CN106789807B - A kind of OFDM timing metric estimation method based on FIR filter - Google Patents
A kind of OFDM timing metric estimation method based on FIR filter Download PDFInfo
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- CN106789807B CN106789807B CN201611091918.7A CN201611091918A CN106789807B CN 106789807 B CN106789807 B CN 106789807B CN 201611091918 A CN201611091918 A CN 201611091918A CN 106789807 B CN106789807 B CN 106789807B
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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
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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
Abstract
The step of OFDM timing metric estimation method based on FIR filter that the present invention provides a kind of, this method is as follows: firstly, signal and its own time delayed signal will be received, conjugate multiplication obtains M0A reception difference sequence；By M0A reception difference sequence carries out FIR filtering, obtains M0Road filtering output p (m, d)；By M0Road filtering output p (m, d) it is averaged, obtain average value P (d), and signal energy R (d) is received using OFDM, average value P (d) is normalized, obtain the normalization timing metric M (d) of the symbol timing synchronization method based on FIR structure；Finally, seeking d corresponding to the maximum value of normalization timing metric M (d) can be obtained OFDM symbol timing estimation amountThis method is based on FIR filter, timing metric can be calculated by the modularized processing of the FIR filter of different coefficients in Project Realization, realize the real time high-speed processing for receiving signal stream in ofdm demodulator, implementation complexity is effectively reduced, reduce hardware resource, save the cost.
Description
Technical field
The invention belongs to digital wireless communication transmission technique field, it is related to filtering in a kind of TTC & DT Systems based on FIR
The Symbol Timing measurement estimation structure of the ofdm demodulator of device.
Background technique
Orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) is capable of providing
The information of large capacity is transmitted, and solves the problems, such as that radio channel performance is deteriorated when detection and control terminal transmitting high speed data, has frequency spectrum
The advantages that utilization rate is high, mitigating frequency-selective fading is classified as next-generation integrated increase telemetry network by international telemetering association
One of technical solution of plan.Under the complicated multipath channel of telemetry communication, OFDM can provide a kind of high speed, efficiently and safety
Data transmission scheme, be effectively relieved the frequency spectrum resource being becoming tight day, improve the anti-interference ability of single carrier TT&C system.
It is received in demodulating process in OFDM, it is necessary first to determine the window's position of FFT transform by timing synchronization, protect
Demonstrate,prove the orthogonality between subcarrier.Common timing synchronization algorithm such as document " Schmidl T, Cox D C.Robust
Frequency and Timing Synchronization for OFDM[J].IEEE Transactions on
Communications, 1997,45 (12): S&C algorithm is using two sections of identical leading characters before and after time domain in 1613~1621. "
Number conjugation is related to carry out timing synchronization, but to cause timing synchronization position to exist fuzzy for the cyclic prefix of OFDM symbol.In order to
Improve the Timing Synchronization performance of S&C algorithm, Ren is in document " Ren G L, Chang Y, Zhang H, et
al.Synchronization Methods Based on a New Constant Envelope Preamble for OFDM
Systems [J] .IEEE Transactions on Broadcasting, 2005,51 (1): in 139~143. " using it is pseudo- with
Machine sequence is weighted the identical leading symbol in two sections of front and back, to two sections of conjugation before and after the leading symbol after weighting in demodulator
Correlation carries out timing synchronization, but the band that pseudo-random sequence will increase ofdm signal power spectrum to the weighting of OFDM leading symbol is outer
Leakage.
Above-mentioned conventional sign timing synchronization algorithm there are aiming at the problem that, document " Awoseyila A B, et
al.Robust Time-domain Timing and Frequency Synchronization for OFDM Systems
[J] .IEEE Transactions on Consumer Electronics, 2009,55 (2): 391~399. " and document " Ma
Y S,Zhou S W,Yan C X,et al.Design of OFDM Timing Synchronization Based on
Correlations of Preamble Symbol[C]//2016 IEEE 83rd Vehicular Technology
Two kinds of symbol timing synchronization methods are proposed in Conference:VTC 2016-Spring, Nanjing. " respectively, it can be not
It influences to obtain the timing metric with pulse characteristic in the case where ofdm signal power spectrum performance, effectively improves multidiameter fading channel
Lower OFDM symbol Timing Synchronization performance, suitable for the TTC & DT Systems under complicated multipath channel characteristic, but the timing degree of the two
Measuring computationally intensive, Project Realization, structure is complicated, hardware resource occupancy is high.By taking the latter as an example, during calculating timing metric
Need to calculate multiple difference correlation functionsObviously, only each difference correlation function in the step
Calculating be just respectively necessary for multiplying again for N-m times and summation operation, lead to the computationally intensive of algorithm, realize that structure is complicated.
Summary of the invention
Technology of the invention solves the problems, such as: overcome the deficiencies in the prior art, proposes a kind of OFDM based on FIR filter
Symbol Timing measures estimation method, and the timing detection performance of the traditional timing synchronization algorithm of solution is poor, realizes that structure is complicated, hardware
The problems such as resources occupation rate is high.
The technical solution of the invention is as follows: one kind being based on FIR filter OFDM symbol timing metric estimation method, OFDM
It include M in signal framesA OFDM symbol, MsFor positive integer, Ms>=2, wherein first OFDM symbol is known leading symbol,
Each symbol includes N=Ns+NcpA sampled value, NsFor the IFFT/FFT transform size of OFDM symbol, NcpBefore the circulation of OFDM
Sew sample number, defines the OFDM for calculating timing metric and receive sequence start position d, and be initialized with 0, this method packet
Include following steps:
(1), received signal r (n+d) is divided into 1,2 ..., M0Road, respectively postpone 1,2 ..., M0After a sampling clock
To r (n+d-1), r (n+d-2) ..., r (n+d-M0), n=m, 1 ..., Nt- 1,2≤Nt≤Ns, M0≤Nt；
(2), will receive signal r (n+d) respectively with r (n+d-1), r (n+d-2) ..., r (n+d-M0) conjugate multiplication is carried out,
It obtains receiving difference sequence { ym(n, d), n=m ..., Nt-1}；
(3), difference sequence { y will be receivedm(n, d), n=m ..., Nt- 1 }, it is respectively fed to M0A corresponding NtThe FIR of-m rank
Filter obtains M after FIR filter filtering processing0Road exports p (m, d):
In formula, { wm(n)=c*(n-m) c (n), n=m ..., Nt- 1 }, c (n) is leading symbol sequential sampling value；
(4), by M0The output p (m, d) of path filter is averaged, and obtains average value P (d), and receive letter using OFDM
Average value P (d) is normalized in number energy R (d), and the normalization for obtaining the symbol timing synchronization method based on FIR structure is fixed
When measure M (d)；
(5), d is added 1, repeats step (1)~step (5), new normalization timing metric M (d) is calculated, until d
=Ms×(Ns+Ncp) -1 obtains amounting to M in a frames×(Ns+Ncp) a timing metric, enter step (6)；
(6), it calculates and amounts to M in a frames×(Ns+Ncp) a timing metric maximum value, d corresponding to the value is OFDM
Symbol Timing estimator
The calculation formula of the step (2) are as follows:
ym(n, d)=r*(n+d-m) r (n+d),
Wherein, m takes positive integer, and value range is 1≤m≤M0。
The calculating that average value P (d) is normalized in signal energy R (d) is received using OFDM described in the step (5)
Formula are as follows:
Wherein, receiving signal energy indicates are as follows:
Compared with the prior art, the invention has the advantages that:
1), the OFDM symbol timing metric estimation method proposed by the invention based on FIR filter is filtered using FIR
Device calculates timing metric, has versatility in Project Realization；
2), the OFDM symbol timing metric estimation method proposed by the invention based on FIR filter is by M0A difference phase
The FIR filter that pass value p (m, d) is used uniformly different coefficients calculates, and realizes modularized processing；
3), the OFDM symbol timing metric estimation method proposed by the present invention based on FIR filter is obtained with pulse
The timing metric of characteristic is consistent with the theoretical performance of timing estimation algorithms；
4) the OFDM symbol timing metric estimation structure based on FIR filter, proposed according to the present invention may be implemented
The real time high-speed processing of signal stream is received in ofdm demodulator；
5) the OFDM symbol timing metric estimation structure based on FIR filter, proposed according to the present invention is effectively reduced
Implementation complexity, reduces occupied hardware resource, has saved Project Realization cost.
Detailed description of the invention
Fig. 1 is that the present invention is based on the OFDM timing metrics of FIR filter to estimate structure；
Fig. 2 is the timing metric value that the embodiment of the present invention emulates.
Specific embodiment
In the following with reference to the drawings and specific embodiments, a specific embodiment of the invention is described in further detail.Following reality
Example is not limited to use scope of the invention for illustrating the present invention.
By taking typical ofdm communication system as an example, ofdm signal is respectively provided with following spy in OFDM modulator and demodulator
Sign:
1), in OFDM modulator, by subcarrier maps by length be NuMPSK/MQAM modulation multiple random sequence
Being mapped to length is NsOFDM frequency domain sequence, and to after mapping frequency domain sequence carry out NsWhen the IFFT of point converts to obtain OFDM
Domain symbol extracts last N from OFDM time-domain symbolcpA point splicing is in OFDM time-domain symbol front end, and final (Ncp is before recycling
Sew length) the OFDM time-domain symbol for having protection interval is obtained, it can indicate are as follows:
Wherein, X (k) is the data on k-th of subcarrier, NsFor the size of IFFT/FFT transform size, NcpBefore circulation
Sew sample number.Each symbol includes N=Ns+NcpA sample value.
2), every frame OFDM transmission signal includes the M of settingsA OFDM symbol, wherein first OFDM symbol is known
Leading symbol, when OFDM time-domain symbol is leading symbol C={ c (n), n=0 ..., NsWhen -1 }, c (n)=x (n).
3), in ofdm demodulator, OFDM receives signal and usually there is the intersymbol interference introduced by channel multi-path time delay,
Therefore receiving signal includes symbol time offset and carrier frequency offset, is expressed as
Wherein, ε is unknown symbol time offset, and v is normalized carrier frequency offset, and w (n) is that variance is's
Zero-mean complex Gaussian noise, h (m) are the impulse response of multidiameter fading channel, and L is channel memory length.
Ofdm signal feature based on said modulator and demodulator is solved for OFDM under telemetry communication complexity multipath channel
Symbol Timing measurement estimation in device is adjusted to realize complicated problem, the present invention provides a kind of OFDM demodulations based on FIR filter
The Symbol Timing of device measures estimation method.This method will receive signal first and be divided into M0Circuit-switched data postpones M respectively0After a clock,
Every circuit-switched data is subjected to conjugate multiplication with current Received Signal respectively, the result on every road is then sent into FIR filter, it is finally right
M0The output of path filter is averaged, and average value is normalized using signal energy is received, and obtains normalization timing
Measurement estimation.
Defining the leading symbol length for calculating timing metric estimation is Nt(2≤Nt≤Ns), NtValue is bigger, timing
Estimate that performance is better, works as NsWhen=1024, settable 128≤Nt≤1024.It is proposed by the invention based on FIR filter
OFDM symbol timing metric estimation method has follow steps:
(1), received signal r (n+d) is divided into 1,2 ..., M0Road, respectively postpone 1,2 ..., M0After a sampling clock
To r (n+d-1), r (n+d-2) ..., r (n+d-M0), the d=0,1 ..., Ms×(Ns+Ncp) -1, n=m, 1 ..., Nt- 1,2≤
Nt≤Ns, M0For positive integer, value range M0≤Nt；
(2), will receive signal r (n+d) respectively with r (n+d-1), r (n+d-2) ..., r (n+d-M0) conjugate multiplication is carried out,
Obtain M0A reception difference sequence { ym(n, d), n=m ..., Nt- 1 }, specific calculation formula are as follows:
ym(n, d)=r*(n+d-m) r (n+d), n=m, 1 ..., Nt- 1,
Wherein, m takes positive integer, and value range is 1≤m≤M0, M0For maximum difference interval, r*(n+d-m) it is r (n+d-m)
Conjugate operation；
(3), by M0A reception difference sequence { ym(n, d), n=m ..., Nt- 1 }, it is respectively fed to M0A corresponding Nt- m rank
FIR filter obtains M after FIR filter filtering processing0Road exports p (m, d):
In formula, { wm(n)=c*(n-m) c (n), n=m ..., Nt-1}；C (n) is leading symbol sequential sampling value；
(4), by M0The output p (m, d) of path filter is averaged, and obtains average value P (d), and receive letter using OFDM
Average value P (d) is normalized in number energy R (d), and the normalization for obtaining the symbol timing synchronization method based on FIR structure is fixed
When measure M (d):
Wherein, receiving signal energy indicates are as follows:
(5), d is added 1, repeats step (1)~step (5), new normalization timing metric M (d) is calculated, until d
=Ms×(Ns+Ncp) -1 obtains amounting to M in a frames×(Ns+Ncp) a normalization timing metric, enter step (6)；
(6), it calculates and amounts to M in a frames×(Ns+Ncp) a normalization timing metric maximum value, d corresponding to the value is
For OFDM symbol timing estimation amount
The timing estimation amountFor the position at the timing metric peak value of a frame data, there was only 1 peak in this segment data
Value, and d is data all in the frame: d=0,1 ..., Ms×(Ns+Ncp)-1。
It, can also be using one reasonable door of setting when solving d since normalization timing metric M (d) has pulse characteristic
The mode of limit, when M (d) is greater than preset thresholding, it is believed that have found the peak value of M (d), and then obtain Symbol Timing estimator
The OFDM symbol timing metric estimation structure based on FIR filter proposed according to the present invention is as shown in Figure 1.Figure
In, multiplier used by each branch difference conjugate multiplication, the multiplier in all FIR filters are complex multiplier.?
Timing metric can be calculated by the modularized processing of the FIR filter of different coefficients in Project Realization, realize ofdm demodulator
The middle real time high-speed processing for receiving signal stream, effectively reduces implementation complexity, reduces occupied hardware resource, save
Project Realization cost.
Embodiment:
For the leading symbol using time domain with two sections of repetitive structures, known pilot can be used as only with wherein one section
Symbol, the leading symbol length for calculating timing metric estimation is N at this timet(Nt≤Ns/ 2), NtThe lower limit of value range can root
According to timing metric estimation performance setting, work as NsWhen=1024,128≤N is sett≤512.In FPGA Project Realization, if OFDM system
Unite IFFT size Ns=256, the symbol lengths for calculating timing metric estimation are Nt=128, because of 256 numbers of leading symbol
According to identical two sections can be divided into, first segment 128, the local phases that in timing estimation use equal with 128 data of second segment
128 that sequence is wherein one section are closed, so can be there are two peak value when leading symbol timing estimation.Using two frame OFDM symbols into
Row emulation estimates structure using the timing metric proposed by the invention based on FIR filter by the observation of Chipscope software
Obtained timing metric is as shown in Figure 2.As shown in Figure 2, estimated using the timing metric proposed by the invention based on FIR filter
The timing metric that meter structure obtains has the peak value of impulse form, and peak amplitude is about 85000000, and bottom is made an uproar lower than 11000000,
I.e. peak amplitude is more than that bottom is made an uproar 7 times of amplitude.
Under a multipath fading channel, the OFDM timing metric estimation structure based on FIR filter is obtained with pulse spy
Property timing metric can effectively improve OFDM symbol Timing Synchronization performance under multidiameter fading channel, be suitable for complicated multipath channel
TTC & DT Systems under characteristic.
The above, a specific embodiment only of the invention, but scope of protection of the present invention is not limited thereto, appoints
In the technical scope disclosed by the present invention, any changes or substitutions that can be easily thought of, all by what those familiar with the art
It is covered by the protection scope of the present invention.
The content that description in the present invention is not described in detail belongs to the well-known technique of professional and technical personnel in the field.
Claims (3)
- It include M in ofdm signal frame 1. one kind is based on FIR filter OFDM symbol timing metric estimation methodsA OFDM symbol, MsFor positive integer, Ms>=2, wherein first OFDM symbol is known leading symbol, and each symbol includes N=Ns+NcpIt is a to adopt Sample value, NsFor the IFFT/FFT transform size of OFDM symbol, NcpFor the cyclic prefix sample number of OFDM, definition is for calculating timing The OFDM of measurement receives sequence start position d, and is initialized with 0, it is characterised in that includes the following steps:(1), received signal r (n+d) is divided into 1,2 ..., M0Road, respectively postpone 1,2 ..., M0R (n is obtained after a sampling clock +d-1)、r(n+d-2)…、r(n+d-M0), n=m, 1 ..., Nt- 1,2≤Nt≤Ns, M0≤Nt；(2), will receive signal r (n+d) respectively with r (n+d-1), r (n+d-2) ..., r (n+d-M0) conjugate multiplication is carried out, it is connect Astigmat sub-sequence { ym(n, d), n=m ..., Nt-1}；(3), difference sequence { y will be receivedm(n, d), n=m ..., Nt- 1 }, it is respectively fed to M0A corresponding NtThe FIR of-m rank is filtered Device obtains M after FIR filter filtering processing0Road exports p (m, d):In formula, { wm(n)=c*(n-m) c (n), n=m ..., Nt- 1 }, c (n) is leading symbol sequential sampling value；(4), by M0The output p (m, d) of path filter is averaged, and obtains average value P (d), and receive signal energy using OFDM Average value P (d) is normalized in R (d), obtains the normalization timing metric M of the symbol timing synchronization method based on FIR structure (d)；(5), d is added 1, repeats step (1)~step (5), new normalization timing metric M (d) is calculated, until d=Ms× (Ns+Ncp) -1 obtains amounting to M in a frames×(Ns+Ncp) a timing metric, enter step (6)；(6), it calculates and amounts to M in a frames×(Ns+Ncp) a timing metric maximum value, d corresponding to the value is OFDM symbol Timing estimation amount
- 2. according to claim 1 a kind of based on FIR filter OFDM symbol timing metric estimation method, feature exists In: the calculation formula of the step (2) are as follows:ym(n, d)=r*(n+d-m) r (n+d),Wherein, m takes positive integer, and value range is 1≤m≤M0。
- 3. according to claim 1 a kind of based on FIR filter OFDM symbol timing metric estimation method, feature exists In: the calculation formula that average value P (d) is normalized in signal energy R (d) is received using OFDM described in the step (5) Are as follows:Wherein, receiving signal energy indicates are as follows:
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| US7027429B2 (en) * | 2001-06-19 | 2006-04-11 | Flarion Technologies, Inc. | Method and apparatus for time and frequency synchronization of OFDM communication systems |
| CN104836770A (en) * | 2015-04-30 | 2015-08-12 | 北京遥测技术研究所 | Timing estimation method based on correlation average and windowing |
| CN105187352A (en) * | 2015-08-07 | 2015-12-23 | 北京遥测技术研究所 | Integer frequency offset estimation method based on OFDM preamble |
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2016
- 2016-12-01 CN CN201611091918.7A patent/CN106789807B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7027429B2 (en) * | 2001-06-19 | 2006-04-11 | Flarion Technologies, Inc. | Method and apparatus for time and frequency synchronization of OFDM communication systems |
| CN1695360A (en) * | 2002-09-25 | 2005-11-09 | 松下电器产业株式会社 | DWMC communication apparatus |
| CN104836770A (en) * | 2015-04-30 | 2015-08-12 | 北京遥测技术研究所 | Timing estimation method based on correlation average and windowing |
| CN105187352A (en) * | 2015-08-07 | 2015-12-23 | 北京遥测技术研究所 | Integer frequency offset estimation method based on OFDM preamble |
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