Low earth orbit inter-satellite communication terminal without attitude pointing requirement and communication method

Abstract

This invention discloses a low-Earth orbit inter-satellite communication terminal with no attitude pointing requirements. Operating in the UHF band, the terminal is equipped with a dual-measuring antenna array that provides quasi-omnidirectional beam coverage. It boasts a receiving sensitivity exceeding -130 dBm, a transmitting EIRP of no less than 22 dBm, and a total power consumption of less than 5 W. It enables reliable inter-satellite communication within a 2000 km range under arbitrary attitudes of two or more satellites. During communication, by sharing satellite attitude information, it solves the problems of acquisition, alignment, and tracking in satellite networking and inter-satellite laser communication. Its directional-free, ultra-high sensitivity, and low power consumption characteristics make it particularly suitable for applications such as space self-organizing networks of micro / nano satellites and inter-satellite laser communication.

Description

Technical Field

[0001] This invention belongs to the technical field of inter-satellite communication, and particularly relates to a low-Earth orbit inter-satellite communication terminal and communication method without attitude pointing requirements. Background Technology

[0002] Two existing technologies can solve the communication acquisition problem in inter-satellite laser communication and networking processes: 1. By using a ground station to inject the BeiDou or GPS position information of the two satellites, the satellite attitude is adjusted so that the turntables of both satellites point to each other. Then, the laser communication capture and tracking are achieved through scanning via the turntables. Because the beam angle of the optical engine for satellite laser communication does not exceed 0.1° and the turntable scanning angle does not exceed ±5°, after injecting the satellite position information through the ground station, the satellites need to be in a staring state during their orbital flight, and the mutual pointing accuracy between them is less than ±5°. Furthermore, during laser communication, the ground station needs to continuously inject position information. When the ground station beam cannot cover both satellites, two ground stations need to be arranged for data uploading. When the distance between the satellites is large, with one in China and the other outside China, a relay satellite needs to be arranged for command injection. The entire process requires too many resources, is costly, and has low real-time performance. 2. By using a Ka-band inter-satellite communicator to obtain the position information of the two satellites, the satellite attitudes are adjusted so that the turntables of both satellites point towards each other. Then, scanning is performed through the turntables to achieve laser communication acquisition and tracking. Because Ka-band inter-satellite communicators experience greater free-space attenuation compared to UHF bands, the spatial attenuation increases by approximately 35 dB for the same communication distance. Therefore, high-gain antennas, higher transmitter EIRP, and higher receiver G / T values ​​are required to achieve reliable inter-satellite communication. The main beam angle of a high-gain antenna is typically no more than ±10°, so there are requirements for the satellite attitude in two-satellite communication scenarios, requiring both satellites to be in a staring state. Furthermore, the cost and power consumption of the product are relatively high. Summary of the Invention

[0003] The purpose of this invention is to provide a low-orbit inter-satellite communication terminal and communication method without attitude pointing requirements. It utilizes dual tape measure antennas to form a quasi-omnidirectional beam coverage range. No attitude pointing requirements are required for satellite during signal acquisition. It adopts narrowband communication, has high receiving sensitivity, and an inter-satellite communication distance of more than 2000km.

[0004] To solve the above problems, the technical solution of the present invention is as follows: A low-Earth orbit inter-satellite communication terminal without attitude pointing requirements includes: an antenna feed system, a radio frequency (RF) module, and a baseband module; the antenna feed system consists of two tape measure antennas arranged in a spatially orthogonal manner to form quasi-omnidirectional beam coverage; the antenna feed system is connected to a low-noise amplifier and a power amplifier in the RF module via a duplexer; the baseband module is communicatively connected to the RF module and uses LoRa modulation / demodulation for data processing to improve the anti-interference capability of the communication link.

[0005] According to one embodiment of the present invention, the noise figure of the low-noise amplifier is ≤0.45 dB and the operating frequency band includes UHF; the transmit EIRP of the power amplifier is ≥22 dBm.

[0006] According to one embodiment of the present invention, the low-noise amplifier uses a TriQuint TQP3M9036 chip, and the power amplifier uses a TriQuint TQP7M9105 chip.

[0007] According to one embodiment of the present invention, the included angle between the two tape measure antennas is 80°–100°, and the beamwidth of each antenna is ≥120°.

[0008] According to one embodiment of the present invention, the baseband module operates in half-duplex mode and interacts with the satellite's onboard computer via a CAN bus.

[0009] According to one embodiment of the present invention, the terminal further includes: an attitude information sharing interface for receiving attitude information of the local satellite and cooperating satellites; and a cooperative control interface with an inter-satellite laser communication terminal for providing coarse alignment data during the acquisition phase.

[0010] An inter-satellite communication method, characterized by comprising the following steps: S1: Continuously transmitting LoRa modulated beacon frames through the quasi-omnidirectional beam, the beacon frames containing the local satellite identifier and attitude information; S2: Performing carrier detection and frame synchronization on the received cooperative satellite beacon frames, and proceeding to step S3 if a valid frame is detected; S3: Calculating a coarse alignment angle based on the cooperative satellite attitude information and outputting the angle to the inter-satellite laser communication terminal to complete the acquisition, alignment, and tracking of the laser link; S4: After the laser link is established, the terminal enters a sleep or low-power listening state.

[0011] According to an embodiment of the present invention, in step S1, the beacon frame adopts an SF12 spreading factor, a bandwidth of 125 kHz, and a coding rate of 4 / 5.

[0012] According to an embodiment of the present invention, in step S3, if the attitude information of the cooperative star remains unchanged within a preset threshold, the coarse alignment angle calculation is skipped and the previous calculation result is directly used.

[0013] Because the present invention adopts the above technical solution, it has the following advantages and positive effects compared with the prior art: This invention discloses a low-Earth orbit (LEO) inter-satellite communication terminal with no attitude pointing requirement. Addressing the issues of existing inter-satellite communication systems requiring continuous injection of position information from ground stations or necessitating relay satellites due to distance limitations, resulting in excessive resource demands and high costs, this terminal utilizes a dual-measuring-scale wide-beam antenna to construct quasi-omnidirectional beam coverage. Signal acquisition requires no satellite attitude pointing requirement. Employing a narrowband LoRa modulation scheme, a low-noise-figure RF channel, and a robust framework, the communication distance exceeds 2000 km without attitude pointing requirements. During communication, by sharing satellite attitude information, it solves the difficulties in acquisition, alignment, and tracking in satellite networking and inter-satellite laser communication. Its no-pointing-requirement, ultra-high sensitivity, and low-power consumption characteristics are particularly suitable for applications such as space self-organizing networks of micro / nano satellites and inter-satellite laser communication. Attached Figure Description

[0014] Figure 1 This is a block diagram of a low-orbit inter-satellite communication terminal without attitude pointing requirements in one embodiment of the present invention. Figure 2 This is a flow diagram of an inter-satellite communication method according to an embodiment of the present invention. Detailed Implementation

[0015] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a low-Earth orbit inter-satellite communication terminal without attitude pointing requirements, as proposed in this invention. The advantages and features of this invention will become clearer from the following description and claims.

[0016] Please refer to Figure 1 This embodiment provides a low-orbit inter-satellite communication terminal without attitude pointing requirements, including: an antenna feed system, a radio frequency module, and a baseband module; wherein, the antenna feed system consists of two tape measure antennas arranged in a spatially orthogonal manner to form quasi-omnidirectional beam coverage; the antenna feed system is connected to the low-noise amplifier and power amplifier in the radio frequency module through a duplexer; the baseband module is communicatively connected to the radio frequency module and uses LoRa modulation / demodulation for data processing to improve the anti-interference capability of the communication link.

[0017] The antenna system uses two tape measure antennas, which are small in size and have a wide beamwidth. The dual antennas provide almost omnidirectional coverage, enabling inter-satellite communication in any orientation. The angle between the two tape measure antennas is 80°–100°, and the beamwidth of each antenna is ≥120°.

[0018] The RF module consists of two parts: a low-noise amplifier (LNA) and a power amplifier (PA). The LNA uses the TriQuint TQP3M9036, a low-noise transistor operating from 400 to 1500 MHz with a noise figure of 0.45 dB, covering the UHF band. It can provide high performance from a bias voltage of +3 V to +5 V without requiring a negative power supply. The bias network maintains stability against temperature changes through a current mirror and feedback circuitry. It also provides a digital power-off switching circuit to block power leakage from high-power interference input signals. The PA has an EIRP ≥ 22 dBm and uses the TQP7M9105 chip, a high-linearity, high-gain 1-watt driver amplifier. This amplifier delivers high performance between 0.05 and 1.5 GHz, while achieving 47 dBm OIP3 and +30 dBm P1dB at 940 MHz, consuming only 220 mA of quiescent current. The amplifier features a dynamic bias circuit that enables stable operation under bias and temperature variations and provides high linearity during backoff operation.

[0019] The baseband module adopts LoRa modulation, and LoRa modulation and demodulation uses patented spread spectrum modulation and forward error correction technology. It integrates digital spread spectrum, digital signal processing and forward error correction coding technology, which has stronger anti-interference ability and can suppress GMSK interference signals in the same channel by more than 20dB.

[0020] Furthermore, the baseband module uses the SX1278 chip, a half-duplex low-IF transceiver. The received RF signal is converted to differential form to improve second-stage linearity and harmonic suppression. The signal is then down-converted to an intermediate frequency (IF) output as an in-phase and quadrature (I&Q) signal. Data conversion is then performed by a pair of analog-to-digital converters (ADCs), with all subsequent signal processing and demodulation occurring in the digital domain. The LoRa modem employs proprietary modulation and demodulation procedures, combining spread spectrum modulation with cyclic error correction coding to improve link budget and interference immunity. The baseband module operates in half-duplex mode and interacts with the satellite's onboard computer via a CAN bus.

[0021] The standalone unit communicates with the satellite via a CAN bus. The protocol has comprehensive error detection capabilities, including detection of bit errors, stuffing errors, and CRC errors. When an error is detected, the node automatically retransmits data to ensure the accuracy of data transmission. It also uses a differential bus for signal transmission, providing strong anti-interference capabilities and effectively suppressing common-mode interference, making it suitable for environments with strong electromagnetic interference.

[0022] Furthermore, the terminal also includes: an attitude information sharing interface for receiving attitude information from the local satellite and cooperating satellites; and a collaborative control interface with the inter-satellite laser communication terminal to provide coarse alignment data during the acquisition phase.

[0023] During launch, the satellite computer first sends 36 bytes of laser coarse alignment data to the MCU of the baseband module via the CAN bus. The MCU then writes the data into the FIFO of the SX1278 via SPI. The SX1278 then completes CRC, Hamming code 4 / 5, and CSS-SF12 spread spectrum modulation, outputting a -4 dBm, 435 MHz single-ended RF signal. This signal enters the RF module, first passing through a matching network to a high-linearity PA (TQP7M9105), where it is amplified to +23 dBm. Then, it passes through an SPDT switch to select one of the dual tape measure antennas, ultimately forming an EIRP electromagnetic wave with a range of ≥22 dBm, achieving omnidirectional transmission over a distance of 2000 km. During reception, the weak carrier at -117 dBm coupled to the tape measure antenna in any orientation enters the LNA (TQP3M9036, NF 0.45 dB, gain 18 dB) via the same SPDT switch. After being amplified to -99 dBm, it is sent to the mixer of the SX1278 and down-converted to 250 kHz low-IF. The internal 12-bit ΣΔ ADC samples I / Q, and after chirp-512-point FFT, Viterbi decoding, and CRC check, 36 bytes of data are recovered. The MCU reads the data via SPI and transmits it back to the satellite via CAN-FD frames. The entire link is maintained by AGC, AFC, and power / frequency adaptive closed loop to ensure reliable transmission and reception under arbitrary orientation and ±20 kHz Doppler conditions.

[0024] LoRa's data processing revolves around the goal of "converting 36-byte satellite ephemeris-attitude frames into CSS signals that can be reliably transmitted over a 2000 km inter-satellite link, and then restoring them as is." The entire process can be coherently summarized into three closed loops: bit-symbol mapping, radio frequency-air transport, and symbol-bit decoding.

[0025] First section: Bit-symbol mapping (transmitter side) The satellite computer sends a 36-byte payload to the MCU via CAN-FD; the MCU then writes it into the SX1278's FIFO via SPI. The baseband processor first performs CRC-32 error detection on the payload, then performs forward error correction encoding using 4 / 5 Hamming code, and subsequently sends it to the LoRa proprietary CSS (Chirp Spread Spectrum) modulator: every 8 bits of data is mapped to a 4096-chip linear frequency modulated pulse (chirp) according to SF12, forming a continuous I / Q complex envelope symbol stream. Symbol rate = BW / 2^SF = 125 kHz / 4096 ≈ 30.5 sps, with an airtime of approximately 1.1 s.

[0026] Second segment: Radio frequency - over-the-air transport The I / Q symbols are up-converted to 435 MHz by the on-chip DAC, amplified to +22 dBm EIRP by the PA, and radiated omnidirectionally by the dual tape measure antenna. The receiving antenna captures the -117 dBm level signal, amplifies it by 18 dB by the LNA, down-converts it again to 250 kHz low-IF, and sends it to the same SX1278.

[0027] Third section: Symbol-bit decoding (receiving side) The on-chip 12-bit ΣΔ ADC samples I / Q signals and performs "chirp removal": the received chirp is multiplied by the local inverse chirp to obtain a narrowband pulse, followed by a 512-point FFT to directly map the frequency offset to the sign value; the soft-decision output is decoded by Viterbi and checked by CRC. If correct, an RxDone interrupt is triggered, and the MCU reads 36 bytes via SPI and transmits them back to the satellite, completing one end-to-end data loop. Throughout the process, SF, BW, and CR can be dynamically adjusted by the MCU based on real-time SNR, achieving link self-adaptation.

[0028] This low-Earth orbit (LEO) inter-satellite communication terminal, operating in the UHF band, features a dual-measuring antenna array providing quasi-omnidirectional beam coverage. It boasts a receiving sensitivity exceeding -130 dBm, a transmitting EIRP of at least 22 dBm, and a power consumption of less than 5 W. It enables reliable inter-satellite communication within a 2000 km range under arbitrary attitudes of two or more satellites. During communication, by sharing satellite attitude information, it solves the challenges of acquisition, alignment, and tracking in satellite networking and inter-satellite laser communication. Its directional independence, ultra-high sensitivity, and low power consumption make it particularly suitable for applications such as space-based self-organizing networks of micro / nano satellites and inter-satellite laser communication.

[0029] This embodiment also provides an inter-satellite communication method based on the aforementioned low-Earth orbit inter-satellite communication terminal without attitude pointing requirements. Please refer to [link / reference]. Figure 2 The process includes the following steps: S1: Continuously transmit LoRa modulated beacon frames via a quasi-omnidirectional beam. The beacon frames contain the local satellite identifier and attitude information. S2: Perform carrier detection and frame synchronization on the received cooperative satellite beacon frames. If a valid frame is detected, proceed to step S3. S3: Calculate the coarse alignment angle based on the cooperative satellite attitude information and output the angle to the inter-satellite laser communication terminal to complete the acquisition, alignment, and tracking of the laser link. S4: After the laser link is established, the terminal enters a sleep or low-power listening state.

[0030] In step S1, the beacon frame uses an SF12 spreading factor, a bandwidth of 125 kHz, and a coding rate of 4 / 5.

[0031] In step S3, if the attitude information of the cooperating star remains unchanged within a preset threshold, the coarse alignment angle calculation is skipped and the previous calculation result is used directly.

[0032] Specifically, after the terminal is powered on, the MCU configures the SX1278 registers via SPI: - RegFrf = 0x1A0AAA (435.000 MHz); - RegModemConfig1 / 2 / 3: BW = 125 kHz, SF = 12, CR = 4 / 5, CRC-ON, Implicit Header = 0; - RegPreamble = 12 symbols, RegSyncWord = 0x34 (private network); Set the CAD (Channel Activity Detection) period T_cad = 8 s, and the RxSingle timeout T_rxto = 2 s.

[0033] Beacon Frame Generation Payload content: 7 B timestamp (32-bit Unix time + 16-bit ms) + 12 B ECI location (int32 ×3, 1 m resolution) + 16 B attitude quaternion (float32 ×4) + 1 B frame number, totaling 36 B; CRC-32 (IEEE 802.3 polynomial) is calculated and appended to the end, for a total length of 40 B.

[0034] Launch scheduling Adaptive TDMA is adopted: the on-board real-time clock (UTC) is divided into 8-second time slots, and the last 3 bits of the satellite ID are used as the time slot offset to achieve collision-free broadcasting of N≤8 satellites; the transmission process within the time slot is as follows: - Set PA_EN=1 to warm up PA 1 ms in advance; - Write 40 B to TX FIFO → Set RegOpMode = TX → DIO0 triggers TxDone → PA_EN=0.

[0035] Receive and capture The remaining time slots enter RxSingle: - Preamble detection threshold: RegRxConfig → AfcAutoOn=1, AgcAutoOn=1; - If the CAD detection energy is ≥-120 dBm and the preamble symbol is ≥6, then lock the frequency and continue receiving the remaining symbols; Demodulation: go to chirp → 512-point FFT → soft decision → Viterbi decoding → CRC check.

[0036] Doppler and frequency offset compensation Use RegFreqError to read the 20-bit frequency offset Δf; if |Δf|>8 kHz, rewrite RegFrf according to Δf_new =f_nom+Δf to achieve a tracking range of ±31 kHz; the average value of Δf for 3 consecutive frames is used to update the local clock drift with an accuracy of <1 ppm.

[0037] Laser coarse alignment data extraction Extract the ECI position and quaternions from the decoded payload, and calculate the azimuth Az and elevation El of the opposing satellite in its local coordinate system: - Az = atan2(y, x); - El = atan2(z, √(x)). 2 +y 2 If |Az|≤5° and |El|≤5°, then output directly to the laser turntable; otherwise, trigger grid scanning (±5° area, 0.5° step).

[0038] Link Adaptive SF Adjustment Rules: - If the SNR of the previous frame is ≥-5 dB, then the SF in the next frame ← max(SF-1, 7); - If the SNR is ≤-15 dB, then the SF ← min(SF+1, 12); Power Control Rules: - If the SNR is ≥-3 dB and SF=7, then the PA output is reduced by 3 dB (RegPaConfig is reduced by 1 level); - If the SNR is ≤-18 dB, then the PA output is increased by 3 dB until it reaches +22 dBm or the thermal control limit.

[0039] Exceptions and retransmissions If a CRC error or RxTimeout occurs, the receiver sends a NACK beacon (1 B frame sequence number + 1 B retransmission request) in the next time slot. After receiving the NACK, the transmitter retransmits the original frame in the next available time slot, with a maximum of 2 retransmissions.

[0040] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they shall still fall within the protection scope of the present invention.

Claims

1. A low-Earth orbit inter-satellite communication terminal without attitude pointing requirements, characterized in that, include: Antenna system, RF module and baseband module; The antenna system consists of two tape measure antennas arranged in a spatially orthogonal manner to form quasi-omnidirectional beam coverage. The antenna feed system is connected to the low-noise amplifier and power amplifier in the radio frequency module via a duplexer; the baseband module is communicatively connected to the radio frequency module and uses LoRa modulation / demodulation for data processing to improve the anti-interference capability of the communication link; During the launch phase, the satellite computer transmits inter-satellite laser coarse alignment service data to the baseband module via a highly reliable serial bus; The baseband module sends the service data into the LoRa modulator with forward error correction and spread spectrum modulation functions to complete channel coding, frame encapsulation and linear frequency modulation spread spectrum modulation, and generate a low-power radio frequency baseband signal. The radio frequency baseband signal is sequentially filtered, amplified, and antenna switched to radiate an omnidirectional beam to the inter-satellite link; During the receiving phase, the antenna feeder system captures weak spread spectrum signals in the inter-satellite link under arbitrary attitude conditions, and sends them to the baseband module after low-noise amplification and filtering. The baseband module performs down-conversion, analog-to-digital conversion, despreading, decoding, and error detection on the radio frequency signal to recover inter-satellite service data consistent with that of the transmitter; and transmits the data back to the satellite computer via a serial bus.

2. The low-Earth orbit inter-satellite communication terminal without attitude pointing requirements as described in claim 1, characterized in that, The noise figure of the low-noise amplifier is ≤0.45 dB, and the operating frequency band includes UHF; the transmit EIRP of the power amplifier is ≥22 dBm.

3. The low-Earth orbit inter-satellite communication terminal without attitude pointing requirements as described in claim 2, characterized in that, The low-noise amplifier uses a TriQuint TQP3M9036 chip, and the power amplifier uses a TriQuint TQP7M9105 chip.

4. The low-Earth orbit inter-satellite communication terminal without attitude pointing requirements as described in claim 1, characterized in that, The included angle between the two tape measure antennas is 80°–100°, and the beamwidth of each antenna is ≥120°.

5. The low-Earth orbit inter-satellite communication terminal without attitude pointing requirements as described in any one of claims 1-4, characterized in that, The baseband module operates in half-duplex mode and interacts with the satellite's onboard computer via a CAN bus.

6. The low-Earth orbit inter-satellite communication terminal without attitude pointing requirements as described in claim 1, characterized in that, The terminal further includes: an attitude information sharing interface for receiving attitude information from the local satellite and cooperating satellites; and a collaborative control interface with the inter-satellite laser communication terminal to provide coarse alignment data during the acquisition phase.

7. An inter-satellite communication method based on the terminal described in any one of claims 1-6, characterized in that, Includes the following steps: S1: Continuously transmit LoRa modulated beacon frames via a quasi-omnidirectional beam. The beacon frames contain the local satellite identifier and attitude information. S2: Perform carrier detection and frame synchronization on the received cooperative satellite beacon frames. If a valid frame is detected, proceed to step S3. S3: Calculate the coarse alignment angle based on the cooperative satellite attitude information and output the angle to the inter-satellite laser communication terminal to complete the acquisition, alignment, and tracking of the laser link. S4: After the laser link is established, the terminal enters a sleep or low-power listening state.

8. The inter-satellite communication method according to claim 7, characterized in that, In step S1, the beacon frame uses an SF12 spreading factor, a bandwidth of 125 kHz, and a coding rate of 4 / 5.

9. The inter-satellite communication method according to claim 7 or 8, characterized in that, In step S3, if the attitude information of the cooperating star remains unchanged within a preset threshold, the coarse alignment angle calculation is skipped and the previous calculation result is used directly.

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