SDR based RF (Radio) Data link – Secure, robust and EW resistant radio communication

Executive summary

Unmanned Areial platforms have been effectively used in recent conflicts across the globe. UAVs provide unmatched advantage of size, cost and scale; thus, they are widely adopted. In order to be effective a UAV Must have following key features

Robust Data Link
- Reliable & Secure long range Radio data link is must; the radio link must provide data rate enough to transport the control messages and video feed.
- Must support key network topologies: Point-to-Point, Relay, Autonomous Mesh network.
- Must be resilient against EW (Electronic warfare) Techniques like Jamming and spoofing.
Dependable Navigation
- A Navigation system that works well in heavy EW environment.

Major C-UAS systems target above two mentioned key areas to make the UAVs in-effective using EW techniques like Jamming & Spoofing. Majority of UAVs currently available use the off-the-shelf modules for both data link and navigation, the challenges with such modules are:

Fixed or hardwired implementation:
- These modules have fixed implementation of data link and navigation which were originally targeted for Leisurely applications like photo filming.
- The hardware is based on either FGPA or ASICs which are hardwired, it is not possible to extend the functionality to make it secure and EW resistant.
Black box implementations:
- In most of the cases the ASIC and the Firmware are like a black box to UAV OEMs, and it is not possible implement solutions to challenges mentioned above.
- For example, it is not possible to update the waveform used for communication, or antenna pattern for GNSS navigation.

The challenges mentioned above can be solved using Software Defined Radio (SDR) for UAV applications.

Software defined Radio (SDR) is well known technology in communication industry; it enables following key outcomes:

Customizable Secured Comms Link
- Non SDR comms platform use either application specific ASICs or FPGAs to implement a given protocol like WIFI, LTE etc.
- Hardware built for LTE in most cases can’t be used for WIFI and Vise-a-versa.
- However, Software defined radio give’s ability to implement a completely new application specific Physical layer and MAC layer enabling wide variety of communication protocols.
- Thus, it is suited to define and implement custom and secured communication protocol for sensitive areas like defence.
Future proof design
- Since the Radio is completely controlled by firmware, the firmware can be updated to implement the requirements that may arise in future without any change in hardware.

SDRs can be used in many relevant industries like UAV/UGVs, Military/defence to implement custom communication protocols in a reliable manner.

At Flextride we have a versatile SDR radio called FLEXTRIDE SDR, it is well suited for defence and military, UAV/UGV applications. Following are the key features of this platform:

No Chinese hardware of software/firmware is used
- We own and understand the hardware & Firmware of SDR completely.
- The SDR can be customized to suit a particular use case of application.
- No risk of hidden Trojan Horses.
SDR board uses the SOCs (system on chip) for reputed chip makers, so no doubts about reliability of underlying chips.
Fully customizable platform:
- We develop custom protocol starting at Physical later ensuring that communication link implemented by FLEXTRIDE SDR remains a guarded secret.

Following chapters in this document will explain how we can solve key challenges for UAVs mentioned above:

Overview of our SDR platform (FLEXTRIDE-SDR introduction)
Secured EW resistant data link using our SDR (Secure Data link)
Anti jamming CRPA antenna for GNSS navigation (CRPA Anti jamming antenna)

FLEXTRIDE-SDR: Introduction

FLEXTRIDE-SDR platform is a small form factor self-sufficient SDR which includes all the major
components of comms system i.e. Application processor, Modem including DSP processors,
Radio Transceiver.

This SDR does not need a host computer to work (which is required for most of SDR platforms
available in market), So it can work as independent Radio module.

This SDR platform supports following key features:

1X2 RF transceiver
Fully Programmable DSP (digital signal processing) cores.
25 dBm power output.
Frequency range:
- Platform shown above supports 100-5800 Mhz
5, 10, 20 MHz bandwidth to provide high data rate capacity

Block diagram of the system (SDR platform shown above) is shown below:

Figure 2 SDR block architecture diagram

FLEXTRIDE-SDR high level architecture is shown in block diagram above.
It mainly consists of following components:

Application core:
- A powerful set of Arm based cores.
- Rich set of interfaces including Camera/Video, Display/HDMI,
  Cryptography hardware accelerators, ethernet for backhaul connectivity.
- Custom application and a part of SDR radio stack runs on this core.
  It has enough processing power to handle both loads.
Modem
- Modem handles all the Digital signal processing of signals received
  from the RF transceiver.
- It includes hardware vector signal processor to efficiently process
  the SDR payload and convert it to Radio signals.
- The Digital signal processor is fully programmable, that means that
  the waveform structure, type, modulation is all coded in C language
  and uploaded as firmware on the modem.
- Fully programmable modem enables development of a secure, and may be
  custom physical layer protocol which is not used in any other wireless
  technology like WIFI, LTE.
- For defence applications this is really important, because using this
  platform a highly secure and secret communication channel can be build
  which will be difficult to hack, because the protocol is not known to anybody.
RF transceiver & Front-end module:
- Zero-IF transceiver(s) supporting frequency ranges: 100-5800 MHz
- RF transceiver supports highly integrated Front-end module supporting
  variable gain at front-end.

FLEXTRIDE-SDR platform is agile, scalable and secure.
It also supports temper proof firmware, that means the firmware is signed
with pre-known cryptographic keys and any attempt to replace the firmware
will make the platform non-functional thus securing the hardware from any
malicious updates.

Multiple use cases in both defence and civilian space can be implemented
using FLEXTRIDE-SDR platform, for each use-case a custom firmware needs
to be developed but the hardware remains same (as long as supported
frequency range remains same).

Following is the summary of major use cases or solutions that are targeted
towards defence applications on FLEXTRIDE-SDR platform:

Use-Case-1: Secured EW resistant Radio data link
- Useful in Man-to-Man or Machine-to-Machine communication.
  It is implemented by designing a secure RF link using two
  FLEXTRIDE-SDR devices.
Use-Case-2: Anti Jamming CRPA antenna
- CRPA (Controlled Reception pattern Antenna) is a very effective
  method that can be used as counter-measure for RF jamming.
  This can be implemented using our SDR architecture.
Use-Case-3: C-UAS system GNSS spoofing and Jamming
- UAV counter measures using GNSS spoofing and jamming techniques
  can be implemented using FLEXTRIDE-SDR platform.

Next chapter explain the above-mentioned use cases in bit more detail for reference.

FLEXTRIDE-SDR based key product applications

Secured EW Resistant Radio Data link

RF data link is essential when two parties need to communicate using wireless medium securely,
without any pre-requisite of existing cellular network. Such a radio link can be used for:

Hand-held Radio for communication between soldiers in tough terrain where there is no other
communication infra is available.
Comms between two equipment in field, for example exchanging video or data feed.
Here applications of such a link are vast, for example:
- UAV to Ground control and comms communication
- Comms between UAV, UGV and control and command centre.
Comms between Multiple equipment/UAVs forming an autonomous mesh network.

FLEXTRIDE-SDR along with FLEXTRIDE SDR firmware implements a radio data link which provides:

1T1R Antenna configuration
20 Mbps data throughput
Encrypted payload at MAC layer itself (Secured Comms)
Frequency hopping Physical layer (EW resistant comms)

The hardware and software architecture are scalable and they can be scaled up to support up to:

4T4R Antenna configuration
100 Mbps data throughput

This solution can work in three network topologies:

Point-to-Point
Relay
Autonomous Mesh

Point-to-Point & Relay

Figure 3 Point-to-Point UAV communication

FLEXTRIDE-SDR device implements a secure communication link between UAV & Ground station,
also it can act as Relay node to communicate to a device which is not in line of site (NLOS).

The example above shows the application of integrating FLEXTRIDE-SDR into UAV/UGV, but same
concept can be used to create hand held device that can be used by soldiers to securely exchange
video, and data.

The link bandwidth is sufficient to exchange high quality (HD) video stream, as the link
supports up-to 20 Mbps (Mega bits per second) throughput rate.

Autonomous Mesh Network

UAVs are also widely used in large groups called drone swarms. In such formation it is very
much desirable that there is an autonomous mesh network that can be created on-the-go between
each drone which is part of swarm, something like this:

Figure 4 Autonomous Mesh network

The Mesh network provides various advantages:

Reliability – UAVs can talk to each other and there could be multiple downlink connections
to the ground. So, if one link fails, other can take over.
Optimized bandwidth & control – All the UAVs don’t talk to ground, they talk to each
other, only few UAVs talk to ground thus it makes managing swarm more efficient.

FLEXTRIDE-SDR & firmware supports autonomous mesh formation, also it supports inter-mesh
communication, it can be extended to non-UAV use cases where there are multiple mesh networks
that communicate with each other and to the backbone.

FLEXTRIDE-SDR Radio software stack

The Key differentiator of FLEXTRIDE SDR is: The ability to customize even lowest layer of
comms stack. This gives us advantages:

Implement custom Layer 1 protocols – It makes the system very tough to hack.
Updatable waveforms – The system is future proof because we can update the waveform that
is used by changing firmware.

Figure 5 FLEXTRIDE-SDR protocol stack

The User interface on FLEXTRIDE-SDR device provides mechanism to feed Video or Data to be
transmitted to the Peer FLEXTRIDE-SDR user.

Firmware in FLEXTRIDE-SDR implements a custom-made MAC (Medium access layer) and PHY
(Physical layer) that is defined jointly between the defence officials and our engineers,
thus making it a secret implementation.

Since the MAC & PHY protocol are not following any open wireless standards like WIFI,
LTE, it will be difficult for any adversary to intercept this communication.

The firmware is designed to be secure and EW resistant by using two techniques:

Encryption: All the payload is encrypted at the MAC layer.
Frequency hopping: Physical layer supports frequency hopping to avoid EW jamming.

Figure 6 Frequency hopping

The communication channel is divided in multiple narrow channels, and the transmitter &
receiver changes these narrow channels continuously at a configurable granularity (in order
of Milli seconds).

The comms module can hop the frequencies in range of 100-3500 Mhz, it can be extended up to
5800 Mhz also.

Frequency hopping makes the communication channel resilient to EW jamming and following
parameters are configurable:

Frequency hop pattern (secret between Transmitter and receiver)
Frequency band: upper and lower bound where the frequencies can be hopped.
Dwell time: How much time to spend at each hop.

If the frequency hop pattern is derived carefully and kept secret, EW jamming can be beaten
using FLEXTRIDE-SDR system.

C-UAS GNSS Spoofing and Jamming

UAVs are a significant threat as far as securing any valuable asset is concerned.
As evident from recent conflicts In India and Abroad, UAVs play a significant role in
surveillance and offensive.

So, it is of prime importance to have a Effective C-UAS system to nullify the UAV threat.
UAVs can be countered by EW techniques as well as kinetic techniques.

We can use FLEXTRIDE-SDR to implement C-UAS EW technique as explained in this section.

Almost all UAVs use some kind of GNSS (Global navigation satellite system) to navigate to
the target.

There are multiple GNSS systems like: GPS, GLONASS, Galileo, BeiDou, NAVIC.

FLEXTRIDE-SDR can be used to develop effective EW mechanism to implement GNSS spoofing and
Jamming called RShield (An affective C-UAS EW system)

Figure 9 FLEXTRIDE-SDR based C-UAS

The system implements two options:

Option1:
For threats known to be using un-encrypted GNSS signals, spoofed GPS signals are sent
impersonating 4 different GPS satellites with wrong coordinates.
This is very effective to make UAV lose its navigation control.
Option2:
For threats known to use encrypted GNSS signals, the GNSS channel can be jammed by
transmitting a jamming radio signal.

Both options can be implemented in very cost-effective manner on FLEXTRIDE-SDR.
One FLEXTRIDE-SDR device imitates 4 or more GPS satellites.

Conclusion

This white-paper is intended to give overview of our capability, which mainly consists of:

FLEXTRIDE-SDR hardware platform:
- A low cost SDR platform that has no Chinese components (hardware & software), and it can be adapted to multiple defence applications.
A highly dedicated and experienced team of engineers (20+ years wireless exp)
- Who can implement various use cases on FLEXTRIDE-SDR as required by demanding defence scenarios.

Using our SDR platform and the capable team we have, we can implement the demanding defence application which are not even given in this paper.