CN111865854B - Frame capturing and synchronizing method of burst OFDM system - Google Patents
Frame capturing and synchronizing method of burst OFDM system Download PDFInfo
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- CN111865854B CN111865854B CN201910344777.2A CN201910344777A CN111865854B CN 111865854 B CN111865854 B CN 111865854B CN 201910344777 A CN201910344777 A CN 201910344777A CN 111865854 B CN111865854 B CN 111865854B
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- H04L27/26—Systems using multi-frequency codes
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- H—ELECTRICITY
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Abstract
The invention discloses a frame capturing and synchronizing method of a burst OFDM system, which comprises the following steps: according to sampling time to continuous N D Performing cross-correlation operation on the data of two sampling points with a first preset value at interval between groups, and performing cross-correlation operation on N D Summing the results of the cross-correlation operations to obtain a first result, and calculating N according to the sampling time D Summing the power of the data of the sampling points to obtain a second result; calculating a normalized correlation coefficient rho of the current sampling time n according to the M first results and the M second results; if the normalized correlation coefficient rho meets the preset condition, recording the current sampling time n as a first time, and recording the normalized correlation coefficient at the time as a first coefficient; and if the preset condition is not met and the first coefficient is not 0, recording the current first time as the frame synchronization time. The frame capturing and synchronizing method of the burst OFDM system provided by the embodiment can meet the capturing probability and precision requirements in a wide signal-to-noise ratio range, and reduce the processing delay.
Description
Technical Field
The present invention relates to an OFDM system, and more particularly, to a frame acquisition and synchronization method for a burst OFDM system.
Background
Currently, more and more communication systems have the characteristic of burst mode, and Orthogonal Frequency Division Multiplexing (OFDM) is a multi-carrier modulation method, which can resist Frequency selective fading channel, and has the advantages of high spectrum efficiency and simple channel equalization, so that it is widely applied to the standards of IEEE802.11 and 802.15.4g, etc. For a burst OFDM system, the primary task of the receiving end is to detect frame synchronization. The frame synchronization is used for detecting the arrival of a frame in a burst system; the role of symbol timing synchronization is to find the exact symbol boundaries in order to demodulate the data correctly. In a bursty OFDM system, there is a standard preamble at the beginning of each frame. The preamble comprises a plurality of identical short training sequences STF and a plurality of identical long training sequences LFT, and is mainly used for frame synchronization, AGC, carrier frequency offset estimation, symbol timing synchronization and channel estimation.
The existing burst OFDM system often uses repeated short training sequences to help the receiving end to perform synchronization acquisition. The scheme uses sliding autocorrelation operation, and in a certain initial frequency deviation range, when a receiving window slides to the initial position of a repeated signal, the autocorrelation amplitude reaches the maximum, and at the moment, the angle of an autocorrelation value can be used for initial frequency deviation estimation.
Based on this, the inventor of the present application finds that the existing synchronization acquisition method based on short training sequences usually works under the condition of relatively large signal-to-noise ratio, and when the signal-to-noise ratio of the expected system work is lower than 0dB and a wide signal-to-noise ratio range is considered, such as from minus several dB to 30dB, the acquisition probability and accuracy of the existing scheme are difficult to meet the requirements.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.
Disclosure of Invention
The invention aims to provide a frame capturing and synchronizing method of a burst OFDM system, which can improve the capturing probability and accuracy in a wide signal-to-noise ratio range.
In order to achieve the above object, the present invention provides a frame capturing and synchronizing method for a burst OFDM system, comprising: sampling the data processed by the receiver to obtain a plurality of sampling points; according to the sampling time N, continuous N D Performing cross-correlation operation on the data of two sampling points with a first preset value at interval between the two sampling points, and performing cross-correlation operation on the data of the two sampling points with the first preset value N D Summing the results of the cross-correlation operations to obtain a first result, wherein N is D The first preset value is N for the length of the repeated short training sequence D Multiple of (1), n = n 0 +2N D -1,n 0 +2N D -1+k,…，n 0 K is a positive integer at the initial sampling moment; calculating the N according to the sampling time N D Summing the power of the data of the sampling points to obtain a second result; repeating the calculation of the first result and the second result to obtain M first results and M second results, wherein M is a positive integer; according to the M first results A S (n) and the M second results B 0S (n) calculating a normalized correlation coefficient rho of the current sampling moment n; if the normalized correlation coefficient rho meets the preset condition, recording the current sampling moment n as a first moment n STF And recording the normalized correlation coefficient at the moment as a first coefficient rho STF Wherein the preset conditions include: greater than a predetermined threshold value p t And is not less than the current first coefficient rho STF The first coefficient p STF Is 0; if the preset condition is not met, and the first coefficient rho is STF If not 0, recording the current first time n STF For synchronizing time of frame
In a preferred embodiment, the calculating the normalized correlation coefficient p of the current sampling time according to the M first summation results and the M second summation results includes: calculating the normalized correlation coefficient of the current sampling time according to a first formula, wherein the first formula is as follows:
n＝n 0 +2N D -1,n 0 +2N D -1+k,…。
in a preferred embodiment, the frame capturing and synchronizing method further includes: according to the frame synchronization time
And performing phase estimation by using a second formula:
where Δ f is the subcarrier spacing of the OFDM system, and N is the length of the FFT sequence of the OFDM system.
In a preferred embodiment, k is 1.
In a preferred embodiment, k is
G is a positive integer greater than 1.
In a preferred embodiment, the current sampling time n is recorded as a first time n STF And recording the normalized correlation coefficient at the moment as a first coefficient rho STF Then, the method also comprises the following steps: when the time interval of the sampling time is gN D And repeating the calculation of the normalized correlation coefficient rho, wherein g is a positive number smaller than 1 or an integer larger than or equal to 1.
Compared with the prior art, the frame capturing and synchronizing method of the burst OFDM system provided by the invention is used for continuously acquiring N according to the sampling time N D Performing cross-correlation operation on the data of two sampling points with a first preset value at interval between groups, and performing cross-correlation operation on N D Summing the results of the cross-correlation operation to obtainTo a first result; calculating N according to the sampling time N D Summing the power of the data of each sampling point to obtain a second result; calculating a normalized correlation coefficient rho of the current sampling time n according to the M first results and the M second results; if the normalized correlation coefficient rho meets the preset condition, recording the current sampling time n as a first time, and recording the normalized correlation coefficient at the time as a first coefficient; if the preset condition is not met and the first coefficient is not 0, recording the current first moment as a frame synchronization moment, meeting the requirements of capture probability and precision in a wide signal-to-noise ratio range, and reducing the processing time delay.
Drawings
Fig. 1 is a flowchart of a frame acquisition and synchronization method of a burst OFDM system according to an embodiment of the present invention.
Fig. 2 is a simulation result of a frame acquisition and synchronization method of a burst OFDM system under AWGN according to an embodiment of the present invention.
Fig. 3 is a simulation result of a frame acquisition and synchronization method of a burst OFDM system under ETU according to an embodiment of the present invention.
Detailed Description
The following detailed description of the present invention is provided in conjunction with the accompanying drawings, but it should be understood that the scope of the present invention is not limited to the specific embodiments.
Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.
Fig. 1 is a flow chart of a frame acquisition and synchronization method of a burst OFDM system according to a preferred embodiment of the present invention, which includes steps S1-S6.
And S1, the receiver samples the processed data to obtain a plurality of sampling points.
Specifically, the receiver down-samples the received signal to baseband data after the received signal is processed by an antenna, a radio frequency front end, carrier down-conversion, AD, digital filtering, and the like. The sampling points are sampling points of baseband data.
S2, according to the sampling time N, continuous N is processed D Performing cross-correlation operation on the data of two sampling points with a first preset value at interval between the two sampling points, and performing cross-correlation operation on the data of the two sampling points with the first preset value N D Summing the results of the cross-correlation operation to obtain a first result A (N), wherein the first preset value is N D Multiples of (a).
Specifically, the calculation can be performed according to the following formula.
Wherein, N D For the length of the repeated short training sequence, n = n 0 +2N D -1,n 0 +2N D -1+k,…，n 0 K is a positive integer at the starting sampling instant.
S3, calculating the N according to the sampling time N D The power of the data of each sampling point is summed to obtain a second result B 0 (n)。
Specifically, the calculation can be performed according to the following formula.
And repeating the calculation of the first result and the second result to obtain M first results and M second results, wherein M is a positive integer.
The specific calculation can be performed according to the following formula.
n＝n 0 +2N D -1,n 0 +2N D -1+k,…
It should be noted that n may be initialized from n to satisfy the above formula 0 +2N D +(M-1)N D 1 starts.
Step S4, according to the M first results A S (n) and the M second results B 0S (n) calculating a normalized correlation coefficient ρ for the current sampling instant n.
Calculating the normalized correlation coefficient of the current sampling time according to a first formula:
n＝n 0 +2N D -1,n 0 +2N D -1+k,…
it should be noted that n may be initialized from n to satisfy the above formula 0 +2N D +(M-1)N D 1 starts.
In this embodiment, the step k may be 1. Or step k is
G is a positive integer greater than 1. Sliding iterative operation is performed at each baseband sampling time, and only the interval is stored
The intermediate variable and the operation judgment of the baseband sampling data moment can save the intermediate data storage amount in the operation process.
Step S5, if the normalized correlation coefficient rho meets the preset condition, recording the current sampling moment n as a first moment n STF And recording the normalized correlation coefficient at the moment as a first coefficient rho STF Wherein the preset conditions include: greater than a predetermined threshold value p t And is not less than the current first coefficient rho STF The first coefficient p STF Is 0.
Wherein, in order to reduce the influence of noise and interference, the comparison can be performed in the first stepCoefficient rho STF The first is multiplied by a factor close to 1.0.
S6, if the preset condition is not met, the first coefficient rho STF If not 0, recording the current first time n STF For synchronizing time of frame
(i.e., the tail of the positive repeat sequence of the STF).
After step S5, the method may further include: when the time interval of the sampling time is gN D And repeating the calculation of the normalized correlation coefficient by the S2-S5, wherein g is a positive number less than 1 or an integer more than or equal to 1.
If the time interval of the sampling time is gN D If the normalized correlation coefficient meets the preset condition, the current sampling time is used to the first time n STF Is updated using the normalized correlation coefficient at that time to the first coefficient ρ STF And (6) updating.
In this embodiment, the method is implemented in a sliding manner. Specifically, the method can be realized by the following steps: repeating the steps S2-S4 to calculate each time one data sampling point slides, and repeating the sliding calculation until M N is obtained D The sum of the cross-correlations and the sum of the powers. At M x N D Extracting M of the cross-correlation summation results at time intervals as a first result, at M N D In the summation result of the powers according to N D And extracting M at intervals as a second result.
The calculation of the normalized correlation coefficient ρ of the current sampling time n can be determined by setting a first preset condition and a second preset condition, respectively. Specifically, if the normalized correlation coefficient ρ satisfies a first preset condition, it is determined that the frame signal detection is passed, and the current sampling time n is recorded as a first time n STF (0) And recording the normalized correlation coefficient at the moment as a first coefficient rho STF (0) While recording A S (n) for subsequent frequency offset estimation, wherein the first predetermined condition comprises: greater than a predetermined threshold value p t 。
If the frame signal is judged to be detectedIf so, the sliding is continued, the process is repeated, and the first time n is recorded STF (0)+N D The normalized correlation coefficient p is calculated in the same way at the sampling time, and the normalized correlation coefficient p at this time is compared with the normalized correlation coefficient p recorded before the normalized correlation coefficient p STF (0) Whether the relationship between the two conditions meets a second preset condition is determined, wherein the second preset condition comprises the following steps: greater than a predetermined threshold value p t Not less than the first coefficient p of the previous recording STF (0) Multiplied by a factor close to 1.0.
If the preset condition II is met, recording the current sampling moment n as the updated first moment n STF (1) And recording the normalized correlation coefficient at the moment as an updated first coefficient rho STF (1) Continuing to slide forward, repeating the above process, at the first moment n of the update of the record STF (i)+N D I =0,1 and … the normalized correlation coefficient p is calculated in the same manner at the sampling time, and the normalized correlation coefficient p at this time is compared with the normalized correlation p recorded immediately before the normalized correlation coefficient p at this time STF (i) Whether the relation between i =0,1 and … meets a preset condition two or not;
if the preset condition II is not met, the sliding process is interrupted, and the current moment is the first moment n of the last updated record STF (t)+N D Detecting the passing of the overall decision frame signal, recording the frame synchronization time
For the first moment of last update record
If the preset condition I is not met, continuously sliding one data sampling point each time to repeat the calculation until the normalized correlation coefficient rho meets the preset condition I or sliding for a period of time set by an upper layer under the condition that the preset condition I is not met all the time, judging that no frame signal detection is passed, and interrupting the sliding process.
Therefore, the frame capturing and synchronizing method of the burst OFDM system provided by the embodiment can meet the requirements of capturing probability and accuracy in a wide signal-to-noise ratio range, and reduce the processing delay.
The frame capture and synchronization method further comprises: according to the frame synchronization time
And performing phase estimation by using a second formula:
where Δ f is the subcarrier spacing of the OFDM system, and N is the length of the FFT sequence of the OFDM system.
The contents of the present application will be described below using simulation data. As shown in fig. 2-3, fig. 2 is a simulation result of a frame acquisition and synchronization method of a burst OFDM system according to a preferred embodiment of the present invention under AWGN, and fig. 3 is a simulation result of a frame acquisition and synchronization method of a burst OFDM system according to a preferred embodiment of the present invention under ETU.
In a typical quasi-static multipath fading channel ETU, the multipath amplitude follows Rayleigh distribution, and the maximum time delay is 5 microseconds. When the frame synchronization passing condition is defined reasonably based on an 802.15.4g MR-OFDM 1.2M (FFT size is 128, STF contains sampling data with 5 FFT lengths) system, if the estimated timing deviation is in a range of [ -N,26] sampling (determined according to the maximum time delay of an ETU multipath channel), and the frequency deviation estimation error is in a range of 0.25 subcarrier frequency intervals, the frame synchronization is correct, otherwise, the frame synchronization error occurs. When the frame detection probability is defined as the statistical number of passing synchronization divided by the total simulation frame (including the synchronization head and the data, and the position of the synchronization head in the simulation frame is completely random, the random frequency offset determined by the maximum expected frequency deviation PPM is added into the received signal and passes through a multipath channel and an AWGN white noise channel) number in the application as the synchronization detection probability, the frame number of passing frame synchronization divided by the frame synchronization number is defined as the frame synchronization correct probability, and the frame number of passing frame synchronization divided by the total simulation frame number is defined as the synchronization detection & correct probability. It can be seen that the reference receiver has good performance, the detection and correct probability meets the design target requirement, the problem of correct probability of frequency offset estimation under the multipath channel is solved, and the reference receiver can work in a-4 dB signal-to-noise ratio and a wide range of-4, 50 signal-to-noise ratio under AWGN.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.
Claims (5)
1. A frame capture and synchronization method for a burst OFDM system, comprising:
sampling the data processed by the receiver to obtain a plurality of sampling points;
according to the sampling time N, continuous N D Performing cross-correlation operation on the data of two sampling points with a first preset value at interval between the two sampling points, and performing cross-correlation operation on the data of the two sampling points with the first preset value N D Summing the results of the cross-correlation operations to obtain a first result, wherein N is D The first preset value is N for the length of the repeated short training sequence D Multiple of (1), n = n 0 +2N D -1,n 0 +2N D -1+k,…，n 0 Is the initial sampling time, and k is a positive integer;
calculating the N according to the sampling time N D Summing the power of the data of each sampling point to obtain a second result;
repeating the calculation of the first result and the second result to obtain M first results and M second results, wherein M is a positive integer;
according to the M first results A S (n) and the M second results B 0S (n) calculating the current sampleN-carving normalized correlation coefficient rho;
if the normalized correlation coefficient rho meets the preset condition, recording the current sampling moment n as a first moment n STF And recording the normalized correlation coefficient at the moment as a first coefficient rho STF Wherein the preset conditions include: greater than a predetermined threshold value p t And is not less than the current first coefficient rho STF The value of the first coefficient ρ STF Is 0;
if the preset condition is not met, and the first coefficient rho is STF If not 0, recording the current first time n STF For synchronizing time of frame
The calculating a normalized correlation coefficient p for a current sampling instant according to the M first summation results and the M second summation results comprises:
calculating the normalized correlation coefficient of the current sampling time according to a first formula, wherein the first formula is as follows:
n＝n 0 +2N D -1,n 0 +2N D -1+k,…。
2. the frame acquisition and synchronization method of claim 1, further comprising: according to the frame synchronization time
And performing phase estimation by using a second formula:
where Δ f is the subcarrier spacing of the OFDM system, and N is the length of the FFT sequence of the OFDM system.
3. The frame acquisition and synchronization method of claim 1, wherein k is 1.
4. The frame acquisition and synchronization method of claim 1, wherein k is
G is a positive integer greater than 1.
5. The frame capture and synchronization method of claim 1, wherein the recording of the current sampling instant n as the first instant n STF And recording the normalized correlation coefficient at the moment as a first coefficient rho STF Then, the method further comprises the following steps: when the time interval of the sampling time is gN D Then, the calculation of the normalized correlation coefficient ρ is repeated, and g is a positive number smaller than 1 or an integer greater than or equal to 1.
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