Communications Technology Learning Opportunities Using LabVIEW-Controlled RF Equipment

Transcription

1 Communications Technology Learning Opportunities Using LabVIEW-Controlled RF Equipment Gale R. Allen, Ph.D. Department of Electrical and Computer Engineering and Technology College of Science, Engineering and Technology Minnesota State University, Mankato Mankato, Minnesota Introduction In Spring 2008 two sets of LabVIEW-controlled National Instruments (NI) RF equipment were installed in the ECET Department s communications laboratory. The ability to rapidly generate a variety of signal generation and signal processing functions using LabVIEW programming tools will provide increased student learning opportunities in analog and digital communications courses. Communications laboratory and course material on modulation, encoding and related topics is being developed using the two stations of National Instruments equipment. Local industry is participating in contributing applications for laboratory experiments. In addition to providing new laboratory experiences, the equipment and software tools will be used to enhance the current antenna development, radio receiver, and other analog/digital communications experiments. Working with the LabVIEW RF software tools involves the opportunity for students to learn much more about programming LabVIEW beyond the basics. The addition of National Instruments LabVIEW-controlled RF equipment was made possible through a combination of funding from the Minnesota Center for Excellence in Manufacturing & Engineering, a Minnesota State Colleges and Universities program and a very significant contribution through National Instrument s education program. The Center was established by a state initiative in 2005 and consists of seven institutions: Alexandria, Anoka, and Hennepin Technical colleges, Normandale Community College, Northeast Higher Education District, South Central College, and Minnesota State University Mankato which serves as the lead institution and headquarters for the center. Additional funding was provided by the Department of Electrical and Computer Engineering and Technology. The ECET communications laboratory is used to support courses offered in engineering programs and technology programs. The new equipment will be used in several different courses. As a start the author is working to integrate the equipment into the technology program digital and analog courses. The results of the technology program efforts will be applied to the engineering courses.

2 Communications Laboratory Equipment Nine nearly identical stations are available in the communications laboratory. The equipment in each station includes a spectrum analyzer, oscilloscope two function generators, counter, multimeter, and Degem modular unit. Figure 1. Communications Lab Station (1 of 9). Several other pieces of equipment are available in the lab including three Tektronix arbitrary waveform generators, several RF signal generators, and a network analyzer. An electricallyshielded room is part of the laboratory. Technology program students perform a variety of experiments and activities in the lab including building and testing communications circuits, observing signals with the spectrum analyzer and oscilloscope, and developing antennas (for example as in Figures 2 and 3). The Degem units shown on the left side of the bench in Figure 1 are used for a few experiments. Many different types of Degem analog and digital modules are available in the lab. Figure 2. Some Communications Test Equipment - SWR meter, Arbitrary Waveform, RF Figure 3. Students Testing AM/FM Receiver

3 Two stations of National Instruments LabVIEW-controlled RF equipment are available in the communications laboratory (Figure 4). Figure 4. Two NI RF Stations Recently Installed in ECET Communications Lab Each station has a signal generator (Figure 5) and a signal analyzer (Figure 6) and a second digitizer. These are housed in the NI PXI-1045 chassis. Each station is supported by a highperformance computer. Figure 5. NI PXI GHz RF Vector Signal with Digital Upconversion Figure 6. NI PXI GHz RF Vector Signal Analyzer with Digital Downconversion

4 Some other examples of analog and digital communications experiments are shown in Figures 7 and 8. In the communications analog technology course students design, simulate, build, and test antennas as part of their laboratory work 1. Figure 7. Analog Communications Technology Antenna Testing S08. Student Teams with Their Yagi Antennas. In the digital communications technology course students build and test several types of data communications systems including those shown in Figure 8. Pulse Amplitude Modulation Time-Division Multiplexing Pulse-Width Modulation Fcn Gen PLL IC Exclusive 15 khz OR square reference wave input Fcn Gen 1.5 khz sine wave Synchronous Detection & DSP Frequency Shift Keying Sine Wave Sine Wave MM74HC4051N-ND 2000 Hz Multiplexer IC 3000 Hz 2 Pulse Counter IC + - I + - Q DM74LS169AN-ND Figure 8. Examples of Experiments Recently Performed in an ECET Digital Communications Course

5 Adapting Results from Other Universities and NI The process of integrating the NI signal generation & analysis equipment and software into the communications courses involves many significant opportunities and challenges. One approach is to adapt the work being done in other universities. NI s RF equipment is being used in the classroom and in research efforts at several Universities as described in the references 2 thru 6, provided by NI. For example a spectrum experiment exploration experiment developed by Professor George Papen 2 was modified and used in the analog communication course in S08. National Instruments provides many education resources. These include webcasts, source-code programs, and training tools. Some examples of NI modulation, measurement, filter, and signal processing experiments are shown in Figure 9. Many of the experiments can be run in simulation mode as well as with NI RF hardware. Amplitude Modulation Phase Modulation Pulse Amplitude Mo Quadrature Amplitude Modulation Orthogonal Frequency Division Multiplexing Time Division Multiplexing Pulse Width Mo Frequency Shift Keying Phase Shift Keying Differential Phase Shift Keying Offset Quadra Phase Shift Ke Figure 9. Examples of NI RF Labs & Exercises. Currently NI provides 22 simulation-based labs and 12 hardware-based labs Most the RF simulations and hardware laboratories include descriptions of a series of task descriptions and expected results; for example, Frequency Shift Keying as indicated Figure 10. Figure 10. National Instruments FSK Experiment task descriptions and expected results.

6 Integrating NI RF and LabVIEW into an Existing Experiment The analog and digital laboratory experiments that students have been performing in ECET communications courses are being modified to incorporate the new NI RF tools. For example the current FSK circuit lab experiment was enhanced by adding steps involving the NI simulation-based lab and use of the NI RF equipment. A summary of the lab is outlined below. 1) Students operate the NI simulation-based FSK program and observe the effects of changes in the control variables (Figure 11). Students use the pre-built vi program provided by National Instruments. Perhaps at later time they will develop their own program. Build vi No. of frequencies FSK deviation Symbol rate Figure 11. Frequency Shift Keying Simulation (figures were taken from National Instruments RF Lab Experiment Document) 2) Students use function generators and two simple IC s to implement a two-frequency FSK circuit (Figure 12). The circuit switches between the two frequencies such as would be done if a bit pattern of was input to an FSK circuit. An oscilloscope and a speaker are used to monitor the results. Sine Wave Sine Wave 2000 Hz 3000 Hz Pulse MM74HC4051N-ND Multiplexer IC 2 Counter IC DM74LS169AN-ND Figure 12. Frequency Shift Keying Digital Communications Laboratory Experiment

7 3) Students incorporate NI RF equipment in the experiment. The RF signal generator is substituted for one of the signal generators. The Signal Analyzer is added to the equipment configuration. Students observe signal spectra as frequencies are varied. 4) The NI RF equipment is substituted for the FSK circuits. Students use the NI RF hardware control program (Figures 13 and 14) and observe results as they vary number of frequencies, amount of deviation, and symbol rate. Figure 13. NI FSK Hardware Experiment LabVIEW Front Panel Figure 14. NI FSK Hardware Experiment LabVIEW Block Diagram

8 Software Defined Radio (SDR) DSP Experiment The NI RF equipment is planned to be used to enhance a DSP experiment that involved amateur radio signals, Fourier Transform and digital filtering 7. In four papers Gerald Youngblood 8,9,10,11 provided an excellent description of the Software Defined Radio technology. The experiment involves synchronous detection of radio signals. The incoming radio carrier and information signal are mixed with the output of an oscillator whose frequency is set equal to the carrier frequency. Four voltage samples of the incoming carrier signal are taken during each period of the carrier. Differential amplifiers are used to produce I & Q signals which contain amplitude and phase information (Figure 15). Synchronous detection and I & Q 40-m circuit kits were assembled by students in a few hours (Figure 16). The picture of radio signals processed SDR software in Figure 17 was provided by Flex-Radio. The signal display obtained using the kit was not as good as that shown due low signal strength, but the kit was shown to be functional. Synchronous Detection & DSP + - I + - Q Figure 15. Concept of SDR Synchronous Detection Figure 16. Assembled SDR Detector Kit Figure 17. PowerSDR GUI From Flex-Radio, Inc. Two ECET graduate students have started to develop LabVIEW programs to perform the PC processing functions. These include inputting the I & Q data, windowing, FFT, filtering, and inverse FFT. Conclusion The capabilities of the National Instruments RF LabVIEW equipment are impressive. The work done at other universities and the resources provided by NI are a great benefit to the new user. No doubt the equipment will provide significant new learning opportunities for engineering and technology students. Much can be done using the existing NI software tools, but the process of creating new programs seems to involve significant learning. Many training resources are available. Some methods of integrating the equipment into the laboratory have been described and these will be followed in the months ahead.

9 References 1. Hands-On Hardware and Simulation Experiences Used To Improve An Analog Communications Technology Course, 2007 ASEE North Midwest Regional Conference, Michigan Tech, Houghton, MI, September 20-22, University of California (San Diego). Professor George Papen teaches a digital communications labs with NI LabVIEW and NI RF modular instruments. The course web site includes lab assignments, lecture slides, and more. Retrieved from 3. University of Illinois. Professor Christopher D. Schmitz teaches digital communications labs using LabVIEW. The course web site includes lab exercises, projects, handouts, and more. Retrieved from 4. UC Berkeley. Professor Ali Niknejad s students design their own 900 MHz front-end software radio, validate their system with hardware, and characterize their radio. Retrieved from 5. Drexel and UT. Professors Robert W. Heath, Jr. and Professor Scott M. Nettles, University of Texas at Austin and Kapil R. Dandekar, Drexel University are prototyping a MIMO communication point-to-point link and implementing a MIMO ad-hoc network. Retrieved from 6. American University of Beirut. Professors Basem Nakhal, Tammam Sahli, and Ziad Zein are researching Wireless OFDM-based Real-Time Video Streaming. Retrieved from D5B?OpenDocument. 7. DSP Communications Experiment, 2008 ASEE IL/IN Section Conference, Engineering Education at the Crossroads, Putting Dialogue Into Practice, Rose-Hulman Institute of Technology, Terre Haute, Indiana, April 3-5, G. Youngblood, A Software Defined Radio for the Masses: Part 1, QEX, Jul/Aug 2002, pp G. Youngblood, A Software Defined Radio for the Masses: Part 2, QEX, Sep/Oct 2002, pp G. Youngblood, A Software Defined Radio for the Masses: Part 3, QEX, Nov/Dec 2002, pp G. Youngblood, A Software Defined Radio for the Masses: Part 4, QEX, Mar/Apr 2002, pp Biographical Information Professor GALE R. ALLEN, Ph.D. held engineering and management positions in companies in the Minneapolis-St. Paul area for many years and in 2004 became a member of the faculty at MSU, Mankato. He is currently teaching and working to improve education in electronics, communications, and industrial automation. He is a Senior Member of IEEE and is active in amateur radio. gale.allen@mnsu.edu