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OFDM Transceiver using HDL

OFDM Transceiver using HDL. Paul pethsomvong Zach asal Dr. in soo ahn Dr. yufeng lu May 6, 2014. Outline. Project Overview Project Goal Project Description Orthogonal Frequency Division Multiplexing (OFDM) Communication Channel Effect Specifications Results Conclusion

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OFDM Transceiver using HDL

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  1. OFDM Transceiver using HDL Paul pethsomvong Zach asal Dr. in sooahn Dr. yufenglu May 6, 2014

  2. Outline • Project Overview • Project Goal • Project Description • Orthogonal Frequency Division Multiplexing (OFDM) • Communication Channel Effect • Specifications • Results • Conclusion • References

  3. Project Overview • Implements an Orthogonal Division Multiplexing (OFDM) communication system. Figure 1: Block Diagram

  4. Project Goal • To implement a complete OFDM system using field programmable gate arrays (FPGA) and VHDL hardware description language. The OFDM system can be reconfigurable.

  5. Project Description • The project is divided into three stages. • Stage 1: MATLAB/Simulink • Stage 2: FPGA board implementation with channel effects

  6. What is OFDM • Orthogonal frequency division multiplexing (OFDM) is a technique for transmitting digital data by using a large number of modulated carriers with sufficient frequency spacing so that the carriers are to be orthogonal. [2] • OFDM involves encoding data on multiple carrier frequencies, all of which are orthogonalto each other

  7. OFDM signal • g(t) is the complex envelope for OFDM signal. • fn(t) are orthogonal carriers.

  8. Orthogonal

  9. Complex Envelope Representation Figure 2: Complex Envelope Representaion

  10. Communication Channel Effects • Attenuation • Multipath • Delay spread • Doppler spread • Multipath fading • Inter-symbol interference

  11. Attenuation • Reduction in power density • Occurs as the distance from the source increases • absorption, free-space loss, refraction , etc.

  12. Multipath • Delay Spread • delay spread is caused by multiple paths with varying lengths. • Doppler Spread • Caused by different movements of various multipath reflectors

  13. Multipath Fading • Fading caused when different multipath reflectors move around slowly and appear and disappear. • Fading is due to the received signals cancelling each other out.

  14. Inter-symbol Interference (ISI) • One symbol interferes with subsequent symbols • Each symbol spreads in time, the pulse for each symbol may be smeared into adjacent symbol slots • Causes communication to be less reliable

  15. Applications & Advantages • Resistant to multipath fading • Low inter-symbol interference • Widely used in digital communication systems • Used in 802.11(a, g, n, ac), 4G, and LTE • 4G - 4th generation wireless communication • LTE- Long Term Evolution

  16. FFT/IFFT • This is the most important block in the OFDM communication system. • The FFT and IFFT are implemented using the Xilinx core generator.

  17. Cyclic Prefix • Trim and align data Figure 3: Cyclic Prefix

  18. Equipment • Genesys FPGA board • Xilinx • Diligent PmodDA2 • Diligent PmodAD1 Figure 4: Genesys FPGA board

  19. Specifications Figure 5: Specifications

  20. FPGA System Clock = 100 MHz • Symbol Rate Rs = 12.5 Msps • Data rate Rb= Rs · N = 50 Mbps • Bits per symbol N = 4 • Symbol time = 1/ Rs

  21. Stage 1 Simulink simulation • A single subcarrier carries data. Figure 6: 1 Frequency

  22. Stage 1 Simulink simulation • Two subcarriers carry data. Figure 7: 2 frequencies

  23. 32 subcarriers Figure 8: 32 frequencies

  24. Simulink Model

  25. Simulink Model

  26. Simulink Model

  27. Simulink Model

  28. Simulink Model

  29. Simulink Model

  30. Simulink Model

  31. Simulink Model

  32. Simulink Model • Model contains transmitter, receiver, and a Gaussian channel model. • Channel model • Y(t) = x(t)*h(t) • where x(t) is the transmitted signal, h(t) is the impulse response of the channel, and y(t) is the received signal.

  33. Simulink results Figure 9: Input and Output from Transceiver

  34. Stage 2: Implementation with channel effects • The transmitter and receiver are implemented on a FPGA board using VHDL. • Analog-to-digital converter (ADC) and digital-to-analog converter (DAC) modules are included. • Channel effects degrade the overall system performance.

  35. Figure 10: 16-QAM Transmitted

  36. Figure 11: 16-QAM Received

  37. Figure 12: Itransmitted and Ireceived

  38. Figure 13: Qtransmitted and Qreceived

  39. Conclusion • In this project, a complete OFDM transceiver has been designed, simulated and tested. • First the simulink model of OFDM transceiver was constructed and simulated • After verifying the simulink model, VHDL is used to describe the transceiver • The system has been implemented on a Virtex 5 FPGA board. • 16 QAM is used for baseband modulation. Some modules from the previous project was reconfigured and used for the project

  40. References • [1] Anthony Gaught, Alexander Norton, and Christopher Brady., “FPGA-based 16 QAM communication system”, Spring 2013. • [2]Leon Couch, Jr. “Analog and Digital Communication Systems”, 8th edition, 2012, Prentice-Hall.

  41. Questions

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