CN106685879B - A kind of orthogonal frequency division multiplexi multiframe synchronization method based on IEEE802.11 agreement - Google Patents
A kind of orthogonal frequency division multiplexi multiframe synchronization method based on IEEE802.11 agreement 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
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2656—Frame synchronisation, e.g. packet synchronisation, time division duplex [TDD] switching point detection or subframe synchronisation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2662—Symbol synchronisation
- H04L27/2663—Coarse synchronisation, e.g. by correlation
Abstract
A kind of OFDM (Orthogonal Frequency Division Multiplexing based on IEEE802.11a is claimed in the present invention; orthogonal frequency division multiplexing) technology multiframe synchronization method; it is related to the communication technology, realizes frame head and the postamble identification of the more burst frames of receiving end baseband signal.It include: to complete thick synchronizing frame head using receiver baseband signal quiet period to estimate；Interception minimum frame length after slightly synchronizing, estimates according to smart synchronizing frame head is obtained there are short training sequence sliding auto-correlation in minimum frame length；According to the quiet period chugging before postamble symbol to next frame, postamble estimation is obtained；Data duplication detection after intercepting End of Frame, until having detected all burst frames for receiving signal and containing.The present invention is happened suddenly frame synchronization using receiving signal self-characteristic and complete receiving end more, is reduced and is realized difficulty and computational complexity, and the frame synchronization of the more burst frames of receiving end baseband signal provides a kind of simple and effective solution scheme.
Description
Technical field
The present invention relates to mobile communication technology frame synchronization fields, more particularly to the OFDM skill of base IEEE802.11a a kind of
Art multiframe synchronization method.
Background technique
In the communications, due to the multipath and time variation of actual wireless channel, the sync bit needs of ofdm system have
Higher accuracy just can guarantee the performance of system.The receiver system block diagram of general communication system is as shown in Figure 1, institute of the present invention
The module being related to is " frame synchronization " part in Fig. 1.
Meet the baseband signal of IEEE802.11a standard agreement by short training sequence, long training sequence, signal and data symbols
Number constitute, as shown in Figure 2.
In IEEE802.11a system, frame synchronization often utilizes 4 duplicate short training sequence completion timings synchronous, this
Flat characteristic is presented in the cost function that kind method obtains at the position that this four short training sequences occur, thus cannot be accurate
Determine the position that frame head starts.Common another kind is to generate short training sequence not affected by noise in receiving end to be used as with reference to letter
Number, carry out related operation respectively with the 10 duplicate short training sequences received, available 10 peak values, but with
Multiple pseudo- peaks can be generated beside the reduction of SNR (Signal Noise Ratio, signal-to-noise ratio) and 10 peak value of influence of multipath fading,
To which peak detection becomes difficult.In addition, receive signal may a not only frame, training sequence is to carry out frame same in the case of multiframe
Can be interfered with each other when step, thus correctly detect in the case where more burst frames each frame head and postamble at challenge, it is above to be retouched
The platform and pseudo- peak and multi frame detection stated all are Research Challenges places.
In conjunction with method above-mentioned, that the simultaneous techniques in ofdm system mainly uses correlated series to carry out related synchronization, and this
A little methods are widely accepted.For general wlan device, ceaselessly related operation will bring time loss, and increase is set
Standby burden.Therefore, the invention firstly uses the approximate locations for slightly synchronizing first positioning signal, then carry out related synchronization, reduce phase
Close synchronization times.Wherein related synchronization algorithm of the invention is applicable not only to 802.11g by taking 802.11a as an example, and is suitable for
Using the 802.11n and 802.11ac of MIMO (Multiple Input Multiple Output, multiple-input, multiple-output) technology.
Summary of the invention
Present invention seek to address that the above problem of the prior art.Propose a kind of method.Technical scheme is as follows:
A kind of orthogonal frequency division multiplexi multiframe synchronization method based on IEEE802.11 agreement comprising following steps:
101, receiver completes thick synchronizing frame head estimation in the quiet period of baseband signal；
102, the minimum frame length after interception slightly synchronizes is slided according to short training sequence existing in minimum frame length from phase
Pass obtains smart synchronizing frame head estimation；
103, according to the quiet period chugging before postamble symbol to next frame, postamble estimation is obtained；
104, the Data duplication detection after intercepting End of Frame, repeats frame head and postamble detection, until having detected reception signal
All burst frames contained, i.e. completion frame synchronization, frame synchronization include frame head and postamble detection.
Further, the IEEE802.11 includes IEEE802.11a, 802.11g and using MIMO technology
802.11n and 802.11ac.
Further, step 101 receiver complete the estimation of thick synchronizing frame head in the quiet period of baseband signal comprising steps of
Quiet period before being arrived using burst frame completes thick synchronizing frame head estimation, determines that parameter mainly includes sliding window
Wcoarse, thresholding TcoarseIt is r (d) with signal is received, d indicates current window position；Since d=1, W is calculatedcoarseIn window
The general power and interval W of signalcoarsePower ratio in next window, by ratio and TcoarseIt compares, if more than Tcoarse,
Then one sampled point of window forward slip, i.e. d add 1, compute repeatedly ratio, are less than T when there is ratiocoarseWhen, illustrate in ratio
Sampled point in molecule window is quiet period sampled point, and performance number contains burst frame power in denominator window in ratio, this
When ratio molecule on window signal position d as thick synchronizing frame head position.
Further, it includes: practical according to signal extraction is received that the step 102, which intercepts the minimum frame length after slightly synchronizing,
Long and short training sequence, signal and data symbol under sample rate, ideal rate, ideal rate, are expressed as Sreal、
Sideal、Mlong、Mshort、NsignalAnd Ndata, practical reception signal long training sequence, short training sequence, signal and data symbol are adopted
Sampling point number is expressed as WithMinimum frame length LminTable
It is shown as:
Further, it is the reception signal updated that the step 102, which intercepts the signal after thick synchronizing frame head, and d is updated to 1,
Determine CupdataWhether L is greater thanmin, CupdataFor the reception signal length of update, if not then whole frame is not present in the data, if
It is to receive data there are whole frames.
Further, when receiving data there are when whole frame, the first sliding window W is setfine, the reception of update is believed
Number, W is taken since d=1fineIt is a, by WfineIt is interior after 1/2 signal take conjugation be multiplied respectively with preceding 1/2 data sum again after modulus
First metric is obtained, is indicated are as follows:N is indicated in the first sliding window
Sampled point, wherein 1≤n≤Wfine/2；Window moves to right one, i.e. d+1 is assigned to d, and P (d) is sought in repetition, until d is slided into and connect
Collect mail number Lmin-WfinePlace, so far obtains Lmin-WfineThe cost function that a metric is constituted, cost function indicate are as follows:
Further, auto-correlation is slided according to short training sequence existing in minimum frame length described in step 102 and obtains essence
Synchronizing frame head estimation specifically: if receiving signal contains short training sequence, cost function
Middle to generate single, sharp relevant peaks, peak value index is the smart synchronizing frame head position for receiving signal.
Further, postamble is obtained according to the quiet period chugging before postamble symbol to next frame described in step 103
Estimation comprises determining that the parameter of postamble estimated service life, including the second sliding window Wend, thresholding TendAnd essence is combined to synchronize again more
New reception signal；Since d=1, W is calculatedendSignal power and interval W in windowendPower ratio in next window, will
Ratio and TendCompare, if more than Tend, then d+WfineIt is assigned to d, computes repeatedly ratio, when there is ratio less than threshold value, i.e.,
Window sliding completes postamble estimation to a last data symbol.
It advantages of the present invention and has the beneficial effect that:
The present invention in view of the drawbacks of the prior art and there are the problem of, design a kind of OFDM skill based on IEEE802.11a
Art multiframe synchronization method.The thinking of algorithm proposed by the present invention avoids the cost function using presentation flat characteristic first, and wishes
Hope the cost function of construction that can form single, sharp relevant peaks in correct sync bit.It is avoided as far as possible due under SNR
The influence of drop and multipath channel, and the fluctuating of cost function is caused, to reduce evaluated error in such a case, simultaneously
Also consider to reduce the complexity on realizing as far as possible, be convenient for hardware realization.Additionally, it is contemplated that can correctly be sorted in multiframe
Each frame out avoids the relevant peaks of multiframe from influencing each frame detection.
The maximum innovative point of the present invention and the core concept for solving technical problem are using receiving end baseband signal power
Detection and the autocorrelative method of sliding, the chugging to be arrived by detecting quiet period to burst frame obtain thick synchronizing frame head, lead to
It crosses short training sequence reception period and only forms single sharp relevant peaks, complete smart synchronizing frame head；Pass through postamble to quiet period function
Rate abrupt climatic change postamble.Known to the those skilled in the relevant arts as, this is the necessary condition of next step modulation demodulation,
It can also cause can not accurately to carry out frame to avoid the influence of decline and multipath channel due to SNR by this technical process same
Walk this technical problem.
Detailed description of the invention
Fig. 1 is that the present invention provides preferred embodiment OFDM receiver system block diagram；
Fig. 2 is IEEE802.11a frame structure schematic diagram；
Fig. 3 is that smart synchronizing frame head estimates flow chart；
Fig. 4 is that smart synchronizing frame head estimates the 4 frame synchronization points obtained after adopting the above method.
Fig. 5 is the outline flowchart of the preferred embodiment of the present invention.
Specific embodiment
Following will be combined with the drawings in the embodiments of the present invention, and technical solution in the embodiment of the present invention carries out clear, detailed
Carefully describe.Described embodiment is only a part of the embodiments of the present invention.
The technical solution that the present invention solves above-mentioned technical problem is to design a kind of OFDM technology based on IEEE802.11a
Multiframe synchronization method, this method include following processing step:
Estimate 1. the quiet period before being arrived using burst frame completes thick synchronizing frame head, determines that parameter mainly includes sliding window
Wcoarse, thresholding TcoarseIt is r (d) with signal is received, d indicates current window position；Since d=1, W is calculatedcoarseIn window
The general power and interval W of signalcoarsePower ratio in next window, by ratio and TcoarseIt compares, if more than Tcoarse,
Then one sampled point of window forward slip, i.e. d add 1, compute repeatedly ratio, are less than T when there is ratiocoarseWhen, illustrate in ratio
Sampled point in molecule window is quiet period sampled point, and performance number contains burst frame power in denominator window in ratio, this
When ratio molecule on window signal position d as thick synchronizing frame head position.
2. intercepting data after thick synchronizing frame head, smart synchronizing frame head estimation is completed, the specific steps are as follows:
2.1 by reception signal extraction actual sample rate, ideal rate, long training sequence, Short Training under ideal rate
Sequence, signal and data symbol are expressed as Sreal、Sideal、Mlong、Mshort、NsignalAnd Ndata, practical to receive Chief Signal Boatswain training
Sequence, short training sequence, signal and data symbol sampler point number are expressed asWithMinimum frame length LminIt indicates are as follows:
Data after the 2.2 thick synchronizing frame heads of interception, as the reception signal of update, d is updated to 1, determines CupdataIt is whether big
In Lmin, CupdataIllustrate that whole frame is not present in signal if being less than minimum frame length for the reception signal length of update, if more than
Show that there are whole frames.
2.3 setting sliding window Wfine, whereinTo the reception signal of update, since d=1
Take WfineIt is a, by WfineIt is interior after 1/2 signal take conjugation be multiplied respectively with preceding 1/2 data sum again after modulus obtain first spend
Magnitude indicates are as follows:
Wherein, 1≤n≤Wfine/ 2, n are sliding window WfineSampled point.
2.4 windows move to right one i.e. d+1, repeat step 2.2, up to window sliding to reception signal Lmin-WfinePlace, until
This obtains the cost function being made of metric, and cost function indicates are as follows:
If 2.5 reception signals contain short training sequence, one can be generated in above-mentioned cost function and is apparently higher than generally
The relevant peaks of value, the index of relevant peaks are smart synchronizing frame head position.
3. terminating to next frame the quiet period before arriving using burst frame data symbol, postamble is obtained using power detection and is estimated
Meter.The parameter of postamble estimated service life, including sliding window Wend, thresholding TendAnd the letter updated again after smart synchronizing frame head estimation
Number, as the reception signal of update, since receiving first sampled point of signal, i.e. d=1, WendIn window signal power and
Every WendPower ratio in next window, by ratio and TendCompare, if more than Tend, then d+WfineIt is assigned to d, computes repeatedly ratio
Value shows on ratio molecule window sliding to a last data symbol, in ratio denominator when there is ratio less than threshold value
Power contain the performance number of quiet period, the power on molecule is exactly the last one data symbol power of a frame, i.e., completion frame
Tail estimation.
4. intercepting behind postamble position, data are as the reception signal updated, and circulation executes 1-4 step, when condition is unsatisfactory for walking
When rapid 2.2, all burst frame frame heads and postamble estimation that initial reception signal includes are completed.
5. being up-sampled each frame of the burst frame sorted out respectively as SidealTimes digital baseband signal, then down-sampling are SrealNumber
Word baseband signal has obtained the synchronization baseband signal under ideal rate.
Based on embodiment of the invention, be applied to the thick synchronizing frame head estimation of IEEE802.11a, smart synchronizing frame head estimation and
Postamble estimation, flow chart is as shown in figure 3, be given below specific implementation step.
1. receiving the complex signal that signal length C is 47687, W is setcoarse=50, TcoarseThe sampling of=0.1 signal first
Point r (1) gets r (50), to the quadratic sums of this 50 sampled point modulus as previous window power, after being spaced 50 sampled points
Next window power, previous window and the latter window ask ratio and thresholding Tcoarse=0.1 compares, if being unsatisfactory for being less than
The condition of thresholding then one sampled point of window forward slip, recalculates ratio, until detecting that ratio is less than threshold value；Work as window
When mouth slides into d=195, ratio 0.0298, previous window performance number is quiet period, and latter window power includes burst frame function
Rate, accordingly available thick synchronizing frame head estimation.
2. data are C as the reception signal length updated after the thick synchronizing frame head of interceptionupdate=C-d, it is synchronous to complete essence
Frame head estimation, Fig. 3 give smart synchronizing frame head estimation procedure, specifically comprise the following steps:
Step 31, signal ideal rate S is receivedidealFor 20MHz, ideal long training sequence, short training sequence, signal and
Data symbol number of sampling points is respectively 160,160,80 and 80 sampled points.Actual sample rate SrealIt is 1/ (2.11 × 10-8)
MHz, practical Chief Signal Boatswain, short training sequence, signal and the data symbol sampler point number of receiving are calculated as 380,380,190 and 190,
Minimum frame length LminIt is calculated as 1140.
Step 32, the reception signal length C of updateupdataWhether L is greater thanmin, deposited if more than the reception signal for illustrating update
In whole frame, show to terminate algorithm there is no whole frame if being unsatisfactory for.
Step 33, setting short training sequence length 380 is window WfineSize, window is from letter
First data starts to take 380 data, calls formula:
First metric P [d] is obtained, at this time d=1.
Step 34, sliding window often moves to right one, repeats step 33, other metrics is obtained, when sliding window reaches
Lmin-WfineStop sliding when=1140-380=760, forms cost function by this 760 metrics.
Step 35, it receives signal and contains short training sequence, cost function generates single and sharp relevant peaks, relevant peaks institute
In index i.e. smart synchronizing frame head position, in this group of data, the point that smart synchronizing frame head estimates is as shown in Figure 4.
3. determining the parameter size that postamble uses, including Wend=190, Tend=0.6；In conjunction with smart synchronizing frame head estimated result
Window W of the more new signal by a data symbol sampler point number 190 as postamble estimated service life againend, intercept smart synchronization frame
Data after head are the reception signal updated, calculate WendSignal power and interval W in windowendPower ratio in next window
Value, by ratio and TendCompare, if more than Tend, then d+WfineIt is assigned to d, computes repeatedly ratio, is less than threshold value when there is ratio
When, show that ratio denominator power compares power contained by molecule and declines i.e. the latter window sliding suddenly and has arrived quiet period, molecule window
Mouth is the last one data symbol of burst frame, so far completes postamble estimation.
4. intercepting the data after postamble as the reception signal updated, circulation executes 1-4 step, when condition is unsatisfactory for step
When 2.2, the frame head for completing all burst frames is synchronous with postamble.
5. all burst frames that will test successively carry out up-sampling 20MHZ, then down-sampling 1/ (2. × 11-81M0Hz) again,
Obtain the synchronization baseband signal under ideal rate.
From the point of view of the realization effect of specific embodiment, the maximum innovative point of the present invention and the core for solving technical problem
Thought is to be detected using receiving end baseband signal power and slides autocorrelative method, is arrived by detection quiet period to burst frame
The chugging come, obtains thick synchronizing frame head, only forms single sharp relevant peaks by short training sequence reception period, completes
Smart synchronizing frame head；Postamble is detected by postamble to quiet period chugging.Known to the those skilled in the relevant arts as, this is
The necessary condition of next step modulation demodulation, by this technical process can also to avoid due to SNR decline and multipath believe
The influence in road and cause accurately carry out this technical problem of frame synchronization.
Fig. 5 is the outline flowchart of the preferred embodiment of the present invention, including reception data, thick synchronizing frame head are estimated, essence is synchronous
Frame head estimation, postamble estimation, with the end of the step the step of.
The above embodiment is interpreted as being merely to illustrate the present invention rather than limit the scope of the invention.?
After the content for having read record of the invention, technical staff can be made various changes or modifications the present invention, these equivalent changes
Change and modification equally falls into the scope of the claims in the present invention.
Claims (3)
1. a kind of orthogonal frequency division multiplexi multiframe synchronization method based on IEEE802.11 agreement, which is characterized in that including with
Lower step:
101, receiver completes thick synchronizing frame head estimation in the quiet period of baseband signal, specifically includes: before being arrived using burst frame
Quiet period complete the estimation of thick synchronizing frame head, determining parameter mainly includes sliding window Wcoarse, thresholding TcoarseWith reception signal
Current window position is indicated for r (d), d；Since d=1, W is calculatedcoarseThe general power of signal and interval W in windowcoarseUnder
Power ratio in one window, by ratio and TcoarseIt compares, if more than Tcoarse, then one sampled point of window forward slip,
I.e. d adds 1, computes repeatedly ratio, is less than T when there is ratiocoarseWhen, illustrate the sampled point in ratio in molecule window for silence
Phase sampled point, and performance number contains burst frame power in denominator window in ratio, at this time the window signal position on ratio molecule
D is set as thick synchronizing frame head position；
102, the minimum frame length after interception slightly synchronizes slides auto-correlation according to short training sequence existing in minimum frame length and obtains
Estimate to smart synchronizing frame head；It includes: practical according to signal extraction is received that the step 102, which intercepts the minimum frame length after slightly synchronizing,
Long and short training sequence, signal and data symbol under sample rate, ideal rate, ideal rate, are expressed as Sreal、
Sideal、Mlong、Mshort、NsignalAnd Ndata, practical reception signal long training sequence, short training sequence, signal and data symbol are adopted
Sampling point number is expressed as WithMinimum frame length LminTable
It is shown as:
It is the reception signal updated that the step 102, which intercepts the signal after thick synchronizing frame head, and d is updated to 1, determines CupdataWhether
Greater than Lmin, CupdataIt is deposited if not then whole frame is not present in the data if then receiving data for the reception signal length of update
In whole frame；
When receiving data there are when whole frame, the first sliding window W is setfine, to the reception signal of update, taken since d=1
WfineIt is a, by WfineIt is interior after 1/2 signal take conjugation be multiplied respectively with preceding 1/2 data sum again after modulus obtain first measure
Value indicates are as follows:N indicates the sampled point in the first sliding window, wherein 1
≤n≤Wfine/2；Window moves to right one, i.e. d+1 is assigned to d, and P (d) is sought in repetition, until d, which is slided into, receives signal Lmin-Wfine
Place, so far obtains Lmin-WfineThe cost function that a metric is constituted, cost function indicate are as follows:
Auto-correlation is slided according to short training sequence existing in minimum frame length described in step 102 and obtains smart synchronizing frame head estimation tool
Body are as follows: if receiving signal contains short training sequence, cost functionIn will generate it is single, sharp
Sharp relevant peaks, related peak-to-peak value index is the smart synchronizing frame head position for receiving signal；
103, according to the quiet period chugging before postamble symbol to next frame, postamble estimation is obtained；
104, the Data duplication detection after intercepting End of Frame, repeats frame head and postamble detection, contains until having detected reception signal
All burst frames, i.e., completion frame synchronization.
2. the orthogonal frequency division multiplexi multiframe synchronization method according to claim 1 based on IEEE802.11 agreement,
Be characterized in that, the IEEE802.11 include IEEE802.11a, 802.11g and using MIMO technology 802.11n and
802.11ac。
3. the orthogonal frequency division multiplexi multiframe synchronization method according to claim 1 based on IEEE802.11 agreement,
It is characterized in that, according to the quiet period chugging before postamble symbol to next frame described in step 103, obtains postamble estimation packet
It includes: determining the parameter of postamble estimated service life, including the second sliding window Wend, thresholding TendAnd it is connect in conjunction with what essence synchronization updated again
The collection of letters number；Since d=1, W is calculatedendSignal power and interval W in windowendPower ratio in next window, by ratio with
TendCompare, if more than Tend, then d+enWifIt is assigned to d, computes repeatedly ratio, when there is ratio less than threshold value, i.e., window is sliding
A last data symbol is moved, postamble estimation is completed.
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| CN114205199B (en) * | 2021-11-30 | 2023-10-20 | 成都中科合迅科技有限公司 | WIFI signal identification method in complex electromagnetic environment |
| CN117479288A (en) * | 2023-11-27 | 2024-01-30 | 中国人民解放军军事科学院系统工程研究院 | Timing synchronization method and device for burst signal test |
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