CN115987741A - Doppler frequency offset compensation method based on OFDM system - Google Patents
Doppler frequency offset compensation method based on OFDM system Download PDFInfo
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Abstract
The invention discloses a Doppler frequency offset compensation method based on an OFDM system, which relates to the technical field of wireless communication and comprises the following steps: s1: obtaining a Doppler scaling factor; s2: the doppler scaling factor is used to adjust the transmitting or receiving end of the signal. The invention changes the digital domain frequency of different subcarriers in the OFDM system by adjusting the IDFT of the transmitter or the DFT operation of the receiver, and has the effects of adjusting the scale of the transmitted or received signal in the time dimension, and the variation of the adjusted different subcarrier frequencies can be mutually offset with the Doppler frequency offset, thereby achieving the effect of resisting the Doppler frequency offset.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to a Doppler frequency offset compensation method based on an OFDM system.
Background
Currently, radio access networks represented by LTE (long term evolution, i.e., fourth generation mobile communication technology) and NR (new air interface, i.e., fifth generation mobile communication technology) all use OFDM (orthogonal frequency division multiplexing) as an air interface transmission key technology, and doppler frequency offset generated by high-speed relative motion of a signal receiving end and a signal transmitting end in a high-speed motion scene can seriously deteriorate system performance.
The essence of the Doppler frequency offset is the scale change of electromagnetic wave signals in the time dimension, specifically, if the signal receiving end and the signal transmitting end move oppositely, the signals are compressed proportionally in the time dimension; if the signal is elongated proportionally in the time dimension when the signal receiving and transmitting ends move reversely, the change of the signal scale in the time dimension generates the Doppler effect, wherein the proportion of the change of the signal scale is called a Doppler scaling factor.
The existing Doppler frequency offset correction technology generally considers that Doppler frequency offsets of different subcarriers of an OFDM system are the same to design a frequency offset estimation and correction algorithm, the method has a good effect in a low-speed or narrow-band OFDM system, but the actual transmission frequencies of different subcarriers in a broadband OFDM system are different according to the analysis of the foregoing, so that the Doppler frequency offsets of different subcarriers are obviously different due to the change of the scale of a signal in the time dimension caused by high-speed motion, and obvious performance loss exists in the prior art.
Disclosure of Invention
The invention aims to provide a Doppler frequency offset compensation method based on an OFDM system, which aims to solve the technical problem of poor Doppler frequency offset resistance effect in the prior art.
The invention is realized by adopting the following technical scheme: a Doppler frequency offset compensation method based on an OFDM system comprises the following steps:
s1: obtaining a Doppler scaling factor;
s2: the doppler scaling factor is used to adjust the transmitting or receiving end of the signal.
Further, the Doppler scaling factor is obtained by measuring or presetting parameter information of the system
Then, the signal scaled by the doppler effect is:
wherein ,
is scaled by the Doppler effectIn a signal of (c), is combined with>
Is a true time domain signal>
Is the doppler scaling factor.
Further, step S2 is: the inverse discrete fourier transform of the IDFT at the transmitting end is adjusted using the doppler scaling factor.
Further, the transmitting end converts the digital domain frequency domain transmitting data into digital domain time domain transmitting data through the following IDFT operation:
wherein ,
indicating that the transmitting terminal is on the subcarrier->
Is transmitted data, is greater than or equal to>
Indicating the time domain samples of the transmitting end
Is greater than or equal to the digital domain time domain transmit data>
Represents a system IDFT point, < > is>
Represents a natural constant, <' > based on>
Representing imaginary units.
Further, step S2 is: the doppler scaling factor is used to adjust the DFT of the receiving end.
Further, the receiving end converts the digital domain time domain received data into digital domain frequency domain received data through the following DFT operation:
wherein ,
indicating that the receiving end is in a time domain sample point->
In the digital domain receives data in the time domain, and>
indicating that the receiving end is on a subcarrier pick>
Receive data in the frequency domain, and->
Represents a system DFT point, < > or >>
Represents a natural constant, <' > based on>
Representing imaginary units.
The invention has the beneficial effects that: the invention changes the digital domain frequency of different sub-carriers in the OFDM system by adjusting the IDFT of the transmitter or the DFT operation of the receiver, and has the effects of adjusting the scale of the transmitted or received signal in the time dimension (the effect is equivalent to adjusting the digital domain frequency of different sub-carriers of the transmitted or received signal), and the variable quantity of the adjusted different sub-carrier frequencies can be mutually offset with the Doppler frequency offset, thereby achieving the effect of resisting the Doppler frequency offset. Specifically, compared with the prior art, the invention has the following advantages:
1. the Doppler frequency offset resisting effect is better: the method of the invention considers the characteristic that the Doppler frequency offset of different subcarriers of the high-speed broadband OFDM system is different, adjusts the frequency of different subcarriers according to a given proportion, and the digital domain frequency variation of different subcarriers after adjustment can offset the actual Doppler frequency offset of the subcarriers, thus obtaining better Doppler frequency offset resisting effect compared with the prior art.
2. The realization is simpler and the compensation precision is higher: at present, other methods for adjusting the signal scale in the time dimension exist, such methods often need to adjust the crystal oscillator frequency of the system or need complex digital filter operation, the former method depends on a high-precision phase-locked loop and needs a certain convergence time to complete the crystal oscillator frequency adjustment, which results in higher implementation difficulty; the latter doppler scaling factor has low adjustment precision (if higher adjustment precision is required, the operation complexity is often not acceptable), and it is difficult to meet the practical application requirement. Compared with the prior art, the method has the advantages that only the adjustment of the baseband signal processing algorithm is needed, other modules of the system are not needed to be changed, the realization is simple, and the adjustment precision is not limited.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the structures shown in the drawings without creative efforts.
FIG. 1 is a flow chart of example 1;
FIG. 2 is a flowchart of example 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. The components of embodiments of the present invention generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus, once an item is defined in one figure, it need not be further defined and explained in subsequent figures.
Some embodiments of the invention are described in detail below with reference to the accompanying drawings. The embodiments described below and the features of the embodiments can be combined with each other without conflict.
Example 1
Referring to fig. 1, a doppler frequency offset compensation method based on an OFDM system includes the following steps:
s1: obtaining the current doppler scaling factor: obtaining Doppler scaling factor by measuring or system presetting parameter information
Assuming that the original time-domain signal is>
Is scaled by the Doppler effect and then becomes a signal->
Then, there are:
s2: adjusting the transmission of the signal using the doppler scaling factor: converting the digital domain frequency domain transmission data into digital domain time domain transmission data at the signal transmitting end by the following IDFT operation (
Time-degeneracy to standard IDFT):
Taking a communication scene that a low earth orbit satellite base station transmits signals to a ground static terminal as an example, the method is implemented according to the following steps:
s1: obtaining the current Doppler scaling factor: knowing the speed of movement of the satellite
The included angle between the connecting line between the satellite base station and the ground terminal and the motion direction of the satellite base station is ^ 5>
(the satellite and terminal can obtain the above information by ephemeris and signal beam direction), then the doppler scaling factor is:
S2: the satellite transmit signal is adjusted using the doppler scaling factor: the satellite base station converts the digital domain frequency domain transmitting signal into a digital domain time domain signal by the following formula:
wherein 
Indicating that a satellite base station is on sub-carrier>
Is transmitted, is greater than or equal to>
Representing samples of a satellite in the time domain
Is greater than or equal to the digital domain time domain transmit signal>
Represents a system IDFT point, < > is>
Represents a natural constant, is greater than or equal to>
Representing imaginary units.
Example 2
Referring to fig. 2, a doppler frequency offset compensation method based on an OFDM system includes the following steps:
s1: obtaining the current Doppler scaling factor: by measuring or systemsPresetting parameter information to obtain Doppler scaling factor
Assume that the original time domain signal is ^ er>
Is scaled by the Doppler effect and then becomes a signal->
Then, there are:
s2: adjusting reception of the signal using the doppler scaling factor: converting the digital domain time domain received data into digital domain frequency domain received data at the receiving end by the following DFT operation (
Time-degenerated to standard DFT):
wherein 
Indicating that the receiver is in a time domain sample point>
Is received in the digital domain time domain, and->
Indicating that the receiving end is on a subcarrier pick>
Receive data in the frequency domain, and->
Represents a system IDFT point, < > is>
Represents a natural constant, is greater than or equal to>
The imaginary number unit is shown, and the effect is to adjust the scale of the received signal in the time dimension in an analog manner, which is also equivalent to adjusting the digital domain frequency of different subcarriers of the received signal.
Based on the above embodiment, the present invention has at least the following technical effects: the method changes the digital domain frequency of different subcarriers in the OFDM system by adjusting the IDFT of a transmitter or the DFT operation of a receiver, and has the effects of adjusting the scale of a transmitted or received signal in the time dimension (the effect is equivalent to adjusting the digital domain frequency of different subcarriers of the transmitted or received signal), and the variable quantity of the adjusted different subcarrier frequencies can be mutually offset with Doppler frequency offset, so that the effect of resisting the Doppler frequency offset is achieved.
It should be noted that, for simplicity of description, the foregoing embodiments are described as a series of acts or combination of acts, but those skilled in the art will recognize that the present application is not limited by the order of acts, as some steps may occur in other orders or concurrently depending on the application. Further, those skilled in the art will also appreciate that the embodiments described in the specification are presently preferred and that no particular act is required in the present application.
In the above embodiments, the basic principle and the main features of the present invention and the advantages of the present invention are described. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are merely illustrative of the principles of the invention, and that various changes and modifications can be made by one skilled in the art without departing from the spirit and scope of the invention, which is to be construed as within the scope of the appended claims.
Claims (6)
1. A Doppler frequency offset compensation method based on an OFDM system is characterized by comprising the following steps:
s1: obtaining a Doppler scaling factor;
s2: the doppler scaling factor is used to adjust the transmitting or receiving end of the signal.
2. The method of claim 1, wherein the doppler scaling factor is obtained by measuring or presetting parameter information of the system
Then, the signal scaled by the doppler effect is:
wherein ,
for a signal scaled by the Doppler effect, is>
Is a true time domain signal>
Is the doppler scaling factor.
3. The method for compensating doppler frequency offset based on OFDM system as claimed in claim 2, wherein step S2 is: the inverse discrete fourier transform of the IDFT at the transmitting end is adjusted using the doppler scaling factor.
4. The method of claim 3, wherein the transmitting end converts the digital domain frequency domain transmission data into the digital domain time domain transmission data through the following IDFT operation:
wherein ,
indicating that the transmitting terminal is in sub-carrier>
Is transmitted data, is greater than or equal to>
Indicating the time domain samples of the transmitting end
Is greater than or equal to the digital domain time domain transmit data>
Represents a system IDFT point, < > is>
Represents a natural constant, is greater than or equal to>
Representing imaginary units.
5. The method for compensating doppler frequency offset based on OFDM system as claimed in claim 2, wherein step S2 is: the doppler scaling factor is used to adjust the DFT of the receiving end.
6. The method of claim 5, wherein the receiving end converts the digital domain time domain received data into the digital domain frequency domain received data by the following DFT operation:
wherein ,
indicating that the receiving end is in a time domain sample point->
In the digital domain receives data in the time domain, and>
indicating that the receiving end is on a subcarrier pick>
Receive data in a frequency domain, and>
represents a system DFT point, < > or >>
Represents a natural constant, is greater than or equal to>
Representing imaginary units. />
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116916436A (en) * | 2023-07-31 | 2023-10-20 | 四川创智联恒科技有限公司 | Method and system for transmitting synchronizing signal |
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| CN102724149A (en) * | 2012-05-16 | 2012-10-10 | 华为技术有限公司 | Frequency offset precompensation method, random access method, equipment and system |
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| CN102724149A (en) * | 2012-05-16 | 2012-10-10 | 华为技术有限公司 | Frequency offset precompensation method, random access method, equipment and system |
| WO2015101418A2 (en) * | 2013-12-30 | 2015-07-09 | Universität des Saarlandes | Methods and devices for doppler shift compensation in a mobile communication system |
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| CN116916436A (en) * | 2023-07-31 | 2023-10-20 | 四川创智联恒科技有限公司 | Method and system for transmitting synchronizing signal |
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