Applying V2X technology to drones
Drone have captured the imagination of the public both for its novelty and the clear potential to simplify and enhance our lives. The drone market is expected to grow in the coming years. The global commercial drone market size was estimated to be USD 552 million in 2014 and is expected to grow at a CAGR of 16.9% over the forecast period.
V2X is a technology that aims to improve traffic safety and efficiency. A typical use case is forward collision warning. When a vehicle emergency brakes, aV2X system receives the car’s messages, issues a warning, preloads the brakes to slow down. This requires the V2X system to provide reliable communication at high travel speed. And to give drivers sufficient response time, it also must be low latency and cover a long range. These are similar to the requirements for Drone communications, making it a promising candidate for technology transfer.
2.Video streaming by IEEE802.11p
In China alone, there were more than 400 drone companies in 2015. In this fast-growing market, it is important for drones to differentiate themselves. To differentiate, DJI has developed a video transmission system Lightbridge that has led to the success of its Phantom series.
2.1 Current technologies for video streaming
We can classify current technologies in the following four categories:
- Analog video transmission
Analog video transmission systems have bigger size and consume more power to reach the same distance compared with digital. Another weakness is its poor resistance to interference. Therefore, analog has been replaced by digital systems in most products. However, its low latency characteristic still makes it popular among drone racers who want real time video displays with zero latency.
After analog systems, Wi-Fi has become the most popular solution. It provides enough data throughput and is offered at a very low price. Nevertheless, Wi-Fi can only reach a few hundred meters under clear channel with line-of-sight communication. Since most Wi-Fi devices are working in 2.4GHz ISM band, which is probably the most crowded band worldwide, the communication range normally drops to less than 100 meters. Other drawbacks include high latency and long reconnection time in cases of signal loss.
- Proprietary solution
To overcome the drawbacks of Wi-Fi, some drone companies have developed proprietary solutions. The Lightbridge from DJI is the most well-known. The newly announced Lightbridge claims to reach 4km (CE power regulation) with good results on communication latency and reconnection speed. However, proprietary solutions also mean high costs. Companies must absorb all development cost themselves.
Intel and AT&T started testing drones with LTE embedded. Convenience is the selling point, since video is directly uploaded to the cloud, but it is certainly not a mainstream solution. The first issue is the cost as LTE modems are relatively expensive. The recurring cost for using LTE network are also a hurdle. Other drawbacks include high latency and limited flying areas due to LTE network coverage.
2.2 Benefits to implement video transmission by IEEE802.11p
V2X is based on the IEEE802.11p, which is an amendment of the IEEE802.11 standard for vehicle environment. It supports data rate from 3Mbps to 27Mbps which is sufficient for HD video. The licensed band to V2X is 5.9GHz band in both EU and US. However, many V2X RF chips also support 5.8GHz ISM band or even cover more bands, such as 2.4GHz.
The combination of robust V2X technology and unlicensed spectrum (2.4/5.8 GHz) makes it a good candidate for video transmission for drones. Major benefits include
- Long distance
To meet the long-distance requirement, 802.11p chip vendors have set their design target much higher than that of Wi-Fi products. In field tests, the NXP Semiconductor’s Roadlink 802.11p solution was proven to provide stable communication link up to 4km at 5.8 GHz with transmission power meeting CE regulation.
- Low latency
The MAC layer of 802.11p was significantly simplified to reduce latency. As a result, the communication adds only a few milliseconds to the end-to-end latency.
- Fast reconnection in case of lost signal
The simplified MAC layer enables to build the communication link instantly, which means there is no extra delay in the case of reconnection, if the signal level is recovered.
- Less interference in 5.8 GHz band
When calculating the link budget, 2.4GHz has 7.7 dB advantage compared to 5.8GHz. This means that 2.4GHz signal can propagate >2 times distance than 5.8GHz signal under same conditions. However, the reality is that too many devices are working in 2.4GHz band and interfering with each other, which dramatically reduces the range.
- High-velocity tolerance
Consumer drones will cross the 100 km/h barrier soon, which will certainly introduce challenges to the communication system. 802.11p product can perfectly solve this issue, since it is designed to support high-speed vehicles. The solution from NXP has been proven to sustain with relative speeds up 500 km/h.
- Affordable solution
Most development costs of V2X system for drones have already been addressed by the automotive industry, such as developing a new standard and a chipset, field tests. Moreover, the cost will drop down further with the V2X market growth.
The NXP 802.11p solution is cost-effective and meets all key requirements of drone video transmission. It outperforms Wi-Fi in several key specifications and provides the state-of-the-art performance.
3.Be safer by cooperative flying
Along with the excitement of the market potential of drones there is concern when it comes to public safety. In Jan 2015, a DJI Phantom crashed on the White House lawn, which immediately put the safety issue of drones under the spotlight. How V2X systems resolve drone safety issue?
3.1 Real-time air space management based on V2X communication & Security system
How can we keep drones away from airports and crowds? The current solution is to set no-fly zones by manufacturer. To identify which areas should be restricted is formidable. And to maintain its correctness over time is even more challenging.
A real-time air space management system can be much more efficient. The foundation of such a system is standardized communication, where 802.11p is a good candidate, as drones can understand commands from the air space controller.
Which frequency can be used? Obviously, a dedicated channel is essential to limit interference. There are 7 channels allocated to V2X services in 5.9GHz band. Currently there is industry discussion on sharing channels with Wi-Fi. Since drones are becoming an important part of the transportation system and will have a major impact on public safety, it makes more sense to open 1 V2X channel to drone instead of Wi-Fi.
Certainly, security must be enforced in the system. Drones and air space controllers must be able to identify each other remotely to avoid unauthorized manipulation. Here the V2X security system can also be reused, which is designed with the purpose to secure the communication between vehicles and infrastructures.
3.2 Collision avoidance by cooperative flying
Cooperative flying already exists in the aviation industry. An example is Traffic collision avoidance system, which actively interrogate the transponders of aircrafts and negotiates collision-avoidance tactics with them in case of a threat. However, TCAS is expensive, large and power hungry, and therefore appears only in large aircrafts. Fortunately, those issues can also be solved by V2X system.
In V2X system, vehicles are required to broadcast their position, speed and other information to identify collision risk. The effectiveness of the V2X system has been proven in extensive field tests, such as Drive C2X in EU and Safety Pilot in US. In 2014, U.S. Department of Transportation published a V2V readiness report and pointed out that V2X can be highly beneficial in collision avoidance.
Drones and cars have similar communication and safety requirements. IEEE802.11p based V2X technology is designed to provide reliable connections between vehicles and improve transportation safety. By applying V2X-based technology to drones, we can build an affordable HD video transmission system with much better performance than those based on consumer Wi-Fi solutions. Moreover, when standardized communication – such as that based on proven V2X technology – is established for drones, it will become possible to implement a real-time air space management system and collision avoidance system, further increasing the possibilities and market growth for drones.
About the author:
Derek Tang (firstname.lastname@example.org) received the B.E. degree from Beijing University of Posts and Telecommunications, China, in 2005 and the M.Sc. degree from Linköping University, Sweden, in 2007. From 2007 to 2014, he was working as senior scientist in the research department of NXP semiconductors. His work focused on reconfigurable channel decoders and advanced reception algorithm for wireless communications. He is now a field technical marketing at NXP, promoting Roadlink IEEE802.11p V2X products.