WirelessSymp802_11adPHY

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2012 Agilent TechnologiesWireless Communications

Greater insight. Greater confidence. Accelerate next-generation wireless.

IEEE 802.11ad PHY Layer Tes tin g

Presented by: David Grieve, Agilent Technologies


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2 2012 Agilent Technologies

Wireless Communications


Agenda

Overview of IEEE 802.11ad

Tutorial introduction to the PHY layer

PHY Measurement challenges

PHY Measurements

Have I got a signal?

Basic diagnostics

Demodulating the CPHY

Modulation quality

Decoding the data

Conclusions


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IEEE 802.11ad Overview

What? A backwards-compatible extension to the IEEE 802.11-2007specification that adds a new MAC/PHY to provide shortrange, high capacity links in the 60 GHz unlicensed band.

Where? The 60 GHz MAC/PHY specification was initially developed

privately by the Wireless Gigabit Alliance. It was contributedto the IEEE TGad in May 2010 and has subsequently beendeveloped to a final draft standard in IEEE.

When? The specification will be signed off by TGad in June 2012and formally released for publication in Dec 2012. Weexpect first commercial silicon in 2H 2012, and anticipatefirst certified product announcements in Jan 2013.



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Why? The 2.4 and 5 GHz wireless bands are congested andfundamentally lack the capacity to deliver multi-gigabit data.802.11ac endeavours to address this, but may find it difficult todeliver to multiple users.

The globally available 60 GHz wireless band is green -field andcan meet the demand for short-range multi-gigabit links, bothtechnically and commercially.

How? A managed ad-hoc network of directional, short-range, point-to-point links at 60 GHz.

The PHY uses RF burst (packet) transmissions. Packets start with a common sync preamble followed by header and payload

data. The common preamble always uses single-carrier (SC) modulation, theheader and data may use SC or OFDM modulation depending on the selectedmode.

The PHY supports active antenna beam forming / steering (but not MIMO). The MAC augments the standard IEEE 802.11 MAC with new, 60 GHz specific,

capabilities.



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60GHz Channel Plan by Region

6

*

Spectrum Mask

Channel 4Channel 3Channel 2Channel 1

U.S. and Canada (57.05 GHz 64.00 GHz)

European Union (57.00 GHz 66.00 GHz)

Japan (59.00 GHz 66.00 GHz)

China (59.00 GHz 64.00 GHz)

South Korea (57.00 GHz 64.00 GHz)

Australia (59.40 GHz 62.90 GHz)

57.00GHz

57.24GHz

59.40GHz

61.56GHz

63.72GHz

65.88GHz

66.00GHz

Fc = 58.32 GHz F c = 60.48 GHz F c = 62.64 GHz F c = 64.80 GHz


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Header Data

Header Data

Header Data

Preamble

Preamble

Preamble

PHY Modes (Packet Overview)

STF CEF

Control

Single Carrier

OFDM

STF

STF CEF

BeamformingTraining

BeamformingTraining

BeamformingTraining

/2-BPSK /2-BPSK/QPSK/QAM16

/2-BPSK QPSK-OFDM SQPSK/QPSK/QAM16/QAM64-OFDM

/2-BPSK /2-DBPSK

CEF







Preambles

The preamble always comprises twofields;

Short Training Field (STF)

Timing estimation

AGC adjustment

Channel Estimation Field (CEF) Channel estimation

Header Data

Header Data

Header Data

Preamble

Preamble

Preamble

STF CEF

STF

STF CEF

BFT

BFT

BFT

CEF







Preamble Variants(showing basic construction)

Gb 128 Gb 128 Gb 128 -Gb 128 -Ga 128

CPHY Short Training Field (STF) 5120 Tc SC Channel Estimation Field (CEF) 1152 T c

Ga 128 Ga 128 Ga 128 Ga 128 -Ga 128

Short Training Field (STF) 2176 T c SC Channel Estimation Field (CEF) 1152 T c

Ga 128 Ga 128 Ga 128 Ga 128 -Ga 128

Short Training Field (STF) 2176 T c OFDM Channel Estimation Field (CEF) 1152 T c

-Gb 128 -Ga 128 Gb 128 -Ga 128 -Gb 128 Ga 128 -Gb 128 -Ga 128 -Gb 128

-Gb 128 -Ga 128 Gb 128 -Ga 128 -Gb 128 Ga 128 -Gb 128 -Ga 128 -Gb 128

-Gb 128 Ga 128 -Gb 128 -Ga 128 -Gb 128 -Ga 128 Gb 128 -Ga 128 -Gb 128







Complementary Golay Codes

Used extensively in 802.11ad;

Synchronization and AGC

Data Spreading

Channel Estimation

Gain and phase tracking

Important attributes of Golay codes are;

Low side lobes and low DC content under /2 rotation.

Sum of Ga and Gb autocorrelations is perfect.

Ga and Gb autocorrelations can be performed in parallelusing a single correlator.

OR

Ga

Gb

Receive side - fast Golay correlator


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Golay Correlator Output

Ga 128 Ga 128 Ga 128 Ga 128 -Ga 128-Gb 128 -Ga 128 Gb 128 -Ga 128 -Gb 128 Ga 128 -Gb 128 -Ga 128

-Gb 128Gv 512Gu 512


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Preamble Variants(showing CEF grouping)

Gv 128

SC Channel Estimation Field (CEF) 1152 T c

Gv 128

SC Channel Estimation Field (CEF) 1152 T c

Gv 128

OFDM Channel Estimation Field (CEF) 1152 T c

Gb 128 Gb 128 Gb 128 -Gb 128 -Ga 128

CPHY Short Training Field (STF) 5120 Tc

Ga 128 Ga 128 Ga 128 Ga 128 -Ga 128

Short Training Field (STF) 2176 T c

Ga 128 Ga 128 Ga 128 Ga 128 -Ga 128

Short Training Field (STF) 2176 T c

-Gb 128 -Ga 128 Gb 128 -Ga 128 -Gb 128 Ga 128 -Gb 128 -Ga 128Gv 512Gu 512

-Gb 128 -Ga 128 Gb 128 -Ga 128 -Gb 128 Ga 128 -Gb 128 -Ga 128

Gv 512Gu 512

-Gb 128 -Ga 128 Gb 128 -Ga 128Gu 512

-Gb 128 Ga 128 -Gb 128 -Ga 128Gv 512


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correlator

Channel Estimation Opportunity

Gb 256 Ga256

Ga

Gb

-Ga 128-Gb 128 -Ga 128 Gb 128 -Ga 128 -Gb 128

Gu 512


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Principle of Channel Estimation(application of Golay codes)

H( )a h t

a Golaycorrelator

( ) R a a a h t

( ) R b b b h t H

( )b h t b

Golaycorrelator

( ) ( )

( )

( )

( )

output R a R b

a a h t b b h t

a a b b h t

t h t

h t

+ =

Ga Gb Ga + Gb

+ =


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Header Variants

4 10 bits 5 bits 16 bits

S

cramblerInitialization

P

ackettype

Length

1 2

T

rainingLength

R

eservedbits

H

CS

S

IFSresponse

1

R

eserved(diffdetectorinit)

1

SIFSresponse

LastRSSI

Beam TrackingRequest

7 bits 18 bits 5 bits 16 bits

ScramblerInitialization

Packettype

Length

1 1

TrainingLength

HCS

5 bits

MCS

AdditionalPPDU

1 1

Aggregation

4 bits

Reserved

4 bits 1

7 bits 18 bits 5 bits 16 bits

ScramblerInitialization

Packettype

Length

1

TrainingLength

HCS

5 bits

MCS

AdditionalPPDU

1 1

Aggregation

2

Reserved

Beam TrackingRequest

TonePairingType

DTPIndicator

1 1 1

SIFSresponse

LastRSSI

4 bits 1

Control

Single Carrier

OFDM

Header Data

Header Data

Header Data

Preamble

Preamble

Preamble

STF CEF

STF

STF CEF

BFT

BFT

BFT

CEF


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Header Data

Header Data

Header Data

Preamble

Preamble

Preamble

PHY Header/Payload Modulation

STF CEF

Control

Single Carrier

OFDM

STF

STF CEF

BeamformingTraining

BeamformingTraining

BeamformingTraining

/2-BPSK /2-BPSK/QPSK/QAM16

/2-BPSK QPSK-OFDM SQPSK/QPSK/QAM16/QAM64-OFDM

/2-BPSK /2-DBPSK

CEF


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Modulation and Coding Schemes (MCS)

Key Points

Very robust 27.5 Mbps ControlChannel

Variable Error Protection

Variable Modulation Complexity

Hence EVM specs.from -6dB to -25dB

Variable Data Rates

from 385 Mbps (MCS1)to 6756.75 Mbps (MCS24)

Mandatory modes ensure all 802.11addevices capable of at least 1Gbps

Control (CPHY)MCS Coding Modulation Raw Bit Rate

0 1/2 LDPC, 32x Spreading /2-DBPSK 27.5 MbpsSingle Carrier (SCPHY)

MCS Coding Modulation Raw Bit Rate1-12 1/2 LDPC, 2x repetition

1/2 LDPC,5/8 LDPC3/4 LDPC

13/16 LDPC

/2-BPSK,/2-QPSK,

/2-16QAM

385 Mbpsto

4620 Mbps

Orthogonal Frequency Division Multiplex (OFDMPHY)MCS Coding Modulation Raw Bit Rate

13-24 1/2 LDPC,5/8 LDPC3/4 LDPC

13/16 LDPC

OFDM-SQPSKOFDM-QPSK

OFDM-16QAM

OFDM-64QAM

693 Mbpsto

6756.75 Mbps

Low-Power Single Carrier (LPSCPHY)MCS Coding Modulation Raw Bit Rate

25-31 RS(224,208) +Block Code(16/12/9/8,8)

/2-BPSK,/2-QPSK

625.6 Mbpsto

2503 Mbps


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OFDM Modulation

Variable modulation depth Date rates up to

6.76 Gbps 16 Static pilots Fc and Fc 1 nulled Shares common preamble

with SCPHY for timing andchannel estimation

Different sample rate to SC.Preamble is up-sampledfrom SC definition by aspecified interpolation filter.

Parameter Value

Occupied BW 1.825 GHz

Ref. sampling rate 2.640 Gsamples/s

No. of subcarriers 512

FFT period ~ 194 ns

Subcarrier spacing 5.15625 MHzCyclic prefix 128 symbols, ~ 48.4 ns

Symbol duration ~242 ns

Data subcarriers 336

DC subcarriers 3

Pilots 16Null subcarriers 157

Modulation SQPSK, QPSK, 16-QAM, 64-QAM

Error Protection LDPC 1/2, 5/8, 3/4 or 13/16


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Control PHY (MCS 0)(Header & Payload Encoding)

/2-BPSKModulation

DifferentialEncoding

32xSpreading

Scrambler (x7+x4+1)

LDPCEncoder (Shortened 3/4)

SpectrumShaping Up Conversion

Ga32 correlator output showingthe results of 32x despreading.


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SC PHY (MCS 1 to 12)(Header & Payload Encoding)

/2-BPSK/2-QPSK

/2-16QAMModulation

Scrambler (x7+x4+1)

LDPCEncoder

(1/2, 3/4, 5/8, 13/16)

2xRepetition

(header only)

SpectrumShaping Up Conversion

Data Blocking andGuard Interval(448 block + 64 GI = 512)

448 symbolsGa 64 guardinterval

512 symbol modulation block

Ga64 correlator output showingthe regular guard interval.


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OFDM PHY (MCS13 to 24)(Header & Payload Encoding)

Scrambler (x7+x4+1)

LDPCEncoder

(1/2, 3/4, 5/8, 13/16)

CarrierMapping

(QPSK, QAM16, QAM64)

CyclicPrefix

(25% repetition)

3xRepetition

(header only)

Pilot andDC NullInsertion

WindowingFunction

(Transition smoothing)

Up ConversionIFFT(512 points)

SQPSK QPSK 16QAM 64QAM


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Low Density Parity Check (LDPC)

First proposed by Gallager in 1960, but ignored

Re- discovered by McKay and others in the mid 1990s

Even better than turbo codes performance hassince stimulated a lot of research.

LDPC codes are systematic block codes that useparity check as the error detection /correctionmechanism.

A large, sparse, randomly populated parity matrix,coupled with a soft-decision iterative decodingalgorithm can produce error correcting codes withperformance within 0.05dB of the Shannon Limit.

The 802.11ad parity matrix is optimized for simplecodeword generation by back-substitution on the paritymatrix and efficient hardware implementation of theiterative soft decoding algorithm.

m-bit message

encode

belief propagation

soft-decision decode

m = r x 672 wherer = 1/2, 5/8, 3/4, or 13/16

m-bit message

m-bit message parity bits

672-bit codeword


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PHY Measurement Challenges

Practical Problems

Connectivity! Modulation Bandwidth

PHY Challenges

Phase stability / frequencyaccuracy

Quadrature errors

DC/LO feedthrough I / Q Mismatch

Transmit power

DAC LPF

DAC LPF

090

Baseband ASIC RF ASIC with antennaarray bonded directly on

top of RFIC.


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Step 1 Have I got a signal?

Time Domain

SNR? Clipping? Transients? Structure? Etc

Frequency Domain

Shape? Flatness?

Bandwidth? Spurs? Etc


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Step 2 Golay Correlator Outputs


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Step 3 Control PHY Demodulation

The CPHY uses differential encoding, codespreading, BPSK modulation and a rate1/2 LDPC FEC to ensure reliablecommunication at very high path loss.


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Phase Error and Carrier Tracking


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Channel Impulse Response(estimated from CEF field)


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Channel Frequency Response


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EVM versus Time and Frequency


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OFDM EVM by Symbol and by Carrier


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Step 5 FEC Codewords and Data


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Agilent 81199A User Interface


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Agilent 60 GHz PHY Test Solution

DUT

8267D-520-016 (I/Q Modulation)

N5152A 5GHz/60GHz U.C.

N5183A-520 MXG (Tx LO)

N1999A 60GHz/5GHz D.C.

M8190A Wideband AWG (I/Q Generation)

N5183A-520 MXG (Rx LO)

Controlling PC(Could be Desktop, Laptop or Embedded)

81199A WidebandWaveform Center (WWC)

Wfm Data

Acq'd Signal

DSO90404A Infiniium Real-time Oscilloscope

89601B Vector Signal Analyzer


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Conclusions

802.11ad capable devices will start to appear late 2012, early 2013.

802.11ad extends the highly successful 802.11 WLAN family.

Wireless Gigabit Alliance, IEEE and Wi-Fi Alliance are working in closecollaboration to specify, certify and promote this technology.

802.11ad mixes single carrier and OFDM modulation techniques tosupport a wide range of price/performance points up to 6.75 Gbps.

Golay codes are a foundation of the WiGig/802.11ad specification thatalso enable significant measurement insight.

There are many design challenges for PHY development at 60 GHz, thinkin terms of 10x to 100x 802.11a, compounded by the need to do RFtesting over-the-air.

Agilent has unique solutions for developing and verifying PHY designs.


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