The ever-growing need for intelligent wireless devices, high-speed / high-throughput telecommunications systems, and RF and digital systems in general is driving the demand for software-defined radios (SDR) to unprecedented levels. These applications vary greatly in performance and cost, as well as in size, weight and power (SWaP). In this scenario, the test and measurement (T&M) industry is key in the process of developing new devices to ensure that wireless equipment is functioning properly and meeting the required standards and qualifications. Fortunately, SDRs provide a high level of flexibility and programmability, not just for the application but for the T&M process itself, reducing the amount of equipment required and allowing the same device to perform various functions without hardware changes.
T&M is a well-known RF development process, required for various phases of new device design, including proof of concept, pre-simulation, simulation, prototyping and validation / certification for release to market. A major challenge in T&M design is compliance with the wide variety of wireless devices ranging from rugged aerospace and defense systems to mobile solutions for healthcare and agriculture. In these applications, T&M equipment is needed to simulate different RF systems by testing and measuring:
- modulation / demodulation schemes
- Transmission (Tx) / Reception (Rx) performance parameters including path loss, noise, dynamic range and spurious-free dynamic range (SFDR)
- Antenna performance in terms of near / far field measurements, antenna coupling, range and radiation pattern
- Electromagnetic compatibility
- Various RF evaluation functions, such as spectrum, signal and network analysis
In this article, we discuss how SDRs can help the T&M market keep pace with the rapid rate of technology development in the wireless industry. We discuss how SDRs can perform several functions found in traditional test benches, from signal generators to spectrum analyzers, while providing much more flexibility and reconfigurability than conventional RF test equipment. Without any hardware modification, the SDRs can be adapted to work with different radio protocols, modulation schemes, frequencies and bandwidths, all evolving in the RF industry and illustrating the long-lasting power and utility that SDRs provide for T&M engineering.
What is a DSP?
SDRs are essentially transceivers that perform most of the radio and signal processing functions in the software domain, implementing only the analog hardware needed for antenna coupling, amplification, and filtering. The analog part of the SDR is called the radio front end (RFE), which contains all the Rx and Tx channels of the project, operating in a very wide tuning range. The highest performing SDRs on the market provide RFE with 3 GHz of instantaneous bandwidth on multiple independent channels, each with a dedicated digital-to-analog / analog-to-digital converter for multiple input multiple output (MIMO) operation. The digital back-end operates on digitized signals, performing all the integrated digital signal processing functions required for RF applications, including modulation / demodulation, up / down conversion, and data packaging over Ethernet optical links. The host connection is extremely important in SDRs for T&M, as it integrates the device with the rest of the system, especially if high data rates are critical. The highest bandwidth SDRs on the market provide 4 × 100 Gbps backhaul throughput on qSFP + transceivers that can be connected to the host architecture via NICs, which is perfect for any high-speed test. data transmission. Figure 1 shows the general structure of the DSP applied in T&M.
The combination of software-based operation and native host connection in the SDRs enables the implementation of open source and customized software with readily available T&M functions. This significantly increases the range of capabilities of the equipment by taking advantage of integrated signal processing and RF functions and software libraries, without having to develop low-level coding and graphical interfaces. In this context, GNU radio is the best example of RF applications, with built-in functions including frequency spectrum, spectrum waterfall diagrams, constellation diagrams (important for DC offset and IQ phase imbalance), oscilloscope and waveform generation. It also provides ready-to-use algorithms to calculate important RF parameters, such as SFDR, noise and dynamic range. By applying a single MIMO SDR with GNU radio, T&M engineers can significantly reduce equipment count in one test and centralize all RF configuration, further reducing cost, time and human error.
SDRs are also capable of working with UHD-based tools and software, which include custom programs based on Python and C / C ++. This greatly increases the range of possibilities for T&M systems, as both custom and proprietary software can be easily deployed to conform to different applications and protocols. For example, UHD-based SDRs can use GPS / GNSS simulation tools, based on different constellations of satellites, while addressing interference and jamming or even implementing readily available open source LTE / 5G base stations to test performance and compliance. One of the main benefits of UHD projects is their trend towards open source solutions, which reduces the need for proprietary licenses and fosters an active and resourceful community.
How are SDRs changing the face of T&M in various markets?
Thanks to their flexibility, programmability, inherent ability to work with multiple channels and high performance, SDRs are helping engineers solve many challenges in the T&M industry. For example, the acquisition of instantaneous wide bandwidths is desirable in several T&M applications, but is very difficult to implement in conventional RF systems, especially when working with high frequencies (e.g. millimeter waves). By providing software-based signal processing with very low latency, SDRs exhibit superior bandwidth capture performance over conventional systems, while also providing better flexibility due to their wide tuning range. State-of-the-art SDRs implement high-speed host communication over optical Ethernet links, enabling the streaming of large amounts of data to a server system or storage solutions, which is critical in 5G and IoT networks. The flexibility and programmability of the FPGA not only provides better performance than legacy radio systems, but allows the T&M system to be tuned to the device under test without any hardware changes, providing a versatile and robust solution.
SDRs also reduce the need for specialized hardware, as a single device can provide a wide range of functionality, including future custom functions. Their modular nature also allows for device customization to meet all application performance and SWaP requirements. T&M architectures can couple one or more SDRs to work cohesively, each providing a different function, such as signal generation and spectrum analysis. Each SDR is an RF world of its own, providing total customization in terms of waveform, modulation pattern and frequency. The higher throughput SDRs can store and transmit huge amounts of data, providing ready-to-use solutions for network applications. Standalone RF solutions typically have a fixed number of RF channels, which limits their applicability and increases the number of equipment. MIMO SDRs, on the other hand, provide a configurable amount of RF channels that can be used to perform different applications, such as waveform generation and signal reception, or to work coherently in antenna arrays, which is great for beamforming / beam steering. Conventional T&M systems have fixed functionality and cannot be easily upgraded, while SDRs can be programmed to work with the latest protocols and algorithms without any hardware changes.
The software-based nature of SDRs naturally makes them compatible with automated solutions, which require a certain level of embedded intelligence and host interface. Automated T&M systems offer numerous advantages over conventional solutions. In the laboratory, tests can be scheduled against predefined power thresholds and task sequences, reducing the chances of hardware damage and improving robustness and reliability by eliminating potential human error. In addition, it allows for remote test control, which is especially important for cooperation between laboratories and tests in distant locations with difficult access, such as cell towers in remote areas. The SDRs can also be preprogrammed to automatically transmit signals at specific time intervals, allowing the system to operate without human intervention.
In the 5G era, the fast-growing RF market requires robust and reliable T&M that can keep pace with continuous technological innovations in terms of wireless devices and communication protocols. Conventional T&M systems are stationary and disposable and cannot provide the flexibility and versatility needed to deal with this ever-growing evolution, which causes SDR-based equipment to become increasingly desirable in the T&M market. SDRs can perform several functions simultaneously through multiple RF channels which can be completely reconfigured to meet different waveform, frequency, sensitivity, modulation and latency requirements. They can be easily programmed to work with new protocols and algorithms, greatly improving device longevity. The SDRs are also compatible with open source software solutions for hosting with integrated T&M functions, including GNU Radio and UHD-based programs, improving their usability and reducing development time and costs.