CN104333525B - A kind of GMSK modulation system synchronization method - Google Patents
A kind of GMSK modulation system synchronization method Download PDFInfo
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- CN104333525B CN104333525B CN201410572532.2A CN201410572532A CN104333525B CN 104333525 B CN104333525 B CN 104333525B CN 201410572532 A CN201410572532 A CN 201410572532A CN 104333525 B CN104333525 B CN 104333525B
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Abstract
The invention discloses a kind of GMSK modulation system synchronization method, including：The GMSK modulation signal of training sequence generation to presetting several outburst types does calculus of differences, obtains local reference signal；GMSK data are received, when the length of the GMSK data segments received is identical with the length of local reference signal, it is sampled point to mark current GMSK data receivers point, and does calculus of differences to current GMSK data segments, obtains GMSK differential signals；According to the local reference signal under same outburst type and GMSK differential signals, vector space cosine similarity is asked for；Judge whether vector space cosine similarity exceedes thresholding, GMSK data are continued to if being not above, otherwise the outburst type is the outburst type of currently received GMSK data, current sampled point is alternative sync bit, then in default GMSK data receipt times, one of sync bit is selected to carry out system synchronization from alternative sync bit.The present invention can be achieved reliably synchronously, more to meet the requirement of engineer applied.
Description
Technical field
The present invention relates to digital communication research field, more particularly to a kind of GMSK modulation system synchronization method.
Background technology
GMSK (Gaussian filtered MSK) signal is to have passed through Gassian low-pass filter before generation msk signal
The premodulated of device, it belongs to permanent envelope digital modulation with MSK.Permanent envelope digital modulation can use the high non-thread of power efficiency
Property amplifier, it is to avoid non-constant enveloped modulation using the caused secondary lobe filtered during the high nonlinear amplifier of power efficiency again
It is raw.
Msk signal is considered as the continuous phase fsk signal that modulation index is 0.5, although there is permanent envelope, phase to connect for it
The advantages of continuous, bandwidth of relative narrower, but its out-of-band radiation is still unsatisfactory for requiring for some communication systems.For effectively suppression
Out-of-band radiation processed, therefore the gauss low frequency filter of one-level premodulated is added before generation msk signal.
The waveform of GMSK modulation signal is typically expressed as：
In above formula, fcIt is carrier frequency；It is carrier phase；E is a code-element period TbInterior signal energy,
For random initial phase, keep constant during whole burst modulation, wherein：
In formula, ak=± 1,
In above formula, g (t) is response of the Gaussian filter to rectangular pulse.
For coherent demodulation, because Crystal Oscillator Errors, Doppler frequency-shift etc. can cause estimating carrier frequencies error and unknown
'sInitial phase is present, and accurate relevant peaks can not be obtained to be used as synchronization metric by directly carrying out related calculation.Meanwhile, for
A certain specific application environment, it is assumed that the energy intensity of noise is stablized relatively, the signal received for different communication distances
Energy intensity is indefinite, can cause the significantly change of correlation, and then dependent threshold cannot also provide definite value, unfavorable Project Realization.
The particularly fast-changing application scenario of communication distance.
For example, a kind of existing adaptive demodulation method is：Upset processing is carried out to I, the Q signal received, to upset
Signal afterwards carries out channel estimation using related method is slided, and Delay Synchronization is carried out according to channel estimation value, and the time of determination carries
Preceding amount, and energy according to channel parameter and the type for determining channel, when the channel parameter on maximal correlation position energy with
Maximum energy and the ratio between ERatioWhen more than certain threshold value, it is demodulated, is sentenced while output is soft using zero forcing equalization method
Certainly it is worth, works as ERatioDuring less than certain threshold value, it is demodulated using Equilized demodulation method.This method does not eliminate frequency deviation and initial phase
The interference caused.
For another example also a kind of GMSK signal acceptance methods are：To raw information before transmitting terminal carries out GMSK modulation
Carry out " precoding ", carry out precoding for double Chirp signals that transmitting terminal is sent, estimate frequency difference and experiment in receiving terminal, so
Afterwards on the basis of correction large frequency-difference, channel impulse response estimation is carried out using least square method, rung finally according to channel impulse
Remaining frequency difference and the skew in correction signal are answered, the semi-coherent demodulation of GMSK signals is realized.This method can eliminate in signal compared with
Small frequency difference and skew, but degree complexity is calculated, and multiple threshold values need to be set, sensitive is changed to energy intensity, is not utilized
Engineering actual use.
To sum up, the shortcoming present in the method for existing related synchronization：(1) do not eliminate frequency deviation and that initial phase is caused is dry
Disturb.(2) synchronization metric changes sensitive to energy intensity, is unfavorable for Project Realization.
The content of the invention
It is a primary object of the present invention to the shortcoming and deficiency for overcoming prior art, there is provided a kind of GMSK modulation system synchronization
Method, it can be used for the receiving terminal of GMSK modulation system, realizes reliably synchronously, is especially applicable among coherent demodulation,
The interference that frequency deviation and initial phase are caused can be resisted, and the GMSK signal energies Strength Changes received are wanted without specific
Ask, make decision threshold relatively stable, more meet the requirement of engineer applied.
The purpose of the present invention is realized by following technical scheme：A kind of GMSK modulation system synchronization method, including it is following
Step：
(1) the GMSK modulation signal of the training sequence generation to presetting several outburst types does calculus of differences, obtains and dashes forward
Send out the corresponding local reference signal of type；
(2) GMSK data are received, when the length and the length phase of the local reference signal of the GMSK data segments received
Meanwhile, it is sampled point to mark current GMSK data receivers point, and carries out calculus of differences to currently received GMSK data segments, is obtained
To GMSK differential signals corresponding with outburst type；
(3) according to the local reference signal under same outburst type and GMSK differential signals, outburst type correspondence is asked for
Vector space cosine similarity；
(4) judge whether the vector space cosine similarity exceedes the corresponding thresholding of the outburst type, if more than described
Thresholding then the outburst type be currently received GMSK data outburst type, current sampled point is alternative sync bit
Put, into step (5)；Step (2) is performed if the pre-determined threshold is no more than；
(5) in default GMSK data receipt times, one of sync bit is selected from alternative sync bit
Carry out system synchronization.
It is preferred that, in the step (5), default GMSK data receipt times are symbol period, selection wherein to
The maximum sync bit of quantity space cosine similarity carries out system synchronization.Symbol period is exactly modulation symbol time interval, can also
Say it is symbol lengths or code-element period.
Specifically, in the step (3), the calculation procedure of vector space cosine similarity is as follows：
If a certain GMSK differential signals and local reference signal are respectively X and Y, data length is n, if GMSK differential signals
In i-th data be that i-th of data is Y (i)=c (i)+jd (i) in X (i)=a (i)+jb (i), local reference signal,
Then the corresponding vector space cosine similarity calculation formula of the outburst type is：
It is preferred that, in the step (4), according to the transmission quality of current outburst type and GMSK data receiver channels,
A selected factor alpha, 0.7 ＜ α ＜ 1, using α n as the threshold value of vector space cosine similarity, wherein n is to be local with reference to letter
Number length.
It is preferred that, the step (2), GMSK differential signals are synchronized processing by the way of stream process and obtained, step
It is：If different outburst types is to that should have m kind local reference signals, then design m shifting cache area, shifting cache section length and
The local reference signal length of each outburst type is consistent, and parallel difference is carried out to the GMSK data segments that each shifting cache area is stored
Partite transport is calculated；After a GMSK data segments progress calculus of differences is received, the last a data in each shifting cache area is removed and right
Remaining data is shifted, and then a new GMSK data are stored in first position of each buffer area.
It is preferred that, the step (1), the local reference signal that different outburst types are generated is solidificated in the reception of signal
End.Because once the standard that system is used is determined, then midamble code also determines that the local reference signal of generation is also true therewith
It is fixed, so signal directly is solidificated in into receiving terminal, it is not necessary to calculated every time, the time of signal transacting can be shortened.
The present invention compared with prior art, has the following advantages that and beneficial effect：
1st, the present invention does calculus of differences to the GMSK modulation signal of generation and the GMSK data of reception, from the production of GMSK signals
It is by after gauss low frequency filter, before integration that raw block diagram, which can be seen that do that the signals revivification after calculus of differences goes out,
Signal, with this signal as asking the local reference signal of synchronization metric can to suppress the interference that first phase and frequency deviation are caused.
2nd, the present invention judges the outburst type of GMSK data, vector space cosine phase using vector space cosine similarity
Like degree ask be two complex signals space angle cosine value, be to be measured from the angle of two complex signals, hardly
Influenceed, only influenceed by 2 π Δs fT and signal to noise ratio by energy intensity size.Thus the present invention can make synchronous gate limit be set to fixed
Value, is greatly improved the robustness of thresholding, and definite value can not be set to by solving synchronous thresholding caused by reception signal energy Strength Changes
The problem of, beneficial to Project Realization.
Brief description of the drawings
Fig. 1 is the schematic flow sheet of the inventive method.
Fig. 2 is GMSK signal generation schematic diagrames in the present embodiment.
Embodiment
With reference to embodiment and accompanying drawing, the present invention is described in further detail, but embodiments of the present invention are not limited
In this.
Embodiment 1
As shown in figure 1, a kind of GMSK modulation system synchronization method of the present embodiment, its implementation process specifically includes following step
Suddenly：
(1), according to the midamble code of the different outburst types of the different systems defined using GMSK modulation, phase is generated respectively
The GMSK modulation signal answered, its modulated process are as shown in Fig. 2 its modulated process is former for classical GMSK orthogonal demodulation signals generation
Reason, therefore will not be described here.Then calculus of differences is done to the GMSK modulation signal of generation, can from the generation block diagram of GMSK signals
Go out, do that the signals revivification after calculus of differences goes out is by the signal after gauss low frequency filter, before integration.
Local carrier dock collect mail number carry out frequency spectrum shift after baseband signal in, exist difference frequency partially and first phase.If
Do not consider noise, the phase of baseband signal can be simply expressed as：
Δ f represents frequency deviation,Represent phase noise.After difference processing, the phase of baseband signal is then changed into：
Wherein
T is code-element period, typically one unusual small value, therefore when frequency deviation is not very big, 2 π Δs fT are to whole
The influence very little of body phase position.Therefore, with this signal, as asking, the local reference signal of synchronization metric can suppress first phase and frequency deviation is made
Into interference.Once the standard that system is used is determined, then midamble code also determines that the local reference signal of generation is also true therewith
It is fixed.It therefore, it can the local reference signal that different outburst types are generated being solidificated in the receiving terminal of signal.
(2) GMSK data, are received, when the length of the corresponding local reference signal of the length of the GMSK data segments received
When spending identical, it is sampled point to mark current GMSK data receivers point, and carries out calculus of differences to current GMSK data segments, is obtained
To GMSK differential signals corresponding with outburst type.This example is realized by the way of parallel processing to current GMSK data segments
Calculus of differences, is comprised the concrete steps that：If different outburst types can then design m shifting cache to that should have m kind local reference signals
Area, shifting cache section length is consistent with the local reference signal length of each outburst type.Each shifting cache area is stored
GMSK data segments carry out parallel calculus of differences.After a GMSK data segments progress calculus of differences is received, by each shifting cache
The last a data in area is removed simultaneously to be shifted to remaining data, then by the of new each buffer area of GMSK data deposit
One position.
(3), according to the local reference signal under same outburst type and GMSK differential signals, outburst type correspondence is asked for
Vector space cosine similarity.
If a certain GMSK differential signals and local reference signal are respectively X and Y, data length is n, if i-th of data in X
For X (i)=a (i)+jb (i), i-th of data is Y (i)=c (i)+jd (i) in Y.The then corresponding vector of the outburst type
Space cosine similarity calculation formula is：
From formula as can be seen that vector space cosine similarity ask be two complex signals space angle cosine value,
It is to be measured from the angle of two complex signals.If not considering the influence of noise, if the complex signal that I, Q two paths of signals are constituted
Direction is consistent, then it represents that the two complex signal similarities are very big, and difference is the size of energy intensity.Now, the vector tried to achieve
Space cosine similarity is cos (0)=1.Therefore, vector space cosine similarity value is bigger, represents the similarity of two signals
It is bigger.
(4), judge whether vector space cosine similarity exceedes the corresponding thresholding of the outburst type, said if thresholding is crossed
The bright outburst type is the outburst type of currently received GMSK data, and current sampled point is alternative sync bit,
Perform step (5)；Step (2) is performed if but thresholding.
The selection of threshold value will be determined according to the length of local reference signal.In the case where not considering noise situations, if two
Complex data direction is consistent, i.e., angle is 0, and its vector space cosine value reaches maximum 1.Therefore it is long for local reference signal
The burst for n is spent, its ρ maximum is n.In view of the shadow of the factor such as noise, empty inspection rate, the loss index of system requirements
Ring, can be integrated in actual use and select a factor alpha, 0.7 ＜ α ＜ 1 are used as the door of vector space cosine similarity using α n
Limit.
(5) symbol period, is waited, vector space cosine phase is selected from several the alternative sync bits obtained
System synchronization is carried out like maximum sync bit is spent.
Above-described embodiment is preferably embodiment, but embodiments of the present invention are not by above-described embodiment of the invention
Limitation, other any Spirit Essences without departing from the present invention and the change made under principle, modification, replacement, combine, simplification,
Equivalent substitute mode is should be, is included within protection scope of the present invention.
Claims (4)
1. a kind of GMSK modulation system synchronization method, it is characterised in that comprise the following steps：
(1) the GMSK modulation signal of the training sequence generation to presetting several outburst types does calculus of differences, obtains and burst class
The corresponding local reference signal of type；
(2) GMSK data are received, when the length of the GMSK data segments received is identical with the length of the local reference signal,
The current GMSK data receivers point of mark is sampled point, and carries out calculus of differences to currently received GMSK data segments, obtain with
The corresponding GMSK differential signals of outburst type；
(3) according to the local reference signal under same outburst type and GMSK differential signals, ask for the outburst type it is corresponding to
Quantity space cosine similarity；
(4) judge whether the vector space cosine similarity exceedes the corresponding thresholding of the outburst type, if more than the thresholding
Then the outburst type is the outburst type of currently received GMSK data, and current sampled point is alternative sync bit,
Into step (5)；Step (2) is performed if the pre-determined threshold is no more than；
(5) in default GMSK data receipt times, one of sync bit is selected to carry out from alternative sync bit
System synchronization；Default GMSK data receipt times are a symbol period, and selection wherein vector space cosine similarity is maximum
Sync bit carry out system synchronization.
2. GMSK modulation system synchronization method according to claim 1, it is characterised in that in the step (3), vector is empty
Between cosine similarity calculation procedure it is as follows：
If a certain GMSK differential signals and local reference signal are respectively X and Y, data length is n, if in GMSK differential signals
I data are that i-th of data is Y (i)=c (i)+jd (i) in X (i)=a (i)+jb (i), local reference signal, then should
The corresponding vector space cosine similarity calculation formula of outburst type is：
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3. GMSK modulation system synchronization method according to claim 1, it is characterised in that in the step (4), according to working as
Preceding outburst type and the transmission quality of GMSK data receiver channels, select a factor alpha, and 0.7 ＜ α ＜ 1 are used as vector using α n
The threshold value of space cosine similarity, wherein n are the length of local reference signal.
4. GMSK modulation system synchronization method according to claim 1, it is characterised in that the step (2), GMSK difference
Signal is synchronized processing by the way of stream process and obtained, and step is：If different outburst types is to that should have m kinds locally to refer to
Signal, then design m shifting cache area, and shifting cache section length is consistent with the local reference signal length of each outburst type, right
The GMSK data segments of each shifting cache area storage carry out parallel calculus of differences；Difference is carried out when receiving a GMSK data segment
After computing, the last a data in each shifting cache area is removed and remaining data is shifted, then by a new GMSK
Data are stored in first position in each shifting cache area.
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| EP3267706B1 (en) | 2015-04-15 | 2020-08-05 | Huawei Technologies Co., Ltd. | Reference signal sending and receiving method and device |
| CN104852876B (en) * | 2015-05-18 | 2018-01-16 | 中国航空无线电电子研究所 | A kind of aviation wireless burst communication system |
| CN109688079A (en) * | 2018-12-20 | 2019-04-26 | 杭州电子科技大学 | The GMSK of low complex degree demodulates time synchronization method in a kind of burst communication |
| CN109462567B (en) * | 2018-12-25 | 2021-07-06 | 成都天奥信息科技有限公司 | Method for improving anti-time slot conflict capability of airborne AIS (automatic identification System) |
| CN111212006B (en) * | 2019-12-25 | 2022-07-15 | 奉加微电子（上海）有限公司 | Signal demodulation system and demodulation method |
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| US6449304B1 (en) * | 1999-05-14 | 2002-09-10 | The Aerospace Corporation | Method of determining the carrier reference phase of coherent demodulation of frequency hopped continuous phase modulated signals with synch words arbitrarily located within the hop |
| CN1710898A (en) * | 2005-06-29 | 2005-12-21 | 西安电子科技大学 | Modulation and demodulation method for continuous phase signals |
| CN104092527A (en) * | 2014-06-26 | 2014-10-08 | 广州海格通信集团股份有限公司 | GMSK coherent demodulation stream processing synchronization method combined with difference |
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6449304B1 (en) * | 1999-05-14 | 2002-09-10 | The Aerospace Corporation | Method of determining the carrier reference phase of coherent demodulation of frequency hopped continuous phase modulated signals with synch words arbitrarily located within the hop |
| CN1710898A (en) * | 2005-06-29 | 2005-12-21 | 西安电子科技大学 | Modulation and demodulation method for continuous phase signals |
| CN104092527A (en) * | 2014-06-26 | 2014-10-08 | 广州海格通信集团股份有限公司 | GMSK coherent demodulation stream processing synchronization method combined with difference |
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