Burst spread spectrum transmission frame structure for helicopter slot communication for broadband signaling

Abstract

The present invention relates to the field of satellite communications, and specifically to a burst spread spectrum communication transmission frame structure for helicopter slot communications for broadband signaling, which is particularly suitable for practical applications in satellite communication transmission for helicopters to resist rotor obstruction under global signaling beams. The frame structure consists of three parts: a frame header, a unique word, and a data frame. The transmission of a coded frame is completed by splitting it into multiple bursts for transmission. Reliable communication in the case of helicopter rotor obstruction is achieved by repeatedly sending coded data in adjacent bursts, and anti-interference and covert communication is achieved by spread spectrum. The frame structure designed by the present invention has the advantages of low signal-to-noise ratio demodulation and high transmission reliability compared to traditional satellite communication designs. It is particularly suitable for FPGA implementation of channel transmission in a satellite communication system for helicopters to resist rotor obstruction under global signaling beams.

Description

Technical Field

[0001] The present invention relates to the field of satellite communication, and in particular to a burst spread spectrum transmission frame structure for helicopter slot communication of broadband signaling, and is particularly suitable for FPGA implementation of channel transmission in a satellite communication system under helicopter rotor shielding under a global signaling beam. Background Art

[0002] Broadband signaling beam transmission signaling can transmit a small amount of business, the communication demand data volume is small, the transmission rate is not high, but the reliability requirement is high. The solution of fountain coding combined with short frame burst overcomes the information loss caused by rotor occlusion and realizes efficient transmission. The existing signal frame structure cannot take into account the signal transmission under the broadband signaling beam, and the fountain coding delay is large, which is not suitable for the transmission of low-speed communication services. A helicopter slot communication transmission frame structure based on burst spread spectrum under a global signaling beam adopts a retransmission mechanism to overcome the influence of rotor occlusion, adopts an efficient coding method to reduce the demodulation threshold; adopts a spread spectrum communication method to reduce the power spectrum density and reduce interference from neighboring satellites; the transmission performance is only related to the occlusion ratio and is suitable for different models. Summary of the invention

[0003] In order to realize helicopter communication under broadband signaling beam, the present invention provides a burst spread spectrum transmission frame structure for helicopter slot communication of broadband signaling, which solves the problem of reliable communication under the cover of helicopter rotor. At the same time, it adopts burst spread spectrum and has the characteristics of anti-interference from neighboring satellites and strong concealment.

[0004] The technical solution adopted by the present invention is:

[0005] A burst spread spectrum transmission frame structure for helicopter slot communication of broadband signaling, wherein the payload data of each transmission frame is the data of a coding block; the transmission frame includes multiple bursts, each burst includes a frame header, a unique word and a data frame, wherein the length of the data frame body is determined according to the coding block length and the helicopter rotor shielding period, and the framed data is spread spectrum using a random sequence.

[0006] Furthermore, the frame header is composed of an all-1 sequence of L symbols and is spread with a spread spectrum code sequence; the frame header of L symbols is used for frame capture and pseudo code synchronization of burst spread spectrum frames under low signal-to-noise ratio, the frame header adopts BPSK modulation, and the size of L is determined according to the signal-to-noise ratio required by the receiving end.

[0007] Furthermore, the unique word is composed of a random sequence of N symbols; the unique word of N symbols is used to determine the starting position of the demodulated data in the burst, the unique word is implemented using BPSK modulation, and the size of N is determined according to the signal-to-noise ratio required by the receiving end.

[0008] Furthermore, each data frame is composed of multiple data frame blocks; the data frame length M is determined based on the length C of a data coding block and the helicopter rotor occlusion period T, satisfying that T is less than or equal to 2(L+M+N) / symbol rate. After the helicopter rotor occlusion period T, the number of frame header symbols L and the unique character symbol format N are determined, the data frame length M can be determined.

[0009] Furthermore, the data frames in every two bursts are repeated. When the data transmission fails due to rotor occlusion during data communication, the rotor occlusion rate and occlusion period are calculated to ensure that at least one of the two bursts with the same data frame load is correctly received.

[0010] Furthermore, the unique word of each burst in each transmission frame uses the unique word corresponding to the burst to identify the grouped data frame blocks and realize the reorganization of the coded frame.

[0011] Compared with the background technology, the present invention has the following characteristics:

[0012] 1. The design of the present invention is very suitable for FPGA implementation of channel transmission in a satellite communication system under the shielding of a signaling beam helicopter rotor.

[0013] 2. Compared with traditional satellite communication designs, the design of the present invention has the advantages of low signal-to-noise ratio demodulation and high transmission reliability, and is very suitable for the application of block code encoding. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the frame structure of the present invention. DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the accompanying drawings.

[0016] A burst spread spectrum transmission frame structure for helicopter slot communication for broadband signaling, wherein the transmission frame includes multiple bursts, and the payload data of each transmission frame is the data of a coded block. Each burst consists of a frame header, a unique word, and a data frame. The length of the data frame body is determined according to the length of the coded code block and the helicopter rotor shielding period. The framed data is spread using a random sequence. The details are as follows:

[0017] 1. Insert the frame header block pilot sequence at the beginning of the current burst to indicate the starting position of the current transmission frame. The frame header consists of a sequence of all 1s of L symbols and is spread with a spread spectrum code sequence. The frame header of L symbols is used for frame capture and pseudo code synchronization of burst spread spectrum frames under low signal-to-noise ratio. The frame header adopts BPSK modulation, and the size of L is determined according to the signal-to-noise ratio required by the receiving end;

[0018] The frame header is used by the demodulator to perform pseudo-code capture and synchronization on the pseudo-random sequence after matched filtering, in order to determine the starting position of the spread spectrum sequence at the receiving end to achieve correct despreading of the spread spectrum signal and frame capture. The frame header length must be reasonably designed, and its length must meet the signal-to-noise ratio required by the system, so that the receiving end can correctly capture and synchronize, and can assist in achieving frame capture.

[0019] 2. Insert a unique word uw after the current burst frame header. The unique word consists of a random sequence of N symbols. The frame header of N symbols is used to determine the starting position of the demodulated data in the burst and to resolve phase ambiguity. The unique word is implemented using BPSK modulation. The length of N is determined according to the signal-to-noise ratio required by the receiving end.

[0020] Among them, the unique word is used to accurately locate the data frame position and correct the phase ambiguity after the data carrier is recovered. Its length must meet the signal-to-noise ratio required by the system for the receiving end to correctly identify it. In order to adapt to the gap communication under the cover of the helicopter rotor, a method of splitting or combining data frames and sending them repeatedly is designed. Different unique words uw are used to mark the split data and the two repeated data frames and store and process them separately. The unique words corresponding to the two split data frames are uw1 and uw2 respectively, and the unique words corresponding to the two repeatedly sent data frames are uw3 and uw4 respectively, which is convenient for realizing the reorganization and recognition of the coded frame.

[0021] 3. Insert a data frame after the unique word of the current burst frame. Each data frame consists of multiple data frame blocks. The data frame length M depends on the length C of a data coding block and the helicopter rotor occlusion period T, and satisfies T less than or equal to (2(L+M+N) / symbol rate). After the helicopter rotor occlusion period T, the number of frame header symbols L and the unique word symbol format N are determined, the data frame length M can be determined.

[0022] The data frame combines the carried data blocks by splitting and combining the coding blocks. If the coding block is large, it is split into two, otherwise it is combined. The appropriate length of the code can also be selected. For the same data, it is sent repeatedly to avoid data loss caused by obstruction. The demodulated data is spliced ​​and restored at the demodulation end to achieve reliable data transmission. The unique word and data frame are mainly used for carrier frequency capture and carrier frequency tracking. The modulation mode of the data frame can be BPSK and QPSK;

[0023] 4. The block pilot sequence of the frame header is implemented by BPSK modulation, the payload data in the frame body is implemented by QPSK modulation, and the unique word is implemented by BPSK modulation;

[0024] 5. Spread the transmission frame and complete the generation of the transmission frame structure to facilitate the implementation of burst spread spectrum helicopter slot communication transmission.

[0025] A transmission frame consists of multiple bursts, in which the data frames in every two bursts are repeated to avoid transmission data failure caused by rotor occlusion during data communication. By calculating the rotor occlusion rate and occlusion period, at least one of the two bursts with the same data frame payload can be correctly received.

[0026] The specific implementation is that after the matched filtering, the demodulator performs pseudo code capture synchronization on the frame header to determine the starting position of the receiving end spread spectrum sequence to achieve the correct despreading of the spread spectrum signal. After the capture synchronization, the despread data is used to capture and track the carrier frequency. After the carrier recovery is completed, the unique word is used to locate the starting position of the data frame block and correct the phase ambiguity. Due to the influence of the rotor shielding in the helicopter application, some signals may be missing, resulting in incomplete received signals. When the same data frame is sent twice, the data after the two carrier recovery are added to obtain a complete data frame to complete the demodulation. Compared with conventional demodulation, the signal-to-noise ratio loss of this method is less than 0.5dB.

Claims

1. A helicopter slot communication method for broadband signaling, characterized in that: The process includes: The processing process at the sending end is: Insert the frame header block pilot sequence at the beginning of the current burst to indicate the starting position of the current transmission frame. The frame header consists of a sequence of all 1s of L symbols and is spread with a spreading code sequence. The frame header adopts BPSK modulation. Insert a unique word after the current burst frame header. The unique word consists of a random sequence of N symbols and is used to determine the starting position of the demodulated data in the burst. The unique word is implemented using BPSK modulation. Insert a data frame after the unique word of the current burst frame, and each data frame consists of multiple data frame blocks; then multiple bursts are combined into a burst spread spectrum transmission frame for transmission; wherein L and N are determined according to the signal-to-noise ratio required by the receiving end; the payload data of each burst spread spectrum transmission frame is the data of a coding block, and the data frame length M is determined according to the length C of a coding block and the helicopter rotor shielding period T, and satisfies that T is less than or equal to 2 (L + M + N) / symbol rate. After the helicopter rotor shielding period T, the number of frame header symbols L, and the number of unique word symbols N are determined, the data frame length M is determined; The processing process at the receiving end is: The receiving end receives the burst spread spectrum transmission frame, performs matched filtering, and uses the frame header to perform pseudo-code capture synchronization on the pseudo-random sequence, determine the starting position of the receiving end spread spectrum sequence to achieve correct despreading of the spread spectrum signal, and achieve frame capture at the same time; and use the unique word to locate the data frame position and correct the phase ambiguity, determine the starting position of the demodulated data in the burst; then the demodulated data is spliced ​​and restored to achieve data transmission.

2. A helicopter slot communication method for broadband signaling according to claim 1, characterized in that: The data frames in every two bursts will be repeated. When the transmission data fails due to rotor occlusion during data communication, the rotor occlusion rate and occlusion period are calculated to ensure that at least one of the two bursts with the same payload data frame is correctly received.

3. A helicopter slot communication method for broadband signaling according to claim 1, characterized in that: The unique word of each burst in each burst spread spectrum transmission frame adopts the unique word corresponding to the burst to identify the grouped data frame blocks and realize the reorganization of the coded frame.

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