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Computationally Simple OFDM Todor Cooklev IPFW Wireless Technology Center cooklevt@ipfw

Computationally Simple OFDM Todor Cooklev IPFW Wireless Technology Center cooklevt@ipfw.edu. Introduction Simple OFDM Preliminary Results Conclusions and directions for future research. Presentation Overview. Conventional OFDM.

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Computationally Simple OFDM Todor Cooklev IPFW Wireless Technology Center cooklevt@ipfw

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  1. Computationally Simple OFDM Todor Cooklev IPFW Wireless Technology Center cooklevt@ipfw.edu

  2. Introduction Simple OFDM Preliminary Results Conclusions and directions for future research Presentation Overview

  3. Conventional OFDM Conventional OFDM is based on the discrete Fourier transform; IFFT performs multicarrier modulation

  4. Conventional OFDM receiver: FFT performs demodulation

  5. Simple OFDM idea • Can we simplify the DFT/FFT operations? • What would be the system performance • Can we simply the algorithms further? • Make a detailed comparison

  6. The DFT, implemented by the Fast Fourier Transform algorithm (FFT), can be simplified via the rounded sine and cosine functions Any number of quantization levels can be used 5-level: -1, -0.5, 0, 0.5, 1 9 level: add -0.75, -0.25, 0.25, 0.75 to the above Rounded DFT idea

  7. Definition of standard DFT: Using the relationship: the rounded DFT is derived with substitution as follows: Simple OFDM k = 0,1,…,N – 1 k = 0,1,…,N – 1

  8. Two possible inverses • Approximate - the conjugate transpose • Exact – possible, but in general is not multiplierless

  9. Simulation • Models of conventional OFDM were created to compare with standard OFDM performance characteristics • Many simulations have be run using the following key parameters: • 64 parallel data channels (64 point DFT/RDFT) • QPSK and 16 QAM modulation schemes • Quantization levels of 5, 9 and 17 • Pairing of IFFT with RDFT

  10. Preliminary Results Comparison of conventional OFDM bit error rate with 5 level rounded system

  11. Preliminary Results Comparison of conventional OFDM bit error rate with 9 level rounded system

  12. Preliminary Results Comparison of conventional OFDM bit error rate with 17 level rounded system

  13. Preliminary Results Comparison of conventional OFDM bit error rate with 5 level RDFT paired with standard IFFT

  14. Benefits • Currently ASICs are used to implement OFDM • A dedicated OFDM chip (ASIC) contains multiple FFTs • Reduction in chip area • Make possible reconfigurable hardware implementation (FPGA) or even an entirely software implementation (on a DSP or GPP)

  15. What we have achieved • Built a software simulation of the new idea • The rounded transform leads to viable OFDM communication systems at specific quantization levels • With performance that approaches conventional OFDM systems • With reduced computational complexity

  16. Future Research • Investigate system performance when faced with carrier offset error • Investigate system performance when faced with inter-symbol interference (short cyclic prefix) • Apply the results to systems with multiple antennas • Develop new and simplified algorithms • Investigate the implementation in greater detail

  17. Thank you!

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