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A software-defined radio system is a radio communication system in which certain hardware components are implemented in software. These hardware components include filters, amplifiers, modulators, and demodulators. Because these components are defined in software, you can adjust a software-defined radio system as needed without making significant hardware changes. With the increase in wireless communications use, as well as changes in wireless standards and the systems used to test and prototype for compliance with these standards, industries that serve a variety of changing radio protocols, such as the military and cell phone industry, are turning to software-defined radio.
Table of Contents
Introduction
Increasingly used for digital signal processing tasks, field-programmable gate arrays (FPGAs) are also well-suited for interfacing with high-speed peripherals such as analog-to-digital and digital-to-analog converters. The NI PXIe-5641R RIO IF transceiver with an onboard Xilinx SX95T Virtex-5 FPGA offers 640 multipliers, more than 14,000 slices, and nearly 100,000 logic cells, which is enough to handle the complex digital signal processing requirements of today’s high-speed digital protocols. A commercial off-the-self (COTS) FPGA-enabled software-defined system is an ideal platform for implementing a wide range of RF applications. Because you can reconfigure the NI PXIe-5641R without new board design work, you can easily retool the same products for future applications.
FPGA-Enabled Software-Defined Radio
By combining the NI PXIe-5641R with the NI PXI-5600 downconverter and NI PXI-5610 upconverter, you can create an FPGA-enabled software-defined radio on the PXI platform covering frequencies from 250 kHz to 2.7 GHz with 20 MHz of real-time bandwidth. The NI PXIe-5641R features 14-bit, 100 MS/s analog-to-digital converters (ADCs) with built-in 20 MHz bandwidth digital downconverters, and 14-bit, 200 MS/s digital-to-analog converters (DACs) with built-in 20 MHz bandwidth digital upconverters. This architecture efficiently delivers I/Q data to the Virtex-5 SX95T FPGA on the module for analysis, demodulation, and signal processing tasks using the NI LabVIEW FPGA Module, so you can create your own unique software-defined radios. With LabVIEW and LabVIEW FPGA configurability, the possibilities of this radio system are limited only by the size of the FPGA. You can use the NI PXIe-5641R to prototype and implement new communication protocols and perform real-time event detection. In addition, you can import preexisting FPGA IP into LabVIEW FPGA or use the LabVIEW FPGA RF Communication Library, which offers a set of fixed-point RF communications IPs for programming your NI PXIe-5641R. A recommended FPGA-enabled software-defined radio system is shown in Figure 1.
Figure 1. FPGA-Enabled Software-Defined Radio Recommended by National Instruments
Reconfigurable I/O IF Transceiver
The NI PXIe-5641R features intermediate frequency (IF) inputs and outputs for interfacing with analog upconverters and downconverters to acquire and generate RF signals. It also has a powerful FPGA that is programmable with LabVIEW and capable of performing complex modulation and signal processing in hardware at high rates with low latency, both requirements of software-defined radios.
Figure 2. NI PXIe-5641R RIO IF Transceiver
PXI-5600 Downconverter
This downconverter accepts RF signals from 9 kHz to 2.7 GHz with up to 20 MHz bandwidth and then downconverts them to 15 MHz IF signals, which is optimal for interfacing with the NI PXIe-5641R.
Figure 3. NI PXI-5600 2.7 GHz Downconverter
PXI-5610 Upconverter
This upconverter accepts IF signals from the output of the NI PXIe-5641R at 25 MHz with up to 20 MHz bandwidth and then upconverts them to RF signals from 250 kHz to 2.7 GHz.
Figure 4. NI PXI-5610 2.7 GHz Upconverter
PXI Controller
The PXI controller is the CPU of the PXI system. LabVIEW provides a unique and easy-to-use graphical programming environment for developing RF applications and offers an ideal multicore processor programming environment for creating parallel algorithms that take advantage of multicore processors. Moreover, PXI Express modular instruments enhance this benefit because they take advantage of the high data transfer rates possible with the PCI Express bus. Two specific applications that benefit from multicore processors and PXI Express instruments are multichannel signal analysis and inline processing (hardware in the loop).
Figure 5. NI PXIe-8106 Controller
Software
The NI PXIe-5641R is programmed with the LabVIEW FPGA Module. LabVIEW FPGA is distinctly suited for FPGA programming because it clearly represents the parallelism and data flow inherent in FPGAs. With LabVIEW FPGA, you can create custom measurements, embed your digital signal processing algorithms, and perform inline demodulation or modulation without expertise in low-level hardware description languages or board-level design.
LabVIEW software delivers a unique and easy-to-use graphical programming environment ideal for multicore processor programming. With this software, you can create parallel algorithms that take advantage of multicore processors.
Using the LabVIEW toolkits described in the next sections, you can extend the built-in capabilities of LabVIEW with powerful host-side tools (VIs) for analyzing, processing, and visualizing RF data.
NI Modulation Toolkit
This toolkit add host-side VI for signal generation, analysis, visualization, and processing of standard or custom digital and analog modulation formats. With this toolkit, you can rapidly develop custom applications for research, design, characterization, validation, and test of communications systems and components. Visit the NI Modulation Toolkit overview to learn more.
NI Spectral Measurements Toolkit
Take advantage of flexible host-side spectral measurement functions to measure parameters such as in-band power, adjacent-channel power, and occupied bandwidth. Visit the NI Spectral Measurements Toolkit overview to learn more.
NI LabVIEW Advanced Signal Processing Toolkit
Access powerful time-frequency analysis functions and create digital filters that run on the host or on the FPGA using the LabVIEW Digital Filter Design Toolkit, which is included with this toolkit. Visit the NI LabVIEW Advanced Signal Processing Toolkit page to learn more.
Conclusion
FPGAs are well-suited for prototyping and interfacing with communication systems. A COTS FPGA-enabled software-defined radio system is an ideal platform for implementing a wide range of RF applications. As your radio protocol changes, you can reconfigure the NI PXIe-5641R without the need for new board design and easily retool the same products for future applications.
Additional Resources
Reconfigurable I/O Intermediate Frequency Transceivers
NI PXIe-5641R Product In-Depth
Spectral Monitoring with the NI PXIe-5641R
Spectral Monitoring Demonstration
Introduction to Programming Using Asynchronous Wires
NI PXIe-5641R RIO IF Transceiver Example: Using the IF Transceiver with an NI PXI-5600 Downconverter
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