5G NTN waveform anti-rotor wing shielding method suitable for helicopter communication

Abstract

The invention provides a 5G NTN waveform anti-rotor-shielding method suitable for helicopter communication, and the method comprises the steps: setting a switching threshold value of an adaptive modulation code and a fountain code, and carrying out the switching according to the channel quality; when the channel quality is good, adaptive modulation and coding are adopted, channel feedback CQI is obtained, and according to the adaptive modulation and coding technology, a proper modulation mode and coding efficiency are selected, and uplink and downlink waveforms of a 5G NTN system conforming to a target modulation mode and a target code rate are constructed; and when the channel quality is poor, using a fountain code, taking the LDPC code under the 5G NTN specification as an outer code, and taking the LT code as an inner code, and constructing uplink and downlink waveforms of the 5G NTN system conforming to the target modulation mode and the target code rate. According to the method, the adaptive modulation coding technology and the Raptor fountain code are utilized, so that the communication quality is ensured under the condition that the helicopter rotor is shielded, and the rotor shielding resistance of helicopter communication is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of communication, and particularly relates to a 5G NTN waveform anti-rotor shielding method for helicopter communication. BACKGROUND

[0002] Helicopter satellite communication has the characteristics of wide regional coverage, less geographical condition restriction, stable communication, etc., and has been widely used in the fields of rescue and disaster relief, search and rescue, etc., and has important research value. However, in the process of helicopter satellite communication, due to the periodic shielding of the helicopter rotor to the antenna, the signal will show the characteristics of periodic fading, which seriously affects the communication performance. The most direct solution is to take retransmission to reduce the influence of rotor shielding on communication, however, the efficiency of retransmission is very low, and with the increase of retransmission times, the resources occupied are also increasing. Even the relatively good secondary retransmission, its efficiency is not more than 50%. With the in-depth research, researchers have proposed a partial retransmission mechanism to reduce the redundancy to improve the efficiency, and the bottleneck is to obtain an accurate rotor shielding model.

[0003] The adaptive modulation and coding technology can change the coding and modulation scheme according to the current state of the channel with the change of the communication environment, control the transmission rate of the information, so that it can adapt to the current channel change, thereby ensuring the transmission quality of the communication. That is, when the channel condition is poor, a lower code rate and modulation mode are adopted, which can reduce the error rate of the receiving end and ensure the reliability and effectiveness of the system. While in the case of excellent channel condition, high-order modulation scheme and higher code rate are adopted to improve the spectrum efficiency and system throughput, and ultimately the transmission efficiency can be doubled without changing the bandwidth and power. Due to the shielding of the helicopter rotor, the channel characteristics at different times are different, and the adaptive modulation and coding technology can effectively improve the reliability and efficiency of communication transmission.

[0004] The Raptor fountain code cascades an error correction code in front of the LT code as pre-coding, which increases a certain amount of redundancy, but does not require the LT code to accurately translate all the information, because a small number of errors can be corrected by the error correction ability of the pre-coding. At the same time, it can ensure that the amount of information received by the Raptor code is less than that of the LT code under the same decoding success rate. Due to its unique error correction characteristics, the application of fountain code in helicopter satellite communication can obtain good performance. SUMMARY

[0005] In view of the above problems, the 5G NTN waveform anti-rotor shielding method suitable for helicopter communication utilizes the adaptive modulation and coding technology and the Raptor fountain code, so as to ensure the quality of communication and improve the anti-rotor shielding capability of helicopter communication under the condition of helicopter rotor shielding.

[0006] Specifically as follows:

[0007] A 5G NTN waveform anti-rotor shelter method suitable for helicopter communication, the method is:

[0008] The switching threshold of adaptive modulation and coding and fountain code is set, and switching is performed according to the channel quality;

[0009] When the channel quality is good, adaptive modulation and coding is adopted, channel feedback CQI is obtained, and according to the adaptive modulation and coding technology, the appropriate modulation mode and coding efficiency are selected to construct the uplink and downlink waveforms of the 5G NTN system conforming to the target modulation mode and target code rate;

[0010] When the channel quality is poor, the fountain code is used, the LDPC code under the 5G NTN specification is used as the outer code, and the LT code is used as the inner code to construct the uplink and downlink waveforms of the 5G NTN system conforming to the target modulation mode and target code rate. Further, the threshold satisfying the block error rate of 0.1 under the AWGN channel is used as the switching threshold of adaptive modulation and coding and fountain code. Further, the switching threshold is calculated and obtained by using the equivalent signal-to-noise ratio mapping algorithm; when the channel environment is good, the signal-to-noise ratio of the channel is mapped to the discrete CQI value according to the threshold, and the adaptive modulation and coding selects the modulation and coding strategy according to the CQI value; when the channel quality is poor, the Raptor fountain code is used, and the length of the encoded code is , wherein represents the original symbol length, represents the decoding overhead. Further, the equivalent signal-to-noise ratio mapping algorithm maps the subcarrier signal-to-noise ratio into the equivalent signal-to-noise ratio, which is compared with the channel decision threshold as follows: ; wherein represents the adjustment factor. Further, when the channel quality is good, the adaptive modulation and coding technology is used to obtain the SNR-BLER curve under the AWGN, find the threshold value of BLER=0.1, calculate the equivalent signal-to-noise ratio of the actual fading channel, and map the equivalent SNR to CQI by querying the threshold table, feedback to the sending end, and select the appropriate MCS modulation and coding strategy for transmission. Further, when the channel quality is poor, in the case of very low signal-to-noise ratio, that is, the depth of the rotor shelter of the helicopter is large, the Raptor fountain code is used as the encoding mode, the source code is first subjected to LDPC encoding to obtain intermediate symbols, and then subjected to LT encoding according to the degree distribution function and the decoding overhead to obtain the encoded symbols. Further, the degree distribution function of the LT encoding adopts the robust arc wave distribution, and its expression is:

[0011] ;

[0012] ;

[0013] ;

[0014] wherein, is a degree value, is the number of original symbols, represents the expected value of the number of encoded symbols that can be found each time in the iteration of the degree value, is a constant greater than 0, represents the maximum probability of decoding failure allowed when decoding. Further, the source code length of the Raptor fountain code is calculated as follows:

[0015] First, according to the parameters configured in the 5G NTN, the size of the transmission data block is calculated, and the size after Raptor encoding is taken as the size after Raptor encoding;

[0016] According to the decoding overhead, the code length before LT encoding, that is, the code length after LDPC encoding, is back calculated, and the calculation formula is as follows:

[0017] ;

[0018] wherein, is the length after LDPC encoding, that is, the input length of LT encoding, is the size of the transmission block in the 5G NTN, is the decoding overhead of the LT code;

[0019] Then, according to the encoding efficiency of the LDPC, the size before LDPC encoding, that is, the size of the original symbol, is back calculated, and the calculation formula is as follows:

[0020] ;

[0021] wherein, is the input length of the LDPC encoding, that is, the input symbol length of the Raptor code, is the encoding efficiency of the LDPC code.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] 1. By setting the intelligent switching mechanism of adaptive modulation and coding and fountain code, the communication quality and reliability under the rotor shielding channel are improved; 2. When the channel quality is good, adaptive modulation and coding are used, the modulation mode and coding efficiency are dynamically adjusted according to CQI feedback, the spectrum utilization and throughput are improved; when the channel quality is poor, it is automatically switched to Raptor fountain code, and the error correction ability and redundancy mechanism are used to ensure uninterrupted communication; strong adaptability, efficiency and reliability are considered; 3. Compared with the traditional retransmission mechanism, the fountain code reduces the number of retransmissions and resource occupation, improves the transmission efficiency, and is especially suitable for high dynamic and high delay satellite communication scenarios. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The flowchart of the present application; Figure 2 The flowchart of adaptive modulation and coding in the present application;

[0025] Figure 3 The construction flowchart of Raptor code in the present application;

[0026] Figure 4 The flowchart of LT encoding;

[0027] Figure 5 The flowchart of Raptor encoding;

[0028] Figure 6 Performance chart and shielding cycle diagram. DETAILED DESCRIPTION

[0029] The technical solutions of the embodiments of the present application will be described clearly and completely in combination with the drawings. The specific embodiments of the present application are described in detail below in combination with the drawings and specific embodiments.

[0030] Embodiment 1:

[0031] As Figure 1 shown, the present embodiment provides a 5G NTN waveform anti-rotor shielding method suitable for helicopter communication, the method is:

[0032] The switching threshold of adaptive modulation and coding and fountain code is set, and switching is performed according to the channel quality.

[0033] Assuming that the modulation mode and coding efficiency corresponding to MCS1 are QPSK and 78 / 1024 respectively, the block error rate curve is obtained under the AWGN channel, and the signal-to-noise ratio corresponding to the target block error rate 0.1 is found as the switching threshold of adaptive modulation and coding. Repeat the operation to find the lowest signal-to-noise ratio threshold in the MCS table, which is used as the switching threshold of adaptive modulation and coding and fountain code. When the channel feedback signal-to-noise ratio is lower than the threshold, the effect of adaptive modulation and coding will be poor, and fountain code needs to be used for transmission; when the channel feedback signal-to-noise ratio is higher than the threshold, the effect of adaptive modulation and coding is good, and there is no need for additional redundancy of fountain code to ensure communication quality.

[0034] The channel feedback signal-to-noise ratio, i.e. the equivalent signal-to-noise ratio, is obtained by the exponential equivalent signal-to-noise ratio mapping algorithm from the subcarrier signal-to-noise ratio, which is as follows:

[0035] ;

[0036] Wherein, The adjustment factor is closely related to the modulation mode and coding efficiency, and the higher the accuracy, the closer the BLER obtained by the mapping algorithm to the BLER under the AWGN channel.

[0037] As Figure 2 shown, when the channel quality is good, the CQI value is determined by mapping the subcarrier signal-to-noise ratio in the actual channel to the equivalent signal-to-noise ratio and comparing it with the threshold value corresponding to the MCS table. The CQI value is fed back to the sending end, and the sending end selects the MCS modulation and coding strategy according to the CQI value. As Figure 3 shown, when the channel quality is poor, Raptor fountain code is used, and the LDPC code of 5G NTN is used as the outer code and the LT code as the inner code.

[0038] The LT encoding process in this embodiment is as shown in Figure 4 , which specifically includes:

[0039] According to the degree distribution function, a random integer between is generated The probability distribution function of

[0040] ;

[0041] Randomly select from original symbols for XOR operation to obtain the encoded symbol :

[0042] ;

[0043] Repeat the above steps until enough encoded symbols are generated.

[0044] Assuming the first 4 bits of the source code are [1, 0, 1, 1], according to the degree value distribution in the formula (1), the first 4 bits of the obtained LT encoding symbol are [0, 1, 1, 1]. Figure 4

[0045] The Raptor encoding process in this embodiment is as shown in the formula (2), and specifically includes the following steps. Figure 5

[0046] The original symbol is pre-encoded by using the LDPC code, redundancy information is added, and an intermediate symbol is obtained;

[0047] The intermediate symbol is encoded by using the LT code, and according to the degree distribution function, XOR operation is performed according to the degree value, to obtain the final encoding symbol.

[0048] The performance graph and the occlusion period in this embodiment are as shown in the formula (3). Figure 6

[0049] Embodiment 2:

[0050] As shown in the formula (4), the embodiment provides a construction method of a Raptor code meeting the 5G NTN system, including the following steps. Figure 3 S210, taking the LDPC of the 5G NTN as an outer code and the LT as an inner code, to generate a Raptor fountain code. First, according to the data block size configured in the 5G NTN, the size after Raptor code encoding is taken as the size after Raptor code encoding;

[0051] S220, according to the decoding overhead, the code length before LT encoding is inversely deduced, that is, the code length after LDPC encoding, and the formula is as follows:

[0052]

[0053] ; Wherein, represents the length after LDPC encoding, that is, the input length of the LT encoding,

[0054] represents the size of the transmission block in the 5G NTN, represents the decoding overhead of the LT code; S230, finally, according to the encoding efficiency of the LDPC, the size before the LDPC encoding is inversely deduced, that is, the size of the original symbol, and the formula is as follows:

[0055]

[0056] ;

[0057] Wherein, represents the input length of the LDPC encoding, that is, the input symbol length of the Raptor code, ​​​​​​The coding efficiency of the LDPC code is represented. For data exceeding the size, chunking should be performed and then transmitted by the 5G NTN.

[0058] For this embodiment, it is assumed that the transport block size is 8000, the coding overhead is 0.3, the symbol length after LDPC encoding is 6154, and the original symbol length is 2051. Therefore, the original data in this example can be transmitted at one time and does not need to be divided.

[0059] The above embodiments are only used to illustrate the patent of the present application, but not to limit the patent of the present application. Although the patent of the present application is described in detail with reference to the embodiments, it should be understood by those skilled in the art that various combinations, modifications or equivalent replacements of the technical solutions of the patent of the present application do not deviate from the spirit and scope of the patent of the present application, and should be covered in the scope of the claims of the patent of the present application.

Claims

1. A 5G NTN waveform anti-rotor blocking method suitable for helicopter communication, characterized in that, The method comprises the following steps: Setting a switching threshold of adaptive modulation and coding and fountain code, and switching according to channel quality; When the channel quality is good, adaptive modulation and coding is used to obtain channel feedback CQI, select appropriate modulation mode and coding efficiency according to adaptive modulation and coding technology, and construct uplink and downlink waveforms of 5G NTN system conforming to target modulation mode and target code rate; When the channel quality is poor, fountain code is used, LDPC code under 5G NTN specification is used as outer code, and LT code is used as inner code to construct uplink and downlink waveforms of 5G NTN system conforming to target modulation mode and target code rate.

2. A 5G NTN waveform anti-rotor-shading method for communication of a helicopter according to claim 1, characterized in that, The threshold satisfying the block error rate of 0.1 under the AWGN channel is used as the switching threshold of adaptive modulation and coding and fountain code.

3. A 5G NTN waveform anti-rotor-shading method for helicopter communications according to claim 2, characterized in that, The switching threshold is calculated by using an equivalent signal-to-noise ratio mapping algorithm; when the channel environment is good, the signal-to-noise ratio of the channel is mapped to discrete CQI values divided according to the threshold value, and the adaptive modulation and coding selects the modulation and coding strategy according to the CQI value; when the channel quality is poor, a Raptor fountain code is used, and the length of the code is wherein, represents the original symbol length, represents the decoding overhead.

4. A 5G NTN waveform anti-rotor-shading method suitable for helicopter communications according to claim 3, characterized in that, The equivalent signal-to-noise ratio mapping algorithm maps the subcarrier signal-to-noise ratio into an equivalent signal-to-noise ratio, which is compared with a channel decision threshold, as follows: wherein, denotes an adjustment factor.

5. A 5G NTN waveform anti-rotor-shading method suitable for helicopter communications according to claim 4, characterized in that, When the channel quality is good, the SNR-BLER curve is obtained by simulation under the AWGN using adaptive modulation and coding technology, the threshold value of BLER=0.1 is found, the equivalent signal-to-noise ratio of the actual fading channel is calculated, the equivalent SNR is mapped to CQI by querying the threshold table, the feedback is sent to the sending end, and the appropriate MCS modulation and coding strategy is selected for transmission.

6. A 5G NTN waveform anti-rotor-shading method suitable for helicopter communications according to claim 4, characterized in that, When the channel quality is poor, the Raptor fountain code is used as the coding mode in the case of extremely low signal-to-noise ratio, i.e. large rotor shielding depth, the source code is first subjected to LDPC coding to obtain intermediate symbols, and then subjected to LT coding according to the degree distribution function and decoding overhead to obtain coded symbols.

7. A 5G NTN waveform anti-rotor-shading method suitable for helicopter communications according to claim 6, characterized in that, The degree distribution function of the LT coding adopts the robust arc wave distribution, and its expression is as follows: ； ； ； where is the degree value, is the number of original symbols, is the degree value found at each iteration, is the expected number of encoded symbols of degree is a constant greater than 0, is the maximum probability of decoding failure allowed during decoding.

8. A 5G NTN waveform anti-rotor-shading method suitable for helicopter communications according to claim 7, characterized in that, The source code length of the Raptor fountain code is calculated as follows: First, the transmission data block size is calculated according to the parameters configured in the 5G NTN, and the size after Raptor coding is taken as the size; According to the decoding overhead, the code length before LT coding, i.e. the code length after LDPC coding, is back calculated, and the calculation formula is as follows: ； wherein, is the LDPC encoded length, i.e., the input length of the LT encoding, is the size of the transport block in 5G NTN, is the decoding overhead of the LT code; According to the coding efficiency of the LDPC, the size before LDPC coding, i.e. the size of the original symbol, is back calculated, and the calculation formula is as follows: ； wherein, is the input length of the LDPC encoding, i.e. the input symbol length of the Raptor code, is the coding efficiency of the LDPC code.

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