37 of the radio link and any environmental interference, as well as the signal-tonoise ratio (SNR). Many MANETs are self-forming and self-healing. If any nodes in the MANET become unavailable for any reason, the algorithm running on the remaining nodes will reroute traffic seamlessly via the most efficient path. A MANET differs from the more static mesh network, which is more reliant on a fixed infrastructure. Typically, a mesh network has one node designated as the ‘Master Node’ to maintain the entire system. This Master Node distributes the network addresses to all other nodes in the network and monitors the flow of traffic to decide on the most efficient route. The whole mesh network is dependent on this Master Node. This creates a single point of failure, however, and restricts the flexibility of the system in the air if one UAV has to act as the master. In contrast, a MANET is entirely dynamic and uses an adaptive routing approach. There is no Master Node to manage the network. All of the nodes in a MANET collaborate collectively to route traffic and maintain a robust link, making it more resilient than a mesh network and less prone to failure. MANETs have been developed that can operate on 3 x 3 multiple-input multiple-output (MIMO) antennas for high-performance data rates for aerial systems, delivering over 120 Mbps. The MIMO antennas allow three different signals to be received at the same time, with algorithms to cancel out any differences in timing or reflections of radio waves that can reduce the efficiency of a link. However, the development of lightweight MIMO antennas for UAVs and HAPS platforms is a key challenge, and this is discussed below. A MANET typically operates at the OSI Layer 2 level, the same layer as a network switch, with the ability for each node, or UAV, to optimally configure its transmission parameters. This provides the user with a ‘transparent network’. The IP address scheme of the MANET doesn’t have to be the same as that of the devices connected to it, providing an almost plug-and-play network. This simplifies the process of adding UAVs to a swarm in the air, supporting multicast traffic where data is sent to all the nodes in the network. There is no limit to the number of nodes in a MANET. During real-world testing of a MANET radio in 2018, a flat network of 320 MANET nodes was successfully evaluated, with plenty of overhead for further expansion. However, the practical size of the network depends on the data being transferred and the range. MANET radio transceivers have been designed into a number of current UAV systems. These devices replace separate, specialised equipment and reduce size, weight, power consumption and cost, enabling increased flight time and releasing valuable payload to embed other sensors. Each system installed with an embedded module extends the MANET’s capability, allowing users to access services such as video or data on any node. One embedded module uses a built-in Android system that enables the direct installation of applications on to the radio, turning a single radio into a pilot system that is able to fly or drive multiple uncrewed systems. This allows a group of UAVs to operate, communicate and swarm on a common network. MIMO Another technique employed in MIMO technology is space-time block coding (STBC). Space-time block coding, which works in conjunction with spatial multiplexing, is a MIMO technique used to transmit multiple copies of the same data across the three antennas and exploit the various received versions to improve the reliability of data transfer. Every time a radio frequency (RF) signal encounters a building, wall or other obstacle, it basically inverts and fades. These constant reflections and refractions of the RF signal are a form of interference, and each reflection reduces its overall clarity. Radio and telemetry | Focus An ad-hoc MANET network (Image courtesy of Steatite Communications ) Uncrewed Systems Technology | February/March 2024
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