Satellite communication system based on Beidou RDSS

Abstract

The invention provides a satellite communication system based on Beidou RDSS. The satellite communication system specifically comprises a receiving channel and a transmitting channel. A receiving channel adopts a low-intermediate frequency structure, an antenna receives a radio frequency signal, the radio frequency signal is directly down-converted into a low-intermediate frequency signal through a mixer, and then the low-intermediate frequency signal is converted into a baseband signal through an analog-to-digital conversion chip. The system adopts a low-intermediate frequency structure and uses primary frequency mixing, so that compared with secondary frequency mixing of a superheterodyne structure, the system has the advantages of simple link, low cost, low power consumption, high integration and the like. Meanwhile, the system is down-converted to low-intermediate frequency, and low-intermediate frequency signals are far away from direct current, so that the problems of direct current offset, flicker noise and the like of the system are solved. A transmitting channel adopts a direct frequency conversion structure, and a baseband signal skips an intermediate frequency stage through a frequency mixer and is directly up-converted to a radio frequency signal transmitted by an antenna. The system not only ensures the advantages of simple link, low cost, low power consumption, high integration and the like of the system, but also improves the stray problem of signals transmitted by the system.

Description

Technical Field

[0001] The invention belongs to the technical field of communications. Background Art

[0002] With the successful global networking of my country's BeiDou-3 system in 2020, the comprehensive capabilities of the BeiDou satellite navigation system have been further enhanced, and it can provide global users with high-precision and high-reliability navigation positioning, timing and short message services. GPS ( GPS ), Russia's GLONASS satellite navigation system ( GLONASS ) and the European Union Galileo satellite navigation system ( GALILEO ) is a special service. Beidou short message communication relies on the Beidou navigation satellite system, inherits the advantages of wide coverage and all-weather satellite communication, and also has the advantages of carrying positioning function and low cost. Based on its significant advantages, Beidou short message communication can not only serve as a supplement and emergency guarantee for the ground communication network, but also provide technical support for real-time data transmission, remote monitoring, resource management, etc. It has been widely used in many fields such as electricity, transportation, meteorology, and environmental protection. The development of Beidou short message continues to evolve with the development of the Beidou system. On the basis of being compatible with the RDSS system, Beidou-3 adopts the generalized RDSS system and the RNSS+ short message communication system, and the short message service capability has been greatly improved. With the continuous expansion of the application scenarios and fields of Beidou short message service, Beidou short message gives the Beidou system a great competitive advantage. In order to meet the application of Beidou short message service, the corresponding terminal equipment will become more important.

[0003] At present, there are two circuit structures of mainstream Beidou short message terminal equipment. One is to use a superheterodyne structure, which mixes the local oscillator and the antenna receiving RF signal through a mixer, down-converts it to an intermediate frequency signal, and then mixes the intermediate frequency signal with the sub-local oscillator again to realize the conversion of the RF analog signal to the baseband digital signal. However, the superheterodyne structure has two-stage mixing and intermediate frequency processing links, which makes the system have great disadvantages in terms of link complexity, cost, power consumption, number of components and physical size. At the same time, since multiple chips on the link need to be interconnected with external lumped devices, it is not suitable for future integrated development. The second is to use a direct frequency conversion structure, where the antenna receives the RF signal and skips the intermediate frequency stage through the mixer and directly down-converts it to the baseband signal. The direct frequency conversion structure uses one mixing and no intermediate frequency stage, which makes the hardware link have certain advantages in terms of complexity, cost, power consumption, number of components and physical size. However, the direct frequency conversion structure has major problems in terms of DC offset, second-order distortion, local oscillator leakage and flicker noise in the receiving stage, which has a great impact on the performance of the communication system.

[0004] In summary, the existing technology has problems of complex links, high cost, high power consumption, and low integration on the one hand, and problems of DC offset, second-order distortion, local oscillator leakage, and flicker noise on the other hand. Summary of the invention

[0005] In view of this, the present invention proposes a satellite communication system based on Beidou RDSS, which solves the problems of complex links, high cost, high power consumption, and low integration, and reduces the DC offset and flicker noise of the system. The present invention has simple links, low cost, low power consumption, high integration, and efficient and stable communication performance, which can provide users with real-time and accurate information transmission means, effectively guaranteeing the smooth execution of communication tasks, and at the same time, the localization rate of the components of the entire system reaches 100%, which completely breaks the situation of long-term dependence on imports and being controlled by others for core components.

[0006] The design idea of ​​the present invention is: in the receiving stage, a low intermediate frequency structure is adopted, and the antenna receives the radio frequency signal and directly down-converts it to a low intermediate frequency signal through a mixer, and then converts the low intermediate frequency signal into a baseband signal through an analog-to-digital conversion chip, rather than directly down-converting it to a baseband signal like a direct frequency conversion structure. The system adopts a low intermediate frequency structure and uses a single mixing. Compared with the secondary mixing of the superheterodyne structure, the system has the advantages of simple link, low cost, low power consumption, high integration, etc. At the same time, the system down-converts to a low intermediate frequency, and the low intermediate frequency signal is far away from DC, so the DC offset and flicker noise of the system are improved. In the transmitting stage, a direct frequency conversion structure is adopted, and the baseband signal skips the intermediate frequency stage through a mixer and is directly up-converted to the radio frequency signal transmitted by the antenna. The system ensures the advantages of simple link, low cost, low power consumption, high integration, etc. of the system, while improving the spurious problem of the system transmitting signal.

[0007] The present invention proposes a satellite communication system based on Beidou RDSS, which specifically includes:

[0008] Receiving stage: The forward RF signal received by the antenna passes through the dielectric filter, limiter, first-stage low-noise amplifier, FBAR filter, second-stage low-noise amplifier, FBAR filter, Beidou transceiver chip, analog-to-digital conversion chip, and baseband chip.

[0009] Among them, the dielectric filter selects a device with low in-band insertion loss and high out-of-band suppression to filter out out-of-band interference signals such as Beidou transmission frequency points;

[0010] The limiter should be a device with low insertion loss and high power handling capacity. It is used to prevent high-power interference from entering the receiving link through the antenna and burning the low-noise amplifier.

[0011] The first-stage low-noise amplifier uses a low-noise coefficient device to perform low-noise amplification on the input receiving signal. At the same time, the front stage uses a low-noise coefficient and high-gain amplifier to ensure that the noise coefficient of the entire receiving link meets the system requirements and improves the receiving sensitivity of the system.

[0012] The first-stage FBAR filter uses a small-size, high-rectangular coefficient device to further suppress out-of-band signals while ensuring that the subsequent amplifier operates in the linear region;

[0013] The second-stage low-noise amplifier uses a low-noise-coefficient device to provide sufficient gain and output power for the link;

[0014] The second-stage FBAR filter selects a device with small size and high rectangular coefficient to further suppress out-of-band interference signals.

[0015] Beidou transceiver chips use high-performance and highly integrated devices that integrate down-conversion mixers, intermediate frequency filters, phase-locked loops, low-noise amplifiers, and up-conversion mixers to down-convert received forward RF signals into low intermediate frequency signals.

[0016] The analog-to-digital conversion chip selects a 14-bit high-resolution device to convert the low-IF analog signal into a baseband digital signal;

[0017] The baseband chip is used to process the baseband signal. At the same time, the chip supports anti-narrowband, spoofing signal, encryption chip, so as to realize information encryption and decryption functions and ensure the safe communication of Beidou short messages. The baseband chip realizes the capture, tracking, despreading and demodulation of the forward signal to obtain the original channel frame data.

[0018] Transmitting phase: Return data passes through the baseband chip, Beidou transceiver chip, SAW filter, low noise amplifier, temperature compensator, low-pass filter, power amplifier unit and antenna.

[0019] Among them, the baseband chip is used to process the baseband signal. At the same time, the chip supports anti-narrowband, spoofing signal, encryption chip, so as to realize the information encryption and decryption function and ensure the safe communication of Beidou short message. The baseband chip realizes the preprocessing of the return transmission signal;

[0020] Beidou transceiver chips use high-performance and highly integrated devices that integrate down-conversion mixers, intermediate frequency filters, phase-locked loops, low-noise amplifiers, and up-conversion mixers to directly up-convert baseband signals to RF signals;

[0021] The SAW filter is a small-sized device with high out-of-band suppression, which is used to initially suppress out-of-band harmonics and spurious signals and reduce out-of-band power spectrum density.

[0022] The low noise amplifier selects a low noise coefficient to perform low noise amplification on the input transmission signal, balance the passive losses such as Π attenuation and filter in the link, and provide sufficient gain margin for the link;

[0023] The temperature attenuator is used to balance the characteristics of low high-temperature gain and high low-temperature gain of active semiconductor devices in the link;

[0024] The low-pass filter uses small-size LTCC devices to suppress the second to fourth harmonics and high-frequency signal interference of the transmission link;

[0025] The power amplifier unit is used to provide sufficient transmission power for the transmission signal.

[0026] Beneficial Effects

[0027] 1. By adopting the design of low intermediate frequency architecture in the receiving stage of the system, it brings technical effects such as simple link, low cost, low power consumption, high integration, low DC offset and low flicker noise;

[0028] 2. The design of direct frequency conversion structure in the transmission stage of the system brings technical effects such as simple link, low cost, low power consumption, high integration and low spurious.

[0029] 3. By adopting the combination of dielectric filter and FBAR filter in the receiving stage of the system, it brings the technical effects of high sensitivity and anti-interference;

[0030] 4. By adopting the design of 14-bit high-resolution and high-sampling frequency analog-to-digital converter in the receiving stage of the system, it brings the technical effects of high sensitivity and anti-interference;

[0031] 5. The present invention adopts domestically produced mature chip design, uses a small number of chips with controllable costs, has good satellite testing performance, and meets the market's large-scale application needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 , flow chart of the method of the present invention;

[0033] Figure 2 , system block diagram of the present invention. DETAILED DESCRIPTION

[0034] The present invention proposes a satellite communication system based on Beidou RDSS, which solves the problems of complex links, high cost, high power consumption and low integration, and reduces the DC offset and flicker noise of the system. The present invention has simple links, low cost, low power consumption, high integration, and efficient and stable communication performance, which can provide users with real-time and accurate information transmission means, effectively guaranteeing the smooth execution of communication tasks, and at the same time, the localization rate of the components of the entire system reaches 100%, which completely breaks the situation of long-term dependence on imports and control by others for core components.

[0035] The design idea of ​​the present invention is: in the receiving stage, a low intermediate frequency structure is adopted, and the antenna receives the radio frequency signal and directly down-converts it to a low intermediate frequency signal through a mixer, and then converts the low intermediate frequency signal into a baseband signal through an analog-to-digital conversion chip, rather than directly down-converting it to a baseband signal like a direct frequency conversion structure. The system adopts a low intermediate frequency structure and uses a single mixing. Compared with the secondary mixing of the superheterodyne structure, the system has the advantages of simple link, low cost, low power consumption, high integration, etc. At the same time, the system down-converts to a low intermediate frequency, and the low intermediate frequency signal is far away from DC, so the DC offset and flicker noise of the system are improved. In the transmitting stage, a direct frequency conversion structure is adopted, and the baseband signal skips the intermediate frequency stage through a mixer and is directly up-converted to the radio frequency signal transmitted by the antenna. The system ensures the advantages of simple link, low cost, low power consumption, high integration, etc. of the system, while improving the spurious problem of the system transmitting signal.

[0036] The present invention proposes a satellite communication method and system based on Beidou RDSS, which specifically include:

[0037] Receiving stage: The forward RF signal received by the antenna passes through the dielectric filter, limiter, first-stage low-noise amplifier, cavity filter, temperature-compensated attenuator, second-stage low-noise amplifier, FBAR filter, Beidou transceiver chip, analog-to-digital conversion chip, FPGA chip and baseband chip.

[0038] Among them, the dielectric filter selects the MC4A2491F20KCD device with an in-band insertion loss of 1dB and an out-of-band suppression of ≥40dB from DC to 2400MHz and 2600MHz to 4000MHz, which is used to filter out out-of-band interference signals such as Beidou transmission frequency points;

[0039] The limiter uses the BW480SM84 device with an insertion loss of 0.5dB, a maximum power handling power of 30dBm, and a limiting output level of 14dBm. It is used to prevent high-power interference from entering the receiving link through the antenna and burning the low-noise amplifier;

[0040] The first-stage low-noise amplifier uses the XND1100MEB device with a noise figure of about 0.7dB, a gain of 20dB, and a P-1dB of 16.5dBm, which is used to perform low-noise amplification on the input receiving signal. At the same time, the front stage uses an amplifier with a low noise figure and a high gain, which can ensure that the noise figure of the entire receiving link meets the system requirements and improve the receiving sensitivity of the system;

[0041] The first-stage FBAR filter uses the RSFK2492F009C1 device with a small size, 1dB bandwidth of 10MHz, 5dB bandwidth of 20MHz, and out-of-band suppression of ≥30dB to further suppress out-of-band signals while ensuring that the subsequent amplifier operates in the linear region;

[0042] The second-stage low-noise amplifier uses the XND1100MEB device with a noise figure of about 0.7dB, a gain of 20dB, and a P-1dB of 16.5dBm to provide sufficient gain and output power for the link;

[0043] The second-stage FBAR filter selects the RSFK2492F009C1 device with small size, 1dB bandwidth of 10MHz, 5dB bandwidth of 20MHz, and out-of-band suppression of ≥30dB to further suppress out-of-band interference signals. By combining this stage of FBAR filter with the above-mentioned first two stages of low-noise amplifiers and filters, while achieving high space utilization to ensure system miniaturization, the ability to suppress out-of-band interference signals is effectively enhanced, the selectivity of the receiver is improved, and it is ensured that the signal has a sufficiently high intermodulation suppression ratio when it is down-converted in the subsequent mixer, thereby reducing the noise intensity of out-of-band signals entering the receiving band through spectrum shifting, improving the receiver carrier-to-noise ratio, and ultimately achieving a receiver sensitivity better than -127dB@8kbps, and the Beidou short message satellite reception success rate is increased to 98%. This design is protection point 1 of the present invention;

[0044] Beidou transceiver chips use high-performance and highly integrated devices that integrate down-conversion mixers, intermediate frequency filters, phase-locked loops, low-noise amplifiers, and up-conversion mixers to down-convert received forward RF signals to low intermediate frequency signals of 11.75MHz. The use of highly integrated devices effectively improves the miniaturization of equipment as well as its reliability and maintainability;

[0045] The analog-to-digital conversion chip selects a 14-bit high-resolution SAD2284MQ device to convert low-IF analog signals into baseband digital signals. At the same time, the theoretical signal-to-noise ratio of the 14-bit analog-to-digital conversion chip is 86.04dB, which can effectively improve the anti-interference ability of the system. At the same time, the sampling rate of the SAD2284MQ device is set to 80MSPS, which can achieve oversampling of low-IF signals, bring additional processing gain, and further improve the sensitivity of the receiver. This design is the protection point 2 of the present invention;

[0046] The baseband chip is used to process the baseband signal. At the same time, the chip supports anti-narrowband, spoofing signals, and encryption chips, thereby realizing information encryption and decryption functions to ensure the safe communication of Beidou short messages. The baseband chip uses an open-loop algorithm to quickly capture weak signals under high dynamics by introducing additional signal frames with specific codes, and then despreads and demodulates the signal, and finally completes deinterleaving, serial-to-parallel conversion, channel decoding, descrambling and deframing to obtain the original channel frame data.

[0047] Transmitting phase: Return data passes through the baseband chip, Beidou transceiver chip, SAW filter, low noise amplifier, temperature compensator, low-pass filter, power amplifier unit and antenna.

[0048] Among them, the baseband chip is used to process the baseband signal. At the same time, the chip supports anti-narrowband, spoofing signals, and encryption chips, thereby realizing information encryption and decryption functions to ensure the safe communication of Beidou short messages. The baseband chip realizes the framing, coding, modulation and filtering of the return transmission signal;

[0049] Beidou transceiver chips use high-performance and highly integrated devices that integrate down-conversion mixers, intermediate frequency filters, phase-locked loops, low-noise amplifiers, and up-conversion mixers to directly up-convert baseband signals to RF signals;

[0050] The SAW filter uses a small-sized D3500 device with an out-of-band suppression of ≥40dB from fc±100MHz to fc±500MHz, which is used to preliminarily suppress out-of-band harmonics and spurious signals and reduce the out-of-band power spectral density; where fc is the center frequency.

[0051] The low noise amplifier uses the XND1100MEB device with a noise figure of about 0.7dB, a gain of 20dB, and a P-1dB of 16.5dBm. It is used to perform low noise amplification on the input transmission signal, balance the passive losses such as Π attenuation and filter in the link, and provide sufficient gain margin for the link.

[0052] The temperature attenuator uses the TVA0603N6W3SQZ device with a temperature compensation coefficient of N6. The attenuation value of the device decreases as the temperature increases, which is used to balance the characteristics of low high-temperature gain and high low-temperature gain of the link active semiconductor device;

[0053] The low-pass filter uses a small-size, LTCC ZHLF-1700 device to suppress the second to fourth harmonics and high-frequency signal interference of the transmission link;

[0054] The power amplifier unit includes a driver amplifier, a dielectric filter, a first-stage isolator, a final power tube, a final isolator, and a cavity filter. Among them: the driver amplifier selects NC30128S with a gain of 15dB and a P-1 of 23dBm, which is used to provide enough power for the final stage to saturate it, and at the same time to ensure the linearity of the entire link; the dielectric filter selects the QMF4R0706A device with a DC-1575MHz and 1800MHz-3000MHz out-of-band suppression of ≥35dB, which is used to suppress the increase of the out-of-band background noise due to the gain of the pre-amplifier, and at the same time suppress the out-of-band spurious signals such as harmonics generated by the pre-amplifier; the first-stage isolator selects the DVRF00230 device with an insertion loss of 0.3dB, which is used to balance the impedance of the driver power tube, the dielectric filter, and the final power tube, so that the three are The matching between the two ends is good to avoid impedance pulling, which will lead to poor passband flatness. The final power tube uses the HEG124E-2 device with a saturated output power greater than 44dBm to provide sufficient gain and output power for the link. The final isolator uses the DVRF00226 device with an insertion loss of 0.3dB, a withstand power of 60W, and a reverse isolation of >20dB to protect the final power tube from being burned due to the open short circuit of the output port and balance the output standing wave. The cavity filter uses a customized device with high power capacity, low insertion loss and out-of-band suppression ≥35dB to suppress the out-of-band background noise raised by the next two amplifiers, as well as the harmonics, spurious, and noise power spectrum density caused by the nonlinearity of the device.

[0055] Finally, the return transmission signal is radiated through the antenna to the Beidou satellite.

Claims

1. A satellite communication system based on Beidou RDSS, characterized in that: It includes a receiving channel and a transmitting channel. The receiving channel adopts a low intermediate frequency structure. The RF signal received by the antenna is directly down-converted to a low intermediate frequency signal through a mixer, and then converted into a baseband signal through an analog-to-digital conversion chip; the transmitting channel adopts a direct frequency conversion structure. The baseband signal skips the intermediate frequency stage through a mixer and is directly up-converted to the RF signal transmitted by the antenna.

2. A satellite communication system based on BeiDou RDSS according to claim 1, characterized in that: The receiving channel includes a dielectric filter, a limiter, a first-stage low-noise amplifier, an FBAR filter, a second-stage low-noise amplifier, an FBAR filter, a Beidou transceiver chip, an analog-to-digital conversion chip and a baseband chip in sequence.

3. A satellite communication system based on BeiDou RDSS according to claim 1 or 2, characterized in that: The transmitting channel includes baseband chip, Beidou transceiver chip, surface acoustic wave filter, low noise amplifier, temperature compensator, low-pass filter and power amplifier unit in sequence.

4. A satellite communication system based on Beidou RDSS according to claim 2, characterized in that: In the receiving channel, The dielectric filter is used to filter out the out-of-band interference signal of the Beidou receiving link; The limiter is used to prevent high-power interference from entering the receiving link through the antenna and burning out the low-noise amplifier; The first-stage low-noise amplifier is used to perform low-noise amplification on the input receiving signal to ensure that the noise coefficient of the entire receiving link meets the system requirements and improve the receiving sensitivity of the system; The first-stage FBAR filter is used to further suppress out-of-band signals while ensuring that the subsequent amplifier operates in the linear region; The second-stage low-noise amplifier is used to provide gain and output power for the link; The second-stage FBAR filter further suppresses out-of-band interference signals. The Beidou transceiver chip is used to down-convert the received forward RF signal to a low intermediate frequency signal; The analog-to-digital conversion chip is used to convert the low-IF analog signal into a baseband digital signal; The baseband chip is used to capture, track, despread and demodulate the forward signal to obtain the original channel frame data.

5. A satellite communication system based on BeiDou RDSS according to claim 4, characterized in that: In the receiving channel, The dielectric filter should be a device with low in-band insertion loss of ≤1.5dB and high out-of-band suppression of ≥35dB. The limiter selects a low insertion loss of ≤1dB and a high power handling device of ≥20dBm; The first-stage low-noise amplifier selects an amplifier device with a low noise figure of ≤1dB and a gain of 20dB; The first-stage filter selects a FBAR filter with a rectangular coefficient ≤ 4; The second-stage low-noise amplifier selects an amplifier device with a low noise figure of ≤1dB and a gain of 20dB; The second-stage filter selects a FBAR filter with a rectangular coefficient ≤ 4; Beidou transceiver chips select devices that integrate down-conversion mixers, intermediate frequency filters, phase-locked loops, low-noise amplifiers, and up-conversion mixers; The analog-to-digital conversion chip should be a high-resolution device of ≥14 bits; The baseband chip is used to process baseband signals. At the same time, the chip supports anti-narrowband, anti-spoofing signals, and encryption chips, thereby realizing information encryption and decryption functions to ensure the secure communication of Beidou short messages.

6. A satellite communication system based on BeiDou RDSS according to claim 5, characterized in that: The size of the first-stage filter is no larger than 3mm x 3mm x 0.85mm, and the size of the second-stage filter is no larger than 3mm x 3mm x 0.85mm.

7. A satellite communication system based on Beidou RDSS according to claim 3, characterized in that: In the launch channel, Baseband chip, used to implement preprocessing of return transmission signals; Beidou transceiver chip, used to directly up-convert baseband signals to RF signals; SAW filter, used to initially suppress out-of-band harmonics and spurious signals and reduce out-of-band power spectral density; Low noise amplifier, used to perform low noise amplification on the input transmission signal, balance the Π attenuation and filter passive loss in the link, and provide sufficient gain margin for the link; Temperature-compensated attenuators are used to balance the characteristics of low high-temperature gain and high low-temperature gain of active semiconductor devices in the link; Low-pass filter, used to suppress the second to fourth harmonics and high-frequency signal interference of the transmission link; The power amplifier unit is used to provide the transmission power of the transmission signal.

8. A satellite communication system based on BeiDou RDSS according to claim 6, characterized in that: In the launch channel, Baseband chip, used to process baseband signals. The chip also supports anti-narrowband, anti-spoofing signals, and encryption chips, thereby realizing information encryption and decryption functions to ensure the secure communication of Beidou short messages; Beidou transceiver chips select devices that integrate down-conversion mixers, intermediate frequency filters, phase-locked loops, low-noise amplifiers, and up-conversion mixers; The SAW filter should be a device with high out-of-band suppression of fc±100MHz~fc±500MHz and out-of-band suppression ≥40dB; The low noise amplifier selects an amplifier device with a low noise figure of ≤1dB and a gain of 20dB; The low-pass filter uses LTCC devices.

9. A satellite communication system based on BeiDou RDSS according to claim 8, characterized in that: The size of the SAW filter is no larger than 3.8mm x 3.8mm x 1.5mm, and the size of the low-pass filter is no larger than 3.2mm x 1.6mm x 0.94mm.

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