Enable Unprecedented Long-Range Data Links

Enable Unprecedented Long-Range Data Links using Simpulse’s SL100 Modem

How Software Defined Radio and innovative technology ensure

reliable transmission of live video and control command

on long-range UAV missions

Enable unprecedented long-range data links

Executive Summary

Software Defined Radio (SDR) technologies make it possible to significantly enhance the performance of radio communication systems.

SDR technologies are used for radio communication in various types of applications, including UAV, broadcast TV, monitoring, civil protection, and even applications that require less bitrate but extreme signal robustness, either on very long distances or in urban or very disturbed indoor environments.

The SL100 mobile data-link modem, developed by Simpulse, is built around robust SDR technology. The modem establishes powerful and secure video links over very long distances, and integrates a sophisticated performance analysis tool to continuously measure the link transmission quality in real time.

This White Paper outlines the techniques used in Simpulse’s SL100 mobile data-link modem. The paper further details the modem’s implementation in a professional UAV system and its performances on a long-range mission in the field.

Today’s Professional UAV Systems Require Innovative Communication Solutions

Professional communication systems’ performance level have greatly increased. Drones and Unmanned Aerial Vehicles (UAVs) keep breaking established flying times and distances thanks to technical advances in materials, navigation systems and energy performance.

Flights of over 30 kilometers are now commonly considered, provided that embedded communication systems ensure robust, secure data-links and excellent Quality of Service (QoS), as well as high and stable throughput of live HD video whenever necessary.

Nowadays the majority of professional UAVs are limited to ranges of about 15 kilometers, as current radio technologies (WiFi, 4G, LPWA, etc.) reach their limits. The ideal data-link solution definitely needs to combine the best of techniques found in today’s cellular networks and wireless standards with advanced communication algorithms adapted to the UAV mission specific needs.

Software Defined Radio provides the means to ensure robust mobile data transmissions over very long distances.

Simpulse’s SL100 SDR data link modem enables attaining distances of up to 50 kilometers (30 miles) while matching the UAV size and power consumption constraints, thereby boosting the efficiency and profitability of field missions.

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SL100, an SDR Data Link Modem for Mobile Long-Range Transmissions

The SL100 mobile data-link modem, developed by Simpulse, is built around robust Software Defined Radio (SDR) technology that establishes powerful and secure video links over long distances and in highly mobile conditions. The modem further integrates a sophisticated tool for performance analysis that allows for real-time characterization of link transmission quality.

The following principles of this SDR solution make it particularly adapted to long range use:

The SL100 Drone/Ground Station and Modem System

Before detailing the field mission, this section first provides an overview of a professional UAV system with the SL100 modem implemented in the drone and the ground station as shown in Figure 1.

The drone and ground station are both equipped with Simpulse’s SL100 radio modem. The drone integrates a camera for live HD video streaming. Videos are compressed to a few Mbits/s which ensures both video compression and multiplexing of the control commands and the telemetry data sent by the drone (GPS position, battery level, speed, acceleration, etc.).

The piloting and the monitoring of the drone are ensured via a mission-dedicated PC.

The mission PC displays the geographical position of the drone on a map together with

• SDR allows to dynamically change the radio algorithms and protocols according to the quality of the transmission channel, via the software and a single piece of equipment.

• The proprietary waveform is optimized for mobile and strong Doppler conditions in presence of selective fading and interferences.

• The receiver features maximum sensitivity (up to -117 dBm), thus guaranteeing long distance mobile transmission from 30 km to 50 km.

• The modem automatically and dynamically selects the best frequency channel every 100 ms (i.e. the channel with the strongest payload capacity).

• Depending on transmission channel quality, the modem can use up to four antennas to compensate for link masking and disturbances caused by variations in a drone’s orientation.

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the associated video. Specific commands point the drone in the right direction with a data rate of a few kbit/s.

An additional PC can be connected to the system to analyze the radio link parameters via a Graphical User Interface (GUI) (see Figure 3 and related paragraph).

Figure 1: The SL100 Drone/Ground Station system

The SL100 modem blocks are detailed below (Figure 2).

Figure 2: Overview of the SL100 modem

The baseband signal processing algorithms developed by Simpulse are implemented in a FPGA. An Analog Device AD 9361 transceiver integrates among other things the Analog Digital Converter (ADC), the DAC converters, the digital filters, carrier frequencies synthesis, and a 70 MHz to 6 GHz converter.

The baseband blocks and the transceiver work in tandem to provide the base for SDR functionality.

The complementary radio module, developed by Simpulse, optimizes the receiver’s sensitivity and the transmitted power in a specific frequency band. It also permits connecting two among four antennas, via two pairs of switches.

SL100 Drone

Ethernet

Video compression + MUX Video

Command control

Telemetry

Ethernet Mission PC

• Video monitoring

• Navigation

SL100 Ground Station

Analysis PC • Expert radio • GUI

Complementary radio

(specific band)

Way 0

Way 1

TX0

RX0

TX1

RX1

AD 9361 Transceiver

RF 2 x 2

I

Q

Digital

Ethernet

BB Simpulse

(FPGA)

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A Sophisticated Tool for Performance Analysis

The link quality can be analyzed using the Graphical User Interface (GUI) installed on the analysis PC. Figure 3 shows an example of a GUI window.

The main measured parameters include: the useful level of received signal (RF_level), Signal to Noise Ratio (SNR), the selected antennas, the Packed Error Rate (PER), the transmitted data bitrate (Avai. Bitrate), the percentage of impulsive noise, and the distance between ground station and drone.

A detailed description of parameters is given in the SL100 User Guide. Figure 3: Example of a GUI window

(analysis PC)

The information delivered by the GUI helps to answer the following questions:

“Does the radio link work correctly?” The Packed Error Rate (PER) provides the answer. For a perfect link, the PER will be null. The acceptable limit for a video of good quality is a PER of 5%.

“How to check the antenna configuration?” To check the antenna configuration before the field test, we recommend carrying the station around the drone on the ground within a radius of a few tens of meters, to force the selection of a pair of antennas on both local and remote modems and to analyze the measured values using the performance analysis tool.

Reading the SNR and RF_level allows us to ensure that the level is close to the theoretical value in free space and that the signal levels are coherent between the selected antennas and the other pair of antennas.

During the flight, the performance analysis tool can also be used to observe the field level received by each antenna and to check that the antenna switch is pertinent.

“What is the margin?” The margin is the difference between received signal level and receiver sensitivity. To guarantee good performance, the margin must be positive by a few dB. In case of Line Of Sight (LOS) without interferer, the margin can be weak.

In case of the presence of multipaths or interferers however, a margin of 2-3 dB is required. For a downlink (from drone to ground station) that transmits a video of a few Mbit/s, the sensitivity of the receiver is of approximately -106dBm.

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Planning the Mission

Figure 4: Link between Boudou and Montauban, France (31.4 km / 19.5 miles)

Prior to the flight, the team first conducted a simulation to determine the right location of the ground station. Suitable sites have a high enough elevation to keep the Fresnel ellipsoid clear of any obstacles.

The first step of the simulation thus consists in calculating the Fresnel ellipsoid, a volume in space that lets us evaluate the attenuation brought by an obstacle (a building, a hill, …) to the propagation of a radio wave. Any obstacle inside the ellipsoid will reflect part of the wave in a diffuse way. As a consequence, the part of the radio wave that arrives at the receiver disoriented as compared to the direct signal, causes interferences that generally weaken the received signal.

To illustrate this step, figure 5 represents the simulated Fresnel ellipsoids for the Boudou – Montauban link over a distance of 31 km. This simulation was carried out at 2.4 GHz, using the very comprehensive and popular “Radio Mobile” free amateur software (www.ve2dbe.com).

Figure 5: Fresnel diagram for the link from Boudou (Ground Station) to Montauban (Drone)

The second step consists in simulating the transmission in free space, without disturbers, based on the parameters as noted in Table 1, including frequency, antennas’ heights and gains, transmitted power, receiver sensitivity, etc. It is noted that the Equivalent Intrinsic Radiated Power (EIRP), sum of the transmitted power and the antenna gain, is limited to 20 dBm in Europe. Adjustments of the ground station transmitted power can be made from 20 dBm to 27 dBm to comply, together with the antenna gain, with other country specific regulations. During the assessment, the margin always has to exceed the receiver threshold by several dB.

Once the right location of the ground station was determined, the team then verified the equipment onsite and proceeded to the field measurements.

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31.4 km Drone

197 m

97 m

160 m


Field Tests Results Several long elongation field tests were undertaken with drone manufacturers. Table 1 shows the main characteristics of the downlink used for video transmission (2.7 Mbits/s) and Command/Control and Telemetry (10 kbits/s).

Downlink

EIRP (drone) 20 dBm Number of antennas (drone) 2 or 4 Number of antennas (ground station) 1 to 2 Antenna gain (drone) 2 dBi Video bit rate 2.7 Mbit/s Control / command bit rate (bidirectional) 10 kbit/s Video receiver sensitivity (ground station) -106 dBm Control/command receiver sensitivity -117 dBm

Table 1: Main downlink parameters

The measured performance of two UAV flights (Boudou-Montauban and Esperce-Morlandier) and one ground-to-ground test (Mont Ventoux-Pierrelate) are synthetized in Table 2, for an EIRP of 20 dBm, and compared with the simulations.

The Performance Analysis Tool estimates the measured margin by using the SNR and the video quality through the Packed Error Rate (PER).

Table 2 shows that the link works accurately and as expected with margins close to the expected values.

Mission Distance Command & Control Quality

Video Quality

Video Margin

Simulation Measured

1 Boudou - Montauban 31.4 km 100 % 90 % 6 dB -2 to 6 dB

2 Esperce - Morlandier 27.7 km 100 % 98 % 7 dB 0 to 6 dB

3 Mont Ventoux - Pierrelate 49.1 km 100 % 100 % 8.5 dB 8 dB

Table 2: Simulated and measured results

Table 2 also shows that the video quality of the second mission is slightly better as compared to the first mission. This is due to the greater number of antennas in the second mission (3 antennas in the drone and 2 in the ground station, instead of respectively 2 and 1 for the other two missions).

Furthermore it can be noted that the quality of the third video link reaches 100% because of Mont Ventoux’s high elevation, which allows long elongation with no obstacles.

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Conclusion This White Paper demonstrates that it is possible to establish a robust video/data-link between a UAV and ground station, over at least 30 km (19 miles) using Simpulse’s SL100 mobile data-link modem, even with an EIRP limited to 20 dBm as is the standard in Europe.

This performance is achieved thanks to:

To ensure country-specific regulatory compliance, SL100’s exit power can be increased up to 27 dBm. The margin or the maximum distance can thus be increased.

About Simpulse

Simpulse offers embedded Software-Defined Radio (SDR) solutions for innovative professional communication systems. Simpulse’s radio links are the answer to professional applications that operate in highly mobile conditions and require a power-optimized, robust and secure solution.

All radio modems integrate Simpulse's PULSAR IP Core, a scalable and programmable DSP co-processor that induces great flexibility and ensures customer products to be scalable, easy to customize and extend.

Simpulse was founded in January 2011 and is headquartered in Palaiseau, France.

For more information on the SL100 data-link modem, please contact Simpulse:

[email protected]

Phone +33 952 636 585

www.simpulse-sdr.com

Simpulse © 2017 All rights reserved

• The modem’s underlying SDR technology that offers optimized sensitivity and robust synchronization in mobile conditions.

• An efficient performance analysis tool that continuously measures the quality of the connection.

• The automatic selection and combination of up to 4 antennas according to the position of the drone.

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Enable Unprecedented Long-Range Data Links