CN111181878A - L-band digital aviation communication system channel estimation method and system - Google Patents
L-band digital aviation communication system channel estimation method and system Download PDFInfo
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- CN111181878A CN111181878A CN202010013516.5A CN202010013516A CN111181878A CN 111181878 A CN111181878 A CN 111181878A CN 202010013516 A CN202010013516 A CN 202010013516A CN 111181878 A CN111181878 A CN 111181878A
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- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
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Abstract
The invention discloses a channel estimation method and a channel estimation system of an L-band digital aviation communication system, which comprise the following steps of; step S1, receiving pilot data and pilot symbol transmitted by transmitting end by receiving end of radio frequency device; step S2, calculating the channel frequency response of the pilot frequency position according to the pilot frequency data received by the radio frequency receiver and the pilot frequency symbol transmitted by the radio frequency transmitter to obtain the channel frequency response value of the pilot frequency position; step S3, carrying out IDFT transformation on the channel frequency response value of the pilot frequency position to obtain the data of the time domain signal of the channel of the pilot frequency position; step S4, performing filter processing on the converted data; step S5, performing DFT transformation on the filtered data; and step S6, calculating the channel frequency response of the data position by using a distance interpolation algorithm, effectively reducing the noise in the channel, improving the channel estimation accuracy and reducing the system error rate.
Description
Technical Field
The invention relates to civil aviation communication, in particular to a channel estimation method and a channel estimation system of an L-band digital aviation communication system.
Background
As civil aviation ground-air communication is easy to suffer from multipath interference caused by scattering effect, and the interference environment suffered by the airplane in different states is greatly different. Among the common scenarios are: a sailing scenario (ENR), a takeoff/landing scenario (TMA), and a berthing scenario (APT). In a navigation scene, the Doppler shift between the ground-air communication equipment can reach 1250Hz at most; under a take-off/landing scene, the number of scattering paths of the ground-air communication signals is up to 7; in a parking scene, the ground-air communication signals have no main path and are all scattered signals, and the communication environment is the most complicated. Therefore, the effectiveness of communication can be guaranteed only by carrying out channel estimation on the ground-air communication channel.
Since the L-DACS1 adopts the OFDM transmission scheme, and the wireless channel environment encountered in the aeronautical communication is complex, it is necessary to perform channel estimation on the wireless transmission channel. Common methods for channel estimation in the prior art are the least squares method (LS), the minimum mean square error method (MMSE). The least square method (LS) is the most widely used method in engineering because of its simple principle and easy implementation, but the linear interpolation method brings extra noise, resulting in poor estimation effect. The minimum mean square error method (MMSE) is relatively complex to implement because it involves a large number of matrix operations.
Disclosure of Invention
The invention firstly carries out filtering processing on the channel frequency response of the pilot frequency position, and then estimates the channel frequency response of the data position by using a distance interpolation algorithm, and aims to provide a channel estimation method and a channel estimation system of an L-band digital aviation communication system, which solve the problems of low channel estimation accuracy and high system error rate.
The invention is realized by the following technical scheme:
a channel estimation method of an L-band digital aviation communication system comprises the following steps;
step S1, the radio frequency receiver receives the pilot frequency data and the pilot frequency symbol transmitted by the radio frequency transmitter;
step S2, calculating the channel frequency response of the pilot frequency position according to the pilot frequency data received by the radio frequency receiver and the pilot frequency symbol transmitted by the radio frequency transmitter to obtain the channel frequency response value of the pilot frequency position; the calculation formula is as follows:
Hp＝Yp/Xp(1)
wherein Y ispFor pilot data, X, received at the receiving end of the RF devicepPilot frequency symbols transmitted for the transmitting end of the radio frequency device;
step S3, IDFT conversion is carried out on the channel frequency response value of the pilot frequency position to obtain the channel time domain response h of the pilot frequency positionpIDFT transforms to prior art;
step S4, performing filter processing on the converted data; because the time domain impulse response of the channel is smaller than the length of the cyclic prefix, and the rest are noise, the value after the maximum cyclic length can be set as the minimum value;
length (cp) is the length of the cyclic prefix, and the length of the cyclic prefix in L-DACS1 is 11;
step S5, performing DFT transformation on the filtered data; transforming the filtered result into the frequency domain
And step S6, calculating the channel frequency response of the data position by using a distance interpolation algorithm.
Further, the pilot symbols described in step S1 are the distribution and values of the pilot symbols specifically defined in the protocol specification of L-DACS1, as agreed by the protocol.
Further, the step S6 specifically includes;
s61, calculating the pilot distance from the current data position to the nearby pilot position according to the position corresponding to the pilot symbol and the position of the data symbol in the frame data; the calculation formula of the pilot frequency distance is as follows:
wherein the data position coordinates are (a)0,b0) The position coordinate of the pilot is (a [ k ]],b[k]),k＝1,2,3,…。
Further, the frame structure of L-DACS1 is fixed, as are the pilot locations.
S62, when the pilot frequency distance is smaller than the pilot frequency distance threshold, recording the channel frequency response and the pilot frequency distance at the pilot frequency position;
and S64, calculating the channel frequency response of the current data position according to the channel frequency response after filtering and DFT conversion and the pilot frequency distance. The calculation formula of the distance interpolation is as follows;
wherein
Is an estimate of the channel frequency response, w, for the ith data locationp[k]To account for the weight coefficients of the pilot location channel frequency response,
the number of the channel frequency responses of the pilot frequency positions is K; weight coefficient wp[k]The calculation formula of (2) is as follows:
and d [ k ] is the pilot distance.
Further, in the step S62, the pilot distance threshold is set to 10.
Further, the step S62 specifically includes;
a channel estimation system of an L-band digital aviation communication system comprises a radio frequency unit, a preprocessing unit, a filtering unit, a main control unit and a statistic evaluation unit;
the radio frequency unit is used for receiving pilot frequency data and transmitting pilot frequency symbols;
the preprocessing unit is used for calculating the channel frequency response of the pilot frequency position according to the pilot frequency data and the pilot frequency symbols of the radio frequency unit to obtain a channel frequency response value of the pilot frequency position and carrying out IDFT (inverse discrete Fourier transform) on the channel frequency response value of the pilot frequency position to obtain a channel time domain response of the pilot frequency position;
the filtering unit is used for filtering channel noise of the time domain response after passing through the preprocessing unit;
the main control unit is used for performing DFT (discrete Fourier transform) on the data filtered by the filtering unit to obtain a frequency domain signal and calculating the channel frequency response of the data position by using a distance interpolation algorithm;
and the statistical evaluation unit is used for counting the data of the main control unit and evaluating the channel according to the counted data.
Compared with the prior art, the invention has the following advantages and beneficial effects:
the invention discloses a channel estimation method and a channel estimation system of an L-band digital aviation communication system.
Drawings
The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:
FIG. 1 is a schematic flow diagram of the present invention;
FIG. 2 is a detailed flowchart of step S6 according to the present invention;
FIG. 3 is a schematic diagram of the system of the present invention;
FIG. 4 is a schematic diagram of the pilot distribution of step S1 according to the present invention;
fig. 5 is a schematic diagram of the pilot distance of step S6 in the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.
Examples
As shown in fig. 1 to 4, a channel estimation method for an L-band digital aeronautical communication system,
the scheme is applied to ground receiving equipment of L-DACS1 (L-frequency band digital aviation communication system 1); the detailed steps comprise:
step S1, pilot frequency data Y of radio frequency receiving endpAnd pilot symbol X of radio frequency transmitting terminalp；
Step S2, calculating the channel frequency response of the pilot frequency to obtain the channel frequency response value of the pilot frequency, wherein the calculation formula is as follows;
Hp＝Yp/Xp(1)
the pilot compliance here is specified by the L-DACS1 protocol, with known values for value and location, as shown in FIG. 4; in the ideal case, the received pilot symbols are equal to the transmitted pilot symbols, i.e. Hp＝1；
Step S3, transforming the channel frequency response value into time domain h by IDFT (inverse discrete fourier transform)p；
Step S4, h after conversionpPerforming filtering processing, wherein; since the time-domain impulse response of the channel is smaller than the length of the cyclic prefix, and the rest are noise, the value after the maximum cyclic length can be set as the minimum value,
length (cp) is the length of the cyclic prefix, and the length of the cyclic prefix in L-DACS1 is 11;
step S5: transforming the filtering result into frequency domain by DFT (discrete Fourier transform)
Step S6: estimating the channel frequency response of the data position by using a distance interpolation algorithm; the method comprises the steps of firstly calculating a pilot frequency position less than or equal to a threshold according to a current data position, recording a corresponding channel frequency response, and then calculating the channel frequency response of the current data position according to a pilot frequency distance and the channel frequency response;
since the frame structure of L-DACS1 is fixed, the pilot locations are also fixed. When calculating channel parameters for a data location, the square of the time-domain distance from the location of the pilot symbol to the current data location is summed with the frequencyThe sum of the squares of the domain distances, and the re-evolution result is recorded as the pilot distance; only pilot symbols smaller than a pilot distance threshold participate in the calculation of the channel parameters of the current data position, and the threshold is set to be 10 in the scheme; FIG. 5 is a diagram illustrating pilot distance calculation; d0 represents data position, P1, P2, P3, P4 and P5 represent inserted pilot positions, and the position coordinate of D0 is (a)0,b0) The position coordinate of the pilot is (a [ k ]],b[k]) And k is 1,2,3, …, the calculation formula of the pilot distance is:
the calculation formula of the distance interpolation is as follows:
wherein
Is an estimate of the channel frequency response, w, for the ith data locationp[k]To account for the weight coefficients of the pilot location channel frequency response,
and K is the number of the channel frequency responses of the pilot frequency positions participating in the calculation. Weight coefficient wp[k]The calculation formula of (2) is as follows:
d [ k ] is the pilot distance;
channel frequency response estimation for multiple data locations
Statistics, recording and evaluation are performed.
Example 2
As shown in fig. 3, the present embodiment provides a channel estimation system for an L-band digital aeronautical communication system; the device comprises a radio frequency unit, a preprocessing unit, a filtering unit, a main control unit and a statistic evaluation unit;
the radio frequency unit is used for pilot frequency data Y of a radio frequency receiving endpAnd pilot symbol X of radio frequency transmitting terminalp；
The preprocessing unit is used for carrying out preliminary processing on the pilot frequency data and the pilot frequency symbols of the radio frequency unit; calculating the channel frequency response of the pilot frequency position to obtain the channel frequency response value of the pilot frequency position, wherein the calculation formula is Hp＝Yp/Xp；
The pilot compliance for this scheme is specified by the L-DACS1 protocol, with known values for value and location, as shown in fig. 4; in the ideal case, the received pilot symbols are equal to the transmitted pilot symbols, i.e. H p1 is ═ 1; transforming the channel frequency response value to the time domain h by using IDFT (inverse discrete Fourier transform) transformationp；
The filtering unit is used for filtering out noise in a channel; performing filtering processing according to the prior art, wherein; since the time-domain impulse response of the channel is smaller than the length of the cyclic prefix, and the rest are noise, the value after the maximum cyclic length can be set as the minimum value,
length (cp) is the length of the cyclic prefix, and the length of the cyclic prefix in L-DACS1 is 11;
the main control unit processes the data in the radio frequency unit and the signals after passing through the filtering unit; estimating the channel frequency response of the data position by using a distance interpolation algorithm; the method comprises the steps of firstly calculating a pilot frequency position less than or equal to a threshold according to a current data position, recording a corresponding channel frequency response, and then calculating the channel frequency response of the current data position according to a pilot frequency distance and the channel frequency response; since the frame structure of L-DACS1 is fixed, the pilot locations are also fixed; when calculating channel parameters for a data location, the average of the time-domain distances from the location of a pilot symbol to the current data locationThe sum of squares of the square and the frequency domain distance, and the re-evolution result is recorded as the pilot frequency distance; only the pilot frequency smaller than the pilot frequency distance threshold can participate in the calculation of the channel parameter of the current data position, and the threshold is set to be 10 in the scheme; FIG. 5 is a diagram illustrating pilot distance calculation; d0 represents data position, P1, P2, P3, P4 and P5 represent inserted pilot positions, and the position coordinate of D0 is (a)0,b0) The position coordinate of the pilot is (a [ k ]],b[k]) And k is 1,2,3, …, the calculation formula of the pilot distance is:
the calculation formula of the distance interpolation is as follows:
wherein
Is an estimate of the channel frequency response, w, for the ith data locationp[k]To account for the weight coefficients of the pilot location channel frequency response,
and K is the number of the channel frequency responses of the pilot frequency positions participating in the calculation. Weight coefficient wp[k]The calculation formula of (2) is as follows:
d [ k ] is the pilot distance;
the statistic evaluation unit is used for counting the data of the main control unit, evaluating the channel according to the statistical data and evaluating the channel frequency response estimation values of a plurality of data positions
Statistics, recordings and evaluations were performed.
The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (5)
1. A channel estimation method of an L-band digital aviation communication system is characterized by comprising the following steps;
step S1, receiving pilot frequency data Y by radio frequency device receiving endpAnd transmitting pilot symbol X by transmitting terminalp；
Step S2, receiving pilot frequency data Y by radio frequency device receiving endpAnd transmitting pilot symbol X by transmitting terminalpCalculating the channel frequency response of the pilot frequency position to obtain a channel frequency response value of the pilot frequency position, wherein the calculation formula is as follows:
Hp＝Yp/Xp(1)
wherein HpA channel frequency response value of a pilot frequency position;
step S3, carrying out IDFT transformation on the channel frequency response value of the pilot frequency position to obtain the channel time domain response h of the pilot frequency positionp；
Step S4, responding to time domain hpCarrying out filtering treatment;
step S5, DFT transform is carried out on the filtered data to obtain frequency domain
And step S6, calculating the channel frequency response of the data position by using a distance interpolation algorithm.
2. The method as claimed in claim 1, wherein the pilot symbols in step S1 are distribution and values of pilot symbols specially defined in protocol specification of L-DACS1 according to protocol convention.
3. The method for channel estimation in an L-band digital aeronautical communication system according to claim 1, wherein the step S6 specifically includes;
s61, calculating the pilot distance from the current data position to the nearby pilot position according to the position corresponding to the pilot symbol and the position of the data symbol in the frame data; the pilot distance calculation formula is as follows:
wherein the position coordinates of the data are (a)0,b0) The position coordinate of the pilot is (a [ k ]],b[k]),k＝1,2,3,…；
S62, when the calculated pilot frequency distance is smaller than the pilot frequency distance threshold, recording the channel frequency response and the pilot frequency distance of the pilot frequency position;
s63, calculating the channel frequency response of the current data position according to the channel frequency response and the pilot frequency distance after filtering and DFT conversion; the calculation formula is as follows;
wherein
Is an estimate of the channel frequency response, w, for the ith data locationp[k]To account for the weight coefficients of the pilot location channel frequency response,
is the channel frequency response of the pilot frequency position, K is the number of the channel frequency responses of the pilot frequency position participating in the calculation, and the weight coefficient wp[k]The calculation formula of (A) is as follows;
and d [ k ] is the pilot distance.
4. The method for channel estimation in an L-band digital aeronautical communication system according to claim 3, wherein the pilot distance threshold in step S62 is set to 10.
5. A channel estimation system of an L-band digital aviation communication system is characterized by comprising a radio frequency unit, a preprocessing unit, a filtering unit, a main control unit and a statistic evaluation unit;
the radio frequency unit is used for receiving pilot frequency data and transmitting pilot frequency symbols;
the preprocessing unit is used for calculating the channel frequency response of the pilot frequency position according to the pilot frequency data and the pilot frequency symbols of the radio frequency unit to obtain a channel frequency response value of the pilot frequency position and carrying out IDFT (inverse discrete Fourier transform) on the channel frequency response value of the pilot frequency position to obtain a channel time domain response of the pilot frequency position;
the filtering unit is used for filtering channel noise of the time domain response after passing through the preprocessing unit;
the main control unit is used for performing DFT (discrete Fourier transform) on the data filtered by the filtering unit to obtain a frequency domain signal and calculating the channel frequency response of the data position by using a distance interpolation algorithm;
and the statistical evaluation unit is used for counting the data of the main control unit and evaluating the channel according to the counted data.
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