CN100420180C - Synchronization method and device of packet wireless communication system - Google Patents
Synchronization method and device of packet wireless communication system Download PDFInfo
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- CN100420180C CN100420180C CNB031166156A CN03116615A CN100420180C CN 100420180 C CN100420180 C CN 100420180C CN B031166156 A CNB031166156 A CN B031166156A CN 03116615 A CN03116615 A CN 03116615A CN 100420180 C CN100420180 C CN 100420180C
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Abstract
The present invention relates to a digital communication technique, more specifically to a synchronization method of a packet wireless communication system and a device thereof. The synchronization method is characterized in that signals received by a receiving antenna are preprocessed in a radio frequency mode and then converted into base band signals; the base band signals are converted into digital signals through an A/D converter, the digital signals are input into a matched filter, and a reference signal is obtained through simple calculation; the reference signal is as the comparison threshold of peak detection, detected peak signals are transmitted to a multi-path response generator so as to obtain a high-accuracy multi-path response synchronization time; subsequently, the peak signals are transmitted to a symbol demodulator in which the peak signals and digital signals of the A/D converter are demodulated in an orthogonal frequency division multiplexing mode; finally, signal decoding is carried out to obtain user data. The synchronization method and the device are suitable for various packet wireless communication systems and can raise the integral performance of the systems.
Description
One, technical field:
The present invention relates to a kind of digital communication technology, more specifically be meant the method for synchronous and the device thereof of packet radio communication system, it adopts the pilot tone synchronizing signal to realize synchronous method and device, is applicable to various packet radio communication systems, can improve the overall performance of system.
Two, background technology:
Packet radio communication system starts from the seventies in last century the earliest, utilizes wireless medium to transmit data in ALOHA system.In the last few years, compunication and Internet technology, wireless communication technology had had develop rapidly and extensive use; And this packet radio communication technology across compunication and radio communication two big fields is a kind of very important technology of digital communicating field now, also is considered to the development in future direction.Its typical case uses WLAN (wireless local area network) (IEEE 802.11 series standards, ETSI Hiperlan2 standard), broadband wireless access (IEEE 802.16) or the like.
In packet radio communication system, when user data (grouping) arrived, system just changed the reception and the processing procedure of data over to.So-called burst that Here it is (Burst) communication.So system is in burst usually and detects in (Busrt Detection) state.And, in case when detecting burst and need accept data, system must obtain synchronously immediately, to guarantee the carrying out of Data Receiving.
In addition, always run into various barriers in the radio propagation process, thereby form multipath transmisstion, the signal that receives is synthetic signal by the mulitpath signal of different propagation delays and intensity.When the data rate height, symbol period can produce intersymbol interference when multipath transmisstion is serious in short-term.At this moment, generally adopt the robustness modulation technique (as OFDM, OFDM), method such as diversity reception, channel equalization resists intersymbol interference.Accurately estimate the multipath effect of channel, could guarantee that the anti-multipath measure of system can be brought into play effectively.
In the packet radio communication system, add the preceding paragraph pilot signal (Preamble) in each burst front usually, as synchronizing signal.At receiving terminal, adopt matched filter then can detect time synchronized.Yet because The noise, synchronous detecting following two kinds of flase drops can occur and survey 1) false-alarm: detect synchronizing signal in the moment that does not have signal; 2) omission: do not detect synchronizing signal in the moment that signal is arranged.Simultaneously, because the automatic gain control error of locking or automatic gain control fully not also, make the received signal level instability.This can have influence on the synchronous detecting performance.
In addition, how to estimate exactly multipath signal power and delay, output to symbol demodulation portion better restituted signal also be a problem to be solved.
Three, summary of the invention:
The objective of the invention is at the deficiencies in the prior art, propose a kind of fast synchronization method, and under multipath channel, can estimate the multipath response exactly; And its implement device.
This method can improve the overall performance of system under the situation that does not roll up system burden.
For achieving the above object, the present invention at first carries out analog-to-digital conversion with baseband signal, and is input to matched filter.This matched filter also utilizes some simply to calculate a reference signal, and the comparison threshold as peak value detects detects performance to improve.
The peak signal that is detected is sent to multipath response maker, obtains high-precision multipath response.According to the needs of symbol demodulator, export corresponding channel information, for example, the optimal synchronisation time of OFDM demodulation is to guarantee the performance of symbol demodulator.
Detailed content of the present invention is as described below.
At first, the signal that reception antenna receives converts baseband signal to through after the radio frequency processing.Baseband signal is digital signal by analog to digital converter with the analog signal conversion that receives, to realize Digital Signal Processing.
Baseband digital signal is fed to matched filter.This matched filter comprises two parts processing.1) peak value matched filtering: (known) pilot symbol transmitted as local symbol, is carried out matched filtering to input signal.When the phase place of phase of input signals and local symbol was consistent, the output of matched filter obtained peak value; Otherwise output signal is a noise.2) reference signal forms: find the solution (or search) in advance and go out and the quasi-orthogonal symbol of frequency pilot sign, carry out matched filtering as local symbol, output signal then is a reference signal.According to the present invention,, find the solution the local symbol of (or search) reference signal filtering with the criterion that is minimised as of maximum cross correlation.
Reference signal is carried out suitable gain adjustment, as the comparison threshold of peak value detection.When the output of peak value matched filtering surpasses this thresholding, think that then synchronization point arrives, its peak value is the intensity of channel response.Because the effect of multipath channel may detect a plurality of synchronization points and a plurality of peak value, promptly so-called multipath channel response.
The synchronization point that is detected removes control channel response maker.During a plurality of repetition frequency pilot signs that arrive subsequently, detected peak value carries out intersymbol average, to remove the influence of various noises and interference, obtains high-precision channel response and estimates.In addition, in the average way of intersymbol, the peak averaging signal also is admitted to synchronous checking, to confirm synchronous authenticity as early as possible.
The multipath channel response that estimates outputs to an optimal synchronisation time maker, for symbol demodulation is found out best lock in time.
The present invention is on the basis of traditional matched filter synchronous circuit, add a simple reference signal circuit, obtain the comparison threshold that peak value detects, can improve the synchronous detecting performance, particularly also not enter fully under the bigger situation of the error of lock-out state or automatic gain control in automatic gain control.
According to the present invention, (a plurality of frequency pilot signs of repetition) carry out enough peak averagings in whole pilot signal interval, obtain accurate multipath channel response.According to these information, extract the required parameter of symbol demodulator (for example, the FFT interval of OFDM), improve the performance of symbol demodulation.
Four, description of drawings:
Accompanying drawing 1 is an OFDM receiving system block diagram involved in the example
Accompanying drawing 2 is synchronization module structural representations
The 3 is-symbol demodulation optimal synchronisation times (OFDM FFT time started) of accompanying drawing
Five, embodiment:
Below with reference to accompanying drawing, be embodiment with WLAN (wireless local area network) IEEE 802.11a system, the present invention is described further.
Fig. 1 is the block diagram that the present invention is used for IEEE 802.11a standard OFDM receiving system.
With reference to the accompanying drawings 1:
From antenna with the signal received through after the radio frequency processing, by analog-to-digital conversion module analog signal conversion is gone out digital signal.Next be that time synchronized detects.At first, received signal is sent into matched filter and is formed correlation peak, and further compares with the thresholding that is obtained by reference signal, detects peak value.Utilizing detected lock in time and peak value to send into the channel response maker then, to carry out intersymbol average, produces accurate multipath channel response.When whole pilot signal was over, optimal synchronisation time maker obtained the lock in time an of the best according to the multipath channel response that multipath channel response maker produces, and supplies with symbol demodulator.
On the other hand, the digital signal after the analog-to-digital conversion enters symbol demodulator, carries out OFDM demodulation (FFT conversion), channel equalization and BPSK/QSPK/QAM demodulation.Send into channel-decoding at last, obtain user data.
With reference to the accompanying drawings 2:
Send into matched filter from the signal that analog-to-digital conversion module comes.Known frequency pilot sign C is arranged
0, C
1..., C
M-1(its cycle is M) as local symbol, carries out matched filtering to input signal.When the phase place that sends signal and local signal was consistent, matched filter was exported peak value.
Simultaneously, finding the solution (or search) in advance goes out and the quasi-orthogonal symbol C of frequency pilot sign
R0, C
R1..., C
RM-1, carry out matched filtering as local symbol, output signal is as the reference signal.Accurate orthogonal symbols and frequency pilot sign all can have influence on the detection performance at the cross correlation value of any phase place.Among the present invention, accurate orthogonal symbols and frequency pilot sign cross-correlation function maximum minimize as the quasi-orthogonal symbol C that selects
R0, C
R1..., C
RM-1Standard.Here, accurate orthogonal symbols adopts binary character, adopts the method for search, just can obtain optimum binary character, and the detection performance is optimized.It is the realization of having simplified circuit that accurate orthogonal symbols adopts another advantage of binary character.Do not need a large amount of multipliers like this, only need adding/subtracter of input more than, just can obtain reference signal.Reference signal multiply by a suitable COEFFICIENT K, and thresholding is sent into the peak value detection as a comparison.The moment that is higher than thresholding is exactly a synchronization point.Because reference signal has been followed the tracks of the variation of received signal level well, even in the received signal level not timing, peak detector also can guarantee stable detection performance.
According to time synchronizing signal, peak value selects module to allow peak signal enter multipath response maker.At multipath response maker, a plurality of peak signals are put into each memory cell.Along with entering of a plurality of repetition frequency pilot signs, peak signal is carried out intersymbol adding up (intersymbol average), is over until the pilot signal signal.
Peak signal after symbol is average is sent into synchronous proof scheme each after average.If greater than comparison threshold, show then that current detection is a false-alarm without any a peak signal, synchro system need be got back to initial condition, carries out peak value again and detects.Can remove false-alarm as soon as possible like this, the minimizing system surveys the probability that causes the lost packets data because of the flase drop of synchronous circuit.
In OFDM (OFDM) system of IEEE 802.11a standard; front at the OFDM of each 4 microsecond symbol; the protection interval (Guard Interval:GI) that has added 0.8 microsecond is to eliminate intersymbol interference (Inter Symbol Interference:ISI) and the inter-carrier interference of bringing owing to multipath channel (Inter Carrier Interference:ICI).Being described in detail of relevant this respect can be referring to " OFDM for Wireless Multimedia Communications ", Richard VanNee and Ramjee Prasad, Artech House 2000.
Determine the FFT interval (i.e. Zui Jia FFT synchronization point) an of the best, could eliminate ISI and ICI to greatest extent.With reference to the accompanying drawings 3: the calculating of optimal synchronisation time of the present invention as shown in Figure 3.At first, judge the maximum between the multipath response delays whether deducting the poor of surplus (Δ) greater than protection interval (Tg).
1) affirms under the situation: accumulative total Tg-Δ multipath signal power at interval; Because maximum delay greater than the Tg-Δ, then must have a plurality of overlapping accumulation interval that have mutually.From these intervals, select an interval of integral power maximum.At last, the optimal synchronisation time (synchronization point of FFT) is the zero-time (+Tg-Δ/2) of the accumulation interval selected;
2) under the situation of Fou Dinging: the optimal synchronisation time is the zero-time the earliest (+Tg-Δ/2) of multipath signal.
Claims (4)
1. the method for synchronous of a packet radio communication system, use rf processor in the method, A/D converter, demodulator, it is characterized in that: reception antenna receives that signal is after radio frequency processing, convert baseband signal to, baseband signal is passed through A/D converter, convert digital signal to, and be input to matched filter, reference signal of matched filter output, comparison threshold as the peak value detection, the peak signal that is detected is delivered to multipath response maker, obtains multipath and responds lock in time, deliver to symbol demodulator then, carry out the OFDM demodulation with the digital signal of A/D converter, last entering signal decoding obtains user data.
2. the method for synchronous of a kind of packet radio communication system according to claim 1, it is characterized in that: described reference signal is after passing through radio frequency processing by the signal that reception antenna receives, convert baseband signal to, be converted to digital signal by analog to digital converter again, then, baseband digital signal is fed to matched filter, a part is handled and is generated reference signal: find the solution in advance or search out and the quasi-orthogonal symbol of frequency pilot sign, carry out matched filtering as local symbol, output signal then is a reference signal.
3. the method for synchronous of a kind of packet radio communication system according to claim 1, it is characterized in that: described multipath response maker is to utilize the frequency pilot sign that repeats in the pilot signal, channel multi-path response is carried out intersymbol average, obtained the multipath channel response intensity.
4. according to the method for synchronous of claim 1 or 3 described a kind of packet radio communication systems, it is characterized in that: described multipath response, after each multipath response symbol was average, the peak value after utilization is average was verified, synchronously to find false-alarm as soon as possible.
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| CNB031166156A CN100420180C (en) | 2003-04-24 | 2003-04-24 | Synchronization method and device of packet wireless communication system |
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| CN100420180C true CN100420180C (en) | 2008-09-17 |
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Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101611606B (en) * | 2007-01-18 | 2013-09-11 | 汤姆逊许可公司 | Method for symbol synchronization of received digital signal and digital signal receiver using the same method |
| CN101340526B (en) * | 2007-07-05 | 2011-04-27 | 上海明波通信技术有限公司 | Digital television signal receiving apparatus and method |
| CN101741480A (en) * | 2008-11-17 | 2010-06-16 | 北京泰美世纪科技有限公司 | Method and device for detecting signal receiving performance of digital broadcasting system |
| CN105680978B (en) * | 2015-11-27 | 2018-03-06 | 中国人民解放军理工大学 | The orthogonal multi tate multiplex transmission method of the feeding link of mixed mobile communication system and system for star |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1198052A (en) * | 1997-02-25 | 1998-11-04 | 三星电子株式会社 | Method and apparatus for synchronizing carrier frequency of orthogonal frequency division multiplexing transmission system |
| CN1334655A (en) * | 2001-08-17 | 2002-02-06 | 清华大学 | Filling method of protecting gap in orthogonal frequency division multiplexing modulation system |
| WO2003017608A1 (en) * | 2001-08-17 | 2003-02-27 | Bermai, Inc. | Digital front-end for wireless communication system |
| US20030072258A1 (en) * | 2001-10-15 | 2003-04-17 | Vahid Tarokh | Efficient OFDM communications with interference immunity |
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2003
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1198052A (en) * | 1997-02-25 | 1998-11-04 | 三星电子株式会社 | Method and apparatus for synchronizing carrier frequency of orthogonal frequency division multiplexing transmission system |
| CN1334655A (en) * | 2001-08-17 | 2002-02-06 | 清华大学 | Filling method of protecting gap in orthogonal frequency division multiplexing modulation system |
| WO2003017608A1 (en) * | 2001-08-17 | 2003-02-27 | Bermai, Inc. | Digital front-end for wireless communication system |
| US20030072258A1 (en) * | 2001-10-15 | 2003-04-17 | Vahid Tarokh | Efficient OFDM communications with interference immunity |
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