Radar devices are among the most important RF applications, with direct impact on aerospace missions, military endeavors, ship and submarine navigation, and road traffic control and monitoring. The critical nature of these applications, along with the need for extended lifetimes with safe operation, requires extreme precision and reliable outcomes; otherwise, the entire mission can be jeopardized. For these applications, software-defined radios (SDRs) can provide modernization and service-life–extension program (SLEP) solutions for aging radar systems.
Unfortunately, the precision and performance of electronic devices wear out with time, and it becomes increasingly challenging and expensive to maintain reliable radar operations past mid-life. This issue is worsened by the increase in non-static clutter, which includes the presence of wind farms, strong telecommunication signals, drones, bird migration, and dense air traffic.
Furthermore, technological advancements in the radar industry are rapidly surpassing the performance capabilities of the existing systems, especially the ones purely based on hardware, which can lead to severe holes in safety and security that can be exploited by malicious parties. As maintenance and support budget can greatly affect and limit the performance, reliability, and bottom-line operations when using old radar systems, the aging effects must be considered when designing or selecting radio transceivers for critical radar applications.
In fact, one of the most common attacks consists of neutralizing radars by directly interfering with the RF signal received, in a method called jamming. Therefore, it is essential that the electronic components involved in the radio transceiver are in good condition.
Software-defined radio background and architecture
Novel solutions based on software instead of hardware can significantly alleviate these challenges in the long run. In this context, software-defined radios play a major role in the development of modern radar systems. Before diving too deep into radar applications and their particularities, let us discuss a bit about the basic concepts of SDRs and their basic architecture so we can better understand how these devices can improve the design and long-term use of radars.
First, SDRs are completely different from conventional radio transceivers, as they implement most of the signal processing and communication functions in the software domain instead of using hardware electronics. This alone allows SDRs to be completely reconfigured, upgraded, and repurposed constantly, remotely, and without any hardware modification, in a way that is virtually impossible in hardware-based systems.
To achieve this level of flexibility, SDRs are designed with two main functional stages: the radio front end (RFE) and the digital back end, as shown in Figure 1. Regardless of the software implementation, there is a minimum amount of analog hardware necessary to transmit and receive RF signals, which is implemented in the RFE.
The RFE performs all receive and transmit functions that the radio requires, including signal amplification, filtering, mixing, and antenna coupling. Therefore, the RFE can significantly limit the SDR performance, so high-end SDRs usually implement RFEs with a wide tuning range, large dynamic range, and spurious-free dynamic range, low noise, and with several simultaneous and coherent channels.
In fact, the highest-bandwidth SDR in the market can operate up to 18 GHz with 16 independent radio chains, each one with an independent ADC/DAC to interface with the digital back end. The digital back end, in turn, is responsible for performing the DSP functions of the system, which include modulation, demodulation, up-/down-converting, data packaging, JESD204B serialization, and application-specific algorithms, including communication protocols, Kalman filters, fast Fourier transform, beamforming, and track algorithms. In high-performance SDRs, the digital back end is implemented using a powerful FPGA, which allows complete reconfiguration of the architecture via programming, embedded DSP blocks, and parallel processing of multiple channels.
Furthermore, modern SDRs are compatible with open-source host software, including GNU Radio, and custom C++ and Python applications, making it easy to develop new solutions using already-existing blocks of code.
Figure 1: The SDR architecture. (Source: Per Vices)
Software-defined radios support incremental modernization
The performance advantages introduced by SDR-based systems make them extremely useful in radar structures, to the point where they are progressively replacing legacy radio systems in radars without negative impact. Because SDRs can be completely reconfigured and tuned to serve specific applications with tight sets of requirements, they can be easily integrated into legacy systems without much redesign, which can solve most of the problems in aging radar systems.
Another feature that enables retrofitting in radars is the modular nature of most high-end SDRs so that commercial off-the-shelf SDRs can satisfy different size, weight, and power requirements demanded by existing units, not only providing a compact solution but allowing the implementation of several RF functions with a small footprint. This all-in-one–solution approach helps reduce the total equipment count, which has positive impacts in the device cost and complexity.
By centralizing the RF functionalities and network interfacing into one device, the designer can better predict the lifetime and maintenance requirements of the radar, in contrast with legacy solutions that implemented hardware from several vendors with different life cycles. Finally, the FPGA in high-performance SDRs provides a means for parallel computation with very low latency, so the digital nature of the signal processing will not interfere significantly in total latency of the radar, ensuring there is no lag in data and the control unit can act quickly in the case of non-static clutters, such as severe weather and drone interference.
Software-defined radios support SLEP
Besides the ability of replacing older RF radar systems to improve performance and eliminating aging effects, SDRs also provide a framework for incremental and constant modernization. First, the FPGA in the digital back end can support algorithms that are still under development or will be developed in the future, which anticipates new upgrades and increases the future-proof capabilities of the radar device.
For instance, the Intel Stratix 10 FPGA has an architecture that enables speeds up to 57.8 Gbits/s with up to 24 transceivers per tile, which allows the very high data rate required for complex radar algorithms, including advanced UAV detection and tracking, as well as non-static clutter elimination. The digital back end can implement advanced filters, modulation schemes, and beamforming algorithms to allow for precise analysis of events and ensure a higher level of safety and security.
Beamforming is an essential technique in modern radars to minimize the impacts of non-static clutters by focusing the RF beam to certain points and rejecting the areas contaminated by clutter. SDRs can significantly improve the beamforming capabilities and signal-to-noise ratio of radars, especially due to the higher levels of synchronization, determinism, and phase coherency between channels that multiple-input, multiple output (MIMO) SDRs provide when compared with their hardware counterparts.
Furthermore, the low-latency processing involved in FPGAs enable the use of fast error detection and fixing, which allows the radar to dynamically self-correct and remotely report the errors to the main controller in the case of anomalies. Finally, because the data is processed digitally early on, capturing and storage of data and waveforms is an effortless process, and this data can be later used to guide the modeling and design of new radar devices and techniques while also providing means for behavior simulation and waveform repositories.
Figure 2: Beamforming in radars. (Source: Per Vices)
Hardware obsoletion is a major concern in aging radar systems, as older hardware cannot keep up with the development of new techniques, tracking methods, and detection algorithms. Obsolete hardware also creates an environmental problem, as most of the electronic components must be discarded at a certain point.
Furthermore, radar systems that are not up to date with novel security and defense algorithms are susceptible to malicious attacks from parts using more advanced RF systems. Software-based technologies can greatly reduce the effects of hardware obsoletion, as most of the updates and upgrades can be done by software on a general-purpose hardware framework. As long as the software updates properly address the hardware capabilities, the radar can be updated for a much longer term than traditional systems.
Moreover, high-end SDRs are designed in a modular architecture, allowing easy replacement and upgrade of hardware when necessary. Software-based upgrades are particularly interesting in large radars installed in remote areas, as software upgrades, troubleshooting, maintenance, performance analysis, and control can be performed remotely through host computers connected to the main network or directly to the radar, significantly reducing service costs and downtime. Finally, the all-in-one approach in modular MIMO SDRs from expert vendors greatly reduces R&D efforts while also ensuring smooth integration with the existing architecture.
Conclusion
Radars are crucial RF components in several critical applications, including the military, aerospace industry, and self-driving vehicles. One of the main challenges in these systems relates to the aging process of the radar itself, which significantly degrades precision and performance after mid-life and makes hardware obsolete as the technology in the industry evolves.
As an alternative, SDRs allow for continued safe operations of radar systems through their available streamlined integration and support. Software-embedded processes reduce the chance of catastrophic hardware failure, enable remote and continuous upgradability, and allow for an extended lifespan by providing a general-purpose framework capable of complying even with algorithms to be developed in the future.
In the radar industry, SDRs are an investment that provide long-term consistent returns by reducing maintenance and replacement costs, R&D expenses, and service downtime while allowing for easy integration with legacy systems and adaptation to new technologies, eliminating the risk of obsolescence.
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