The datalink is one of the most essential components of an unmanned aerial system (UAS), providing command and control for the operator as well as allowing the aircraft to send telemetry and payload data back to base. In this article we will look at and compare two communications methodologies that can be used to establish UAV datalinks – the commonly-used RF (radio frequency), and cellular bonding.
Before we continue, a note on terminology – although cellular communications are also carried out via waves in the radio frequency portion of the spectrum, the term “RF” is often used as a shorthand for non-cellular and non-SATCOM communication methods.
RF drone datalinks for commercial systems most commonly fall into certain portions of the spectrum that lie between 433 MHz and 5.8 GHz. Many of these bands are labelled as ISM (industrial, scientific and medical), meaning that they can be used without a separate radio operator license. In general, RF communications have a tradeoff between range and data throughput – low-frequency, long-wavelength signals can travel further but carry less information, and higher frequency, shorter-wavelength signals have a greater data capacity but their propagation distance is much less.
With the advent of 4G and 5G technology, cellular drone communications are beginning to be explored as a potential alternative. To improve further on the capabilities provided by a single link, cellular bonding technology can be incorporated into a drone’s communication system. Cellular bonding combines two or more cellular links, either from the same or different providers, allowing drones to aggregate the capacity of the combined links and to use them for redundancy.
Range considerations and BVLOS
One of the main disadvantages of RF communications is range. RF datalinks require line of sight between the drone and its GCS (ground control station) or controller, meaning that long-range drone operations can be thwarted by factors and obstacles such as buildings, mountains, and the curvature of the Earth. RF range is also dependent on transmission power, and getting the most out of a datalink, especially a high-frequency one, may require a SWaP (size, weight and power) budget that is out of reach for many smaller UAVs.
A cellular connection allows a drone to operate as far away from its control station as required, as long as it is within range of a cell tower belonging to one of its networks. This unlocks truly BVLOS (beyond visual line of sight) applications without the need for a SATCOM terminal, which can often be large and bulky and requires an expensive subscription service to use.
As cellular bonding allows you to install SIM cards from multiple providers, this provides an additional range advantage, as it allows the drone to continue operating over a wide geographical area that may not be served by a single provider.
Spectrum crowding and interference
As the number of wirelessly broadcasting devices continues to increase, spectrum crowding has become an issue, leading to interference as vast numbers of devices all try to use the same frequencies at the same time. This is particularly an issue with the ISM bands, on which many commercial and civilian drones operate.
The vision of future smart cities and connected landscapes includes large numbers of drones and robotic vehicles all operating within a busy urban landscape, and wireless RF systems alone will hit their limit in trying to support this vision. Cellular connections can help solve this problem, and 5G looks particularly promising with its theoretical capacity of a million mobile devices per square kilometre.
Data throughput and latency
Cellular communications can provide faster data speeds and more throughput than RF datalinks, with 5G potentially delivering up to 10 gigabits per second. This makes them ideal for many modern data-intensive streaming drone applications such as ultra-high definition video and the transfer of massive amounts of mapping data. Cellular bonding is particularly advantageous, as it can aggregate the capacity of all connected datalinks, providing more bandwidth for data transfer.
5G also provides latency of as little as 1 millisecond. Rapid response times on this level could be a game-changer for autonomous BVLOS drones, which require features such as hazard recognition and collision avoidance to be as fast as possible.
Redundancy and resilience
One of the major advantages of cellular bonding is the built-in carrier diversity. Network conditions and coverage may change over time and as you move from area to area, and cellular bonding allows the drone to seamlessly switch between connections when signal strength is diminished or when networks are congested.
Having multiple connections for redundancy is also crucial for BVLOS operations. These operations are highly regulated in the vast majority of countries around the world, and aviation regulators will only approve BVLOS drone flights if constant uptime can be assured. Incorporating a reliable failover mechanism into your BVLOS drone platform is therefore essential to getting it off the ground.
A tried and tested cellular bonding solution for UAVs
Elsight’s Halo connectivity platform is ideal for exploring the potential of cellular bonding technology as an alternative to traditional RF drone datalinks. The low-SWaP solution can be provided in an OEM form factor, enabling deep integration with your drone platform’s RF communications system.
The 5G-capable Halo can aggregate up to four unique cellular datalinks from multiple providers, allowing you to take advantage of the enhanced reliability and redundancy of cellular bonding communications. Halo has also received FCC and CE certifications, allowing it to be freely deployed in the United States and in Europe.
Are cellular drone communications secure?
Cellular technologies such as 4G LTE and 5G do have built-in security measures, and while these are robust, vulnerabilities can occur. To provide an extra level of cybersecurity for sensitive data transmission during drone operations, Elsight’s Halo uses an encrypted VPN tunnel and secure cloud server for all traffic.
What are the different levels of drone autonomy?
The six levels of autonomy framework was originally devised by SAE International in order to categorize self-driving cars, and is often applied to drones and other robotic vehicles. The levels range from Level 0, where the pilot is completely in control all the time and there is no obstacle avoidance capability, through to level 5 where no human intervention or monitoring is required.
What advantages does cellular bonding provide over single-link solutions?
Cellular bonding allows drone datalinks to aggregate the bandwidth of multiple 3G, 4G or 5G connections, providing greater throughput. It also allows automatic failover to another link if one connection is lost, providing a level of redundancy that is essential for safety-critical applications.
To find out more about harnessing the advantages of cellular bonding for BVLOS drones with Halo, please get in touch!