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IEEE 802.11 - Wireless Local Area Networks. 802.11n. Wireless Communication Technology according to IEEE. 802.11a. 802.11h. Local wireless networks WLAN 802.11. 802.11i/e/…/w. WiFi. 802.11b. 802.11g. ZigBee. 802.15.4. 802.15.4a/b. Personal wireless nw WPAN 802.15. 802.15.5.

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Ieee 802 11 wireless local area networks

IEEE 802.11 - Wireless Local Area Networks

Communication Technology Laboratory

Wireless Communication Group


Wireless communication technology according to ieee

802.11n

Wireless Communication Technology according to IEEE

802.11a

802.11h

Local wireless networks

WLAN 802.11

802.11i/e/…/w

WiFi

802.11b

802.11g

ZigBee

802.15.4

802.15.4a/b

Personal wireless nw

WPAN 802.15

802.15.5

802.15.3

802.15.3a/b

802.15.2

802.15.1

Bluetooth

Wireless distribution networks/ Wireless metropolitan area nw

WMAN 802.16 (Broadband Wireless Access)

WiMAX

+ Mobility

802.20 (Mobile Broadband Wireless Access), 802.16e (WiMAX mobile)

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks


Wireless access technologies wireless local area networks wlan 802 11

Wireless Access Technologies:Wireless Local Area Networks (WLAN) 802.11

Structure:

Introduction

Network architecture

Reference model

Physical layer

MAC sublayer 

MAC sublayer management

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Prologue 1

Prologue (1)

  • According to In-Stat and ABI Research, demand for WLAN is still expected to grow strongly over the next years.

  • “Faster Wi-Fi Will Grow Rapidly.”[In-Stat, 2011]

    • “The emerging 802.11ac standard, which is aimed at gigabit-speed wireless LANs, will be quickly adopted over the next four years…“

    • “In-Stat estimates that nearly 350 million routers, client devices and attached modems with 11ac will ship annually by 2015 …”

    • “… 1.5 billion products equipped with 11n will be sold that year [2015], more than double the estimated 700 million in 2011.”


Prologue 2

Prologue (2)

  • “800 mln WiFi households globally by 2016” [IT Facts, 2012]

    • “Already used in some 439 mln households worldwide, equivalent to 25% of all households, Wi-Fi home network penetration will expand to 42%, reaching nearly 800 mln by 2016.”

  • “58% of Americans have a mobile phone with Web connectivity.” [IT Facts, 2009]

  • “49.7% of Americans own smartphones” [IT Facts, 2012]

  • “Hotspot Usage to Reach 120 Billion Connects by 2015” [In-Stat, 2012]

    • “Worldwide hotspot venues will increase to over 1 million in 2013.”

    • “Notebooks continue to account for the majority of connects in the hotspot market; however, the rate of smartphone and tablet access is increasing rapidly.”

Communication Technology Laboratory

Wireless Communication Group


Prologue 3

Prologue (3)

  • WLAN: fast growing market

    • Expanding year after year (along with the rapid spread of broadband infrastructure)

    • Hot Spots: WLANs at airports, railway stations, universities, cafes, etc.

    • Already in 2006: “82% of US hotels offer wireless Internet”

    • Wifi chipsets in PCs, notebooks, smartphones, tablets

  • Dominant standards:

    • IEEE 802.11g with 54 Mbit/s @ 2,4 GHz (successor of 802.11 b with11 Mbit/s @ 2,4 GHz, the former dominant standard)

    • The high throughput 802.11n MIMO standard

  • WiFi Alliance (1999/ 2000), WiFi Certification

  • Topics of this lecture:

  • Standardization

  • OSI reference model

  • PHY

  • MAC

Communication Technology Laboratory

Wireless Communication Group

6


Introduction to ieee 802

Introduction to IEEE 802

  • IEEE 802.11: WLAN – standard (’97/ ‘99)

    • Purpose: provide wireless connectivity to automatic machinery, equipment, or stations, which may be portable or hand-held, or which may be mounted on movingvehicles within a localarea

  • Differences: wired LAN / WLAN

    • destination location < >dest. Address

    • channel: wired < > wireless

    • portable < > mobile

    • CSMA/CD <> CSMA/CA

    • security issues, power saving ...

  • Other IEEE standards:

    • 802.2: Logical Link Control (LLC)

    • 802.3: CSMA / CD, Ethernet

    • 802.4: Token Bus, 802.5 Token Ring

  • IEEE802.11(3,4,5) specifies MAC and PHY layer

  • Physical Layer (PHY): Layer 1 of OSI basic reference model

  • Medium Access Control (MAC): lower half of layer 2 in OSI reference model (layer 2a)

  • Logical Link Control (LLC):

    • upper half of layer 2 (layer 2b)

    • can provide connection-oriented and connectionless services

    • flow control, sliding window, error checking, confirmation of received data

    • LLC standardized for all 802 MACs

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Ieee 802 11 seamless integration

IEEE 802.11 – Seamless Integration

CSMA/CDEthernet

Token Bus

Token Ring

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Network structure 1

Network structure (1)

Internet TCP/IP layered architecture

9

Wireless Networks, 802.11


Network structure 2

LLC

Quelle: MR

Ethernet

Network structure (2)

Thanks to Maximilian Riegel, Siemens Mobile;some pictures of this lecture are taken from

his presentations (formerly at http://www.max.franken.de).

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Characteristics of wireless lans

Characteristics of wireless LANs

  • Advantages

    • very flexible within the reception area

    • mobile communications

    • Ad-hoc networks without previous planning possible

    • (almost) no wiring difficulties (e.g. historic buildings)

    • more robust against disasters like, e.g., earthquakes, fire - or users pulling a plug...

  • Disadvantages

    • typically very low data rate per user compared to wired networks due to shared medium

    • products have to follow many national restrictions if working wireless, it takes a vary long time to establish global solutions

    • low coverage range

Wireless Networks, 802.11


Design goals for wireless lans

Design goals for wireless LANs

  • Low power for battery use

  • No special permissions or licenses needed (ISM band)

  • Robust transmission technology (for the wireless channel)

  • Simplified spontaneous cooperation at meetings (ad hoc)

  • Easy to use for everyone, simple management

  • Security (no one should be able to read my data), privacy (no one should be able to collect user profiles), safety (e.g. low radiation)

  • Transparencyconcerning applications and higher layer protocols, but also location awareness if necessary

  • Using existing LAN infrastructure (global, seamless operation)

Wireless Networks, 802.11


Wlan standardization

WLAN standardization

802.11F: Inter Access Point Protocol

DFS: dynamic frequency selection

TPC: transmit power control

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Wlan ieee 802 11

WLAN IEEE 802.11

Structure:

  • Introduction

  • Network architecture

  • Reference model

  • Physical layer

  • MAC sublayer 

  • MAC sublayer management

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


802 11 network architectures

802.11 Network architectures

  • Station (STA): Any device that contains an IEEE 802.11 conformant MAC and PHY interface to the wireless medium (WM).

  • Basic Service Set (BSS): Set of stations controlled by a single coordination function (CF).

  • CF: logical function, determines when a STA operating within a BSS is permitted to transmit and may be able to receive protocol data units (PDUs) via the WM.

  • Station Services (SS): set of services that support transport of MAC service data units (MSDUs) between STAs within a BSS.

  • Independent Basic Service Set (IBSS): BSS that forms a self-contained network, and in which no access to a distribution system (DS) is available (=> Ad Hoc network)

Quelle: MR

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Ad hoc mode 802 11 ibss

Ad Hoc Mode: 802.11 IBSS

  • Network composed solely of stations within mutual communication range of each other via the wireless medium (WM); typically created in a spontaneous manner.

  • Principal distinguishing characteristic: limited temporal and spatial extent.

Quelle: MR

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Infrastructure mode 1

Quelle: MR

Infrastructure Mode (1)

transport layer

network

layer

LLC

(layer 2b)

  • Access Point (AP): Any entity that has STA functionality and provides access to the DS via the wireless medium (WM) for associated stations => AP implements both the 802.11 MAC and the DS MAC protocols.

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Infrastructure mode 2

Access Point

(AP) A

AP B

Infrastructure Mode (2)

  • Several connected BSSs may form (together with integrated LANs) an Extended Service Set (ESS)

  • The architectural component used to interconnect BSSs is the distribution system (DS).

  • 802.11: Distribution System Services (DSS) are specified (not the DS itself)

  • The medium used by the DS is called Distribution System Medium (DSM), and is not specified. Examples are a Wireless Medium, a cable, or a fibre-optic cable, ...

STA 2

Quelle: MR

STA 1

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Infrastructure mode 3

Infrastructure Mode (3)

  • Portal: The logical point at which MAC service data units (MSDUs) from a non-IEEE 802.11 local area network (LAN) enter the DS of an ESS.

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Ieee 802 11 wireless local area networks

WLAN IEEE 802.11

Structure:

Introduction

Network architecture

Reference model

Physical layer

MAC sublayer 

MAC sublayer management

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Osi basic reference model

OSI basic reference model:

  • 802.11 specifies the layers 1 and 2a

  • Coexistence

    • with other 802 LANs (Bridge on LLC layer)

    • several 802.11 WLANs

  • Compatibility to other (802) LANs:

    • Mobility of STAs handled in the MAC layer; so, for upper protocol layers, 802.11 shows no differences to other 802 networks

  • One MAC for all 802.11 PHYs

    • Enhancements: 802.11e, 802.11n, …

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Reference model protocol entities

IEEE 802.11

LLC

(Logical Link Control)

Reference model: Protocol Entities

DATA Link

MAC

Sublayer

MAC Sublayer

Management

Station

Management

PLCP Sublayer

PHY

PHY Layer

Manage-ment

PMD Sublayer

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Ieee 802 11 wireless local area networks

WLAN IEEE 802.11

Structure:

Introduction

Network architecture

Reference model

Physical layer

MAC sublayer 

MAC sublayer management

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


5 different physical layer technologies

5 different Physical layer technologies

  • FHSS (Frequency Hopping Spread Spectrum)

    • 2.4 GHz band: 1 and 2 Mbit/s, 2GFSK, 4GFSK

    • frequency hopping: 79 frequencies

  • DSSS (Direct Sequence Spread Spectrum)

    • 2.4 GHz band: 1, 2, 5.5 and 11 Mbit/s

    • DBPSK, DQPSK, 11-chip Barker Sequence, CCK

  • OFDM (Orthogonal Frequency Division Multiplexing)

    • 802.11a: 5 GHz band, 6, 9, 12, 18, 24, 36, 48 and 54 Mbit/s

    • BPSK, QPSK, 16-QAM and 64-QAM (each with 2 different coding rates)

    • 52 sub-carriers

    • 802.11g: OFDM in 2.4 GHz with 54 Mbit/s

  • Baseband IR

    • 1 and 2 Mbit/s, 4-PPM and 16-PPM

  • MIMO (Multiple Input – Multiple Output) – OFDM

    • 802.11n: upto 600 Mbit/s (details see 802.11n chapter)

Quelle: MR

Communication Technology Laboratory

Wireless Communication Group


Physical layer ofdm

Physical Layer – OFDM

, 802.11 g and 802.11n

and 802.11 g

IEEE 802.11 a: (in CH) OFDM@ 5.15 – 5.35 GHz (Indoor)

and @ 5.47 – 5.725 GHz (Indoor&Outdoor)

802.11 g: OFDM @ 2,4 - 2,4835 GHz

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Physical layer 802 11a ofdm

Physical Layer – 802.11a. OFDM

Transmitter and receiver block diagram for the OFDM PHY

Communication Technology Laboratory

Wireless Communication Group


802 11a phy data format

802.11a PHY Data Format

http://www.ewh.ieee.org/r6/scv/comsoc/0205.pdf

27


Physical layer ofdm 802 11a

Physical Layer – OFDM (802.11a)

Subcarrier frequency allocation

Bandwidth: 20 MHz

FFT block length : 64

Number of used carriers: 52 (including 4 pilots)

Guard interval: 0.8 µs

Wireless Networks, 802.11


802 11a ofdm parameters

802.11a OFDM Parameters

29


802 11a subcarrier assignment

802.11a Subcarrier Assignment

http://www.ewh.ieee.org/r6/scv/comsoc/0205.pdf

30


Subcarrier modulation schemes

Subcarrier Modulation Schemes

modulation

Correction

http://www.ewh.ieee.org/r6/scv/comsoc/0205.pdf

31


802 11a phy data rates

802.11a PHY Data Rates

32


Comparison of mostly used 802 11 phys

Comparison of mostly used 802.11 PHYs

Data rates

802.11a: OFDM, up to 54 Mbit/s

802.11b: DSSS, up to 11 Mbit/s

802.11g: DSSS (downwardly compatible to 802.11b) /

OFDM (up to 54 Mbit/s)

Channels

802.11a: 8 (non-overlapping) channels @ 5.15 – 5.35 GHz (20 MHz each)

=> up to 8 APs in the same area

802.11b/ g: only 3 non-overlapping (out of 13) channels (25 MHz each)=> only up to 3 APs in the same area

Communication Technology Laboratory

Wireless Communication Group


Channels 802 11b

Channels: 802.11b

European channel selection—non-overlapping

European channel selection—overlapping

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Channels 802 11a

Channels: 802.11a

OFDM PHY frequency channel plan for the United States

Communication Technology Laboratory

Wireless Communication Group


Ieee 802 11 wireless local area networks

WLAN IEEE 802.11

Structure:

Introduction

Network architecture

Reference model

Physical layer

MAC sublayer 

MAC sublayer management

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Overview mac sublayer

Overview: MAC Sublayer

  • Two multiple access schemes -> two Coordination Functions:

    (1)Distributed Coordination Function (DCF): CSMA / CA (contention based)

    or optional

    (2)Point Coordination Function (PCF): Polling (central allocation)

  • Different frame formats

  • Fragmentation / defragmentation

  • Encryption

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Multiple access schemes

Multiple access schemes

Distributed Coordination Function:

  • For IBSS and Infrastructure mode (ESS)

  • Based on Carrier Sense Function in PHY, called Clear Channel Assessment (CCA)

  • CSMA / CA for broadcast frames

  • CSMA / CA + ACK otherwise

  • Optional: (parameterised) RTS / CTS – handshake for Virtual Carrier Sense (protection against „Hidden Nodes“)

Point Coordination Function (optional):

  • Only in Infrastructure Mode (ESS)

  • Onlyfor systems using an AP as central point of BSS

  • AP gives transmit right to the STAs; STAs are polled one after another (Polling)

  • Higher priority than DCF (seeInterframe Spacing)

Wireless Networks, 802.11


Mac sublayer dcf 1

transmit, if medium is free >= DIFS

DIFS

Contention Window

PIFS

DIFS

SIFS

Backoff-Window

Medium busy

Slot time

Next

Frame

Decrement Backoff Timer as long as medium idle

Defer access

MAC Sublayer: DCF (1)

CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance):

  • Channel access:

    • If WM seems to be free for a time >= DIFS, STA transmits immediately

    • If WM busy, STA waits until the end of the ongoing transmission and starts Backoff Procedure

    • After this the status of the channel is checked again

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer dcf 2

MAC Sublayer: DCF (2)

  • Backoff Procedure (for a STA willing to transmit):

    • STA sets its Backoff Timer to a random backoff time. In this time STA waits and uses carrier-sense mechanism.

    • Only if the WM seems to be idle, the STA decrements the Backoff Timer.

    • Backoff procedure starts also, if a collision is detected.

  • Backoff procedure reduces the probability of collisions

    • without such a procedure this probability would be high after a successful transmission, because then all the STAs prepared to transmit would start their transmissions at the same time.

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer dcf 3

MAC Sublayer: DCF (3)


Mac sublayer dcf 4 csma ca ack protocol

DIFS

Data

Src

SIFS

Ack

Dest

Contention Window

DIFS

Other

Next MPDU

Defer transmission

Backoff Procedure

MAC Sublayer: DCF (4) - CSMA / CA + ACK – Protocol

  • In a direct transmission between 2 STAs successful transmissions (CRC correct) are acknowledged immediately (positive acknowledgement) using ACK Frames.

  • If no ACK is received the frame is repeated.

  • The (physical) Carrier-Sense mechanism is provided by the PHY (CCA).

  • After unsuccessful transmissions the max. backoff time increases exponentially up to a limit.

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer dcf 5 rts cts handshake optional

DIFS

Data

RTS

Src

CTS

Ack

Dest

CW

Next MPDU

Other

NAV

(RTS)

NAV

(CTS)

Backoff Procedure

Defer transmission

MAC Sublayer: DCF (5) - RTS-CTS Handshake (optional)

  • All STAs receiving at least one of the two control frames are now informed about the length of the upcoming transmission (Virtual Carrier Sense)

  • STAs store this information in their Net Allocation Vector (NAV)

  • Carrier-Sense mechanism: CCA + NAV

  • Control frames are exchanged:

    • “Ready To Send“: RTSSTA wants to start transmission

    • “Clear To Send”: CTSreceiver is ready for transmission

  • These frames contain a field indicating the length of the upcoming transmission.

Communication Technology Laboratory

Wireless Communication Group


Mac sublayer dcf 6 hidden nodes

STA

AP

RTS

RTS Range

CTS

CTS Range

Data

Ack

AP

STAs can’t hear each other

but the AP.

STA

STA

MAC Sublayer: DCF (6) - Hidden Nodes

The „Hidden Nodes“problem can be eased by the RTS / CTS mechanism.

  • STAs can be configured, to use the RTS / CTS mechanism always, never or from a given threshold upwards (for short frames the overhead may be too high).

Communication Technology Laboratory

Wireless Communication Group


Exposed nodes

Exposed Nodes

  • STA S1/S2 does not generate interference at STA R2/R1

  • S1 and S2 on the other hand are in communication range of each other

    • They are „exposed nodes“

  • Thus S1 and S2 could transmit simultaneously

    • CSMA/CA prevents this, as e.g. S2 senses the channel busy if S1 transmits

  • RTS/CTS can help here: if e.g. S2 detects the RTS message of S1 but does not receive the CTS answer from R1 it can conclude, that it is an exposed node and transmit concurrently with S1

45


Mac sublayer fragmentation

DIFS

PIFS

SIFS

Other

Backoff

NAV (RTS)

NAV (Fragment 0)

NAV (CTS)

NAV (ACK 0)

SIFS

Src

RTS

Fragment 0

Fragment 1

Dest

CTS

ACK 1

ACK 0

MAC Sublayer: Fragmentation

  • Partitioning MSDUs (MAC Service Data Units) or MMPDUs (MAC Management Protocol Data Units) into smaller MAC level frames

  • Purpose: increase reliability, by increasing the probability of successful transmission

  • Fragmentation: MSDU or MMPDU are sent as independent transmissions, each of which is separately acknowledged (not for Broadcast frames)

  • Backoff procedure and retransmission if no ACK received

  • Information about duration of transm. included in fragments and in ACKs => NAV is set

  • Defragmentation at receiver

  • Can be combined with RTS - CTS

Communication Technology Laboratory

Wireless Communication Group


Mac sublayer pcf 1

PCF waits when medium is busy:delay

CFP repetition interval

CFP repetition interval

CFP

CP

DCF

PCF

WM busy

CF burst (PCF)

Variable length

"Reset NAV"

Async traffic waits

NAV

MAC Sublayer: PCF (1)

  • AP of a BSS can become Point Controller (PC) -> Polling Master

  • PCF gains control of the WM by using Beacon Management Frames to set the NAV in STAs

  • Contention Period (CP): DCF has control in this period (CSMA/CA: contention based multiple access)

  • Contention Free Period (CFP): PCF has control (Polling: central allocation, no contention)

  • CP and CFP alternate under PC control

  • Length and repetition interval of the CFPs are controlled by the PC

Communication Technology Laboratory

Wireless Communication Group


Mac sublayer pcf 2

MAC Sublayer: PCF (2)

  • STA immediately responses to a CF-Poll_Frame

  • Responses have variable length

  • “Reset NAV“bylast frame of AP

  • No RTS / CTS under PCF (Polling)

  • PCF better suited for time critical services

However, legacy PCF was rarely (or even never) used;

=> But, it is the basis for a CF in 802.11e

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer interframe spacing

MAC Sublayer: Interframe Spacing

  • SIFS (Short Interframe Space):time between ACK frames, CTS frames, fragmented data frames and PCF polls. E.g.: Frequency Hopping PHY - 28ms (802.11a: 16µs)

  • PIFS (PCF Interframe Space):PCF has higher priority than DCF=> PIFS < DIFS; PIFS = SIFS + Slot TimeE.g.: Frequency Hopping PHY - 78ms (802.11a: 25µs)

  • DIFS (DCF Interframe Space):= SIFS + 2 Slot TimeE.g.: Frequency Hopping PHY - 128ms (802.11a: 34µs)

  • EIFS (Extended Interframe Space):used if in previous transmission an error occurred

  • IFS independent of the STA bit rate

Communication Technology Laboratory

Wireless Communication Group


Ieee 802 11 wireless local area networks

WLAN IEEE 802.11

Structure:

Introduction

Network architecture

Reference model

Physical layer

MAC sublayer 

MAC sublayer management

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Overview mac sublayer management

Overview: MAC Sublayer Management

  • Synchronization needed for

    • Detection of WLANs

    • Staying in a WLAN

    • Synchronization functions:

      • TSF (Time Synchronisation Function) Timer, Beacon generation

  • Power management

    • Sleep mode (without missing a message)

    • Power management functions

      • Periodic sleep, frame buffering, Traffic Indication Map

  • Association and Reassociation

    • Connection to a network

    • Roaming

    • Scanning

  • Management Information Base

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer management synchronisation

Beacon Interval

"Actual time" in Beacon

Time axis

X

X

X

X

Medium busy

Beacon

MAC Sublayer Management: Synchronisation

  • All STAs in a BSS are synchronized to a common clock

    • important for Hop Timing in FH PHY

    • for Point Coordination Timing

    • for Power Management

  • Timing Synchronization Function (TSF) keeps timers for all STAs in a BSS synchronized

    • Each STA has a local TSF Timer

    • Beacons contain timestamps

      • Beacons contain also further management information (e.g. for power management, roaming)

    • The timestamps calibratethe local clocks of the STAs

    • In an IBSS (ad hoc) network all STAs transmit Beacons

    • In an ESS the AP controls the timing

    • Beacons are generated periodically, but they can be delayed due to CSMA/CA

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer manag power management

MAC Sublayer Manag.: Power Management

  • Power Save (PS) / Sleep Mode for STAs, to save energy

  • ESS (infrastructure mode):

    AP buffers frames for STAs in PS mode and transmits them at “known times”

    • STAs that currently have buffered MSDUs within the AP are identified in a Traffic Indication Map (TIM)

    • TIM is included in all Beacons of the AP

    • STAs in PS mode wake up in periodical intervals to receive Beacons (also because of the TSF)

      => Contention Period, under control of DCF

      If there is a MSDU for a STA buffered in the AP, the STA transmits PS-Poll to the AP,

      which shall respond with the corresponding buffered MSDU immediately

      => CFP, PCF

      No PS-Poll, STA remains active until MSDU is received or CFP ends

    • Broadcast, multicast frames: also buffered by AP, delivered after Delivery TIM (DTIM)

  • IBSS (ad hoc mode):

    • If destination is in PS mode, source notifies using ATIM (Announcement Traffic Indication Message, or ad hoc TIM)

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer management scanning

MAC Sublayer Management: Scanning

  • Scanning necessary for:

    • Finding and joining a new network

    • Setting up an IBSS (ad hoc network)

    • Finding a new AP while performing handover or roaming

  • MAC used by different PHYs, most of them using more than one channel

  • Scanning:

    • Active:

      • STA sends Probe on each channel

      • waits for an answer (Probe Response)

    • Passive:

      • listening for Beacons

  • Beacon as well as Probe Response contain all information needed to join the network

  • Seamless handover not defined in 802.11

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Mac sublayer management association

Authentication: “Shared Key”(using WEP/WPA encryption) or “Open System”

Goal: provide access control equal to a wired LAN

Authentication service: provides a mechanism for one STA to identify another STA

Association

establishing a logical connection between STA and AP

each STA must become associated with an AP before it is allowed to send data through the AP onto the DS

connection is necessary for the DS to know where and how to deliver data to the STA

Successful

Association or

Reassociation

MAC Sublayer Management: Association

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Active scanning association handover

Quelle: MR

Active Scanning, Association, Handover

Handover: Scanning,

(Re) association request

Communication Technology Laboratory

Wireless Communication Group

Wireless Networks, 802.11


Outline

Outline

IEEE 802.11e

MAC Quality of Service Enhancements

IEEE 802.11n:

Enhancements for higher throughput

Communication Technology Laboratory

Wireless Communication Group

57

802.11e


Wlan ieee 802 11e

WLAN IEEE 802.11e

  • Introduction

  • MAC Architecture

    • DCF

    • HCF: EDCA, HCCA

  • Main Differences from legacy IEEE 802.11

    • Traffic Classification

    • TXOP

    • Polling during CP

    • Admission Control

    • Block Acknowledgment

    • No Acknowledgment

    • DLS operation

802.11e


Introduction

Introduction

IEEE802.11e: MAC Quality of Service Enhancements

  • Finalized in Nov. 2005

  • Defines MAC procedures to support LAN applications with QoS requirements

    • Transport of voice, audio, and Video over 802.11 WLANs.

  • QoS enhancements available to

    • QoS stations (QSTAs) associated with a QoS access point (QAP) in a QoS basic service set (QBSS).

  • nQSTA: HCF not present

  • QSTA: both DCF and HCF are present.

    • PCF is optional in all STAs.

802.11e


Main qos problems with legacy 802 11

Main QoS Problems with legacy 802.11

  • Unknown transmission durations of the polled stations

  • No prioritization

  • Unpredictable beacon delays

  • Unpredictable throughput per STA

TBTT: Target Beacon Transmission Time

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802.11e


Wlan ieee 802 11e1

WLAN IEEE 802.11e

  • Introduction

  • MAC Architecture

    • DCF

    • HCF: EDCA, HCCA

  • Main Differences from legacy IEEE 802.11

    • Traffic Classification

    • TXOP

    • Polling during CP

    • Admission Control

    • Block Acknowledgment

    • No Acknowledgment

    • DLS operation

802.11e


Ieee 802 11 wireless local area networks

HCF

The HCF uses both methods

  • contention-based: enhanced distributed channel access (EDCA), and

  • contention-free: HCF controlled channel access (HCCA)

    New feature of 802.11e MAC: Transmission Opportunity (TXOP)

  • interval of time when a STA has the right to initiate transmissions

  • defined by a starting time and a maximum duration

  • allocated via contention (EDCA-TXOP) or

  • granted through HCF (polled-TXOP)

  • duration of an EDCA-TXOP is limited by a QBSS-wide TXOP limitdistributed in beacon frames

  • duration of a polled TXOP specified by duration field inside the poll frame

    Although the poll frame is a new frame as part of 802.11e, also the legacy

    stations set their NAVs upon receiving this frame.

802.11e


Traffic specification tspec 1 2

Traffic Specification (TSPEC) 1/2

  • TSPEC:

    • Quality of service (QoS) characteristics of a data flow to and from a non-access point (non-AP) QSTA

    • Contains the set of parameters that define the characteristics and QoS expectations of a traffic flow (like data rate, burst size, and service interval).

  • Parameterized QoS:

    • Treatment of MAC protocol data units (MPDUs) depends on the parameters associated with the MPDU

    • Primarily provided through HCCA mechanism

    • Also provided by EDCA when used with a traffic specification (TSPEC) for admission control.


Traffic specification tspec 2 2

Traffic Specification (TSPEC) 2/2

  • Traffic stream (TS):

    • Set of MAC service data units (MSDUs) to be delivered subject to the QoS parameter values provided to the MAC in a particular TSPEC.

    • TSs are meaningful only to MAC entities of QSTAs.

    • These MAC entities determine the TSPEC applicable for delivery of MSDUs belonging to a particular TS using the TS identifier (TSID)


Overview of mac services 1

Overview of MAC services (1)

  • By default, asynchronous MSDU transport is performed on a best-effort connectionless basis.

  • However, the QoS facility uses a traffic identifier (TID) to specify differentiated services on a per-MSDU basis.

    • The QoS facility also permits more synchronous behavior to be supported on a connection-oriented basis using TSPECs.

  • No guarantees that the submitted MSDU will be delivered successfully.

  • Asynchronous data service provided by the MAC: Broadcast and multicast transport available.


Overview of mac services 2

Overview of MAC services (2)

  • QSTAs in a QBSS differentiate their MSDU delivery according to the designated traffic category or traffic stream (TS) of individual MSDUs

  • QSTA: MAC uses a set of rules that tends to cause higher UP (user priority) MSDUs in a BSS to be sent before lower UP MSDUs.

  • MAC sublayer entities determine the UPs for MSDUs based on the TID values provided with MSDUs.

  • a TSPEC has been provided for a TS => MAC attempts to deliver MSDUs belonging to that TS in accordance with the QoS parameter values contained in the TSPEC.


Wlan ieee 802 11e2

WLAN IEEE 802.11e

  • Introduction

  • MAC Architecture

    • DCF

    • HCF: EDCA, HCCA

  • Main Differences from legacy IEEE 802.11

    • Traffic Classification

    • TXOP

    • Polling during CP

    • Admission Control

    • Block Acknowledgment

    • No Acknowledgment

    • DLS operation

802.11e


Edca enhanced distributed channel access

EDCA (Enhanced Distributed Channel Access)

802.11e

Up to 8 UPs (or TCs)

EDCA

EDCA

EDCA

EDCA

transmission attempt

  • DCF access to the medium depending on Traffic Categories (TCs)

    • 8 different priorities (UP: User Priority)

  • 4 different buffers with different priority of access to the medium: Access Categories (ACs);

    • Average time to wait depends on priority

  • Per-queue channel access: internal collision resolution (EDCAF)

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802.11e


Edca 2

EDCA(2)

BK: Background

BE: Best effort

VI: Video

VO: Voice

UP-to-AC mappings

  • For each AC: an enhanced distributed channel access function (EDCAF) contends for TXOPs using a set of EDCA parameters

  • EDCAF: enhanced variant of the DCF

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Edca 3

EDCA (3)

  • EDCA delivers traffic according to different ACs by varying the following quantities:

    • Amount of time a QSTA senses the channel to be idle before backoff or transmission (AIFS), or

    • length of the contention window to be used for the backoff, or

    • duration a STA may transmit after it acquires the channel (length of TXOP).

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802.11e


Edca 4

EDCA (4)

  • EDCA: priority according to AC by varying:

    • AIFS[AC]

    • length of the contention window to be used for the backoff

    • length of TXOP

with 802.11a:

Slot: 9 μs

SIFS: 6 μs

PIFS: 25 μs

DIFS: 34 μs

AIFS: ≥34 μs

  • AIFS: Arbitration Inter frame Space - shall be used by QSTAs to transmit:

    • all Data type frames (MPDUs), all Management type frames (MMPDUs), the following control frames: PS-Poll, RTS

Communication Technology Laboratory

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802.11e


Edca parameters lengths of cw ifs txop

EDCA parameters (lengths of CW, IFS, TXOP)

0 indicates that a single MSDU or MMPDU

802.11a: aCWmin = 15, aCWmax 1023

BK: Background

BE: Best effort

VI: Video

VO: Voice

DSS

OFDM

AIFS number-AIFSN: number of slots after a SIFS duration a QSTA should defer before either invoking a backoff or starting a transmission (minimum value for a QSTA is 2, for a QAP it is 1).

AIFS[AC] = AIFSN[AC] × aSlotTime + aSIFSTime

Communication Technology Laboratory

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802.11e


Edca txop

EDCA TXOP

Beacon

Beacon

Frame 2

Backoff

Backoff

Access Point

AIFS

AIFS

SIFS

SIFS

t

Ack

Ack

t

Wireless Station

TXOP Bursting – Multiple Frame Tx

(Reduces Backoff Overhead)

t < EDCA TXOP limit

Busy

Frame 1

  • TXOP: Transmit Opportunity

  • given to the TC with highest priority of the colliding TCs,

  • all Management type frames (MMPDUs), and the following control

  • frames: PS-Poll, RTS, CTS (when not transmitted as a response to the RTS),

  • BlockAckReq and BlockAck

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Wireless Communication Group

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802.11e


Wlan ieee 802 11e3

WLAN IEEE 802.11e

  • Introduction

  • MAC Architecture

    • DCF

    • HCF: EDCA, HCCA

  • Main Differences from legacy IEEE 802.11

    • Traffic Classification

    • TXOP

    • Polling during CP

    • Admission Control

    • Block Acknowledgment

    • No Acknowledgment

    • DLS operation

802.11e


Hcca 1

HCCA (1)

  • The HCCA mechanism uses a QoS-aware centralized coordinator, called a hybrid coordinator (HC).

  • HC:

    • collocated with the QAP

    • higher medium access priority than non-AP STAs

    • allocates TXOPs to itself and other QSTAs in order to provide limited-duration controlled access phase (CAP) for contention-free transfer of QoS data.

  • HCCA TXOP allocation may be scheduled during the CP and CFP.

802.11e


Hcca 2

HCCA (2)

  • HCF Controlled Channel Access (HCCA):

    • Like PCF mechanism, HCCA controls channel access through AP-directed polling.

    • AP's Hybrid Controller takes QoS into consideration when scheduling STA transmission times and durations, giving some traffic a bigger share of the channel.

    • STAs using HCCA submit reservation requests

    • AP then assigns transmit opportunities based on 8 possible Traffic Stream Identifiers (TSIDs).

      • TSIDs are themselves based upon Transmission Specification (TSPEC) parameters like data rate, burst size, and service interval.

    • This parameterized QoS mechanism is arguably more complex than prioritized QoS.

      • E.g., HCCA requires STAs to know what they'll want to send in advance.

      • However, in WLANs used primarily for voice or video streams, HCCA with well-tuned QoS parameters can enable more efficient channel utilization by eliminating "wasted" backoff time.


Controlled access phase cap generation

Controlled Access Phase (CAP) Generation

  • HC shall sense the WM.

    • If WM is determined idle for one PIFS period, HC transmits first frame of any permitted frame exchange sequence.

    • Duration value is set to cover the CFP or the TXOP.

    • First permitted frame in a CFP after a TBTT is the Beacon frame.

(controlled access phase)

802.11e


Hcca txop

Access Point

SIFS

SIFS

SIFS

Piggybacking

(Reduces Poll and Ack Overheads)

Wireless Station

PIFS

PIFS

HCCA TXOP

UPLINK TXOP

DOWNLINK TXOP

Polled TXOP limit

Downlink TXOP limit

Beacon

Poll + Data

Ack

Data

Busy

Data

Ack

t

SIFS

SIFS

SIFS

Ack

Data

Data + Ack

t

802.11e


Wlan ieee 802 11e4

WLAN IEEE 802.11e

  • Introduction

  • MAC Architecture

    • DCF

    • HCF: EDCA, HCCA

  • Main Differences from legacy IEEE 802.11

    • Traffic Classification

    • TXOP

    • Polling during CP

    • Admission Control

    • Block Acknowledgment

    • No Acknowledgment

    • DLS operation

802.11e


Admission control

Admission Control

  • Important for the provision of guaranteed QoS parameters

  • Goal: Limit amount of traffic admitted into a service class so that QoS of existing flows will not degrade, while the medium resources can be maximally utilized

  • An IEEE 802.11 network may use admission control to administer policy or regulate the available bandwidth resources.

  • Admission control is also required when a QSTA desires guarantee on the amount of time that it can access the channel.

  • HC administers admission control in the network.

  • Admission control, in general, depends on vendors’ implementation of the scheduler, available channel capacity, link conditions, retransmission limits, and the scheduling requirements of a given stream.

802.11e


Block acknowledgment

Block Acknowledgment

  • The Block Ack mechanism improves channel efficiency by aggregating several acknowledgments into one frame.

  • There are two types of Block Ack mechanisms: immediate and delayed.

  • The Block Ack mechanism is initialized by an exchange of ADDBA (add Block Acknowledgment) Request/Response frames.

  • The number of frames in the block is limited, and the amount of state that is to be kept by the recipient is bounded.

  • Acknowledgments of frames belonging to the same TID (Traffic Identifier assigned by higher layers), but transmitted during multiple TXOPs, may be combined into a single BlockAck frame.

802.11e


No acknowledgment

No Acknowledgment

  • ACK does not need to be used in a QBSS in case of time-critical services when a retransmission is not reasonable.

  • There is no MAC-level recovery, and the reliability of this traffic is reduced, due to the increased probability of lost frames from interference, collisions, or time-varying channel parameters.

  • A protective mechanism (such as transmitting using HCCA, RTS/CTS, should be used to reduce the probability of other STAs transmitting during the TXOP.

802.11e


Dls direct link setup operation 1

DLS (direct-link setup) Operation (1)

  • DCF: In general, STAs are not allowed to transmit frames directly to other STAs in a BSS (exception: IBSS, i.e. Ad-hoc network)

    • They should always rely on the AP for the delivery of the frames

  • However, STAs with QoS facility (i.e., QSTAs) may transmit frames directly to another QSTA by setting up such data transfer using DLS.

    • Need for this protocol: motivated by the fact that the intended recipient may be in PS mode, in which case it can be awakened only by the QAP.

  • Second feature of DLS: exchange of rate set and other information between the sender and the receiver

  • DLS prohibits STAs going into PS mode for the duration of the direct stream as long as there is an active DLS between the two STAs.

  • DLS does not apply in a QIBSS, where frames are always sent directly from one STA to another.

802.11e


Dls direct link setup operation 2

DLS (direct-link setup) Operation (2)

  • The handshake involves four steps

    • QSTA-1 intending to exchange frames directly with another non-AP STA (QSTA-2) sends a DLS Request frame to the QAP (step 1a);

      • request contains the rate set, capabilities of QSTA-1, and the MAC addresses of QSTA-1 and QSTA-2.

    • If QSTA-2 is associated in the BSS, and direct streams are allowed in the policy of the BSS, and QSTA-2 is indeed a QSTA => QAP forwards the DLS Request frame to QSTA-2 (step 1b).

    • If QSTA-2 accepts the direct stream, it sends a DLS Response frame to the QAP (step 2a) containing rate set, capabilities of QSTA-2, and the MAC addresses of QSTA-1 and QSTA-2.

    • QAP forwards the DLS Response frame to QSTA-1 (step 2b)=> direct link becomes active and frames can be sent from QSTA-1 to QSTA-2 and from QSTA-2 to QSTA-1

802.11e


Wlan ieee 802 11e5

WLAN IEEE 802.11e

  • Introduction

  • MAC Architecture

    • DCF

    • HCF: EDCA, HCCA

  • Main Differences from legacy IEEE 802.11

    • Traffic Classification

    • TXOP

    • Polling during CP

    • Admission Control

    • Block Acknowledgment

    • No Acknowledgment

    • DLS operation

802.11e


Outline1

Outline

IEEE 802.11e

MAC Quality of Service Enhancements

IEEE 802.11n:

Enhancements for higher throughput

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802.11e


Wlan 802 11n high throughput wlan

WLAN 802.11n: High Throughput WLAN

  • MIMO- OFDM WLAN standard

  • Goals: Using MIMOPHY for

    • higher data rates

    • higher spectral efficiency

    • higher diversity gains (i.e. increased link reliability)

    • extended communication range

  • Several MAC enhancements (e.g. MSDU aggregation to reduce overhead, RIFS – Reduced IFS, Block ACK, …)

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802.11n


Ieee wlan 802 11n mimo ofdm

IEEE WLAN 802.11n: MIMO-OFDM

  • IEEE 802.11n standard specifies MAC and PHY for a highthroughput WLAN

    • PHY is based on MIMO OFDM in the 2.4 GHz and 5 GHz band

      • operating in 20 MHz bandwidth

      • operation in 40 MHz bandwidth is optional.

  • Mandatory in 802.11n

    • for an AP: support of 1 and 2 spatial streams for 20 MHz bandwidth (MIMO)

    • for an 802.11n STA: one spatial stream

  • Optional features include

    • transmit beamforming

    • space-time block codes (STBC) or hybrid STBC/ Spatial Multiplexing (SM)

    • support of 3–4 spatial streams in 20 MHz mode and of 1–4 spatial streams in 40 MHz mode is optional.

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Wireless Networks, 802.11


Wlan 802 11n phy

WLAN 802.11n: PHY

  • OFDM in 2.4 and 5 GHz (ISM) band

  • Mandatory payload communication capabilities of up to 135 Mbit/s

  • Optional modes capable of supporting data rates up to 540 Mbit/s (600 Mbit/s for reduced OFDM Guard Interval (GI))

  • 1 TX, 2 TX, 3 TX, and 4 TX (transmit antenna modes)

  • MIMO Spatial Multiplexing (SpaMuX) gain: 1, 2, 3, or 4 (spatial sub-channels)

  • 540 Mbit/s mode: 64-QAM, code rate = 5/6, # spatial sub-channels = 4 (600 Mbit/s: optional 400 ns GI instead of 800ns)

  • NTX-STBC (Space Time Block Coding) Modes: more TX antennas than # of used spatial sub-channels

  • Low Density Parity Check (LDPC) codes: optional error correction codes

  • Extended communication range (Txbeamforming, STBC, LDPC)

Communication Technology Laboratory

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802.11n


Mandatory and optional phy features

Mandatory and Optional PHY Features

  • Up to 4 spatial streams: 4x4 MIMO (up to factor 4 in data rate)

  • 40 MHz bandwidth (factor 2)

  • 802.11a/g encoder rate ¾:for .11n increased to 5/6 (11% increase in data rate)

  • Four extra OFDM subcarriers squeezed into the spectral mask (48 -> 52: 8% increase)

  • Optional OFDM guard interval of 400 ns (11% increase)

  • Mixed format: backward compatible to .11a/g OFDM

    • but additional training fields in preamble for MIMO training (20μs in .11a to 48 μs in .11n with 4 streams)

Eldad Perahia: “IEEE 802.11n Development: History, Process, and Technology,”IEEE Communications Magazine, July 2008.

90

802.11n

90


Summary of 802 11n mac enhancements

Summary of 802.11n MAC Enhancements

  • Frame aggregation as key method to increase efficiency on MAC

    • Increases the length of the data portion of the frame relative to PHY and MAC overhead

  • Block Ack: -> 802.11e

    • Enhanced by reduced interframe spaces (RIFS)

    • Reverse direction protocol: e.g. FTP over TCP, TCP Ack in the same TXOP

  • TxBF: PHY, but MAC for exchange of beamforming weights, CSI, channel sounding, …

91

802.11n

91


Wlan 802 11n code rates 1

WLAN 802.11n: Code Rates (1)

  • IEEE 802.11n, October 2009

92

802.11n

92


Wlan 802 11n code rates 2

WLAN 802.11n: Code Rates (2)

  • IEEE 802.11n, October 2009

93

802.11n

93


Wlan 802 11n code rates 3

WLAN 802.11n: Code Rates (3)

  • IEEE 802.11n, October 2009

94

802.11n

94


Wlan 802 11n code rates 4

WLAN 802.11n: Code Rates (4)

95

802.11n

95


Wlan 802 11n transmitter

WLAN 802.11n: Transmitter

  • IEEE 802.11n, October 2009

  • CSD: Cyclic Shift Diversity

96

802.11n

96


A glimpse on 802 11ac

A Glimpse on 802.11ac

  • Expected Throughput: per single link at least 500 Mbit/s, for 2 users simultaneously (i.e. 1 Gbit/s sum throughput)

    • Up to 1.75 Gbit/s expected per single link (as a first step)

  • 5 GHz band mandatory (2.4 GHz band still supported => backward compatible to 802.11n)

  • Bandwidth: 80 and 160 MHz @ 5 GHz

  • MIMO: 8 antennas, multi-user MIMO

  • Symbol alphabet: 256-QAM

  • Beamforming

  • MAC modifications

  • Approval of .11ac standard: expected not before early 2014

Communication Technology Laboratory

Wireless Communication Group


Multi user mimo

Multi-User MIMO

  • Uplink: Multiple Access Channel(MIMO-MAC)

  • Downlink: Broadcast Channel (MIMO-BC)

STA 1

AP

STA 2

Diversity, MIMO


Mu mimo downlink

MU-MIMO - Downlink

  • MIMO transmit processing at AP (to separate both STAs)

  • No joint decoding at STAs on receive side

    • The Tx MIMO signals for different STAs interfere with each other

    • AP to use Tx signal processing to cancel (or reduce) this interference

    • Rates to the STAs are bounded by the achievable rate region (capacity region) of the MIMO broadcast channel

      • See, for instance: D. Tse, P. Viswanath, "Fundamentals of Wireless Communication", Cambridge University Press, 2005. [Tse, 2005]

LTE Advanced


Mu mimo uplink

MU-MIMO - Uplink

  • MIMO receive processing at AP

    • STAs transmit simultaneously to AP

    • Extension to legacy MAC necessary (!)

    • No joint Tx processing at STAs

    • However, each STA may use CSITfor beamforming

    • Rates of STAs are bounded by achievable rate region (capacity region)given by the MIMO multiple access channel

      • See, for instance: D. Tse, P. Viswanath, "Fundamentals of Wireless Communication", Cambridge University Press, 2005. [Tse, 2005]

LTE Advanced


A glimpse on 802 11ad wikipedia 21 06 2013

A Glimpse on 802.11ad [Wikipedia, 21.06.2013]

  • Wireless Gigabit Alliance (WiGig): Organization promoting the adoption of multi-gigabit speed wireless communications technology operating over the unlicensed 60 GHz frequency band.

  • Creation of WiGig (IEEE 802.11 ad) was announced on May 7, 2009

    • The completed version 1.0 WiGig specification was announced in December 2009.

    • In May 2010, WiGig announced the publication of its specification, the opening of its Adopter Program, and the liaison agreement with the Wi-Fi Alliance to cooperate on the expansion of Wi-Fi technologies.

    • In June 2011, WiGig announced the release of its certification-ready version 1.1 specification.

  • WiGig specification will allow devices to communicate at multi-gigabit speeds.

  • Enables high performance wireless data, display and audio applications that supplement the capabilities of today’s wireless LAN devices.

Communication Technology Laboratory

Wireless Communication Group


A glimpse on 802 11ad wikipedia 21 06 20131

A Glimpse on 802.11ad [Wikipedia, 21.06.2013]

  • WiGig tri-band enabled devices, which operate in the 2.4, 5 and 60 GHz bands,

    • will deliver data transfer rates up to 7 Gbit/s, about as fast as an 8 antenna 802.11ac transmission, and nearly 50 times faster than the highest 802.11n rate,

    • while maintaining compatibility with existing Wi-Fi devices.

    • However, the promised 7 Gbit/s rate makes use of the 60 GHz band which cannot go through walls; it is a line-of-sight technology.

    • When roaming away from the main room the protocol will switch to make use of the other lower bands at a much lower rate, but which propagate through walls.

Communication Technology Laboratory

Wireless Communication Group


Appendix

Appendix


The steps to an amendment of the standard in the 802 11 working group

The Steps to an Amendment of the Standard in the 802.11 Working Group

  • Discussion of new ideas in the Wireless Next Generation Standing Committee

  • Development of the purpose and scope of the amendment in a Study Group

  • Drafting of the amendment in a Task Group

    • Letter ballot votes in Working Group for iterative improvement of draft

  • Approval of the draft by the Working Group

  • Review by a sponsor ballot pool

  • Approval and ratification by the IEEE Standards Association Board


Ieee 802 11 wireless local area networks

Overview of 802.11 Task Groups and Study Groups (as of October 2010) source http://www.ieee802.org/11/QuickGuide_IEEE_802_WG_and_Activities.htm


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