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Internet access has historically been terrestrial or based on networks, such as fiber or other data cabling that is based on the ground. Cellular data is another common method of providing internet access. Satellite Internet access is Internet access provided through communication satellites. Satellite connections are often employed in remote areas that are not serviced by terrestrial networks or cellular data. They also can be effective backup systems for critical business and government services.
Satellite Internet generally relies on three primary components: a satellite – historically in geostationary orbit (or GEO) but now increasingly in Low Earth orbit (LEO) or Medium Earth orbit MEO). Modern consumer-grade satellite Internet service is typically provided to individual users through geostationary satellites that can offer relatively high data speeds, with newer satellites using Ku band to achieve downstream data speeds up to 506 Mbit/s. In addition, new satellite internet constellations are being developed in low-earth orbit to enable low-latency internet access from space.
The second is the user terminal to serve each subscriber— the antenna on a home, business, ship, plane, or other location and transceiver.
The third is the ground network, a collection of earth stations connected to the internet by fiber optic cable. These ground stations are known as gateways that relay Internet data to and from the satellite via radio waves (microwave). Another component of a satellite Internet system is a centralized network operations center (NOC) for monitoring the entire system.
Satellite Gateway
The system of gateways comprising the satellite ground system provides all network services for satellite and corresponding terrestrial connectivity. Each gateway provides a multiservice access network for subscriber terminal connections to the Internet.
A satellite gateway also referred to as a teleport or hub, is a ground station that interfaces one side with the fleet of satellites orbiting Earth and the other side with a national fiber network or LAN (Local Area Network). It houses the large antennas and equipment that convert the Radio Frequency (RF) signal to an Internet Protocol (IP) signal for terrestrial connectivity and vice versa as per terrestrial connections. IP refers to Internet Protocols used for internet access and for data transfer. Voice information can also be carried using Voice over IP protocol.
Working in concert with a broadband gateway, the satellite operates a Star network topology where all network communication passes through the network’s hub processor, which is at the centre of the star. With this configuration, the number of ground stations that can be connected to the hub is virtually limitless.
Traditionally, gateway antennas are quite large — 7 meters or more in diameter. They’re often accompanied by a secure, air-conditioned room or shelter full of servers and other electronics, power supplies, a backup generator and other infrastructure.
One big reason many satellite networks have such large antennas on the ground is to accommodate high-powered signals able to cut through weather. Rain and clouds can hamper performance, and when you only have a small number of gateways, you want to ensure they’re all working at optimum performance levels.
Gateway Installation
The gateway antennas for a geostationary satellites can stay pointed at a fixed position. The satellite gateway is installed with a clear line of sight with the satellite from the ground. It is the only system that interfaces satellite from the earth for various services viz. voice, data and video over IP. In the continental United States, because it is north of the equator, all gateway and subscriber dish antenna must have an unobstructed view of the southern sky.
It has to be maintained for years to provide support to long life of the satellites which is about 15 to 25 years. There should be sufficient place near the antenna of the satellite gateway to house indoor equipments for future expansion as well as to counter severe weather conditions. In order to avoid other regulatory issues, the land where satellite gateway has to be installed should be owned by the gateway operator in that region.
Gateway preferences for the current generation of satellites.
- Sufficient and good quality electrical supply.
- Mild temperatures with a very dry climate (minimal rain and no snow).
- No obstructions, such as buildings or mountains, blocking any views to satellites.
- Access to national fiber from a variety of Tier-1 providers such as AT&T, Verizon, Level 3, etc.
- Proximity to a talented technical labor pool, such as a major university or other tech employers.
- Ample land to install as many antennas as necessary in the future.
- The absence of common natural disasters such as floods, fires, tornadoes, tsunamis, hurricanes, typhoons or earthquakes.
- Free from civil unrest or war zones that could impact gateway sites.
While a certain minimum amount of latency is unavoidable with satellite internet, poorly designing and placing of gateways can increase delays and make the network run sub-optimally.
Redundancy
Geographic redundancy is important to ensure high availability of business-critical systems across multiple locations, mitigating the risk of environmental outages. Since satellite internet outages result most often from weather-related events, it is crucial for redundancy to be physically remote.
Businesses can mitigate downtime by replicating applications and data across multiple “geo-diverse” locations. Also termed “geo-redundancy,” the data that is created or updated in a primary location is asynchronously replicated to a secondary location so that the same data exists and is readily accessible in both locations.
Regarding physical location of gateways, they should ideally be geographically separated (California and New Mexico for example), so that should one experience a catastrophic event, the secondary location can quickly and seamlessly take over the primary role. All traffic is automatically rerouted to the secondary site with minimal service downtime for users.
Natural disasters such as hurricanes and earthquakes can have a relatively wide-reaching effect, but few of these events can exceed 500 miles or so, and even these would have to involve a mega-storm or event. Petaluma, California and Las Cruces, New Mexico, are a comfortable 1,200 miles apart. A globally catastrophic event would be required in order to compromise both locations.
When reviewing the list of ideal satellite location characteristics, prognostication about risk is an essential skill.
Below are examples of unanticipated problems to gateway operators in the past:
- Ownership and control over the land was not secure. Upon completion of a lease, the owner chooses not to renew and instead redevelop the land. Often ownership of the land can change with the new owner having different ideas on the most profitable use of property.
- Zoning changes. If a municipality modifies the legal use of a property, it can prevent future development that is needed to reach new spacecraft being launched.
- Neighboring developments can be built (or trees can grow), obstructing line of sight to the satellites.
- Location being so isolated that fiber providers will not upgrade their networks or keep up with regular maintenance. Population clusters can change over time, and network providers roll out fiber in populated areas, with coverage thinning as you travel away from these zones.
- Insufficient room for expansion. Often gateway operators do not leave adequate growing room for expansion, including new antennas and equipment.
Other technologies can help reduce latency that results from the distance between individual gateways and satellites. Through TCP Acceleration and IP Spoofing, latency can be managed so that it minimally impacts user experience.
Gateway trends
Along with dramatic advances in satellite technology over the past decade, ground equipment has similarly evolved, benefiting from higher levels of integration and increasing processing power, expanding both capacity and performance boundaries.
Gateways for LEO satellite Constellations
Using satellite constellations to provide global Internet access services has recently drawn increasing attention. A low-Earth orbit (LEO) satellite network with multiple satellites provides global coverage, low latency, and operates independently, by which it effectively complements terrestrial IP networks.
LEO satellites are in constant motion as they orbit Earth, so an individual satellite can only cover (or capture) small areas of the planet with each pass. So, many LEO constellations will be comprised of dozens, hundreds or thousands of small satellites. Some of the better known and now in-development constellations include SpaceX (4,000 satellites), Boeing (1,300+ satellites), OneWeb (600+ satellites), and LeoSat (100+ satellites).
All new LEO constellations will require gateways for tracking the satellites, downloading data, and sending information back to each satellite. Depending on the frequency, gateway antennas vary in size and complexity. The higher the frequency, the harder it is to position the antenna to track
and communicate with each satellite. Gateway antennas must have absolute pointing accuracy and no backlash. And the larger the constellation, the more terminals or gateways will be needed to maintain frequent communications with each satellite.
New LEO constellations will be heavily populated with satellites (i.e. have high orbit density), and most will require significantly more gateways than GEO constellations. Many gateways are comprised of three antennas: An active antenna, a passive (ready) antenna, and a spare. Some gateways with quick retrace antennas may have one active antenna and a spare. Rarely is a gateway an individual antenna. Because of this, gateways can be a significant investment. Amir Yafe, head of Global Accounts for Gilat Satellite Networks, notes that LEOs will require an “order-of-magnitude increase in the number of gateways and a two-orders-of-magnitude increase in the number of gateway antennas.”
As such, most new LEO constellations are working with Earth station antenna designers to provide smaller and moveable (or relocatable) gateway antennas. Instead of a large 10m antenna, a LEO constellation can easily communicate with a 2m class to 4m class antenna, such as the multi-band transportable antennas , and thus drive down costs. These antennas can be permanently ‘fixed’ to a site, or temporarily anchored at a site as needed, then packed into cases, relocated and temporarily anchored to a new site
Tracking and communicating with LEO satellites is challenging for three reasons. First, LEOs move very quickly and most are only visible for 20 to 30 minutes during each pass. This requires an antenna that can acquire the signal, track the satellite’s path, and upload or download as much
data as possible in this short amount of time.
Traditionally, satellites have been accessed and tracked via parabolic-dish antennas. This equipment is poorly suited to LEO constellations, which will have numerous satellites all rapidly crossing a ground receiver’s field of view at the same time.
Second, with so many satellites flying within each constellation, antennas must be able to communicate through handoffs from one satellite to the next to the next. Conventional antennas may require tens of seconds to locate and track a follow-on LEO satellite. This type of communications outage, though brief and predictable, is undesirable for data communications, and in many circumstances, such as voice or video communications, unacceptable.
Third, the high duty cycle (constant movement and continual use) requires antennas
that are rugged and high-performing. The excessive wear and tear that comes from continual movement, as compared to a stationary GEO application, creates a different set of
performance criteria for LEO and MEO ground stations.
X/Y antennas are the most widely used and most efficient mechanically steered antennas for tracking LEO satellites. X/Y antennas range in size from a small fixed or transportable 1.2m aperture to a much larger fixed 12m aperture. An X/Y design places the X or elevation positioner parallel to the ground. The Y positioner is placed in a vertical plane above and perpendicular to the X positioner, and its rotation ranges from horizontal to vertical depending on the rotation of the elevation positioner. This design, though simple, pushes keyholes (areas of data loss) out to the horizons and provides full hemispheric coverage. To track LEO satellites, X/Y antennas need to move quickly at a typical speed of three degrees per second, and even quicker to track a new satellite once the current satellite passes beyond the ground station’s field of view.
Antennas with electronically scanned apertures (ESAs), also called electronically steerable antennas, can shift beams (and track and access large numbers of satellites) without physical movement. ESAs can also be designed for modular assembly, which could allow manufacturers to produce large numbers of basic parts for use in both constellation ground stations and consumer equipment, thereby improving economies of scale. Other important advances in ground equipment include new predictive analytics and network-optimization techniques that use available ground-entry points more effectively.
One trend is relocating many of the processor functions to a nearby data center — essentially a private cloud. Rather than having banks of servers at the gateway, most of that is virtualized using open computer platforms. That eliminates a lot of the space required for the servers and all the infrastructure needed to power and cool them, as well as backup generators and redundant fiber lines. By driving down the cost of the ground system while improving it at the same time, better service can be provided and increase capacity over the network
References and Resources also include:
https://x2n.com/blog/satellite-internet-gateway-location-whitepaper/
http://interactive.satellitetoday.com/leo-advances-on-the-ground/
