NEWS

4 May 2021

Satellite communications: what’s the difference between LEO, MEO and GSO?

Satellite communications: what’s the difference between LEO, MEO and GSO?

We’ve been talking a lot about terrestrial communications technology recently. However, that’s not the only kind of communications technology we work with at Darwin. Today, we’re discussing different types of satellite orbit.

We’ve been talking a lot about terrestrial communications technology recently. For example, take a look at our articles on the history of mobile technology, or on the applications of 5G. However, that’s not the only kind of communications technology we work with at Darwin. We’re enabling seamless, reliable connectivity by harnessing transmitters both on Earth and in space. Today, we’re discussing different types of satellite orbit. How do satellites get into orbit? Satellites are taken into space by rockets and released at high speed, travelling over the Earth at thousands of kilometres per hour. The pull of Earth’s gravity prevents the satellite from flying off into space, but the speed of the satellite prevents it from being pulled down to the surface, as the curvature of the Earth means the ground is always falling away. This combination means that the satellite falls into orbit, looping constantly around the planet. What does LEO stand for? LEO stands for ‘low Earth orbit’. LEO satellites orbit the Earth between 160 km and 1,000 km above the planet’s surface, or between 160 km and 2,000 km according to some definitions. The pull of Earth’s gravity becomes stronger as you approach the planet. Because of this, LEO satellites, being relatively close to Earth, need to move very, very fast to counteract gravity. For example, the International Space Station (ISS), at the relatively low altitude of 400 km, is moving at roughly 27,600 km per hour and orbits Earth about 16 times per day. Geostationary satellites, at the much higher altitude of 35,786 km, move at less than half that speed: about 11,000 km per hour. What does MEO stand for? MEO stands for ‘medium Earth orbit’, and refers to satellites orbiting the Earth between the LEO and GSO levels. As there’s disagreement over whether LEO ends at 1,000 or 2,000 km, some satellites may be considered to be in either LEO or MEO, depending on the definition used. What does GSO stand for, and what’s the difference between GSO and GEO? You might hear GSO and GEO satellites mentioned in similar contexts. The terms have some overlap, but they’re not identical. GSO stands for ‘geosynchronous orbit’, meaning the satellite’s orbit is synchronised with the rotation of the Earth. In other words, it takes a day for the Earth to complete a revolution, and it also takes a day for a GSO satellite to complete one orbit of the Earth. GEO stands for ‘geostationary equatorial orbit’. This is a type of GSO that follows the equator, travelling in the direction of Earth’s rotation. Satellites in GEO always appear to be in the same place, relative to Earth – so, for example, as the Earth rotates, a GEO satellite above Brazil will keep moving so it constantly remains above Brazil. All GSO satellites (including GEO satellites) are approximately 35,786 km above the Earth’s surface: the only altitude at which geosynchronous orbit can be maintained. Are there HEO satellites? Knowing that low and medium Earth orbit satellites exist, you might expect there to be a high Earth orbit satellite, or HEO. The acronym HEO is sometimes used for satellites, but it doesn’t stand for ‘high Earth orbit’. HEO is short for ‘highly elliptical orbit’, and it refers to orbits where, rather than remaining at approximately the same height above the Earth at all times, the satellite is much closer to the planet at some points in its orbit than at others. Satellites with elliptical orbits spend longer over some parts of the planet than over others, which can be useful for communications. What are the practical differences between LEO, MEO and GSO? The altitude of a satellite can affect a number of things. For example: Cost of launch. Travelling to higher altitudes requires more powerful, more expensive rockets and larger quantities of fuel, meaning that low-altitude satellites are less expensive to launch. This can pay off multiple times; for example, the low orbit of the ISS makes it less expensive to send up supply craft. Cost of satellite. Low-altitude satellites can be smaller and less powerful – and therefore less expensive – because they don’t have to transmit signals as far as high-altitude satellites. Function. Some orbits are more useful for particular purposes than others. For example, satellites designed to observe or photograph Earth are often in relatively low orbits. Ability to provide consistent or widespread coverage. Because they have to move so quickly, a single LEO communications satellite won’t stay over any one location for long, meaning that you’ll need a lot of them to provide reliable coverage to that location. GEO satellites will stay in position, and their high altitude means that they can cover a large area, but they can only be positioned above the equator. The further from the equator you are, the less useful GEO satellites become. Latency. Signals have further to travel to and from high-altitude satellites, which means that a person connecting to a satellite may notice slightly longer delays in retrieving information from satellites at higher altitudes. Speed of orbital decay. Satellites in low orbit can encounter atmospheric drag, slowing them down and allowing gravity to draw them closer to the Earth. The lower they are, the greater the drag, and the faster their orbit decays. This means that LEO satellites often need to be either reboosted, using their own engines or another spacecraft to restore speed and altitude, or replaced. Either option is expensive. In 2010, the Ad Astra Rocket Company estimated the annual cost of keeping the ISS in a stable orbit, which requires multiple reboosts per year, at $210 million. Maximum number of satellites possible. GEO satellites have a natural limit on how many can exist at a time, as they’re at a specific height (35,786 km) and need to travel a specific route (the equator). In his 2000 paper ‘A Lost Connection’, published in the Berkeley Technology Law Journal, Lawrence D Roberts estimates that the equator can only hold up to 1,800 GEO satellites, and that many of the potential satellite positions wouldn’t be useful. At the moment, there are over 500 active GEO satellites. According to the UCS, there are currently over 3,000 operational satellites in our skies. We’ve come a long way since the Soviet Union launched the first manmade satellite, Sputnik 1, in 1957. In a future post, we’ll look in more detail at what those satellites are actually used for.
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29 April 2021

Darwin Advent Challenge trees planted

Darwin Advent Challenge trees planted

In December, the Darwin team completed the Darwin Advent Wellbeing Challenge: we managed to walk a total of one million steps over the Advent period. We planned to celebrate our success by planting a tree at Harwell campus for each day of the challenge.

The planting itself was slightly delayed by frost. On Tuesday 27 April, though, we were able to plant our wellbeing challenge trees!

In December, the Darwin team completed the Darwin Advent Wellbeing Challenge: we managed to walk a total of one million steps over the Advent period. We planned to celebrate our success by planting a tree at Harwell campus for each day of the challenge. The planting itself was slightly delayed by frost. On Tuesday 27 April, though, we were able to plant our wellbeing challenge trees! A small group of Darwin employees went to the campus to help. Aided by Harwell’s STFC and gardening teams, Daniela, Ram, Soheyl, Richard and Rodrigo worked together to get the trees into the soil. It’s particularly appropriate that Ram was involved in commemorating Darwin’s achievement, as he was one of our most enthusiastic walkers! In the end, we planted 25 trees, rather than the originally planned 24. Most of Harwell’s new trees line roads on the campus, with three planted near the Darwin SatCom Lab. Three of the trees are mature Chinese red birches, and the others are young trees: a mixture of crab apple, whitebeam, hawthorn, maple, rowan, sweetgum and silver birch. We’re looking forward to watching them grow. Hopefully, Darwin’s contribution will be visible at Harwell for many years to come. If you’re interested in learning more about Darwin and sustainability, our green strategy document outlines some of the work we’re doing in this area. You can see some more shots from the day below. Many thanks to Daniela Petrovic and Sonali Subhedar for contributing their photographs!
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20 April 2021

The possibilities of 5G

The possibilities of 5G

In a recent post, we talked about mobile technology, and about the differences between the different generations. We touched on the fact that 5G technology offers possibilities going far beyond mobile phones. In this post, we’re going to take a closer look at that.

In a recent post, we talked about mobile technology, and about the differences between the different generations. We touched on the fact that 5G technology offers possibilities going far beyond mobile phones. In this post, we’re going to take a closer look at that. 5G and transportation We’re on the verge of exciting developments in the transport industry: self-driving cars, smart roads, immersive in-car entertainment, improvements to safety and reductions to environmental impact. 5G is the technology driving many of these changes. 5G is particularly important for autonomous vehicles, which need to process and transmit large quantities of data, and to be able to communicate with each other in real time. There are some interesting ways 5G-enabled autonomous vehicles might change our roads. For example, you may begin to see vehicles travelling unusually close together. Many of the road rules that currently exist are based on the assumption that a human will be driving. For example, in good conditions, you need to leave a distance of at least two seconds between your car and the car in front, in case the car ahead of you suddenly stops. As a human driver, you need time to notice that the car ahead of you is stopping, time to react to the realisation by braking yourself, and then time for the brakes to stop your car. If an autonomous vehicle can connect to the one in front through 5G, however, it doesn’t need time to notice the vehicle ahead is braking, or to make the decision to brake itself. 5G’s low latency means that information can be sent by one vehicle and received by others in almost the same instant. This lets two or more connected vehicles accelerate or brake simultaneously, with the one in front setting the pace. In other words, with 5G communication, autonomous vehicles can safely take actions that would be risky or impossible for a human driver, freeing up space on the road. There are other ways 5G can benefit drivers. For example, road sensors or cameras could feed information about traffic to 5G-enabled traffic lights. If the traffic lights have real-time information on actual traffic, they can adjust their timings to be as efficient as possible, rather than changing at pre-programmed times. In Pittsburgh, Pennsylvania, Carnegie Mellon University has experimented with smart traffic signals and discovered that they could lead to substantial improvements for both drivers and the environment, reducing the time spent waiting by 40% and projected emissions by 21%. This experiment is from 2012 and therefore predates 5G, but it helps to illustrate how communications technology can be used to transform roads in ways that benefit everyone. Medical uses of 5G technology During the COVID-19 pandemic, many people have discovered the frustrations of a slow internet connection when trying to work remotely, and particularly when making video calls. For remote medical consultations, it’s particularly important to have a connection that can transmit a lot of data very quickly. After all, it’s hard to diagnose a problem through a low-definition video call; the video needs to be high-quality so the consultant can see any visible symptoms clearly. In situations like this, 5G’s large capacity for data transmission can be very valuable. If it’s feasible to have checkups over a video call, this could free up time for overstretched GPs, improve the health of people who don’t live near a surgery and reduce the time vulnerable patients spend in waiting rooms, where they might be exposed to airborne illness. O2 has a video explaining how 5G can be used in ‘smart ambulances’, helping paramedics in the ambulance communicate with medical specialists elsewhere. This reduces strain on hospitals, as in some cases the patient can be treated in the ambulance, and it enables a faster response to medical emergencies, such as strokes. Through projects like this, 5G can be used to save lives. 5G in other industries We’ve only touched on a few examples, to give a general overview of what 5G can be used for, but there are many areas where 5G can offer practical improvements. For example, we talked recently about drone applications. Many of these – filming, aerial photography, mapping, gathering environmental information etc. – involve the transfer of a lot of data, which 5G can facilitate. 5G could also help autonomous delivery drones to communicate, avoid obstructing each other and navigate to their destination. If you’re interested in learning more about the potential of 5G, O2’s Solutions Navigator offers a wide variety of situations where 5G might be useful. In its 2021 report ‘The Impact of 5G on the European Economy’, Accenture predicts huge economic benefits from 5G’s potential to create new industries, improve productivity and enhance products and services: ‘Between 2021 and 2025, 5G will drive up to €2.0 trillion in total new sales across all major industries in the European economy. Over this time period, 5G will create or transform up to 20 million jobs and drive up to €1.0 trillion to GDP.’ As a step forward in mobile technology, 4G opened up the potential for online activities that often needed a faster connection than 3G: video streaming, for example, or playing games. 5G’s potential is very different. Its relatively huge speeds give it many real-world applications, making it a valuable tool for multiple industries. 4G’s domain is the internet, but 5G’s domain is the world. We’ve reached the present, but there’s more to come in this series of articles on connectivity. In the near future, we’ll be talking about the possibilities of 6G, and about satellite technology.
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12 April 2021

Darwin website now available in Spanish

Darwin website now available in Spanish

We are pleased to announce that the Darwin website is now available in Spanish! You can switch languages in the drop-down menu at the top right of each page.

We are pleased to announce that the Darwin website is now available in Spanish! You can access the Spanish version of the site by clicking this link, or by switching languages in the drop-down menu at the top right of each page. Many thanks to Leticia, our translator, for her hard work preparing all the Spanish text. You may notice that a few things are still in English on the Spanish site; for example, the blog posts aren’t yet available in Spanish. These are currently being translated, and we’ll have Spanish versions soon. We’re also opening a Spanish Darwin office in Málaga, which is going to offer exciting new facilities. We’re looking forward to showing you around.
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6 April 2021

What’s the difference between 3G, 4G and 5G?

What’s the difference between 3G, 4G and 5G?

Many of us use 4G or 5G technology on a daily basis: to connect to the internet on our phones, for example. What is this technology, though? How do 3G, 4G and 5G work, and what are the differences between them? We’re going to take a look at those questions here.

Many of us use 4G or 5G technology on a daily basis: to connect to the internet on our phones, for example. What is this technology, though? How do 3G, 4G and 5G work, and what are the differences between them? We’re going to take a look at those questions here. What does the ‘G’ in ‘5G’ stand for? The ‘G’ in terms like 3G, 4G and 5G stands for ‘generation’. So, for example, 5G means ‘fifth generation’. This can feel a bit vague. The fifth generation of what, exactly? The generations refer to mobile telecommunications technology. The ‘mobile’ here means wireless and therefore capable of being moved around, rather than only referring to mobile phones. Mobile phones are the most obvious hardware making use of this technology, of course, so we’ll be talking a lot about them in this post, but it also has many other applications. For example, connected and autonomous vehicles (CAVs) can make use of 5G to communicate with each other. This way, self-driving cars can alert each other to accidents or congestion, letting them change their routes to avoid traffic jams. How does mobile technology work? Terrestrial communication networks, such as 3G, 4G and 5G networks, rely on Earth-based masts to receive and transmit signals. You may have seen a 4G tower, for example. As these are essentially situated on the planet, whether they’re at ground level or at the top of a building, they are terrestrial. In contrast, satellite networks relay signals using satellites in space. Your mobile phone converts information, such as your voice on a call, or your request for a webpage, into radio waves. It sends these radio waves out to be picked up by the nearest mast. The mast processes the information from your phone and transmits it to wherever it needs to go; it connects to the internet on your behalf, say, or transmits a signal to the device you’re trying to contact. This may involve communicating with other masts, if, for example, you’re trying to call someone who’s not within range of the same mast. It then retrieves any response and sends it back to you. The networks created by these connected masts are sometimes called cellular networks, because each mast provides connectivity to a defined area, or ‘cell’. A brief overview of mobile generations As mentioned, the generations are confined to mobile technology. More specifically, they apply to technology relying on cellular networks, so early radio telephones don’t entirely fit in, although you’ll sometimes hear them referred to as 0G. Of course, it’d take a long time to go over every difference between the generations of mobile technology, but we can give a quick overview here. 1G refers to the technology behind the first-generation mobile phones of the 1980s. This wasn’t called 1G at the time; the name came about after 2G was introduced. Unlike the later generations, all of which are digital, 1G devices used analogue radio waves to transmit information. 2G refers to the technology used by the digital mobile phones introduced in the 1990s, which allowed text and picture messages to be sent between phones for the first time. Neil Papworth, an engineer testing the technology, sent the first SMS text message on 3 December 1992. Papworth used a computer, as phones didn’t yet have keyboards, but Richard Jarvis of Vodafone received the message on his mobile phone, an Orbitel 901. It was ‘Merry Christmas’. Although some 2G devices could connect to the internet at slow rates, 3G networks, introduced in 2001, made mobile internet access more widespread and much faster. 3G’s greater data capacity meant it could be used for, for example, video calls or watching relatively low-resolution videos on wireless devices. 4G networks were introduced in 2009, and they’re still widely relied upon, despite the introduction of 5G. 2G and 3G marked substantial changes to what we considered phones to be capable of – 2G made the switch from analogue to digital signals and introduced text messaging; 3G popularised mobile internet use – but the main difference between 3G and 4G was speed. 4G is up to five times faster than 3G, making it far more useful for streaming and playing games: activities that many of us have found very valuable in the past year. Due to its higher speeds, 4G technology contributed hugely to the popularisation of smartphones. 5G: where we are now 5G is the most recent generation, and mobile providers started offering it in 2019. Its data capacity is dramatically higher than 4G, making it much faster and able to accommodate more users at once. However, that high capacity is in part obtained by using high-frequency radio waves. Although they can carry more information, high-frequency signals can’t travel as far as signals at a lower frequency, so more masts are required to provide coverage to the same area. High-frequency signals can also struggle to pass through obstacles, such as walls, meaning gradual investment is necessary to build indoor 5G coverage. The expense and time of establishing complete 5G coverage, both indoors and outdoors, may help to explain why 4G still dominates mobile phone use. Mobile providers such as O2 are still investing in 4G infrastructure to support 4G users, and to make sure 5G devices can still connect to 4G networks when 5G isn’t available. 4G and 5G technologies are expected to coexist for the foreseeable future. So, if 4G is still the dominant mobile technology, why are we so excited about 5G? Well, as we mentioned earlier, this technology isn’t just for mobile phones. 5G’s high data capacity lets buildings, vehicles and robots send large amounts of data to each other almost instantaneously, and that opens up new technological paths to us. We’ll take a look at those new paths in future posts. Over the next few weeks, we’ll be talking about the potential of 5G for smart roads, CAV convoying and medical care, and what we can expect from 6G.
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