Network measurements with drones: The next step to a connected sky

In Singapore, the Ministry of Transport is working with multiple government agencies to assess the use of UAVs for commercial applications on land as well as in the southern seaport. Dedicated “drone estates”, such as the “maritime drone estate”, have been designated to offer companies and research institutions different environments to test and develop drone technology for different applications¹.

Singapore can very well imagine a future in which UAVs are roaming the skies and executing these newly developed commercial applications. So, how does a country effectively deploy UAVs in densely populated urban environments?

In order to have a coordinated approach and to ensure safety guidelines, Unmanned Traffic Management (UTM) systems are being developed to connect and operate multiple drones simultaneously. UTMs will thus require a reliable, wide-area backhaul communication network. With LTE being a proven and readily available technology², many UTM companies choose this cellular technology as one of the networks for UTM deployment.

This makes us wonder whether the existing communication networks (i.e., LTE networks) cater sufficiently for these new drone use cases. Most LTE networks are designed for use at street level, so what is LTE network coverage at the flight altitudes of UAVs like? Network latency is another important consideration as every millisecond delay in communicating with the UAVs might cause a mid-air collision between UAVs. And, will there be sufficient data throughput for specific UAV applications such as video surveillance?

Measurement solutions mounted on a drone

Rohde & Schwarz mobile network testing (R&S MNT) is a leading provider of drive test tools, including RF scanners and specialized handsets (smartphones) for testing network quality of service (QoS) and quality of experience (QoE). With their small and compact form factor, the R&S scanners and QualiPoc Android handsets are easily mounted on UAVs that are used for flight tests over designated “drone estates” to test the network quality at flight altitudes.

By testing the QoS and QoE of LTE networks at flight altitude, we can identify problem areas in the UAVs’ path and altitude such as insufficient network coverage, a lack of data throughput, or high latency, which can be problematic for the UTM communicating with the UAVs. Rohde & Schwarz has partnered with UTM vendors for flight trials in different parts of the world to collect valuable information regarding LTE network characteristics in the varying heights of the UAV flight paths.

Coverage at different flight altitudes

In a recent trial, conducted with R&S®TSMA6 RF scanners and QualiPoc Android handsets mounted on a UAV, we determined the coverage of a UAV’s flight path at different altitudes by measuring and plotting network coverage parameters such as Reference Signal Received Power (RSRP) and Signal-to-Interference-plus-Noise Ratio (SINR). At the same time, we used the mounted QualiPoc Android handsets to conduct latency and data throughput tests to identify potential problem areas at different altitudes.

From the map plots above, we see that the LTE network coverage at an altitude of 50 feet is much better than at 200 feet. At 200 feet above sea level, the current network coverage would not be sufficient for the deployment of UTM systems, as communication with the UAVs cannot be guaranteed. The diminishing network coverage is probably due to the downtilt of the LTE base station antennas aiming to cover street levels instead of flight altitudes.

Operators to improve coverage and latency

LTE coverage measurements with R&S®TSMA6 RF scanners, and data throughput and latency measurements with QualiPoc Android handsets provide telecom authorities and operators with a valuable overview of current LTE capabilities.

Given our trial, the mobile network operator will need to improve network coverage and resolve any latency or data throughput issues at flight altitude so that UTMs can have complete control of the deployed UAVs in this particular “drone estate”. Looking ahead, 5G will help to improve the UTM’s needs further, in particular, the latency KPI by using special means for URLLC (ultra-reliable low-latency communications) use cases.

As discussed earlier, it is vital to ensure that the quality of the UTM’s communication network is reliable in order to have seamless control of the UAVs in the designated areas. Thus, it is critical to test the network quality at the high altitudes in which UAVs fly before any UTM can be successfully deployed. R&S MNT has the expertise, experience, and tools to support this important network testing phase as we are partnering with UTM companies to move into the era of IoT.

Find more information about our network measurement solutions mounted on drones in the video below:

References:
¹ Maritime drone testing area to be set up near Marina South Pier, The Straits Times, March 7, 2019
² A Telecom Perspective on the Internet of Drones: From LTE-Advanced to 5G, China Mobile Research Institute