WP3 approach

  • consider scenario covering a range of relevant flight/connectivity situations
  • develop simulation models and software for cellular/satellite/hybrid C2 links
  • evaluate performance using simulation
  • visualize and analyze the results

Scenario region and trajectory

  • Baltic sea between Stralsund (D) and Bornholm (DK)
  • semi-urban, rural, offshore flight segments

Scenario network data

Cellular Network
  • 237 sites with 711 LTE800 cells (3-sectored)
  • publicly available data
Satellite Network
  • single geostationary satellite
  • two overlapping beams
  • data provided by Thales

Modelling

  • UAV dynamics / trajectory
  • Cellular connectivity
  • Cellular network load (terrestrial)
  • Satellite connectivity
  • Hybrid link model
  • C2 traffic

UAV dynamics / trajectory

  • cruising altitude of 100 m
  • path roughly avoids land and protected areas
  • smooth trajectory (piecewise cubic)

Cellular connectivity

  • pathloss and shadow fading according to 3GPP model (almost free space propagation due to line of sight between drone and base stations)
  • drone connects to base station with highest reference signal level
  • hand over to better base station only if improvement at least 2 dB
  • multiple antennas: select beam with highest reference signal level
  • delay model consists of components for
    • U-Space/base station transmission time
    • cellular transmission time
    • handover time

Cellular network load (terrestrial)

  • downlink (U-space to drone):
    • calls of each cell are independent M/M/1 processes
    • cell contributes interference if at least one call
  • uplink (drone to U-space):
    • random distribution of terrestrial users (UEs) in the scenario region
    • iid call arrivals to all UEs, fixed call duration
    • cell contributes interference for the duration of a call
  • average network load for both directions: 30%

Satellite connectivity

  • serving beam is the one with higher signal level
  • handover between beams without additional delay
  • no service classes/priorities

Hybrid link model

  • packets sent simultaneously over cellular and satellite network
  • first correctly received packed determines latency

C2 traffic

  • packet-based model according to 3GPP parameters
  • downlink (U-space to drone):

    21 packets of 100 bytes per second (17 kbps)

  • uplink (drone to U-space):

    9 packets of 100 bytes per second (7 kbps)

C2 performance indicators

  1. availability Is the radio network for the C2 link working properly?
    • measured as the absence of radio link failures (RLFs)
  2. service level compliance Is the C2 link performant enough?
    • measured as the 99% percentile of the packet latency within 10 seconds
    • OK if below threshold for acceptable latency (ms)

Simulation results for C2 link variants

  1. cellular only, 1 on-board antenna
    • issues due to heavy interference
  2. cellular only, 6 on-board antennas
    • reduced interference due to sectoring, still some issues
  3. hybrid cellular and satellite, 6 on-board antennas for cellular
    • satellite as backup in case of cellular issues

Comparison of C2 link performance

100
  1. cellular link, 1 onboard antenna
    Quality of the C2 performance indicators along the trajectory of the drone shown on the following map. The first part of the flight starts in an urban area and continues in a rural environment. The second part of the flight is is offshore with distances of up to 50 km to the closest base station. Change the value of the threshold for acceptable acceptable latency to see what latencies can be achieved with very high probability.
  2. cellular link, 6 onboard antennas
  3. hybrid cellular and satellite, 6 on-board antennas for cellular