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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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slide1

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

Zaipeng Xie

Muwu Hou

Daphne J Franklin

topics covered
Topics Covered
  • Motivation
  • IEEE 802.11a Standard
  • OFDM System
    • Transmitter
    • Receiver
  • Quantization Error Analyses
  • Simulation Results
  • Conclusion
  • Future Work
motivation
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
ieee 802 11a standard
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
fft algorithm
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

quantization error analysis
Quantization Error analysis
  • matlab Fixed point package
    • 6 bit input symbol
subword parallelism of fft

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

bet evaluation of wlan system
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

conclusion
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
future work
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.
slide15
Thanks

Questions?