CN102347924A - Frequency offset estimation and timing method and device - Google Patents
Frequency offset estimation and timing method and device Download PDFInfo
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- CN102347924A CN102347924A CN2010102410869A CN201010241086A CN102347924A CN 102347924 A CN102347924 A CN 102347924A CN 2010102410869 A CN2010102410869 A CN 2010102410869A CN 201010241086 A CN201010241086 A CN 201010241086A CN 102347924 A CN102347924 A CN 102347924A
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Abstract
The invention discloses a frequency offset estimation and timing method and a frequency offset estimation and timing device. The method comprises the following steps of: performing rough timing on a received signal according to a rough timing scheme to obtain a rough timing result; performing decimal frequency offset estimation based on a repetitive structure of the received signal according to the rough timing result to obtain a decimal frequency offset estimation result; determining a searching window according to an error range of the rough timing result and the positions of ghost peaks produced by integral frequency offsets; and in the searching window, performing integral frequency offset detection on the received signal by utilizing the decimal frequency offset estimation result and at least one integral frequency offset, and obtaining an integral frequency offset estimation result and a precise timing result according to an integral frequency offset detection result. By the method and the device, the influence of the ghost peaks and noises on the frequency offset estimation results can be eliminated, the problem of over-high processing load caused by an irrational searching range in related technologies can be solved, and the frequency offset estimation and timing precision can be effectively improved; and the method and the device can be effectively adapted to scenes with high noises and frequency offsets.
Description
Technical field
The present invention relates to the communications field, relate in particular to a kind of frequency offset estimating and method and apparatus regularly.
Background technology
Multi-transceiver technology is a kind of high speed data transfer technology; It is decomposed into data flow at a high speed the data flow of several low speed; Each rate data streams is parallel transmission on the subcarrier of quadrature, and than single-carrier system, multicarrier system has higher frequency efficiency.OFDM (Orthogonal Frequency Division Multiplexing; Abbreviate OFDM as) be a kind of typical multicarrier system; It has introduced Cyclic Prefix (Cyclic Prefix abbreviates CP as), can overcome the intersymbol interference that multipath fading causes effectively.OFDM is the core technology of Long Term Evolution (Long Term Evolution abbreviates LTE as) system and the 4th third-generation mobile communication system, and is adopted by a plurality of industrial standard.
Timing and frequency offset estimating are key factors that influences the ofdm system performance; Regularly be meant the original position of confirming multicarrier frame or blocks of multicarrier symbols; So that carry out anti-fast fourier transform (Inverse Fast Fourier Transform, IFFT) operation.Because the carrier wave frequency deviation that difference produced of Receiver And Transmitter crystal oscillator frequency, the orthogonality with destroying between the subcarrier will produce between serious subcarrier and disturb, and reduces the performance of system.So before the IFFT operation, must carry out timing and frequency offset estimating and compensation.
Ofdm system commonly used regularly has based on the autocorrelation method of reception signal repetitive structure with based on the cross-correlation method of training sequence with the method for frequency offset estimating.Typically be based on timing and the frequency deviation combined estimation of CP based on the autocorrelation method that receives the signal repetitive structure.This method has reasonable timing performance under Gaussian channel.Because the auto-correlation peak value that this method adopts is sharp-pointed inadequately, under multipath channel, regularly performance obviously descends.Estimation range based on the frequency deviation estimating method of CP is less, only limits to the half subdetector carrier spacing.At zero-frequency on the lower side, have preferably regularly performance, can produce sharp-pointed relevant peaks, but under the non-zero frequency deviation, relevant peaks receives the influence of frequency deviation and the influence of the training sequence correlation that adopts based on the cross-correlation method of training sequence.Zero correlation (Zero Correlation abbreviates ZC as) sequence is a kind of training sequence commonly used.At zero-frequency on the lower side, this sequence has the good autocorrelation ability.But when having big frequency deviation and even integer frequency offset, the correlation of ZC sequence seriously descends, and can produce a lot of bigger secondary lobes, adopts usual method can't carry out timing and frequency offset estimating.
Particularly, the LTE system is the evolution of the third generation (3G) communication system, is third generation partner program (3rd Generation Partnership Project, 3GPP) the global radio mobile communication standard of the 3.9G that proposed in 2004.LTE can improve and strengthen the air interface technologies of 3G system, adopts OFDM and multiple-input and multiple-output (Multiple-Input Multiple-Output the abbreviates MIMO as) sole criterion as its wireless network evolution.The LTE system can provide the peak rate of descending 100Mbit/s and up 50Mbit/s under the system bandwidth of 20MHz.Simultaneously, the LTE system can also improve the performance of Cell Edge User, improves cell capacity, and can reduce system delay.
The LTE system descending adopts OFDM (Orthogonal Frequency Division Multiple Access; OFDMA) access way; Has higher band efficiency than single-carrier system; And can and change the time that prolong each symbol greatly through string, can effectively resist the frequency selective fading that multidiameter delay caused in the mobile radio telecommunications; But the symbol period that increases also causes the LTE system more responsive more than single-carrier system for carrier shift relatively, and the LTE systematic function is seriously descended.
The reason that causes carrier frequency shift (abbreviating frequency shift (FS) as frequency deviation among this paper) mainly is that the unsteadiness and the terminal high-speed of transmitter and receiver crystal oscillator moves the Doppler frequency shift that causes.When having frequency deviation between receiving and transmitting signal, be easy to cause the interference between each subcarrier, influence the right demodulation of data, cause the increase of the error rate; When having integer frequency offset; Though there is not the interference between subcarrier; But because the integral multiple of subcarrier skew; Make and lose correlation between the data of data that demodulation is come out and transmission; Cause error rate of system to increase (in most cases the error rate can reach 50%), can not satisfy the basic demand of communication.
Existing frequency offset estimating and timing method mainly contain following two kinds among the LTE:
(method 1) adopts master sync signal (Primary Synchronization Signal abbreviates PSS as) to carry out frequency offset estimating and timing.For this mode, it is that in 3 candidate ZC sequences of 25,29,34 one representes that the master sync signal of LTE adopts radical exponent.This ZC sequence has good correlated performance on the lower side at zero-frequency, can reach higher frequency offset estimating and timing accuracy; But when having frequency departure, when particularly having big frequency deviation or even integer frequency offset, the correlation of ZC sequence can obviously reduce, and can produce more great secondary lobe, can't effectively solve frequency deviation.
(method 2) adopts Cyclic Prefix (Cyclic Prefix abbreviates CP as) to carry out frequency offset estimating and timing.But; Because this relevant peaks that obtains based on CP mode regularly is sharp-pointed inadequately; Receive The noise easily; Can reduce precision regularly, and when frequency deviation greater than half subdetector during the carrier spacing, the accumulation of phase that causes owing to frequency deviation between two sampling points of difference can surpass one-period; Cause to carry out correct Frequency Estimation; Therefore, this method based on CP only is adapted at low noise and frequency deviation is used during the carrier spacing less than half subdetector, has bigger limitation.
Equally, in other employing multicarriers, signal structure, comprise in the communication system of repeating part, can there be similar problem in frequency offset estimating equally with timing.
To frequency offset estimating in the correlation technique and timing accuracy is low and limitation is big problem, effective solution is not proposed as yet at present.
Summary of the invention
To frequency offset estimating in the correlation technique and timing accuracy is low and limitation is big problem; The present invention proposes a kind of frequency offset estimating and method and apparatus regularly; Frequency offset estimating and precision regularly can be effectively improved, and the scene of strong noise and big frequency deviation can be applicable to.
Technical scheme of the present invention is achieved in that
According to an aspect of the present invention, a kind of frequency offset estimating and method regularly are provided.
Comprise according to frequency offset estimating of the present invention and method regularly: carry out thick timing to received signal according to thick timing scheme, obtain thick timing results; Carry out the fractional part of frequency offset estimation based on the repetitive structure of said reception signal and according to said thick timing results, obtain the fractional part of frequency offset estimated result; Search window is confirmed in the position at the false peak that causes according to the error range and the integer frequency offset of said thick timing results; In said search window; Utilize said fractional part of frequency offset estimated result and at least one integer frequency offset that said reception signal is carried out integer frequency offset and detect, and obtain integer frequency offset estimated result and accurate timing result according to the integer frequency offset testing result.
Wherein, Obtain the integer frequency offset estimated result and the accurate timing result comprises according to the integer frequency offset testing result: detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Said reception signal is carried out compensate of frequency deviation; And in said search window, utilize predetermined local signal and the said reception signal behind the compensate of frequency deviation to carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Local signal to predetermined carries out compensate of frequency deviation; And the said local signal after in said search window, utilizing compensate of frequency deviation and said reception signal carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset that predetermined local signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that said reception signal is carried out the fractional part of frequency offset compensation; Said reception signal to after the compensation of the local signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset that said reception signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that predetermined local signal is carried out the fractional part of frequency offset compensation; Local signal to after the compensation of the reception signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result.
In addition; Obtain the integer frequency offset estimated result and the accurate timing result comprises according to the integer frequency offset testing result: the cross correlation value in the pairing testing result of all integer frequency offsets is compared; With the pairing integer frequency offset of the maximum cross-correlation value that relatively obtains as said integer frequency offset estimated result, and with the time location of said maximum cross-correlation value as said accurate timing result.
In addition, according to said thick timing scheme said reception signal being carried out thick timing comprises: based on the repetitive structure of said reception signal, according to said thick timing scheme said reception signal is carried out Autocorrelation Detection, obtain said thick timing results.
Preferably, based on the repetitive structure of said reception signal and according to said thick timing results said reception signal is carried out fractional part of frequency offset and estimate to comprise:
Sampled point in the error range of said thick timing results in the following sampled point set of deletion: { K; K+1 ..., K+N-1} and { K+L-N; K+L-N+1; ..., K+L-1}, wherein; K is the pairing sampled point of said thick timing results; [N, N] is the error range of said thick timing results, and L is the sampling number of repeating part in the repetitive structure of said reception signal; Based on the auto-correlation scheme reception signal after the sampled point deletion is carried out fractional part of frequency offset and estimate, obtain said decimal frequency bias estimated result.
In addition, the said search window of confirming comprises said thick timing error scope, and does not comprise said false peak.
According to an aspect of the present invention, a kind of frequency offset estimating and device regularly are provided.
Comprise according to frequency offset estimating of the present invention and device regularly: thick time block, be used for carrying out thick timing to received signal according to thick regularly scheme, obtain thick timing results; First estimation module is used for carrying out the fractional part of frequency offset estimation based on the repetitive structure of said reception signal and according to said thick timing results, obtains the fractional part of frequency offset estimated result; Determination module, search window is confirmed in the position that is used for the false peak that error range and integer frequency offset according to said thick timing results cause; Detection module is used in said search window, utilizes said fractional part of frequency offset estimated result and at least one integer frequency offset that said reception signal is carried out integer frequency offset and detects; Second estimation module is used for obtaining integer frequency offset estimated result and accurate timing result according to the integer frequency offset testing result.
Wherein, Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Said reception signal is carried out compensate of frequency deviation; And in said search window, utilize predetermined local signal and the said reception signal behind the compensate of frequency deviation to carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Local signal to predetermined carries out compensate of frequency deviation; And the said local signal after in said search window, utilizing compensate of frequency deviation and said reception signal carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset that predetermined local signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that said reception signal is carried out the fractional part of frequency offset compensation; Said reception signal to after the compensation of the local signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset that said reception signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that predetermined local signal is carried out the fractional part of frequency offset compensation; Local signal to after the compensation of the reception signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result.
In addition; Said second estimation module is used for the cross correlation value of the pairing testing result of all integer frequency offsets is compared; With the pairing integer frequency offset of the maximum cross-correlation value that relatively obtains as said integer frequency offset estimated result, and with the time location of said maximum cross-correlation value as said accurate timing result.
In addition, said thick time block specifically is used for the repetitive structure based on said reception signal, according to said thick timing scheme said reception signal is carried out Autocorrelation Detection, obtains said thick timing results.
Alternatively; When said first estimation module is carried out the fractional part of frequency offset estimation based on the repetitive structure of said reception signal and according to said thick timing results to said reception signal; Said first estimation module is used for the sampled point of the following sampled point set of deletion in the error range of said thick timing results: { K; K+1; ...; K+N-1}; And { K+L-N; K+L-N+1; ..., K+L-1}, wherein; K is the pairing sampled point of said thick timing results; [N, N] is the error range of said thick timing results, and L is the sampling number of repeating part in the repetitive structure of said reception signal; And be used for based on the auto-correlation scheme reception signal after the sampled point deletion being carried out fractional part of frequency offset and estimate, obtain said decimal frequency bias estimated result.
In addition, the said search window of being confirmed by said determination module comprises said thick timing error scope, and does not comprise said false peak.
The present invention is through confirming the rational position and the size of search window according to the position at thick timing results and false peak; And in the search window of confirming, carry out integer frequency offset and detect; Obtain integer frequency offset estimated result and accurate timing result; Can eliminate the influence of false peak and noise to frequency offset estimation result; And can avoid in the correlation technique causing the excessive problem of treating capacity owing to the hunting zone is unreasonable; Effectively improve frequency offset estimating and accuracy regularly, can effectively adapt to the scene of strong noise, big frequency deviation.
Description of drawings
Fig. 1 is the flow chart according to frequency offset estimating with the method regularly of the embodiment of the invention;
Fig. 2 is according to the frequency offset estimating of the embodiment of the invention and the flow chart of the concrete processing instance of method regularly;
Fig. 3 is a process chart of confirming search window in the method according to the frequency offset estimating of the embodiment of the invention and timing;
Fig. 4 is according to the frequency offset estimating of the embodiment of the invention and the block diagram of device regularly.
Embodiment
To frequency offset estimating in the correlation technique and timing accuracy is low and limitation is big problem; The present invention confirms rational search window at the give chapter and verse position at thick timing results and false peak; And in the search window of confirming, carry out integer frequency offset and detect; Obtain integer frequency offset estimated result and accurate timing result; Can avoid in the correlation technique hunting zone unreasonable and cause the excessive problem of treating capacity; And can eliminate the influence of false peak and noise, effectively improve frequency offset estimating and accuracy regularly frequency offset estimation result.
To combine accompanying drawing to describe embodiments of the invention in detail below.
According to embodiments of the invention, a kind of frequency offset estimating and method regularly are provided.
As shown in Figure 1, the frequency offset estimating according to the embodiment of the invention comprises with method regularly:
Step S101 carries out thick timing to received signal according to thick timing scheme, obtains thick timing results;
Step S103, based on the repetitive structure that receives signal (for example, in the LTE system; Repetitive structure is CP; And in the 802.11a system, the part of repetition is short leader sequence and long preambles sequence) and carry out fractional part of frequency offset according to thick timing results and estimate, the fractional part of frequency offset estimated result obtained;
Step S105, search window is confirmed in the position at the false peak that causes according to the error range and the integer frequency offset of thick timing results;
Step S107; In search window; Utilizing fractional part of frequency offset estimated result and at least one integer frequency offset to carry out integer frequency offset to received signal detects; And obtain integer frequency offset estimated result and accurate timing result according to the integer frequency offset testing result; Like this; According to before the fractional part of frequency offset estimated result and the integer frequency offset estimated result that obtain, just can access final frequency offset estimation result.
By means of above-mentioned processing; Through confirm rational position and suitably big or small search window according to the position at thick timing results and false peak; And in the search window of confirming, carry out integer frequency offset and detect; Obtain integer frequency offset estimated result and accurate timing result; Can eliminate the influence of false peak and noise to frequency offset estimation result; And can avoid in the correlation technique causing the excessive problem of treating capacity owing to the hunting zone is unreasonable; Effectively improve frequency offset estimating and accuracy regularly, can effectively adapt to the scene of strong noise, big frequency deviation.
In above-mentioned processing, obtain integer frequency offset estimated result and accurate timing as a result the time according to the integer frequency offset testing result, be mainly concerned with local signal and receive signal, and need utilize fractional part of frequency offset estimated result and a plurality of integer frequency offset (for example, f
Sc, 2f
ScDeng, f wherein
ScBe subcarrier spacing) carry out repeated detection, concrete detection can be divided into following 4 kinds of processing modes:
Processing mode one: detect each integer frequency offset adopted (promptly for carrying out integer frequency offset; When utilizing an integer frequency offset to carry out one-time detection); Utilize this integer frequency offset and fractional part of frequency offset estimated result; Carry out compensate of frequency deviation to received signal; And in search window, utilize predetermined local signal and the reception signal behind the compensate of frequency deviation to carry out computing cross-correlation, with the computing cross-correlation result as testing result; Perhaps
Processing mode two: detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset and fractional part of frequency offset estimated result; Local signal to predetermined carries out compensate of frequency deviation; And in search window, utilize behind the compensate of frequency deviation local signal with receive signal and carry out computing cross-correlation, with the computing cross-correlation result as testing result; Perhaps
Processing mode three: detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset that predetermined local signal is carried out the integer frequency offset compensation; And utilize the fractional part of frequency offset estimated result to carry out the fractional part of frequency offset compensation to received signal; Reception signal to after the compensation of the local signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as testing result; Perhaps
Processing mode four: detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset to carry out the integer frequency offset compensation to received signal; And utilize the fractional part of frequency offset estimated result that predetermined local signal is carried out the fractional part of frequency offset compensation; Local signal to after the compensation of the reception signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as testing result.
Obtaining integer frequency offset estimated result and accurate timing according to the integer frequency offset testing result as a result the time; Can be (promptly with the pairing testing result of all integer frequency offsets; All testing results) cross correlation value in compares; With the pairing integer frequency offset of the maximum cross-correlation value that relatively obtains as the integer frequency offset estimated result, and with the time location of maximum cross-correlation value as the accurate timing result.
For example, suppose after comparison that the maximum cross-correlation value that obtains is with f
ScObtain when detecting as integer frequency offset, at this moment, with f
ScAs the integer frequency offset estimated result, with f
ScThe time location of pairing this maximum cross-correlation value is as the accurate timing result.
In addition, thick process regularly is following carrying out according to thick regularly scheme: the repetitive structure based on receiving signal, carry out Autocorrelation Detection to received signal according to thick timing scheme, and obtain thick timing results.
In order to improve the accuracy of fractional part of frequency offset estimated result, when carrying out the fractional part of frequency offset estimation, can in the error range of thick timing results, delete the sampled point in the following sampled point set: { K; K+1 ..., K+N-1} and { K+L-N; K+L-N+1; ..., K+L-1}, wherein; K is the pairing sampled point of thick timing results; [N, N] is the error range of thick timing results, and L is the sampling number of repeating part in the repetitive structure that receives signal; Based on the auto-correlation scheme reception signal after the sampled point deletion is carried out fractional part of frequency offset and estimate, obtain the decimal frequency bias estimated result.Sampled point through in the deletion error range can effectively improve the accuracy of fractional part of frequency offset estimated result, thereby helps further to improve the accuracy that integer frequency offset is estimated.
In addition; The search window of confirming should comprise thick timing error scope; Thereby make follow-up integer frequency offset detect and to traverse all positions that correct timing possibly occur; In addition; Search window should not comprise false peak, thereby avoids false peak to frequency offset estimating and the harmful effect that is regularly brought.When confirming search window; Can be with the scope of thick timing results as minimum search window; With the peak-to-peak zone of falseness (this zone comprises the error range of thick timing results) as maximum search window (the maximum search window does not comprise false peak); When practical operation; Can detect with minimum search window or maximum search window; In addition; Can also confirm the actual search window that adopts according to minimum search window and maximum search window; The window that should confirm should comprise thick timing error scope, and does not comprise false peak.
To be example with the LTE downlink system below, and describe the present invention in detail and in the LTE downlink system, carry out frequency offset estimating and process regularly.Those skilled in the art are to be understood that; Below the application process of Miao Shuing only is used to set forth scheme of the present invention; And be not used in qualification the present invention; The present invention goes for various employing multicarriers and signal has the wireless communication system of repetitive structure, and reaches the purpose of accurately carrying out frequency offset estimating and timing.
As shown in Figure 2, in the LTE downlink system, the method for the employing embodiment of the invention carries out frequency offset estimating and process regularly is following:
Step 21 is carried out the thick timing of OFDM symbol according to formula (1) and formula (2).In this step, can carry out thick timing based on CP, the CP symbol regularly belongs to auto-correlation processing; Can adapt to certain channel variation; Though the relevant peaks regularly is sharp-pointed inadequately, carry out thick timing offset statistics through adding up of some symbols, can be with timing error Δ T
sBe controlled in tens sampling points.
Wherein, r
l(n) be l the descending ofdm signal of LTE that receives, N
CPBe circulating prefix-length, N is the OFDM symbol lengths, and l is the sequence number of OFDM symbol, and, n ∈ { N
CP, N
CP+ 1 ..., N+N
CP.In order to reduce The noise, after handling, can carry out M symbol according to formula (2) and add up according to formula (1), get maximum, the pairing time location of this maximum is thick timing results K.
Step 22 is accomplished fractional part of frequency offset according to formula (3) and is estimated.In order to remove the influence of timing error in the formula (1), when carrying out the fractional part of frequency offset estimation, can remove the sampled point in the timing error scope through formula (3).
By means of formula (3), through the error sampled point in the error range is removed, can effectively improve the precision that fractional part of frequency offset is estimated, and then can accurately estimate the frequency deviation result under the situation of decimal frequency bias.The influence that causes when frequency deviation surpasses one-period, that is, exist under the situation of integer frequency offset between LTE OFDM receiving and transmitting signal; Only estimate to obtain correct estimated result through fractional part of frequency offset; Therefore need to continue to carry out subsequent step, that is, carry out integer frequency offset and estimate.
Step 23 according to CP precision (that is, according to the error range of thick timing) regularly, is confirmed the minimum search window W of frequency offset estimating
MinMinimum search window is wanted to travel through the CP timing error, that is, and and minimum search window W
MinSize can pass through formula (4) expression:
W
Min＞Δ T
sFormula (4)
That is to say that search window should comprise the whole error range of thick timing results.
Step 24 is confirmed the maximum search window according to the peak distance of integer frequency offset.Owing to exist under the situation of integer frequency offset, the IFFT conversion that constitutes the ZC sequence of LTE PSS is the ZC sequence of circulation weighting displacement, adds frequency deviation and is equivalent to it is carried out cyclic shift; At this moment; The correlation of PSS is destroyed, and produces secondary lobe, can't distinguish different integer frequency offsets.But because under different integer frequency bias, the position of ZC sequence relevant peaks is different, so can adopt the position difference of relevant peaks to distinguish integer frequency offset.
Suppose when no integer frequency bias; Relevant peaks is positioned at the original position of symbol; Exist under the situation of integer frequency bias; The false relevant peaks distance nearest apart from the symbol original position is D sample value; Wherein, The relevant peaks that D obtains for three ZC sequences that constitute LTE PSS adopt maximum likelihood method to detect when different integer frequency offset (, false peak) and the position, can be through obtaining through calculating and statistics in advance.
Maximum search window W
MaxThe position that false relevant peaks possibly occur should be do not surpassed, formula (5) expression maximum search window can be passed through:
W
Max＜D formula (5)
Step 25 according to maximum search window and the minimum search window confirmed before, can be determined the search window W of final employing
SearOwing to need the maximum frequency deviation scope of traversal, therefore, can between minimum and maximum search window, select final search window, the final search window of confirming can be represented through formula (6):
W
Min＜W
Sear＜W
MaxFormula (6)
Step 26, the search window according to step 25 is confirmed adopts based on the maximum likelihood method of window search and carries out integer frequency offset detection (can utilize a plurality of integer frequency offsets to attempt), finally confirms integer frequency offset f
IFO, can obtain accurate timing K as a result simultaneously
Pric
Particularly, be example with above-mentioned (processing mode one), the decimal frequency bias that obtains through step 22 is f
FFO, carry out the decimal frequency bias compensation to the received signal, the reception signal after being compensated, shown in formula (7):
S (n)=r (n) exp (j2 π f
FFONT
s) formula (7)
Local ZC sequence is L (n) after through the IFFT conversion, according to formula (8) with different integer frequency offset exp (j2 π mf
ScKT
s) the reception signal after the fractional part of frequency offset compensation is detected, that is:
Wherein, l is the sequence number of OFDM symbol, l ∈ 0 ..., N
Symb-1}, N
SymbBe the PSS of 5ms OFDM symbolic number in the cycle, m is the integer frequency offset of traversal, and K is the thick timing results of symbol that step 21 obtains, and N is the length of OFDM symbol, N
CPBe the length of Cyclic Prefix, f
ScBe OFDM subcarrier spacing, T
sBe the sample time, L
*(n) be the conjugation of local sequence L (n), p is the sampling point sequence number of search in the OFMD symbol, and scope is following:
I in the formula (8) is a PSS 5ms cycle sequence number, and through searching for a plurality of PSS cycle, the search correlation to different cycles adds up then, can effectively suppress The noise, improves accuracy of detection.Utilizing integer frequency offset to carry out to confirm integer frequency offset f by formula (9) after integer frequency offset detects
IFOWith accurate OFDM symbol timing P
Pric
Wherein, f
IFO=m
0, P
Pric=p
0
In above-mentioned processing, step 22 and step 23 can independently of one anotherly be carried out to 25, that is, step 22 and step 23 also can be that sequencing is carried out to 25 being executed in parallel.And step 24 can also be carried out before step 21.
Step 23,24 and 25 is to confirm the step of search window, and Fig. 3 shows the detailed process of confirming search window, as shown in Figure 3, confirms that the mistake of search window is as follows old:
Step 31 is carried out thick timing based on Cyclic Prefix;
Step 32 is carried out thick timing offset statistics, obtains the error range of thick timing results;
Step 33 according to the error range of thick timing results, is confirmed minimum search window (minimum search window should comprise error range);
Step 34 is carried out integer frequency offset time domain peak distance and is calculated, and, confirms the position at false peak that is;
Step 35 is confirmed the maximum search window according to the position at false peak;
Step 36 is confirmed the actual search window according to minimum search window and the definite maximum search window of step 35 that step 33 is confirmed, and this actual search window can comprise minimum search window, and is contained in the maximum search window.
Wherein, step 31 can independently of one anotherly be carried out to 35 with step 34 to 33, that is, step 31 to 33 with step 34 to 35 being executed in parallel, also can be that sequencing is carried out.
By means of above-mentioned processing; Through to regularly and the reasonable limits of the ofdm signal search window estimated of fractional part of frequency offset through thick symbol; Can on the basis of the thick regularly scheme of existing OFDM symbol, combine PSS to carry out frequency offset estimating and accurate timing; The harmful effect that secondary lobe brought has been eliminated in the appearance of PSS secondary lobe when having avoided integer frequency offset.And because the window that search window is adopted in the correlation technique, treating capacity and Processing Test in the time of can effectively reducing each integer frequency offset and detect reduce the complexity of system.Above-mentioned processing not only can be issued to precision preferably in little frequency deviation, low noise situation, under the situation that has strong noise, big frequency deviation even integer frequency offset, still can access accurate sending and receiving end frequency offset estimating and timing results.
According to embodiments of the invention, a kind of frequency offset estimating and device regularly are provided also.
As shown in Figure 4, the frequency offset estimating according to the embodiment of the invention comprises with device regularly:
Processing mode one: detection module 44 is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset and fractional part of frequency offset estimated result; Carry out compensate of frequency deviation to received signal; And in search window, utilize predetermined local signal and the reception signal behind the compensate of frequency deviation to carry out computing cross-correlation, with the computing cross-correlation result as testing result; Perhaps
Processing mode two: detection module 44 is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset and fractional part of frequency offset estimated result; Local signal to predetermined carries out compensate of frequency deviation; And in search window, utilize behind the compensate of frequency deviation local signal with receive signal and carry out computing cross-correlation, with the computing cross-correlation result as testing result; Perhaps
Processing mode three: detection module 44 is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset that predetermined local signal is carried out the integer frequency offset compensation; And utilize the fractional part of frequency offset estimated result to carry out the fractional part of frequency offset compensation to received signal; Reception signal to after the compensation of the local signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as testing result; Perhaps
Processing mode four: detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset to carry out the integer frequency offset compensation to received signal; And utilize the fractional part of frequency offset estimated result that predetermined local signal is carried out the fractional part of frequency offset compensation; Local signal to after the compensation of the reception signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as testing result.
When first estimation module 42 is carried out the fractional part of frequency offset estimation to received signal based on the repetitive structure that receives signal and according to thick timing results; First estimation module 42 is used for the sampled point of the following sampled point set of deletion in the error range of thick timing results: { K; K+1; ...; K+N-1} and { K+L-N; K+L-N+1; ...; K+L-1}; Wherein, K is the pairing sampled point of thick timing results, [N; N] be the error range of thick timing results, L is the sampling number of repeating part in the repetitive structure that receives signal; And be used for based on the auto-correlation scheme reception signal after the sampled point deletion being carried out fractional part of frequency offset and estimate, obtain the decimal frequency bias estimated result.In addition, the search window of being confirmed by determination module 43 comprises thick timing error scope, and does not comprise false peak.
Fig. 4 is the device corresponding with previous methods, the processing of this device shown in equally can execution graph 1 to 3, and its course of work and operation principle are described in detail in the method part, repeat no more at this.
It should be noted that; Although with the LTE system and according to the OFDM symbol frequency offset estimating and process regularly are described before; But the present invention is not limited to this; In other system, can reach the purpose of frequency offset estimating and accurate timing equally based on above-mentioned processing procedure; For example; In the 802.11a system; Can carry out above-mentioned processing according to the short leader sequence and the long preambles sequence that repeat; And in other system; Those skilled in the art know the repeating part of signal equally; Therefore the detailed process in the other system is similar with the process of describing before, and this paper no longer details.
In sum; By means of technique scheme of the present invention, delete through the thick symbol of process is regularly carried out error, and search window is carried out reasonable limits; Can effectively improve frequency offset estimating and precision regularly, avoid false peak frequency offset estimating and influence regularly; And, under the situation of strong noise, big frequency deviation even integer frequency offset, still can access accurate sending and receiving end frequency offset estimating and timing results; In addition, because the window that search window is adopted in the correlation technique, treating capacity and Processing Test in the time of can effectively reducing each integer frequency offset and detect reduce the complexity of system.
The above only is preferred embodiment of the present invention, and is in order to restriction the present invention, not all within spirit of the present invention and principle, any modification of being done, is equal to replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (12)
1. frequency offset estimating and method regularly is characterized in that said method comprises:
Carry out thick timing to received signal according to thick timing scheme, obtain thick timing results;
Carry out the fractional part of frequency offset estimation based on the repetitive structure of said reception signal and according to said thick timing results, obtain the fractional part of frequency offset estimated result;
Search window is confirmed in the position at the false peak that causes according to the error range and the integer frequency offset of said thick timing results;
In said search window; Utilize said fractional part of frequency offset estimated result and at least one integer frequency offset that said reception signal is carried out integer frequency offset and detect, and obtain integer frequency offset estimated result and accurate timing result according to the integer frequency offset testing result.
2. method according to claim 1 is characterized in that, obtains the integer frequency offset estimated result and the accurate timing result comprises according to the integer frequency offset testing result:
Detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Said reception signal is carried out compensate of frequency deviation; And in said search window, utilize predetermined local signal and the said reception signal behind the compensate of frequency deviation to carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Local signal to predetermined carries out compensate of frequency deviation; And the said local signal after in said search window, utilizing compensate of frequency deviation and said reception signal carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset that predetermined local signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that said reception signal is carried out the fractional part of frequency offset compensation; Said reception signal to after the compensation of the local signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Detect each integer frequency offset that is adopted for carrying out integer frequency offset; Utilize this integer frequency offset that said reception signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that predetermined local signal is carried out the fractional part of frequency offset compensation; Local signal to after the compensation of the reception signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result.
3. method according to claim 1 is characterized in that, obtains the integer frequency offset estimated result and the accurate timing result comprises according to the integer frequency offset testing result:
Cross correlation value in the pairing testing result of all integer frequency offsets is compared; With the pairing integer frequency offset of the maximum cross-correlation value that relatively obtains as said integer frequency offset estimated result, and with the time location of said maximum cross-correlation value as said accurate timing result.
4. method according to claim 1 is characterized in that, according to said thick timing scheme said reception signal is carried out thick timing and comprises:
Based on the repetitive structure of said reception signal, according to said thick timing scheme said reception signal is carried out Autocorrelation Detection, obtain said thick timing results.
5. method according to claim 1 is characterized in that, based on the repetitive structure of said reception signal and according to said thick timing results said reception signal is carried out fractional part of frequency offset and estimate to comprise:
Sampled point in the error range of said thick timing results in the following sampled point set of deletion: { K; K+1 ..., K+N-1} and { K+L-N; K+L-N+1; ..., K+L-1}, wherein; K is the pairing sampled point of said thick timing results; [N, N] is the error range of said thick timing results, and L is the sampling number of repeating part in the repetitive structure of said reception signal;
Based on the auto-correlation scheme reception signal after the sampled point deletion is carried out fractional part of frequency offset and estimate, obtain said decimal frequency bias estimated result.
6. according to each described method in the claim 1 to 5, it is characterized in that the said search window of confirming comprises said thick timing error scope, and does not comprise said false peak.
7. frequency offset estimating and device regularly is characterized in that said device comprises:
Thick time block is used for carrying out thick timing to received signal according to thick regularly scheme, obtains thick timing results;
First estimation module is used for carrying out the fractional part of frequency offset estimation based on the repetitive structure of said reception signal and according to said thick timing results, obtains the fractional part of frequency offset estimated result;
Determination module, search window is confirmed in the position that is used for the false peak that error range and integer frequency offset according to said thick timing results cause;
Detection module is used in said search window, utilizes said fractional part of frequency offset estimated result and at least one integer frequency offset that said reception signal is carried out integer frequency offset and detects;
Second estimation module is used for obtaining integer frequency offset estimated result and accurate timing result according to the integer frequency offset testing result.
8. device according to claim 7 is characterized in that,
Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Said reception signal is carried out compensate of frequency deviation; And in said search window, utilize predetermined local signal and the said reception signal behind the compensate of frequency deviation to carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset and said fractional part of frequency offset estimated result; Local signal to predetermined carries out compensate of frequency deviation; And the said local signal after in said search window, utilizing compensate of frequency deviation and said reception signal carry out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset that predetermined local signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that said reception signal is carried out the fractional part of frequency offset compensation; Said reception signal to after the compensation of the local signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result; Perhaps
Said detection module is used for detecting each integer frequency offset that is adopted to carrying out integer frequency offset; Utilize this integer frequency offset that said reception signal is carried out the integer frequency offset compensation; And utilize said fractional part of frequency offset estimated result that predetermined local signal is carried out the fractional part of frequency offset compensation; Local signal to after the compensation of the reception signal behind the integer frequency offset compensation and fractional part of frequency offset carries out computing cross-correlation, with the computing cross-correlation result as said testing result.
9. device according to claim 7; It is characterized in that; Said second estimation module is used for the cross correlation value of the pairing testing result of all integer frequency offsets is compared; With the pairing integer frequency offset of the maximum cross-correlation value that relatively obtains as said integer frequency offset estimated result, and with the time location of said maximum cross-correlation value as said accurate timing result.
10. device according to claim 7 is characterized in that, said thick time block specifically is used for the repetitive structure based on said reception signal, according to said thick timing scheme said reception signal is carried out Autocorrelation Detection, obtains said thick timing results.
11. device according to claim 7; It is characterized in that; When said first estimation module is carried out the fractional part of frequency offset estimation based on the repetitive structure of said reception signal and according to said thick timing results to said reception signal; Said first estimation module is used for the sampled point of the following sampled point set of deletion in the error range of said thick timing results: { K; K+1; ...; K+N-1}; And K+L-N, K+L-N+1 ...; K+L-1}; Wherein, K is the pairing sampled point of said thick timing results, [N; N] be the error range of said thick timing results, L is the sampling number of repeating part in the repetitive structure of said reception signal; And be used for based on the auto-correlation scheme reception signal after the sampled point deletion being carried out fractional part of frequency offset and estimate, obtain said decimal frequency bias estimated result.
12., it is characterized in that the said search window of being confirmed by said determination module comprises said thick timing error scope, and does not comprise said false peak according to each described device in the claim 7 to 11.
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