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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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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 • Conclusion • Future Work
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 • 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 • 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 • matlab Fixed point package • 6 bit input symbol
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 • 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 • 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 • 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.
Thanks Questions?