Interview with Abolfazl Razi

Featured Engineer

Abolfazl Razi

Abolfazl Razi - PhD Student at the University of Maine, ECE Department, WiseNet Lab

Image: I am sitting in front of a small model of an inflatable lunar habitat. We use it to put our sensors for shape monitoring. We’ve got a bigger one in another building, you can check it out.

How did you get into electronics/engineering and when did you start?

I have always been interested in mathematics because to me, it is the only science completely based on solid proofs—one follows from another. Most physical phenomena, hypothesizes and theories, are not understandable and provable without the magic of mathematical equations. When I was in high school, I got the book “Schaum’s Mathematical Handbook of Formulas and Tables” as a gift. I studied this book and got familiar with new topics like derivatives and integrals. This book made me so eager to learn math theory and become more knowledgeable about these things. I also was very interested in assembling electronic kits like radio and led blinkers. While studying in high school, I realized how fantastically an electrical phenomenon can be described by mathematical equations. All of this led me into the field of electrical engineering, so I chose it as my academic major, and as time passes I love it more.

What are your favorite hardware tools that you use?

I have used different hardware based on different projects’ requirements. This spans a wide category from a tiny smart card reader to a huge mobile switching center. Recently I am working with Xilinx Virtex-4 FPGA board to design a new interrogator system for passive sensors. It is a very multipurpose and powerful board and at the same time easily programmable by MATLAB DSP tools. I am also very lucky to have access to a powerful and expensive SPIRENT SR5500 wireless channel simulator in our lab that helps me simulate different cellular systems like GSM, WiMAX and LTE. I can examine the performance of various transmission techniques and coding schemes on wireless radio channels. Sometimes it shows us how far could be the optimistic performance of the codes developed in MATLAB under idealistic assumptions from what is really happening in the wireless channels. This instrument makes a good connection between the theory stuff we learned in university and the practical world of industry.

What are your favorite software tools that you use?

Maybe I’d better tell you my second favorite software, since I think the most popular software among all communication engineers is definitely MATLAB, and I am not an exemption. I use MATLAB mostly to simulate communication systems. I also use different software in different projects. I prefer the VB family for general programming because of its capabilities and simplicity. I recommend it for anyone who wishes to enter the programming world. I developed a professional software built to control a company’s call center using VB6. I also developed a SIMCARD test suite under VB.NET. I am a c++ fan too, and have developed a charging entity of a PABX switching center. I have used other software like TEMS Investigation, GemXplore, and Mentum planet v4.5 when I was working on cellular networks. Recently I have used 4nec2 software for array antenna modeling, which is a very powerful software to easily model any wire-based antennas. I like to try different software and can’t imagine how hard it would be to research without it.

What is the hardest/trickiest bug you have ever fixed?

I believe every problem looks easy just after it is solved! One very challenging problem I faced goes back to three years ago when I was working for a mobile operator. We realized that some customers were being pushed out of the network and couldn’t make phone calls. Two technical groups had worked on the problem without any progress before a team of two other experts and I got into the project. We started very time-consuming tests and traced calls and mobile activities in the region at three different levels. One test involved checking the signaling links between a radio base transceiver station (BTS) and the network, which was called A-Interface using a network analyzer. Another test was monitoring Air-interface between the BTS and mobile stations (MS) with TEMS Investigation toolbox, and I was checking the interface between the mobile equipment (ME) and the SIMCARD using PC/SC debugging tools. At last our teamwork paid off and we found the signaling problem that was due to a wrong error code that MSs were receiving from an adjacent local mobile network. The code was “No PLMN Access” while it had to be “PLMN prohibited.” This wrong signaling message caused the FPLMN file in the SIMCARD to be filled with a wrong value and prevented MSs from making calls. I always remember this successful mission that solved an annoying problem for many customers in that area.

What is on your bookshelf?

Most of my books are Ebooks in my computer. On my bookshelf, I have a few reference books in my research area. Two of them that I most frequently need to read, are Tomas Cover’s book on Information Theory, and Costello’s on Coding Theory. I recently borrowed a book from the library titled “Surface Acoustic Wave Devices for Mobile and Wireless Communications” written by Colin K. Campbell. This book has been very useful for me. My experience says that reading the right book that teaches the fundamentals is always a necessary step when getting into a new area of research.

Do you have any tricks up your sleeve?

My first trick is asking somebody who may know the answer before endlessly fighting a problem. This way we can spend our time more efficiently. The second point I always remind myself is that the computers are developed to work fine and almost error-free. So, I very often try to shift my math or engineering problems into the computer world by means of simulation. Sometimes, I compare my results on a piece of paper with the simulation results step by step. It is a time-consuming process and needs patience, but usually it works and helps me to localize the issues in my problems.

What has been your favorite project?

My recent favorite project is dealing with interference effect in passive wireless sensor networks (PWSN). Passive sensors are widely used to sense various parameters like temperature, humidity, and stress, where battery-run active sensors do not operate well due to harsh conditions. The passive sensors we are using are reflective delay lines implemented on Surface Acoustic Wave (SAW) devices.

Can you tell us more about the Surface Acoustic Wave (SAW) devices?

These devices are composed of an antenna, an interdigital transducer (IDT), and bunch of reflectors, all printed on a piezoelectric substrate like YZ-LiNbO3. To utilize these devices, an electromagnetic wave is radiated by an interrogator system. The electromagnetic wave is received by the antenna and is converted to an acoustic wave by the IDT, and is propagated through the device surface. The wave is partially reflected back by the reflectors and is radiated back to the interrogator system by the same antenna. The reflected wave carries information about the sensing parameter, in our case temperature, as well as the sensor’s identity defined by the reflector patterns.

In this project we try to develop an efficient algorithm to extract this information by analyzing the reflected wave. The goal is to achieve higher accuracy in the range of operation and to increase the number of sensors in a single-interrogator system. The difficulty of employing traditional signal processing techniques is that these devices are passive in nature and all the intelligence should be moved to the interrogator side. Also the signal level is very low compared to the active battery-powered sensors that makes the analysis even more challenging. I think we are still in the beginning, and there is still much to be done.

Do you have any note-worthy engineering experiences?

I remember a fun trick I learned from one of my professors when I was an undergraduate. In Microwave circuit design lab, sometimes the high frequency circuits like oscillators and RF filterers were not working properly even after comprehensive checks and careful analysis. Our professor taught us a very easy trick to use as a last step when every regular test looked disappointing. He said to just put your finger on the back of the electric board and move it slowly and check the output signal carefully. When you obtain the desired signal, just solder a 20 to 100 pico Farad capacitor where you have put your finger on the board. It was very surprising to us to see that this trick was working fine for some circuits.

What are you currently working on?

Currently I am working on developing interference reduction algorithms for passive wireless sensor networks. Our projects are financially supported by NASA.

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