A communication method against multipath fading suitable for ionospheric scattering channels

Abstract

The invention discloses a multipath fading resistant communication method applicable to an ionospheric scattering channel, comprising the following steps: a transmitting end frames coded data and two UW sequences generated locally in a specific manner and then sends them out; a receiving end samples a signal transmitted through an ionospheric scattering channel, cross-correlates the sampled signal with a sequence stored locally, and obtains multipath data; removes cyclic prefixes from each multipath data, and then performs FFT transformation to the frequency domain, uses a known sequence inserted in a subframe to perform channel estimation, obtains the channel response of the ionospheric scattering channel, performs frequency domain equalization on the data, and then transforms it to the time domain through IFFT; performs weighted summation on the equalized multipath data to obtain the merged signal data. The invention separates multipath data from the receiving end sampling signal and then performs balanced merging, and has good multipath fading resistance performance; it is very convenient to use in engineering.

Description

Technical Field

[0001] The invention relates to the field of scattering communication, and in particular to an anti-multipath fading communication method suitable for an ionospheric scattering channel. Background Art

[0002] Ionospheric scattering communication refers to over-the-horizon communication that uses the scattering effect of electromagnetic waves caused by the inhomogeneity of the ionosphere. Compared with line-of-sight wireless communication, the biggest advantage of over-the-horizon communication using ionospheric scattering channels is that the transmission distance is long, with a single hop of up to one or two thousand kilometers, and it is easy to cross sparsely populated areas such as mountains, lakes, seas, and deserts. In addition, over-the-horizon communication using ionospheric scattering channels is basically not affected by magnetic storms, auroras, lightning, and even atmospheric nuclear explosions. It is relatively stable and is an important civil and military wireless communication method.

[0003] However, ionospheric scattering communication also has its disadvantages. In addition to the large transmission loss caused by ultra-long-distance propagation, over-the-horizon communication using ionospheric scattering channels also has time-varying fading characteristics caused by multipath propagation of signals in ionospheric scattering channels. In actual tests, the delay spread of signals propagating in ionospheric scattering channels can reach more than 200 microseconds in severe cases. The phases of signals arriving through different paths are inconsistent. These multiple signals with inconsistent phases on different paths are eventually superimposed at the receiving end, resulting in severe multipath fading. Conventional single-carrier frequency domain equalization technology performs poorly in actual use. How to better resist multipath fading caused by signal transmission in ionospheric scattering channels is a problem that needs to be solved at present. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides an anti-multipath fading communication method applicable to ionospheric scattering channels, so as to improve the anti-multipath fading performance of the ionospheric scattering communication system, which is suitable for the purpose of engineering implementation.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A multipath fading resistance communication method applicable to an ionospheric scattering channel comprises the following steps:

[0007] (1) Generate UW sequence UW1 and UW sequence UW2, and store UW sequence UW1 and UW sequence UW2 at the transmitting end and receiving end of the system;

[0008] (2) The transmitter divides the data to be transmitted into multiple segments of equal length, copies the UW sequence UW1 into three copies and inserts them between the multiple segments at equal intervals, and copies the tail data of each segment of data and the tail data of each segment of UW sequence UW1 and adds them to their heads as the cyclic prefix of the segment of data, thereby obtaining a subframe;

[0009] (3) A plurality of subframes are connected to the UW sequence UW2 to form a frame and send it out;

[0010] (4) The receiving end samples and receives the signal generated by the transmitted signal passing through the ionospheric scattering channel, and cross-correlates the sampled data with the locally stored UW sequence UW2 to obtain a correlation peak diagram. The amplitude of the main path on the correlation peak diagram is A max , find all the points near the main path that are larger than The diameters of the m ,...,A M ) and positions (loc1,loc2,...,loc m ,...,loc M ), A m Indicates that the mth one is greater than The modulus of the diameter, loc m Indicates that the mth one is greater than The position of the path, m∈[1,M], M is the main path near all the The total number of paths; respectively use the positions of these paths as synchronization positions to obtain multi-path multi-path data equal to the number M, and remove the cyclic prefix of each data path according to the position of the added cyclic prefix;

[0011] (5) Each multipath data is processed in subframe units, and the LS channel estimation algorithm is used to perform channel estimation using the three UW sequences UW1 inserted in the subframe sequence, and the MMSE equalization algorithm is used to perform channel equalization to obtain the channel equalization result of the multipath data;

[0012] (6) Weighted combination of the results of multi-path data channel equalization.

[0013] In the above scheme, in step (1), the UW sequence used is the Zadoff-Chu sequence, which is generated by the following formula:

[0014]

[0015] Wherein, N is the length of the generated sequence, j is the imaginary unit, and k is the sequence number in the UW sequence; wherein, the UW sequence UW1 and the UW sequence UW2 are generated using different sequence lengths N1 and N2, the value of N1 is a positive integer power of 2, and the value of N2 is determined by the bandwidth occupied by the system when transmitting data.

[0016] In the above scheme, in step (2), the encoded data to be transmitted is equally divided into 12 segments. The length of each segment of data after segmentation is the same as the length of the UW sequence UW1. The UW sequence UW1 is inserted after the 2nd, 6th and 10th segments of data respectively.

[0017] In the above scheme, in step (2), the length of the cyclic prefix is ​​1 / 8 of the length of the data segment, and the result of dividing the length of the cyclic prefix by the signal transmission rate is greater than the channel delay.

[0018] In the above scheme, in step (5), the specific method of channel estimation is:

[0019] The receiving end extracts three segments of UW sequence UW1 according to the original insertion position of UW sequence UW1 in the subframe, and obtains the FFT transformation value U of the three segments of UW sequence UW1 after passing through the ionospheric scattering channel through FFT transformation. k1 (k) U k2 (k) and U k3 (k) Perform FFT transformation on the locally stored UW sequence UW1 to obtain the FFT transformation value U of the UW sequence UW1 k (k); Thus, the frequency domain estimate of the ionospheric scattering channel transmitted in this subframe is obtained for:

[0020]

[0021] In the above scheme, in step (5), the specific method of channel equalization is:

[0022] Assume that the i-th data segment in this subframe is transformed into X by FFT i (k) Represents the average power of the noise in this subframe, Represents the average power of the received signal in this subframe, The frequency domain estimate of the ionospheric scattering channel through which this subframe is transmitted The conjugate of , then the result of MMSE equalization of the i-th data segment in this subframe is:

[0023]

[0024] Where, IFFT stands for inverse fast Fourier transform;

[0025] The average power of the noise and the average power of the received signal The estimation methods are:

[0026]

[0027]

[0028] Where N1 is the length of the inserted UW sequence UW1, u k1 (k),u k2 (k) and uk3 (k) are the received values ​​of the three UW sequences UW1 inserted in this subframe after passing through the ionospheric scattering channel;

[0029] After performing channel equalization on all data segments in a subframe, the channel equalization results of these data segments are sequentially connected to obtain the channel equalization result of this subframe, and the channel equalization results of all subframes in this multipath data are sequentially connected to obtain the channel equalization result of this multipath data. For the mth data segment greater than The path of the multipath data obtained as the synchronization position after MMSE channel equalization is expressed as y m .

[0030] In the above scheme, in step (6), the weighted coefficient for weighted combination of multi-path data is:

[0031]

[0032] Among them, A m The modulus represents the diameter whose amplitude is greater than 1 / 2 of the main diameter. M represents the modulus of all diameters greater than 1 / 2 of the main diameter. The total number of diameters;

[0033] The specific method for weighted merging of multi-path data is as follows:

[0034]

[0035] Among them, w m is the weighting coefficient, y m Because the mth one is greater than The path is taken as the result of MMSE channel equalization of the multipath data obtained at the synchronization position, and y is the combined data obtained after weighted combination.

[0036] Through the above technical solution, the present invention provides a multipath fading resistance communication method applicable to ionospheric scattering channels, which has the following beneficial effects:

[0037] The present invention frames data and two UW sequences generated locally at a transmitting end according to a specific format, sends them out after framing, cross-correlates the received sampling signal with a locally stored known sequence at a receiving end, separates multi-path data, performs channel estimation and channel equalization on each multi-path data in units of subframes, and then weighted-combines the equalized multi-path data, fully utilizes the multi-path information of the signal passing through the ionospheric scattering channel, superimposes the dispersed energy after equalization, and has better anti-multipath fading performance; the method of the present invention is simple and effective, can be implemented in a software manner, and can also be implemented by embedding a hardware module such as an FPGA into a communication system, and is very convenient to use in engineering. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0039] Figure 1 A flow chart of a method for resisting multipath fading communication in an ionospheric scattering channel provided in an embodiment of the present invention.

[0040] Figure 2 Schematic diagram of the subframe structure used in the present invention.

[0041] Figure 3 Schematic diagram of the frame structure used in the present invention.

[0042] Figure 4 Schematic diagram of the correlation peak after the sampling signal at the receiving end is cross-correlated with the locally stored known sequence.

[0043] Figure 5 A schematic diagram of obtaining multipath data from a receiving-end sampling signal using different paths as synchronization start positions. DETAILED DESCRIPTION

[0044] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0045] The present invention provides a multipath fading resistance communication method applicable to ionospheric scattering channels, such as Figure 1 As shown, the following steps are included;

[0046] Step (1), generate UW sequence UW1 and UW sequence UW2, and store UW sequence UW1 and UW sequence UW2 at the transmitting end and receiving end of the system.

[0047] Specifically, the Zadoff-Chu sequence is used to generate the UW sequence, which is generated by the following formula:

[0048]

[0049] Wherein, N is the length of the generated sequence, j is the imaginary unit, and k is the generation number of the UW sequence; wherein, the UW sequence UW1 and the UW sequence UW2 are generated using different sequence lengths N1=256 and N2=6000.

[0050] In step (2), the transmitter divides the data to be transmitted into multiple segments of equal length, copies the UW sequence UW1 into three parts and inserts them between the multiple segments at equal intervals, and copies the tail data of each segment of data and the tail data of each segment of UW sequence UW1 and adds them to their heads as the cyclic prefix of the segment of data, thereby obtaining a subframe.

[0051] Specifically, the data to be transmitted is the data generated by the original information after LDPC encoding and then interleaving. Its length is 3072 and is divided into 12 equal segments. The length of each segment of data after segmentation is the same as the length of the UW sequence UW1, which is 256. The UW sequence UW1 is inserted after the 2nd, 6th and 10th segments of data respectively. The length of the cyclic prefix is ​​1 / 8 of the data segment length, that is, the data of the tail of each segment of data is copied and added to the head of the segment of data as the cyclic prefix of the segment of data, and the result of dividing the length of the cyclic prefix by the signal transmission rate is greater than the channel delay. The final subframe structure is as follows: Figure 2 As shown, the gray filled block represents the cyclic prefix, and the sequence numbers 1 to 12 represent data segments 1 to 12.

[0052] Step (3), UW sequence UW2 is followed by multiple subframes to form a frame and send it out, and the frame structure is as follows: Figure 3 shown.

[0053] Step (4), the receiving end samples and receives the signal generated by the transmitted signal passing through the ionospheric scattering channel, and cross-correlates the sampled data with the locally stored UW sequence UW2. Figure 4 The figure shows a typical correlation peak diagram after cross-correlation between a sampled received signal at the receiving end and a locally stored UW sequence UW2.

[0054] Assume that the amplitude of the main path on the correlation peak graph is A max , half of the main diameter, that is As the threshold, find all values ​​near the main path greater than The diameters (including the main diameter) of the pipe and the moduli of these diameters (A1, A2, ..., A m ,...,A M ) and positions (loc1,loc2,...,loc m ,...,loc M ), A m Indicates that the mth amplitude is greater than 1 / 2 of the main diameter A max The modulus of the diameter, loc m Indicates that the mth amplitude is greater than 1 / 2 of the main diameter A maxThe position of the path, m∈[1,M], M is the total number of paths near the main path with an amplitude greater than 1 / 2 of the main path. The positions of these paths are used as synchronization positions to obtain multipath data equal to the number of M. The obtained M-path multipath data is as follows: Figure 5 As shown, the gray block represents the received value of the UW sequence UW2 in this multipath data after passing through the ionospheric scattering channel.

[0055] After obtaining M multipath data, the cyclic prefix of each data path is removed according to the position of the added cyclic prefix.

[0056] Step (5), each multipath data is processed in subframe units, and the LS channel estimation algorithm is used to perform channel estimation using the three UW sequences UW1 inserted in the subframe sequence, and the channel equalization is performed using the MMSE equalization algorithm to obtain the channel equalization result of the multipath data.

[0057] Specifically, under the above subframe structure, the specific method of channel estimation is:

[0058] The receiving end extracts three segments of UW sequence UW1 according to the original insertion position of UW sequence UW1 in the subframe, and obtains the FFT transformation value U of the three segments of UW sequence UW1 after passing through the ionospheric scattering channel through FFT transformation. k1 (k) U k2 (k) and U k3 (k) Perform FFT transformation on the locally stored UW sequence UW1 to obtain the FFT transformation value U of the UW sequence UW1 k (k); Thus, the frequency domain estimate of the ionospheric scattering channel transmitted in this subframe is obtained for:

[0059]

[0060] Furthermore, the average power of the three UW sequences UW1 in the subframe after passing through the ionospheric scattering channel and the average power of the superimposed noise are used to approximately replace the average power of the received signal and the average power of the noise superimposed on the received signal. Average power of noise and the average power of the received signal The estimation methods are:

[0061]

[0062]

[0063] Where N1 is the length of the inserted UW sequence UW1, u k1 (k),u k2 (k) and u k3(k) are the received values ​​of the three UW sequences UW1 inserted in this subframe after passing through the ionospheric scattering channel.

[0064] The specific method of channel equalization is:

[0065] Assume that the i-th data segment in this subframe is transformed into X by FFT i (k) Represents the average power of the noise in this subframe, Represents the average power of the received signal in this subframe, The frequency domain estimate of the ionospheric scattering channel through which this subframe is transmitted The conjugate of , then the result of MMSE equalization of the i-th data segment in this subframe is:

[0066]

[0067] Where IFFT stands for inverse fast Fourier transform.

[0068] Further, after performing channel equalization on all data segments in a subframe, the channel equalization results of these data segments are sequentially connected to obtain the channel equalization result of this subframe, and the channel equalization results of all subframes in this multipath data are sequentially connected to obtain the channel equalization result of this multipath data. For the mth data segment greater than The path of the multipath data obtained as the synchronization position after MMSE channel equalization is expressed as y m .

[0069] Step (6), weighted combination of the results of multi-path data channel equalization.

[0070] Specifically, the weighted coefficient for weighted combination of multi-path data is:

[0071]

[0072] Among them, A m The modulus represents the diameter whose amplitude is greater than 1 / 2 of the main diameter. M represents the modulus of all diameters greater than 1 / 2 of the main diameter. The total number of diameters.

[0073] Specifically, the specific method for weighted combination of multi-path data is as follows:

[0074]

[0075] Among them, w m is the weighting coefficient, y m Because the mth one is greater than The path is taken as the result of MMSE channel equalization of the multipath data obtained at the synchronization position, and y is the combined data obtained after weighted combination.

[0076] Furthermore, the combined data is deinterleaved and then LDPC soft decoding is performed to restore the original information.

[0077] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A communication method for ionospheric scattering channels to combat multipath fading, characterized in that: The steps include: (1) Generate UW sequence UW1 and UW sequence UW2, and store UW sequence UW1 and UW sequence UW2 at the transmitting end and receiving end of the system; (2) The transmitter divides the data to be transmitted into multiple segments of equal length, copies the UW sequence UW1 into three copies and inserts them between the multiple segments at equal intervals, and copies the tail data of each segment of data and the tail data of each segment of UW sequence UW1 and adds them to their heads as the cyclic prefix of the segment of data, thereby obtaining a subframe; (3) A plurality of subframes are connected to the UW sequence UW2 to form a frame and send it out; (4) The receiving end samples and receives the signal generated by the transmitted signal passing through the ionospheric scattering channel, and cross-correlates the sampled data with the locally stored UW sequence UW2 to obtain a correlation peak diagram. The amplitude of the main path on the correlation peak diagram is A max , find all the points near the main path that are larger than The diameters of the m ,...,A M ) and positions (loc1,loc2,…,loc m ,…,loc M ), A m Indicates that the mth one is greater than The modulus of the diameter, loc m Indicates that the mth one is greater than The position of the path, m∈[1,M], M is the main path near all the The total number of paths; respectively use the positions of these paths as synchronization positions to obtain multi-path multi-path data equal to the number M, and remove the cyclic prefix of each data path according to the position of the added cyclic prefix; (5) Each multipath data is processed in subframe units, and the LS channel estimation algorithm is used to perform channel estimation using the three UW sequences UW1 inserted in the subframe sequence, and the MMSE equalization algorithm is used to perform channel equalization to obtain the channel equalization result of the multipath data; (6) Weighted combination of the results of multi-path data channel equalization.

2. The method for anti-multipath fading communication applicable to ionospheric scattering channels according to claim 1, characterized in that: In step (1), the UW sequence used is the Zadoff-Chu sequence, which is generated by the following formula: Wherein, N is the length of the generated sequence, j is the imaginary unit, and k is the sequence number in the UW sequence; wherein, the UW sequence UW1 and the UW sequence UW2 are generated using different sequence lengths N1 and N2, the value of N1 is a positive integer power of 2, and the value of N2 is determined by the bandwidth occupied by the system when transmitting data.

3. The method for anti-multipath fading communication applicable to ionospheric scattering channels according to claim 1, characterized in that: In step (2), the encoded data to be transmitted is equally divided into 12 segments. The length of each segment of data after segmentation is the same as the length of the UW sequence UW1. The UW sequence UW1 is inserted after the 2nd, 6th and 10th segments of data respectively.

4. The method for anti-multipath fading communication applicable to ionospheric scattering channels according to claim 1, characterized in that: In step (2), the length of the cyclic prefix is ​​1 / 8 of the length of the data segment, and the result of dividing the length of the cyclic prefix by the signal transmission rate is greater than the channel delay.

5. The method for anti-multipath fading communication applicable to ionospheric scattering channels according to claim 1, characterized in that: In step (5), the specific method of channel estimation is: The receiving end extracts three segments of UW sequence UW1 according to the original insertion position of UW sequence UW1 in the subframe, and obtains the FFT transformation value U of the three segments of UW sequence UW1 after passing through the ionospheric scattering channel through FFT transformation. k1 (k) U k2 (k) and U k3 (k) Perform FFT transformation on the locally stored UW sequence UW1 to obtain the FFT transformation value U of the UW sequence UW1 k (k); Thus, the frequency domain estimate of the ionospheric scattering channel transmitted in this subframe is obtained for:

6. The method for anti-multipath fading communication applicable to ionospheric scattering channels according to claim 1, characterized in that: In step (5), the specific method of channel equalization is: Assume that the i-th data segment in this subframe is transformed into X by FFT i (k) Represents the average power of the noise in this subframe, represents the average power of the received signal in this subframe, Represents the frequency domain estimate of the ionospheric scattering channel through which this subframe is transmitted The conjugate of , then the result of MMSE equalization of the i-th data segment in this subframe is: Where, IFFT stands for inverse fast Fourier transform; The average power of the noise and the average power of the received signal The estimation methods are: Where N1 is the length of the inserted UW sequence UW1, u k1 (k) and u k2 (k) and u k3 (k) are the received values ​​of the three UW sequences UW1 inserted in this subframe after passing through the ionospheric scattering channel; After performing channel equalization on all data segments in a subframe, the channel equalization results of these data segments are sequentially connected to obtain the channel equalization result of this subframe, and the channel equalization results of all subframes in this multipath data are sequentially connected to obtain the channel equalization result of this multipath data. For the mth data segment greater than The path of the multipath data obtained as the synchronization position after MMSE channel equalization is expressed as y m .

7. The method for anti-multipath fading communication applicable to ionospheric scattering channels according to claim 1, characterized in that: In step (6), the weighted coefficient for weighted combination of multi-path data is: Among them, A m The modulus represents the diameter whose amplitude is greater than 1 / 2 of the main diameter. M represents the modulus of all diameters greater than 1 / 2 of the main diameter. The total number of diameters; The specific method for weighted merging of multi-path data is as follows: Among them, w m is the weighting coefficient, y m Because the mth one is greater than The path is taken as the result of MMSE channel equalization of the multipath data obtained at the synchronization position, and y is the combined data obtained after weighted combination.

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