CN103581100A - Coarse synchronization method for restraining multipath time delay and Doppler effect in LTE-FDD system - Google Patents

Coarse synchronization method for restraining multipath time delay and Doppler effect in LTE-FDD system Download PDF

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CN103581100A
CN103581100A CN201310429713.5A CN201310429713A CN103581100A CN 103581100 A CN103581100 A CN 103581100A CN 201310429713 A CN201310429713 A CN 201310429713A CN 103581100 A CN103581100 A CN 103581100A
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ofdm symbols
time slot
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陈赟
丁娜
吴迪
曾晓洋
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Fudan University
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Abstract

The invention belongs to the technical field of wireless digital communication, and particularly relates to a coarse synchronization method for restraining the multipath time delay and the Doppler effect in the LTE-FDD system. Coarse synchronization detection is carried out by utilizing a cyclic prefix of an OFDM symbol in a time slot, and the method comprises the steps of signal storage, correlation energy calculation, signal energy calculation, threshold value judgment, starting point judgment, decimal-times carrier frequency offset judgment and the like. A computer conducts simulation display, and the method has the excellent synchronization performance and is suitable for a high-speed mobile wireless communication system. Compared with a traditional correlation detection method, the method has the advantages that the accuracy of decimal-times carrier frequency offset detection can be improved by 10%, and the accuracy of frame starting point detection can be improved by 80%.

Description

LTE-FDD systems suppress the coarse synchronization method of multipath delay and Doppler effect
Technical field
The invention belongs to radio digital communication technical field, and in particular to a kind of LTE-FDD systems suppress the coarse synchronization method of multipath delay and Doppler effect. 
Background technology
3GPP was organized in for the end of the year 2004 and proposes 3GPP Long Term Evolution projects（LTE）.On the basis of the second generation mobile communication system based on time-division and frequency division multiple access access technology and the 3-G (Generation Three mobile communication system) based on CDMA, LTE employs the OFDM for belonging to 4G technologies（OFDM）And orthogonal frequency division multiplexing multiple access（OFDMA）Technology.Backward compatibility good LTE allows it to benefit from HSPA and HSPA+ technology development with newest understanding, while LTE can freely use state-of-the-art technology. 
The performance of LTE system is a bit that each Virtual network operator is valued the most.For the consideration of the market factor, in the LTE system main performance requirements issued first, LTE system is in the case of maximum bandwidth 20MHz, under the hypothesis of two reception antennas and a transmitting antenna, up-downgoing hardware circuit solution is respectively 100Mbits/s and 50Mbits/s, is respectively 5bits/Hz and 2.5bits/Hz corresponding to spectrum efficiency；Go to consider from ambulant angle, LTE system needs that normal communication still can be supported in the case where moving velocity of terminal reaches 350Km/h, or even support under using higher frequency range 500Km/h translational speed, this require between cell without interrupting switching；In terms of time delay, LTE requires that the time delay of Radio Access Network under optimum condition will as little as 5ms；LTE up-downgoing can be operated in extensive frequency band range and adapt to the frequency spectrum distribution of various bandwidth. 
According to Release 11,6 kinds of bandwidth are had in LTE system available, it is 1.4MHz, 2.5MHz, 5MHz, 10MHz, 15MHz and 20MHz respectively, corresponding subcarrier number is respectively 128,256,512,1024,1536 and 2048 for 72,180,300,600,900 and 1200, FFT points respectively.Subcarrier spacing is 15KHz, in MBSFN（Multimedia Broadcast Single Frequency Network, multimedia broadcasting SFN）Under pattern, subcarrier spacing is 7.5KHz.In LTE system, QPSK, 16QAM and 64QAM modulation system are used, and use the turbo encoding and decoding of 1/3 code check.LTE system has the pattern of two kinds of transmission data, is frequency domain duplex respectively（FDD）And time domain duplex（TDD）, fdd mode is the mode of operation of the present invention.The environmental difference that LTE is supported is very big, therefore designers are directed to the different circulating prefix-length of different Environment Designs.Under general modfel, under 20MHz bandwidth, for the time slot that time span is 0.5ms, LTE downlinks are using 5.2 μ s and the cyclic prefix of 4.7 two kinds of different time lengths of μ s, first OFDM symbol uses 5.2 μ s cyclic prefix in one time slot, remaining 6 OFDM symbols use 4.7 μ s cyclic prefix, are integers this is done to the OFDM symbol number ensured in 0.5ms；In order to ensure even in the larger cell in suburb and rural area, delay spread can also meet the requirement much smaller than circulating prefix-length, mode of extension is just used in such case.Under mode of extension, circulating prefix-length is 16.7 μ s or 33.3 μ s, corresponds respectively to subcarrier spacing for 15KHz and 7.5KHz, and certain this way just increases overhead, reduces the availability of frequency spectrum.I.e. the present invention so can keep the bandwidth availability ratio of system for the shorter situation of general mode cyclic prefix while ensureing and receiving signal accuracy. 
Because the mismatch and Doppler frequency shift of transmitter and receiver crystal oscillator frequency can cause carrier wave frequency deviation.Carrier wave frequency deviation, the presence of particularly small several times carrier wave frequency deviation can cause intersymbol interference（ISI）, inter-sub-carrier interference（ICI）And the orthogonality between the energy of signal, destruction subcarrier is reduced, the performance of receiver is greatly affected, immeasurable influence also is caused on decoding below and deciphering information.For the LTE standard using OFDM technology, it is ensured that the orthogonality between subcarrier is can be properly received the premise of information, therefore the estimation and correction of carrier wave frequency deviation are an indispensable steps in LTE system. 
In addition, to obtain correct transmitting information, it is necessary to know information original position where, so can just obtain correct transmitting information by the detection of receiver.Due to the presence of carrier wave frequency deviation and the time delay of channel, cause there is certain time delay between reception signal and transmission signal, therefore Timing Synchronization is also very important. 
The function of thick synchronized algorithm is the small several times carrier wave frequency deviation of detection and timing offset and corrected, traditional thick synchronized algorithm has ML (Maximum Likelihood), MMSE (Minimum Mean Square Error), MC (Maximum Correlation) and S＆C（Schmidl&Cox）Algorithm, these four algorithms are detected using the correlation between cyclic prefix and effective information, in the case where circulating prefix-length is shorter, and these four algorithms can not all obtain performance well.Proposed by K. B. professors Letaief of University of Texas at Dallas H. Minn professors, University of British Columbia V. K. Bhargava professors and Hong Kong University of Science and Technology a kind of for havingThe multicarrier algorithm of individual same sequence, the substandard preamble sequences of such as CMMB, this algorithm proposes the collection of energy concept in thick synchronized algorithm. 
Under above-mentioned technical background, in order to keep the bandwidth availability ratio of LTE system, suppress multipath delay and Doppler effect, the present invention proposes the new thick synchronized algorithm for the general circulating prefix-length of fdd mode. 
The content of the invention
It is an object of the invention to provide the coarse synchronization method that a kind of LTE-FDD systems suppress multipath delay Doppler effect, it can keep the bandwidth availability ratio of LTE system, suppress multipath delay and Doppler effect. 
The LTE-FDD systems that the present invention is provided suppress the coarse synchronization method of multipath delay Doppler effect, and it carries out small several times carrier wave frequency deviation detection using the cyclic prefix of all OFDM symbols in a time slot and frame starting point is detected, comprises the following steps that： 
1）Store signal
The signal of receive slot length is stored, defined
Figure 33111DEST_PATH_IMAGE002
To solve the reception signal before constellation mapping,
Figure 35702DEST_PATH_IMAGE003
For FFT length,
Figure 496771DEST_PATH_IMAGE004
,
Figure 661036DEST_PATH_IMAGE005
For two kinds of circulating prefix-lengths in LTE system.The OFDM symbol received is defined as
Figure 902661DEST_PATH_IMAGE006
Figure 630315DEST_PATH_IMAGE007
Figure 8207DEST_PATH_IMAGE008
Represent the received
Figure 608952DEST_PATH_IMAGE009
Individual complete OFDM symbol；Expression receives the counting of OFDM symbol.
In the general cyclic prefix modes of LTE, 7 OFDM symbols are had in a time slot, therefore the sequence length that needs are stored every time is
Figure 354371DEST_PATH_IMAGE010
。 
2）Calculate correlation energy value
In order to make full use of the energy entrained by all cyclic prefix, use the correlation window of different length to carry out related operation for the cyclic prefix of different length, calculate the correlation energy value between cyclic prefix and effective information；With the symbol of current detection
Figure 586770DEST_PATH_IMAGE011
For starting point, and assume to be currently located starting point a little for a time slot, first progress length is
Figure 545367DEST_PATH_IMAGE012
Related operation, then to thereafterThe signal of length carries out 6 length
Figure 378511DEST_PATH_IMAGE014
Related operation, then all correlation energy is added, realizes the concept of collection of energy.Correlation function is as follows：
Represent the correlation energy sum of 7 OFDM symbols in a time slot；
Figure 49161DEST_PATH_IMAGE017
Expression pair
Figure 922308DEST_PATH_IMAGE018
Carry out conjugate operation； mThe counting to participating in the symbol numbers that correlation energy is calculated is represented, maximum is the length of cyclic sequence； kRepresent the counting to rear 6 OFDM symbols in a time slot；
Figure 129298DEST_PATH_IMAGE005
For two kinds of circulating prefix-lengths in LTE system.
3）Signal energy computation
For the purposes of making full use of the energy entrained by cyclic prefix, energy balane window is made adjustment according to the cyclic prefix of different length.
Figure 242748DEST_PATH_IMAGE019
Similarly, we to be currently located a little as under the hypothesis of slot starting point, are calculating energy and the addition of the cyclic prefix of 7 OFDM symbols respectively.
Figure 167978DEST_PATH_IMAGE020
Represent the self-energy sum of 7 OFDM symbols in a time slot； dRepresent the symbol of current detection；mThe counting to participating in the symbol numbers that correlation energy is calculated is represented, maximum is the length of cyclic sequence； kRepresent the counting to rear 6 OFDM symbols in a time slot；G1、G2Represent two kinds of circulating prefix-lengths in LTE system. 
4）Threshold value is adjudicated
Judgement formula value is calculated according to following threshold value judgement formula proposed by the present invention
Figure 329969DEST_PATH_IMAGE021
。
WhereinRepresent small several times carrier wave frequency deviation.
Figure 281154DEST_PATH_IMAGE016
Represent the correlation energy sum of 7 OFDM symbols in a time slot；Represent the self-energy sum of 7 OFDM symbols in a time slot. 
5）Judge starting point and small several times carrier wave frequency deviation
As shown in above-mentioned threshold value judgement formula, if
Figure 490735DEST_PATH_IMAGE011
Be just the starting point of time slot, it is assumed that influence of the channel to signal is ignored, then using cyclic prefix characteristic and
Figure 883671DEST_PATH_IMAGE016
,
Figure 517914DEST_PATH_IMAGE020
Computing formula understand
Figure 84025DEST_PATH_IMAGE024
, now
Figure 385693DEST_PATH_IMAGE025
；Conversely, then
Figure 198797DEST_PATH_IMAGE026
, now.If
Figure 690139DEST_PATH_IMAGE011
The starting point of a time slot is not in, but in the starting point of other OFDM symbols in time slot, then because the circulating prefix-length of first OFDM symbol in a time slot is slightly longer than other 6,
Figure 783997DEST_PATH_IMAGE016
Calculating will be because of
Figure 581051DEST_PATH_IMAGE028
Deviations make it that the correlation energy of cyclic prefix does not reach maximum, the value of judgement formula can also be slightly less than maximum.But if
Figure 189887DEST_PATH_IMAGE011
It is not on the starting point of any one OFDM symbol, then the correlation of sequence is just not present,Value close to 0, the value for now adjudicating formula is much smaller than first two situation.If it is considered that multipath delay, frequency deviation, Doppler effect that channel strip comes etc., the correlation between cyclic prefix and effective information can be destroyed, and cause the maximum for adjudicating formula to be less than 1.Traditional maximum Likelihood is exactly because the correlation destroyed by channel can not suppress the influence that multipath delay, Doppler effect etc. are brought in the case where relevant information length is inadequate for the dependence of circulating prefix-length.
According to above-mentioned principle, the starting point of an OFDM symbol
Figure 295432DEST_PATH_IMAGE029
It can be determined by following formula： 
Figure 263388DEST_PATH_IMAGE030
According to maximum likelihood principle（Stefan H. Muller-Weinfurtner,“On the Optimality of Metrics for Coarse Frame Synchronization  in OFDM: A Comparison”,Personal Indoor ans Mobile Radio Communications 9th IEEE,1998）, the small several times carrier wave frequency deviation of ofdm system can obtain by following formula：
Figure 359520DEST_PATH_IMAGE031
The beneficial effects of the present invention are：Set forth herein method there is outstanding net synchronization capability, it is adaptable to high-speed mobile wireless communication system；Its judgment variables has more clean judgment variables figure under identical simulated environment compared to traditional coarse synchronization method, and peak value becomes apparent, and is less susceptible to the influence of channel circumstance.It is very capable to anti-multipath, antinoise and Doppler effect.The accuracy of the inventive method is significantly larger than other conventional methods always, and systematic function highest can lift 80% or so.
Brief description of the drawings
Fig. 1 is the comparison of the invention with conventional method judgment variables.Wherein,（a）For the judgment variables of the inventive method（b）The judgment variables of ML algorithms and MC algorithms（c）The judgment variables of MMSE and S＆C algorithms. 
Fig. 2 is that in TU-6 channels, under 30Km/hr translational speed, in the case of 0.2 times small several times carrier wave frequency deviation, the present invention detects the square mean error amount of small several times carrier wave frequency deviation with reference method（MSE）Compare. 
Fig. 3 is that in awgn channel, under 30Km/hr translational speed, in the case of 0.2 times small several times carrier wave frequency deviation, the present invention detects the square mean error amount of small several times carrier wave frequency deviation with reference method（MSE）Compare. 
Fig. 4 be in awgn channel, in the case of 0.2 times small several times carrier wave frequency deviation, the comparison of accuracy that the present invention and reference method are detected for slot starting point. 
Fig. 5 is the frame structure schematic diagram in LTE fdd mode Normal Mode. 
Fig. 6 is the flow chart of this method. 
Embodiment
The present invention is described in more detail with reference to the accompanying drawings and examples. 
The present invention provides a kind of coarse synchronization method for suppressing multipath delay Doppler effect towards LTE-FDD systems, comprises the following steps that： 
Step 1, the signal of receive slot length is stored, defined
Figure 8807DEST_PATH_IMAGE002
To solve the reception signal before constellation mapping,
Figure 873995DEST_PATH_IMAGE003
For FFT length,
Figure 12853DEST_PATH_IMAGE004
,
Figure 596281DEST_PATH_IMAGE005
For two kinds of circulating prefix-lengths in LTE system.For 20MHz bandwidth,.The OFDM symbol received is defined as
Figure 327979DEST_PATH_IMAGE007
Wherein
Figure 336387DEST_PATH_IMAGE008
Represent the received
Figure 389793DEST_PATH_IMAGE009
Individual complete OFDM symbol；
Figure 229573DEST_PATH_IMAGE009
Expression receives the counting of OFDM symbol.In LTE Normal Mode patterns, 7 OFDM symbols are had in a time slot, therefore the sequence length that needs are stored every time is
Figure 710233DEST_PATH_IMAGE010
。
Step 2, the correlation energy value between cyclic prefix and effective information is calculated, in order to make full use of the energy entrained by all cyclic prefix, cyclic prefix when carrying out related operation for different length uses the correlation window of different length, as follows： 
Figure 455204DEST_PATH_IMAGE033
With the symbol of current detection
Figure 46722DEST_PATH_IMAGE011
For starting point, and assume to be currently located starting point a little for a time slot, first progress length is
Figure 741009DEST_PATH_IMAGE012
Related operation, then to thereafter
Figure 595832DEST_PATH_IMAGE013
The signal of length carries out 6 length
Figure 375570DEST_PATH_IMAGE014
Related operation, then all correlation energy is added, the concept of collection of energy is realized.
Step 3, signal energy computation is carried out
For the purposes of making full use of the energy entrained by cyclic prefix, energy balane window is made adjustment according to the cyclic prefix of different length.
Similarly, we to be currently located a little as under the hypothesis of slot starting point, are calculating energy and the addition of the cyclic prefix of 7 OFDM symbols respectively.
Step 4, formula is adjudicated according to threshold value proposed by the present invention（It is as follows）Calculate decision value
Figure 772102DEST_PATH_IMAGE021
。 
Figure 594564DEST_PATH_IMAGE034
Wherein
Figure 861598DEST_PATH_IMAGE035
Represent small several times carrier wave frequency deviation. 
Step 5, slot starting point is judged according to the size of judgement formula
Figure 998181DEST_PATH_IMAGE011
With small several times carrier wave frequency deviation. 
The starting point of one OFDM symbol can be determined by following formula： 
Figure 667060DEST_PATH_IMAGE036
The small several times carrier wave frequency deviation of system can be obtained by following formula：
Figure 660423DEST_PATH_IMAGE037
When maximum is judged, it is not necessary to which the result of calculation of all judgment variables is all stored, it is only necessary to which the maximum in result of calculation is compared by current result of calculation and before, if greater than the maximum in result of calculation before, maximum is then updated, if it is not greater, then discarding.Using first calculated value of judgment variables as maximum initial value.
We carry out floating-point emulation to the algorithm below, and main simulation parameter is shown in Table 1, and channel model uses awgn channel and TU-6 channels（Channel parameter is shown in Table 2）, it is proposed that method name be Minn algorithms. 
The DTMB system emulation parameters of table 1
Figure 2013104297135100002DEST_PATH_IMAGE001
The TU-6 channel model parameters of table 2
Figure 338715DEST_PATH_IMAGE039
First we compare in the environment of awgn channel set forth herein method and other four kinds of conventional methods judgment variables, as shown in Figure 1, set forth herein the judgment variables of method there is more clean judgment variables figure compared to traditional coarse synchronization method under identical simulated environment, peak value becomes apparent, and is less susceptible to the influence of channel circumstance.
Secondly we simulation algorithm detects the square mean error amount of small several times carrier wave frequency deviation under awgn channel and TU-6 multipath channels respectively（MSE）, as shown in Figures 2 and 3. 
It is in TU-6 channels, under 30Km/hr translational speed, in the case of 0.2 times small several times carrier wave frequency deviation, to detect the square mean error amount of small several times carrier wave frequency deviation shown in Fig. 2（MSE）.It can be seen that set forth herein new method relatively low square mean error amount is maintained in the case where signal to noise ratio is relatively low compared to traditional algorithm, in signal to noise ratio from during 0dB rises to 9dB, its MSE is far below four kinds of traditional algorithms always.Illustrate it to the very capable of anti-multipath and Doppler effect. 
It is in awgn channel, in the case of 0.2 times small several times carrier wave frequency deviation, to detect the square mean error amount of small several times carrier wave frequency deviation shown in Fig. 3.It can be seen that set forth herein new method compared to traditional algorithm can also keep relatively low square mean error amount in awgn channel, and with the change of signal to noise ratio, its MSE size variation it is unobvious.This two figures illustrate the superiority of new method performance on to channel effects such as anti-multipath, noise, Doppler effect well. 
Fig. 4 shows in awgn channel, in the case of 0.2 times small several times carrier wave frequency deviation, the accuracy that each method is detected for slot starting point, as can be seen from the figure signal to noise ratio is from during -8dB changes to 9dB, it is proposed that the accuracy of method be significantly larger than other conventional methods always, systematic function highest can lift 80% or so. 
The implementation process to the present invention is described in detail above, but the present invention is not limited to above-described embodiment, and under the spirit of claims hereof, present invention encompasses the various remodeling of above-mentioned implementation process. 

Claims (3)

1. a kind of LTE-FDD systems suppress the coarse synchronization method of multipath delay Doppler effect, it is characterised in that carry out small several times carrier wave frequency deviation detection using the cyclic prefix of all OFDM symbols in a time slot and frame starting point is detected, comprise the following steps that：
Step 1：Store signal
The signal of receive slot length is stored, defined
Figure 25077DEST_PATH_IMAGE001
To solve the reception signal before constellation mapping,
Figure 18440DEST_PATH_IMAGE002
For FFT length,
Figure 897404DEST_PATH_IMAGE003
,For two kinds of circulating prefix-lengths in LTE system；The OFDM symbol received is defined as：
Figure 157801DEST_PATH_IMAGE005
Figure 649962DEST_PATH_IMAGE006
；
Wherein：
Figure 891587DEST_PATH_IMAGE007
Represent the received
Figure 166711DEST_PATH_IMAGE008
Individual complete OFDM symbol；
Figure 872499DEST_PATH_IMAGE008
Expression receives the counting of OFDM symbol；    
Step 2：Correlation energy is calculated
The correlation window of different length is used to carry out related operation for the cyclic prefix of different length, with the symbol of current detection
Figure 207665DEST_PATH_IMAGE009
For starting point, and assume to be currently located starting point a little for a time slot, carry out the related operation of 7 OFDM symbols, then by all correlation energy additions, correlation function is as follows：
Figure 15401DEST_PATH_IMAGE011
Wherein：
Figure 575695DEST_PATH_IMAGE012
Represent the correlation energy sum of 7 OFDM symbols in a time slot；kRepresent the counting to rear 6 OFDM symbols in a time slot；mThe counting to participating in the symbol numbers that correlation energy is calculated is represented, maximum is the length of cyclic sequence；
Figure 347342DEST_PATH_IMAGE013
Expression pair
Figure 297981DEST_PATH_IMAGE014
Carry out conjugate operation；For two kinds of circulating prefix-lengths in LTE system；
Step 3：Signal energy computation
Energy balane window is made adjustment according to the cyclic prefix of different length, energy and the addition of the cyclic prefix of 7 OFDM symbols are calculated respectively；The energy balane formula of cyclic prefix is as follows：
Wherein：
Figure 537835DEST_PATH_IMAGE017
Represent the self-energy sum of 7 OFDM symbols in a time slot； dRepresent the symbol of current detection；
Figure 975770DEST_PATH_IMAGE004
For two kinds of circulating prefix-lengths in LTE system；kThe counting of 6 OFDM symbols after representing in a time slot；N is FFT length；
Step 4：Threshold value is adjudicated
Threshold value judgement is carried out using below equation, obtains adjudicating formula value：
Figure 931273DEST_PATH_IMAGE019
Wherein
Figure 44723DEST_PATH_IMAGE020
Represent small several times carrier wave frequency deviation；
Figure 969954DEST_PATH_IMAGE012
Represent the correlation energy sum of 7 OFDM symbols in a time slot；
Figure 256578DEST_PATH_IMAGE017
Represent the self-energy sum of 7 OFDM symbols in a time slot；
Step 5：Judge starting point and small several times carrier wave frequency deviation
Principle and maximal possibility estimation principle, the starting point of an OFDM symbol are adjudicated according to above-mentioned threshold value
Figure 318075DEST_PATH_IMAGE021
With small several times carrier wave frequency deviation
Figure 602426DEST_PATH_IMAGE020
Determined by following formula：
Figure 105269DEST_PATH_IMAGE023
Figure 286851DEST_PATH_IMAGE024
Represent judgement formula value.
2. coarse synchronization method according to claim 1, it is characterised in that：Needed in step 1 storage sequence length be
Figure 476524DEST_PATH_IMAGE025
；Wherein N is FFT length,For two kinds of circulating prefix-lengths in LTE system. 
3. coarse synchronization method according to claim 1, it is characterised in that：During the related operation of described 7 OFDM symbols of progress, first carrying out length is
Figure 998915DEST_PATH_IMAGE026
Related operation, then to thereafter
Figure 300584DEST_PATH_IMAGE027
The signal of length carries out 6 length
Figure 661158DEST_PATH_IMAGE028
Related operation, wherein N be FFT length；
Figure 110594DEST_PATH_IMAGE004
For two kinds of circulating prefix-lengths in LTE system.
CN201310429713.5A 2013-09-22 2013-09-22 Coarse synchronization method for restraining multipath time delay and Doppler effect in LTE-FDD system Pending CN103581100A (en)

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Publication number Priority date Publication date Assignee Title
CN107342961A (en) * 2017-05-27 2017-11-10 国网浙江余姚市供电公司 A kind of method of the unmanned plane image transmitting asthenia based on CP ML algorithms
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CN114257480B (en) * 2020-09-23 2023-09-15 紫光展锐(重庆)科技有限公司 Frequency offset estimation method and device, storage medium and terminal
CN117979423A (en) * 2024-03-28 2024-05-03 杰创智能科技股份有限公司 Positioning method, positioning device, electronic equipment and storage medium
CN117979423B (en) * 2024-03-28 2024-05-31 杰创智能科技股份有限公司 Positioning method, positioning device, electronic equipment and storage medium

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