The ever-growing need for smart wireless devices, high-speed/high-throughput telecom systems, and overall RF and digital systems is increasing the demand for software-defined radio (SDR) to levels never seen before.
The ever-growing need for smart wireless devices, high-speed/high-throughput telecommunication systems, and overall RF and digital systems is increasing the demand for software-defined radio (SDR) to levels never seen before. These applications vary greatly in terms of performance and cost, as well as size, weight, and power (SWaP). In this scenario, the test and measurement (T&M) industry is crucial in the development process of new devices to ensure that wireless equipment operates properly and meets the required standards and qualifications. Fortunately, SDRs provide a high level of flexibility and programmability, not only for the application but for the T&M process itself, reducing the amount of equipment required and allowing the same device to perform several different functions without hardware modification.
T&M is a well-known process of RF development, required for various design stages of new devices, including proof of concept, pre-simulation, simulation, prototyping, and validation/certification for market release. A major challenge in T&M design is compliance with the large variety of wireless devices that range from robust aerospace and defense systems to mobile health-care and agriculture solutions. In these applications, T&M equipment is required to simulate different RF systems through the testing and measuring of:
In this article, we discuss how SDRs can help the T&M market to keep up with the fast rate of technology development in the wireless industry. We discuss how SDRs can perform several functions found in traditional testbenches, from signal generators to spectrum analyzers, while providing much more flexibility and reconfigurability than conventional RF test equipment. Without any hardware modification, SDRs can be adapted to work with different radio protocols, modulation schemes, frequencies, and bandwidths, all of which are continuously evolving in the RF industry and illustrate the power and long-lasting utility that SDRs provide for T&M engineering.
What is an SDR?
SDRs are essentially transceivers that perform most of the radio and signal-processing functions in the software domain, implementing only the analog hardware necessary for antenna coupling, amplification, and filtering. The analog portion of the SDR is called the radio front end (RFE), which contains all the Rx and Tx channels of the design, operating under a very wide tuning range. The highest-performance SDRs in the market provide RFEs with 3 GHz of instantaneous bandwidth over multiple independent channels, each one with a dedicated digital-to-analog converter/analog-to-digital converter for multiple-input multiple-output (MIMO) operation. The digital back end operates on the digitized signals, performing all on-board digital-signal–processing functions necessary for RF applications, including modulation/demodulation, up-/down-converting, and data packetization over Ethernet optical links. 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 throughput is critical. The highest-bandwidth SDRs in the market provide backhaul throughput of 4× 100 Gbps over qSFP+ transceivers that can be connected to the host architecture via network interface cards, which is perfect for any high-data–rate testing. Figure 1 shows the general SDR structure being applied in T&M.
The combination between the software-based operation and native host connection in SDRs allows the implementation of open-source and custom software with readily available T&M functions. This significantly increases the range of functionalities of the equipment by taking advantage of built-in signal-processing and RF functions and libraries of the software, without having to develop low-level coding and graphical interfaces. In this context, GNU radio is the best example for RF applications, with built-in functions including frequency spectrum, spectrum waterfall plots, constellation diagrams (important for DC offset and IQ phase imbalance), oscilloscope plots, and waveform generation. It also provides ready-to-use algorithms to calculate important RF parameters, such as SFDR, noise, and dynamic range. By applying only one MIMO SDR with GNU radio, T&M engineers can significantly decrease the equipment count in a test and centralize all RF configuration, which further reduces costs, time, and human error.