CN115378783B - OFDM system time offset calculation method based on cyclic prefix - Google Patents
OFDM system time offset calculation method based on cyclic prefix Download PDFInfo
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- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
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Abstract
The application relates to the technical field of signal processing, in particular to a cyclic prefix-based OFDM system time offset calculation method, which comprises the following steps: acquiring a time domain signal, wherein the time domain signal comprises M+1 continuous OFDM symbols, and each OFDM symbol is provided with a plurality of sampling points; presetting two sliding windows, screening sampling points respectively in the two sliding windows, separating the screened two sampling points by Ns sampling points, and sequentially carrying out absolute value, difference value and square operation on sampling values corresponding to the screened two sampling points to generate difference value search data of OFDM symbols; and sequentially generating difference search data of M OFDM symbols, carrying out average value operation on the M difference search data, generating an average value curve according to an average value operation result, and screening out sampling points corresponding to the lowest points of the average value curve. By adopting the scheme, the technical problem that the time synchronization precision of the OFDM system is low under the conditions of large frequency offset and low signal to noise ratio in the prior art can be solved.
Description
Technical Field
The application relates to the technical field of signal processing, in particular to a cyclic prefix-based OFDM system time offset calculation method.
Background
OFDM (collectively, orthogonal Frequency Division Multiplexing), an orthogonal frequency division multiplexing technique, is one type of multicarrier modulation scheme. In OFDM systems, inter-symbol interference can lead to higher bit error rates, degrading system performance, and guard intervals are typically inserted in the OFDM symbols to mitigate the effects of inter-symbol interference. The guard interval may not contain any signal but this introduces inter-carrier interference, destroying orthogonality between the sub-carriers, so the guard interval is typically constituted by a cyclic extension of the signal, i.e. introducing a cyclic prefix. CP (Cyclic Prefix), i.e., cyclic Prefix, is formed by copying a signal at the tail of an OFDM symbol to the head.
Since the OFDM system is very sensitive to synchronization errors, to reduce the time synchronization errors, time offset estimation is performed based on cyclic prefixes, thereby determining the time synchronization position. In the prior art, the cyclic prefix-based time offset estimation comprises a correlation method and a difference method, and when the time offset estimation is carried out by adopting the correlation method, the time offset estimation is sensitive to frequency offset, so that a larger error is easy to occur in the time offset estimation; when the bias estimation is performed by adopting a difference method, the anti-bias performance is good, but under the condition of low signal-to-noise ratio, the bias estimation error can be increased. Therefore, a time offset calculation method for improving time synchronization accuracy under the conditions of large frequency offset and low signal to noise ratio in an OFDM system is needed.
Disclosure of Invention
The application aims to provide a cyclic prefix-based OFDM system time offset calculation method, which aims to solve the technical problem that the time synchronization precision of an OFDM system is low under the conditions of large frequency offset and low signal to noise ratio in the prior art.
The application provides the following basic scheme:
a cyclic prefix-based OFDM system time offset calculation method comprises the following steps:
acquiring a time domain signal, wherein the time domain signal comprises M+1 continuous OFDM symbols, and each OFDM symbol is provided with a plurality of sampling points;
presetting two sliding windows, screening sampling points respectively in the two sliding windows, separating the screened two sampling points by Ns sampling points, and sequentially carrying out absolute value, difference value and square operation on sampling values corresponding to the screened two sampling points to generate difference value search data of OFDM symbols;
and sequentially generating difference search data of M OFDM symbols, carrying out average value operation on the M difference search data, generating an average value curve according to an average value operation result, and screening out sampling points corresponding to the lowest points of the average value curve.
The basic scheme has the beneficial effects that:
according to the scheme, sampling points are selected based on a sliding window to obtain sampling values, difference search data of each OFDM symbol are obtained through operation based on the two selected sampling values, mean value operation is conducted on the difference search data, and corresponding sampling points are screened out from a mean value curve based on a mean value operation result, namely time synchronization positions.
Compared with the prior art, the scheme is based on the characteristics of the OFDM symbols, does not need additional data symbols, signal to noise ratio and other channel information, and effectively utilizes channel resources. Meanwhile, the scheme generates difference search data according to absolute values, difference values and square operation, reduces the influence of frequency offset on time offset estimation accuracy, and improves the anti-frequency offset performance. According to the scheme, operation and positioning are performed based on the plurality of difference value search data, so that the anti-noise performance of time offset estimation is improved, and the accuracy of time offset estimation under the condition of low signal-to-noise ratio is improved.
Further, a time domain signal is acquired, including the following:
and acquiring a receiving signal of the receiving end, and randomly intercepting the receiving signal according to a preset data length to acquire a time domain signal.
The beneficial effects are that: the time domain signal is obtained by adopting a random interception mode, and the sampling mode is simple and visual.
Further, the OFDM symbol includes a cyclic prefix, and the data length of the sliding window is equal to the data length of the cyclic prefix.
The beneficial effects are that: when the cyclic prefix can completely fall in the sliding window, part of effective data in the OFDM symbol falls in the other sliding window, and the calculation of time offset is realized through the data falling in the two sliding windows.
Further, absolute value, difference value and square operation are sequentially carried out on sampling values corresponding to the two screened sampling points according to the following formula, so as to generate difference value search data of OFDM symbols:
wherein Ng is the number of sampling points of the cyclic prefix, n and i are counting units, y m [n+i]For the (n+i) th sampling signal on the received (m) th OFDM symbol, corresponding y m [n+Ns+i]For the n+ns+i sample signal on the received mth OFDM symbol, δ is the timing offset value.
The beneficial effects are that: thereby realizing the generation of the difference search data.
Further, carrying out mean value operation on M difference search data according to the following formula, generating a mean value curve according to a mean value operation result, and screening out sampling points corresponding to the lowest points of the mean value curve:
in the method, in the process of the application,is an optimal estimate of the timing offset value delta.
The beneficial effects are that: thus, the screening of the final sampling points is realized.
Further, the number of sampling points of each OFDM symbol is Nc, where the effective data length is Ns sampling points, and two sliding windows are separated by Ns sampling points.
The beneficial effects are that: the number of sampling points at intervals of the two sliding windows is the same as that of the screened sampling points at intervals of the two sampling points, so that each sampling point in the two sliding windows corresponds to each other one by one.
Drawings
Fig. 1 is a flowchart of an embodiment of a cyclic prefix-based time offset calculation method of an OFDM system according to the present application;
fig. 2 is a schematic diagram of a timing signal of an embodiment of a cyclic prefix-based time offset calculation method of an OFDM system according to the present application;
fig. 3 is a simulation graph of timing deviation sto=5, carrier frequency offset cfo=0;
fig. 4 is a simulation graph of timing deviation sto= -3, carrier frequency offset cfo=0;
fig. 5 is a simulation graph of timing deviation sto=5, carrier frequency offset cfo=0.5;
fig. 6 is a simulation graph of timing deviation sto= -3, carrier frequency offset cfo=0.5;
fig. 7 is a simulation graph when timing deviation sto=5, carrier frequency offset cfo= -0.3;
fig. 8 is a simulation graph of timing deviation sto= -3, carrier frequency offset cfo= -0.3.
Detailed Description
The following is a further detailed description of the embodiments:
examples
A cyclic prefix-based OFDM system time offset calculation method, as shown in figure 1, comprises the following steps:
s1: and acquiring a time domain signal, wherein the time domain signal comprises M+1 continuous OFDM symbols, each OFDM symbol has a plurality of sampling points, and specifically, the number of the sampling points of each OFDM symbol is Nc. As shown in fig. 2, the OFDM symbol includes a cyclic prefix and effective data, where the number of sampling points of the cyclic prefix is Ng, and the number of sampling points of the effective data is Ns, that is, the effective data length is Ns sampling points.
Acquiring a time domain signal, including the following: and acquiring a receiving signal of the receiving end, and randomly intercepting the receiving signal according to a preset data length to acquire a time domain signal. For example, the time domain signal data of one slot in a 5G NR system.
S2: two sliding windows W1 and W2 are preset, sampling points are respectively screened in the two sliding windows, and the screened two sampling points are separated by Ns sampling points. The data length of the sliding window is equal to the data length of the cyclic prefix, namely, the number of sampling points of the sliding window is Ng, the two sliding windows are separated by Ns sampling points, and specifically, the left ends of the two sliding windows are separated by Ns sampling points.
S3: and sequentially carrying out absolute value, difference value and square operation on sampling values corresponding to the two screened sampling points to generate difference value search data of the OFDM symbol.
Specifically, absolute value, difference value and square operation are sequentially carried out on sampling values corresponding to the two screened sampling points according to the following formula, so as to generate difference value search data of OFDM symbols:
in the formula (1), ng is the number of sampling points of the cyclic prefix, n and i are counting units, y m [n+i]For the (n+i) th sampling signal on the received (m) th OFDM symbol, corresponding y m [n+Ns+i]For the n+ns+i sample signal on the received mth OFDM symbol, δ is the timing offset value.
S4: and sequentially generating difference search data of M OFDM symbols, carrying out average value operation on the M difference search data, generating an average value curve according to an average value operation result, and screening out sampling points corresponding to the lowest points of the average value curve.
Sequentially generating difference search data of M OFDM symbols according to the steps S2 and S3, carrying out mean value operation on the M difference search data according to the following formula, generating a mean value curve according to a mean value operation result, and screening sampling points corresponding to the lowest points of the mean value curve:
in the formula (2), the amino acid sequence of the compound,for optimal estimation of the timing offset value delta, arg min is a function of the sampling point corresponding to the lowest point of the calculated mean curve.
Compared with the prior art, the method and the device have the advantages that the difference search data are generated according to absolute values, difference values and square operation, the influence of frequency offset on time offset estimation accuracy is reduced, and the anti-frequency offset performance is improved. And meanwhile, the operation and positioning are carried out based on a plurality of difference value search data, so that the anti-noise performance of time offset estimation is improved, and the accuracy of time offset estimation under the condition of low signal-to-noise ratio is improved.
As shown in fig. 3-8, the simulation curves of the time offset estimation performed by the solution and the prior art difference method are shown, wherein the abscissa is the signal-to-noise ratio (SNB), and the ordinate is the Root Mean Square Error (RMSE) of the corresponding time offset estimation value. According to the simulation results of fig. 3-8, compared with the prior art, the time offset estimation error is smaller under the condition of low signal-to-noise ratio, the relative time offset estimation precision is higher, and along with the increase of the signal-to-noise ratio, the time offset estimation error of the scheme tends to 0, and the time offset estimation precision is higher than that of the prior art. Meanwhile, simulation results show that under different carrier frequencies, the time offset estimation error is smaller and even tends to 0, and the anti-frequency offset performance is improved.
The foregoing is merely an embodiment of the present application, and a specific structure and characteristics of common knowledge in the art, which are well known in the scheme, are not described herein, so that a person of ordinary skill in the art knows all the prior art in the application date or before the priority date, can know all the prior art in the field, and has the capability of applying the conventional experimental means before the date, and a person of ordinary skill in the art can complete and implement the present embodiment in combination with his own capability in the light of the present application, and some typical known structures or known methods should not be an obstacle for a person of ordinary skill in the art to implement the present application. It should be noted that modifications and improvements can be made by those skilled in the art without departing from the structure of the present application, and these should also be considered as the scope of the present application, which does not affect the effect of the implementation of the present application and the utility of the patent. The protection scope of the present application is subject to the content of the claims, and the description of the specific embodiments and the like in the specification can be used for explaining the content of the claims.
Claims (6)
1. The OFDM system time offset calculation method based on the cyclic prefix is characterized by comprising the following steps:
acquiring a time domain signal, wherein the time domain signal comprises M+1 continuous OFDM symbols, and each OFDM symbol is provided with a plurality of sampling points;
presetting two sliding windows, screening sampling points respectively in the two sliding windows, separating the screened two sampling points by Ns sampling points, and sequentially carrying out absolute value, difference value and square operation on sampling values corresponding to the screened two sampling points to generate difference value search data of OFDM symbols;
sequentially generating difference search data of M OFDM symbols, carrying out mean value operation on the M difference search data, generating a mean value curve according to a mean value operation result, and screening out sampling points corresponding to the lowest points of the mean value curve;
the OFDM symbol comprises a cyclic prefix and effective data, wherein the number of sampling points of the cyclic prefix is Ng, and the number of sampling points of the effective data is Ns, namely the length of the effective data is Ns sampling points;
sequentially carrying out absolute value, difference value and square operation on sampling values corresponding to the two screened sampling points according to the following formula to generate difference value search data of OFDM symbols:
wherein Ng is the number of sampling points of the cyclic prefix, n and i are counting units, y m [n+i]For the (n+i) th sampling signal on the received (m) th OFDM symbol, corresponding y m [n+Ns+i]For the n+Ns+i sampling signal on the received mth OFDM symbol, delta is the timing deviation value;
carrying out mean value operation on M difference search data according to the following formula, generating a mean value curve according to a mean value operation result, and screening out sampling points corresponding to the lowest points of the mean value curve:
in the method, in the process of the application,to aim atAnd (3) optimally estimating the time deviation value delta, wherein arg min is a function of a sampling point corresponding to the lowest point of the calculated mean curve.
2. The method for calculating the time offset of the OFDM system based on the cyclic prefix according to claim 1, wherein: acquiring a time domain signal, including the following:
and acquiring a receiving signal of the receiving end, and randomly intercepting the receiving signal according to a preset data length to acquire a time domain signal.
3. The method for calculating the time offset of the OFDM system based on the cyclic prefix according to claim 1, wherein: the OFDM symbol includes a cyclic prefix, and the data length of the sliding window is equal to the data length of the cyclic prefix.
4. The method for calculating the time offset of the OFDM system based on the cyclic prefix according to claim 1, wherein: sequentially carrying out absolute value, difference value and square operation on sampling values corresponding to the two screened sampling points according to the following formula to generate difference value search data of OFDM symbols:
wherein Ng is the number of sampling points of the cyclic prefix, n and i are counting units, y m [n+i]For the (n+i) th sampling signal on the received (m) th OFDM symbol, corresponding y m [n+Ns+i]For the n+ns+i sample signal on the received mth OFDM symbol, δ is the timing offset value.
5. The method for calculating the time offset of the OFDM system based on the cyclic prefix according to claim 1, wherein: carrying out mean value operation on M difference search data according to the following formula, generating a mean value curve according to a mean value operation result, and screening out sampling points corresponding to the lowest points of the mean value curve:
in the method, in the process of the application,is an optimal estimate of the timing offset value delta.
6. The method for calculating the time offset of the OFDM system based on the cyclic prefix according to claim 1, wherein: the number of sampling points of each OFDM symbol is Nc, wherein the effective data length is Ns sampling points, and two sliding windows are separated by Ns sampling points.
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