Wireless LAN OverviewWireless LAN Overview

Sunggeun Jin2005-10-17

OutlineOutline

IEEE802.16 MAC IEEE802.11 MAC

IEEE802.16 (a, e, Wibro)IEEE802.16 (a, e, Wibro)

Original goal alternative to cabled access network to provide network access to buildings it came from DOCSIS spec.

Amendments IEEE802.16a

for fixed service subscribers IEEE802.16e

for movable service subscribers Feature

FDD or TDD TDD as to Wibro

TDM, TDMA, OFDM, OFDMA OFDM/OFDMA for Wibro

Protocol Layers of IEEE802.16Protocol Layers of IEEE802.16

-System Access-Bandwidth Allocation-Connection set-up -Connection maintenance- QoS

-Authentication-Secure key exchange-Encryption

-Transformation ofexternal network datainto MAC SDUs;

-Payload header suppression

System operationsSystem operations

BS

SS trying to access to BS

SS performing periodic ranging

CD

Transmit Initial Ranging Code

Transmit Periodic Ranging Code

Transmit BW-Req. Code

Data transmission service

Requesting BW allocation

MAP

UL Data

DL Data

CD/MAP

• BS access inf.• Burst Profile• Power Control • BW allocations

• Frame Information

Initial RangingInitial Ranging

BS

SS

Get sync.

SS

BS BS

SS

BS

SS

BS

SS

MAP

BS

SS

MAP

RNG-REQ(MAC_Address)

Adjustment of timing and frequency offset

CD/MAP

Transmit “Initial Ranging Code”

RNG-REQ (Code)

RNG-RSP(Success)

SS

BS

SS

BS BS

SS

RNG-RSP(Management CIDs)

RNG-REQ (Code)

Binary-exponential Random Backoff

Transmit RNG-REQ message with MAC Addr.

RNG-RSP (Management CIDs)

RNG-REQ (Code)

RNG-RSP(Continue)

timing and frequency offset adjustments obtaining management CID

CIDsCIDs

Basic CID

Primary Management CID

Secondary Management CID

Transport CID1

Transport CID2

Management Connection Basic CID

Short, Urgent MAC Messages Primary Management CID

Longer, More Delay Tolerant MAC Messages

Secondary Management CID Delay Tolerant, Standard-Based

Management Messages E.g., : DHCP, TFTP, SNMP

Transport Connection Multiple CIDs exist BS assigns them to SS Data transmission

MAP and frame structureMAP and frame structure

Preamble

MAP_Bursts#(N-1)**

Traffic Bursts #1

Traffic Bursts #5

Traffic Bursts #(M-1)

Traffic Bursts #3

L_0*

Traffic Bursts #4

SICH

Traffic Bursts #2

.

.

.

MAP_Bursts#1**

MAP_Bursts#0**

.

.

.

Traffic Bursts #1

Traffic Bursts #5

Traffic Bursts #(M-1)

Traffic Bursts

#3Traffic Bursts #4

Traffic Bursts #2

.

.

.

Ranging slot#0

.

.

.

Ranging slot#1

Ranging slot

#(N-1)

TTG

L_1*

L_(N-1)*

.

.

.

Frame in case of TDD

Frames in case of FDD

IEEE802.11IEEE802.11

Application overview Wireless Ethernet with compatible speed Enable (indoor) wireless and mobile high-speed

networking Functional overview

Runs at unlicensed bands at 2.4GHz and 5GHz Connectionless MAC and multiple PHYs Supports up to 11 and/or 54 Mbps within >100

m range

802.11 Reference Model802.11 Reference Model

MAC Sublayer

MAC Management Sublayer Entity

(MLME)

PHY Management Sublayer Entity

(PLME)

PLCP Sublayer

PMD Sublayer

Station Management

Entity(SME)

MAC SAP

PHY SAP

PMD SAP

MLME_PLME SAP

MLME SAP

PLME SAP

MAC

PHY

IEEE 802.2Logical Link Control

(LLC)

Two ModesTwo Modes

Infrastructure mode Infrastructure Basic Service Set BSS An access point (AP) and multiple stations (STAs) Every transmission is with AP; no peer-to-peer communica

tion

Station 3

Access Point (AP)

Station 1

Station 2

Two Modes cont.Two Modes cont.

Ad hoc mode Independent Basic Service Set IBSS Multiple stations (STAs), and no AP Peer-to-peer communication only

Station 3Station 1

Station 2

Two Coordination FunctionsTwo Coordination Functions

Mandatory Distributed Coordination Function (DCF) For distributed contention-based channel access

Optional Point Coordination Function (PCF) For centralized contention-free channel access

Distributed Coordination Function (DCF)Distributed Coordination Function (DCF)

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) similar to IEEE 802.3 Ethernet CSMA/CD

BusyMedium

SIFS

PIFS

DIFS

BackoffWindow

Slot Time

Defer Access Select Slot and decrement backoffas long as medium stays idle

DIFS

Contention WindowImmediate access whenmedium is idle >= DIFS

Next Frame

Carrier-Sense MechanismsCarrier-Sense Mechanisms

Physical carrier-sense Provided by PHY, and depends on PHY Clear Channel Assessment (CCA) by PHY

Virtual carrier-sense Provided by MAC via Network Allocation Vector (NAV)

counter Each frame carries Duration value in the header Any correctly received frame updates NAV if the new

NAV is larger Assumes busy channel if non-zero NAV irrespective of

CCA!

Stop-and-Wait ARQStop-and-Wait ARQ

Receiver of a directed frame returns an ACK If ACK not received, sender retransmits after another back-off

DATA

SIFS

DIFS

Backoff

DIFS

Next Frame

ACK

Source

Destination

Others

Defer Access Backoff after Defer

NAV

ReferencesReferences

Carl Eklund and et al, “IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access,” IEEE Comm. Mag. Jun. 2002

IEEE802.11 tutorial material presented by Sunghyun Choi, Seoul Natl. Univ. IEEE802.16 tutorial material presented by Samsung IEEE802.16 tutorial material presented by ETRI