ENSC 427: Communication Networks Spring 2020 NS-3 Simulation Model - - PowerPoint PPT Presentation
ENSC 427: Communication Networks Spring 2020 NS-3 Simulation Model for LEO Satellite Networks Project URL: http://www.sfu.ca/~anysam/ensc427project.html Anysa Jyoti Manhas (301290035) anysam@sfu.ca Amneet Kaur Mann (301275521)
Anysa Jyoti Manhas (301290035) — anysam@sfu.ca Amneet Kaur Mann (301275521) — amneetm@sfu.ca Jasmandeep Singh Batra (301288075) — jasmanb@sfu.ca Team 11
Project URL: http://www.sfu.ca/~anysam/ensc427project.html
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broadband Internet services
○ SpaceX is deploying StarLink [1], a constellation of nearly 12,000 satellites [2], to provide near global coverage by 2021 ○ Other examples: OneWeb is deploying a constellation of 588 satellites [2], Amazon’s Project Kuiper will consist of 3236 satellites [3], Telesat LEO [4]
1998 and consists of 66 satellites at 780 km [5]
○ Lower than geostationary satellites — provide lower latency to transmit data ○ Orbit around the Earth at a speed of about 8 km/s
fiber optic cables) while offering mobile and broadcast services[7]
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○ The Iridium LEO satellite constellation is supported in ns2
latency
○ LEO satellite nodes to be organized in orbital planes ○ As LEO satellites orbit, the distance of satellites links and the links between satellites will change ○ Packets will be routed between two ground stations through the LEO satellite constellation network
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○ Explored design and use of LEO satellite networks, and issues related to building satellites networks ○ Pointed to key considerations when evaluating LEO satellite networks: constellation, coverage, frequency issues, multiple access methods, hand-offs, intersatellite network topology ○ Two main types of orbital constellations: polar and inclined ■ The Iridium satellite utilizes a polar orbit with four connections per satellite (two inter-plane and two intra-plane) ○ Lower altitude satellites have a smaller footprint, and require frequent hand-offs between ground stations
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Figure 1: The interconnection pattern of the Iridium system. Source: [8]
○ Implemented and evaluated a simulation of SpaceX’s StarLink using details provided from SpaceX’s public FCC filing ○ Constellation included 1600 satellites with optical communication links ○ Performed routing by running Dijkstra routing algorithm every 50 ms and caching the results for 200 ms in the future to determine which links will still be present when packet reaches those satellites ○ Evaluated multiple network configurations via modifying links between satellites ○ Concluded that the SpaceX network could provide faster Internet services than terrestrial networks for large distances
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Figure 2: Networks with varying link configurations simulated Source: [9]
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the following structures which were not currently present in ns-3
○ A mobility model for the LEO satellites in the constellation network ■ Must take into account the total number of LEO satellites in the simulation and configure their positions appropriately ■ Must determine the new positions of the orbiting satellites as time passes according to the speed of the satellites and their orbital plane and direction ■ Must calculate the distance between satellites as they change positions to calculate link delays ○ A mobility model for ground stations interacting with the LEO satellites ■ Must determine position of ground stations ■ Must calculate the distance between themselves and the orbiting satellites
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the following structures which were not currently present in ns-3 (con’t)
○ A top level controller module for LEO satellite constellation network ■ Must keep track of all inter-plane satellite links, all intra-plane satellite links, ground station links to satellites, and appropriately trigger link updates between orbiting satellites and between ground stations and satellites ■ Must account for hand-offs between satellites (detaching and reattaching links between satellites so each satellite is only connected to its closest neighbors), and between ground stations and satellites ■ Must keep track of all channels between nodes, their corresponding net devices, and the IP interfaces for each of the nodes
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Figure 3: High level overview of leo-satellite model integrated into ns-3
and src/leo-satellite/model/mobility/leo-satellite-mobility.cc
○ The class is derived from the existing ns-3 MobilityModel class
○ Given number of planes and number of satellites per plane, LeoSatelliteMobilityModel::DoSetPosition() configures orbital planes, and satellites within planes, equidistant from each other ○ Adjacent orbital planes are configured to move in opposite directions relative to each other
○ Given altitude of satellite constellation, speed is calculated as follows: [10] ■ G = gravitational constant = 6.673 x 10^(-11) Nm^2/kg^2 ■ M = mass of Earth = 5.972 x 10^(24) kg ■ R = radius of Earth + altitude of LEO satellite
Haversine formula (used to determine distance between two points on a sphere):
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[11]
Figure 4: Example of satellite positions configured by LEO Satellite Mobility Model; nine orbital planes and eight satellites per plane
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src/leo-satellite/model/mobility/ground-station-mobility.cc
○ The class is derived from the existing ns-3 MobilityModel class
below orbital planes
an orbiting satellite using the following formula:
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[12]
src/leo-satellite/model/leo-satellite-config.cc
stations
○ Keeps track of the satellites in NodeContainers corresponding to orbital planes, and keeps track of ground stations in their own NodeContainer
○ Two intraplane links ■ Links between adjacent satellites in same NodeContainer ■ Constant throughout simulation ○ Two initial interplane links ■ Links between satellites in adjacent planes initially directly across from each other
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Figure 5: Example of initial satellite link configuration and ground station placement
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Indicates that a ground station is placed directly under this satellite for initial configuration
○ Created using ns-3 Point-to-Point Network Devices (between two nodes) [13]
with hand-offs during the simulation (the links are dynamic)
○ Creating using ns-3 CSMA Network Devices [14] ■ Allows for dynamic links through link attachment and detachment methods ○ LeoSatelliteConfig::UpdateLinks() can be called periodically in a simulation to update the dynamic links based on the new distances between the relevant nodes
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void LeoSatelliteConfig::UpdateLinks() { For each plane: Find reference satellite (satellite closest to the equator) Find closest satellite to reference satellite in the plane east to the current plane Calculate reference increment from node displacement between reference satellite and its closest eastern satellite For each node in this plane: Determine closest eastern satellite based on reference increment obtained If closest eastern satellite has not changed since last update: Update link delay based on new distance Else Detach channel between node and its previous closest eastern neighbor Create channel between node and new closest eastern neighbor with link delay based on distance For each ground station Find closest satellite, detach/create channels as required, and update link delay based on distance }ENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 20 of 31
255.255.255.0
○ Base address increments for each subnet created within the system
○ For dynamic links (interplane links, and links between ground stations and satellites), the Ipv4Interface::SetDown() function is used to disable interfaces for links that are not attached at that time
○ Assumes a global knowledge of the system ○ Finds shortest paths to all other nodes in the network ○ Each time UpdateLinks() is called the routing tables are recomputed
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varying sizes
○ Ground stations are configured on opposite sides of the globe at different latitudes (such that a combination of inter- and intra-plane link traversals are required to transmit packets between the two) ○ ns-3’s UDPEchoServerHelper and UDPEchoClientHelper are used to configure these ground stations as client and server, and send UDP packets between them [17]
○ LeoSatelliteConfig::UpdateLinks() is called every 100 seconds in the simulation to update the dynamic links ○ Each time links are updated, a new UDP packet is sent ○ Round trip time (RTT) is calculated as the average for all the packets sent during the full simulation
○ On an Intel i7 quad-core processor, simulations involving the largest satellite network (11 planes, 28 satellites per plane) resulted in a processing time of 47 minutes
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Figure 6: Average RTT vs total number of satellites
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Figure 7: Average RTT vs number of satellites per orbital plane organized into number of orbital planes
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Figure 8: Number of hops vs number of satellites per orbital plane organized into number of orbital planes
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Figure 9: Average RTT vs altitude of LEO satellite network
○ Increasing the number of satellites per orbital plane decreases RTT up to a point. After this point, further increasing the number of satellites per orbital plane no longer significantly benefits RTT ○ Increasing number of satellites per orbital plane increased the number of hops required to transmit data from source to destination and back ○ We hypothesize that in a more robust model that takes into account the overhead involved in satellite transmission, increasing the number of satellites per orbital plane will actually increase average RTT as there would be a tradeoff between total satellite transmission delay (which will increase as number of hops between source and destination increase) and propagation delay due to link distances (which will decrease as number of satellites per orbital plane increase)
○ A lower altitude network involves a smaller propagation delay when transmitting packets from ground station to satellites ○ In a more robust model which takes into account overhead involved in modifying links between satellites, a tradeoff may be
reasonable amount of time, limiting the scope of data we were able to collect
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○ Ex: a LEO satellite network constellation at an altitude of 500 km versus a LEO satellite network constellation at an altitude of 2000 km ○ Satellite network constellations at lower altitudes will experience lower latency for transmission between a ground station and a satellite, but will decrease the footprint of each satellite (require more satellites for good coverage) ○ Satellite network constellations at higher altitudes will experience greater latency between a ground station and a satellite and increase the footprint of each satellite
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useful to be able to simulate these network topologies and analyze their properties
and figuratively) that are not currently supported in ns-3
○ Difficulties arose in implementing the LEO Satellite Mobility Model due to operating in GPS coordinates ○ Organization and maintenance of all the dynamic components of the satellite network configuration was not trivial
○ A different orbital configuration (ex: inclined instead of polar orbits) ○ Different configurations of channels between satellites ○ Alternative mathematical models for configuring and maintaining satellite positions in GPS coordinates
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○ Work towards a more robust model ■ Support for collisions in polar orbits (disabling satellites as they move past poles) ■ Positioning ground stations anywhere on the globe, instead of restricting position to be directly under an orbital plane ■ Including consideration for radio frequencies used and any possible interferences between neighboring satellites ■ Taking into account overhead of satellite transmission ○ Expanding simulation experiments ■ Greater number of ground stations ■ Sending heavier traffic
○ Satellites and satellite networks ■ LEO network configurations ■ Mathematics behind satellite motion ■ Factors involved in satellite communications ○ How to utilize the ns-3 tool ■ Creating our own module ■ Creating our own mobility models
■ Running simulations and evaluating results
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[5] “About Us,” Iridium, 2019. [Online]. Available: https://www.iridium.com/. [Accessing: Mar. 5, 2020]. [6] G. Ritchie, “Why Low-Earth Orbit Satellites Are the New Space Race,” The Washington Post, para. 3, Aug. 15, 2019. [Online]. Available: https://www.washingtonpost.com/business/why-low-earth-orbit-satellites-are-the-new-space-race/2019/08/15/6b2 24bd2-bf72-11e9-a8b0-7ed8a0d5dc5d_story.html. [Accessed: Mar. 5, 2020].
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[7] S. J. Campanella and T. J. Kirkwood, “Faster than fibre: Advantages and challenges of LEO communication satellite systems,” AIP Conference Proceedings, vol. 325, no. 39, May 12, 2008. [Online]. Available: https://aip.scitation.org/doi/abs/10.1063/1.47249. [Accessed: Mar. 5, 2020]. [8] P. Gvozdjak, “Modelling Communications in Low-Earth Orbit Satellite Networks,” Ph.D. dissertation, School of Computing Science, Simon Fraser Univ., Burnaby, 2000. [Online]. Available: https://www.collectionscanada.gc.ca/obj/s4/f2/dsk1/tape3/PQDD_0011/NQ61647.pdf [Accessed: Apr. 5, 2020]. [9] M. Handley, “Delay is Not an Option: Low Latency Routing in Space,” in Proc. of the 17th ACM Workshop on Hot Topics in Networks, November, 2018, Washington, USA [Online]. Available: ACM Digital Library, https://dl.acm.org/doi/10.1145/3286062.3286075. [Accessed: Apr. 5, 2020]. [10] E. Zeleny, “Orbital Speed and Period of a Satellite,” Wolfram Demonstrations Project, Mar. 2011. [Online]. Available: https://demonstrations.wolfram.com/OrbitalSpeedAndPeriodOfASatellite/. [Accessed: Apr. 11, 2020]. [11] M. Basyir, M. Nasir, S. Suryati, and W. Mellyssa, “Determination of Nearest Emergency Service Office Using Haversine Formula Based on Android Platform, Emitter International Journal of Engineering Technology, vol, 5, no. 2, pp. 270-278, Jan. 13, 2018. [Online]. Available: https://emitter.pens.ac.id/index.php/emitter/article/view/220. [Accessed: Apr. 11, 2020].
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[12] “How to calculate distance from a given latitude and longitude on the earth to a specific geostationary satellite,” Stack Exchange Mathematics, Aug. 28, 2019. [Online]. Available: https://math.stackexchange.com/questions/301410/how-to-calculate-distance-from-a-give n-latitude-and-longitude-on-the-earth-to-a. [Accessed: Apr. 11, 2020]. [13] “Point-To-Point Network Device,” ns-3. [Online]. Available: https://www.nsnam.org/doxygen/group__point-to-point.html. [Accessed: Apr. 11, 2020]. [14] “CSMA Network Device,” ns-3. [Online]. Available: https://www.nsnam.org/doxygen/group__csma.html. [Accessed: Apr. 11, 2020]. [15] I. del Portillo, B. G. Cameron, and E. F. Crawley, “A technical comparison of three low earth orbit satellite constellation systems to provide global broadband,” Acta Astronautica, vol. 159, pp. 123-135, June, 2019. [Online]. Available: https://www.sciencedirect.com/science/article/abs/pii/S0094576518320368. [Accessed: Apr. 5, 2020]. [16] “Internet,” ns-3. [Online]. Available: https://www.nsnam.org/doxygen/group__internet.html. [Accessed: Apr. 11, 2020]. [17] “UdpClientServer,” ns-3. [Online]. Available: https://www.nsnam.org/doxygen/group__udpclientserver.html. [Accessed: Apr. 11, 2020].
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[18] “Flow Monitor,” ns-3. [Online]. Available: https://www.nsnam.org/docs/models/html/flow-monitor.html. [Accessed: Apr. 12, 2020].
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