Low Earth Satellite (LEO) Broadband Service Delivery - An Overview - David Williams
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Low Earth Satellite (LEO)
Broadband Service
Delivery
An Overview
David Williams
David.williams@fiber-rise.com
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Contents
Summary ....................................................................................................................................................... 2
Understanding LEO Satellites ........................................................................................................................ 2
Available Spectrum, Bandwidth and Coverage............................................................................................. 3
System Costs ................................................................................................................................................. 5
Observations and Conclusion ....................................................................................................................... 5
December 9, 2020
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Summary
LEO satellite for rural broadband access does not solve the Digital Divide. Available spectrum limits
projected downlink speeds per satellite to 14Gbps to be shared among users covering an area of over
16,000 square miles. Consistent gigabit broadband rates to subscribers are not possible with LEO
satellite solution based on an appreciable take rate. Rural communities will continue to fall behind the
broadband performance of suburban and urban broadband areas.
The end goal for rural areas is to bring technology, quality of life AND prosperity to the area. Satellite
simply enables Internet access to homes but does little for economic development. Commercial
enterprises and industry require fiber for infrastructure, which in turn bring jobs to rural areas.
Telemedicine, education and IoT will continue to demand more bandwidth, especially in the upstream
direction. Satellite is not enough.
LEO’s subscriber cost is currently high and does not bode well for the addressable rural market. In the
final analysis, the people we intend to help by improving broadband delivery will remain behind with
only an LEO solution.
Understanding LEO Satellites
Broadband delivered over a satellite connection has been available for many years from companies such
as HughesNet and Viasat, Inc. These traditional satellite services have often been the only broadband
alternative for rural areas, and the latency—or roundtrip delay—associated with the service has been
problematic for the user experience.
A new generation of satellite service has
emerged utilizing Low Earth Orbit (LEO)
Non-GeoStationary Orbit (NGSO) satellites
that promise much lower latency and
higher broadband rates. Elon Musk, of
SpaceX, established Starlink to address the
needs of broadband coverage across the
world. Other LEO providers include Kuiper
Amazon, OneWeb, Boeing and Telesat.
Musk cites the support of global stock
transaction as a key application for Starlink.
In the trading world, seconds translate to
billions of dollars, and faster, lower latency
Figure 1 - Global Broadband Network? (©Starlink) connections are a tremendous advantage.
Starlink seeks to capitalize on the low
latency associated with light in a vacuum (outer space) to improve latency—even over transoceanic
fiber connections—if just by a few milliseconds. Musk suggests that premium stock exchange
memberships could generate revenue for Starlink in the $30 to $50 billion range.
December 9, 2020
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LEO satellites form a grid in outer space along prescribed orbital planes designed to maximize coverage,
as shown in Figure 1. Satellites communicate with each other via laser. Four separate connections are
employed to ensure paths are maintained as the satellites move through their orbits. LEOs use Ka-, Ku-
and V spectrum bands to communicate with user terminals and ground stations. Traditional satellites
occupy a stationary orbit more than 35,000km above the earth, with an associated latency of 500 to
600ms. LEOs are non-stationary at 550km, with an advertised latency of 50ms.
Original Parameters
Orbital Planes 72 32 8 5 6
Satellites-per-Plane 22 50 50 75 75
Altitude in KM 550 1,100 1,130 1,275 1,325
Inclination (deg.) 53° 53.8° 74° 81° 70°
Modified Parameters
Orbital Planes 72 72 36 6 4
Satellites-per-Plane 22 22 20 58 43
Altitude in KM 550 540 570 560 569
Inclination (deg.) 53° 53.2° 70° 97.6° 97.6°
Table 1 - LEO Satellite Plan (Starlink)
Eventually, 12,000 satellites will occupy Starlink’s LEO satellite grid, with each satellite completing its
orbit within 90 minutes. Currently approximately 900 LEOs are in orbit with a plan to launch 4,400 by
2024. The first phase of the latest modified plan will establish 72 orbital planes with 22 satellites per
plane for a total of 1,584 LEOs as shown in Figure 2. With Starlink, each launch includes the Falcon 9
recoverable rocket carrying a payload of 60 LEO satellites. For reference, each satellite is roughly the size
of an office desk and can be produced for around $250K. Each launch costs in the neighborhood of
$30M. Thus, the first phase of Starlink’s plan costs approximately $810M dollars. Extrapolating this
number for an overall plan of 12,000 satellites equals $6.1B. Add in the cost of ground station
infrastructure and overall project cost nears the $10B previously quoted by Musk, with a completion
date of 2026.
Available Spectrum, Bandwidth and Coverage
Transmissions from LEOs to user terminals utilize Ku and V
bands occupying 10.7-12.7GHz and 37.5 – 42.5GHz, with each
user beam designed to cover a number of users within a cell.
Ground stations utilize the Ka- and V bands with a total of
7GHz (expandable to 12GHz) shared by all subscribers covered
by one satellite @ 2bits/Hz, which means 14Gbits maximum
capacity could be shared among all users. By comparison,
broadband subscribers served by fiber, typically using Passive
Optical Network (PON), share from 2.5Gbits to 10Gbits among
just 32 users, whose traffic aggregates into multiple 100Gbit
Figure 2 - Frequency Spectrum Image
links connecting to the Internet.
(NASA Public Domain)
December 9, 20204
If the number of satellite users is intended to satisfy the broadband demand in very low-density rural
areas, then the oversubscription of a ground station’s available bandwidth could result in services in the
100M/20M range. For suburban and urban areas, there are likely too many users sharing too little
bandwidth, and performance would suffer accordingly.
Elon Musk has acknowledged the limitations of the LEO satellite approach in gigabit broadband service
delivery. "Starlink is not some huge threat to telcos. I want to be super clear: it is not," according to
Musk. “So Starlink will effectively serve the three or four percent hardest to reach customers for telcos,
or people who simply have no connectivity right now. Or the connectivity is really bad. So, I think it will
be actually helpful and take a significant load off the traditional telcos."
A few points to consider regarding LEO satellite coverage:
Earth’s total surface area = 197 million sq miles.
Full 12,000 constellation without overlap would give each satellite a coverage area of 16,416 sq
miles.
Initial constellation 1584 will require each satellite to cover 124,525 sq miles.
Total area of the state of Alabama = 52,419 sq miles.
As an example, LEO satellite users in Alabama will have access to less than half of the satellite’s
capacity for its given coverage area in the near-term constellation.
Starlink is not the only LEO satellite player and the possibility of interference among competing
companies is worth consideration. Other companies occupy the same frequency bands, which can cause
interference and reduce performance. Amazon claims their Kuiper system will be negatively impacted by
Starlink’s modified coverage for the contiguous United States (CONUS) as shown in Figure 3.
Figure 3 - Interference Possibilities Among Competing LEO Systems
December 9, 20205
Weather remains a factor as well. Rain fade is a typical issue which causes up to a 5% service outage per
year, even with advance coding.
System Costs
Currently under beta testing, the cost of Starlink subscriber service is $99 per month with a $499
installation fee for the dish and router. That’s about 2x the cost of gigabit broadband service to rural
areas served by fiber.
Consider 129 million households in the United States alone. If Starlink dominated the LEO satellite
market and claimed 3% of these households, that would translate to 3.87 million homes @ $1,200 per
year revenue or $4.6B. One might assume this number could be lower, given the poverty-challenged
areas and fixed income homes that could not afford $1,200 per year for Internet access.
The lifespan of the LEO satellite is 5 to 7 years. Of the 12,000 LEOs that will occupy the full constellation,
1,500 must be replaced yearly, translating to 25 rocket launches, costing $750M dollars. This does not
include ground station support, which may be hundreds of millions per year.
One can draw their own conclusions regarding the long-term profitability of Starlink or any other LEO
satellite service, and what might happen to rural communities should it be discontinued or purchased by
another entity.
Observations and Conclusion
The downlink capacity of a Starlink LEO satellite is projected at 14Gbps. At full constellation of
12,000 satellites, three satellites would presumably cover Alabama for an aggregate capacity of
42Gbps. At 100Mbps service rate, 420 simultaneous streams can be supported. This considers
no oversubscription. Over 1M people live in rural areas within the state of Alabama.
LEO satellite service, like wireless, DSL, or HFC, is spectrum based, requiring allocation of
upstream and downstream bandwidth, which are by necessity asymmetrical. Fiber provides
symmetric gigabit service and is practically unlimited in its bandwidth.
Every access technology, except for fiber, requires a technology refresh every 5 to 7 years. Fiber
plant will only need replacement due to age, which can last a generation or more.
While the 550km (320 miles) orbit is relatively close to Earth, the round trip and hops to ground
stations create latency upwards to more that 50ms which does not meet the low latency
required by many applications such as autonomous driving cars and gaming. This is where fiber
and 5G will continue to dominate the use cases.
The outage cause by rain fading and other weather events make it a poor choice for public
safety. On the other hand, the wide coverage to any corner of the globe is the main selling point
for this technology as the last resort communication method for airlines, cruise ships,
expeditions, or war zone.
December 9, 20206
The profitability of LEO remains to be seen. Rural broadband is a benefit of the system but will not
ensure its long-term survival. LEO will likely depend on other applications beyond residential to maintain
profitability, e.g., business, government, or military.
As a last resort technology, LEO offers benefit, but it should not be viewed as the final broadband
solution for rural communities.
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