June 26, 2011
June 26, 2011
June 29, 2011
22.1130.1 - 22.1130.10
Orthogonal Frequency Division Multiplexing (OFDM) Development and Teaching PlatformThe computer engineering technology program has a very robust course sequence in digital andembedded systems design with a strong emphasis on hands-on experience for the students. Thestudents in our program are currently being exposed to digital design using hardware descriptionlanguages (HDL) such as VHDL, as well as software and firmware code design using high-levellanguages such as C and C++.One industry trend is to use Field Programmable Gate Arrays (FPGA) as hardware verificationplatforms for digital communications systems and digital signal processing systems. Thesesystems will most likely are targeted to an Application Specific Integrated Circuit (ASIC) due totheir final cost under volume production.Orthogonal Frequency Division Multiplexing (OFDM) is a modulation technique that is not new,but the technology required for its implementation has evolved over the last ten years to make itsimplementation feasible. Nowadays a large number of communication standards (e.g. IEEE802.16e (WiMax), 3GPP LTE, DVB-H, 802.11a and 802.11n) have adopted this modulationtechnique due to its performance advantage over other communication techniques.The heart of the OFDM modulation technique lies in the use of the Fast Fourier Transform(FFT), which is a very structured algorithm to convert a time domain signal into the frequencydomain and by taking the inverse FFT can be transformed back to the time domain. Theapproach in OFDM systems is to have digital information modulated by traditionally a phasemodulation technique such as quadrature amplitude modulation (QAM). This modulationprocess maps a series of bits into symbols. The number of used symbols for each OFDM frame istraditionally a power of two. Then the inverse FFT is performed on the frame to convert it backinto a time domain representation that can be further sent through the transmitter chain andthrough the antenna. On the receiver side the process is reversed and the QAM symbols areregenerated and demodulated. This sounds pretty straightforward but there are many subtledetails that could be investigated in terms of the effects of: distortion, channel noise, multipathpropagation, fading, Doppler shift, synchronization, etc.The objective in the development of this platform is to allow the students to work in relatedcourses in particular signal processing blocks at a different level of abstraction. These could bedivided into: • Algorithmic: Use of Matlab/Simulink and Altera DSP Builder to create a system that can be selectively run on the hardware platform. This could be the objective of a digital communications or digital signal-processing course. • Electronic System Level Design: Convert an architectural untimed C to Register Transfer Logic (RTL) using Mentor Graphics CatapultC, or equivalent tool. This could be the objective of an advanced digital systems design course that could allow the student to explore different architectures and trade-offs in terms of area, power and speed. • RTL Level: Design an efficient architectural level description of the algorithm implemented in an HDL language. This could be the objective of a regular course where different blocks in the transceiver chain could be specified, designed and their performance measured against a reference model. The outcome of the implementation of this development platform should be stable OFDMreference system that will allow the students to interact at different levels of abstraction,obtaining a vision of a whole modern digital communications system and how the changes madeby them could have an impact on the overall system performance. Further reports will begenerated once the platform is completed and under assignment to different courses. Theexperience of a real implementation will allow the students to separate the theory from theimplementation and to evaluate the real effects on an algorithm’s hardware implementation.
Mondragon-Torres, A. F., & Kommi, M. N., & Bhattacharya, T. (2011, June), Orthogonal Frequency Division Multiplexing (OFDM) Development and Teaching Platform Paper presented at 2011 ASEE Annual Conference & Exposition, Vancouver, BC. 10.18260/1-2--18656
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