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

36 V2V for UAVs The emerging vehicle-to-everything (V2X) radio technology at 5.9 GHz (using DSRC) will be fitted to millions of self- driving cars by 2020, and that will drive down the price of the transceivers. These radio systems use the IEEE 802.11p standard and are currently on two chips, a radio front end and a digital baseband. They are however being combined in a single chip and designed for economic production in 2020, which will reduce their cost. That will open up the technology for use in other areas such as UAVs. Compared with the wi-fi standard, the hardware layer of 802.11p was significantly simplified to reduce latency as much as possible. As a result, the comms will add only a few milliseconds to the end-to-end (camera-to-display) latency. That will do much to help operators control a UAV more accurately. The 2.4 GHz ISM band for wi-fi has been very popular with UAVs as it provides enough bandwidth for video and a longer range than the 5.8 GHz band. A free-space path loss model used to calculate the link budget shows that 2.4 GHz systems have a 7.7 dB advantage compared with 5.8 GHz systems. This means that with the same transmission power and receiver sensitivity, 2.4 GHz systems can achieve more than double the comms range compared with 5.8 GHz systems. However, with multiple systems all using the same 20 channels, there is a lot of interference, and that reduces the range to around 100 m in practical terms. Because 802.11p was designed for cars, it can handle transmissions from fast-moving vehicles, an area where protocols such as wi-fi can struggle. The current chipsets have been tested to 200 kph, which is more than sufficient for UAV applications. The hardware layer (media access controller, or MAC layer) of IEEE 802.11p uses Enhanced Distributed Channel Access from the IEEE 802.11e standard, which can provide data traffic prioritisation with four different access categories. Assigning flight control messages to the highest priority category avoids any contention with June/July 2017 | Unmanned Systems Technology Focus | Radio links and telemetry V2V radio technology developed for connected cars can be applied to UAVs (Courtesy of NXP Semiconductors) Technology Custom analogue Wi-fi LightBridge Cellular 802.11p (custom digital) Distance <500 m <1 km 4 km Base station coverage 4 km Latency <100 ms 100-200 ms 10 ms >1 s <5 ms Reconnection speed Fast Slow Fast Very slow Fast Velocity tolerance Weak Weak Strong Strong Strong Frequency 915 MHz 2.4/5.0 GHz 2.4 GHz Multi-band 5.8 GHz Cost Low Low High High Medium Types of radio technology used for video transmission (Courtesy NXP Semiconductor)