CN115987742B - OFDM communication system-based frequency domain Doppler frequency offset expansion resisting method - Google Patents
OFDM communication system-based frequency domain Doppler frequency offset expansion resisting method Download PDFInfo
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Abstract
The invention discloses an anti-frequency domain Doppler frequency offset expansion method based on an OFDM communication system, which comprises the following steps: s1: acquiring Doppler scaling factors and carrier frequency offset; s2: calculating the frequency domain Doppler frequency offset expansion quantity; s3: calculating the number of system sub-bands and Doppler frequency offset compensation values of each sub-band according to a preset Doppler expansion threshold of the system; s4: and copying the received data into multiple paths according to the number of the sub-bands, and performing independent Doppler frequency offset compensation on each path. The invention copies the received data according to the number of sub-bands, and each path carries out independent Doppler frequency offset compensation, thereby effectively reducing the influence of frequency domain Doppler frequency offset expansion.
Description
Technical Field
The invention relates to the technical field of wireless communication, in particular to an anti-frequency domain Doppler frequency offset expansion method based on an OFDM communication system.
Background
At present, 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 the system performance is seriously deteriorated due to doppler frequency offset generated by high-speed relative motion at a signal receiving end and a signal transmitting end of a high-speed motion scene.
The Doppler frequency offset is essentially the dimensional change of an electromagnetic wave signal in the time dimension, specifically, if a signal receiving end and a signal transmitting end move in opposite directions, the signal is compressed in proportion in the time dimension; if the signal is stretched in proportion to the time dimension when the signal is received and transmitted and the signal is in reverse motion, the change of the scale of the signal in the time dimension generates Doppler effect, wherein the proportion of the change of the scale of the signal is called 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 better effect in a low-speed or narrowband OFDM system, but according to the analysis, actual transmitting frequencies of different subcarriers in a broadband OFDM system are different, so that the Doppler frequency offsets of different subcarriers are obviously different due to the fact that a signal caused by high-speed motion changes in a time dimension scale (the phenomenon is called frequency domain Doppler spread), and obvious performance loss exists in the prior art.
Disclosure of Invention
The invention aims to provide an anti-frequency domain Doppler frequency offset expansion method based on an OFDM communication system, which aims to solve the technical problem that the anti-Doppler frequency offset expansion effect in the prior art is poor.
The invention is realized by adopting the following technical scheme: an anti-frequency domain Doppler frequency offset expansion method based on an OFDM communication system comprises the following steps:
s1: acquiring Doppler scaling factors and carrier frequency offset;
s2: calculating the frequency domain Doppler frequency offset expansion quantity;
s3: calculating the number of system sub-bands and Doppler frequency offset compensation values of each sub-band according to a preset Doppler expansion threshold of the system;
s4: and copying the received data into multiple paths according to the number of the sub-bands, and performing independent Doppler frequency offset compensation on each path.
Further, the step S1 specifically includes: obtaining Doppler scaling factors by measuring or system preset parameter information
And carrier frequency offset->
。
Further, the calculation method in step S2 is as follows:
wherein ,
for Doppler frequency offset spread +.>
Is the difference between the lowest frequency of the system bandwidth and the carrier frequency, < >>
Is the difference between the highest frequency of the system bandwidth and the carrier frequency.
Further, in step S3, the number of subbands
The calculation method of (1) is as follows:
wherein ,
representing a round up->
Representing the doppler spread threshold.
Further, in step S3, the method for calculating the doppler shift compensation value includes:
wherein ,
representing the doppler frequency offset compensation value.
Further, step S4 includes the following sub-steps:
s41: multipath frequency offset compensation of the time domain received signals;
s42: FFT and subcarrier extraction;
s43: and (5) data demodulation.
Further, the calculation method in step S41 is as follows:
wherein ,
digital time-domain received signal representing a receiver, < >>
Representing the index of the received signal in the digital domain of the receiver,
the representation will->
Go->
Way parallel frequency offset compensation, < > and >>
Representing the system subcarrier spacing,/->
Representing the number of FFT points of the system.
Further, the calculation method in step S42 is as follows: first, the FFT is used to perform
Conversion of the time domain data into->
Road frequency domain data:
then, from
The data of sub-carriers at corresponding positions are respectively extracted from the path frequency domain data to form frequency domain spliced receiving data
：
wherein ,
representing a rounding down.
The invention has the beneficial effects that: the invention copies the received data according to the number of sub-bands, and each path carries out independent Doppler frequency offset compensation, thereby effectively reducing the influence of frequency domain Doppler frequency offset expansion. In particular, the present invention has the following advantages over the prior art:
1. the Doppler frequency offset resisting effect is better: the method has the advantages that the method is equivalent to compensating different frequency offset values for different frequency domain position signals, comprehensively considers the influence of carrier frequency offset during frequency offset compensation, and can effectively reduce the influence of carrier frequency offset and frequency domain Doppler frequency offset expansion on system performance simultaneously compared with the prior art.
2. The realization is simpler: the current technology of resisting the Doppler expansion of the frequency domain often needs to adjust the crystal oscillator frequency of the system, which depends on a high-precision phase-locked loop and requires a certain convergence time to complete the crystal oscillator frequency adjustment, thus leading to higher implementation difficulty. The method only needs to adjust the physical layer signal processing process of the receiver, and is simpler to realize compared with the prior art.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to the structures shown in these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. The components of the 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 numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.
Some embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following embodiments and features of the embodiments may be combined with each other without conflict.
Example 1
Referring to fig. 1, an anti-frequency domain doppler frequency offset spreading method based on an OFDM communication system firstly obtains a doppler scaling factor and a carrier frequency offset, calculates an average value of a frequency domain doppler frequency offset spreading amount and a doppler frequency offset, then calculates a system subband number and a doppler frequency offset compensation value of each subband according to a preset doppler spreading threshold of the system, copies received data according to the subband number in multiple ways, and performs independent doppler frequency offset compensation on each way, thereby achieving an effective anti-doppler frequency offset spreading effect. The method specifically comprises the following steps:
s1: acquiring Doppler scaling factors and carrier frequency offset;
s2: calculating the frequency domain Doppler frequency offset expansion quantity;
s3: calculating the number of system sub-bands and Doppler frequency offset compensation values of each sub-band according to a preset Doppler expansion threshold of the system;
s4: and copying the received data into multiple paths according to the number of the sub-bands, and performing independent Doppler frequency offset compensation on each path.
The step S1 specifically comprises the following steps: obtaining the obtainedTaking the current Doppler scaling factor and carrier frequency offset: obtaining Doppler scaling factors by measuring or system preset parameter information
Assume that the original time domain signal is +.>
Becomes a signal after being scaled by Doppler effect
Then there are:
obtaining carrier frequency offset by measuring or presetting parameter information
(in hertz) here>
Is defined as the frequency deviation between the carrier frequency used by the receiver and the carrier frequency of the received signal.
The step S2 specifically comprises the following steps: calculating the frequency domain Doppler frequency offset expansion quantity: firstly, calculating the system bandwidth range according to the system parameters
, wherein />
(in hertz) represents the carrier frequency of the receiver configuration, < >>
(in hertz) represents the difference between the lowest frequency of the system bandwidth and the carrier frequency, < >>
(in hertz) represents the difference between the highest frequency of the system bandwidth and the carrier frequency, then the doppler frequency offset spread is:
the step S3 specifically comprises the following steps: calculating the number of system sub-bands and Doppler frequency offset compensation value of each sub-band: a given system presets a Doppler spread threshold
First, calculate the number of system subbands +.>
：
wherein 
Representing an upward rounding; then calculating Doppler frequency offset compensation value of each sub-band:
the step S4 specifically comprises the following steps: multipath frequency offset compensation of time domain received signals: assume that the digital time domain received signal of the receiver is
（/>
Representing the index of the received signal in the digital domain of the receiver), then +.>
Go->
And (3) path parallel frequency offset compensation:
wherein 
Representing the system subcarrier spacing (in hertz),/and ∈>
Representing the number of system fast discrete fourier transform (FFT) points.
FFT and subcarrier decimation: first by FFT
Conversion of the time domain data into->
Road frequency domain data:
then from
The data of sub-carriers at corresponding positions are respectively extracted from the path frequency domain data to form frequency domain spliced receiving data
：
wherein 
Representing a rounding down.
And (3) data demodulation: treatment using prior art
And carrying out data demodulation.
Further, taking a communication scenario in which a low-orbit satellite base station transmits signals to a ground stationary terminal as an example, the invention is implemented according to the following steps:
acquiring current Doppler scaling factorThe following steps: knowing the velocity of motion of satellites
The included angle between the connecting line between the satellite base station and the ground terminal and the movement direction of the satellite base station is +.>
(satellites and terminals can obtain the above information through ephemeris and signal beam direction), then the doppler scaling factor is:
wherein 
Indicating the speed of light.
Calculating the frequency domain Doppler frequency offset expansion quantity: firstly, calculating the system bandwidth range according to the system parameters
, wherein />
(in hertz) represents the carrier frequency of the receiver configuration, < >>
(in hertz) represents the difference between the lowest frequency of the system bandwidth and the carrier frequency, < >>
(in hertz) represents the difference between the highest frequency of the system bandwidth and the carrier frequency, then the doppler frequency offset spread is:
calculating the number of system sub-bands and Doppler frequency offset compensation value of each sub-band: a given system presets a Doppler spread threshold
First, calculate the number of system subbands +.>
：
wherein 
Representing an upward rounding; then calculating Doppler frequency offset compensation value of each sub-band:
multipath frequency offset compensation of time domain received signals: assume that the digital time domain received signal of the receiver is
（/>
Representing the index of the received signal in the digital domain of the receiver), then +.>
Go->
And (3) path parallel frequency offset compensation:
wherein 
Representing the system subcarrier spacing (in hertz),/and ∈>
Representing the number of system fast discrete fourier transform (FFT) points.
FFT and subcarrierExtracting: first by FFT
Conversion of the time domain data into->
Road frequency domain data:
then from
The data of sub-carriers at corresponding positions are respectively extracted from the path frequency domain data to form frequency domain spliced receiving data
：
wherein 
Representing a rounding down.
Finally, using prior art processes
And carrying out data demodulation.
Based on the above embodiments, the present invention has at least the following technical effects: the invention copies the received data according to the number of sub-bands, and each path carries out independent Doppler frequency offset compensation, thereby effectively reducing the influence of frequency domain Doppler frequency offset expansion.
It should be noted that, for simplicity of description, the foregoing embodiments are all described as a series of combinations of actions, but it should be understood by those skilled in the art that the present application is not limited by the order of actions described, as some steps may be performed in other order or simultaneously according to the present application. Further, those skilled in the art will also appreciate that the embodiments described in the specification are presently preferred embodiments, and that the acts referred to are not necessarily required for the present application.
In the above embodiments, the basic principle and main features of the present invention and advantages of the present invention are described. It will be appreciated by persons skilled in the art that the present invention is not limited by the foregoing embodiments, but rather is shown and described in what is considered to be illustrative of the principles of the invention, and that modifications and changes can be made by those skilled in the art without departing from the spirit and scope of the invention, and therefore, is within the scope of the appended claims.
Claims (4)
1. An anti-frequency domain Doppler frequency offset expansion method based on an OFDM communication system is characterized by comprising the following steps:
s1: acquiring Doppler scaling factors
Frequency offset with carrier wave>
；
S2: calculating the frequency domain Doppler frequency offset expansion quantity;
s3: calculating the number of system sub-bands and Doppler frequency offset compensation values of each sub-band according to a preset Doppler expansion threshold of the system; in step S3, the method for calculating the doppler shift compensation value includes:
wherein ,
representing Doppler frequency offset compensation value, < >>
Representing carrier frequency offset +.>
Is the difference between the lowest frequency of the system bandwidth and the carrier frequency, < >>
The difference value between the highest frequency of the system bandwidth and the carrier frequency;
s4: copying the received data into multiple paths according to the number of sub-bands, and performing independent Doppler frequency offset compensation on each path; step S4 comprises the following sub-steps:
s41: multipath frequency offset compensation of the time domain received signals; the calculation method of step S41 is:
wherein ,
representing a digital time domain signal>
Digital time-domain received signal representing a receiver, < >>
Index representing the digital domain received signal of the receiver,/->
The representation will->
Go->
Way parallel frequency offset compensation, < > and >>
Representing the system subcarrier spacing,/->
Representing system speedFast discrete fourier transform, FFT, points;
s42: FFT and subcarrier extraction; the calculation method of step S42 is: first, the FFT is used to perform
Conversion of road time domain data into
Road frequency domain data:
then, from
The data of sub-carriers at corresponding positions are respectively extracted from the path frequency domain data to form frequency domain spliced receiving data
：
wherein ,
representing a downward rounding;
s43: and (5) data demodulation.
2. The method for resisting frequency domain doppler frequency offset expansion based on an OFDM communication system as claimed in claim 1, wherein step S1 specifically comprises: obtaining Doppler scaling factors by measuring or system preset parameter information
And carrier frequency offset
。
3. The method for resisting frequency domain doppler frequency offset expansion based on an OFDM communication system as claimed in claim 2, wherein the calculation method in step S2 is as follows:
wherein ,
is the Doppler frequency offset expansion.
4. The method for resisting frequency domain Doppler frequency offset expansion based on OFDM communication system as claimed in claim 3, wherein in step S3, the number of sub-bands is equal to the number of sub-bands
The calculation method of (1) is as follows:
wherein ,
representing a round up->
Representing the doppler spread threshold.
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