CN101267417B - Estimation method for integer frequency deviation of digital communication system - Google Patents
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Abstract
The invention discloses an estimation method of a digital communication system integer frequency offset, comprising the steps of: selecting a plurality of symbols in a frequency domain signal; selecting two sections of data with the same length from each symbol; adding absolute value of real and imaginary parts of each data point; accumulating the plurality of symbols; subtracting the produced two sections of sequence point by point and extracting the symbol so as to produce a comparative sequence; accumulating the comparative sequence point by point to produce a symbol accumulative sequence, and searching a minimum value; calculating an integer frequency offset according to the minimum value. The invention is capable of reducing complexity of calculation with high reliability and less time consuming, which is not only appropriate for an OFDM system, but also a single carrier system.
Description
Technical field
The present invention relates to digital communication technology field, particularly relate to a kind of method of estimation of integer frequency deviation of digital communication system.
Background technology
OFDM (Orthogonal Frequency Division Multiplexing, OFDM) is a kind of multi-carrier modulation, has the advantage that spectrum efficiency height, bandwidth autgmentability are strong, anti-multipath disturbs.
In ofdm system, owing to send and receive the mismatch that exists between the crystal oscillator to a certain extent, or have Doppler frequency shift at the mobile wireless passage, there are carrier frequency shift in transmitting terminal and receiving terminal, are called carrier wave frequency deviation (hereinafter to be referred as frequency deviation).Frequency deviation can be divided into integer frequency bias and mark frequency deviation to subcarrier spacing normalization, i.e. subcarrier spacing integral multiple part and less than the subcarrier spacing part.Ofdm system is very responsive for frequency deviation.Fractional spaced meeting causes ICI (Inter CarrierInterference disturbs between subcarrier), and integer frequency bias can cause the cyclic shift of frequency domain symbol data.
Usually, the mark frequency deviation estimated and proofreaied and correct in time domain, the data after the correction at frequency domain to estimating greater than the integer frequency bias of 1 subcarrier and correcting.Existing method of estimation complexity generally all needs to use a large amount of complex multiplication operations than higher, and bigger to the overhead of hardware resource, computing time is long.
A kind of integer frequency bias method of estimation commonly used is based on known symbol, and to do cyclic shift relevant with given data on frequency domain for receiving symbol, estimates integer frequency bias by seeking relevant peaks.For example exist.In T-DMB (Terrestrial Digital MultimediaBroadcasting, the T-DMB) system, it is relevant that the PRS (Phase Reference Symbol, phase reference symbol) and the known PRS sequence that receive are done cyclic shift.In this example, consider the influence of eliminating channel, also will carry out Difference Calculation between the PRS symbol adjacent sub-carrier to reception usually before relevant, the complex multiplication operation meeting of being introduced thus further increases the complexity of algorithm.Reliability is lower usually under the situation of fading channel for this method.Because the correlation of known array, the integer frequency bias estimation range is smaller; For example in described example, estimation range is ± 16 sub-carrier separation.Because calculation of complex and known symbol are usually located at the frame head position, so need to consume the time of a frame usually.
Summary of the invention
The technical problem to be solved in the present invention provides a kind of method of estimation of integer frequency deviation of digital communication system, and it can reduce the complexity of calculating, the reliability height, and required time is short.
In order to solve the problems of the technologies described above, the method for estimation of integer frequency deviation of digital communication system of the present invention is to adopt following technical scheme to realize, chooses continuous a plurality of symbols in frequency-region signal, estimates as follows then:
Step 1 is chosen first section and second section two sections frequency-region signal data sequence of equal length in each symbol of frequency-region signal data, establish a
K, iBe k the frequency-region signal data that symbol loads on i subcarrier, choose data
Wherein, k=0,1 ..., M-1, i=0,1 ..., 2L
1+ 2L
2-1, m is first section original position in symbol, and n is second section original position in symbol, L
1+ L
2Be every section length of choosing data;
The standard of choosing is that being located at the length of choosing in each symbol is L
1+ L
2, first section frequency-region signal data sequence is designated as P
j, second section frequency-region signal data sequence is designated as Q
j, j=0,1 ..., L
1+ L
2-1; First section frequency-region signal data sequence P
jFrom the first half of symbol, choose, and satisfy and work as j=0,1 ..., L
1-1, when supposing not have frequency deviation in the received signal, P
jCorrespond to the virtual subnet carrier wave; Work as j=L
1, L
1+ 1 ..., L
1+ L
2-1, when supposing not have frequency deviation in the received signal, P
jCorrespond to effective subcarrier; Second section frequency-region signal data sequence Q
jChoose half from the back of symbol, and satisfy and work as j=0,1 ..., L
1-1, when supposing not have frequency deviation in the received signal, Q
jCorrespond to effective subcarrier, work as j=L
1, L
1+ 1 ..., L
1+ L
2-1, when supposing not have frequency deviation in the received signal, Q
jCorrespond to the virtual subnet carrier wave;
Step 2 is with the real part of each data point of each symbol and the absolute value addition of imaginary part; The frequency-region signal data sequence that generates after the addition is c
K, i=| Re (b
K, i) |+| Im (b
K, i) |, wherein, k=0,1 ..., M-1, i=0,1 ..., 2L
1+ 2L
2-1;
Step 3 is with frequency-region signal data sequence c
K, iIn a plurality of symbols add up, the result who adds up forms new frequency-region signal data sequence d
i,
Step 4 is with the new frequency-region signal data sequence d of step 3 formation
iAgain be divided into two sections, first section sequence is p
i=d
i, i=0,1 ..., L
1+ L
2-1, i.e. d
iThe first half of sequence; Second section sequence is
I=0,1 ..., L
1+ L
2-1, i.e. d
iSequence back half; First section sequence p
iWith second section sequence q
iPointwise is subtracted each other, perhaps with second section sequence q
iWith first section sequence p
iPointwise is subtracted each other, and gets the symbol of result of calculation, generates frequency-region signal data comparative sequences;
Step 5 adds up the pointwise of frequency-region signal data comparative sequences, generates the symbol sequence that adds up, and seeks minimum value or peaked positional value;
Step 6 is according to minimum value or peaked positional value computes integer frequency deviation value.
Adopt method of the present invention, can be after time domain only to be estimated the mark frequency deviation and is proofreaied and correct, data are carried out the estimation of integer frequency bias through FFT (fast fourier transform) at frequency domain.Owing to there is not multiply operation, can effectively reduce algorithm complex, it is little that circuit realizes that extra resource consumes.The circuit that adopts method of the present invention to realize only needs hundreds of gates, and the required hardware resource of prior art is generally of the present invention more than tens of times; Computational speed is fast, only needs the time of some symbols; Estimation range is big, and good reliability can overcome the influence that a plurality of single-tones disturb effectively.
Description of drawings
The present invention is further detailed explanation below in conjunction with accompanying drawing and embodiment:
Fig. 1 is a control flow chart of the present invention;
Fig. 2 is the result schematic diagram that is produced after implementation step one and the step 2 in the method for the present invention;
Fig. 3 be in the method for the present invention implementation step three to the process schematic diagram of step 6;
Embodiment
In ofdm system, only use the low frequency part subcarrier in the whole bandwidth.In the high frequency edge part, insertion amplitude usually is that zero subcarrier is used as boundary belt, and these subcarriers are called the virtual subnet carrier wave.By seeking the border of virtual subnet carrier wave and other subcarriers, just can estimate the integer frequency bias value.
The method of specific implementation is, obtaining the ofdm system frequency-region signal, and promptly the ofdm system receiver carries out after the FFT, chooses continuous a plurality of symbols and carry out integer frequency bias and estimate in frequency-region signal.Suppose to choose M symbol, label is k respectively, k=0, and 1 ..., M-1.If the ofdm system number of sub carrier wave is N, received frequency-region signal data can be described as a
K, i, k=0,1 ..., M-1, i=0,1 ..., N-1, a
K, iBe k the frequency-region signal data that symbol loads on i subcarrier.Estimate by step as shown in Figure 1 then:
Step 1 is chosen data in the frequency-region signal data.Common virtual subnet carrier wave is increased in the beginning and end both sides in the ofdm system, utilizes the character of virtual subnet carrier position, chooses the data that meet following standard.In each symbol, choose identical two sections of length, remember that a certain symbol sebolic addressing is A
i, i=0,1 ..., N-1, the length of choosing is L
1+ L
2, first section frequency-region signal data sequence choosing in symbol is designated as P
j, second section frequency-region signal data sequence is designated as Q
j, j=0,1 ..., L
1+ L
2-1.First section frequency-region signal data sequence is from frequency-region signal data sequence A
iThe first half, i.e. i=0,1 ..., choose among the N/2-1, and satisfy and work as j=0,1 ..., L
1-1, when supposing not have frequency deviation in the received signal, P
jCorrespond to the virtual subnet carrier wave, i.e. P
jPairing frequency-region signal data sequence A
iIn point generated by the virtual subnet carrier data; Work as j=L
1, L
1+ 1 ..., L
1+ L
2-1, when supposing not have frequency deviation in the received signal, P
jCorrespond to data subcarrier.That is to say selected frequency-region signal data sequence P
jPreceding L
1Individual data point all is the virtual subnet carrier data, back L
2Individual data point all is effective subcarrier data.According to similar rule at symbol A
iIn choose second section frequency-region signal data sequence Q
j, second section frequency-region signal data sequence Q
jFrom frequency-region signal data sequence A
iBack half, i.e. i=N/2, N/2+1 ..., choose among the N-1, and satisfy and work as j=0,1 ..., L
1-1, when supposing not have frequency deviation in the received signal, Q
jCorrespond to effective subcarrier; Work as j=L
1, L
1+ 1 ..., L
1+ L
2-1, when supposing not have frequency deviation in the received signal, Q
jCorrespond to the virtual subnet carrier wave.That is to say L before satisfying
1Individual data point all is effective subcarrier data, back L
2It all is the virtual subnet carrier data.With sequence P
jAnd Q
jMerge into new sequence
I=0,1 ..., 2L
1+ 2L
2-1.
L
1With L
2Choice relation to the estimation range of integer frequency bias, in theory, estimation range just should be-L
2+ 1～L
1Individual sub-carrier separation.So L
1With L
2That should select is bigger, but should keep selected two sections respectively within the scope of the first half symbol and half symbol of back.But L
1With L
2Length will have influence on amount of hardware resources and amount of calculation when realizing.Usually, can choose L
1=L
2Make estimation range keep symmetry at positive and negative two ends.
At frequency-region signal sequence a
K, iEach symbol in choose data according to identical method, be designated as
K=0,1 ..., M-1, i=0,1 ..., 2L
1+ 2L
2-1, wherein m is first section original position in symbol, and n is second section original position in symbol.
Step 2 is with the real part of each data point and the absolute value addition of imaginary part.The amplitude of virtual subnet carrier wave is zero, because the influence of channel and system noise, the virtual subnet carrier wave that receives has smaller amplitude.In order to seek the border of virtual subnet carrier wave, need to investigate the amplitude of signaling point.Ask amplitude computing relative complex, and complex point real part imaginary part absolute value sum implements convenient and simple.The data b of selecting for step 1
K, i, k=0,1 ..., M-1, i=0,1 ..., 2L
1+ 2L
2-1 calculates, and then the frequency-region signal data sequence of Sheng Chenging is c
K, i=| Re (b
K, i) |+| Im (b
K, i) |, k=0,1 ..., M-1, i=0,1 ..., 2L
1+ 2L
2-1 (in conjunction with shown in Figure 2).
Step 3 is with frequency-region signal data sequence c
K, iIn a plurality of symbols add up, the result who adds up forms new frequency-region signal data sequence
After a plurality of symbols are added up, because the gain of noncoherent accumulation, can further increase the poor of virtual subnet carrier wave and effective subcarrier amplitude, can also eliminate because caused some the sub-carrier signal amplitude fading of channel.During concrete enforcement, when the symbol quantity of choosing is many,, can considers in calculating, to carry out right shift and handle, promptly in order to save resource
Wherein t is the number of times of right shift.Shifting processing has reduced virtual subnet carrier wave and other subcarrier amplitude differences, but still has had the average effect (in conjunction with shown in Figure 2) that adds up and produced when saving resource.The sequence that is generated is divided into two sections again.First section sequence is p
i=d
i, i=0,1 ..., L
1+ L
2-1, i.e. d
iThe first half of sequence; Second section sequence is
I=0,1 ..., L
1+ L
2-1, i.e. d
iSequence back half.
If there is no frequency deviation, first section frequency-region signal data sequence p
iIn before L
1Individual data point produces second section frequency-region signal data sequence q for the virtual subnet carrier wave calculates
iMiddle back L
2Individual data point produces for the virtual subnet carrier wave calculates.If there is frequency deviation in the system, suppose that frequency deviation is a F subcarrier spacing, F can get on the occasion of or negative value, then actual conditions then be in first section frequency-region signal data sequence before L
1-F data point, L after second section frequency-region signal data sequence
2+ F data point calculated by the virtual subnet carrier wave and produced.Therefore, find at frequency-region signal data sequence p
iIn the true length X of virtual sub-carrier section, just can calculate F=L
1-X (in conjunction with shown in Figure 3).
Step 4 generates frequency-region signal data comparative sequences.With first section frequency-region signal data sequence p
iWith second section frequency-region signal data sequence q
iPointwise is subtracted each other, and gets the symbol of result of calculation, obtains new only comprising+1 ,-1 and 0 sequence, r
i=sign (p
i-q
i), i=0,1 ..., L
1+ L
2-1, generate frequency-region signal data comparative sequences.This sequence may comprise 0 in theory, because choosing of step 1 frequency domain signal data sequence, one of them is to be calculated by the virtual subnet carrier wave for two data that assurance is subtracted each other, another one is to be calculated by the carrying data subcarrier, therefore, it is very little in fact to subtract each other null probability.This process has just been carried out pointwise relatively to two segment data sequences, and the gained result should be preceding L in theory
1-F data are-1, back L
2+ F data are+1.Can certainly subtract first section frequency-region signal data sequence (pointwise is subtracted each other) with second section frequency-region signal data sequence and calculate (in conjunction with shown in Figure 3).
Step 5 adds up the pointwise of frequency-region signal data comparative sequences, generates the symbol sequence that adds up, and seeks minimum value.
The sequence that adds up that generates is:
I=0,1 ..., L
1+ L
2-1.Because the result that adds up, the symbol of the generation sequence that adds up is a shape of falling spike.That is to say preceding L
1-F data are for reducing back L successively
2+ F data are for increasing successively.Therefore, L
1-F data should be the minimum values of whole sequence.Find the position of this minimum value, be designated as X.Calculate if in step 4, adopted second section frequency-region signal data sequence to subtract first section frequency-region signal data sequence (pointwise is subtracted each other), then should look for the maximum of whole sequence.Obviously, the span of X is 0～L
1+ L
2-1.Note, also can not change minimum value or peaked position (in conjunction with shown in Figure 3) even exist a plurality of single-tones to disturb usually.
Step 6 is according to minimum value or peaked positional value computes integer frequency deviation value.Minimum value or peaked positional value X by step 5 found just can calculate integer frequency bias value F=L
1-X.Span by positional value X is 0～L
1+ L
2-1, the scope that can obtain integer frequency bias value F is L
1-(L
1+ L
2-1)～L
1-0, promptly-L
2+ 1～L
1, this point was once mentioned (in conjunction with shown in Figure 3) in step 1.
Adopt the reliability of the integer offset frequency that method of the present invention obtains further to verify.The method of checking is as follows: require the minimum value in the step 5 only to have one; Perhaps adopt more conservative checking, require for resulting minimum value of step 5 or peaked positional value X, at the sequence p that step 3 produced
i, q
iIn should satisfy 2p
X＜q
X, p
X+1＞2q
X+1
For the situation of authentication failed, think that then estimated result does not possess reliability, need estimate again.In most cases, reliability demonstration can be passed through.Only under the situation of channel very severe, discontented situation that can the property leaned on may appear.
Though above be to be that example describes method of the present invention with the ofdm system, the present invention is not limited in ofdm system, also can be applied to single-carrier system.As long as frequency spectrum is a similar shapes, promptly frequency spectrum the right and left is a null value, just can use method of the present invention equally.
Provide a concrete example that is applied to ofdm system below, set forth performing step of the present invention.It is pointed out that this example does not influence generality of the present invention.
T-DMB mode standard I, sub-carrier number are 2048, and effectively sub-carrier number is 1536, system bandwidth 2.048MHz, sub-carrier separation 1kHz.The virtual subnet carrier number is 511.The subcarrier sequence number is designated as 0～2047 in every symbol, and then virtual subnet carrier wave sequence number is 0～255,1793～2047, direct current subcarrier 1024.In mark frequency offset estimating and correction, and after the FFT, in a frame, choose last tens symbols and calculate.Suppose that choosing frequency offset estimation range is ± 192kHz that then choosing two sections corresponding respectively subcarrier sequence numbers of calculated data the symbol planted agent is 64～448,1601～1985.
Claims (3)
1. the method for estimation of an integer frequency deviation of digital communication system is characterized in that: choose a plurality of symbols in frequency-region signal, estimate as follows then:
Step 1 is chosen first section and second section two sections frequency-region signal data sequence of equal length in each symbol of frequency-region signal data, establish a
K, iBe k the frequency-region signal data that symbol loads on i subcarrier, choose data
Wherein, k=0,1 ..., M-1, i=0,1 ..., 2L
1+ 2L
2-1, m is first section original position in symbol, and n is second section original position in symbol, L
1+ L
2Be every section length of choosing data, M is a symbol numbers;
The standard of choosing is that being located at the length of choosing in each symbol is L
1+ L
2, first section frequency-region signal data sequence is designated as P
j, second section frequency-region signal data sequence is designated as Q
j, j=0,1 ..., L
1+ L
2-1; First section frequency-region signal data sequence P
jFrom the first half of symbol, choose, and satisfy and work as j=0,1 ..., L
1-1, when supposing not have frequency deviation in the received signal, P
jCorrespond to the virtual subnet carrier wave; Work as j=L
1, L
1+ 1 ..., L
1+ L
2-1, when supposing not have frequency deviation in the received signal, P
jCorrespond to effective subcarrier; Second section frequency-region signal data sequence Q
jChoose half from the back of symbol, and satisfy and work as j=0,1 ..., L
1-1, when supposing not have frequency deviation in the received signal, Q
jCorrespond to effective subcarrier, work as j=L
1, L
1+ 1 ..., L
1+ L
2-1, when supposing not have frequency deviation in the received signal, Q
jCorrespond to the virtual subnet carrier wave;
Step 2 is with the real part of each data point and the absolute value addition of imaginary part; The frequency-region signal data sequence that generates after the addition is c
K, i=| Re (b
K, i) |+| Im (b
K, i) |, wherein, k=0,1 ..., M-1, i=0,1 ..., 2L
1+ 2L
2-1;
Step 3 is with frequency-region signal data sequence c
K, iIn a plurality of symbols add up, the result who adds up forms new frequency-region signal data sequence d
i,
Step 4 is with the new frequency-region signal data sequence d of step 3 formation
iAgain be divided into two sections, first section sequence is p
i=d
i, i=0,1 ..., L
1+ L
2-1, i.e. d
iThe first half of sequence; Second section sequence is
I=0,1 ..., L
1+ L
2-1, i.e. d
iSequence back half; First section sequence p
iWith second section sequence q
iPointwise is subtracted each other, perhaps with second section sequence q
iWith first section sequence p
iPointwise is subtracted each other, and gets the symbol of result of calculation, generates frequency-region signal data comparative sequences;
Step 5 adds up the pointwise of frequency-region signal data comparative sequences, generates the symbol sequence that adds up, and seeks minimum value or peaked positional value;
Step 6 is according to minimum value or peaked positional value computes integer frequency deviation value.
2. the method for estimation of integer frequency deviation of digital communication system as claimed in claim 1, it is characterized in that: in the length of choosing is L
1+ L
2Middle L
1=L
2, make estimation range keep symmetry at positive and negative two ends.
3. the method for estimation of integer frequency deviation of digital communication system as claimed in claim 1 is characterized in that: when the symbol quantity of choosing is many, the accumulation result in the step 3 is carried out right shift handle, promptly
Wherein t is the number of times of right shift.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1032975A1 (en) * | 1997-11-17 | 2000-09-06 | Telefonaktiebolaget LM Ericsson (publ) | Method and apparatus for estimating a frequency offset |
| CN1719815A (en) * | 2004-07-07 | 2006-01-11 | 华为技术有限公司 | Method and device for estimating and correcting frequency offset |
| CN1822582A (en) * | 2005-02-18 | 2006-08-23 | 三星电子株式会社 | Dual carrier modulator, OFDM transmitter and method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1032975A1 (en) * | 1997-11-17 | 2000-09-06 | Telefonaktiebolaget LM Ericsson (publ) | Method and apparatus for estimating a frequency offset |
| CN1719815A (en) * | 2004-07-07 | 2006-01-11 | 华为技术有限公司 | Method and device for estimating and correcting frequency offset |
| CN1822582A (en) * | 2005-02-18 | 2006-08-23 | 三星电子株式会社 | Dual carrier modulator, OFDM transmitter and method thereof |
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Address after: 214072 Jiangsu province Binhu District of Wuxi City Liyuan Development Zone 530 No. 1 building twelve room 1203 Patentee after: MAXSCEND MICROELECTRONICS Co.,Ltd. Address before: 214072 Jiangsu province Binhu District of Wuxi City Liyuan Development Zone 530 No. 1 building twelve room 1203 Patentee before: MAXSCEND TECHNOLOGIES Inc. |
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Denomination of invention: Estimation method of integer frequency offset in digital communication system Granted publication date: 20111005 Pledgee: Industrial and Commercial Bank of China Limited Wuxi Binhu Branch Pledgor: MAXSCEND MICROELECTRONICS Co.,Ltd. Registration number: Y2024980039405 |
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