Unmanned Systems Technology 014 | Quantum Tron | Radio links and telemetry | Unmanned Aerial Vehicles | Protonex fuel cell | Ancillary systems | AUVSI 2017 Show report

33 way locations that do not have wireless infrastructure links. For example, trials in the US are linking satellite services with base stations on the ground to provide connectivity to UAVs in remote areas. What is also becoming an issue is the security of the link. Video feeds from military UAVs are showing up on the internet, and developers are looking at ways to encrypt that data in the craft. This can add power consumption and complexity to the design, although developers are exploring the use of quantum cryptography as a lower-power solution. Types of link Radio connectivity is a combination of the frequency band and the protocol used. Analogue and digital protocols used at frequencies such as 915 MHz have a long range but can’t support data rates much above 1 Mbit/s. The popular 2.4 GHz band meanwhile can support protocols such as wi-fi for payload and Bluetooth for control, and the high volume of chips produced for the mobile phone and home markets makes it cost-effective, but it has a shorter range than the 915 MHz band and is prone to interference. Wi-fi and Bluetooth also include standardised security protocols such as WPA2, although their popularity makes the devices a target for hacking, and there are numerous examples of such links being compromised in different ways. Wi-fi also operates at 5 GHz, giving more potential for high-speed data transmission, and digital short-range control (DSRC) for vehicle-to-vehicle (V2V) comms operates at 5.9 GHz in the US and so can also support higher data rates. There are also ways to use modulation schemes such as quadrature amplitude modulation (QAM) to boost the bandwidth of the radio link, though usually at the expense of higher power consumption and shorter range (as there are more errors). Bit error rate (BER) is the arbiter of range, as the receivers have a limit on how low the BER can be for a given data rate. Cellular modems can also be used to carry payload data such as video. 4G data rates go up to 50 Mbit/s and can potentially carry UHD video, although the latency of 10-50 ms is too long and too variable for control data. Also, if the connection drops it can take a considerable time (up to 1 s) to reconnect. The proposals for next-generation 5G will see the data rates increased to over 100 Mbit/s, with a latency of 1 ms, which is much lower than 4G, but this will require an infrastructure of cell towers. The latency is more important for the control data, as it naturally needs to be delivered quickly. 5G is set to be agreed as a standard in 2018, with early demonstration systems available beforehand, but it is not expected to roll out until 2020 and will only be viable for unmanned systems in the 2020 timeframe as the infrastructure develops. The roll-out of 5G will be focused on urban areas, so it will take many years before the infrastructure is available for UAVs and UGVs operating in rural areas. For those rural applications, L-band satellite links operate at 1.5-2.0 GHz range and the smaller satellite antennas are more suitable. Many UAV systems currently use Bluetooth or wi-fi in the unlicenced Industrial, Scientific and Medical (ISM) band at 2.4 GHz for their connections. The band is quite crowded, however, what with all the home and business wi-fi systems and large number of Bluetooth connections, and is only set to get worse. 802.11n wi-fi can be used in the 5 GHz band for higher data rates, but the leading UAV makers have developed their own radio chips and baseband software, particularly for handling UHD video reliably over distances up to 1 km. The next generation of wi-fi, at 2.4 and 5 GHz, is 802.11ax. This standard is currently in draft form and brings a technique from 4G cellular technology to multiplex more users in the same channel bandwidth: orthogonal frequency-division multiple access. Building on the existing orthogonal frequency-division multiplexing (OFDM) digital modulation scheme that 802.11ac already uses, 802.11ax further assigns specific sets of subcarriers to individual users, opening up the use to swarm applications. The existing 802.11 channels (20, 40, 80 and 160 MHz wide) are each divided into a minimum of 26 smaller sub-channels called resource units. Based on the needs of all the users, a controller decides how to allocate the channel, always assigning all available resource units on the downlink. It may allocate the whole channel to only one user at a time – just as 802.11ac currently does – or it may partition it Radio links and telemetry | Focus Unmanned Systems Technology | June/July 2017 This is said to be the smallest Bluetooth 5 silicon for the next generation of radio links (Courtesy of Hayek/Swatch)