Considerations for choosing a data link for UAV

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Data link selection for UAV
Yaron Benita
I.M.C Microwave Industries

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Data link main components
GDT (Ground Data Terminal)
(Including RF Box
power amplifier, tracking, filters, diplexer,
receiver, transmitter)
ADT (Air Data Terminal)
(Receiver, Transmitter.
(Filters, LNA, Diplexer, SPDT, 2
Anetnnas)

Data link selection considerations
 Range and environment factors (link budget,
line of sight, precipitation, etc.)
 Antenna tracking mechanism
 Analog system vs. Digital system
 Encryption and anti jam requirements
 Available frequency and bandwidth
 General requirements (size, weight, input
power, computer interface, etc.)
 Redundancy requirements
So many factors, I am totally lost…..

Range and Environment Factors
 Line of sight between the GDT and the ADT.
 Factors that impact line of sight are: trees,
constructions , curvature of earth and topographic
structure.
 Due to curvature of earth the maximal range between
GDT and ADT depends on the UAV attitude and the
GDT height.
 Ways to resolve non-line of sight cases:
 Using a relay GDT on the ground, UAV or Airborne
to increase range
 Use satellite communication
as a relay between UAV
and Ground station.
(Ka, Ku band)

Range and Environment factors
 Link Budget Calculation - all the gains and losses from
GDT, through cables, antennas and free space to the ADT.
 Fade Margin – the total gain remaining after adding gains
and subtracting losses in the link budget (uplink &
downlink).
 The exact amount of the fade margin required for a UAV
system depends on the desired reliability of the link and
the environmental conditions.

Range and Environment factors
 Example for Fade Margin Calculation: (Downlink ADT GDT)
 ADT Antenna gain: 0dBi
 ADT Video & Data Transmitter power: 50dBm
 ADT cables loss: 1dB
 Path loss: 150km (loss in 2.4GHz is: 143dBm)
 GDT Antenna Gain: 17dBi
 GDT receiver Sensitivity: -97dBm
 GDT cables loss: 1dB
Fade Margin: 18dB
(0dBi+50dB-1dB – 143dB + 17dB +97dB - 1dB)

Antenna Tracking Mechanism
 The beam width of a directional antenna is narrow.
 For long range UAV (> 10km) the GDT should include
Azimuth/Elevation tracking. (using Antenna Pedestal)
 Major Tracking mechanism:
 Manual Tracking – manual antenna
transportation based on the input signal level
 GPS tracking – using GDT GPS location and GPS
target location. (can’t work when GPS signal is
jammed)
 RSSI tracking using software – automatic tracking
by determination of maximal signal power.
(spewing out multiple narrow-beam pulses in
different directions and looking for the maximal
return)
 Monopulse tracking - automatic tracking, most
accurate and reliable solution. (with a single pulse,
the antenna can gather angle information)

Analog vs Digital
 The difference between analog and digital technologies is:
 Analog technology - information is translated into electric
pulses of varying amplitude.
 Digital technology - information is translated into a binary
format (zero or one) where each bit is representative of two
distinct amplitudes.

Main advantages of a digital system
 Better resilience to noise and interference
 Capacity utilization(less bandwidth) –
 Compresses the input video using MPEG4, H264
technics.
 Mixes multiple video and data inputs in one link
 Allows data manipulation using software
 Encryption - better applied to digital data
 Anti Jamming – spread spectrum, frequency hopping
 Forward Error Correction method (improves receiver
sensitivity)
 Smaller size
 RF components and data processing is implemented by
software.
 Combines data modulation and data processing in the
same unit
 Easy integration with modern flight computers and GCS.

UAV Antenna - Considerations
 Using Two Antenna solution ( one receiver
& one transmitter ) vs. using One Antenna
to receive and transmit applying a Diplexer.
 Interference to the antenna reception
 UAV structure and movements - might
require multiple antennas
 UAV material type
 Antenna Switching – used with multiple
antennas solution
 Temperature

General considerations
 Size & Weight
 Input Current/Power – low power transmitter on a UAV
requires compensation on Antenna size on the ground to
achieve long range.
 Autonomous system that can work when GPS signal is lost.
 ADT – GDT range
 Azimuth/Elevation Angles (GDT - ADT)
 UAV Altitude
 GPS location of GDT (acquire when the system is installed)
 Interface with the ground station and the flight computer.
 Use of Half duplex vs. Full duplex RF communication
 Half duplex Transceiver (TDD) - uplink bit rate is low. Use
the available slot of the downlink to transmit uplink data
 Separate frequency for receiving and transmitting

UGV & USV – Specific Considerations
 Multipath
 The arrival of a transmitted signal at a receive
antenna from multiple paths is due to reflections.
 Reflections - ground, water, trees, constructions,
people, or any other obstacle .
 Diversity, COFDM modulation
 Tunnel Robots –
 Communication through cable
 Multiple antennas for relay.

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Thank you for your attention
You can reach me at:
yaron@imc-mw.co.il

Considerations for choosing a data link for UAV

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Considerations for choosing a data link for UAV