CN104301264A - Frequency offset compensation method - Google Patents
Frequency offset compensation method Download PDFInfo
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- CN104301264A CN104301264A CN201310301204.4A CN201310301204A CN104301264A CN 104301264 A CN104301264 A CN 104301264A CN 201310301204 A CN201310301204 A CN 201310301204A CN 104301264 A CN104301264 A CN 104301264A
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Abstract
The present application discloses a frequency offset compensation method: predetermining a frequency offset value in a frequency offset range, calculating a corresponding frequency offset compensation sequence for each frequency offset value when the initial phase is zero, and recording in a mapping table of the frequency value and the frequency offset compensation sequence; when frequency offset compensation is necessary, estimating a carrier frequency offset; looking the mapping table for the frequency offset compensation sequence corresponding to the frequency offset estimate; conducting a corresponding vector multiplication by using the frequency offset compensation sequence and a time domain signal having a cyclic prefix removed, performing fast Fourier transform on the result, and performing a de-mapping operation on the result output after the transform so as to obtain a frequency domain subcarrier; for each OFDM symbol in the result output from the fast Fourier transform, calculating a complex exponential function according to a starting time of the OFDM symbol and the frequency offset estimate so as to obtain a phase error compensation value; and performing phase error compensation on the frequency domain subcarrier by using the compensation value. The present invention can reduce the calculation and storage overhead for frequency offset compensation.
Description
Technical field
The present invention relates to mobile communication technology, particularly relate to the frequency bias compensation method in a kind of OFDM (OFDM) wireless communication system.
Background technology
In OFDM wireless communication system, the carrier frequency synchronization between base station and terminal is extremely important.Due to the reason such as difference of base station crystal oscillator and terminal crystal oscillator, receiving end signal often also exists frequency deviation, has a strong impact on systematic function, therefore needs to carry out compensate of frequency deviation to received signal.
As shown in Figure 1, in existing OFDM wireless communication system, conventional processing method receiving end signal being transformed to frequency domain data comprises the following steps:
Step 101, compensate of frequency deviation is carried out to the time-domain signal received;
Step 102, Cyclic Prefix (CP) is gone to the time-domain signal after compensate of frequency deviation;
Step 103, to going the time-domain signal after CP to carry out 1/2nd sub-carrier offset process;
Step 104,1/2nd sub-carrier offset results are carried out to fast Fourier transform (FFT) process;
Step 105, subcarrier demapping is carried out to FFT result, obtain frequency domain data.
At present, the main method of carrying out compensate of frequency deviation is in a step 101: estimate carrier wave frequency deviation according to certain algorithm; According to the carrier wave frequency deviation value estimated, obtain compensate of frequency deviation sequence; Compensate of frequency deviation sequence is multiplied with time-domain received signal, carries out compensate of frequency deviation.
Wherein, for the acquisition of compensate of frequency deviation sequence, existing system adopts the method calculating complex exponential method or directly search the list of setting up in advance to realize.
For directly searching the method setting up list in advance, the list of wherein setting up in advance generally uses the sine value tabulation of first quartile, sin (n θ) can be expressed as, θ is the minimum phase in order to reach needed for frequency accuracy, θ=2 π f0/fs, fs is base band sampling rate, and f0 is for needing accurate minimum frequency; N is look-up table index, 0≤n≤N; N=(pi/2)/θ.In order to obtain the compensate of frequency deviation sequence that a length is N1, frequency is f1, first calculate Δ=f1/f0, interim look-up table index be [0,1,2 ...., N1] Δ; Be decided to be whole value because Δ differs, thus need to [0,1,2 ...., N1] computing of carrying out rounding up of each element in Δ obtains searching index sequence and is denoted as S (n), 0≤n≤N1.Need when calculating compensate of frequency deviation sequence to calculate sine and cosine value; if S (n)≤N; then this phase place is at first quartile; for sine value by under be designated as S (n) sin (n θ) value take out; for cosine value, then by under be designated as N-S (n) sin (n θ) value take out; If S (n) is >N, then resemble item to first, then computation of table lookup according to four quadrant sine and cosine relation transformation.
The method that above-mentioned employing is tabled look-up is look-up table index with n, and from obtaining n=pi/2/θ=fs/ (4f0) above.Fs and data transfer rate proportional, because modern communications data transfer rate is very high, fs is very large, and requires very high to frequency accuracy, and f0 is very little, and therefore, n value is more, and corresponding list item is more, carries out larger to the demand of internal memory.And adopt the complex exponential method that calculates, then can there is the very large problem of computing overhead.
Summary of the invention
In view of this, main purpose of the present invention is to provide a kind of frequency bias compensation method, and the method can reduce operand and the storage overhead of compensate of frequency deviation.
In order to achieve the above object, the technical scheme that the present invention proposes is:
A kind of frequency bias compensation method, comprising:
Pre-determine the frequency deviation value preset in frequency deviation region, for each described frequency deviation value, compensate of frequency deviation sequence corresponding when calculating first phase is zero, and be recorded in the mapping table of frequency deviation value and compensate of frequency deviation sequence, the length of described compensate of frequency deviation sequence is the length after OFDM symbol removes Cyclic Prefix;
When needs carry out compensate of frequency deviation, current carrier wave frequency deviation is estimated, obtain frequency deviation estimated value; Inquire about described mapping table, obtain the compensate of frequency deviation sequence that described frequency deviation estimated value is corresponding;
Whether process together with 1/2 sub-carrier offset according to compensate of frequency deviation, utilize the time-domain signal after the compensate of frequency deviation sequence and removal Cyclic Prefix obtained, carry out corresponding vector multiplication process;
Fast Fourier transform is carried out to described vector multiplication result, demapping operation is carried out to fast Fourier transform Output rusults, obtains subcarrier in frequency domain;
For each OFDM symbol in fast Fourier transform Output rusults, calculate according to the initial time of this OFDM symbol and described frequency deviation estimated value and refer to function again, obtain phase error compensation value, the described subcarrier in frequency domain utilizing described phase error compensation value corresponding to this OFDM symbol carries out phase error compensation.
In sum, the frequency bias compensation method that the present invention proposes, generates the map listing of frequency deviation value and compensate of frequency deviation sequence in advance; When carrying out compensate of frequency deviation, in described mapping table, directly searching compensate of frequency deviation sequence corresponding to the current frequency deviation calculated, this compensate of frequency deviation sequence can be obtained.Owing to being directly index with frequency deviation value in the map listing of described frequency deviation value and compensate of frequency deviation sequence, and the negligible amounts of this frequency deviation value, therefore relative to the method for traditional look-up table, the length of table is shorter, less to the overhead requirements of memory space, in addition, owing to adopting the method for tabling look-up to obtain compensate of frequency deviation sequence, therefore the expense of operand also can be less.
Accompanying drawing explanation
Fig. 1 is conventional process flow schematic diagram to received signal in existing OFDM wireless communication system;
Fig. 2 is the schematic flow sheet of the embodiment of the present invention one.
Embodiment
For making the object, technical solutions and advantages of the present invention clearly, the present invention is described in further detail below in conjunction with the accompanying drawings and the specific embodiments.
Core concept of the present invention is: turn to limited frequency deviation value by discrete for possible frequency deviation region in advance, and the compensate of frequency deviation sequence that when generation first phase is 0, each frequency deviation value is corresponding, sets up the map listing of frequency deviation value and compensate of frequency deviation sequence accordingly; When carrying out compensate of frequency deviation, in described mapping table, directly searching compensate of frequency deviation sequence corresponding to the current frequency deviation calculated, this compensate of frequency deviation sequence can be obtained.Owing to being directly index with frequency deviation value in the map listing of frequency deviation value here and compensate of frequency deviation sequence, and the negligible amounts of this frequency deviation value, therefore relative to the method for traditional look-up table, the length of table is shorter, less to the overhead requirements of memory space, in addition, owing to adopting the method for tabling look-up to obtain compensate of frequency deviation sequence, therefore the expense of operand also can be less.
Fig. 2 is the schematic flow sheet of the embodiment of the present invention one, and as shown in Figure 2, this embodiment mainly comprises:
Step 201, the frequency deviation value pre-determined in default frequency deviation region, for each described frequency deviation value, compensate of frequency deviation sequence corresponding when calculating first phase is zero, and being recorded in the mapping table of frequency deviation value and compensate of frequency deviation sequence, the length of described compensate of frequency deviation sequence is the length after OFDM symbol removes Cyclic Prefix.
In this step, in order to reduce the list item of list, to reach the object reducing memory cost, here, when building mapping table, directly provide the compensate of frequency deviation sequence that each frequency deviation value in frequency deviation region is corresponding, can take after this frequency deviation value as index entry, directly find out corresponding compensate of frequency deviation sequence.
In actual applications, compensate of frequency deviation can process together with 1/2 sub-carrier offset, also can process respectively with 1/2 sub-carrier offset, and determine under two kinds of different situations that the method for the frequency deviation value in default frequency deviation region is by different, preferably concrete grammar is as follows:
Suppose that described frequency deviation region is for [-Δ f
chz, Δ f
chz], Δ f is the frequency of 1/2 subcarrier, Δ f
0for the frequency deviation step-length preset.
If processed together with 1/2 sub-carrier offset by compensate of frequency deviation, then produce Δ f-Δ f
chz to Δ f+ Δ f
cthe compensate of frequency deviation sequence table of Hz, so can reduce operand further, and one has
individual compensate of frequency deviation value, the frequency deviation value namely in described frequency deviation region is
If do not processed together with 1/2 sub-carrier offset by compensate of frequency deviation, then produce 0Hz to Δ f
cthe sequence table of Hz, one has
individual compensate of frequency deviation value, the frequency deviation value namely in described frequency deviation region is
obvious the method can reduce the frequency deviation index value quantity of list further, thus can save memory cost further.
As can be seen from the above-mentioned preferred approach determining the frequency deviation value in default frequency deviation region, the frequency deviation value determined here is
or
individual, significantly can reduce the list item for searching compensate of frequency deviation sequence.
In addition, the length of the compensate of frequency deviation sequence in described mapping table is the length after OFDM symbol removes Cyclic Prefix, so can reduce computational complexity further.
Step 202, when needs carry out compensate of frequency deviation, current carrier wave frequency deviation to be estimated, obtain frequency deviation estimated value; Inquire about described mapping table, obtain the compensate of frequency deviation sequence that described frequency deviation estimated value is corresponding.
The frequency deviation of this step estimates the same existing system of concrete grammar, does not repeat them here.
Step 203, whether to process together with 1/2 sub-carrier offset according to compensate of frequency deviation, utilize the compensate of frequency deviation sequence that obtains and the time-domain signal after removing Cyclic Prefix, carry out corresponding vector multiplication process.
Preferably, this step specifically can adopt following method to realize:
When being processed together with 1/2 sub-carrier offset by compensate of frequency deviation, obtained compensate of frequency deviation sequence and the time-domain signal after removing Cyclic Prefix are carried out vector multiplication process;
When not processed together with 1/2 sub-carrier offset by compensate of frequency deviation, obtained compensate of frequency deviation sequence and the time-domain signal after removing Cyclic Prefix are carried out vector multiplication process; Vector multiplication process is carried out to this vector multiplication result and 1/2 sub-carrier offset table.
Described 1/2 sub-carrier offset table is default form, and the same existing system of concrete method to set up, does not repeat them here.
In above-mentioned two situations, concrete vector multiplication processing method is grasped by those skilled in the art, does not repeat them here.
Step 204, fast Fourier transform is carried out to described vector multiplication result, demapping operation is carried out to fast Fourier transform Output rusults, obtains subcarrier in frequency domain.
The those skilled in the art that are implemented as of this step grasped, and do not repeat them here.
Step 205, for each OFDM symbol handled by described fast Fourier transform, calculate according to the initial time of this OFDM symbol and described frequency deviation estimated value and refer to function again, obtain phase error compensation value, and the described subcarrier in frequency domain utilizing described phase error compensation value corresponding to this OFDM symbol carries out phase error compensation.
Here it should be noted that, due in the list preset provide the compensate of frequency deviation sequence that when first phase is 0, each frequency deviation value is corresponding, and the phase place of reality is not zero, therefore, needs further excute phase error compensation here.
Concrete phase error compensation method is grasped by those skilled in the art, does not repeat them here.
In sum, these are only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any amendment done, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (3)
1. a frequency bias compensation method, is characterized in that, comprising:
Pre-determine the frequency deviation value preset in frequency deviation region, for each described frequency deviation value, compensate of frequency deviation sequence corresponding when calculating first phase is zero, and be recorded in the mapping table of frequency deviation value and compensate of frequency deviation sequence, the length of described compensate of frequency deviation sequence is the length after OFDM symbol removes Cyclic Prefix;
When needs carry out compensate of frequency deviation, current carrier wave frequency deviation is estimated, obtain frequency deviation estimated value; Inquire about described mapping table, obtain the compensate of frequency deviation sequence that described frequency deviation estimated value is corresponding;
Whether process together with 1/2 sub-carrier offset according to compensate of frequency deviation, utilize the time-domain signal after the compensate of frequency deviation sequence and removal Cyclic Prefix obtained, carry out corresponding vector multiplication process;
Fast Fourier transform is carried out to described vector multiplication result, demapping operation is carried out to fast Fourier transform Output rusults, obtains subcarrier in frequency domain;
For each OFDM symbol handled by described fast Fourier transform, calculate according to the initial time of this OFDM symbol and described frequency deviation estimated value and refer to function again, obtain phase error compensation value, and the described subcarrier in frequency domain utilizing described phase error compensation value corresponding to this OFDM symbol carries out phase error compensation.
2. method according to claim 1, is characterized in that, describedly determines that the frequency deviation value in default frequency deviation region comprises:
When being processed together with 1/2 sub-carrier offset by compensate of frequency deviation, the frequency deviation value in described frequency deviation region is
When not processed together with 1/2 sub-carrier offset by compensate of frequency deviation, the frequency deviation value in described frequency deviation region is
Wherein, described frequency deviation region is [-Δ f
chz, Δ f
chz], described Δ f is the frequency of 1/2 subcarrier, described Δ f
0for the frequency deviation step-length preset.
3. method according to claim 2, is characterized in that, described in carry out corresponding vector multiplication process and comprise;
When being processed together with 1/2 sub-carrier offset by compensate of frequency deviation, obtained compensate of frequency deviation sequence and the time-domain signal after removing Cyclic Prefix are carried out vector multiplication process;
When not processed together with 1/2 sub-carrier offset by compensate of frequency deviation, obtained compensate of frequency deviation sequence and the time-domain signal after removing Cyclic Prefix are carried out vector multiplication process; Vector multiplication process is carried out to this vector multiplication result and 1/2 sub-carrier offset table.
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| CN112565131A (en) * | 2020-12-08 | 2021-03-26 | 上海擎昆信息科技有限公司 | Frequency offset compensation method and system |
| CN112637097A (en) * | 2020-12-25 | 2021-04-09 | 西安鼎研科技股份有限公司 | FPGA (field programmable Gate array) implementation method based on 5G large frequency offset phase compensation |
| WO2021072832A1 (en) * | 2019-10-17 | 2021-04-22 | 辰芯科技有限公司 | Channel flatness compensation method and apparatus, storage medium, baseband chip, and device |
| CN114430290A (en) * | 2022-01-13 | 2022-05-03 | 北京四季豆信息技术有限公司 | Residual sampling clock deviation compensation method and device based on BPLC system |
| CN115378780A (en) * | 2021-12-29 | 2022-11-22 | 比科奇微电子(杭州)有限公司 | Carrier aggregation method and device for carrier modulation signal and electronic equipment |
| CN117527497A (en) * | 2024-01-05 | 2024-02-06 | 中国电力科学研究院有限公司 | Frequency offset calibration method, device, electronic equipment and storage medium |
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| CN117527497B (en) * | 2024-01-05 | 2024-03-22 | 中国电力科学研究院有限公司 | Frequency offset calibration method, device, electronic equipment and storage medium |
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