CN108011660B

CN108011660B - Global real-time Internet of things constellation system

Info

Publication number: CN108011660B
Application number: CN201711164281.4A
Authority: CN
Inventors: 彭金杨; 刘倩; 张双兰; 张守蓉; 林金芹; 李红珠; 邹洋; 胡宇波; 陶伟
Original assignee: Hunan Lingxing Space Information Technology Co ltd
Current assignee: Hunan jingling Zhilian Information Technology Co.,Ltd.
Priority date: 2017-11-21
Filing date: 2017-11-21
Publication date: 2020-12-22
Anticipated expiration: 2037-11-21
Also published as: CN108011660A

Abstract

The invention provides a global real-time Internet of things constellation system. The global real-time Internet of things constellation system comprises: a space segment comprising a plurality of low earth orbit satellites intercommunicated and interconnected by inter-satellite links; the system comprises a ground section and a control section, wherein the ground section is used for completing an operation control function and a data distribution and recovery processing function, and comprises a plurality of constellation gateway stations; and a user segment for collecting sensing data, the user segment comprising a plurality of user terminals; and the constellation gateway station of the ground segment and the user terminal of the user segment are respectively communicated with the low-orbit satellite of the space segment through respective links. The invention has the beneficial effects that: the global real-time Internet of things constellation system is designed in a cloud, network and end system level mode for global wide area space-based Internet of things application, and brand new connection and management capacity of the Internet of things with mass application in multiple industries is achieved.

Description

Global real-time Internet of things constellation system

Technical Field

The invention belongs to the technical field of Internet of things, and particularly relates to a global real-time Internet of things constellation system.

Background

The Internet of things (IoT) is a network concept that any object is connected through Internet of things domain names according to an agreed protocol by various information sensing devices (such as radio frequency identification, infrared sensors, global positioning systems, laser scanners, etc.) to exchange and communicate information, so as to realize intelligent identification, positioning, tracking, monitoring and management. The Internet of things is an important component of a new generation of information technology and is also an important development stage of the 'informatization' era. The internet of things is widely applied to network fusion through communication perception technologies such as intelligent perception, identification technology and pervasive computing, and is also called as the third wave of development of the world information industry after computers and the internet. The internet of things can be divided into a sensing layer, a network layer and an application layer according to the data flow direction and the processing mode:

a sensing layer: the sensing layer has the functions of sensing and identifying the state of an object or environment and acquiring and capturing information in real time, and comprises devices such as a two-dimensional code tag, a reader, an RFID tag, a reader, a camera, a GPS, a sensor, a meter and the like, an M2M terminal, a sensor network, a sensing gateway and the like, information is acquired through the sensor, and a control command is acquired through the receiving gateway. The challenge of the internet of things in a sensing layer is how to make a sensor more sensitive, have more comprehensive sensing capability and have the attributes of low power consumption, small size and low cost;

network layer: the information is accessed to a network, such as the internet, a telecommunication network and other communication networks, through a wireless or wired communication mode, and the information is transmitted between the sensing layer and the application layer. The network layer is required to have network operation and information operation capabilities, and the network layer also comprises a part for intelligently processing mass information, such as a cloud computing platform, an internet of things management center and the like. The challenge facing the network layer is the special requirements of large-scale M2M connections on system capacity and Qos;

an application layer: the application layer has the functions of realizing deep contact between the information technology of the Internet of things and the professional technology of the terminal industry, completing the functions of cooperation, sharing, analysis, decision making and the like of object information, and forming a solution of intelligent application. The system consists of an input and output control terminal consisting of terminals such as a computer, a mobile phone and the like. The challenges facing the application layer are information sharing and information security issues.

However, the conventional access means, such as Wi-Fi, ZigBee, bluetooth, etc., have too short transmission distance, and data is sent to the base station through the user mobile phone, the relay gateway, or the AP point, which may cause the problems of low data accuracy and high power consumption. The 2G/3G/4G network can be used for transmitting sensor data with low data volume, but the cost and the power consumption are higher.

In order to promote the development of the internet of things to the field of low cost and low power consumption, the research and development of a novel narrow-band internet of things technology are gradually promoted in recent years. Unlike the demand of traditional cellular communication, currently, over 60% of the internet-of-things market is low-rate, low-power-consumption, wide-area application with bandwidth lower than 100kb/s, namely LPWAN low-power-consumption wide-area network technology. The application requires that the internet of things have the capabilities of supporting massive connection number, low terminal cost, low terminal power consumption, super-strong coverage capability and the like.

Disclosure of Invention

The invention aims to provide a global real-time Internet of things constellation system aiming at the defects of the prior art, and the global real-time Internet of things constellation system has the advantages of being compatible with a ground low-power Internet of things system, being capable of realizing a global-coverage real-time narrow-band satellite Internet of things communication satellite system and allowing millions of Internet of things equipment to be directly connected.

The technical scheme of the invention is as follows: a global real-time internet of things constellation system comprising: a space segment comprising a plurality of low earth orbit satellites intercommunicated and interconnected by inter-satellite links; the system comprises a ground section and a control section, wherein the ground section is used for completing an operation control function and a data distribution and recovery processing function, and comprises a plurality of constellation gateway stations; and a user segment for collecting sensing data, the user segment comprising a plurality of user terminals; and the constellation gateway station of the ground segment and the user terminal of the user segment are respectively communicated with the low-orbit satellite of the space segment through respective communication links.

Preferably, the satellites of the space segment are low-orbit circular sun synchronous satellites and provide 24-hour full real-time effective coverage globally for user terminals at any work site.

Preferably, the inter-satellite link adopts a Ka frequency band to realize information transmission and exchange between satellites, the access mode of the inter-satellite link is to establish an annular inter-satellite link in the orbit, semicircular equal annular TDD transmission in the orbital plane is performed, satellites in different orbital planes are distinguished by different frequency FDD, and time synchronization is determined by a GPS.

Preferably, the inter-satellite link forms a dual-ring communication network by using two-end transceiving interleaving.

Preferably, the data routing strategy of the inter-satellite link selects a nearest landing route according to an OLSR routing algorithm, and the OLSR protocol of the inter-satellite link reduces the amount of signaling data by reducing the size of a control packet, and the satellite node issues link information between the satellite node and the relay selection node.

Preferably, the ground segment further comprises a network server and a user server, wherein the network server is used for carrying all required network control and management functions and distributing data to the user server, and the user server is used for providing heterogeneous application services for different application providers; and a satellite-ground feeder link is established between a plurality of constellation gateway stations respectively positioned at a plurality of global positions and a low-orbit satellite in a coverage area, so as to realize the real-time aggregation of constellation global Internet of things data and be responsible for transmitting user data to the network server.

Preferably, the constellation feeder link adopts Ka data transmission load as information transmission and exchange equipment for realizing satellite-ground communication.

Preferably, the constellation feeder link load adopts a CCSDS standard, a virtual channel VC is introduced, and complex information source data on the satellite is processed by adopting a plurality of services provided by an AOS proposal; and, the data stream is processed by using the bit stream service provided by the AOS proposal, and is packaged into a bit stream protocol data segment and filled into a VCDU data field to form an AOS transmission frame.

Preferably, the context switching when the user terminal accesses different satellites is managed and maintained by the network server of the ground segment.

Preferably, the data transmitted by each of the user terminals can be received by a plurality of low earth orbit satellites in the coverage area, and each low earth orbit satellite gateway payload can receive data packets from the user terminal node and forward the data packets to the ground segment through the inter-satellite link.

Preferably, the user satellite-ground link between the space segment and the user segment adopts an ISM free frequency band of 400MHz-1GHz, and when the low-earth satellite is used for the connection of the Internet of things in different regions of the world, the combined coverage of multiple frequency bands is realized by adjusting the frequency of the satellite transceiver.

Preferably, in each satellite-to-ground beam coverage area, the user terminals in the same latitude and different longitude areas randomize the frequency point of the transmitted signal through the UTC time, the ephemeris and the self position to realize the dynamic allocation of the FDMA frequency point; and the user terminals in the same longitude and different latitude areas randomize the time slot of the transmitted signal on the basis of FDMA frequency point allocation according to the UTC time, the ephemeris and the self position to realize the dynamic allocation of the TDMA time slot.

Preferably, the improved asynchronous ALOHA access protocol based on TDMA/FDMA of the doppler effect is adopted to solve the doppler effect of the constellation of the low-orbit internet of things caused by relative motion, and the steps of the improved asynchronous ALOHA access TDMA/FDMA multiple access configuration based on the doppler effect are as follows: each user terminal of the low-orbit Internet of things constellation has DevAddr and NwkSKey parameters, an information complete code in a communication frame of the terminal is subjected to 128AES encryption and decryption by NwkSKey, and a key for TDMA/FDMA multiple access randomization calculation adopts NwkSKey; the TDMA/FDMA multiple access randomization calculation is carried out by adopting an advanced encryption standard, the block length of AES is fixed to be 128 bits, and the key length is 128 bits; and dynamically allocating the FDMA frequency points and the TDMA time slots based on the DevAddr and the NwkSKey parameters respectively.

The technical scheme provided by the invention has the following beneficial effects:

the global real-time Internet of things constellation system is a cloud, network and end system level design oriented to global wide area space-based Internet of things application, and realizes the brand new connection and management capability of the Internet of things with mass application in multiple industries; establishing an inter-satellite/satellite-ground/feed/measurement and control full link system which accords with ITU global ISM multi-frequency standard by adopting a broadband software radio technology and a novel CCS spread spectrum anti-interference technology, and realizing a frequency-coordinated global coverage M2M/IoT private network; compatible with a mainstream standard M2M/IoT system, and realizes a low-power-consumption and low-cost space-based Internet of things system with integrated application in the world; the very-large-capacity space-based Internet of things system is realized based on software defined loads and on-satellite Internet of things gateways; and the global real-time space-based Internet of things constellation is realized by adopting an advanced millimeter wave phased array technology and an inter-satellite networking protocol.

Drawings

Fig. 1 is a schematic structural diagram of a global real-time internet of things constellation system provided in an embodiment of the present invention;

FIG. 2 is a schematic diagram of a single satellite coverage area in the global real-time Internet of things constellation system shown in FIG. 1;

fig. 3 is a schematic diagram of an inter-satellite link access mode in the global real-time internet of things constellation system shown in fig. 1;

FIG. 4 is a schematic diagram of a forward time slice inter-satellite link connection topology relationship in the global real-time Internet of things constellation system shown in FIG. 1;

FIG. 5 is a schematic diagram of a topological relationship of link connections between reverse time slices and stars in the global real-time Internet of things constellation system shown in FIG. 1;

fig. 6 is a schematic overall structure diagram of a routing OLSR protocol of an inter-satellite link in the global real-time internet of things constellation system shown in fig. 1;

FIG. 7 is a flow chart of Ka data transfer load antenna pointing work in the global real-time Internet of things constellation system shown in FIG. 1;

fig. 8 is a schematic diagram of downlink data transmission in the global real-time internet of things constellation system shown in fig. 1;

fig. 9 is a schematic diagram of an AOS transmission frame format of a unit for transmitting bit stream service data in the global real-time internet of things constellation system shown in fig. 1;

FIG. 10 is a schematic diagram of AOS bit stream service processing in the global real-time Internet of things constellation system shown in FIG. 1;

fig. 11 is a schematic diagram of an internet of things constellation multi-gateway parallel access mechanism in the global real-time internet of things constellation system shown in fig. 1;

figure 12 is a diagram of doppler frequency distribution of terminals located at different latitudes and longitudes within the beam coverage area.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Unless the context clearly dictates otherwise, the elements and components of the present invention may be present in either single or in multiple forms and are not limited thereto. Although the steps in the present invention are arranged by using reference numbers, the order of the steps is not limited, and the relative order of the steps can be adjusted unless the order of the steps is explicitly stated or other steps are required for the execution of a certain step. It is to be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

Referring to fig. 1, a global real-time internet of things constellation system provided by the embodiment of the present invention includes a space segment, and a ground segment and a user segment that are respectively in communication with the space segment through respective links.

The space section comprises a plurality of low earth orbit satellites which are intercommunicated and interconnected through inter-satellite links, the ground section comprises a plurality of constellation gateway stations which are respectively positioned at a plurality of global positions, and the user section comprises a plurality of user terminals connected with the sensors;

when the satellite is empty through the user terminal or the constellation gateway station, the user terminal and the constellation gateway station are communicated with the satellite through respective links respectively to obtain corresponding service data of the internet of things. The satellite transmits the service data of the internet of things to a target satellite through an inter-satellite link according to certain QoS (quality of service) management and routing strategies of service data of the internet of things on the satellite, so that the data of the internet of things can be transmitted back to the ground with the highest timeliness.

The satellite of the space segment is a low-orbit circular sun synchronous satellite, and global 24-hour full real-time effective coverage is provided for the user terminal of any work place. That is, the space segment can fully utilize the advantages of global coverage of constellation of low-orbit satellites, low time delay, low link loss and the like.

Specifically, as can be seen from the analysis of the coverage of a single satellite on the ground, due to the orbiting motion of the satellite, the coverage of the satellite also moves on the ground, and coverage time slots and coverage gaps are generated for the ground service area. In order to improve the coverage rate of a certain area, a constellation is formed by a plurality of satellites, and the coverage of the target area by each satellite is finished by mutual connection of the coverage time slots of the target area. The designed track configuration scheme is different according to different multi-satellite/single-satellite coverage requirements. For general communication, performance requirements can be met by adopting single-satellite coverage; for highly reliable communications, it is generally required to have more than two stars (including two stars) for multi-star coverage. The polar orbit satellite constellation scheme design comprises two aspects of orbit design and constellation design, wherein the satellite orbit design comprises the selection of the orbit height, eccentricity and inclination of a satellite, and the constellation design comprises the total number of the satellites in the system, the number of orbital planes, the ascending focus interval between the orbital planes, the number of the satellites in the orbital planes and the interval between the satellites as well as the phase interval between the adjacent orbital planes.

In the embodiment of the invention, the design content of the low-orbit circular solar synchronous polar orbit Internet of things constellation is as follows:

1. satellite orbit altitude selection: avoiding the two van-arrhen radiation bands centered at 3700km and 18500km, respectively. The atmospheric resistance increases along with the descending of the altitude of the satellite, and when the altitude of the orbit is less than 700km, the atmospheric resistance seriously affects the orbit parameters, and the service life of the satellite is shortened. For example, when the orbital altitude is 400km, the satellite has a lifetime of about 160 days or so. In addition, when the orbit height is low, the satellite can be corroded by oxygen ions, and the solar cell is also resistant to radiation. The track height is therefore typically greater than 700 km. In addition, for convenience of network operation and track control, it is preferable to select the track period to have an integral multiple relationship with one sidereal day (23h56min4.09s, i.e., 86164 s).

2. Designing the eccentricity of the track: as an important parameter in orbit design, the eccentricity of the orbit affects the coverage of the satellite in a local area and the length of transit time. In order to uniformly cover the south and north hemispheres, the global low-orbit communication constellation systems in foreign countries such as an Iridium system and a Globalstar system adopt circular orbits. This is not necessarily the case for regional satellite systems, such as using an elliptical frozen orbit with an inclination of 63.4 ° (or 116.2 °) to maintain a longer visibility time for some high altitude regions, thereby enlarging the corresponding coverage area and extending the coverage time. However, for other elliptical orbits, due to perturbation, the orbit near-location may precess, thereby affecting satellite coverage to the corresponding service area.

3. Designing the inclination angle of the track: optimal coverage of a given area can be achieved by adjusting the track inclination from 0 ° to 180 ° (equator). Continuous global coverage (e.g., "Iridium") is achieved with only polar orbiting satellites, provided that there are enough satellites and appropriate phase relationships; continuous global coverage can also be achieved with only inclined orbits (e.g., "Globalstar"); the combination of polar, equatorial and inclined orbits also allows continuous global coverage. For regional satellite communication systems, equatorial orbits, inclined orbits for mid-latitudinal regions, and polar orbits or large inclination (>70 °) orbits for polar regions may be used if they are in the equatorial region. The determination of the track inclination depends mainly on the latitude of the desired coverage area. For a circular orbit, continuous coverage of a certain area actually means continuous coverage of a latitude band where the area is located, and the relation with longitude is not large.

4. Designing a single-star coverage area: the coverage of a single satellite to the ground is mainly determined by the satellite altitude, the satellite antenna beam half-power angle and the minimum elevation angle required by the constellation gateway station for reliable communication. Fig. 2 is a schematic diagram of a single satellite coverage area. Wherein R is_eThe radius of the earth, h the height of the satellite, gamma the lowest observation elevation angle and phi the half-power angle of the satellite antenna beam. Only whenWhen the elevation angle of the satellite to the user is higher than gamma, the satellite can observe or communicate with the user. The calculation formula of the sub-satellite viewing angle phi, the geocentric angle theta corresponding to the ground coverage area and the coverage area radius r is as follows:

r＝R_eθ

5. designing a coverage band combined constellation: the inclination angle of the polar orbit constellation satellite orbit is close to 90 degrees, the heights of the satellite orbits forming the constellation by utilizing the combination method of the coverage zones are consistent, the inclination angles of the orbits are the same, the satellites in the same orbit are distributed at equal intervals, so that uniform and consistent coverage zone channels are formed, and the coverage of the global or latitudinal zone is realized by utilizing the combination of the coverage channels of different orbit planes. According to the in-orbit satellite coverage zone relation graph, the half width psi of the coverage zone can be calculated as:

wherein n is the number of satellites in the same orbital plane. At a latitude of

On the equatorial ring, the covering belt has a corresponding central angle of latitude plane

Ensuring that the included angle between adjacent track planes is not greater than

Without interruption of coverage of the above-equator zone.

In the space segment, inter-satellite links are established between the satellites so that any satellite in the world can land through inter-satellite link data transmission of the orbital plane at any time. The introduction of the inter-satellite link enables the low earth orbit satellite mobile communication system to rely on a ground network less, so that the low earth orbit satellite mobile communication system can carry out routing and network management more flexibly and conveniently; meanwhile, the number of ground gateways is reduced, so that the complexity and investment of ground sections can be greatly reduced.

In this embodiment, the inter-satellite link adopts the Ka band to realize information transmission and exchange between satellites, and due to the mobility of the low-earth satellite and the narrow beam characteristic of the Ka band antenna, the inter-satellite link load of the low-power global real-time internet-of-things constellation satellite realizes dynamic beam scanning by adopting the Ka band phased array antenna, so that the defects of large inertia, slow speed and low omnidirectional antenna gain of a mechanical rotating antenna are overcome, the volume and the weight are small, the power synthesis efficiency is high, and the application on the micro-nano satellite is very facilitated.

As shown in fig. 3, the access mode of the inter-satellite link is to establish a ring-shaped inter-satellite link in the orbit. Specifically, at least one satellite on each orbital plane can cover a constellation gateway station, and inter-satellite transmission can be performed in the orbit. Moreover, semicircular equal annular TDD transmission in the track plane is realized; different track surfaces are distinguished by different frequency FDDs, and time synchronization is determined by a GPS.

In order to average landing time delay, two-end receiving and transmitting interleaving is adopted to form a double-ring communication network, and each time slot is 2T seconds and comprises a T second forward time slice and a T second reverse time slice. The topological relation of the link connection between the forward time slice and the reverse time slice is shown in fig. 4 and 5, if one orbital plane of a constellation has N satellites, any data can be relayed to the landing satellite at most NT seconds.

For example, in order to average the landing delay, a dual-ring communication network is formed by using transmit-receive interleaving at two ends, and each time slot is 200ms and comprises a forward time slice of 100ms and a reverse time slice of 100 ms. One orbit plane of the constellation comprises 20 satellites, and any data can be relayed to the landing satellites after at most 1 second.

It should be noted that, the data routing policy of the inter-satellite link adopts to select the nearest landing route according to an OLSR routing algorithm, the OLSR protocol is a standardized table-driven routing protocol, and a core concept used by the protocol is a multipoint relay mechanism, by which the protocol significantly reduces the overhead of packet messages.

Specifically, the protocol mainly optimizes the conventional link state algorithm by: by adopting a multipoint relay mechanism, the flooding range of the control packet is effectively reduced: the node selects a part of nodes as its Multipoint relay nodes (MPR) among all its neighboring nodes. Compared with the classical flooding mechanism, each node forwards each message when receiving a control message for the first time, only the MPR node of the node forwards the control packet sent by the node in the OLSR protocol, and other non-MPR nodes only process and do not forward the control packet. This significantly reduces the number of control packets broadcast in the network and avoids broadcast storms.

In addition, the OLSR protocol for the inter-satellite link reduces the amount of signaling data by reducing the size of a control packet, and a satellite node does not issue link information connected to all neighboring nodes but only issues a link between itself and a multipoint relay selection node (MPR Selector). In the inter-satellite link OLSR protocol, each control packet carries a sequence number, which can be used to distinguish new and old information, so the protocol does not require sequential transmission of control packets.

In this embodiment, the routing packet of the OLSR protocol of the inter-satellite link includes a hello packet, a tc packet, node information, and two-hop neighbor node information. the tc packet is used for maintaining a hello packet and is used for maintaining node information of more than two hops of a neighbor.

The hello packet and the tc packet are broadcast at a predetermined transmission interval. The protocol issues MPR Selector information by nodes periodically sending tc (topology control) packets to help other nodes establish routes to it and maintain the network topology by periodically exchanging information. Each node in the network maintains a route to all reachable destination nodes in the network.

Moreover, the inter-satellite link OLSR protocol improves the packet format of the OLSR protocol standard message aiming at the inter-satellite access MAC characteristic, and performs bit compression and mapping modification, so that the overhead is reduced, and the method is suitable for the wireless ad hoc network with limited resources. Aiming at the requirements of network capacity and maximum service hop count, the message validity period is improved, and the optimal message validity time is obtained through simulation. And a fast routing mechanism is added in the networking stage, and all time slots of the nodes are used for transmitting routing message packets, so that the fast routing establishment is completed, and the fast networking is realized. The overall architecture of the routing protocol implementation is shown in fig. 6.

For example, the inter-satellite link adopts a 22.5GHz frequency band, and the antenna adopts a 64-channel Ka array tile type phased array antenna form. The Ka frequency band phased-array antenna adopts a high-efficiency and low-profile tile-type integration mode, chips or circuits with the same functions of a plurality of channels are integrated on tiles placed in parallel through a layered structure, and then are vertically interconnected, so that an emitting assembly of the Ka frequency band phased-array antenna is of a two-dimensional planar array structure and adopts a rectangular or triangular array mode. The phased array antenna comprises a transmitting antenna subarray, a receiving antenna subarray, a T module, an R module, a cooling plate, a waveguide feed network, a wave control extension, a power supply extension and a structural member.

It should be noted that the basic format of the inter-satellite link OLSR routing algorithm protocol packet is as follows:

wherein the Packet Sequence Number (PSN) must be increased by one each time a new OLSR packet is transmitted;

in MESSAGE type, this field indicates which type of MESSAGE is to be found in the "MESSAGE" field, MESSAGE type ranges between 0-127;

for the length of the message, counting from the beginning of the message type until the beginning of the next message type (if not, to the end of the message packet);

for the source address, this field contains the primary address of the node that generated the message, where confusion with the source address in the IP header should be avoided, the latter being each time changed to the interface address of the node that retransmits the message in the middle. The former never changes in retransmissions;

for time-to-live (TTL), the TTL is decremented by one before the message is retransmitted, and when a node receives a message with TTL of 0 or 1, the message should not be retransmitted in any case. By setting this field, the source address of a message can limit the flooding range of the message;

for hop count, this field contains the hop count obtained for a message, which is incremented by one before a message is retransmitted. Initially, this field is set to 0 by the message source;

for the message sequence number, when a message is generated, the source node assigns a unique identification number to the message and places the unique identification number in the field, and the identification number is increased by one every time the message is generated. The message sequence number is used to ensure that a message is not retransmitted twice by any node.

The format of the HELLO message of the inter-satellite link OLSR routing algorithm is defined as follows:

nouns in the HELLO message format correspond to the following meanings:

reserved: the reserved field must be set to all 0's;

htime: indicating a period in which the node transmits a HELLO message;

willingess: indicating that the willingness of the node to forward the traffic for other nodes is strong, if the willingness of one node is WILL _ NEVER, the node does not forward the traffic for any node, and if the willingness of one node is WILL _ ALWAYS, the node is selected as an MPR node by other nodes. By DEFAULT, the node should set the willingness level to WILL _ DEFAULT. The willingness degree is an integer from 0 to 7, wherein, wide _ NEVER is 0, wide _ ALWAYS is 7, wide _ DEFAULT is 3, and larger numerical values represent higher willingness degrees;

link Code: link state information between a node and its neighbor nodes is illustrated;

link Type: the domain indicates the type of link, for a total of 4 types: 1) UNSPEC _ LINK: information indicating that no link is specified; 2) ASYM _ LINK: indicating that the link is asymmetric (i.e., unidirectional); 3) SYM _ LINK: indicating that the link is symmetric (i.e., bi-directional); 4) LOST _ LINK: indicating a link disconnection;

neighbor Type this field indicates the Type of Neighbor, for a total of 3 types: 1) SYM _ neighbor: indicating at least one symmetric (i.e., bi-directional) link 2) MPR _ neighbor between the node and the neighbor nodes: indicating that the node and the neighbor node have at least one symmetric (i.e., bidirectional) link and that the neighbor node is selected as MPR by the node; 3) NOT _ new: indicating that the neighbor is not a symmetric neighbor;

link Message Size: the size of the Link message, in bytes, is calculated from the Link Code field to the next Link Code field. If there is no next Link Code field, then to the end of the HELLO message;

neighbor Interface Address: which is used to indicate the interface addresses of all one-hop neighbors of the node sending the HELLO message, which possess the current link code.

The inter-satellite link OLSR routing algorithm TC message format is as follows:

the corresponding meanings of nouns in the TC message format are as follows:

ANSN (amplified Neighbor Sequence number): when a node finds that a neighbor node set of the node changes, adding 1 to ANSN in a TC message, and when other nodes receive the TC message, determining whether the message is a newer message or not by comparing the ANSN;

reserved: this field is used as a reserved field, is temporarily not used, and is fully filled with 0;

modified Neighbor Main Address: the MPR selector node, the node sending the TC message encapsulates at least all MPR selector main addresses in the TC message. If it is desired to provide some redundancy (to increase robustness), the primary addresses of other non-MPR Selector neighbors may be included.

For the ground segment, the ground segment completes system operation control and data distribution and recovery processing, and comprises a plurality of constellation gateway stations, a network server and a user server. The constellation gateway stations respectively positioned at a plurality of global positions and the low-orbit satellite in the coverage area establish a satellite-ground feeder link, are used for realizing the real-time aggregation of constellation global Internet of things data and are responsible for transmitting user data to the network server; the network server is used for bearing all required network control and management functions and distributing data to the user server, and the user server is used for providing heterogeneous application services for different application providers. It should be understood that the constellation gateway may be a satellite receiving base station for establishing a communication connection with a satellite.

In this embodiment, in order to complete the satellite-ground data backhaul of tens of thousands of user terminals accessing data, and in order to reduce the difficulty of the load on the satellite and improve the transmission rate, the constellation feeder link adopts Ka data transmission load as information transmission and exchange equipment between the satellites and the ground.

Due to the mobility of the low-earth orbit satellite and the narrow beam characteristic of the Ka frequency band antenna, the dynamic beam scanning is realized by the Ka frequency band phased array antenna in the constellation feeder link load, the defects of large inertia, low speed and low omnidirectional antenna gain of a mechanical rotating antenna are overcome, the volume and the weight are small, the power synthesis efficiency is high, and the application on the micro-nano satellite is very facilitated. As shown in fig. 7, the Ka data transfer load starts up at a specific time according to the content of the work package, and may direct the antenna to a satellite according to the ground injection pointing data, or calculate the antenna pointing data according to the GNSS data (position, velocity, and time), ephemeris and attitude data, and the ground injection orbit, and program the pointing function of the antenna according to the pointing data.

In addition, the Ka data transmission load antenna pointing mode has a direct injection mode and an autonomous calculation mode. The direct injection mode injects a pointing angle data packet (the pointing angle of the antenna work) from the ground, and the comprehensive interface and the controller drive the antenna to point; the autonomous calculation mode is used for calculating the antenna pointing angle according to the appointed satellite instantaneous orbit parameters and by combining the information such as GNSS data, ephemeris and attitude data output by the satellite comprehensive electronic subsystem and the Ka data transmission load.

Moreover, the Ka data transmission load adopts the CCSDS standard, and introduces the concept of virtual channel vc (virtual channel). The physical channel is divided into a plurality of logical data channels for use by different application processes on a time division basis. As shown in fig. 8, for the application of the virtual channel on the satellite, the multiple services provided by the AOS proposal are used to process the complex information source data on the satellite, so as to realize the integration of the services on the satellite.

The data stream is processed by using the bit stream service provided by the AOS proposal, and is packed into a bit stream protocol data segment, and is filled into a VCDU data field to form an AOS transmission frame, and the transmission frame format is shown in fig. 9.

After the information and the data transmission information are merged into a unified data stream, the unified data stream is packed into a bit stream protocol data segment B _ PDU by using the bit stream service processing shown in fig. 10, and the bit stream protocol data segment B _ PDU is filled into the data field of the virtual channel data segment VCDU. After framing is completed, the AOS transmission frame enters a buffer area of each virtual channel to wait for transmission. The measurement information is packed into bit stream protocol data segment B _ PDU by bit stream service, and is filled into the data field of VCDU, and a virtual channel special for transmitting measurement information is occupied. Because the measurement information transmission has a high real-time requirement, in order to ensure the reliability of the measurement information transmission, a proper virtual channel scheduling strategy needs to be selected to schedule the dedicated virtual channel to transmit the measurement information. And making a proper virtual channel scheduling strategy according to the data frame buffer amount, the frame delay and the real-time requirement in the virtual channel, thereby realizing reasonable allocation of the transmission time slot of the physical channel.

It should be noted that, in this embodiment, the Ka data transmission payload includes a data transmission phased array antenna and a data transmission integrated controller. The data transmission integrated controller receives attitude, orbit, time and satellite related information sent by the integrated electronics in real time, calculates the pointing angle of an antenna beam in real time, and sends the pointing angle to the data transmission phased array antenna, and the data transmission phased array antenna performs resolving and distributing according to the pointing angle and controls a vector modulator chip to perform amplitude and phase adjustment;

in addition, the data transmission integrated controller also converts I, Q data streams sent by the data transmission subsystem, completes SQPSK modulation at radio frequency, sends the data streams to the data transmission phased array antenna after amplification, and radiates signals by the data transmission phased array antenna according to a specified direction. And the data transmission integrated controller receives the telemetering signal which is output by the data transmission phased array antenna and is used for state judgment, and compensates and corrects the related parameters of the data transmission phased array antenna.

As shown in the figure, the data transmission phased array antenna comprises an antenna array, a T component, a feed network, a wave control network, a power supply network and an autonomous temperature control structure. Moreover, the main functions of the data transmission phased array antenna are as follows:

(1) according to the angle information sent by the integrated controller, the continuous switching of the beam direction is realized;

(2) amplifying the received radio frequency modulation signal and then transmitting the amplified radio frequency modulation signal in a specified direction;

(3) the antenna has an automatic temperature control function, controls the temperature of each component of the antenna and realizes the balance of array surface temperature;

(4) the remote measuring channel is used for providing an antenna array surface coupling output signal for the remote measuring of the integrated controller;

(5) the T channel temperature acquisition function is provided, and the temperature is transmitted to the integrated controller in a digital quantity mode.

The data transmission integrated controller mainly comprises a modulator, a power supply module, an antenna controller and a telemetry module. Moreover, the main functions of the data transmission integrated controller are as follows:

(1) calculating the angle information of the wave beam pointing to the satellite under the phased array antenna coordinate system according to the program control;

(2) data sent by the logarithm transmission subsystem is modulated, up-converted and power-amplified, and high-code-rate transmission of the satellite is completed in a visible arc section of the satellite;

(3) finishing the storage, analysis, execution and telemetering analysis of the instructions required by the operation of the on-orbit service;

(4) collecting telemetering information of a phased array antenna, summarizing the telemetering information with local telemetering, and sending comprehensive electrons according to protocol requirements;

(5) providing a secondary power supply for the phased array antenna, and performing on-off control on the power supply of the phased array antenna according to the requirements of the working process;

(6) receiving a telemetering signal sent by a phased array antenna, realizing adjustment of antenna transmitting power and amplitude-phase self-inspection of a T assembly of the phased array antenna;

(7) processing the temperature remote measurement of the array element of the phased array antenna, and performing temperature compensation on the T component according to the temperature curve of the T component;

(8) providing an interface between the subsystem and other subsystems of the satellite.

For the user segment, the user segment is mainly used for collecting sensing data and is comprised of a plurality of user terminals connected with the sensors. And a satellite-ground user link is established between the user terminal in the user segment and the satellite in the coverage area, and is transmitted to the satellite-borne high-capacity Internet of things gateway load through an interface specification protocol of the Internet of things service.

Specifically, the data transmitted by each user terminal can be received by a plurality of low earth orbit satellites in the coverage area, and each low earth orbit satellite gateway load can receive a data packet from a user terminal node and forward the data packet to the ground segment through the inter-satellite link.

As shown in fig. 11, each satellite gateway load forwards a data packet received from a terminal node to a ground network server based on a cloud platform through an inter-satellite link, and neither the satellite nor the terminal needs to maintain registration information, and no mobility management or inter-satellite gateway load switching needs to be performed on the satellite. Because the large-capacity satellite-borne Internet of things gateway has the receiving characteristics of multiple channels and multiple data rates, the data packet on any active channel can be scanned and detected and demodulated, roaming between gateways does not need to be considered by a terminal and a satellite, and a terminal node broadcasts the data packet without considering which gateway can receive the data packet.

Multiple gateways can receive the data packets but have no impact on the energy consumption of the gateways themselves, so that the user terminals do not need a handover procedure or synchronization.

Since Context Switch (Context Switch) when the user terminal accesses different satellites is managed and maintained by the network server of the ground segment, the complicated handover work is eliminated. In the embodiment, the intelligent and complex processing task is put on the network server, the network is managed through the network server, redundant received data are filtered, and safety check is executed, so that the design of a satellite system is greatly simplified, and a global real-time Internet of things constellation system can be implemented through the micro-nano satellite.

In this embodiment, the space segment and the user satellite-ground link between the user segments adopt an ISM free frequency band of 400MHz to 1GHz, which takes into account long distance, antenna size and efficiency. And the space segment and the user segment have the terminal capability of global access LoraWAN system Internet of things.

Since the frequencies used by LoraWAN are different in different regions, the supported frequency bands include 434MHz, 470, 510MHz, 780MHz, 868 MHz, and 915 MHz. Not only the frequency band distinction, the refinement to the channel division, even the data rate, the transmission power, the maximum data length, and so on are distinguished. Therefore, when the low earth orbit satellite is used for the connection of the Internet of things in different regions of the world, the combined coverage of multiple frequency bands is realized by adjusting the frequency of the on-satellite transceiver.

Aiming at the fact that Doppler effect is generated due to relative motion of low-orbit Internet of things constellations, the embodiment of the invention provides an improved asynchronous ALOHA access protocol of TDMA/FDMA based on the Doppler effect. As shown in fig. 12, in each satellite-to-ground beam coverage area, the doppler frequencies of different ues in the same latitude area are not greatly different, while the doppler frequencies of different ues in the same longitude area have a larger difference.

In each satellite-to-ground beam coverage area, firstly, a user terminal (approximate Doppler frequency) in the same latitude and different longitude areas randomizes frequency points of transmitted signals through UTC time, ephemeris and self position to realize dynamic allocation of FDMA frequency points; secondly, the user terminals in the same longitude and different latitude areas randomize the time slot of the transmitted signal according to the UTC time, the ephemeris and the self position on the basis of the FDMA frequency point allocation to realize the dynamic allocation of the TDMA time slot.

The steps of the improved asynchronous ALOHA access TDMA/FDMA multiple access configuration based on the Doppler effect are as follows:

1. each terminal of the low-orbit Internet of things constellation has DevAddr and NwkSKey parameters, MIC (Message Integrity Code) in a communication frame of the terminal is encrypted and decrypted by NwkSKey in 128AES, the MIC is mainly used for information Integrity check and preventing pseudo node attack, and a key for TDMA/FDMA multiple-access randomization calculation adopts NwkSKey;

2. the TDMA/FDMA multiple access randomization calculation is carried out by adopting Advanced Encryption Standard (AES), the block length of the AES is fixed to be 128 bits, and the key length is 128 bits;

3. respectively dynamically allocating an FDMA frequency point and a TDMA time slot based on the DevAddr and the NwkSKey parameters; and, the formula of the dynamic allocation of the FDMA frequency points is as follows: freq _ Offset ═ aes128_ encrypt (NwkSKey, UTC | DevAddr | Lon | Lat); the dynamic allocation formula of the TDMA time slot is as follows: slot _ Offset ═ aes128_ encrypt (NwkSKey, Freq _ Offset | UTC | DevAddr | Lon | Alt).

In addition, in order to realize mass access of user terminals of the internet of things, the requirement on the network capacity of a single satellite access user is not less than 10 thousands, wherein the design of the node capacity of the single satellite network comprises the number of nodes connected at the same time, the average packet length, the transmission time, the transmission frequency density channel and the anti-interference capacity of the system.

In order to meet the requirement of the embodiment of the invention on the capacity index of a single satellite user, the embodiment of the invention adopts a method of user service class division rule, user service volume calculation and channel number distribution design to realize the calculation of the user network capacity, and the specific steps are as follows:

1. user service class division rules: in the low-power-consumption global real-time Internet of things constellation, the low-power-consumption global real-time Internet of things constellation is divided into three types according to the priority of terminal access frequency, wherein a minute-level access terminal (A type terminal) accounts for about 1 percent of the total, a ten-minute-level access terminal (B type terminal) accounts for about 10 percent of the total, and an hour-level access terminal (C type terminal) accounts for about 89 percent of the total. Calculating according to the network capacity of a single satellite access user not less than 10 ten thousand to obtain 1000A-class terminals, 10000B-class terminals and 89000A-class terminals;

2. GOS (call loss rate) model setting: in wireless system access, traffic can be divided into incoming traffic and completion traffic. The incoming traffic depends on the average number of calls occurring in a unit time and the average time of occupying the radio channel for each call, and among the system incoming traffic, the part of traffic that completes the connection is called the completion traffic, the part of traffic that does not complete the connection is called the loss traffic, and the ratio of the loss traffic to the incoming traffic is called the call loss rate or the blocking rate. The call loss rate requirements for each type of terminal are set as follows: the call loss rate requirement of the A-type terminal is GoSA, the call loss rate requirement of the B-type terminal is GoSB, and the call loss rate requirement of the C-type terminal is GoSC;

3. terminal traffic model algorithm: the method is characterized in that Ireland (Erl) is used as a unit for measuring the size of the traffic load when the traffic of a certain type of terminal of the low-power-consumption global real-time Internet of things constellation is calculated, the traffic intensity that a channel is completely occupied in an investigation time is represented, and 1Erl means that the channel is completely occupied in one hour. The service volume of a certain type of terminal of a single satellite is equal to the total accessible quantity of the certain type of terminal multiplied by the service volume of a single terminal;

4. the single terminal traffic calculation method comprises the following steps: the product of the access times in a specific time and the average occupation time of each access is calculated as formula A ═ C × T. A is the traffic volume in Erl (Ireland), C is the number of accesses per hour in units of times, T is the average duration of the access per time in units of hours.

For example, according to the loraWAN model shown in table 1, the standard length of each user terminal per communication is 32 bytes, and the average per-user service access time is 32 × 8/Rb seconds, calculated according to the radio rate Rb. The access times per hour of the minute-level access terminal (class A terminal) are 60 times, the access times per hour of the ten-minute-level access terminal (class B terminal) are 6 times, and the access times per hour of the hour-level access terminal (class C terminal) are 1 time. The traffic model for each class of terminal is therefore calculated as follows:

a type terminal: EA 1000 × (60 × (32 × 8/Rb)/3600) Erl;

b type terminal: EB 10000 × (6 × (32 × 8/Rb)/3600) Erl;

c type terminal: EC 89000 × (1 × (32 × 8/Rb)/3600) Erl;

TABLE 1 configuration relationship between transmission rate, bandwidth and spreading ratio of Lora modulation system

5. The number of channels required by each type of user terminal is distributed according to the algorithm: the ireland B table reflects the relationship between GoS (call loss rate), user traffic (Erl) and the number of traffic channels, and both are known to be available to the third party. The distribution algorithm of the number of channels needed by each type of user terminal obtains the approximate number of the needed channels through the table look-up of the traffic volume and the call loss rate of each type of terminal obtained above. The required channel numbers of A, B, C three types of terminals obtained by inquiring an Ireland B table are respectively CHA, CHB and CHC;

6. calculating the number of channels required by the A-type terminal as GoS/EA, the number of channels required by the B-type terminal as GoS/EB and the number of channels required by the C-type terminal as GoS/EC;

7. the total number of channels, which satisfy 10 ten thousand requirements for user network capacity under the aforementioned constraint condition, of a single satellite is CHX ═ CHA + CHB + CHC, at this time, CHX may be lower than the total number of physical channels designed for single satellite internet of things gateway load, and the remaining channels may be used to further increase the network capacity of the class C terminal, and the method for calculating the updated network capacity of the class C terminal is as follows:

a. assuming that the total physical channel number of the load of the single satellite internet-of-things gateway is CH, the number of the remaining channels is CHY-CH X;

b. and adding CHY channels for the class C terminal, wherein the final distribution channel numbers of A, B, C three types of terminals are respectively as follows: CHA, CHB, CHC + CHY;

c. re-inquiring the corresponding traffic of the Ireland B table as ECx (erl) according to the channel number CHC + CHY of the C-type terminal;

d. the updated network capacity of the class C terminal is ECx/(1 × (32 × 8/Rb)/3600).

8. And finally: the user network capacity of the low-power consumption global real-time internet of things constellation is 11000+ ECx/(1 x (32 x 8/Rb)/3600).

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.

Claims

1. A global real-time Internet of things constellation system is characterized in that: the method comprises the following steps:

a space segment comprising a plurality of low earth orbit satellites intercommunicated and interconnected by inter-satellite links;

the system comprises a ground section and a control section, wherein the ground section is used for completing an operation control function and a data distribution and recovery processing function, and comprises a plurality of constellation gateway stations; and

a user segment for collecting sensing data, the user segment comprising a plurality of user terminals;

the constellation gateway station of the ground segment and the user terminal of the user segment are respectively communicated with the low-orbit satellite of the space segment through respective communication links;

the data routing strategy of the inter-satellite link adopts a method of selecting a nearest landing route according to an OLSR routing algorithm, the OLSR protocol of the inter-satellite link reduces the amount of signaling transmission data by reducing control packets, and the satellite node issues link information between the satellite node and the relay selection node;

in the OLSR protocol, only the MPR node forwards the control packet sent by the node, and other non-MPR nodes only process and do not forward the control packet; each control packet carries a sequence number, which can be used to distinguish between old and new information;

the data sent by each user terminal can be received by low earth orbit satellites in a plurality of coverage areas, and the gateway load of each low earth orbit satellite can receive a data packet from a user terminal node and forward the data packet to the ground segment through the inter-satellite link;

the user satellite-ground link between the space section and the user section adopts an ISM free frequency band of 400MHz-1GHz, and when the low-orbit satellite is used for the connection of the Internet of things in different regions of the world, the multi-band combined coverage is realized by adjusting the frequency of the on-satellite transceiver;

in each satellite-to-ground beam coverage area, randomizing frequency points of transmitted signals by user terminals in the same latitude and different longitude areas through UTC time, ephemeris and self positions to realize dynamic allocation of FDMA frequency points;

the user terminal in the same longitude and different latitude areas randomizes the time slot of the transmitted signal on the basis of FDMA frequency point allocation according to UTC time, ephemeris and self position to realize dynamic allocation of TDMA time slot;

the improved asynchronous ALOHA access protocol of the TDMA/FDMA based on the Doppler effect is adopted to solve the Doppler effect of the low-orbit Internet of things constellation caused by relative motion, and the improved asynchronous ALOHA access TDMA/FDMA based on the Doppler effect is configured by the following steps:

each user terminal of the low-orbit Internet of things constellation has DevAddr and NwkSKey parameters, an information complete code in a communication frame of the terminal is subjected to 128AES encryption and decryption by NwkSKey, and a key for TDMA/FDMA multiple access randomization calculation adopts NwkSKey;

the TDMA/FDMA multiple access randomization calculation is carried out by adopting an advanced encryption standard, the block length of AES is fixed to be 128 bits, and the key length is 128 bits;

and dynamically allocating the FDMA frequency points and the TDMA time slots based on the DevAddr and the NwkSKey parameters respectively.

2. The global real-time internet of things constellation system of claim 1, wherein: the satellite of the space section is a low-orbit circular sun synchronous satellite, and provides 24-hour full real-time effective coverage for the user terminal of any work place.

3. The global real-time internet of things constellation system of claim 1, wherein: the inter-satellite link adopts Ka frequency band to realize information transmission and exchange between satellites, the access mode of the inter-satellite link is to establish annular inter-satellite link in orbit, semi-circles in the orbital plane are transmitted in an equal annular TDD mode, satellites in different orbital planes are distinguished by FDDs with different frequencies, and time synchronization is determined by a GPS.

4. The global real-time internet of things constellation system of claim 1, wherein: and the inter-satellite link adopts the receiving and transmitting of two ends to be staggered to form a double-ring communication network.

5. The global real-time internet of things constellation system of claim 1, wherein: the ground segment also comprises a network server and a user server, wherein the network server is used for bearing all required network control and management functions and distributing data to the user server, and the user server is used for providing heterogeneous application services for different application providers;

and a satellite-ground feeder link is established between a plurality of constellation gateway stations respectively positioned at a plurality of global positions and a low-orbit satellite in a coverage area, so as to realize the real-time aggregation of constellation global Internet of things data and be responsible for transmitting user data to the network server.

6. The global real-time internet of things constellation system of claim 5, wherein: the constellation feeder link adopts Ka data transmission load as information transmission and exchange equipment for realizing satellite-ground transmission.

7. The global real-time internet of things constellation system of claim 5, wherein: the constellation feeder link load adopts a CCSDS standard, a virtual channel VC is introduced, and complex information source data on the satellite is processed by adopting a plurality of services provided by an AOS suggestion;

and, the data stream is processed by using the bit stream service provided by the AOS proposal, and is packaged into a bit stream protocol data segment and filled into a VCDU data field to form an AOS transmission frame.

8. The global real-time internet of things constellation system of claim 5, wherein: context switching when the user terminal accesses different satellites is managed and maintained by the network server of the ground segment.