11

802.11a/g Kernel 802.11a/g Kernel IdentificationIdentification

Saba ZiaSaba Zia

Bilal SaqibBilal Saqib

22

Physical Layer Architecture and Kernel Physical Layer Architecture and Kernel Identification (802.11a)Identification (802.11a)

Ref: IEEE Std 802.11a-1999(R2003)

33

Physical Layer Architecture and Kernel Physical Layer Architecture and Kernel IdentificationIdentification

Data Scrambler/ DescramblerData Scrambler/ Descrambler

Convolutional Encoder / Viterbi decoder

Convolutional Encoder / Viterbi decoder

Data interleaver/ DeinterleaverData interleaver/ Deinterleaver

Guard interval insertionGuard interval insertion

OFDM modulationOFDM modulation

Subcarrier Modulation Mapping

Subcarrier Modulation Mapping

Individual Properties of each KernelIndividual Properties of each KernelData Scrambler/DescramblerData Scrambler/Descrambler

44

127 bit frame synchronous scrambler127 bit frame synchronous scrambler S(x)=xS(x)=x77 +x +x44 +1 +1

Ref: IEEE Std 802.11a-1999(R2003)

Individual Properties of each KernelIndividual Properties of each KernelConvolutional Encoder/ Viterbi DecoderConvolutional Encoder/ Viterbi Decoder

55

R = ½, 2/3, ¾R = ½, 2/3, ¾ For R= 1/2, GFor R= 1/2, G00=133=13388 G G11 = 171 = 17188

Decoding by Viterbi AlgorithmDecoding by Viterbi AlgorithmRef: IEEE Std 802.11a-1999(R2003)

Individual Properties of each KernelIndividual Properties of each KernelPuncturing/De-puncturing PatternsPuncturing/De-puncturing Patterns

66Ref: IEEE Std 802.11a-1999(R2003)

Individual Properties of each KernelIndividual Properties of each KernelPuncturing/De-puncturing PatternsPuncturing/De-puncturing Patterns

77Ref: IEEE Std 802.11a-1999(R2003)

Individual Properties of each KernelIndividual Properties of each KernelData Interleaver/ DeinterleaverData Interleaver/ Deinterleaver

Block size corresponding to the number Block size corresponding to the number of bits in a single OFDM symbol, NCBPSof bits in a single OFDM symbol, NCBPS

Two-step permutationTwo-step permutation i = (Ni = (NCBPSCBPS/16) (k mod 16) + floor(k/16) where k = 0,1,/16) (k mod 16) + floor(k/16) where k = 0,1,

…,N…,NCBPS CBPS – 1– 1

j = s × floor(i/s) + (i + Nj = s × floor(i/s) + (i + NCBPSCBPS – floor(16 × i/N – floor(16 × i/NCBPSCBPS)) mod s )) mod s

where i = 0,1,… Nwhere i = 0,1,… NCBPSCBPS – 1 – 1

The value of s is determined by the number of coded bits per The value of s is determined by the number of coded bits per subcarrier, Nsubcarrier, NBPSCBPSC, according to s = max(N, according to s = max(NBPSCBPSC/2,1)/2,1)

88

Individual Properties of each KernelIndividual Properties of each KernelSubcarrier Modulation MappingSubcarrier Modulation Mapping

BPSK,QPSK,16 QAM or 64 QAM BPSK,QPSK,16 QAM or 64 QAM depending on the rate requesteddepending on the rate requested

Gray coded constellation mappingsGray coded constellation mappings Resultant, d = (I + jQ) X KResultant, d = (I + jQ) X KMODMOD

99

Ref: IEEE Std 802.11a-1999(R2003)

Individual Properties of each KernelIndividual Properties of each KernelOFDM modulation (IFFT)OFDM modulation (IFFT)

Divide the complex number string into groups of 48 complex Divide the complex number string into groups of 48 complex numbers. Each such group will be associated with one OFDM numbers. Each such group will be associated with one OFDM symbol.symbol.

Each complex number is mapped into OFDM subcarriers 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 numbered –26 to –22, –20 to –8, –6 to –1, 1 to 6, 8 to 20, and 22 to 26. to 26.

The “0” subcarrier, associated with center frequency, is omitted The “0” subcarrier, associated with center frequency, is omitted and filled with zero value. and filled with zero value.

Four subcarriers are inserted as pilots into positions –21, –7, 7, Four subcarriers are inserted as pilots into positions –21, –7, 7, and 21. The total number of the subcarriers is 52 (48 + 4). and 21. The total number of the subcarriers is 52 (48 + 4).

For each group of subcarriers –26 to 26, convert the subcarriers For each group of subcarriers –26 to 26, convert the subcarriers to time domain using inverse Fourier transformto time domain using inverse Fourier transform

1010

Individual Properties of each KernelIndividual Properties of each KernelOFDM modulation (IFFT)OFDM modulation (IFFT)

1111Ref: IEEE Std 802.11a-1999(R2003)

Individual Properties of each KernelIndividual Properties of each KernelGuard Interval InsertionGuard Interval Insertion

Prepend to the Fourier-transformed waveform a circular extension Prepend to the Fourier-transformed waveform a circular extension of itself thus forming a GI, and truncate the resulting periodic of itself thus forming a GI, and truncate the resulting periodic waveform to a single OFDM symbol length by applying time waveform to a single OFDM symbol length by applying time domain windowing. domain windowing. 1212

Ref: IEEE Std 802.11a-1999(R2003)

Rate Dependent ParametersRate Dependent Parameters

1313Ref: IEEE Std 802.11a-1999(R2003)

Timing Related ParametersTiming Related Parameters

1414Ref: IEEE Std 802.11a-1999(R2003)

Physical Layer Architecture and Kernel Physical Layer Architecture and Kernel Identification (802.11g)Identification (802.11g)

802.11g offers four operational modes802.11g offers four operational modesDSSS /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)

1515

DSSS/CCK based kernelsDSSS/CCK based kernels

CRCCRC Data Scrambler/DescramblerData Scrambler/Descrambler DQPSK/DBPSKDQPSK/DBPSK

1616