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1 802.11a/g Kernel Identification Saba Zia Bilal Saqib
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2 Physical Layer Architecture and Kernel Identification (802.11a) Ref: IEEE Std 802.11a-1999(R2003)
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3 Physical Layer Architecture and Kernel Identification Data Scrambler/ Descrambler Convolutional Encoder / Viterbi decoder Data interleaver/ Deinterleaver Guard interval insertion OFDM modulation Subcarrier Modulation Mapping
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Individual Properties of each Kernel Data Scrambler/Descrambler 4 127 bit frame synchronous scrambler S(x)=x 7 +x 4 +1 Ref: IEEE Std 802.11a-1999(R2003)
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Individual Properties of each Kernel Convolutional Encoder/ Viterbi Decoder 5 R = ½, 2/3, ¾ For R= 1/2, G 0 =133 8 G 1 = 171 8 Decoding by Viterbi Algorithm Ref: IEEE Std 802.11a-1999(R2003)
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Individual Properties of each Kernel Puncturing/De-puncturing Patterns 6 Ref: IEEE Std 802.11a-1999(R2003)
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Individual Properties of each Kernel Puncturing/De-puncturing Patterns 7 Ref: IEEE Std 802.11a-1999(R2003)
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Individual Properties of each Kernel Data Interleaver/ Deinterleaver Block size corresponding to the number of bits in a single OFDM symbol, NCBPS Two-step permutation i = (N CBPS /16) (k mod 16) + floor(k/16) where k = 0,1,…,N CBPS – 1 j = s × floor(i/s) + (i + N CBPS – floor(16 × i/N CBPS )) mod s where i = 0,1,… N CBPS – 1 The value of s is determined by the number of coded bits per subcarrier, N BPSC, according to s = max(N BPSC /2,1) 8
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Individual Properties of each Kernel Subcarrier Modulation Mapping BPSK,QPSK,16 QAM or 64 QAM depending on the rate requested Gray coded constellation mappings Resultant, d = (I + jQ) X K MOD 9 Ref: IEEE Std 802.11a-1999(R2003)
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Individual Properties of each Kernel OFDM modulation (IFFT) Divide the complex number string into groups of 48 complex numbers. Each such group will be associated with one OFDM symbol. Each complex number is mapped into OFDM subcarriers numbered –26 to –22, –20 to –8, –6 to –1, 1 to 6, 8 to 20, and 22 to 26. The “0” subcarrier, associated with center frequency, is omitted and filled with zero value. Four subcarriers are inserted as pilots into positions –21, –7, 7, and 21. The total number of the subcarriers is 52 (48 + 4). For each group of subcarriers –26 to 26, convert the subcarriers to time domain using inverse Fourier transform 10
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Individual Properties of each Kernel OFDM modulation (IFFT) 11 Ref: IEEE Std 802.11a-1999(R2003)
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Individual Properties of each Kernel Guard Interval Insertion Prepend to the Fourier-transformed waveform a circular extension of itself thus forming a GI, and truncate the resulting periodic waveform to a single OFDM symbol length by applying time domain windowing. 12 Ref: IEEE Std 802.11a-1999(R2003)
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Rate Dependent Parameters 13 Ref: IEEE Std 802.11a-1999(R2003)
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Timing Related Parameters 14 Ref: IEEE Std 802.11a-1999(R2003)
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Physical Layer Architecture and Kernel Identification (802.11g) 802.11g offers four operational modes DSSS /CCK DSSS /CCK OFDM (Kernels identical to 802.11a) OFDM (Kernels identical to 802.11a) PBCC (optional) PBCC (optional) DSSS/OFDM (optional) DSSS/OFDM (optional) 15
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DSSS/CCK based kernels CRC Data Scrambler/Descrambler DQPSK/DBPSK 16
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