阅读说明：本技术 一种实现卫星物联网突发信号快速捕获的方法 (Method for rapidly capturing burst signals of satellite Internet of things ) 是由 郑爱武 于 2021-04-13 设计创作，主要内容包括：一种实现卫星物联网突发信号快速捕获的方法,增加地面终端的计算降低星上载荷计算量,将多普勒频移从±8～12KHz压缩至±3KHz以下,降低星上解调信息频率不确定性,消除多普勒频移对短时突发扩频信号捕获性能的影响,缩短捕获时间。卫星广播自身星历和全网其他卫星星历；地面终端在首次入网时确定自己的位置,并实时获取自己的位置,根据导航数据校正本地时间和时间精度,在开机后尝试捕获卫星广播帧,在捕获卫星广播帧后获取当前卫星星历,根据卫星星历在后续时间计算卫星位置、相对距离和相对速度；计算最佳发射时刻和使用的扩频码；计算最佳发射时刻的时延和星地多普勒频移；计算真正的发射时刻；到达真正的发射时刻终端反向预置频偏,突发数据。(A method for realizing rapid capture of burst signals of a satellite Internet of things increases calculation of a ground terminal to reduce satellite load calculation amount, compresses Doppler frequency shift from +/-8-12 KHz to be below +/-3 KHz, reduces satellite demodulation information frequency uncertainty, eliminates influence of the Doppler frequency shift on short-time burst spread spectrum signal capture performance, and shortens capture time. Broadcasting self ephemeris and other satellite ephemeris of the whole network by the satellite; the method comprises the steps that a ground terminal determines the position of the ground terminal when the ground terminal is connected to a network for the first time, acquires the position of the ground terminal in real time, corrects local time and time accuracy according to navigation data, tries to capture a satellite broadcast frame after the ground terminal is started, acquires a current satellite ephemeris after the satellite broadcast frame is captured, and calculates the position, relative distance and relative speed of the satellite according to the satellite ephemeris at the subsequent time; calculating the optimal transmitting time and the used spread spectrum code; calculating the time delay and the satellite-ground Doppler shift of the optimal transmitting moment; calculating the real transmitting time; and when the real transmission moment is reached, the terminal reversely presets frequency deviation and burst data.)

1. A method for realizing rapid capture of satellite Internet of things burst signals is characterized in that the method reduces the calculation amount of satellite loads by adding some calculations of a ground terminal, compresses Doppler frequency shift from +/-8-12 KHz to +/-3 KHz or less, reduces the frequency uncertainty of satellite demodulation information, effectively eliminates the influence of the Doppler frequency shift on the capture performance of short-time burst spread spectrum signals, and greatly shortens the capture time.

2. The method for realizing rapid acquisition of the burst signals of the internet of things of the satellite according to claim 1, comprising the following steps: the satellite continuously broadcasts the self ephemeris and other satellite ephemeris of the whole network at preset time intervals; the ground terminal determines the position of the ground terminal through a GPS and/or a BD when the ground terminal is firstly accessed to the network, so that the ground terminal acquires the position of the ground terminal in real time and corrects local time and time precision according to navigation data; thereafter, the ground terminal attempts to acquire a satellite broadcast frame after being powered on; the ground terminal acquires the current satellite ephemeris after successfully capturing the satellite broadcast frame, and calculates the satellite position, the relative distance and the relative speed at the subsequent time according to the satellite ephemeris; calculating the optimal transmitting time and the used spread spectrum code; then calculating the time delay and the satellite-ground Doppler shift of the optimal transmitting moment; calculating the difference value of the optimal transmitting time minus the time delay as the real transmitting time; and after the real transmission time is reached, the terminal reversely presets frequency deviation and burst data.

3. The method for realizing rapid acquisition of burst signals of the internet of things of the satellite according to claim 1 or 2, wherein the predetermined time interval is settable and is 10s by default.

4. The method for realizing rapid acquisition of the burst signals of the internet of things of the satellite according to claim 1 or 2, wherein the ground terminal adopts a low-power-consumption acquisition strategy of the pilot frequency to acquire the satellite broadcast frames.

5. The method for realizing rapid acquisition of the burst signal of the internet of things of the satellite according to claim 1 or 2, wherein the ground terminal calculates the optimal transmission time slot by using a plurality of parameters as random numbers.

Technical Field

The invention relates to the field of satellite Internet of things, in particular to a method for rapidly capturing burst signals of the satellite Internet of things.

Background

In recent years, the internet of things is gradually developed, so that the life style of people, intelligent home, environment monitoring, smart cities and the like are greatly changed, the ground internet of things is limited by the coverage area of a ground base station and cannot realize global coverage, and satellite communication can provide global quasi-real-time short data transmission service due to the characteristics of wide coverage range and no limitation of geographic and climate factors, so that real 'everything interconnection' is realized in the global range.

The communication frequency of the satellite internet of things mainly works in a VHF frequency band (30 MHz-300 MHz, the wavelength is 1 m-10 m) and a UHF frequency band (300 MHz-3 GHz, the wavelength is 1 m-0.1 m), but the VHF frequency band is mostly used for broadcasting of radio stations and television stations and is also a communication frequency band for aviation and navigation, and the UHF frequency band is widely applied to mobile communication. Since the communication coverage of the satellite internet of things is required to be 100% of the global coverage, the user terminals are distributed in different regions and airspaces, including the sea and the desert and the wasteland without people. Therefore, the uplink and downlink frequency bands are extremely easy to be interfered, and even common radio fans can cause interference to the communication of the satellite internet of things. Wherein the uplink of satellite communications is relatively vulnerable. The interference to the uplink of the satellite of the internet of things is mainly interference of tens of thousands of various ground stations and radio stations, and the interference is highlighted by local noise elevation and high-power burst interference.

The user terminal of the satellite Internet of things sends the acquired data or the communication data in a burst mode, so that how to ensure that the user terminal of the satellite Internet of things sends the acquired data in a burst mode without collision is realized, and meanwhile, in order to ensure the frame efficiency and the minimum frame leakage rate, burst capture synchronization must be completed with high probability within a short time of each burst starting. The burst capture and carrier fast synchronization technology is a key technology of the satellite burst demodulation system of the Internet of things.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a method for rapidly capturing burst signals of the satellite internet of things in the environment of low signal-to-noise ratio and large Doppler frequency shift of the internet of things satellite, which can ensure that massive user terminals of the satellite internet of things send acquired data in an uplink burst mode without collision and ensure that burst capture synchronization is completed at high probability in a short time at the beginning of each burst; and the problem that the short frame burst direct sequence spread spectrum communication of the satellite Internet of things requires to capture signals with low false alarm and false alarm missing probability in a short time is solved.

According to the method for rapidly capturing the satellite Internet of things burst signals, the calculation of the ground terminal is increased at a low cost, the calculation amount of the satellite load is greatly reduced, the Doppler frequency shift is compressed from +/-8-12 KHz to +/-3 KHz below, the frequency uncertainty of satellite demodulation information is reduced, and the capturing time is greatly prolonged.

Preferably, the method for realizing rapid acquisition of the satellite internet of things burst signal includes: the satellite continuously broadcasts the self ephemeris and other satellite ephemeris of the whole network at preset time intervals; the ground terminal determines the position of the ground terminal through a GPS and/or a BD when the ground terminal is firstly accessed to the network, so that the ground terminal acquires the position of the ground terminal in real time and corrects local time and time precision according to navigation data; thereafter, the ground terminal attempts to acquire a satellite broadcast frame after being powered on; the ground terminal acquires the current satellite ephemeris after successfully capturing the satellite broadcast frame, and calculates the satellite position, the relative distance and the relative speed at the subsequent time according to the satellite ephemeris; calculating the optimal transmitting time and the used spread spectrum code; then calculating the time delay and the satellite-ground Doppler shift of the optimal transmitting moment; calculating the difference value of the optimal transmitting time minus the time delay as the real transmitting time; and after the real transmission time is reached, the terminal reversely presets frequency deviation and burst data.

Preferably, the predetermined time interval is settable (default is 10 s).

Preferably, the ground terminal adopts a low power consumption acquisition strategy of the pilot frequency to acquire the satellite broadcast frame.

Preferably, the ground terminal calculates an optimal transmission slot using a plurality of parameters as random numbers.

The invention carries out the calculation in a planetary and ground matched manner, although the calculation amount of the ground terminal is increased, the calculation amount of the load on the satellite is greatly reduced, and the calculation of the ground terminal is easy to realize and has low cost; therefore, the problem that the short frame burst direct sequence spread spectrum communication of the satellite Internet of things requires to capture signals with low false alarm and false alarm missing probability in a short time is solved.

In summary, the advantages of the present invention include at least: 1. the calculation amount of the load on the satellite is reduced. 2. The calculation of the ground terminal is easy to realize and the realization cost is not large. 3. The Doppler frequency shift is compressed from +/-8-12 KHz to be less than +/-3 KHz, so that the frequency uncertainty of on-satellite demodulation information is reduced, and the influence of the Doppler frequency shift on the short-time burst spread spectrum signal acquisition performance is effectively eliminated. 4. The capture time is increased by 3-4 times.

Drawings

A more complete understanding of the present invention, and the attendant advantages and features thereof, will be more readily understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein:

fig. 1 schematically shows a flowchart of a method for realizing rapid acquisition of burst signals of the satellite internet of things according to a preferred embodiment of the invention.

It is to be noted, however, that the appended drawings illustrate rather than limit the invention. It is noted that the drawings representing structures may not be drawn to scale. Also, in the drawings, the same or similar elements are denoted by the same or similar reference numerals.

Detailed Description

In order that the present disclosure may be more clearly and readily understood, reference will now be made in detail to the present disclosure as illustrated in the accompanying drawings.

The satellite internet of things user terminal distributed in various regions around the world senses and collects data, the data are suddenly uploaded to the satellite when the satellite crosses the border, are downloaded to a gateway station through the internet of things satellite, are transmitted to an information processing center through a ground network, are distributed to corresponding industry users after being classified, can acquire terminal data distributed in a global wide area in a short time, is a novel real-time short data receiving and transmitting system based on a space-based system, and has the main characteristics of high capacity, real-time performance, low cost and the like.

The difficulty of uplink burst communication lies in parameter estimation such as signal acquisition, coherent carrier and positioning, especially for short-time burst direct sequence spread spectrum signals, spread spectrum code synchronization and parameter estimation are mixed together, so that the problem becomes more complicated. In order to achieve fast synchronization and channel parameter estimation, the prior art often inserts a specific preamble sequence, such as an all "1" or all "0" sequence, in front of the data packet, and the burst demodulator uses the preamble sequence to achieve fast synchronization acquisition and estimation of carrier phase and bit timing information.

Some prior arts design a short-time burst spread spectrum signal frame structure only using a unique code, and the spread spectrum code and the unique code are regarded as a composite spread spectrum code at a receiving end, and a high dynamic burst signal capturing method based on FFT is provided, which can simultaneously and rapidly complete tasks such as burst signal detection, spread spectrum code capturing, frequency offset estimation, frame synchronization detection and bit timing capturing, and simulation results also show that the algorithm can effectively eliminate the influence of Doppler frequency shift on the short-time burst spread spectrum signal capturing performance.

As can be seen from the implementation methods of the prior art, the algorithms are complex and have large calculation amount. The technologies are used for realizing rapid acquisition of burst signals, and strong computing power is required to be provided on the basis of satellites, and due to the limitation of low-cost and low-power-consumption internet-of-things satellite platforms, the load computing power carried by the internet-of-things satellites is very limited. In order to not increase the cost of the internet of things satellite and realize the rapid acquisition of burst signals, simplifying the algorithm or further reducing the calculation amount is one of the approaches for solving the problem.

The satellite Internet of things communication system generally adopts short frame burst direct sequence spread spectrum communication and has the characteristics of low signal-to-noise ratio, large Doppler frequency shift and the like. Under the conditions of low signal-to-noise ratio and large Doppler frequency shift, spread spectrum signals are relatively difficult to capture, and the average capture time is greatly increased. The spread spectrum code capture under the condition of large frequency offset needs to consider not only the code phase uncertainty factor of the received signal, but also the influence of carrier frequency offset and code frequency offset caused by Doppler frequency shift effect and the drift of a receiving and transmitting clock source, and mainly takes the influence of Doppler frequency shift effect as the main factor.

Doppler shift f_dCan be given by the formula (1-1):

wherein f is_cV is the moving speed of the user terminal, c is the speed of light, and theta is the angle between the moving direction of the user terminal and the incident direction of the radio wave.

The orbit height of the satellite of the Internet of things is about 500 km-900 km, and through calculation, the Doppler frequency shift of the UHF/VHF frequency band can reach +/-8-12 KHz, so the Doppler effect cannot be ignored. Such a large doppler is still costly to process even with a sufficiently long pilot sequence in the case of non-time-to-satellite synchronization. If the satellite frequency searching range is compressed to be less than or equal to +/-3 KHz by an effective technical means, the acquisition time is improved by 3 times under the condition of the same algorithm. This is very advantageous for burst channels.

The invention provides a method for realizing rapid capture of burst signals in an environment with low signal-to-noise ratio and large Doppler frequency shift of an Internet of things satellite, namely a reverse synchronization method based on GPS/BD-2+ broadcast information + pilot frequency measurement is adopted. And increasing the calculation amount of the ground terminal based on the calculation capacity of the ground terminal by utilizing the satellite ephemeris and the position of the user terminal, reducing the calculation amount of the satellite load, and compressing the Doppler to be less than or equal to +/-3 KHz by adopting a reverse compensation method. The frequency uncertainty of the on-satellite demodulation information is greatly reduced, and therefore the on-satellite despreading and demodulation burden is remarkably reduced.

Specifically, fig. 1 schematically shows a flowchart of a method for realizing rapid acquisition of a satellite internet of things burst signal according to a preferred embodiment of the present invention.

As shown in fig. 1, a method for rapidly acquiring a burst signal of the internet of things of a satellite according to a preferred embodiment of the present invention includes:

the satellite continuously broadcasts the self-ephemeris and other satellite ephemeris of the whole network at a preset time interval (the preset time interval can be set, for example, the interval of 10 s); the ground terminal determines the position of the ground terminal through the GPS and/or the BD when the ground terminal is firstly accessed to the network, so that the ground terminal acquires the position of the ground terminal in real time and corrects the local time and the time precision according to the navigation data.

Thereafter, the terrestrial terminal attempts to acquire the satellite broadcast frame after being powered on (preferably using a low power acquisition strategy for the pilot to acquire the satellite broadcast frame).

The ground terminal acquires the current satellite ephemeris (preferably simultaneously acquires other satellite ephemeris of the whole network) after successfully acquiring the satellite broadcast frame, and calculates the satellite position, the relative distance and the relative speed according to the satellite ephemeris at the subsequent time (preferably, the validity period is less than or equal to 10 minutes).

On the basis that the relative distance and the relative speed are calculated accurately, the ground terminal calculates accurate sending frequency offset, sending time and sending power in a specified time slot (preferably, the frequency of a signal received by a satellite is ensured to be within a range of +/-3 KHz) according to the reverse channel frequency configuration, the code word configuration and the time slot configuration in the broadcast information, and the satellite can be ensured to demodulate quickly.

As the reverse synchronization frequency offset compensation, the calculation added by the ground terminal mainly includes:

and calculating the satellite position and Doppler parameters at the appointed time according to the satellite ephemeris.

The satellite-ground distance at a specified time in the future (delay time) is calculated from the satellite position and the terminal position (local GPS).

An optimal transmission time slot is calculated (e.g., using a plurality of parameters as random numbers).

And when the optimal transmission time is reached, the time is advanced (delay time), and the data is burst by the terminal through reverse preset frequency offset.

The calculation is carried out in a planetary and ground matched manner, although the calculation amount of the ground terminal is increased, the calculation amount of the load on the satellite is greatly reduced, and the calculation of the ground terminal is easy to realize and has low cost; therefore, the problem that the short frame burst direct sequence spread spectrum communication of the satellite Internet of things requires to capture signals with low false alarm and false alarm missing probability in a short time is solved.

In summary, the advantages of the present invention include at least: 1. the calculation amount of the load on the satellite is reduced. 2. The calculation of the ground terminal is easy to realize and the realization cost is not large. 3. The Doppler frequency shift is compressed from +/-8-12 KHz to be less than +/-3 KHz, and the frequency uncertainty of on-satellite demodulation information is reduced. 4. The capture time is increased by 3-4 times.

It should be noted that the terms "first", "second", "third", and the like in the description are used for distinguishing various components, elements, steps, and the like in the description, and are not used for indicating a logical relationship or a sequential relationship between the various components, elements, steps, and the like, unless otherwise specified.

It is to be understood that while the present invention has been described in conjunction with the preferred embodiments thereof, it is not intended to limit the invention to those embodiments. It will be apparent to those skilled in the art from this disclosure that many changes and modifications can be made, or equivalents modified, in the embodiments of the invention without departing from the scope of the invention. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention are still within the scope of the protection of the technical solution of the present invention, unless the contents of the technical solution of the present invention are departed.