spring 2020 ensc 427: communication networks ns-3 …anysam/presentation.pdf · 2020. 4. 12. ·...

ENSC 427: Communication Networks Spring 2020

NS-3 Simulation Model for LEO Satellite Networks

Anysa Jyoti Manhas (301290035) — [email protected] Kaur Mann (301275521) — [email protected]

Jasmandeep Singh Batra (301288075) — [email protected] Team 11

Project URL: http://www.sfu.ca/~anysam/ensc427project.html

mailto:[email protected]



Roadmap

● Introduction

● Overview of Related Work

● Problem Description

● Implementation

● Discussion & Conclusion

● References

ENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 2 of 31

Roadmap

● Introduction



● Implementation


● References


Introduction● Low-Earth orbiting (LEO) satellites are an emerging technology for providing global, low-latency

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]

● The Iridium satellite constellation, which provides voice and data connections, became operational in

1998 and consists of 66 satellites at 780 km [5]

● LEO satellites orbit at an altitude between 500 km and 2000 km [6]○ Lower than geostationary satellites — provide lower latency to transmit data

○ Orbit around the Earth at a speed of about 8 km/s

● LEO satellite networks offer shorter propagation delays than terrestrial communication networks (i.e.,

fiber optic cables) while offering mobile and broadcast services[7]


Introduction● There is currently no implementation for a LEO satellite module in Network Simulator 3 (ns-3)

○ The Iridium LEO satellite constellation is supported in ns2

● Our project purpose: to construct a LEO satellite constellation network in ns-3 and evaluate network

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


Roadmap

● Introduction



● Implementation


● References


Overview of Related Work● Modelling Communications in Low-Earth-Orbit Satellite Networks [8]

○ 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


Figure 1: The interconnection pattern of the Iridium system.Source: [8]

Overview of Related Work● Delay is Not an Option: Low Latency Routing in Space [9]

○ 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


Figure 2: Networks with varying link configurations simulatedSource: [9]

Roadmap

● Introduction



● Implementation


● References


Problem Description● To construct a LEO satellite constellation network, we needed to design and implement support for

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


Problem Description● To construct a LEO satellite constellation network, we needed to design and implement support for

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


Roadmap

● Introduction



● Implementation


● References


ImplementationOverview of Implementation


Figure 3: High level overview of leo-satellite model integrated into ns-3

ImplementationLEO Satellite Mobility Model● The LEO Satellite Mobility Model is implemented in src/leo-satellite/model/mobility/leo-satellite-mobility.h

and src/leo-satellite/model/mobility/leo-satellite-mobility.cc ○ The class is derived from the existing ns-3 MobilityModel class

● We chose a polar orbit similar to Iridium○ 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

● At any point in simulation time, LeoSatelliteMobilityModel::DoGetPosition() updates satellites positions based

on elapsed time and satellite speed, and returns satellite positions○ 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

● LeoSatelliteMobilityModel::CalculateDistance() calculates the distance between two satellites using the

Haversine formula (used to determine distance between two points on a sphere):

ENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 14 of 31[11]

ImplementationLEO Satellite Mobility Model

Figure 4: Example of satellite positions configured by LEO Satellite Mobility Model; nine orbital planes and eight satellites per plane


ImplementationGround Station Mobility Model● The Ground Station Mobility Model is implemented in src/leo-satellite/model/mobility/ground-station-mobility.h and

src/leo-satellite/model/mobility/ground-station-mobility.cc○ The class is derived from the existing ns-3 MobilityModel class

● To simplify our implementation, GroundStationMobilityModel::DoSetPosition() positions ground stations directly

below orbital planes

● GroundStationMobilityModel::CalculateDistanceGroundToSat() calculates the distance between a ground station and

an orbiting satellite using the following formula:


[12]

ImplementationLEO Satellite Module● This is the top level controller module, implemented in src/leo-satellite/model/leo-satellite-config.h and

src/leo-satellite/model/leo-satellite-config.cc

● The module assigns the appropriate mobility models to the satellites in the constellation network and the ground

stations○ Keeps track of the satellites in NodeContainers corresponding to orbital planes, and keeps track of ground stations in their own

NodeContainer

● The module sets up four links per satellite (similar to Iridium constellation)○ 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

● The module sets up initial links between ground stations and the satellites nearest to them


ImplementationLEO Satellite Module

Figure 5: Example of initial satellite link configuration and ground station placement


Indicates that a ground station is placed directly under this satellite for initial configuration

ImplementationLEO Satellite Module● Intraplane links are constant throughout the duration of the simulation

○ Created using ns-3 Point-to-Point Network Devices (between two nodes) [13]

● Interplane links, between satellites in adjacent orbiting planes, and between ground stations and satellites, must deal

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

● Link delays were calculated using the distance between the nodes and the speed of light

● Link data rates were taken to be 5.36Gbps [15]


ImplementationLEO Satellite Modulevoid 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

ImplementationLEO Satellite Module● ns-3’s InternetStackHelper is used to install IP stack on all nodes [16]

● ns-3’s Ipv4AddressHelper is used to assign IP addresses to all nodes with a base 10.1.1.0 and a network mask

255.255.255.0○ Base address increments for each subnet created within the system

● ns-3’s Ipv4Interface class is used to create the interfaces between all nodes○ 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

● Ns-3’s Ipv4GlobalRoutingHelper is used to populate routing tables on each of the satellites○ 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

● Top level controller maintains net devices and interfaces for all links


ImplementationSimulation● Simulation is implemented in src/leo-satellite/examples/leo-satellite-example.cc

● LEO satellite constellations network in simulations are placed at an altitude of 2000 km

● Simulation involves two ground stations (client and server) and a LEO satellite network constellation composed of

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]

● Simulations are run for 2000 seconds○ 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

● Data was collected using ns-3’s Flow Monitor model [18]○ 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


ENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 23 of 31Figure 6: Average RTT vs total number of satellites

ENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 24 of 31Figure 7: Average RTT vs number of satellites per orbital plane organized into number of orbital planes

ENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 25 of 31Figure 8: Number of hops vs number of satellites per orbital plane organized into number of orbital planes

ENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 26 of 31Figure 9: Average RTT vs altitude of LEO satellite network

ImplementationSimulation Analysis● No clear relationship noted between average RTT and total number of satellites in LEO satellite constellation network

● In simulations run with a set number of orbital planes○ 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)

● Increasing the altitude of LEO satellite constellation network increased average RTT nearly linearly ○ 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

observed when repeating this experiment ● Our laptop CPUs did not provide enough processing power to run simulations with a large number of nodes within a

reasonable amount of time, limiting the scope of data we were able to collect


ImplementationOther Experiments Possible with Current Simulation Model● Comparing latency of LEO satellite network constellations at different altitudes

○ 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

● Comparing number of hops between LEO satellite network constellations of varying sizes


Roadmap

● Introduction



● Implementation


● References


Discussion & Conclusion● As LEO satellite network constellations emerge as technologies for communication and Internet connections, it is

useful to be able to simulate these network topologies and analyze their properties

● Implementing a LEO satellite network constellation involved implementing support for many moving parts (literally

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

● Alternative approaches to implementing a LEO satellite network involve○ 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


Discussion & Conclusion● Future work

○ 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

● What we have learned about through completing this project:○ 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

● More generally, extending existing ns-3 classes

■ Running simulations and evaluating resultsENSC 427: COMMUNICATION NETWORKS, April 6, 2020 | Slide 31 of 31

Roadmap

● Introduction



● Implementation


● References


References[1] “StarLink Mission,” SpaceX, Mar., 2020. [Online]. Available:

https://www.spacex.com/sites/spacex/files/sixth_starlink_mission_overview_0.pdf. [Accessed: Mar. 5, 2020].[2] D. Oberhaus, “How SpaceX’s Satellite Internet Will Actually Work,” Wired, para. 9, Jan. 6, 2020. [Online]. Available:

https://www.wired.com/story/how-spacexs-satellite-internet-will-actually-work/. [Accessed: Mar. 5, 2020].[3] M. Sheetz, “Amazon wants to launch thousands of satellites so it can offer broadband internet from space,” CNBC, para.

2, Apr. 4, 2019. [Online]. Available: https://www.cnbc.com/2019/04/04/amazon-project-kuiper-broadband-internet-small-satellite-network.html. [Accessed: Mar. 5, 2020].

[4] “Telesat LEO - Why LEO?,” Telesat, 2020. [Online]. Available: https://www.telesat.com/services/leo/why-leo. [Accessed: Mar. 5, 2020].

[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/2019/08/15/6b224bd2-bf72-11e9-a8b0-7ed8a0d5dc5d_story.html. [Accessed: Mar. 5, 2020].


References[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].


References[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-given-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].


References[18] “Flow Monitor,” ns-3. [Online]. Available:

https://www.nsnam.org/docs/models/html/flow-monitor.html. [Accessed: Apr. 12, 2020].


spring 2020 ensc 427: communication networks ns-3 …anysam/presentation.pdf · 2020. 4. 12. ·...

Documents