Download - 802.11g & 802.11e

802.11g & 802.11e

Presenter : Milk

Outline

802.11g Overview of 802.11g 802.11g & 802.11b co-exist

QoS Limitations of 802.11 802.11e

Overview of 802.11e EDCA HCCA DLP Block Acknowledgement Admission Control Power Management

802.11g



Overview of 802.11e EDCA HCCA DLP Block Acknowledgement

Overview of 802.11g

Provide high data ratesBackward compatibility with legacy 802.11

and 802.11b devicesThe new features of 802.11g

The provision of four different physical layers Protection Mechanisms

802.11g PHY layers

CCK - Complementary code keying

OFDM - Orthogonal frequency division multiplexing

PBCC - Packet Binary Convolutional Code

Different WLAN system characteristics

802.11a 802.11b 802.11g

Operating

frequencies

5 GHz U-NII

Band

2.4 GHz ISM

Band

2.4 GHz ISM

Band

Modulation

techniques

OFDM Barker Code

/ CCK

Barker Code

/ CCK / OFDM

Data rates

(Mbps)

6,9,12,18,24,

36,48,54

1,2,5.5,11 1,2,5.5,11,

6,9,12,18,24,36,

48,54

Preamble OFDM Long

Short (optional)

Long / Short /

OFDM

CWmin 15 31 15 / 31

Slot time 9 us 20 us 20us /

9us (optional)

802.11g




802.11g & 802.11b co-exist

Many legacy 802.11b devices cannot detect the ERP-OFDM signals and it can result in collisions between 802.11b and 802.11g stations.

The 802.11g suggests a solution, which is based on the channel reservation for the ERP-OFDM transmissions. Use RTS/CTS to protect ERP-OFDM Use CTS-to-Self to protect ERP-OFDM

Protection Mechanisms

sender

receiver

Non-ERPCTS

ERP-OFDMdata

sender

receiver

Non-ERPRTS

Non-ERPCTS

ERP-OFDMdata

RTS/CTS

CTS to Self

ERP-OFDMACK

ERP-OFDMACK

RTS NAV

CTS NAV

CTS NAV

QoS Limitations of 802.11




QoS Limitations of 802.11

DCF (Distributed Coordination Function) Only support best-effort services No guarantee in bandwidth, packet delay and jitter

PCF (Point Coordination Function) Unpredictable beacon frame delay due to incompatible

cooperation between CP and CFP modes Transmission time of the polled stations is unknown Point Coordinator(PC) does not know the QoS requirem

ent of traffic

Beacon delay example

TBTTTBTT

TBTT - target beacon transmission time

802.11e




Overview of 802.11e

Support QoS in WLANBackwardly compatible with the DCF and

PCFHybrid Coordination Function (HCF) acce

ss method is added, including Contention-Based channel access

Enhanced Distributed Channel Access (EDCA) Controlled channel access

HCF Controlled Channel Access (HCCA)

Major Enhancements in 802.11e

Basic elements for QoS Traffic Differentiation Concept of Transmission Opportunity (TXOP)

New Contention-based channel access Enhanced Distributed Channel Access (EDCA)

New Contention-free channel access HCF Controlled Channel Access (HCCA)

Other new mechanisms for higher throughput Block Acknowledgement (Block Ack) Direct Link Protocol (DLP)

Traffic Differentiation

802.11e




EDCA

Difference from original DCF Contention between ACs (Not STAs) New Inter-frame Space (IFS) for each AC: Arbitr

ation Inter frame Space (AIFS) Transmission Opportunity (TXOP)

Access Category (AC)

In EDCA, media access is based on the AC of MSDU

4 AC’s are defined AC_BK (background) AC_BE (best-effort) AC_VI (Video) AC_VO (Voice)

In EDCA, the size of Contention-Window (CW) and Inter-frame space (IFS) is dependent on AC

Arbitration Interframe Space (AIFS)

QSTA use AIFS to defer the contention window or transmission for each AC

AIF[AC] =

AIFSN[AC]x aSlotTime+ aSIFSTime AIFSN for each AC is broadcast via beacon fra

me containing “EDCA Parameter Set” element

DIFS = 2 x aSlotTime+ aSIFSTime

AC CWmin CWMax

AC_BK aCWmin aCWmax

AC_BE aCWmin aCWmax

AC_VI (aCWmin+1)/2 -1 aCWmin

AC_VO (aCWmin+1)/4 -1 (aCWmin+1)/2 -1

Transmission Opportunity (TXOP)

TXOP: the duration of a QSTA to transmit frame(s)

When will a QSTA get a TXOP ? Win a contention in EDCA during CP Receive a CF-poll (“polled TXOP”) from HC

Transmission Opportunity (TXOP) (cont.)

In TXOP, frames exchange sequences are separated by SIFS

Multiple backoff of MSDU streams withdifferent priorities

802.11e




HCF Controlled Channel Access (HCCA)

The procedure is similar to PCFHybrid Coordinator (HC)

Operate at QAP Control the iteration of CFP and CP

By using beacon and CF-End frame and NAV Mechanism (Same as PCF)

Use polling Scheme to assign TXOP to QSTA Issue CF-poll frame to poll QSTA Polling can be issued in both CFP & CP

802.11e Superframe

802.11e




Direct Link Protocol (DLP)

Direct Link Directly send frames from one QSTA to another

in QBSS

The handshake procedure

Notes:

1.DLS Request and DLS Response are both Action management frame

2.The direct link will become inactive if no frames have been exchanged for DLPTimeoutValue duration.

3.Recipient shall not go into power save for DLPTimeoutValue duration.

4.After timeout, the frames are transmitted via AP again.

802.11e




Brief of Block Ack

(Optional function in implementation)Improve channel efficiency

By aggregating several acks into one frame

Two types Immediate Block Ack

Suitable for High-bandwidth, low latency traffic Delayed Block Ack

Suitable for applications tolerating moderate latency

Procedure of Block Ack

Immediate Block Ack

Delayed Block Ack

Download - 802.11g & 802.11e

Top Related