An implementation of IEEE802.11a WLAN system using Subword Parallelism and its Quantization Error...
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Transcript of An implementation of IEEE802.11a WLAN system using Subword Parallelism and its Quantization Error...
An implementation of IEEE802.11a WLAN system using Subword Parallelism and its Quantization Error EvaluationZaipeng Xie
Muwu HouDaphne 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 sec
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
0 10 20 30 40 50 60 70-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15Quantization error of fixed point FFT (16bit fixed point)
ideal output
output due to quantization
0 10 20 30 40 50 60 70-0.3
-0.25
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15Quantization error of fixed point FFT (8 bit fixed point)
ideal output
output due to quantization
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
imag real
imag real
t
y2
Pmushr.15 imag real
real imag
excheckPsub.8
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.