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An implementation of IEEE802.11a WLAN system using Subword Parallelism and its Quantization Error Evaluation

An implementation of IEEE802.11a WLAN system using Subword Parallelism and its Quantization Error Evaluation. Zaipeng Xie Muwu Hou Daphne J Franklin. Topics Covered. Motivation IEEE 802.11a Standard OFDM System Transmitter Receiver Quantization Error Analyses Simulation Results

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An implementation of IEEE802.11a WLAN system using Subword Parallelism and its Quantization Error Evaluation

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  1. An implementation of IEEE802.11a WLAN system using Subword Parallelism and its Quantization Error Evaluation Zaipeng Xie Muwu Hou Daphne J Franklin

  2. Topics Covered • Motivation • IEEE 802.11a Standard • OFDM System • Transmitter • Receiver • Quantization Error Analyses • Simulation Results • Conclusion • Future Work

  3. Motivation • Increasing demand of greater communication capacity • High bandwidth efficiency • Effects of multipath fading and delay alleviated • Frequency selective fading • Narrowband interference • Exploit sub-word parallelism to optimize IFFT/FFT implementations

  4. IEEE 802.11a Standard • Wireless LAN Standard • High Data Rates • IEEE 802.11b for 2.4GHz Operation • IEEE 802.11a for 5GHz Operation • Offers three time the operating bandwidth • Less susceptible to interference • Modulation : BPSK, QPSK, 16-QAM, 64-QAM • Coding rate : 1/2, 2/3 and 3/4. • Number of subcarriers is 52 • OFDM symbol duration : 4

  5. Block Diagram – OFDM System

  6. FFT algorithm • A radix-2 Cooley-Tukery FFT, recursive function, O(Nlog(N)) Function Y = fft(N,x) If N==1, Y = x; Else xeven=[x(0)x(2)… x(N-2)]; xodd=[x(1) x(3) … x(N-1)]; Yeven=fft(N/2,xeven); Yodd=fft(N/2,xodd); For k=0:N-1, Y(k)=Yeven(k mod N/2)+Wk*Yodd(k mode N/2); end end

  7. Quantization Error analysis • matlab Fixed point package • 6 bit input symbol

  8. imag imag imag real real real real imag Subword Parallelism of FFT • C source code: out[k].real = y1.real + ((t.real * y2.real) >> 15) - ((t.imag * y2.imag) >> 15) out[k].imag = y1.imag + ((t.real * y2.imag) >> 15) + ((t.imag * y2.real) >> 15); out[k+N/2].real = y1.real - ((t.real * y2.real) >> 15) + ((t.imag * y2.imag) >> 15); out[k+N/2].imag = y1.imag - ((t.real * y2.imag) >> 15) - ((t.imag * y2.real) >> 15); • PLX instructions: • pmulshr , padd, psub, pshift t Pmushr.15 Psub.8 y2 excheck

  9. BET Evaluation of WLAN system • Established an IEEE802.11a WLAN system • AWGN channel model • Coding Rate ¾ • 64 QAM (Quadrature Amplitude Modulation) • SNR 10dB • Randomly Generated Packet: -number:100 -width: 1 byte • Simulate with Different FFT data width - 8, 16, 24, 32, 40, 48, 56 bits

  10. Simulation Result: Raw data BER vs FFT Data Width

  11. Simulation Result: Data BER vs FFT Data Width

  12. Simulation Result: Data PER vs FFT Data Width

  13. Conclusion • Better BER and PER performance by increasing the FFT Data Width • FFT Data Width represents the size of Complex multiplier, Adder and Subtractor • Tradeoff between FFT Processor size and its Performance and possible Optimization

  14. Future Work • Finish PLX subword parallelism implementation • Evaluate Error Rates vs FFT width in other Modulation mode: BPSK, QPSK, 16-QAM, 64-QAM • Evaluate Error Rates vs FFT width with different Coding rate : 1/2, 2/3 and 3/4.

  15. Thanks Questions?

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