CN112511481A - Signal receiving method based on single carrier frequency domain equalization technology - Google Patents
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Abstract
The invention relates to a signal receiving method based on a single carrier frequency domain equalization technology, overcomes the defects and the defects of the overhead and the channel estimation precision of the existing single carrier frequency domain equalization system, and provides a method for improving the data frame structure design and the signal synchronization and channel estimation based on a training sequence.
Description
Technical Field
The invention belongs to the technical field of unmanned aerial vehicle cluster communication, and particularly relates to a signal receiving method based on a single carrier frequency domain equalization technology.
Background
The large-scale unmanned aerial vehicle cluster realizes resource sharing and cooperative combat through transverse networking of the weapon platform, improves the combat efficiency of the weapon platform to the maximum extent, and plays an important role in future combined combat. The unmanned aerial vehicle network realizes real-time sharing and interaction of information through data link networking in a complex combat environment, and further performs task execution adjustment and autonomous control iteration so as to quickly adapt to a new environment, reasonably plan a path and efficiently finish a task. The unmanned aerial vehicle cluster communication network has a ground-air link and an air-air link, the ground-air link channel is a typical multipath fading channel, and the communication signals are affected by frequency selective fading and time delay expansion to generate serious intersymbol interference, thereby reducing the reliability of the system.
The main methods currently used to combat channel ISI are: orthogonal Frequency Division Multiplexing (OFDM), single carrier time domain equalization (SC-TDE), single carrier frequency domain equalization (SC-FDE) and the like, when ISI is serious, the SC-TDE needs too many time domain equalizer tap coefficients and has higher complexity; the OFDM transmits information in parallel through a plurality of subcarriers, expands the signal time on each subcarrier, enhances the resistance of the OFDM to fast fading of a pulse channel, but has the defects of sensitivity to frequency offset and phase noise and high peak-to-average ratio, increases the system cost, and is not suitable for the situation that the airborne power of an unmanned aerial vehicle is limited.
According to the different selection of the known sequences, the frequency domain channel estimation is roughly divided into two types, 1) the auxiliary data-based channel estimation technology has low realization complexity and higher estimation precision. 2) And taking the decision output of the equalizer as a known sequence to carry out decision-oriented channel estimation, wherein the estimation value of the channel estimation changes along with the channel. However, the unstable signal spectrum can cause the noise enhancement of channel estimation, which seriously affects the estimation accuracy and has long convergence time, and is not suitable for the unmanned aerial vehicle trunking communication network.
The accurate synchronization is a key point for recovering transmission data, and is a premise for completing SC-FDE, a traditional SC-FDE system generally utilizes different unique words to carry out signal synchronization and channel estimation, the data frame structure has the problem of high system overhead, the channel estimation based on the cyclic prefix method has the characteristics that the number of points is too small to detect the whole channel due to the limited length, and the accuracy is relatively low. Although increasing the number of blocks of a sequence improves the channel estimation accuracy, it comes at the cost of increased system overhead and has an error floor.
Disclosure of Invention
The technical problem solved by the invention is as follows: the invention mainly aims to overcome the defects and shortcomings of the overhead and channel estimation precision of the existing single carrier frequency domain equalization system, and provides a method for improving data frame structure design and signal synchronization and channel estimation based on a training sequence, so that the timing precision is improved, the system consumption is reduced, and the communication quality is improved.
The technical scheme of the invention is as follows: a signal receiving method based on single carrier frequency domain equalization technology comprises the following steps:
step 1: the telemetering data frame of the unmanned aerial vehicle is modulated and transmitted out through an antenna after passing through a radio frequency channel;
step 2: filtering, down-converting and digitally sampling a radio frequency signal received by a ground antenna of the unmanned aerial vehicle to obtain a baseband signal y;
and step 3: the local NH sequences p and y are correlated to obtain the autocorrelation variable
Where N is the channel estimation window length.
Defining a normalization function P as
Defining the timing function m as:
and 4, step 4: changing the value position of N (N, N +1, N +2, … N + 20N) to obtain a group of mn；
And 5: get mnA point n _ stat corresponding to the peak position is the correct initial position of the training sequence;
step 6: taking the signal y (N _ stat: N _ stat +2 x N) to be correlated with the local NH code to obtain a signal y';
and 7: superposing y 'with N as a period to obtain a signal y';
and 8: y' is subjected to N-point FFT to obtain Yk;
and step 9: performing N-point FFT on a local UW sequence to Xk, wherein UW is a training sequence;
step 10: performing division on the values obtained in the step 8 and the step 9 to obtain frequency domain response estimation Hk of the channel;
step 11: obtaining a channel signal-to-noise ratio estimated value snr by using a second moment and a fourth moment method;
step 12: calculating equalizing coefficient W of MMSE equalizer by using results obtained in steps 10 and 11k；
Wherein
Estimating the conjugate of the channel frequency domain response Hk obtained in the step 10;
step 13: frequency domain data S after MMSE equalizationkCan be expressed as:
Sk＝WkYk
step 14: for the data S obtained in step 13kAnd performing inverse FFT of N points to obtain time domain data y _ new.
The further technical scheme of the invention is as follows: the telemetry data adopts a packet transmission mode, wherein one packet consists of a synchronization frame Tn and M data frames Cn (n is 1,2, … M); the synchronous frame Tn consists of a cyclic prefix CP and a train, the data frame Cn consists of a cyclic prefix CP and data, the length of the CP is larger than the maximum multipath time delay, and the lengths of the train and the data are 2 × N; the synchronous frame sequence is composed of xn and pn, where xn is a UW sequence with length N and pn is an NH sequence with length 2 × N.
The further technical scheme of the invention is as follows: and y _ new in the step 14 is the equalized unmanned aerial vehicle telemetering data, channel compensation is performed, subsequent decoding and judgment can be performed to recover unmanned aerial vehicle telemetering information, and the system error rate is reduced.
Effects of the invention
The invention has the technical effects that: the same training sequence is used for realizing signal synchronization and channel estimation, the system overhead is reduced, and multiple complex frequency domain channel estimation is converted into time domain noise reduction processing to obtain more accurate channel frequency domain response estimation. Compared with the traditional equalization algorithm, the method has the advantages that the error rate is lower, when the error rate is 1e-5, the performance gain of about 2-3 dB is achieved, the method can be suitable for unmanned aerial vehicle cluster data links and most multipath fading channels, and single carrier frequency domain equalization of signals under different scenes can be achieved.
Drawings
FIG. 1 is a SC-FDE baseband model of the present invention;
FIG. 2 is a multiframe structure of telemetry data for a drone according to the present invention;
FIG. 3 is a synchronization frame based on NH sequence according to the present invention;
FIG. 4 shows an unmanned aerial vehicle cluster link packet transmission mode according to the present invention;
FIG. 5 is a graph of the channel amplitude frequency response of the present invention;
Detailed Description
Referring to fig. 1 to 5, in order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced, 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 contents of the embodiments of the present invention and the drawings without creative efforts.
The technical solution of the present invention is further explained by taking the remote measurement signal of the unmanned aerial vehicle as an example through a specific implementation mode with reference to the attached drawings:
(1): according to the frame structure of the telemetering data of the unmanned aerial vehicle, a packet transmission mode is adopted, wherein a multiframe is composed of a synchronous frame Tn and 9 data frames Cn, as shown in figure 2, the synchronous frame Tn is composed of a cyclic prefix CP and a UW sequence, and the data frames Cn are composed of the cyclic prefix CP and data, as shown in figure 3; the synchronization frame adopts the structure shown in figure 4, and the telemetering data frame is transmitted out through an antenna after being modulated and passing through a radio frequency channel. As shown in the front half of figure 1. The unmanned aerial vehicle telemetry data adopts a sub-packet transmission mode, wherein one packet is composed of a synchronization frame Tn and M data frames Cn (N is 1,2, … M) (M is selected by itself), as shown in fig. 2, wherein the synchronization frame Tn is composed of a cyclic prefix CP and train, the data frame Cn is composed of a cyclic prefix CP and data, the length of the CP is larger than the maximum multipath time delay, and the lengths of the train and the data are 2N (N is selected by itself), as shown in fig. 3; the synchronization frame adopts the structure shown in figure 4, the sequence is composed of xn and pn, where xn is a UW sequence with the length of N, pn is an NH sequence with the length of 2 × N, and the telemetry data frame is modulated and transmitted via an antenna after a radio frequency channel. As shown in the front half of figure 1.
(2) Filtering, down-converting and digitally sampling a radio frequency signal received by a ground antenna of the unmanned aerial vehicle to obtain a baseband signal y;
(3): the local NH sequences p and y are correlated to obtain the autocorrelation variable
Where N is the channel estimation window length.
Defining a normalization function P as
Defining the timing function m as:
(4): changing the value position of N (N, N +1, N +2, … N + 20N) to obtain a group of mn；
(5): get mnA point n _ stat corresponding to the peak position is the correct initial position of the training sequence;
(6): taking the signal y (N _ stat: N _ stat +2 x N) to be correlated with the local NH code to obtain a signal y';
(7): superposing y 'with N as a period to obtain a signal y';
(8): y' is subjected to N-point FFT to obtain Yk;
(9): performing N-point FFT on a local UW sequence to Xk, wherein UW is a training sequence;
(10): the values obtained in the steps (8) and (9) are divided to obtain the frequency domain response estimation Hk of the channel, and the result is shown in figure 5;
(11): obtaining a channel signal-to-noise ratio estimated value snr by using a second moment and a fourth moment method;
(12): calculating equalizing coefficient W of MMSE equalizer by using results obtained in steps (10) and (11)k；
Wherein
And (4) estimating the conjugate of the Hk for the channel frequency domain response obtained in the step (10).
(13): frequency domain data S after MMSE equalizationkCan be expressed as:
Sk＝WkYk
(14): for the data S obtained in the step (13)kAnd performing inverse FFT of N points to obtain time domain data y _ new. y _ new is the equalized unmanned aerial vehicle telemetering data, channel compensation is carried out, subsequent decoding and judgment can be carried out to recover unmanned aerial vehicle telemetering information, and the system error rate is reduced.
Claims (3)
1. A signal receiving method based on single carrier frequency domain equalization technology is characterized by comprising the following steps:
step 1: the telemetering data frame of the unmanned aerial vehicle is modulated and transmitted out through an antenna after passing through a radio frequency channel;
step 2: filtering, down-converting and digitally sampling a radio frequency signal received by a ground antenna of the unmanned aerial vehicle to obtain a baseband signal y;
and step 3: the local NH sequences p and y are correlated to obtain the autocorrelation variable
Where N is the channel estimation window length.
Defining a normalization function P as
Defining the timing function m as:
and 4, step 4: changing the value position of N (N, N +1, N +2, … N + 20N) to obtain a group of mn；
And 5: get mnA point n _ stat corresponding to the peak position is the correct initial position of the training sequence;
step 6: taking the signal y (N _ stat: N _ stat +2 x N) to be correlated with the local NH code to obtain a signal y';
and 7: superposing y 'with N as a period to obtain a signal y';
and 8: y' is subjected to N-point FFT to obtain Yk;
and step 9: performing N-point FFT on a local UW sequence to Xk, wherein UW is a training sequence;
step 10: performing division on the values obtained in the step 8 and the step 9 to obtain frequency domain response estimation Hk of the channel;
step 11: obtaining a channel signal-to-noise ratio estimated value snr by using a second moment and a fourth moment method;
step 12: calculating equalizing coefficient W of MMSE equalizer by using results obtained in steps 10 and 11k；
Wherein
Estimating the conjugate of the channel frequency domain response Hk obtained in the step 10;
step 13: frequency domain data S after MMSE equalizationkCan be expressed as:
Sk＝WkYk
step 14: for the data S obtained in step 13kAnd performing inverse FFT of N points to obtain time domain data y _ new.
2. A signal receiving method based on single carrier frequency domain equalization technique according to claim 1, characterized in that said telemetry data is transmitted in a packetized mode, wherein one packet consists of a sync frame Tn and M data frames Cn (n ═ 1,2, … M); the synchronous frame Tn consists of a cyclic prefix CP and a train, the data frame Cn consists of a cyclic prefix CP and data, the length of the CP is larger than the maximum multipath time delay, and the lengths of the train and the data are 2 × N; the synchronous frame sequence is composed of xn and pn, where xn is a UW sequence with length N and pn is an NH sequence with length 2 × N.
3. The signal receiving method based on single carrier frequency domain equalization technology according to claim 1, wherein y _ new in step 14 is equalized unmanned aerial vehicle telemetry data, channel compensation is performed, subsequent decoding and decision recovery can be performed to unmanned aerial vehicle telemetry information, and system error rate is reduced.
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