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As the world national economies become more global and as all parts of the globe, the oceans, and the atmosphere are exploited by human enterprise, the need for effective wireless interconnection via terrestrial wireless and satellite communications will expand.
Satellites play a crucial role to improve lives in today’s digital economy. Nearly every industry relies upon satellite technology in some way — from agriculture to banking to transportation. Satellites help save lives in emergencies and provide critical knowledge about how to better protect the environment.
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Satellite communication refers to any communication link that involves the use of an artificial satellite in its propagation path. Satellite communications play a vital role in modern life. There are over 2000 artificial satellites in use. They can be found in geostationary, Molniya, elliptical, and low Earth orbits and are used for traditional point-to-point communications, mobile applications, and the distribution of TV and radio programs.
Transmissions via satellite communications systems can bypass the existing ground-based infrastructure, which is often limited and unreliable in many parts of the world. They are ideally suited to meet the global communications requirements of military, government and commercial organizations because they provide economical, scalable and highly reliable transmission services that easily reach multiple sites over vast geographic areas.
A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. A satellite consists of the spacecraft bus (which is the primary spacecraft structure containing power, temperature control and directional thrusters) and the communications payload (which receives, amplifies and retransmits the signals over a designated geographic area).
Military and commercial satellite communications is growing exponentially as both government and private satellites increase in volume and use case.
Communication architecture
Satellite communications networks consist of user terminals, satellites and a ground network that provides control and interface functions.
The basic structure of a satellite communication system consists of a space segment that includes the satellite constellation, a ground segment including GW stations and large ground facilities for control, network operations and backhauling, and a user segment with the user terminals deployed on fixed and mobile platforms (e.g. airplanes and ships).
Satellite communications tend to use high frequency signals: Ultra High Frequency (UHF), 300 MHz – 3 GHz and Super High Frequency (SHF), 3 – 30 GHz. Radio signals propagating to and from a satellite in orbit are affected by the environmental conditions along the propagation path. In a vacuum, radio signals propagate at the speed of light, but in the presence of plasma in the ionosphere, the signals are affected by group delay and phase advance and attenuation due to absorption and scintillation. The environment’s effect on the signal is frequency dependent and to a first approximation is proportional to the amount of structure in the plasma present along the propagation path.
The communication topology depends primarily on the target application of the communication system. The two typical topologies are star and mesh. In both cases, the satellite acts as a relay between each node and the hub (backhaul) or between multiple peer nodes, respectively. The point-to-multipoint connectivity as in traditional broadcast services, internet connections via satellite and data collection from the sensors deployed on the earth surface, the star topology is used, where each terminal is connected to the hub via satellite on a single-hop basis. The data collection from the sensors deployed on board of the satellite (e.g. in earth observation applications), can be viewed as a special case of star topology, since the satellite acts both as a relay and as a signal source.
For point-to-point connectivity as in video conferencing, the star topology would imply two-hop transmissions, which might be crucial with respect to the end-to-end latency of packet transmission. Hence, mesh topology is usually preferred, where each peer node can communicate with another peer node via satellite relay. However, this topology may require intelligent routing of data packets by the satellite. In addition, mesh topology has been recently proposed for various LEO and GEO satellite constellations based on optical ISLs in order to ensure a
sufficient connectivity and cooperation between satellites.
Upon being employed as a relay, the satellite can be either transparent or regenerative. Transparent satellites do not perform any signal processing besides amplification, spatial filtering and frequency conversion. Hence, the functionality of the satellite resembles an amplify-and-forward relay structure from traditional wireless communications. In contrast, regenerative satellites perform additional signal processing, e.g. decoding, interference cancellation, signal regeneration, etc., similar to decode-and-forward relaying. The payload of the satellite is designed accordingly.
Satellite communication technology trends
The increase in small satellites, the use of high-throughput satellites and low-Earth orbiting (LEO) satellites, launches on reusable rocket launch vehicles, satellites with all-electric propulsion and new use cases for 5G and the Internet of Things (IoT) are some of the are among the game-changing innovations enabling a range of solutions from digital financial services to better health care to smarter cities.
Explosion of Smallsats
The satellite industry has seen a major shift from the manufacturing of massive traditional, multi-hundred-million-dollar satellites (>5000 kg) to the generation of several-million dollar smallsats (<500 kg). SmallSats can be constructed and launched less expensively and more quickly than traditional, large, geosynchronous orbit satellites.
The incredibly shrinking satellite has given rise to less expensive rockets designed specifically to launch batches of small satellites. With traditional satellites taking a decade and hundreds of millions of dollars to develop and deliver into service, next-generation small satellites are delivered at 1/10th the time, and 1/100th the cost. SpaceX has been phenomenally successful in reducing launch costs to less than US$1,000/kg.
In addition constellation of smallsats address one of the most significant limitations of geosynchronous systems: high latency. Multiple companies, such as SpaceX, Amazon, OneWeb, TeleSAT, have already announced large LEO plans including thousands of satellites that will enable them to provide low-latency broadband with pervasive connectivity. OneWeb plans to launch at least 900 satellites, with broadband access while SpaceX, with its Starlink constellation comprised of nearly 12,000 satellites.
Launch vehicle innovations, such as SpaceX’s reusable rocket system Falcon 9, have reignited interest in LEO. Iridium is now in the process of rolling out its broadband Iridium Next constellation, using SpaceX as a launch provider. The potential for reusable rocket launch vehicles is a key driving factor in SmallSat growth; the small payload means that a launch vehicle can deliver them in large quantities. Moreover, satellites from more than one company can hitch a ride on a single launch.
The small satellite industry has also caught the attention of the Pentagon and intelligence agencies that want to deploy swarms of small satellites, able to launch quickly and easily replaced carrying out surveillance of adversary activities such as missile launches.
Geostationary (GEO) satellites evolving to High Throughput Satellite (HTS) systems
Traditionally, Geostationary (GEO) satellites have been mainly used for SatComs since they avoid fast movement between the terminals and the satellite transceiver and they allow for wide coverage using a single satellite.
Today, a single 28 GHz band satellite can serve 1/3 of the Earth. The wide coverage provides all communities within a satellite’s footprint access to service. Coupled with easy-to-deploy user terminals, this means that consumers and businesses have near-instant access to fast, affordable broadband, anywhere. People can stream their favorite videos at home, walking around town, and even on an airplane. 28 GHz satellite-powered Wi-Fi now connects millions living in urban and rural centers and villages — many for the first time.
Recent years have also seen several advances in satellite systems and networks, allowing better efficiency, reliability, increased data rates, and new applications. Multibeam satellite systems have been specifically developed to allow efficient frequency reuse and high-throughput broadband rates across the coverage area, not unlike their terrestrial cellular counterparts.
Satellite broadcasting via geostationary satellites will remain in widespread use. It will be a main source of revenue for satellite operators for the foreseeable future. But technology evolution in the coming years will also offer the possibility of new services via “very high throughput satellites (VHTS)” and “multispot” geostationary satellites, says ITU.
However, new more ambitious constellation types are currently being developed, motivated by advanced communication technologies and cheaper launch costs. In this direction, there has recently been a tremendous interest in developing large Low Earth Orbit (LEO) constellations that can deliver high-throughput broadband services with low latency. By 2020-2025 there will be more than 100 High Throughput Satellite (HTS) systems using Geostationary (GEO) orbits but also mega-constellations of Low Earth Orbit (LEO) satellites, delivering Terabit per second (Tbps) of capacity across the world.
High-throughput (HTS) Satellites
The global demand for broadband communications continues unabated, and is not location specific. Such demand includes requirements of connectivity for users on aircraft, ships and vehicles (including first responders) that operate at both fixed locations and while in motion. These three different platforms need continuous connectivity along their travel routes, which often take them through unserved parts of major metropolitan areas, as well as less-densely populated areas.
The Broadband Global Area Network (BGAN) constellation of satellites (in L-band) offer seamless global mobile coverage, connecting people and machines in remote locations on land, at sea and in the air — enabling the Internet of Things (IoT), voice calls and Internet access.
Today’s 30/20 GHz geostationary orbit (GSO) fixed-satellite service (FSS) networks provide affordable and reliable connectivity that meet the broadband connectivity requirements of passengers and crew on aircraft, vehicles, and ships, including high-throughput (HTS) applications.
High-throughput satellite (HTS) systems represent a new generation of satellite communications systems, capable of delivering vast throughput compared to conventional fixed, broadcast and mobile satellite services (FSS, BSS, and MSS), as well as utilizing frequency reuse and multiple spot beams to reduce costs. HTS provides at least twice, though usually by a factor of 20 or more, the total throughput of a classic FSS satellite for the same amount of allocated orbital spectrum thus significantly reducing cost-per-bit. This further precipitates the need for highly efficient transmitters with solid-state power amplifiers (SSPA), highly sensitive receivers, and reconfigurable phased array antennas for flexibility.
Very Low Earth Orbit
VLEO platforms operate closer to the Earth than LEO satellites. This allows them to be simpler, smaller, and thus, cheaper. However, such low altitudes contain a denser part of the atmosphere, and therefore, larger aerodynamic forces. This can be seen as a challenge, but they can also represent an opportunity for orbit and attitude control. Moreover, the increased drag represents a shortening of the orbital lifetime, but this also means a more frequent fleet replacement of smaller and cheaper spacecrafts, thus, becoming more responsive to technology and market changes. Several private companies such as SpaceX, OneWeb or Telesat are planning to launch their Mobile Satellite Services (MSS) at VLEO.
Hybrid Constellations
In addition, there will be new non-geostationary satellites, low earth orbit (LEO) and medium Earth orbit (MEO), of different sizes and capabilities.
There is also interest in Medium Earth Orbit (MEO) where a constellation of 20 satellites (O3B) has been placed in a circular orbit along the equator at an altitude of 8063 km. Each satellite is equipped with twelve mechanically steerable antennas to allow tracking and handover of terminals. The next generation of O3B satellites is planned to use an active antenna that can generate thousands of beams along with an onboard digital transparent processor. This constellation type is unique since it manages to hit a trade-off between constellation size and latency.
Each of these orbits brings its own unique benefits such as lower latency, better performance, the ability to offer mobile connectivity, increased throughput or lower cost per bit. Finally, the proliferation of new constellation types has given rise to hybrid constellations which combine assets in different orbits.
One such example is the combination of MEO and GEO connectivity, where the terminals can seamlessly hand over between the two orbits. Another example is the backhauling of LEO satellite data through higher-orbit satellites.
Intersatellite Links (ISL)
In order to enhance the performance of satellite constellations, ISLs can be created, such that multiple satellites can cooperatively accomplish complicated missions. Correspondingly, the complexity of each satellite is reduced. Furthermore, ISLs can be employed for data offloading.
The link can be established between multiple satellites of the same orbit (e.g. LEO-LEO) as well as between satellites of different orbits (e.g. GEO-LEO). A typical example for the latter is the use of GEO satellites as relays for the links between LEO satellites and GWs. This technique is employed by specifically designed GEO satellite constellations, such as European Data Relay System (EDRS) or Tracking and Data Relay Satellite System (TDRSS) in order to improve the connectivity and coverage. Both systems are intended to provide the requested on-demand services in nearly realtime, especially for emergency applications.
On-board Capabilities
Traditionally, the onboard processing capabilities have been the limiting factor for advanced SatCom strategies. Firstly, the majority of satellites operate as a relay whose frequency converts, amplifies, and forwards, and thus the onboard processing has to be waveform agnostic. Secondly, there is usually a large path loss to combat and a limited power supply which is tightly correlated with the satellite mass and launch cost. Thirdly, employed on-board components and technologies have to be ultra-reliable and robust since there is very little chance of repairing/replacing after the asset is put in orbit.
Recent advances in the efficiency of power generation and the energy efficiency of radio frequency and digital processing components have allowed for enhanced on-board processing which can enable innovative communication technologies, such as flexible routing/channelization, beamforming, free-space optics, and even signal regeneration. Furthermore, space-hardened software-defined radios can enable onboard waveform-specific processing which can be upgraded during the satellite’s lifetime.
Flexible payloads and Software-defined satellites
One of the concepts that are revolutionizing the infrastructure of current communication systems
is the so-called SDR technology. SDR refers to a radio communication system where the major part of its functionality is implemented by means of software. The main advantage of SDR is the capacity of adaptation which has been identified as a crucial characteristic of future broadband satellite systems. By replacing as much hardware with software, the satellite payload becomes much more flexible and allows to deliver of cost-competitive connectivity in response to evolving consumer demand and price expectations.
Software defined payloads are less dependent on hardware and becomes more flexible and automatically reactive, able to face the dynamicity envisaged in the forthcoming wireless
traffic. The ability to reprogram beam pattern, frequency and power allocation dynamically in at anytime during the satellite mission, makes SDR technology very attractive in the forthcoming day where the data markets are more uncertain.
Current communications satellites generally have over a 15 year mission lifetime, in that time several scenarios can occur that require an adjustment in the operational requirements of the payload including changing business and political landscapes, new technologies and applications. Flexible payloads that can reconfigure its frequencies, coverage, and power allocation pose a solution to the rapidly evolving business, political, and technological environment.
Reduced costs can be achieved by producing generic software-defined satellites that can be manufactured at scale and then configured once in space for specific service offerings. Software-defined satellites bring the capability to reconfigure the shape of the beam, capacity or power in real time.
Where conventional satellites were earlier tailored to comply with single mission requirements, satellite developers are gradually adapting the vision of software-defined satellite which can be reprogrammed and reconfigured, to allow a satellite to take up new applications and expand its performance. Instead of viewing a satellite as monolithic piece of hardware and software, designed to perform a specific mission, one can see the same satellite as a platform capable of running multiple different missions (defined as software applications) on the same hardware platform. Three capabilities are necessary for a reduced cost-per-bit: Flexible coverage; Flexible power allocation to beams; Flexible spectrum allocation to beams.
This definition follows the same approach as other “software-defined” entities, such as “software-defined radio” transceivers that can be reconfigured for a variety of RF tasks or “software-defined networking” appliances that can support a wide range of telecommunications applications. In many ways today’s satellites are digital processors in the sky and specialized software defines how they perform and defines their communications capabilities.
The new on-board processing capabilities combined with the emerging role of active antenna systems require advanced resource management techniques capable of maximizing the satellite
resource utilization while maintaining QoS guarantees, and dynamically matching the distribution of the satellite capacity on the ground to the geographic distribution of the traffic demand and following its variations in time. SDR-based satellite systems bring important improvements from a network management point of view, by allowing a better orchestration of the satellite resources
There are remarkable new technologies still to be developed in terms of space-based satellite communications systems, more powerful processors, new encoding capabilities, and new user terminal capabilities that can make user systems more mobile, more versatile, more personally responsive, more powerful in terms of performance, and yet lower in cost (Pelton 2005; Iida et al. 2003).
Complement 5G
The 5G network is referred to as the 5th generation of wireless global mobile networks after 1G, 2G, 3G, and 4G networks. 5G helps in enabling a network that has the capability of connecting virtually everything and everyone together, such as devices, objects, and machines. This technology is designed to provide higher data speed, huge network capacity, more reliability, and a better user experience.
In the future, 5G networks will represent the global telecommunication infrastructure of the digital economy, which should cover the whole world including inaccessible areas not covered by 5G terrestrial networks. However, there are several use cases where standard terrestrial coverage is either not present or possible, making satellite systems uniquely positioned to provide a solution to bridge this gap.
Satellite communication plays a significant role in overcoming these challenges and helps with the better extension of 5G networks to rural areas, including boats, trains, airplanes, and other such vehicles. Satellite communication will play a significant role in 5G and beyond as a complementary solution for ubiquitous coverage, broadcast/multicast provision, aeronautical & maritime communications, emergency/disaster recovery, and remote rural area coverage.
Moreover, recent advancements, such as the new generation of the low Earth orbit (LEO) in the ecosystem of satellite communications, are helping in overcoming the previous limitations such as latency in communications. Furthermore from a deployment point-of-view, the cost can be largely decreased by using 5G chipsets/systems and tapping into economies of a larger scale.
Non-Terrestrial Networks (NTN) is a term coined under 5G standardization to designate communication systems that include satellites, Unmanned Aerial Systems (UAVs) or High Altitude Platforms (HAPs). The main objective of this initiative is to seamlessly integrate these assets into the 5G systems by studying their peculiarities in terms of architecture and air interface.
Three major groups of use cases for NTN 5G systems have been defined by the 3GPP. Firstly, NTN can significantly enhance the 5G network reliability by ensuring service continuity, in cases where it cannot be offered by a single or a combination of terrestrial networks. This is especially true in case of moving platforms (e.g. car, train, airplane etc.) and mission-critical communications. Secondly, NTN can guarantee the 5G service ubiquity in un-served (e.g. desert, oceans, forest etc.) or underserved areas (e.g. urban areas), where a terrestrial network does not exist or it is too impractical/cost-ineffective to reach.
With the availability of high-throughput, high-capacity broadband geostationary satellite orbit (GSO) networks, such as the Hughes JUPITER System, and pending deployment of mega-constellations of non-geostationary satellite orbit (NGSO) systems, it is clear that the benefits of 5G can reach parts of the globe where terrestrial 5G networks may never be available. The demand for more bandwidth will only increase with Multiple Radio Access Technology (Multi-RAT) planning for 5G that will rely on various heterogeneous networks for over 99% availability such as WiGig, 4G, 100G Ethernet, and satellite networks.
Last but not least, NTN can enable the 5G service scalability due to the efficiency of the satellites in multicasting or broadcasting over a very wide area. This can be extremely useful to offload the terrestrial network, by broadcasting popular content to the edge of the network or directly to the users
The value of the global 5G satellite communications market was at $2,708.3 million in 2021 and is expected to touch $43,215.4 million by 2032 with a growth rate of 28.12% during the period of 2022-2032, according to the report by BIS Research.
Very High throughput satellites (V/HTS), with spot beams, can provide more than 100 Gbits/ sec
VHTS (Very High Throughput Satellite) systems utilizing spot beams in order to provide broadband services to end-users with bit rates in excess of Terabit/s. They are ideally suited to support 5G as they provide more flexibility than HTS and are capable of being able to better match traffic distributions, accommodate more demand per beam and support dynamic service delivery. Very High throughput satellites (V/HTS), with their multiple spot-beams, are key for delivering the future rate demands.
Expanding Satellite IoT Market
The Internet of Things (IoT) is a system of interrelated computing devices, mechanical and digital machines, objects, animals or people that are provided with unique identifiers (UIDs) and the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction.
Satellite technology has the potential to be a strong player in Internet of Things (IoT) connectivity, along with “connecting the unconnected” in parts of the world where alternative communication paths, at present, simply do not exist. Satellites will cover large geographic areas, and so can be accessed from both rural and urban locations. Satellites are essential part of building the framework for a global IoT infrastructure.
New Space has inspired new opportunities in terms of collecting data from ground sensors directly via satellites, i.e. Satellite Internet of Things. In this direction, a wealth of data collection constellations have made it into orbit, spanning a wide range of services e.g. earth observation, radio frequency (RF) monitoring, asset tracking, sensor data collection etc.
Currently, tens of private companies are building demonstrators and competing to launch a viable commercial service. Almost all such ventures rely on low earth orbits and this raises additional communication challenges in efficiently downlinking the collected data back to
the ground for processing. Conventionally, each such venture would require an extensive network of earth stations for high availability. However, cloud-based services (e.g. Amazon Web Services) have rolled out ground station networks that can be shared among the various constellations, while providing easy access to high performance computing for the data processing.
Even though small in nature, the traffic generated by these IoT devices, will have a significant impact on the network load. Therefore, the satellites can help to offload the terrestrial IoT network through backhauling, or provide service continuity in cases where a terrestrial network cannot reach. This group of uses cases can be categorized into two smaller subgroups depending on the type of application that the satellite can support and on how the IoT sensors are distributed on Earth.
Wide area IoT services: This use case has to do with applications based on a group of IoT devices distributed over a wide area and reporting information to or controlled by a central server. Typical applications where the satellite can play a role include:
– Energy: Critical surveillance of oil/gas infrastructures (e.g. pipeline status)
– Transport: Fleet management, asset tracking, digital signage, remote road alerts
– Agriculture: Livestock management, farming
Local area IoT services: The IoT devices in this kind of applications are used to collect local data and report to the central server. Some typical applications can be a smart grid sub-system (advanced metering) or services to on-board moving platforms (e.g. container on board a
vessel, a truck or a train).
Satellite terminals
Advances in satellite manufacturing and directional earth-station technology, particularly the development of multi-axis stabilized earth-station antennas capable of maintaining a high degree of pointing accuracy, while stationary or on rapidly moving platforms, have made earth stations with very stable pointing characteristics both available and practical.
These earth stations can operate in the same interference environment, and comply with the same regulatory and technical constraints as typical GSO FSS earth stations, says ITU. Satellite network operators are designing, coordinating, and bringing into use GSO FSS networks that can offer broadband services to both stationary and moving earth stations using a single stabilized directional antenna within existing GSO FSS technical parameters.
Cybersecurity
The issue of cybersecurity has been highlighted as a critical feature of business communications.
LeoSat was established to deliver a viable satellite solution for enterprise data. To support the developing digital ecosystem, we plan to launch a constellation of up to 108 lowEarth-orbit, laser-connected satellites to provide the fastest, most secure, and the widest coverage international and intercontinental carrier-class, data network in the world, says Diederik Kelder Chief Strategy Officer, LeoSat.
The LeoSat constellation is designed with absolute security and resiliency in mind. Data will travel end-to-end across a single network. This physically separated network ensures security on the lowest networking level, additionally, the multi-satellite constellation provides inherent redundancy, should issues arise with a single satellite. At any one time, there are always 2–7 satellites in view, depending on the latitude of operation.
Regardless of technical or weather issues there are alternatives to route traffic. This underlines the myriad of safety options and high availability capabilities that the LeoSat constellation has inherently built in to ensure network resilience.
Overall, there is likely to be major competition for services. Market forces will bring service costs down. Furthermore, future user terminals will achieve a larger degree of flexibility and lower costs. Finally, cheap launching costs and conveyor-belt manufacturing allow for deploying more risky/innovative approaches while keeping up with the latest evolutions in communication technology.
Machine Learning Applications
Machine Learning (ML) techniques in the literature can be broadly categorized into supervised, unsupervised and Reinforcement Learning (RL). Out of these, supervised learning requires the labelled training data-set while the unsupervised learning does not require the labelled data-sets. In contrast to these approaches which require training data-sets, the RL does not need a training data-set and enables a learning agent to learn from the prior experience.
The ML/AI techniques can find potential applications in addressing various issues in satellite
communications including interference mitigation to enable the coexistence of satellite systems with terrestrial systems, optimization of radio resources (spectrum, power),optimization of SatCom network operation, and management of large satellite constellations.
Some promising use-cases to investigate the applications of ML techniques include: (i) adaptive
allocation of carrier/power for the hybrid satellite-terrestrial scenarios, (ii) adaptive beamforming to enhance the performance of multibeam satellites with non-uniform demand, (iii) scheduling and precoding to mitigate interference in multibeam satellites, (iv) beamhopping and resource scheduling in multi-beam satellite systems with heterogeneous traffic demand per beam, and (v) detection of spectrum events in spectrum monitoring applications
References and Resources also include:
https://arxiv.org/pdf/2002.08811.pdf
