UC Berkeley Develops Communications Lab with NI Tools
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In a novel initiative to increase interactive learning, professors at the University of California at Berkeley tightly integrate communication theory classes with real-world wireless communication signals and systems. Traditionally, equipment required for communication laboratory classes is expensive, complex, and inflexible, making it difficult for universities to provide students with a meaningful learning experience. Dr. Ali Niknejad, an electrical engineering and computer science professor at Berkeley, overcame this challenge by developing a laboratory class in which students learn wireless communications using a software-defined architecture based on National Instruments LabVIEW and PXI modular instrumentation. In this class, students design their own 900 MHz front-end software radio, validate their system with hardware, and characterize their radio.
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Figure 1. This diagram illustrates how UC Berkeley professors use NI LabVIEW and PXI custom hardware to teach wireless communications applications.
The cost-effective NI LabVIEW and PXI platform streamlines experimental development in any wireless communications class by simplifying design with an intuitive graphical environment and tight integration with both standard PXI modular instrumentation and custom student-designed hardware.
Simulating Code, Modulation, Transmission, and Reception in LabVIEW
With the flexibility of LabVIEW and its included analysis, signal processing, and visualization tools, students can simulate an entire wireless communications system in software. The National Instruments Modulation Toolkit for LabVIEW is a tool for developing communication systems in which professors and students can experiment with coding and modulation configurations in software while adding impairments such as DC offset, IQ gain imbalance, and fading profiles to test theoretical signals and systems. Once they complete a design, it can be modified to target hardware devices to validate theory with experimental data.
Figure 2. A UC at Berkeley student uses NI LabVIEW and PXI interactively in the wireless lab.
Transmitting and Receiving Wireless Signals with PXI
A large part of creating a wireless lab for students is implementing hardware and software radios. To create a software radio, Dr. Niknejad uses LabVIEW to modulate and demodulate radio signals. He implements the baseband TX/RX components in LabVIEW and PXI – using the NI PXI-5421, a 100 MS/s 16-bit arbitrary waveform generator, and the NI PXI-5620, a 64 MS/s 14-bit frequency domain digitizer. The PXI-5421 and PXI-5620 are ideal for communication applications because they combine high resolution and deep memory to facilitate the generation and digitization of long, precise aperiodic waveforms. In addition, the NI PXI-5610 and PXI-5600 modules can respectively upconvert and downconvert the baseband signals to frequencies up to 2.7 GHz. Students can create a complete, software-defined transceiver by combining the generator with the upconverter and the digitizer with the downconverter.
Interchanging Custom and Common Radio Components for Test and Validation
Each student in the EECS 142 course at Berkeley has the opportunity to build his or her own high-frequency circuits using single-transistor building blocks on a printed circuit board. An important part in validating radios includes testing student-built custom hardware, including transmitters, amplifiers, antennae, and more. Students can use LabVIEW and PXI to easily interchange standard/common and custom hardware to test their entire system. Dr. Niknejad also can control the hardware radio built by his students using the flexibility of LabVIEW. In addition, with the wide real-time bandwidth and highly stable time base available on PXI RF and communication modules, students can characterize the linearity, phase noise, tuning range, noise figure, and bit error rate of their radio.
Figure 3. This diagram is an example of a receiver created by students at UC at Berkeley using NI LabVIEW and PXI.
Improving the Learning Experience
Cost-effective National Instruments LabVIEW and PXI modular instrumentation solutions give professors and students the opportunity to have a meaningful learning experience, taking communications theory in laboratory classes to new levels. The modularity of the platform opened the door for multiple experiments and study phenomena – such as electromagnetic wave transmission and propagation, the effects of multipath fading and interference, and the comparison of digital and analog modulation and encoding on a communications system – all on a single platform.
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This article first appeared in the Q2 2006 issue of Instrumentation Newsletter.
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