CN115314349B - Frequency offset estimation method of wireless system - Google Patents
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Abstract
The invention discloses a frequency offset estimation method of a wireless system, and relates to the technical field of wireless communication. Receiving target data, preprocessing the target data, and calculating a signal-to-noise ratio estimated value of the target data; according to the signal-to-noise ratio estimation value and a preset threshold value, matching a frequency offset estimation algorithm for processing target data; if the signal-to-noise ratio estimated value is smaller than a preset threshold value, processing target data by using a first frequency offset estimation algorithm; and if the signal-to-noise ratio estimated value is not smaller than the preset threshold value, processing the target data by using a second frequency offset estimation algorithm. The method solves the problem of poor accuracy and precision of frequency offset estimation when the signal-to-noise ratio is low and frequency offset is small, and is switched to a frequency offset estimation algorithm with higher precision in the environment of poor signal-to-noise ratio, so that the accuracy of the frequency offset estimation algorithm is effectively improved, the communication performance of a wireless system is enhanced, the effect similar to or even better than that of multiple phase angle calculation and average value calculation can be achieved through one-time phase angle calculation, and the module calculation cost and calculation time are reduced.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a frequency offset estimation method of a wireless system.
Background
The power line dual-mode communication system combines two modes of power line carrier communication and wireless communication, and has important application in scenes such as intelligent home, intelligent ammeter and the like. The wireless system is mainly applied to a collection blind zone of power line carrier communication, and data is transmitted through a wireless space by adopting an OFDM modulation technology. OFDM technology is a modulation method that can effectively combat multipath channel fading. However, in the OFDM modulation and demodulation system, the carrier frequency offset generated by the incomplete matching of local oscillators at the two ends of the transceiver and the nonlinearity or doppler shift of the wireless channel may reduce the signal amplitude, generate phase distortion, and destroy the orthogonality between OFDM sub-carriers, thereby causing inter-carrier interference, resulting in the loss of signal to noise ratio. Thus, OFDM modulation is sensitive to carrier frequency offset, and small frequency offsets can severely degrade system performance.
If the frequency offset can be accurately estimated and compensated, the performance of the wireless system is greatly improved, so that the estimation performance of the carrier frequency offset is a key factor affecting the communication system. A wireless communication system in the dual-mode communication system designs a special training sequence before signals, and can be used for position synchronization, frequency offset estimation and the like. However, the power line dual-mode communication system has complex and changeable environment, wide frequency offset range, large signal-to-noise ratio variation range, and relatively limited accuracy and precision of estimating frequency offset by using a common frequency estimation scheme, and does not consider the influence of error of frame synchronization results and the existence of more high-complexity calculation.
Disclosure of Invention
The present invention aims to solve the above-mentioned problems of the background art, and provides a frequency offset estimation method for a wireless system.
The aim of the invention can be achieved by the following technical scheme:
the embodiment of the invention provides a frequency offset estimation method of a wireless system, wherein a preamble structure of a physical layer protocol data unit (PPDU) comprises a Short Training Field (STF) and a Long Training Field (LTF), and the method is applied to the physical layer of the wireless communication system and comprises the following steps:
receiving target data, preprocessing the target data, and calculating a signal-to-noise ratio estimated value of the target data; the target data accords with a preamble structure of the PPDU;
according to the signal-to-noise ratio estimation value and a preset threshold value, matching and processing a frequency offset estimation algorithm of the target data;
if the signal-to-noise ratio estimated value is smaller than a preset threshold value, a first frequency offset estimation algorithm is used for processing the target data; the first frequency offset estimation algorithm is a high-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the STF in the target data and calculating phase angle values, and frequency offset values are calculated according to the relation between the phase angle values and the frequency offset values;
if the signal-to-noise ratio estimation value is not smaller than a preset threshold value, a second frequency offset estimation algorithm is used for processing the target data; the second frequency offset estimation algorithm is a low-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the LTF in the target data and calculating a phase angle value, and calculating a frequency offset value according to the relation between the phase angle and the frequency offset value.
Optionally, receiving target data, preprocessing the target data, and calculating a signal-to-noise ratio estimated value of the target data, including:
receiving target data, and intercepting data R with preset length of the target data at a preset position test ；
Calculating R test Power P of (2) sn ：
Wherein X is R test Is a length of (2);
estimating signal-to-noise ratio SNR of the target data esti ：
Alternatively, R test And the target data is data with the FFT period length of 0.5 to the FFT period length of 1.5 after the frame synchronization position.
Optionally, processing the target data using a first frequency offset estimation algorithm includes:
intercepting a target signal frame in the target data according to a frame synchronization position;
intercepting a first part of symbols of the STF at a first preset position in a target signal frame, and intercepting a second part of symbols of the STF at a second preset position in the target signal frame according to the current mode of a physical layer of a wireless communication system;
conjugation is taken for the second part of symbols, the second part of symbols are multiplied with corresponding points in the first part of symbols in sequence, and then the point multiplication results are summed to obtain a correlation value:
wherein s is 1i A value s representing the i-th sample point in the first partial symbol 2i A value representing the ith sample point in the second partial symbol, L being the first partial symbolThe total number of sampling points;
calculating an angle value corresponding to the correlation value:
phase_s＝angle(cor_s)
calculating a corresponding frequency offset value according to the angle value:
wherein d=nl, n is the number of space symbols between the first partial symbol and the second partial symbol, T s Is the sampling period.
Optionally, the STF includes n STF The s symbols; the modes of the physical layer of the wireless communication system include a first mode, a second mode, and a third mode; when the physical layer of the wireless communication system is in the first mode, n STF 40 and n is 32; when the physical layer of the wireless communication system is in the second mode, n STF 20, n is 15; when the physical layer of the wireless communication system is in the third mode, n STF 10, n is 7; the first part of symbols are 2 s symbols of the STF, and the second part of symbols are n+2th s symbols of the STF.
Optionally, processing the target data using a second frequency offset estimation algorithm includes:
intercepting a target signal frame in the target data according to a frame synchronization position;
according to the current mode of a physical layer of the wireless communication system, intercepting a third part of symbols of the LTF in a third preset position in a target signal frame, and intercepting a fourth part of symbols of a fourth preset position of the LTF in the target signal frame;
conjugation is taken for the fourth part of symbols, the fourth part of symbols are multiplied with corresponding points in the third part of symbols in sequence, and then the point multiplication results are summed to obtain a correlation value:
wherein l 1i Representing the third partial symbolThe value of the i-th sampling point, l 2i A value representing the i-th sampling point in the fourth partial symbol, M being the total number of sampling points in the third partial symbol;
calculating an angle value corresponding to the correlation value:
phase_l＝angle(cor_l)
calculating a corresponding frequency offset value according to the angle value:
wherein n=2m is the interval between the third partial symbol and the fourth partial symbol, T s Is the sampling period.
Alternatively, one LTF symbol contains two lengths of 0.5N FFT Denoted as a and B, respectively, the LTF consists of 5 sub-symbols in the order BABAB; the modes of the physical layer of the wireless communication system include a first mode, a second mode, and a third mode; when the physical layer of the wireless communication system is respectively in the first mode, the second mode and the third mode, N FFT 128, 64 and 32, respectively; the third partial symbol is two sub-symbols a in the LTF.
The embodiment of the invention provides a frequency offset estimation method of a wireless system, wherein a preamble structure of a physical layer protocol data unit (PPDU) comprises a Short Training Field (STF) and a Long Training Field (LTF), and the method is applied to the physical layer of the wireless communication system and comprises the steps of receiving target data, preprocessing the target data and calculating a signal to noise ratio estimated value of the target data; the target data conforms to the frame structure of the PPDU; according to the signal-to-noise ratio estimation value and a preset threshold value, matching a frequency offset estimation algorithm for processing target data; if the signal-to-noise ratio estimated value is smaller than a preset threshold value, processing target data by using a first frequency offset estimation algorithm; the first frequency offset estimation algorithm is a high-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the STF in the target data and calculating phase angle values, and calculating frequency offset values according to the relation between the phase angle values and the frequency offset values; if the signal-to-noise ratio estimated value is not smaller than the preset threshold value, processing target data by using a second frequency offset estimation algorithm; the second frequency offset estimation algorithm is a low-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the LTF in the target data and calculating a phase angle value, and calculating a frequency offset value according to the relation between the phase angle and the frequency offset value. The frequency offset estimation method solves the problem that the traditional frequency offset estimation method has poor accuracy and precision when the frequency offset estimation method has low signal to noise ratio and small frequency offset, and is switched to the frequency offset estimation algorithm with higher precision in the environment with poor signal to noise ratio, thereby effectively improving the precision of the frequency offset estimation algorithm, enhancing the communication performance of a wireless system, achieving the effect similar to or even better than the average value of multiple phase angle calculation through one-time phase angle calculation and reducing the module calculation cost and calculation time.
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The invention is further described below with reference to the accompanying drawings.
Fig. 1 is a preamble structure diagram of a PPDU frame of a wireless physical layer of power dual mode communication;
fig. 2 is a block diagram of an STF in an STF mode of a wireless physical layer of power dual mode communication;
fig. 3 is a flowchart of a method for estimating frequency offset of a wireless system according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of a first frequency offset estimation algorithm used to intercept a target signal frame in target data;
fig. 5 is a schematic diagram of a second frequency offset estimation algorithm used to intercept a target signal frame in target data.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
In the prior art, a corresponding training sequence is designed for a wireless signal at a frame head in power dual-mode communication, and is used for estimating factors such as frequency offset and the like which influence system performance. The complete PPDU (Physical Layer Protocal Data Unit, physical layer protocol data unit) frame structure is composed of an STF (Short Training Field ), an LTF (Long Training Field, long training field), a PHR (Physical Header), SIG (PHR Control Signal, PHR control word) and a PSDU (PHY Service Data Unit, physical layer service data unit), wherein the STF and the LTF constitute a preamble of the PPDU, as shown in fig. 1.
The wireless physical layer of the power dual mode communication has three STF modes, for example, mode three, and the internal structure of the STF is shown in fig. 2. STF comprises n STF S symbols, n in three modes STF The values are respectively 40, 20 and 10, and a single s symbol corresponds to 1/8, 1/4 and 1/2 FFT period lengths.
In order to calculate the frequency offset estimation value of a signal carrier, firstly, the first s symbol and the second s symbol are intercepted to carry out conjugate correlation, the phase angle of the correlation value is sequentially calculated, then the average value is obtained, and the frequency offset value is calculated by the phase angle average value, wherein the specific formula is as follows:
wherein s is 1 S is the 1 st s symbol in STF 2 S is the nth s symbol in STF 1i The sign s 1 The i-th sampling point in (1), L is s 1 Total number of sampling points T s Is the sampling period.
The frequency offset range that mode three can estimate in this scheme is [ -f c ,f c ) When the signal-to-noise ratio is low, the estimation accuracy of the scheme is low, the estimated value of each point has larger fluctuation in the frequency deviation range which can be estimated, the number of sampling points in s symbols is smaller, the accuracy is low, and the average value of the estimation result is disabled. The remaining frequency offset between the estimated value and the actual frequency offset value will have a serious impact on the communication system.
The embodiment of the invention provides a frequency offset estimation method of a wireless system. Referring to fig. 3, fig. 3 is a flowchart of a method for estimating frequency offset of a wireless system according to an embodiment of the present invention. The preamble structure of the physical layer protocol data unit PPDU includes a short training field STF and a long training field LTF, and the method applied to the physical layer of the wireless communication system may include the steps of:
s301, receiving target data, preprocessing the target data, and calculating a signal-to-noise ratio estimated value of the target data.
S302, matching a frequency offset estimation algorithm for processing target data according to the signal-to-noise ratio estimation value and a preset threshold value.
S303, if the signal-to-noise ratio estimation value is smaller than a preset threshold value, processing target data by using a first frequency offset estimation algorithm.
S304, if the signal-to-noise ratio estimation value is not smaller than a preset threshold value, processing the target data by using a second frequency offset estimation algorithm.
The first frequency offset estimation algorithm is a high-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the STF in the target data and calculating phase angle values, and calculating frequency offset values according to the relation between the phase angle values and the frequency offset values; the second frequency offset estimation algorithm is a low-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the LTF in the target data and calculating a phase angle value, and calculating a frequency offset value according to the relation between the phase angle and the frequency offset value.
The target data conforms to the preamble of the PPDU.
The frequency offset estimation method of the wireless system solves the problem that the frequency offset estimation accuracy and precision are poor when the traditional frequency offset estimation method is used for carrying out small frequency offset with low signal to noise ratio, and is switched to a frequency offset estimation algorithm with higher precision in the environment with poor signal to noise ratio, so that the precision of the frequency offset estimation algorithm is effectively improved, the communication performance of the wireless system is enhanced, the effect similar to or even better than that of repeatedly calculating phase angles and then taking an average value can be achieved through one-time phase angle calculation, and the module calculation cost and calculation time are reduced.
In one embodiment, step S301 may include the steps of:
step one, receiving target data, and intercepting data R with preset length of the target data at a preset position test 。
Step two, R is calculated test Power P of (2) sn ：
Wherein X is R test Is a length of (2);
estimating the signal-to-noise ratio SNR of the target data esti ：
In one embodiment, R test The target data is data with 0.5FFT cycle length to 1.5FFT cycle length after the frame synchronization position.
In one implementation, using a signal at 0.5FFT period length to 1.5FFT period length can enhance the synchronization error tolerance of the system.
In one embodiment, processing target data using a first frequency offset estimation algorithm includes:
step one, intercepting a target signal frame in target data according to a frame synchronization position.
And step two, intercepting a first part of symbols of the STF in a first preset position in the target signal frame, and intercepting a second part of symbols of the STF in a second preset position in the target signal frame according to the current mode of a physical layer of the wireless communication system.
Step three, conjugate is taken for the second part of symbols, and the conjugate is multiplied with the corresponding points in the first part of symbols in sequence, and then the point multiplication results are summed to obtain a correlation value:
wherein s is 1i A value representing the i-th sample point in the first partial symbol, s 2i And a value representing the i-th sampling point in the second part of the symbols, and L is the total number of sampling points in the first part of the symbols.
Step four, calculating an angle value corresponding to the correlation value:
phase_s＝angle(cor_s)
calculating a corresponding frequency offset value according to the angle value:
wherein d=nl, n is the number of interval symbols between the first partial symbol and the second partial symbol, T s Is the sampling period.
In one embodiment, n is included in the STF STF The s symbols; the modes of the physical layer of the wireless communication system include a first mode, a second mode, and a third mode; when the physical layer of the wireless communication system is in the first mode, n STF 40 and n is 32; when the physical layer of the wireless communication system is in the second mode, n STF 20, n is 15; when the physical layer of the wireless communication system is in the third mode, n STF 10, n is 7; the first part of symbols are the 2 s symbols of the STF, and the second part of symbols are the n+2th s symbols of the STF.
In one implementation, referring to fig. 4, fig. 4 is a schematic diagram of a first frequency offset estimation algorithm used to intercept a target signal frame in target data. The first part is denoted by s in FIG. 4 1 The second part is denoted by s in FIG. 4 2 。
In one embodiment, processing the target data using a second frequency offset estimation algorithm includes:
step one, intercepting a target signal frame in target data according to a frame synchronization position.
And step two, according to the current mode of the physical layer of the wireless communication system, intercepting a third part of symbols of the LTF in a third preset position in the target signal frame, and intercepting a fourth part of symbols of the LTF in a fourth preset position in the target signal frame.
Step three, conjugation is taken for the fourth part of symbols, the conjugation is multiplied with corresponding points in the third part of symbols in sequence, and then the point multiplication results are summed to obtain a correlation value:
wherein l 1i A value representing the i-th sample point in the third partial symbol, l 2i And representing the value of the ith sampling point in the fourth part of symbols, and M is the total number of sampling points in the third part of symbols.
Step three, calculating an angle value corresponding to the correlation value:
phase_l＝angle(cor_l) (7)
calculating a corresponding frequency offset value according to the angle value:
wherein n=2m is the interval between the third partial symbol and the fourth partial symbol, T s Is the sampling period.
In one embodiment, one LTF symbol includes two symbols of length 0.5N FFT Denoted as a and B, respectively, the LTF consists of 5 sub-symbols in the order BABAB; the modes of the physical layer of the wireless communication system include a first mode, a second mode, and a third mode; when the physical layer of the wireless communication system is respectively in the first mode, the second mode and the third mode, N FFT 128, 64 and 32, respectively; the third partial symbol is two sub-symbols a in the LTF.
In one implementation, referring to fig. 5, fig. 5 is a schematic diagram of a second frequency offset estimation algorithm used to intercept a target signal frame in target data. The third part is denoted by l in FIG. 5 1 The fourth part is denoted by l in FIG. 5 2 。
The foregoing describes one embodiment of the present invention in detail, but the description is only a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. All equivalent changes and modifications within the scope of the present invention are intended to be covered by the present invention.
Claims (6)
1. The method is applied to a physical layer of a wireless communication system and comprises the following steps:
receiving target data, preprocessing the target data, and calculating a signal-to-noise ratio estimated value of the target data; the target data accords with a preamble structure of the PPDU;
according to the signal-to-noise ratio estimation value and a preset threshold value, matching and processing a frequency offset estimation algorithm of the target data;
if the signal-to-noise ratio estimated value is smaller than a preset threshold value, a first frequency offset estimation algorithm is used for processing the target data; the first frequency offset estimation algorithm is a high-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the STF in the target data and calculating phase angle values, and frequency offset values are calculated according to the relation between the phase angle values and the frequency offset values;
if the signal-to-noise ratio estimation value is not smaller than a preset threshold value, a second frequency offset estimation algorithm is used for processing the target data; the second frequency offset estimation algorithm is a low-precision frequency offset estimation algorithm and is used for taking conjugate correlation sums of partial symbols of the LTF in the target data and calculating a phase angle value, and calculating a frequency offset value according to the relation between the phase angle and the frequency offset value;
receiving target data, preprocessing the target data, and calculating a signal-to-noise ratio estimated value of the target data, wherein the method comprises the following steps:
receiving target data, and intercepting data R with preset length of the target data at a preset position test ；
Calculating R test Power P of (2) sn ：
Wherein X is R test Is a length of (2);
estimating signal-to-noise ratio SNR of the target data esti ：
2. The method of frequency offset estimation for a wireless system of claim 1, wherein R test And the target data is data with the FFT period length of 0.5 to the FFT period length of 1.5 after the frame synchronization position.
3. The method of frequency offset estimation in a wireless system of claim 1, wherein processing the target data using a first frequency offset estimation algorithm comprises:
intercepting a target signal frame in the target data according to a frame synchronization position;
intercepting a first part of symbols of the STF at a first preset position in a target signal frame, and intercepting a second part of symbols of the STF at a second preset position in the target signal frame according to the current mode of a physical layer of a wireless communication system;
conjugation is taken for the second part of symbols, the second part of symbols are multiplied with corresponding points in the first part of symbols in sequence, and then the point multiplication results are summed to obtain a correlation value:
wherein s is 1i A value s representing the i-th sample point in the first partial symbol 2i A value representing the i-th sampling point in the second partial symbol, L being the total number of sampling points in the first partial symbol;
calculating an angle value corresponding to the correlation value:
phase_s＝angle(cor_s)
calculating a corresponding frequency offset value according to the angle value:
wherein d=nl, n is the number of space symbols between the first partial symbol and the second partial symbol, T s Is the sampling period.
4. A method for frequency offset estimation in a wireless system as defined in claim 3, wherein,
the STF comprises n STF The s symbols; the modes of the physical layer of the wireless communication system include a first mode, a second mode, and a third mode; when the physical layer of the wireless communication system is in the first mode, n STF 40 and n is 32; when the physical layer of the wireless communication system is in the second mode, n STF 20, n is 15; when the physical layer of the wireless communication system is in the third mode, n STF 10, n is 7; the first part of symbols are 2 s symbols of the STF, and the second part of symbols are n+2th s symbols of the STF.
5. The method of frequency offset estimation in a wireless system of claim 1, wherein processing the target data using a second frequency offset estimation algorithm comprises:
intercepting a target signal frame in the target data according to a frame synchronization position;
according to the current mode of a physical layer of the wireless communication system, intercepting a third part of symbols of the LTF in a third preset position in a target signal frame, and intercepting a fourth part of symbols of a fourth preset position of the LTF in the target signal frame;
conjugation is taken for the fourth part of symbols, the fourth part of symbols are multiplied with corresponding points in the third part of symbols in sequence, and then the point multiplication results are summed to obtain a correlation value:
wherein l 1i A value representing the i-th sample point in the third partial symbol, l 2i A value representing the i-th sampling point in the fourth partial symbol, M being the total number of sampling points in the third partial symbol;
calculating an angle value corresponding to the correlation value:
phase_l＝angle(cor_l)
calculating a corresponding frequency offset value according to the angle value:
wherein n=2m is the interval between the third partial symbol and the fourth partial symbol, T s Is the sampling period.
6. The method for estimating frequency offset of a wireless system according to claim 5, wherein,
one LTF symbol contains two lengths of 0.5N FFT Denoted as a and B, respectively, the LTF consists of 5 sub-symbols in the order BABAB; the modes of the physical layer of the wireless communication system include a first mode, a second mode, and a third mode; when the physical layer of the wireless communication system is respectively in the first mode, the second mode and the third mode, N FFT 128, 64 and 32, respectively; the third partial symbol is two sub-symbols a in the LTF.
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| CN109150784A (en) * | 2017-06-28 | 2019-01-04 | 大唐移动通信设备有限公司 | A kind of frequency deviation estimating method and device |
| CN110868368A (en) * | 2019-11-18 | 2020-03-06 | 紫光展锐(重庆)科技有限公司 | Channel estimation method, system, electronic device, and medium |
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