them sync bit is selected to carry out system synchronization.
2. GMSK modulation system synchronization method according to claim 1, it is characterized in that, in described step (5), the GMSK data receipt time preset is a symbol period, selects the sync bit that wherein vector space cosine similarity is maximum to carry out system synchronization.
3. GMSK modulation system synchronization method according to claim 1, is characterized in that, in described step (3), the calculation procedure of vector space cosine similarity is as follows:
If a certain GMSK differential signal and local reference signal are respectively X and Y, data length is n, if i-th data is X (i)=a (i)+jb (i) in GMSK differential signal, in local reference signal, i-th data is Y (i)=c (i)+jd (i), then the vector space cosine similarity computing formula that this outburst type is corresponding is:
4. GMSK modulation system synchronization method according to claim 1, it is characterized in that, in described step (4), according to the transmission quality of current outburst type and GMSK data receiver channel, a selected factor alpha, 0.7 < α < 1, the threshold value using α n as vector space cosine similarity, wherein n is the length of local reference signal.
5. GMSK modulation system synchronization method according to claim 1, it is characterized in that, described step (2), GMSK differential signal adopts the mode of stream process to carry out synchronous process and obtains, step is: establish different outburst types to there being m kind local reference signal, then design m shifting cache district, shifting cache section length is consistent with the local reference signal length of each outburst type, to the calculus of differences that the GMSK data segment of each shifting cache district storage walks abreast; After reception GMSK data segment carries out calculus of differences, last bit data of each shifting cache district is shifted out and is shifted to remaining data, then by first position of new GMSK data stored in each buffer area.
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