CN1758636A - Frame detection and synchronous device for radio communication network - Google Patents
Frame detection and synchronous device for radio communication network Download PDFInfo
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- CN1758636A CN1758636A CN 200410080419 CN200410080419A CN1758636A CN 1758636 A CN1758636 A CN 1758636A CN 200410080419 CN200410080419 CN 200410080419 CN 200410080419 A CN200410080419 A CN 200410080419A CN 1758636 A CN1758636 A CN 1758636A
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Abstract
A detection and synchronization device of IEEE 802.11a or HiperLan2 frame head is featured as utilizing match filter to carry out inter-correlation operation on short Preamble series for obtaining a correlation series, determining that standard signal consistent to IEEE 802.11a or HiperLan2 is detected out and seeing that synchronous position can be confirmed preliminarily according to it if specific correlation peak value situation is obtained i.e. wave peak appeared in equal distance continuously and then no wave peak exceeding threshold in the same distance.
Description
Technical field
Generally speaking the present invention relates to a kind of baseband signal receiver apparatus in the radio communication device that is applied to, the frame head that this baseband signal receiver that particularly the present invention relates to comprises based on IEEE 802.11a or HiperLan2 agreement detects and the synchronous device circuit of judging.
Background technology
WLAN (wireless local area network) is a data communication system flexibly, can be used as replenishing or substituting of cable LAN in building or the campus.WLAN can use the radio wave transmissions data, has so just reduced the needs to wired connection, just data can connective be combined with user mobility, and is applied to some as portable terminals such as notebooks.Such wireless data communication system can use in many occasions, such as hotel, departure hall, hospital, campus etc.
WLAN can have multiple technologies available, multicarrier system, spread spectrum system, narrowband systems and infrared system are arranged, in these communication systems, each have their own characteristics, advantage and defective are also deposited, but theory and practice is verified, and ofdm system (OFDM) is very suitable for wireless LAN communication.
OFDM is the more superior technology of performance that high efficiency sends data on channel, and this technology has used a plurality of subcarrier frequencies in the channel width to send data.(FDM) compares with frequency division multiplexing, and the latter need separate subcarrier for fear of the interference of intercarrier, thereby wasted a part of frequency resource.Although and the subcarrier of ofdm system may be overlapped, but still can make the information that is modulated on each subcarrier obtain differentiating and recovering at receiving terminal.
Simultaneously, ofdm system also has tolerance degree to multidiameter expansion and frequency selective fading, effectively frequency spectrum use and good characteristic such as anti-interference.
In communication system, when receiving terminal receives signal, at first want the frame head of detection signal, also to carry out synchronously, the present invention is exactly in order to detect the frame head of 802.11a or HiperLan2 standard agreement, to find synchronous points simultaneously.
The baseband signal that meets 802.11a or HiperLan2 standard agreement is made of short preamble (1), long preamble (2), SIGNAL (3) and DATA signal (4), as shown in Figure 1.
The receiver circuit structure of general communication system as shown in Figure 4, antenna receiving signal is sent into RF module (5), obtain analog baseband signal after the down-conversion, through A/D conversion (6), obtain digital baseband signal, pass through " eliminating residual carrier wave " (7), frame head detection and sampling clock (8) synchronously again, demodulation and decoding circuit (9) just obtain data output.Also has " automatic gain control " circuit (10) simultaneously, its effect is detection signal amplitude or energy, feedback control signal gives the RF module with control received signal amplitude, after its control stabilization, can send an index signal and represent that the received signal amplitude is stable.
Circuit involved in the present invention is exactly " frame head detection and clock are synchronous " (8) part among Fig. 4.
Receiver will be finished with short preamble and survey and preliminary synchronizing function.When sampling rate is 20MHz, Short preamble is made up of 10 identical, 16 burst unit, in the ideal case, if received signal amplitude stability, short preamble is relevant with matched filter can to obtain 10 higher relevant crests, as shown in Figure 2, if detect such signal, just can judge that the signal of receiving is the 802.11a signal, but also can determine synchronous points.
But actual conditions more complicated, when just beginning received signal, its amplitude possibility is bigger than normal also may be less than normal, therefore to (AGC) adjust with " automatic gain control ", adjustment time maximum can take 6 sequence units in front among the short preamble, just means that also these 6 sequence units may use.
The general method that detects frame head is directly to test correlation whether to surpass thresholding, correlated process is such: the conjugation with 16 complex values of a short preamble symbol is formed matched filter, when received signal is come in, sequence is through matched filter, carry out related operation, each the time hour produce a correlation.But the defective of this mode is might be owing to The noise makes correlation surpass thresholding, rather than genuine correlation peak, makes and can't find out synchronous points.
Therefore, press for use a kind of technology can short preamble during this period of time in accurate detection signal and synchronously preliminary to realize by accurate detection data, frame head detection mistake and the frequency departure avoiding causing owing to external interference are out of one's reckoning.
Summary of the invention
The present invention designs circuit, adopts the local signal method relevant with received signal, finds last 4 relevant crests, and determines synchronous points according to the position of crest.
Feature of the present invention comprises following steps successively:
1. use among the short preamble in 10 symbols one, by the conjugate of 16 sequences of forming as matched filter, itself and received signal are carried out related operation.
2. base band A/D sample rate is 20MHz, when receiving the 802.11a signal, get 16 points in order successively, be equivalent in receiving sequence, take successively in relevant burst with a sliding window, it is relevant with matched filter, and promptly the data of corresponding points are carried out complex multiplication, and result of product adds up, add up and real part and respectively square addition again of imaginary part, or the direct addition that takes absolute value.As add and contain short preamble burst in the received signal, in above-mentioned sequence of correlation values, can produce several relevant crests so apparently higher than general value.
3. because various deviations and The noise in the actual conditions, make that the correlation of non-crest location is higher than thresholding under some situation, for avoiding this situation, need at first to determine that the correlation that is compared is a crest, method is to judge that the correlation of this point necessarily is higher than the correlation of two points that are adjacent.
4. ideally, above-mentioned correlated process can produce several relevant crests, and these several crests necessarily are on 16 the position of being separated by.But under the situation of low signal-to-noise ratio, because The noise, can produce some irrelevant crests, be higher than the correlation of thresholding, in order to get rid of this interference, need to add the decision condition of determining the position, promptly the crest location of Pan Dinging must be a distance with 16.
5. because the power of received signal is unsettled when beginning, the regulation and control of AGC need the regular hour, generally to use preceding 60% of the short preamble time period, be that t1 among Fig. 1 is to time period of t6, so when carrying out related calculation, can both occur next 4 stable relevant crests usually at least, be necessary to detect this 4 crests, method is: detect 4 be divided into 16 crest mutually after, be no more than thresholding every 16 locational correlations again, can judge that then these 4 crests are last 4 relevant crests, corresponding is the signal of the final stage t7 of short preamble to t10; Detecting these 4 another methods of crest is: detect 4 mean values of correlation that are divided into mutually at 16 greater than thresholding, next distance is that the correlation of 16 point is less than thresholding, can judge that then these 4 crests are last 4 relevant crests, corresponding is the signal of the final stage t7 of shortpreamble to t10.
6. after finding last 4 relevant crests of short preamble related operation, can determine sample-synchronous according to crest location.It in the position that relevant crest occurs the position when symbol and matched filter data sequence correspondence position are in full accord among the shortpreamble of received signal, the position of last 4 symbols among the short preamble can be determined, also just sync bit can be determined in view of the above.
Description of drawings
1. Fig. 1 is the structural representation of the baseband signal of IEEE 802.11a or HiperLan2, has wherein comprised Short Preamble (1), Long Preamble (2), SIGNAL (3) and information data (4) etc.
2. Fig. 2 is desirable correlation output sequence, illustrates in the ideal case, carry out related operation with local signal and received signal after, the sequence of correlation values that obtains wherein has 10 correlation peaks.
3. Fig. 3 is general correlation output sequence, illustrate that in the ordinary course of things the one segment signal time of front of received signal is used for being AGC (10) and adjusts, and may not go out correlation peak, in Short Preamble back a period of time, minimum 4 correlation peaks should appear.
4. Fig. 4 is the primary structure in the communication system, and circuit such as RF, A/D, AGC, the residual carrier wave of elimination, frame head detection, clock synchronization, rectification and decoding are arranged.
5. Fig. 5 is a circuit structure of the present invention.
Embodiment
Based on embodiment of the present invention, be applied to the detection of IEEE 802.11a frame head with synchronously, circuit block diagram provides concrete implementation step as shown in Figure 5 below.
1.A/D sample rate is 20MHz, with one in 10 symbols among the short preamble, by the conjugate of 16 sequences of forming as matched filter (11).
2. collecting mail and number sending into a length is 16 shift register (15), each constantly this shift register move forward one, and receive a new signal.
3. at each constantly, data on register (15) and (11) are all carried out related operation one time, be that data on the correspondence position multiply each other, the The above results to 16 points that multiplies each other adds up, the real part of accumulation result and imaginary part are asked a square also addition respectively, or the addition that takes absolute value, just obtain the correlation in a moment.
4. above-mentioned correlation is sent into a shift register (14), each this shift register of the moment moves forward one, and receives a new correlation.
5. register (14) length of storage sequence of correlation values is 67, and crest testing circuit (13) is used for the correlation on the position 2,18,34,50,66 in the detected register (14), and whether detect on these positions is crest value, and condition is:
A) correlation is higher than thresholding;
B) correlation is higher than adjacent correlation at 2.
6. if the correlation that detects on the position 18,34,50,66 in the register (14) reaches above-mentioned requirements, and the correlation on the position 2 does not reach requirement, can judge that then above-mentioned 4 crest locations are last 4 relevant crests of short preamble related operation.
7. register (14) length of storage sequence of correlation values is 67, crest testing circuit (13) is used for the correlation on the position 2,18,34,50,66 in the detected register (14), judge that above-mentioned 4 crest locations are last 4 relevant crests of short preamble related operation, condition can also be:
A) mean value of 18,34,50,66 locational correlations is higher than thresholding;
B) 2 locational correlations are lower than threshold value;
8. after finding last 4 relevant crests of short preamble related operation, also just can determine the position of last 4 symbols of short preamble, that is to say that crest receiving symbol sequence constantly is fully corresponding on the position with local correlated series, so just can determine sync bit.Realization effect by embodiment, designed its maximum innovative point of circuit that goes out of the present invention and technical solution the very corn of a subject thought are the method that adopts local signal relevant with received signal, by detecting last 4 relevant crests of short preamble, can obtain the frame head sync bit with this.As known to the various equivalent modifications, this is the necessary condition of next step baseband signal demodulation, by this technical process can avoid since can't accurately carrying out of causing of noise jamming frame head detects and the thresholding deviation can't accurately be judged this technical barrier of synchronous points.
Claims (10)
1. the frame head that the present invention relates to a kind of IEEE of being used for 802.11a or HiperLan2 standard detects and method for synchronous, is characterised in that may further comprise the steps: the cross correlation value sequence that obtains standard Short Preamble symbol and received signal with a cross-correlator; Judge whether sequence of correlation values particular condition occurs, be the signal that meets IEEE 802.11a or HiperLan2 standard with definite received signal, and tentatively determine sync bit.
2. method according to claim 1 is characterized in that: the conjugate with a symbol among the Short Preamble does cross-correlation with the value of input sample signal.As shown in Equation (1), s (m), m=1,2 ... N is the symbol sebolic addressing of Short Preamble, and r (n) is input baseband sampling preface
Row, c (n) is a correlation.
Obtain behind the correlation with its mould value square, as correlation magnitude value d (n), see formula (2).And available realistic the absolute value sum with imaginary part replaces, and sees formula (3).
d(n)＝c(n)·c
*(n) (2)
d(n)＝|Re[c(n)]|+|Im[c(n)]| (3)
3. according to claim 1 and the described method of claim 2, it is characterized in that: sequence of correlation values particular condition occurs and is meant that the crest of symbolic distance appears waiting in sequence of correlation values continuously.Promptly on the position of waiting symbolic distance, occur continuously being no less than four crests, and crest on the equidistant position of the next one, do not occur, promptly can judge the last several symbols that found Short Preamble.
4. method according to claim 3 is characterized in that: the standard for relevant crest of detecting can be that the correlation at this place is not only greater than thresholding, and greater than the correlation of adjacent the right and left.It can also be to detect the mean value of four correlations that wait symbolic distances greater than thresholding that particular condition appears in sequence of correlation values, and is lower than thresholding at the equidistant locational correlation of the next one.
5. the present invention relates to the frame head checkout gear of a kind of IEEE of being used for 802.11a or Hiperlan2 standard, be characterised in that to comprise: correlation module is used for reception sample sequence and standard Short Preamble symbol are carried out related calculation; The peak value determination module judges particular condition whether occurs in sequence of correlation values, be the signal of IEEE 802.11a or Hiperlan2 standard with definite received signal, and tentatively determine sync bit.
6. correlation module according to claim 5, its course of work is such: the data on the sampled value correspondence position that receives with a winding with one group of conjugate of the symbol of ShortPreamble in the standard multiply each other, real part that obtains after multiplied result adds up and imaginary part are asked a square also addition respectively, perhaps directly ask absolute value and addition, just obtain the correlation in this moment.Getting the different sampled values that constantly receive does computing cross-correlation and just obtains a sequence of correlation values.
7. according to the device of claim 5, it is characterized in that: the effect of described peak value determination module is in sequence of correlation values, to detect the relevant peaks of four continuous phases every a symbolic distance.Relevant peaks does not appear in the position of detecting the next symbolic distance of sequence of correlation values again.
8. according to the device of claim 6, it is characterized in that: the standard for relevant peaks of detecting is that the correlation of this point is not only greater than thresholding, and greater than the correlation of two adjacent points.The device that detects four serial correlation peaks can be these four peak values all greater than a definite thresholding, perhaps the mean value of four peak values is greater than a definite thresholding.
9. device according to claim 5 is characterized in that: from receiving signal, pointwise detects to received signal, up to the point that detects the standard of reaching.
10. according to claim 6 or the described device of claim 7, determine the position of last 4 symbols among the Short Preamble, also just can determine sync bit in view of the above.
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| CN 200410080419 CN1758636A (en) | 2004-10-09 | 2004-10-09 | Frame detection and synchronous device for radio communication network |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101867543A (en) * | 2010-02-08 | 2010-10-20 | 北京韦加航通科技有限责任公司 | Frame arrival detection method based on signal-to-noise rate estimation |
| CN102970688A (en) * | 2011-08-31 | 2013-03-13 | 北京中电华大电子设计有限责任公司 | Method and device for detecting frame signals of wireless local area network (WLAN) equipment |
| CN103944850A (en) * | 2014-03-27 | 2014-07-23 | 西安星河亮点信息技术有限公司 | WLAN system frame synchronization method based on OFDM technology |
| CN107359959A (en) * | 2016-05-09 | 2017-11-17 | 上海复旦微电子集团股份有限公司 | The original position detection method and receiver of data frame |
| CN114268528A (en) * | 2021-12-06 | 2022-04-01 | 深圳智微电子科技有限公司 | Frame capture synchronization method and device |
-
2004
- 2004-10-09 CN CN 200410080419 patent/CN1758636A/en active Pending
Cited By (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101867543A (en) * | 2010-02-08 | 2010-10-20 | 北京韦加航通科技有限责任公司 | Frame arrival detection method based on signal-to-noise rate estimation |
| CN101867543B (en) * | 2010-02-08 | 2016-03-30 | 北京韦加航通科技有限责任公司 | A kind of frame arrival detection method based on signal-to-noise ratio (SNR) estimation |
| CN102970688A (en) * | 2011-08-31 | 2013-03-13 | 北京中电华大电子设计有限责任公司 | Method and device for detecting frame signals of wireless local area network (WLAN) equipment |
| CN102970688B (en) * | 2011-08-31 | 2015-11-25 | 北京中电华大电子设计有限责任公司 | A kind of frame signal detection method for WLAN devices and device |
| CN103944850A (en) * | 2014-03-27 | 2014-07-23 | 西安星河亮点信息技术有限公司 | WLAN system frame synchronization method based on OFDM technology |
| CN103944850B (en) * | 2014-03-27 | 2018-01-16 | 西安星河亮点信息技术有限公司 | A kind of wlan system frame synchornization method based on OFDM technology |
| CN107359959A (en) * | 2016-05-09 | 2017-11-17 | 上海复旦微电子集团股份有限公司 | The original position detection method and receiver of data frame |
| CN107359959B (en) * | 2016-05-09 | 2019-12-24 | 上海复旦微电子集团股份有限公司 | Method for detecting initial position of data frame and receiver |
| CN114268528A (en) * | 2021-12-06 | 2022-04-01 | 深圳智微电子科技有限公司 | Frame capture synchronization method and device |
| CN114268528B (en) * | 2021-12-06 | 2024-01-05 | 深圳智微电子科技有限公司 | Frame capturing synchronization method and device |
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