ESM Processor for 3D Passive Localization

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"Because of the relatively shorter delivery times, complexity, and research and development efforts involved in the application, we decided to work with LabVIEW and LabVIEW FPGA."

- Avinash Reddy Ch , Digilogic Systems Pvt. Ltd.

The Challenge:
Finding the 3D locations of airborne targets with the help of signals received by sensors placed at different positions based on time difference of arrival (TDOA). Localization is more complex because the sensors are passive, meaning they do not transmit signals, and the signals coming from the target can be in any frequency band. This means the sensors have to be able to identify which signals are coming from the correct target.

The Solution:
Developing a system that processes the received data using complex localization algorithms to find the location of airborne targets in three dimensions. The realization of this system would not have been possible without the powerful combination of LabVIEW FPGA, FlexRIO, and NI’s PXI Express platform, which offered high-speed synchronous data streaming and easily programmable FPGAs for real-time processing.

Avinash Reddy Ch - Digilogic Systems Pvt. Ltd.
Prashanth P - Digilogic Systems Pvt. Ltd.

About Us

We are RF signal processing algorithm engineers at Digilogic Systems Pvt. Ltd. (DSPL), which has a corporate office in Hyderabad, India. DSPL is an ISO 9001-2008 certified company that provides systems, solutions, and products for the defense, aerospace, automotive, and manufacturing market segments. We are an NI Gold Alliance Partner as well as an RF and Communications Specialty Partner.

About the Challenge

In general, the locations of targets are found using active radars that provide only 2D locations. Because these active radars transmit signals, they are prone to be

detected by other electronic intelligence (ELINT) systems. To address this problem, the system should receive RF emissions only from the targets. The presence of multiple cooperative and noncooperative transmitters and different types of targets adds to the complexity of signal analysis. The processor of the electronic support measures (ESM) system needs robust and complex localization algorithms to find the 3D location of target radars.

Locating the targets without being located by those targets is essential in electronic warfare (EW) scenarios. The passive localization technology offers this advantage. At the same time, providing locations of the targets in 3D is critical, which makes the ESM systems more efficient.

Application Overview

An ESM system consists of five sensors placed kilometers apart at different locations that only receive signals. These sensors receive RF emissions from targets, convert them into pulse descriptor words (PDWs), and transmit the PDWs to the central processor of the ESM system. The processor receives the PDWs over point-to-point Gigabit Ethernet or microwave links. The received data is sorted and streamed to FlexRIO modules for processing. The location of the target is found using TDOA-based localization algorithms and is streamed to subsequent tracking systems over a fiber-optic link using the PXIe-6592R PXI High-Speed Serial Instrument.

Figure 1. Overview of ESM System

Application Details

The ESM system processor comprises a PXIe-­‐1075 PXI Chassis, which houses the embedded controller, Ethernet interface modules, FlexRIO modules, and NI high-­‐speed serial modules. The PXIe-8135 PXI Controller hosts the modules in the chassis. Running Windows OS, it allows us to configure and control all the modules and develop applications using LabVIEW and LabVIEW FPGA. We use it to buffer, presort, and validate the PDWs received over Ethernet links. It also controls the data flow among modules and hosts the GUI.

PXIe-8234 PXI Ethernet Modules are used to establish five point-to-point Ethernet links to receive PDWs from five sensors.

The PXIe-7975R PXI FPGA Module for FlexRIO features FPGAs that we can program using LabVIEW FPGA. The ESM system processor consists of three PXI FPGA Modules for FlexRIO. The presorted PDWs received on Ethernet links are streamed to the first PXI FPGA Module for FlexRIO to segregate targets. Using peer-to-peer streaming, we stream the target-segregated PDWs to the second and third PXI FPGA Modules for FlexRIO, where TDOA-based localization algorithms are implemented. TDOA is the difference in the time of arrivals of a pulse at two different sensors. We implement a localization algorithm for omni radars on the second PXI FPGA Module for FlexRIO and a localization algorithm for scanning radars on the third PXI FPGA Module for FlexRIO.

For omni radars, each TDOA value localizes the target on a hyperboloid. We can find the point of intersection of these hyperboloids, which gives the 3D location of the target radar. Starting from the first pulse, we can find 3D locations for every pulse emitted by the target radar.

For scanning radars, we calculate the scan rate and TDOA, which localizes the target on a circle. Two TDOAs localize the target on two different circles, and the point of intersection of these two circles gives the location of the target in 2D. We find the third dimension of the target location using a grid-based TDOA comparison method. Starting from the second scan, we can find the 3D location of scanning radars for every scan.

We use the PXIe-6592R PXI High-Speed Serial Instrument to stream the calculated 3D location to a tracking system that is part of the ESM system. The location is streamed along with the pulse parameters over a fiber-optic link using the Aurora 8B/10B protocol. The socketed component-level intellectual property (CLIP) shipped with the High-Speed Serial Instrument supports the Aurora 64B/66B Protocol, whereas, we were required to use the Aurora 8B/10B protocol. We developed a new socketed CLIP for the Aurora 8B/10B protocol using a Xilinx IP core and Very High Speed Integrated Circuit Hardware Description Language (VHSIC HDL or VHDL).

Figure 2. Localization for Omni-Type Airborne Targets

We use Real-Time Hypervisor 3.0 to run LabVIEW Real‐Time in parallel with Windows 7 OS. We run the most critical parts of the application in real time and other parts such as GUI and controls in Windows OS.

We use the PXI‐6683H PXI Synchronization Module to synchronize the system with a universal clock in the ESM system.

Powerful NI Product Features

The peer‐to‐peer streaming capability of the PXIe-1075 PXI Chassis enables us to share the complex signal processing blocks among the three PXIe‐7975R PXI FPGA Modules for FlexRIO without compromising on the data throughput.

With the LabVIEW FPGA Simulation feature, we can experiment and validate multiple methods to reduce our software development efforts. This eliminates the need for regular compilations to test the codes and saves us a lot of time.

Using customizable CLIP with the High-Speed Serial Instrument allows us to modify the protocol IP core so that we achieve the maximum compatibility while integrating our system with other systems using different protocols. Thanks to the standards of NI documentation, our custom CLIP development is easy and faster.

Why We Chose NI Technology

We chose NI technology for the commercial off-the-shelf (COTS) nature and power of LabVIEW. Because of the relatively shorter delivery times, complexity, and research and development efforts involved in the application, we decided to work with LabVIEW and LabVIEW FPGA. We needed to implement the time-critical localization algorithms on FPGAs. Implementing the FPGA programming on VHDL/Verilog and custom hardware for the complexity of the application we were addressing would have taken us more than two years. LabVIEW FPGA made our FPGA programming both easy and faster, and we realized the complete system, from concept to predeployment, within eight months.

We knew that the COTS PXI Express platform would help us in multiple ways. It handled the high data rates, achieved the synchronization required, and provided peer-to-peer streaming capabilities that were essential in the application. Also, we were unsure about the complexity of the algorithm localization and the algorithms’ FPGA resource utilization while configuring the system for application. We wanted a platform we could use to expand FPGA resources without much effort. We chose NI PXI Express technology to easily scale the FPGA resources and accommodate unanticipated resource increases due to complex blocks of algorithms.

As for long-term maintenance, the NI COTS platform offered us a long life cycle and a planned product road map that is useful for upgrading with minimal effort in the future. Because of this, the total cost of ownership for us was less compared with any other solution.

Why Our Solution Is Better

We use Real-Time Hypervisor 3.0 to run both LabVIEW Real-Time and Windows 7 in parallel. This is a unique feature we achieve using NI products that gives the user access to the best of both worlds with no performance compromises. Moreover, a friendly GUI is offered without the need for a second computer.

The ESM processor we developed is part of the ESM system that includes other systems such as tracking and display systems. To integrate the processor in the ESM system, we needed a variety of interfaces and protocols such as Ethernet and fiber optic. Because the ESM processor we provided is modular in nature, we can easily add other interface modules to seamlessly integrate with other subsystems. In addition, we can even upgrade it to include tracking and display in the same system rather than having multiple independent subsystems.

There Was a Problem

During application development, we had to run some of the resource-intensive and time-critical preprocessing blocks on the host where the timing was not guaranteed. We thought of using a real-time OS, but we couldn’t because of its limited support and the GUI requirement. The Real-Time Hypervisor, which was not part of the earlier system, helped us overcome this problem.

What We Gained

We developed the application originally to locate two different targets, but when we needed to locate five targets, we reused all the FPGA program blocks and shared them among all the FlexRIO modules to achieve it. It helped us meet customer expectations and gain a very good reputation. Being rare, our system quickly grew popular within the user groups of interest.


This application paved the way for our company to enter the strategic ESM systems development market. It gave us an opportunity to gain confidence and experience. We are looking forward to developing a complete passive localization ESM system including the receivers, microwave link, and tracking and display subsystems.


Author Information:
Avinash Reddy Ch
Digilogic Systems Pvt. Ltd.
Tel: +9140 2781 9935

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