CN105429922B - The channel estimation method based on Comb Pilot for DDO-OFDM systems - Google Patents
The channel estimation method based on Comb Pilot for DDO-OFDM systems Download PDFInfo
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- CN105429922B CN105429922B CN201510761756.2A CN201510761756A CN105429922B CN 105429922 B CN105429922 B CN 105429922B CN 201510761756 A CN201510761756 A CN 201510761756A CN 105429922 B CN105429922 B CN 105429922B
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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
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/024—Channel estimation channel estimation algorithms
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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
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
- H04L27/2695—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation with channel estimation, e.g. determination of delay spread, derivative or peak tracking
Abstract
The invention discloses a kind of channel estimation methods based on Comb Pilot for DDO ofdm systems.The present invention includes the following steps：Step 1 finds out pilot frequency locations；Step 2, the pilot frequency locations in the transmission signal of transmitting terminal are inserted into pilot sub-carrier；Step 3 docks in receiving terminal and at same pilot frequency locations is extracted pilot sub-carrier by signal；Step 4, the average frequency response that pilot sub-carrier is estimated using the LS estimations method of average；Step 5, the frequency response that data subcarrier in channel is estimated using linear interpolation method.Under the spending of same pilot tone, algorithm of the invention reduces the bit error rate, improves estimated accuracy, improves snr gain；The algorithm bit error rate of the present invention is influenced small by pilot tone spending, i.e., is paid wages using smaller pilot tone and also can guarantee low error rate, improve band efficiency；The algorithm complexity of the present invention is low, highly practical.
Description
Technical field
The invention belongs to technical field of photo communication, more particularly to it is a kind of for DDO-OFDM systems based on Comb Pilot
Channel estimation method.
Background technology
Development with the communication technology and the continuous improvement to communicating requirement, optic communication show two apparent development and become
Gesture：The data rate of single channel transmission greatly increases, and levels off to 100Gb/s；Network must have dynamic adjustment capability quickly.
But when data rate reaches 100Gb/s, the compensation of traditional fiber segment becomes costly and time consuming, very to the compensation of system dispersion
It is difficult accurate to realize, and OFDM is due to having good estimated performance, by the complex operation in frequency domain, it may be convenient to optical fiber
Dispersion compensates.Particular reference：SHIEHW,BAOH,TANGY.Coherent Optical OFDM：Theoryand
De-sign[J].Optics Express 2008,16:41-859。
2005, N.E.Jolley and T.M.Tang et al. were put forward for the first time in OFC2005 meetings and OFDM technology have been answered
For in fibre-optic transmission system (FOTS), and the experiment proves that the signal of 10Gb/s can transmit 1km in multimode fibre, from this, people
The research of light orthogonal frequency division multiplexi (O-OFDM) is started.Bibliography：Jolley N E,Kee H,Pickaed P,
etal.Generation and propagation of a 1550nm 10Gbit/s optical orthogonal
frequency division multiplexed signal over 1000m of multimode fibre using a
directly modulated DFB.In:Optical Fiber Communication Conference,
2005.Technical Digest.OFC/NFOEC.Harlow,UK,2005,6-11。
Orthogonal frequency division multiplexing (Orthogonal Frequency Division Multiplexing, OFDM) is that one kind is more
Carrier modulation technique, basic principle are to carry out inverse fourier transform (IFFT) using Digital Signal Processing, and one group of generation is orthogonal
Subcarrier be used for lower-rate digital signals parallel transmission, to complete the transformation task of high-speed digital signal.This process
Most prominent advantage is to improve the availability of frequency spectrum of system, while reducing the complexity of calculating.
For O-OFDM compared with traditional optic communication, it has shown high spectrum efficiency, confrontation dispersion and non-linear effect
The advantage of many protrusions such as with obvious effects is answered, and these all will be particularly significant to next-generation high rate communication systems it.It is many at present
Result of study also shows potential using values of the O-OFDM in the following large capacity, long distance optical communication systems.It is particularly important
, since it has the ability of adaptive single tap frequency domain equalization, O-OFDM has weight in the following dynamic exchange optical-fiber network
The application value wanted.
It needs to estimate channel in the direct detection of O-OFDM systems, the precision of channel estimation will directly affect whole
The performance of a system.Channel parameter estimation is to realize a key technology of wireless communication system.Detailed channel can be obtained
Information is the important indicator for weighing an optical communication system performance to correctly demodulate transmitting signal in receiving terminal.
Premenstruum (premenstrua) literature survey it is found that at present channel estimation method with based on Block-type pilot the method for average and blind estimate algorithm be
It is main, but all there is certain deficiency in both algorithms.Method of average frequency spending based on Block-type pilot is big, and the availability of frequency spectrum is low；It is blind
Dow process there are precision it is low, complexity is high, timing statistics are long the defects of, be difficult to play a role in practical applications.Therefore, it is necessary to
Study a kind of new algorithm overcoming present channel algorithm for estimating existing defects.
Invention content
In order to overcome the conventional channel estimation technique availability of frequency spectrum low, the deficiencies such as precision is low, the present invention proposes a kind of novel
The channel estimation method based on Comb Pilot for DDO-OFDM systems.The present invention can reduce pilot tone spending, improve band utilization
Rate reduces the bit error rate, improves snr gain.Early period, simulation result showed that this algorithm has good reliability and stability.
The technical solution adopted by the present invention to solve the technical problems：It is a kind of suitable for DDO-OFDM systems based on pectination
The channel estimation method of pilot tone first estimates pilot tone with LS (least square least square methods) channel estimation method method of average
The frequency response of carrier wave, after data subcarrier is estimated by linear interpolation on the basis of the frequency response of pilot sub-carrier
Frequency response.
Steps are as follows for specific implementation：
Step 1 finds out pilot frequency locations.
Step 2, the pilot frequency locations in the transmission signal of transmitting terminal are inserted into pilot sub-carrier.
Step 3 docks in receiving terminal and at same pilot frequency locations is extracted pilot sub-carrier by signal.
Step 4, the average frequency response that pilot sub-carrier is estimated using the LS estimations method of average；
Step 5, the frequency response that data subcarrier in channel is estimated using linear interpolation method.
The solution of step 1 pilot frequency locations is specific as follows：
(1-1) finds out pilot tone number p, and formula is：
Wherein, N is actually active variable number, and L is pilot interval.Ceil (X) expressions take more than or equal to specified table
Up to the smallest positive integral of Formula X.
(1-2) calculates the position of pilot sub-carrier.
Wherein, inIndicate the position of n-th of pilot tone on the frequency axis.
The pilot sub-carrier vector that the step 2 is inserted into sending signal is：
Xp=[X (i1,：)；X(i2,：)；...；X(in,：)；...；X(ip,：)]p×M
Wherein, X (in,:) it is to send the nth bar pilot sub-carrier being inserted into signal.
The step (3) extracts pilot sub-carrier vector in receiving signal and is：
Yp=[Y (i1,：)；Y(i2,：)；...；Y(in,：)；...；Y(ip,：)]p×M
Wherein, Y (in,:) it is the nth bar pilot sub-carrier for receiving extracting data and going out.
The step (4) estimates the average frequency response of pilot sub-carrier using the LS estimations method of average, specific as follows：
(4-1) utilizes the frequency response of LS estimation technique estimating pilot frequency subcarriers, and formula is：
Wherein,For the frequency response of the nth bar pilot sub-carrier estimated.
(4-2) averages on a timeline to the frequency response at pilot frequency locations, obtains the average frequency of pilot sub-carrier
Response.The average frequency response vector of the pilot sub-carrier acquired is：
Wherein,For the average frequency response of nth bar pilot sub-carrier.
The step (5) estimates the frequency response of data subcarrier in channel using linear interpolation method, specific as follows：
(5-1) does linear interpolation on the frequency axis to the average frequency response of pilot sub-carrier, estimates data in channel
The frequency response of subcarrier.The data subcarrier frequency estimated responds：
The frequency response of data subcarrier continuation on a timeline is obtained required channel frequency response by (5-2).When
On countershaft expand after channel frequency response be：
Wherein, M is OFDM symbol number.
Compared with prior art, the present invention having the following advantages that and advantageous effect：
1. under the spending of same pilot tone, algorithm of the invention reduces the bit error rate, improves estimated accuracy, improves noise
Compare gain.
2. the algorithm bit error rate of the present invention is influenced small by pilot tone spending, i.e., is paid wages using smaller pilot tone and also can guarantee low mistake
Code check improves band efficiency.
3. the algorithm complexity of the present invention is low, highly practical.
Description of the drawings
Fig. 1 is the system block diagram of O-OFDM.
Fig. 2 is the flow chart of implementation.
Fig. 3 is the data frame structure schematic diagram of transmitting terminal O-OFDM.
Fig. 4 is the calculation based on Block-type pilot LS the estimation method of average and the present invention in embodiment when pilot tone spending is 1/512
The previous experiments bit error rate (ber) of method-to-noise ratio (SNR) comparison diagram.
Specific implementation mode
Further detailed description is done to the present invention with reference to example and attached drawing, but embodiments of the present invention are not limited to
This.
The present invention is directed primarily to the direct detection channel estimation problems of light orthogonal frequency division multiplexing O-OFDM systems.Such as Fig. 1
Shown, O-OFDM includes S/P, QAM mapping, data subcarrier modulation, is inserted into pilot sub-carrier, IFFT plus CP, adds M sequence, go
M sequence goes multiple steps such as CP, FFT, extraction pilot sub-carrier, channel estimation, data subcarrier demapping, QAM demappings, P/S
Suddenly.It is wherein inserted into pilot sub-carrier, extraction pilot sub-carrier and channel estimation and belongs to channel estimation module.
The step of LS channel estimation methods based on Comb Pilot of the invention, is carried out with reference to Fig. 2 and Fig. 3 detailed
Explanation.
(1) shared N=2 is setKCarrier wave, shares M OFDM symbol, pilot interval L, then it is a to share p for pilot sub-carrier.
(2) as shown in figure 3, the pilot frequency locations in the transmission signal of transmitting terminal are inserted into pilot sub-carrier, remember n-th of pilot tone
The position of subcarrier on the frequency axis is in, note nth bar pilot sub-carrier is X (in,:), note pilot sub-carrier vector is Xp。
Xp=[X (i1,：)；X(i2,：)；...；X(in,：)；...；X(ip,：)]p×M
(3) it is docked by signal in same pilot frequency locations i in receiving terminalnPlace extracts pilot sub-carrier, remembers n-th extracted
Pilot sub-carrier is Y (in,:), remember that the pilot tone vector extracted is Yp.And go out pilot tone in channel using Least Square Method
The frequency response of subcarrier remembers that the frequency response of nth bar pilot sub-carrier isRemember that frequency response vector is
Yp=[Y (i1,：)；Y(i2,：)；...；Y(in,：)；...；Y(ip,：)]p×M
(4) to the frequency response vector of pilot frequency locationsAveraging on a timeline (by row), it is flat to calculate pilot sub-carrier
Equal frequency response remembers that the average frequency response of nth bar pilot sub-carrier isRemember the average frequency response of pilot sub-carrier
Vector is Hmean。
(5) to the average frequency response H of pilot sub-carriermeanLinear interpolation is done on the frequency axis, estimates number in channel
According to the frequency response H of subcarrierlinear。
(6) continuation obtains H on a timeline, and H is the channel frequency response for finally estimating to obtain.
Wherein, M is OFDM symbol number.
Embodiment：
As shown in figure 4, for the LS based on Block-type pilot in the present embodiment estimate in the method for average and the present invention based on pectination
Previous experiments to-noise ratio-SNR the comparison diagrams of the LS channel estimation methods of pilot tone.It sets O-OFDM and emits 1023 OFDM symbols,
Including 1024 carrier waves (wherein the first row does not put data, i.e., effective subcarrier is since the 2nd to the 1024th, that is to say, that
Actually active subcarrier number is 1023), pilot tone spending is 1/512.It is as follows using the method for the present invention：
(1) pilot tone spending is 1/512, i.e. pilot interval L is 511, then pilot sub-carrier shares 3, respectively the 2nd,
513,1024 subcarriers, pilot tone vector are denoted as X3。
X3=[X (2,:)；X(513,:)；X(1024,:)]3×M
First subcarriers do not put data, and remaining sub-carriers are all data subcarrier.
(2) pilot frequency locations in receiving data extract pilot sub-carrier, and composition pilot tone vector is Y3。
Y3=[Y (2,:)；Y(513,:)；Y(1024,:)]3×M
(3) frequency response of pilot sub-carrier in channel is estimated with LS channel estimation methods
(4) to the frequency response of pilot frequency locationsIt averages on a timeline (by row) and estimates the flat of pilot sub-carrier
Equal frequency response Hmean。
(5) the average frequency response H to the pilot sub-carrier estimatedmeanLinear interpolation is done on the frequency axis, is estimated
The frequency response H of data subcarrier in channellinear。
(6) continuation obtains H on a timeline, and H is the channel frequency response for finally estimating to obtain.
Two bit error rate-SNR curves in comparison diagram 4 are it is found that when the bit error rate is controlled 10-3When the order of magnitude, with traditional base
It is compared in the channel estimation of Block-type pilot, the to-noise ratio gain of this algorithm about 5dB or so.
To of the present invention, the channel estimation method of LS estimations and linear interpolation based on Comb Pilot carries out above
Introduce in detail, the explanation of above example be merely used to help understand the present invention algorithm and its core concept rather than to its into
Row limitation, other any changes made without departing from the spirit and principles of the present invention, modification, combination, simplification, should all
For equivalent substitute mode, it is included within the scope of the present invention.
Claims (4)
1. the channel estimation method based on Comb Pilot for DDO-OFDM systems, it is characterised in that include the following steps：
Step 1 finds out pilot frequency locations；
Step 2, the pilot frequency locations in the transmission signal of transmitting terminal are inserted into pilot sub-carrier；
Step 3 extracts pilot sub-carrier in the receiving terminal docking collection of letters number at same pilot frequency locations；
Step 4, the average frequency response that pilot sub-carrier is estimated using the LS estimations method of average；
Step 5, the frequency response that data subcarrier in channel is estimated using linear interpolation method；
The solution of step 1 pilot frequency locations is specific as follows：
(1-1) finds out pilot tone number p, and formula is：
Wherein, N is actually active variable number, and L is pilot interval；Ceil (X) expressions take more than or equal to specified expression formula X
Smallest positive integral；
(1-2) calculates the position of pilot sub-carrier；
Wherein, inIndicate the position of n-th of pilot tone on the frequency axis；
The pilot sub-carrier vector that the step 2 is inserted into sending signal is：
Xp=[X (i1,：)；X(i2,：)；...；X(in,：)；...；X(ip,：)]p×M
Wherein, X (in,:) it is to send the nth bar pilot sub-carrier being inserted into signal, M is OFDM symbol number.
2. the channel estimation method based on Comb Pilot according to claim 1 for DDO-OFDM systems, feature exists
Extracting pilot sub-carrier vector in receiving signal in the step 3 is：
Yp=[Y (i1,：)；Y(i2,：)；...；Y(in,：)；...；Y(ip,：)]p×M
Wherein, Y (in,:) it is to receive the nth bar pilot sub-carrier extracted in signal.
3. the channel estimation method based on Comb Pilot according to claim 2 for DDO-OFDM systems, feature exists
The average frequency response of pilot sub-carrier is estimated using the LS estimations method of average in the step 4, it is specific as follows：
(4-1) utilizes the frequency response of LS estimation technique estimating pilot frequency subcarriers, and formula is：
Wherein,For the frequency response of the nth bar pilot sub-carrier estimated；/ indicate YpAnd XpAt corresponding position
Element does division arithmetic；
(4-2) averages on a timeline to the frequency response at pilot frequency locations, obtains the average frequency response of pilot sub-carrier；
The average frequency response vector of the pilot sub-carrier acquired is：
Wherein,For the average frequency response of nth bar pilot sub-carrier.
4. the channel estimation method based on Comb Pilot according to claim 3 for DDO-OFDM systems, feature exists
The frequency response of data subcarrier in channel is estimated using linear interpolation method in the step 5, it is specific as follows：
(5-1) does linear interpolation on the frequency axis to the average frequency response of pilot sub-carrier, estimates data in channel and carries
The frequency response of wave；The data subcarrier frequency estimated responds：
The frequency response of data subcarrier continuation on a timeline is obtained required channel frequency response by (5-2)；In time shaft
Channel frequency response after upper expansion is：
Wherein, M is OFDM symbol number.
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| CN101237433A (en) * | 2008-03-05 | 2008-08-06 | 中科院嘉兴中心微系统所分中心 | A channel estimation device for wireless sensor network |
| CN104683268A (en) * | 2013-11-28 | 2015-06-03 | 中南大学 | QR (quick response) decomposition based orthogonal frequency division multiplexing (OFDM) system channel estimation method |
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| CN101237433A (en) * | 2008-03-05 | 2008-08-06 | 中科院嘉兴中心微系统所分中心 | A channel estimation device for wireless sensor network |
| CN104683268A (en) * | 2013-11-28 | 2015-06-03 | 中南大学 | QR (quick response) decomposition based orthogonal frequency division multiplexing (OFDM) system channel estimation method |
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| 《兼容单边带直接检测光OFDM系统基于导频的信道估计研究》;舒清龙;《中国优秀硕士学位论文全文数据库信息科技辑》;20140731(第7期);第11-12、14-17、37-38页 * |
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