Major Leaps in Evolution of IEEE 802.11 WLAN Technologies · PDF fileIEEE Standard description Release date 802.11 1-2 Mbit/s, 2.4 – 2.485 GHz RF and IR All other standards below

Major Leaps in Evolution of

IEEE 802.11 WLAN Technologies

Thomas A. KNEIDELRohde & SchwarzProduct ManagementMobile Radio Tester

Evolution of IEEE 802.11 WLAN Technologies 2

WLAN – Mayor Player in Wireless CommunicationsHealthcare AutomotiveWearables Smart CitiesSmart Homes

Smart Buildings LAN Retail …..Agriculture

Anything that benefits from network connection will be connected

IEEE Standard description Release date

802.11 1-2 Mbit/s, 2.4 – 2.485 GHz RF and IRAll other standards below are Ammendments (Except 802.11f and 802.11t)

1997

802.11a 54 Mbit/s, 5GHz, OFDM 1999

802.11b DSSS, CCK, 11 Mbit/s, 2.4 GHz 1999

802.11c Bridge operation procedures (not used) 1997

802.11d International (country-to-country) roaming extensions 2001

802.11e QoS and VoIP including packet bursting 2004

802.11f Roaming with IAPP (Inter Access Point Protocol) 2003

802.11g 802.11b OFDM for 2.4 GHz 2003

802.11h DFS (dynamic frequency selection) and TPC (transmit power control) for 802.11a 2004

802.11i Enhanced Security 2004

802.11j Extensions for Japan, 4.9 – 5 GHz, 10 MHz BW 2004

802.11-2007 Incorporates all standards above 2007

The 802.11-2007 standard supersedes the 802.11 standard released 1997 and

incorporated all approved ammendments up to that point, ie 802.11a, 802.11g, 802.11j etc.

WLAN Standardisation 802.11-2007


IEEE Standard description Release date

802.11n 600 Mbit/s, MIMO, Packet Aggregation, 40 MHz BW, OFDMA 2009

802.11p WAVE / C2C (car to car), 10 MHz BW 2010 planned

802.11r Fast roaming 2008

802.11s Mesh networking, Extended Service Set 2010 planned

802.11u Interworking with non-802 networks (for example, cellular) 2010 planned

802.11y 5 Km range, 3.7 GHz for the US 2008

802.11aa Robust streaming of Audio Video Transport Streams 2011 planned

802.11mb Maintenance of the standard. Expected to become 802.11-2011 2011 planned

802.11ac Very High Throughput <6GHz 2012 planned

802.11ad Extremely High Throughput 60GHz 2012 planned

WLAN Standardisation 802.11n-ad



Mayor Steps in WLAN Evolution

a b g n ac ax802.11

IEEE 802.11bSingle Carrier Transmission

a b g n ac ax802.11

• Direct Sequence Spread Spectrum (DSSS)Complimentary Code Keying (CCK) Technique

• @ 2.4 GHz

• Support of 4 data rates from 1 to 11 Mbps


Phase changePhase change0 � 01 � π

1 bit input1 MBit/s

11 BPSK chips output@ 11 MHz

Barker sequence+1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1Barker sequence+1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1

DBPSK

2 bits input2 MBit/s

Phase changePhase change00 � 001 � π/211 � π10 � -π/2

11 QPSK chips output(complex) @ 11 MHz

Barker sequence+1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1Barker sequence+1, -1, +1, +1, -1, +1, +1, +1, -1, -1, -1DQPSK

1 Mbps

2 Mbps

DSSS / Spreading with Baker Code1 and 2 Mbps

Occupied Bandwidth: 22 MHz


DSSS / Spreading with Baker CodeIntersymbol Interference Protection

The 11 Chip Baker code autocorrelation function

High immunity of the system to multipath interference and collisions with other DSSS signals

Chip rate: 11 McpsChip Size: 11Chip duration: 90.9 ns

Multipath delays between 1 and 10 chips (90.9 ns to 909 ns) are not of concern

Assuming a propagation speed of 3 · 108 m/s

→ Path difference of about 27 to 272 meters

Code length of 11→ Process gain: 10.41 dB

10 log (code length)

→ Presence of informationeven below noise level


CCK – Complementary Code Keying5.5 Mbps and 11 Mbps

4 bit Block

Transmitter

Data

DQPSKPhaseRotate

one of four, 8 bit code words

Bit stream

IEEE 802.11b 8 QPSK chips output at 5.5 Mbps

8 bit Block

Transmitter

Data

DQPSKPhaseRotate

one of 64, 8 bit code words

Bit stream

IEEE 802.11b 8 QPSK chips output at 11 Mbps

Chip rate: 11 McpsChip Size: 8Chip duration: 90.9 ns



Up to 14 WLAN Channels @ 2.4 GHz Band


a b g n ac ax802.11

• Orthogonal Frequency Division Multiplexing (OFDM)

• 802.11g @ 2.4 GHz / 802.11a @ 5 GHz

• Support of 8 data rates from 6 to 54 Mbps

• 802.11g as an extension of 802.11b, additional 1, 2, 5.5 and 11 Mbps

IEEE 802.11a/gMulti-Carrier Transmission


Single Carrier Modulation: Multipath Interference Sensitivity

Problem of multipath interference with one carrier:

TransmitterSignal

t

Multipath interference when symbol duration shorter than delay spread

Delay Delay spread

ReceiverSignal

t

Limitation of Single Carrier modulation – as soon as symbol rate increases→ symbol interval becomes shorter than the delay spread.

Solution : Multiple low-rate carriers instead of a single high-rate carrier

Decreasing the symbol rate and increasing the number of carriers

t

Symbol C0 Symbol C1 Symbol C2



delay

delay


Multichannel System – FDM SystemConventional Multichannel System

Non Overlapping Adjacent Channels.

Channels separated by more than their two sided bandwidth

OFDM Multichannel System

Higher Spectral efficiency compare to conventional FDM50% Overlap of Adjacent Channels

Channels separated by Half their two sided bandwidth

f

f


f

1/TS

f0 f2f1

Characteristics of orthogonal waveforms:

� fCarrier= f0+n/TS where n is an integer

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

�The cross correlation of sine waves is zero

� This is obtained by the following setting

∆f = 1/TS , therefore: fn = n x ∆f

OFDM – Orthogonal Frequency Division MultiplexingPrinciple of Orthogonality of Frequency

Two signals f(t) and g(t) are called orthogonal, if the correlation integral is zero

0)()( =⋅∫ dttgtfST

TS is the duration Single Carrier Symbol C0 Symbol C1 Symbol C2

tSymbol time Ts

Symbol C1f1

Symbol C2f2

Symbol C0

tSymbol time TS’

f0Multi Carrier


• 48 Subcarriers for Data

• 4 Pilot carriers for Reference

• Channel distance 312.5 kHz

• 12 unused carriers as guard bands (left, center and right)

• Channel Spacing: 20 MHz

• Nominal/Occupied bandwidth of 16.6 MHz(48 + 4 + 1) x 312.5 kHz = 16.5625 MHz

• OFDM Symbol Duration: 3.2 µs // additional Guard Interval 800 ns

• Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM

• Coding Rate: ½, 2/3, ¾

• Coded Data Rates: 6, 9, 12, 18, 24, 36, 48, 54 Mbps

• Center Carrier is not used

IEEE 802.11a/g: OFDM Sub-Carrier Structure

20 MHz

Channel divided into 64 sub-carriers


-26

(fc) 0

+26

+21

+7

-7

-21

+24

+16

+12

+4

-4

-12

-16

-24

Sub

carr

ier In

dex

Time(in µs)

2 Long TrainingSequence Symbols

10 Short TrainingSequence Symbols

SIGNALSymbol

SERVICE+DataSymbol Data

SymbolLast DataSymbol

8.0 8.03.21.60.8 0.8

4.0

PLCP Preamble PCLP Header PSDU + Tail + Pad

GI2 GI GI GI GI GI

R=1/2BPSK

Rate is indicated in SIGNAL symbol

Pilots

Signal Detect.AGC, DiversitySelection

Coarse Freq.Offset Estimationtiming Synchronize

Channel and fine FrequencyOffset Estimation Rate length Service+ Data Data

SubCarriers

� Short Training Sequenceonly every 4th carrier is used

� Start of Frame Detection� Signal Strength Indication� Frequency Offset Resolution

� Long Training Sequence

� Channel Estimate� Fine Time Resolution

� Pilot Signals

� Carrier Tracking� Sample Clock Tracking

BPSK Modulation used in Preambles, Signal Symbol and Pilot Signals


IEEE 802.11a/g 64QAM: I/Q Constellation Diagram

OFDM – Points of View

Advantages

ı High resistance to Multi-path Fading

ı Efficiently Deals With Channel Delay Spread

ı Enhanced Channel Capacity (use of bandwidth)

ı Adaptively Modifies Modulation Density

ı Robustness to Narrowband Interference

ı Scalable data rate

Disadvantages

ı Sensitive to Small Carrier Frequency Offsets

ı Higher Peak to Average Power Ratio (crest factor)

ı Sensitive to High Frequency Phase Noise

ı Sensitive to Sampling Clock Offsets

Equalization is simpler than in one carrier transmission

Principles of OFDM is known for more than 30 years. Implementation of OFDM-Baseband processing, which use Fast-Fourier-Transformation (FFT) in Modulation and inverse FFT (IFFT) in Demodulation, requires powerful signal processing, which was not available for a long time.



Inter-Symbol Interference (ISI) Symbol Smearing Due to Channel

t

t

Adjacent Symbols

Channel

h(t)

tt

x(t)

Symbol Distorted Symbol

y(t)

x(t) y(t)h(t)

t


Guard Interval (GI)Elimination of ISI

Channel

h(t)

tt

x(t)


y(t)

x(t) y(t)h(t)

t

t

t

Symbol seperation by Guard Interval


�

�.� �� 312.5kHz

Cyclic Prefix (CP)Better Alternative to Null GI

CP

0.8 µs 3.2 µs

OFDM Symbol

Channel

h(t)

tt

x(t)


y(t)

x(t) y(t)h(t)

t

t

t

CP CP CP CP

Prefixing of symbol with a repetition of the end


Up to 14 WLAN Channels @ 2.4 GHz Band

802.11 a / g (OFDM) 20 MHz Channel width – 16.5625 MHz only used by Sub-Carriers

22 MHz 20 MHz


a b g n ac ax802.11

IEEE 802.11nMultiple Antenna Systems

• MIMO – Multiple Input, Multiple Output

• @ 2.4 GHz and 5 GHz

• 20 /40 MHz Bandwidth

• Physical Layer: data rate up to 600 Mbps




• Channel distance 312.5kHz


• Channel Spacing: 20MHz / 40MHz


• OFDM Symbol Duration: 3.2 µs // additional Guard Interval: 400ns or 800ns

• Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM

• MIMO up to 4 spatial streams

IEEE 802.11n: OFDM Sub-Carrier Structure

20 MHz

… in case of 20 MHz bandwidth


Multi-Path Progagation - Fading

Frequency shifts due to Doppler effects, caused by moving transmitters or receivers

Receiver detects signals with different time delays, levels and phases.

The higher the statistcal independence of the different fading channels, the better the achievable data transfer rate.

Uncorrelaeted, fading channels are required to distinguish the data streams coming from different transmit antennas


MIMO Systems – Multiple Input, Multiple OutputSpatial Diversityincreases robustnes of data transmission

e.g. Alamouti space-time coding

MISOMultiple Input, Single Output

SIMOSingle Input, Multiple Output

Spatial Diversity

Spatial Multiplexingincreases data rates or channel capacity

Spatial Multiplexing

2x2 MIMO MU MIMO

Multi-User


SIMO Systems – Rx Diversity

Received Signal Switched Diversity Maximum Ratio Combining

C = max (x, x´) C = (x + x´)

MRC

increases robustnes of data transmission

Spatial Diversityx

x´


SIMO Systems – MRCMaximum Ratio Combining

1x2 MIMOSIMO

�� + ��

�� = �� + ��

��

= �� x + ��

Y=Hx+ N


Spatial Diversityx

x´

�� =��∗ ��

∗ ��

��

�

TXAnt

RXAnt 1

n1

y1xLO

n2

y2

RXAnt 2

Estimatesx

e

MR

Cal

gorit

hm

Improved Signal-to-Noise Ratio �

�


MISO Systems – Tx Diversitye.g. Alamouti // Space Time Block Coding

Spatial Diversity

2x1 MIMOMISO

Tx 1 Tx 2

Time t ��

Time t + T ��∗ ��

∗


TXAnt 1

TXAnt 2

RXAnt

n

y2 y1

HH

xe

2

Estimates

-x2*

x1*

x1

x2

xe

Space-Time-Block

LOx1x2�� = �� + �� + ��

�� = �� ∗ + ��

∗ + ��

��

= �� ∗ ��

∗

��

+ ��

Y = H X + N

xe

1

��

= ��

+ ��

��+ ��#

��

= ��

+ ��

��+ ��#

Alamouti scheme has the same diversity as the two-branch maximum ration combining (MRC)

Improved Signal-to-Noise Ratio �

�


MIMO Systems – Spatial Multiplexing

increases data rates or channel capacity

y = H x

�

�

�

�

�

�

1

2

m

1

2

n

h11

h21

h12h22

h1m hn1

hnm

m transmit antennas n receive antennas

h11 h12 h.. h1m

h21 h22 h.. h2m

h.. h.. h.. h.m

hn1 hn2 hn. hnm

H =

X Y

Channel Matrix


MIMO Systems – Spatial Multiplexing

increases data rates or channel capacity

�� = �� + �� + ��

�� = �� + �� + ��

H = �11 �12�21 �22

Channel�1

�2 �2Tx antennas Rx antennas

� = Hx " n

+ ��

2x2 MIMO

��

��

��

��

��

�1

h21


Spatial Streams

Space-Time Streams TX antenna signals

Spa

tial –

Ant

enna

–M

appi

ng

ST

BC

Str

eam

Par

ser

FE

C e

ncod

erF

EC

enc

oder

Scr

ambl

er

Insert GI and Window

IDFTCSDConstellationmapper

Interleaver

Enc

oder

Par

ser


IDFTConstellationmapper

Interleaver



Interleaver



Interleaver

Data

WLAN 11n Baseband Transmitter Model

CSD Cyclic Shift Diversity

Dire

ctM

appi

ng

Bea

mfo

rmin

g

- 400 ns

- 200 ns

- 600 ns

Beamforming

TX antenna signals


IDFT


IDFT


IDFT


IDFT

Spa

tial –

Ant

enna

–M

appi

ngD

irect

Map

ping

Bea

mfo

rmin

g

Beamforming steering matrix: %& is any matrix that improves the reception in the receiver based on some knowledge of the channel between the transmitter and the receiver

Spa

ce-T

ime

Str

eam

s

Antenna map matrix %&

802.11n introduced implicit and explicit beamforming, but did not clearly defined

It was not widely used



a b g n ac ax802.11

IEEE 802.11acMulti-User MIMO

• MU-MIMO – Multi-User MIMO (Downlink)

• @ 5 GHz

• Channel Bandwidth: 20 /40 /80 /80+80 /160 MHz

• Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM






• Channel Spacing: 20 / 40 / 80 / 80+ 80 / 160MHz


• OFDM Symbol Duration: 3.2 µs // additional Guard Interval: 400ns or 800ns

• Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM


• Physical Layer – data rate up to 6.933 Gbps (160 MHz; 8 SS)

IEEE 802.11ac: OFDM Sub-Carrier Structure

20 MHz

… in case of 20 MHz bandwidth


WLAN 11ac Channel Allocation36 40 44 48 52 56 60 64 10

0

104

108

112

116

120

124

128

132

136

140

IEEE channel #

20 MHz

40 MHz

80 MHz

160 MHz

5170MHz

5330MHz

5490MHz

5730MHz

144

149

153

157

161

165

5735MHz

5835MHz

Explicit Beamforming

802.11ac focus on use of explicit beamforming and discarded possibility of implicit beamforming.

Announcementsending soon sounding frames

Null Data Packet (NDP)Soundingin various directions

Report requestBeamforming Feedback'&-Matrix

Re-calibration of phase shift for each of the transmitted signal from each antennaReaching maximum signal strength at client

( → Beamforming steering matrix: %& )

Measures the channel martices

Implicit BeamformingAP measures the received upstream and based on the result derive the parameters for subsequent downstream beam


MU-MIMO Systems – Spatial Multiplexingbased on Explicit Beamforming

Multi UserMU-MIMO beamforming addresses multiple users located in spatially diverse positions

MISO

MISO

MIMO

Null-steering transmit beamformers aim to maximize the received signal power in the direction of the intended receiver while substantially reducing the power impinging on the unintended receivers located in other directions.


a b g n ac ax802.11

IEEE 802.11axHigh-Efficiency Wireless

• Medium Access Control: CSMA/CA // OFDMA – Orthogonal Frequency Division Multiplexing Access

• @ 2.4 GHz and 5 GHz

• Channel distance: 78.125 kHz (4 times less) // Symbol duration: 12.8 µs (4 times longer)

• Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM, 1024QAM





• 14 unused carriers as guard bands (6 left, 3 center and 5 right)

• Channel Spacing: 20 / 40 / 80 / 80+ 80 / 160MHz


• OFDM Symbol Duration: 12.8 µs // additional Guard Interval: 0.8, 1.6, 3.2 µs

• Data carrier modulation: BPSK, QPSK, 16QAM, 64QAM, 256QAM, 1024QAM

• Coding BCC – Binary Convolutional Code // LDPC – Low-Density Parity-Check


• Physical Layer – data rate up to 9.6078 Gbps (160MHz, 8 SS)

IEEE 802.11ax: OFDM Sub-Carrier Structure

20 MHz

… in case of HE-SU 20 MHz bandwidth


Medium Access Control: CSMA/CACarrier Sense Multiple Access/Collision Aviodance

AP

STA 1

STA 2

STA 3

SIF

S

Ack

DIF

S

Bac

koff

Bac

koff

Ack

Bac

koff

Data

Data

Data

Distributed Coordination Function Interframe SpaceDIFS 50 µs (DSSS)

34 µs (OFDM)

Backoff 42 – 178 µs

Short Interframe SpaceSIFS* 10 µs (DSSS)

16 µs (OFDM) *) incl. 2.4GHz signal extention

Ack 24 µs

SIF

S

DIF

S

DIF

S


CSMA/CA extension: RTS/CTSRequest-to-Send / Clear-to-Send

AP

STA 1

STA 2S

IFS

Ack

DIF

S

Bac

kof

f

DataRTS

SIF

S

CTS

SIF

S

RTSBac

kof

f

CTS

DIF

S

SIF

S

SIF

S

Data

CBA


IEEE 802.11ax: Multi-user Operations

STA1RTS

CTS ACK

STA2RTS

CTS ACK

AP

STA

STA1+2MU-RTS

CTS ACKSTA1+2

OFDMA

½ BW => 2x duration

Simultaneous Response

AP

Time saved



OFDMA = OFDM + FDMA

•••••••••

•••••••••

•••••••••

•••••••••

•••••••••

•••••••••

WLAN 11ac: OFDM allocates users in time domain only

WLAN 11ax: OFDMA allocates users in time and frequency domain

•••••••••

•••••••••

•••••••••

•••••••••

•••••••••

•••••••••

Time domain Time domain

Fre

quen

cy d

omai

n

Fre

quen

cydo

mai

n

User3

User3

User2

User2

User1

User1


From single-user to multi-user OFDMAExample: 20 MHz bandwidth

RU1 RU2 RU3 RU4 13 13 RU6 RU7 RU8 RU9RU

RU1 RU2 RU3 RU4

RU1 RU2

SU 242RU1

13

1313

13

• Channel bandwidth isdivided into resource units, RU

• One RU belongs to oneuser. In the next timeslot, the RU may be anotheruser

• Each RU may have a different modulationscheme and/or codingrate

• RU size:26 -52 -

106 -242 -484 -996 -

2x996 - SubCarriers


OFDMA @802.11ax: Various Combinations

There are various combinations of how the frequencyaxis is divided into RUs. Which one is applied isgiven by control information, e.g. scheduling

52 26 2613

13

106

RU1 RU3 RU4 RU2RU5

20MHz

RU1 RU2 RU3 RU413

13

RU6 RU7 RU8 RU9RU

RU1 RU2 RU3 RU4

RU1 RU2

SU 242RU1

13

13

13

13

ı RU sizes can be mixed:


OFDMA @802.11ax: Multi-User DownLink

Ack

AP

STA 1

STA 2

STA 3

Data

Packet Protocol: HE-MUDL only

SIF

S

Ack

Ack

imm

edia

te U

L O

FD

MA

A

ck

OR

Ack

Ack

Ack

Blo

ck A

ck R

eque

st

SIF

S

Blo

ck A

ck R

eque

st

SIF

S

CTS

CTS

CTS

SIF

S

MURTS


OFDMA @802.11ax: Multi-User UpLinkSynchronisation by Trigger Frame

Multi-User Operations are controlled by AP

Multi-User Uplink is initiated by Trigger Frame from AP

Trigger Frame includes:• Device IDs

• RU allocations, MCS, Number of

spatial streams, …

• Power Control

AckAP

STA 1

STA 2

STA 3Data

Data

Data

Trigger Frame

SIF

S

SIF

S

Packet Protocol: HE-TBUL only TB – Trigger Based

MU

-STA

Blo

ck A

ck


OFDMA @802.11ax: Time of Departure Accuracy

Packet Protocol: HE-TBUL only

AckAP

STA 1

STA 2

STA 3

Data

Data

Trigger Frame

SIF

S

SIF

S

MU

-STA

Blo

ck A

ck

Specified Tolerance: ± 0.4 µs

Data


OFDMA @802.11ax: Dynamic Power Control

AP

STA 1

STA 2

STA 3

Power differences between STAs in a UL MU transmission results in a degradation of the performance

Arrival power of different STAs at AP should be roughly the same

Need for Transmit Power Pre-Correction Transmit Power Control (TPC)

Reference: Target Receiver Signal Strength Indicator (RSSI) at the AP side.

AP reports its used transmit power and the expected Target RSSI together with each data-package

STA measures RSSI of received data-package and calculate its path loss

STA transmit signal with power equal to Target RSSI of AP plus calculated path loss.

If necessary AP send a appropriate command to each STA to increase or decrease their power levels

Class A Class B

Absolute transmit ± 3dB ± 9dBPower accuracy

RSSI measurement ± 2dB ± 5dBaccuracy


EVM SpecificationTransmitter Relative Constellation Error (RCE)

Specification is independent of channel bandwidth


OFDMA @802.11ax: Unused Tone Error

Unused tone eror (In-band Emission) limit value for RU26.

For other RU sizes, different limit values and step widths apply.


MU-MIMO Systems – Spatial MultiplexingDownlink and Uplink

In the downlink, beamforming ensures targeted station coverage.

In the uplink, the data streams can be separated without beamforming.


Thank youfor your attention !

Documents

Major Leaps in Evolution of IEEE 802.11 WLAN Technologies · PDF fileIEEE Standard description Release date 802.11 1-2 Mbit/s, 2.4 – 2.485 GHz RF and IR All other standards below