ASE 6990 Reda McHareg
rm2250
LTE For Unmanned Aircraft Vehicles
Drones, once reserved for technology enthusiasts and youngsters aspiring to become pilots, are now used everywhere, starting from playgrounds and suburbs to the fields and circuits of race. Named officially Unmanned Aerial Vehicles (UAV), drones are a way to start new services. For example, they give farmers the opportunity to monitor their fields and follow their livestock in a more economical way, allow the agents to show their customers entire neighborhoods and the proximity to important shops and services, and to the first responders to handle emergencies and disasters in a more efficient way. Drones also guarantee broadband wireless services in remote areas affected by disasters natural, and the list does not stop there.
Currently, these new cases of usage can be deployed to a small scale. However, it is expected that the usage of UAVs will witness major large scale changes in several industries including agriculture, construction, delivery, entertainment, insurance, mapping, news gathering, public safety, public services, railways, the real estate sector and the preservation of wildlife. A study prepared by the business group representing the unmanned and robotic systems predicted that the UAVs will generate an economic impact of $13.6 billion in the United States during first three years after successful operations in the United States Air System, an amount that will to grow to more than $ 82.1 billion by 2025.
As these new drone applications become more frequent, it is necessary to bear in mind the question of safety associated with the advanced research and development. The usage of drones to a wide scale requires coordination and traffic management just as the today's air traffic control does. This will be necessary, especially for large fleets of autonomous drones and/ or flying at proximity to controlled airspace (e.g. an airport or military air base).
Many commercial small UAVs today are equipped with Wi-Fi connectivity so that they are remotely accessible. Wi-Fi connectivity, however, may not be sufficient for beyond visual line-of-sight (LOS) communications needs, particularly for those that require wide-area connectivity.
Cellular technology can bring a new dimension of broad credibility, robust security, comprehensive coverage, and integrated mobility of the drone operation to a large scale. Cellular networks make it possible to operate and control drones beyond the driver's line of sight, which will be essential for undertaking safe operations on a large scale and provide the new services that drones will introduce. In addition, the cellular connectivity can enhance the safety of drones’ autonomous operations by speeding up the delivery of optimal flight plans and transmission of flight authorizations, thus following the location of the drones and adjusting flight routes in near real time. The cellular connectivity can also be used to share videos in real time, from a surveillance drone for example.
Leader in the world of 4G LTE technology, Qualcomm and its engineers seized the opportunity to test drones controlled by LTE in real world scenarios and analyzed how and if drones can operate in a safe manner based on today's commercial 4G LTE networks.
Currently, cellular networks are designed to serve the smartphones and other land mobile devices, which is why discovering how cellular networks can serve drones operating at higher altitudes would be beneficial on many levels. Conventionally, current cellular networks cannot guarantee coverage for drones at higher altitudes because the relay antennas of mobile phones are pointing down to serve the devices mobile.
First, Qualcomm Technologies worked with the Administration Federal Aviation Office (FAA) on issuing a certificate authorization to test drones at higher altitudes (400 feet), around the headquarters of the company in San Diego. The FAA authorized UAS flight center not only guarantees ideal proximity to the research and development institutions of Qualcomm, but also allowed to test the drones in the Class B of airspace since it is close to the very active military air station, known as Marine Corps Air Station (MCAS) Miramar.
In addition, the flight center is surrounded by the real environment where autonomous drones will someday navigate, which involves commercial areas, populated areas, and vast uninhabited areas. All of these areas make the location of the flight center one of the most challenging test environments.
Flights were restricted to a cylindrical volume with 1.0 nautical mile radius and 400 ft altitude above ground level (AGL), as represented in Figure 2-1.
Figure 1: Flight test volume
After receiving permission from the FAA, Qualcomm collaborated with AT&T to try the operation of drones on its commercial networks in order to test the key performance indicators (KPIs) such as coverage, signal strength and mobility under different conditions on LTE commercial networks.
Flights and measurements for this study were performed by a custom-designed quadrotor drone, the 390QC as shown in the figure below.
Figure 2: 390QC Quadrotor drone
The 390QC has a takeoff weight of 1050 grams and flight time of 16 minutes. It is equipped with the Qualcomm Snapdragon Flight platform running Qualcomm Snapdragon Navigator flight control software.
The drone executes fully autonomous data collection missions and can be monitored and controlled over Wi-Fi and/or LTE while in flight. An RC transmitter/receiver is active during all flights enabling immediate takeover from a ground operator for safety. The Snapdragon Flight platform connects to the LTE module capable of connecting in 700 MHz.
Rich LTE modem logs are collected simultaneously with Snapdragon Navigator logs enabling correlation of flight status and data with modem logs from synchronized timestamps. Logs are stored on an SD card on the drone, and transferred (either over network or by physically moving the SD card) to a database for long-term storage.
During the field trial, hundreds of flights were performed to:
• Validate the safety of the flight platform
• Validate the completeness and correctness of the logged data
• Collect the data sets for final analysis
The first results have shown that current cellular networks can eventually guarantee a cover for UAVs at higher altitudes. Received signal strengths for drones at altitude were strong despite the down-tilted antennas in the network. In fact, signals are statistically stronger in altitudes than on the ground because of the free space propagation conditions at altitude. The simulations conducted during this study have also shown that commercial LTE networks should be able to support downlink communications requirements of initial LTE connected drone deployment without any change. Handover performance is also superior for drones at altitudes. This is attributed to the increased stability of signals with free space propagation relative to those subjected to the multipath, shadowing, and clutter experienced on the ground.
Moreover, several opportunities to further optimize the LTE commercial network were brought to perspective:
• Interference management: although drones can be served by multiple base stations at an altitude of 400 feet above ground level (AGL), increased interference at high altitudes can affect link quality. Which means more improvement and research should be done to manage the interference received by drones from a number of "neighboring" base stations emitting radiation up to 400 feet AGL.
• Optimization of the passage: Different characteristics of UAV passage compared to land mobile devices have also been observed. The impact and optimization are under study.
• Specific requirements for drones’ LTE : in order for the network to optimize the service for drones, it will be necessary to distinguish between a drone and a land mobile device. The network could also reject drones that affect KPIs and that are harmful.
In addition to optimizing the existing 4G LTE networks to undertake safe operations of drones, these results also helped to speed up the development of 5G. This technology will bring a very high degree reliability and availability, very low latency, and long-term security.With all the capabilities of 5G, drone fleets flying independently, communicating, and adjusting their behaviors through real-time data sharing can be feasible.
The results of the flight tests conducted by Qualcomm were however subject to certain limitations. It was important to construct a consistent flight path that could be executed repeatedly at different altitudes to enable apples-to-apples comparisons of results. However this flight path does not exhaustively cover all conditions. For example, the path was chosen to give diversity of serving cells in order study handover events and interference at cell edges. Thus, it was not possible to fly directly over any cells where the signal strengths would be expected to be even higher than those reported in the article. Also, the environment was a suburban residential/commercial area with good cellular network coverage in the bands studied and these results may not directly extend to urban or rural environments with different coverage and propagation characteristics. Further, simulation results can only approximate performance of a deployed and operation network. The simulations are intended to give insights on trends and relative comparisons rather than produce accurate absolute metrics.
More work is needed to reach the goal of effectively and efficiently supporting drones at low altitudes while protecting and maintaining performance of ground drones. This is true for the short term with optimizations of existing networks as well as for next generation networks that will employ new advanced technologies. Long term, the main goal would be to introduce techniques into next generation cellular standards that will provide simultaneous services to ground and airborne UAVs optimized to meet the performance requirement of each class of device.
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