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    R&S | 802.11ac Introduction | 1

    WLAN IEEE 802.11acIntroduction

    Coen van Bergen

    Evolution of WLAN 802.11 standards Technologies OFDM, SDMA, MIMO, MU-MIMO Facts about WLAN IEEE 802.11ac Test Solutions for WLAN 802.11ac

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    Evolution of WLAN 802.11 Standards

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    802.11 WLAN Evolution

    under developmentOct. 2009June 2003Sep. 1999Sep. 1999Release

    500 Mbps 37.2 to 150 Mbps 26 to 54 Mbps1 to 11 Mbps6 to 54 MbpsData rate 1

    SDMA (OFDM)OFDMOFDM, DSSSFDMA, DS-CDMAOFDMAccess method

    BPSK, QPSK,16 / 64 / 256 QAM

    BPSK, QPSK,16 / 64QAM

    DBPSK, DQPSK,DBPSK, DQPSK,BPSK, QPSK

    BPSK, QPSK,16 / 64QAMModulation

    BCC, LDPC, STBCConvolutionalCoding, LDPC

    CCK, PBCC11 chip Barkersequence, CCK,PBCC

    Forward errorcorrection coding(convolutional;code rates 1/2, 2/3,3/4)

    Coding

    4 x 4

    20 / 40 MHz

    2.4 GHz ISM band,

    5 GHz U-NII bands

    802.11n

    8 x 8111MIMO stream

    20 / 40 / 80 / 160 MHz20 MHz20 MHz20 MHzBandwidth

    5 GHz U-NII bands

    2.4 GHz ISM band2.4 GHz ISM band

    5 GHz U-NII bandsCarrier freq.

    802.11ac802.11g802.11b802.11a

    1 The maximum data rate can be achieved by higher order modulation2 In case of 4 streams the maximum data rate is 600 Mbps3 For 160 MHz and 8 streams theoretically 6.93 Gbps

    802.11ac = Backwards compatible with 802.11a and n

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    Technologies:

    OFD! "DA! IO! #$IO

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    Facts about WLAN 802.11ac OFDM

    l 802.11ac PHY is based on the well known OFDM (OrthogonalFrequency Division Multiplexing) PHY used for 802.11a and 802.11n

    f

    duration TS 1/TS

    f0 f2f1

    fCarrier= f0+n/TS where n is an integer, f = 1/TS , therefore: fn = n x f

    The maximum of one carrier is at the zero crossings of all others

    f2

    f1

    f0

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    MMO Multi!l" n!ut Multi!l" Out!ut

    Throughput:

    Data 1

    Coding Fading on the air interface

    Data 2

    100%200%

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    M#$MMO % Multi#s"r MMO

    SDMA = Spatial Division Multiple Access = Access Method

    - Downstream only- Max. 8 Streams- Max 4 Users

    - Max 4x4 antennes per user

    Beamforming ?

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    Facts a%out WLAN IEEE 802.11ac

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    Facts about WLAN 802.11ac OFDM

    l OFDM Subcarriers

    l Subcarrier Rotationreduces Peak to

    Average Power Ratio

    PAPR

    -122 to -2 and 2 to 122, 16 Pilots256 per 80MHz Chan80+80

    -250 to-130, -126 to -6,

    6 to 126 and 130 to 250, 16 Pilots

    512160

    -122 to -2 and 2 to 122, 8 Pilots25680

    -58 to -2 and 2 to 58, 6 Pilots12840

    -28 to -1 and 1 to 28, 4 Pilots6420

    Subcarriers Transmitting SignalNumber of SubcarriersBandwidth (MHz)

    Same as 80MHzSame as 80 MHz80+80

    180 degrees (-1)-192 to -1 and 64160

    180 degrees (-1)-6480

    90 degrees (j)040

    N/A20

    Rotation ValueRotated SubcarriersBandwidth

    (MHz)

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    Facts about WLAN 802.11ac &'ann"li(ation

    l Support of 20, 40, 80 MHz, 160 MHz channel bandwidth

    l The 80MHz channel will consist of two adjacent, non-overlapping40MHz channels.

    l The 160MHz channels will be formed by two 80MHz channelsl adjacent (contiguous)

    l non-contiguous

    l Europe, Japan and Global Operating Class Channel Allocation

    140

    136

    132

    128

    124

    120

    116

    112

    108

    104

    100

    64

    60

    56

    52

    48

    44

    40

    36IEEE channel #

    20 MHz

    40 MHz

    80 MHz

    5170

    MHz

    5330

    MHz

    5490

    MHz

    5710

    MHz

    160 MHz

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    Facts about WLAN 802.11ac Fra)" For)at

    l All 802.11 devices (L= Legacy) to synchronize to the signal

    l L-STF (Short Training Field)

    l L-LTF (Long Training Field)l L-SIG (Signal).

    l New for 802.11ac: VHT (Very High Throughput.)

    l VHT-SIG-A field contains two OFDM symbols (BPSK, 90 rotated BPSK)

    l

    VHT-STFl VHT-LTFs..

    l The VHT-SIG-B is the last field in the preamble

    VHT auto-detection

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    XLow Density Parity Check (LDPC)

    XSpace Time Block Coding (STBC)

    X400 ns short guard interval

    XMulti-User MIMO (MU-MIMO)

    X2 to 8 spatial streams

    X80+80 MHz, 160 MHz channels

    X256QAM

    XBPSK, QPSK, 16QAM, 64QAM

    X1 spatial stream

    X20 MHz, 40 MHz, 80 MHz channels

    OptionalMandatoryProperties

    Peak Data Rate ~293 Mbps ~3.5 Gbps

    Facts about WLAN 802.11ac Optional/Mandatory

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    Facts about WLAN 802.11ac

    &alculation of Data *at"

    l Mandatory

    l 242 carrier 8 pilot carriers = 234 carriers

    l Sample Frequency 80 MHz

    l Guard Interval 800 ns

    l

    FFT 256l MCS7, 64 QAM (6 bits), Coding 5/6

    l Symbol time: 256/80 MHz + 800 ns = 4 s

    l Number of bits 6 x 234 x 5/6 = 1170 bits/symbol

    l Maximum data rate: 1170 bits/symbol / 4 s /symbol =l 292.5 Mbit/s

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    Facts about WLAN 802.11acOv"rvi"+ of datarat"s d"!"ndin, on M&S

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    Facts about WLAN 802.11ac Mar-"t i"+

    l First wave of chips will support:

    l 80 MHz bandwidth

    l

    256 QAM support expectedl MIMO support plans vary for customers

    Some start with 2x2, some plan 3x3 initially

    l Some plan MU-MIMO initially with 2 streams for 2 users

    l Next wave will support 160 MHz

    l Planned for mid to end of this year

    l Some indicating plans for 4x4 MIMO

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    &'" Test "olutions WLAN IEEE 802.11ac

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    Max. bandwidth 80 MHz

    Max. bandwidth 160 MHz

    R&S SMU

    R&S SMBV

    R&S FSQ

    R&S FSW

    /"st Solutions for 80M( and 10 M(

    R&S SMU

    R&S SMBV

    R&S FSW +R&S FSW-B160

    R&S AFQ100A/B

    +

    R&S SGS

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    l Spectral Mask for 20, 40, 80 and 160 MHz Channels

    WLAN 802.11ac Analsis +it' *3S FSWTransmiter Specifications Spectrum Measurements with R&S FSW

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    l Transmitter Constellation Error

    -325/6256-QAM9

    -303/4256-QAM8

    -275/664-QAM7

    -253/464-QAM6

    -222/364-QAM5

    -193/416-QAM4-161/216-QAM3

    -133/4QPSK2

    -101/2QPSK1

    -51/2BPSK0

    RCE (dB)Coding RateModulationMCS

    For error < 1dB a residual EVMof < -38 dB for T&M is needed

    WLAN 802.11ac Analsis +it' *3S FSWModulation Analysis

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    WLAN 802.11ac Analsis +it' *3S FSWModulation Analysis R&S FSW-!"/!"ac

    Bandwidth 160 MHz

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    WLAN 802.11ac Analsis +it' *3S FSWModulation Analysis R&S FSW-!"/!"ac

    Constellation diagram R&S FSW-K91acResidual EVM < -45 dB at 5 GHz

    DUT EVM: -33 dBWith -45 dB res. EVM, the result is -32.7 dB

    R&S FSW quality is needed, becausewith e.g. -35 dB res. EVM, the result is -30.9 dB,which does not meet the spec.

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    WLAN 802.11ac Analsis +it' *3S FSW

    M#MO Analysis

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    nfor)ation about 802.11ac

    l R&S Technology paper 1MA192

    l Wikipedia -> http://en.wikipedia.org/wiki/IEEE_802.11ac