There are two absolute truths about wireless military radios. The first is that wireless military radios must be accurate and reliable in mission-critical applications to guarantee the safety of their users, which places a great significance on testing plans and their ability to deliver the best final product possible. The second truth is that wireless military radios have become complex, digital devices that act much like computers. The software-defined radio (SDR) architecture of many of today’s military radios gives manufacturers the ability to implement complex and custom functionality for modulation and baseband processing. However, as customer demand increases, so do the demands on the test equipment.

Components of a software-defined instrumentation system.

For years, radio manufacturers have used traditional box instruments to test military radios; however, as radios become more complex, reconfigurable devices, manufacturers are looking for hardware that is more adaptive to changing test requirements than traditional instruments, while delivering the same level of test speed and accuracy. With software-defined instrumentation, which consists of modular hardware and a combination of off-the-shelf and user-defined software, test engineers can build highly integrated and flexible systems using commercial off-the-shelf (COTS) components.

Software-defined instrumentation is a natural fit for military radio and SDR, capable of adapting to changing test requirements as quickly as they evolve. While used by some, software-defined instrumentation has not been widely adopted by military radio manufacturers yet because it is not familiar and marks a significant shift from traditional instrumentation. But the speed at which military radios are advancing makes traditional instrumentation more costly and less timely test solutions, and makes software-defined instrumentation an ideal option for military radio testing. Here are three reasons why.

Flexibility to Adapt to Changes

Simply stated, software-defined instrumentation is more flexible and adaptable than traditional box instruments. It is the difference between defining your measurements and waveforms flexibly in software, versus using a box instrument that only offers pre-determined and fixed functionality. Military radios are no longer static devices, and the changes are not limited to high-level functionality. Custom military wireless protocols are continuously being introduced, and still-evolving commercial protocols, such as LTE, are being adopted for military applications at nearly the same rate.

So how do radio manufacturers keep up with the pace of change? If using traditional box instruments, the answer is slowly and with a large expense in purchasing new equipment. Every time a protocol or standard is introduced or revised, traditional instrument vendors have to design and manufacture a new piece of hardware or firmware to test it, leaving radio manufacturers in a holding pattern. With software-defined instrumentation, however, the radio manufacturers can test the new protocol or standard more quickly because their test equipment can evolve fluidly.

Software-defined instrumentation also gives radio manufacturers the ability to test multiple standards and protocols, as well as multiple feature sets, using the same test equipment. For example, many of today’s military radios use geolocation for better situational awareness to the user and team. If using traditional instrumentation, radio manufacturers would need a separate GPS simulator to test the GPS receiver, and a separate RF generator to test the radio communications for the receiver chain test. Using modular instruments and a software-defined approach, manufacturers could test both of those using the same hardware; thereby, delivering time, cost, and space savings.

One of the most significant arguments for software-defined modular instrumentation is the inclusion of field-programmable gate arrays (FPGAs) into a system of modular test equipment. FPGAs make it possible for radio manufacturers to customize test hardware for added functionality, and this type of hardware customization can be accomplished by programming an FPGA integrated into the test system. For example, radio manufacturers can customize hardware and augment the overall signal processing chain with on-the-fly modulation and demodulation, signal intelligence, and data encryption. This level of on-the-fly processing and hardware customization cannot be easily accomplished with traditional box instruments.

Test systems based on software-defined modular hardware offer the portability that a full rack of traditional box instruments cannot provide. Deployed military radios in the field have their own lifecycles in terms of usage and breakage, and need to be repaired and tested in the field. An ideal test solution should be as portable as the radios themselves. The modular hardware used in software-defined instrumentation is compact and has low power consumption, making it an ideal solution for in-the-field radio testing. Because the test solution is software-based, it can be adapted to changing conditions in the field.

Users Can Achieve the Results They Need

Modular PXI system with a PC controller, 3 RF generators, 1 RF analyzer, DMM switching, power supplies, and DIO.

A significant advantage that software-defined instrumentation delivers over traditional instrumentation is that it empowers its users to do more. Take signal processing, for example. Radio manufacturers typically relied on traditional instruments to perform signal processing; however, changing standards mean changing modulation formats and coding schemes. In order to do the necessary signal generation and analysis, radio manufacturers need to be able to manipulate raw data to achieve the desired results. Traditional instruments are capable of advanced signal processing, but there are limitations to how much can be achieved by configuring the knobs and dials on the box. The only true way for radio manufacturers to really manipulate raw data to achieve the results needed is to do so in software through digital signal processing.

It is important to note that test engineers need to become more skilled in the domain of signal processing in general. Signal quality is important, especially in military radio applications where users depend on that quality for their safety. If a manufacturer’s test equipment does not have the ability to fully conform to the designer’s specifications and the design engineers modify the device design based on those results, the design is modified based on weaknesses in the test equipment. By being able to see and manipulate the raw data, test engineers can test for and ensure the highest signal quality and deliver a more reliable platform to the design engineers to implement. Additionally, engineers working in software and skilled in signal processing will have an easier time taking measurements on new wireless standards than others using traditional instruments who will have to wait on the instrumentation vendor to design new test hardware or firmware.

A software-defined instrumentation approach empowers its users because it can offer an integrated testing solution that can save countless man hours of development and integration time. National Instruments’ LabVIEW, for example, integrates the hardware, drivers, digital signal processing, user interface, and the results generated in a single development environment. Users can build, iterate, test, and prototype a solution faster in LabVIEW because they are not forced to operate in-between development environments, domains, files, and drivers. LabVIEW also offers several toolkits and deep signal processing libraries to help users create and visualize algorithms in software and build programs to test the algorithms, saving them even more development and testing time.

Providing Speed Needed to Switch Between Modes

Traditional instruments typically deliver high-performance test solutions at the cost of flexibility, size, and speed; however, software-defined instrumentation not only delivers high-performance test solutions because it combines the desired flexibility and space savings, but it also continually benefits from the rapid advances of PC processing.

In addition to performing measurements quickly, users can also quickly switch between the many modes needed to be tested on military radios, which is typically an oversight when planning test time. Today’s radios are reconfigurable computers with programs running on them rather than the pre-canned personalities of yesterday, and users have to test all those modes. If the test system instrumentation takes significantly longer to reconfigure or change modes than it does to take the measurements, the instruments become a drain on efficiency. With end users demanding more functionality, those modes are changing or growing at a rapid rate.

As a device is being designed, it goes through many revisions of firmware, each of which needs to be regression tested to ensure that one positive change has not caused a negative change on another subsystem in the device, and the speed at which the device is tested must be fast to keep up with the changes. By using a software-defined approach, radio manufacturers can not only manage testing diverse subsystems in a single environment, but also can switch between them at a rate not attainable with traditional instrumentation.

The Bottom Line

Wireless military radios are evolving rapidly, and traditional box instruments with fixed functionality are not an ideal solution to keep pace. A software-defined modular instrumentation approach is the most ideal solution, providing the flexibility, user empowerment, and speed to adapt to the changing landscape of military radios and deliver the high-performance testing required.

This article was written by Norman Kirchner Jr., Senior RF Systems Engineer at National Instruments, Austin, TX. For more information, Click Here 

RF & Microwave Technology Magazine

This article first appeared in the June, 2011 issue of RF & Microwave Technology Magazine.

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