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Session C6: Collaborative and Networked Navigation

Utilize Aerostat to Realize Emergency Service of Integrated Network for Navigation and Communication
Weiyi Chen Haitao Wu Pingke Deng Xiaoguang Zhang YiQu, Chinese Academy of Science, China
Location: Windjammer
Alternate Number 5

This paper presents a regional integration of position, navigation and communication network architecture.We propose the concept of an aerostat cluster, which is an autonomous system covering a local area. A number of aerostat clusters constitute a complete near space network. We design the geometric layout of the aerostat space.Due to the limitation of the communication bandwidth of the terrestrial equipment, it cannot guarantee that each aerostat can keep the connection with the ground equipment at any time. Therefore, only the cluster head node is connected to the ground equipment. The cluster nodes transmit data through the connection of the cluster head.the near space aerostat network layer (NSNET) and the aerostat backbone network layer (ABNET). This method is beneficial to the load balancing of the network and reduce the dependence of the space network on the bandwidth of the terrestrial transmission equipment. What's more, this paper designs the NS_G (near space gateway), which solves the access problem between the terrestrial network and the aerostat network. Experiments show that the proposed scheme of PNCN can meet the application requirements well and achieve the design goal. This paper provides a new idea for regional emergency communication services and even global network layout.
The transponder of the aerostat is used to receive the ground navigation signal. Then the aerostat broadcasts the signal in the broadcasting way, and realizes the position and navigation. The ground station uses RTK (real-time dynamic difference) technology to solve the real-time position of the aerostat The position information of the aerostat is sent to the control station via a communication network, and the time of all the ground station and master station is synchronous. The master station is responsible for generating and maintaining of system time, controlling the carrier signal frequency of the aerostat, measuring and calculating the launch time of the aerostat signal, preparing and editing the navigation message according to the real time position of the aerostat, and preparing the navigation signal for each aerostat and going up to the aerostat. Aerostat again broadcasts the navigation signals to the ground receiver, and the receiver can receive navigation signals from 4 aerostats to calculate their positions, so as to realize the navigation.
The star structure is composed of an aerostat cluster. Each cluster contains a cluster head, one or more gateways, and cluster members. An aerostat cluster can be formally described as a set C: C = {(c1, c2, c3, …, cn) | L<=n <= U}, where L<=n <= U means the range of the number of nodes in the aerostat cluster. In each cluster, the cluster head manages other nodes. In this way, we assign the cluster ID to the cluster head ID, and the gateway node is adjacent to the nodes of the other clusters. Between clusters, packets are transmitted through the gateway. In the process of clustering, the number of nodes is dynamically adjusted in the upper (U) and lower limit (L) of the nodes in the pre-set cluster. The aerostats in an aerostat cluster interconnect with each other and form the aerostat cluster network, denoted by G_V(C, E), where E represents the links between the aerostats.
If the aerostats need to cover the whole world, theoretically the number should be around 1000. Thus, we design the length of network address to be 16 bits, in which the first 10 bits represent the aerostat cluster address and the last 6 bits represent the aerostat address in the cluster The space and ground integration network communicates by unified addressing. In this section, we creatively propose independent addressing of the ground network and space network, and achieve the network accessing through network address translation. The ground network accesses the space network according to the aerostat cluster network covering the area. We assume the address of the aerostat, which is nearest from the access point, as the access translation address. The ground network covered by aerostat clusters accesses the space network using an external access translation address, and then sends the message to the destination address. Meanwhile, the mapping relation is recorded in the network address translation table of NS_G. We apply the adaptive learning way to update the mapping table. The process described above is transparent to the terminal. As for aerostat cluster network, the ground network address is the translation address. Thus, NS_G conceals the ground network address. Assuming a ground IP address as 192.168.1.3, and it contacts to a network address 1.1.1.2. Assuming the translation address of the near space aerostat cluster, which covers the ground network, is 0000000001000001, expressed as 1.1. Same as the IP address 1.1.1.2; its translation address is 0000000010000001, expressed as 2.1
When constructing the aerostat cluster network, how to design a structure with the shortest link and the lowest communication cost is the critical issue. In this paper, we propose to build the network topology based on the minimum spanning tree solution .
What’s more, we design the routing algorithm between the nodes in the aerostat cluster network, named ISPR (Internal Shortest Path Route). The algorithm learns from the Shortest Path Algorithm [10] to compute the shortest paths from a specific vertex to all other aerostats in the network, and design the routes according to the sum of the minimum distances between nodes.
Let n be the number of aerostats in the cluster network G_V = (C, E); set A stores the current shortest path length from the source point to the end point; set B stores the corresponding paths; set S stores the end points of shortest path obtained; W represents V-S and initially stores all aerostats except the source points. The steps in ISPR are described as follows.
(1) Initialize S to contain only the starting point of the aerostat, S = {v}.
(2) Select an aerostat k from W, which has the shortest distance from v, and add k to S (the selected distance is the shortest path length from v to k).
(3) Consider k as the relay point, and change the distances in A. If distance from the source point v to the point u (v, u) (through the relay point k) is less than the original distance (not through the relay point k), then modify the distance of u to the distance of k plus value on edge from k to u.
(4) Repeat steps (2) and (3) until all points are included in S.
In this paper, the constellation configuration of the aerostst is analyzed from the single-layer structure and the double-layer structure.Respectively, in-depth analysis of the different geometric configuration corresponding to the positioning accuracy of PDOP and GDOP value.Based on different constellation configuration for communication network design.Experiments show that the double-layer star geometry of the spatial layout of the lowest GDOP value.After using the optimized layout algorithm, the use of 20 aerostats can make the GDOP value less than 2. On this basis, the design of the wireless ad hoc network.The network is a dynamic ad hoc network. This paper also designs a network routing algorithm. The experiment shows that the communication bandwidth can reach 10Mbps and the network delay is about 80ms in the range of 200km. The network architecture can be well coupled With the integration of communications services.



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