Wimax Mac Ieee 802-16

8/3/2019 Wimax Mac Ieee 802-16

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IEEE 802.16/a/d/e/m (WiMAX)

Dr. Debabrata Das

IIIT-Bangalore

[email protected]

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Outline

WiMAX What is WiMax?

WiMAX standard: 802.16*

Different Services will be supported by WiMAX MAC concepts

Media Independent Handover (MIH) Why we need it?

Handoff over Circuit Switched Network Mobility over Pakcet switched network

MIH Functions

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What is WiMAX?

Worldwide Interoperability for Microwave Access (WiMAX) is thecommon name associated to the IEEE 802.16a/d(REV)/estandards.

It supports fixed and mobile wireless broadband connectivity

Connectivity at rates of up to 100 Mb/sec (802.16m, Varies with respect to

distance and condition of medium) WiMAX working group defines its

- Medium access control and Physical Layer Profile

Better security, authentication, and protection against theft of service

Possibility to use both licensed and unlicensed frequencies

GOAL of WiMAX: Provide Telecom type services to Voicewithout silence suppression (T1/E1) + Packet switched networkfor real time voice with silence suppression or video conferencing+ Non real time traffic like on Internet over broadband wirelesswith QoS

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Wireless MAN

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Base Sstation

(BS)Subscriber Station(SS)

UpLink

DownLink

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Introduction to 802.16 IEEE 802.16 (2001)

Air Interface for Fixed Broadband Wireless Access System MAC and PHYSpecifications for 10 66 GHZ (LoS)

One PHY: Single Carrier

Connection-oriented, TDM/TDMA MAC, QoS, Privacy

IEEE 802.16a (January 2003) Amendment to 802.16, MAC Modifications and Additional PHY

Specifications for 2 11 GHz (NLoS) Three PHYs: OFDM, OFDMA, Single Carrier

Additional MAC functions: OFDM and OFDMA PHY support, Mesh topologysupport, ARQ

IEEE 802.16d (July 2004) Combines both IEEE 802.16 and 802.16a

Some modifications to the MAC and PHY IEEE 802.16e (2005-07)

Amendment to 802.16-2004

MAC Modifications for limited mobility

IEEE 802.16m (2008-10) Support of very high speed mobility

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Evolution in WiMAX Technologies

802.16(OriginalFixed BWA,10-66GHz,2001)

802.16d, FixedWiMAX, QoS,2-11 GHz,

2004

802.16e,MobileWiMAX, QoS,


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Types of Services Supported

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802.16e Scheduled Services

Class Possible Applications Expected

Application Traffic

Traffic Parameters

UGS CBR Voice (no silencesubmission), circuit emulation

Fixed-size packets at

fixed intervals

Sustained maximum

traffic rate

rtPS MPEG Video Variable-size packets atfixed intervals

Maximum sustained

traffic rate, minimum

reserved traffic rate

Extended

rtPS (ertPS)

Voice with silence suppression Variable-size packets Same as rtPS

nrtPS Data application with minimumrate requirements, e.g. FTP

Variable-size packets,variable intervals

Same as rtPS

BE Data applications with nominimum rate requirements

Who cares Maximum sustained

traffic rate

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IEEE 802.16 MAC Services QoS

Three components of 802.16 QoS Service flow QoS scheduling

Dynamic service establishment

Two-phase activation model (admit first, then activate)

Service Flow A unidirectional MAC-layer transport service characterized by

a set of QoS parameters, e.g., latency, jitter, and throughputassurances

Identified by a 32-bit SFID (Service Flow ID)

Three steps to provide service flows

Provisioned: controlled by network management system Admitted: the required resources reserved by BS, but not

active

Active: the required resources committed by the BS

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UGS: Unsolicited Grant Services

For CBR or CBR-like services, e.g.,

T1/E1

The BS scheduler offers fixed size ULBW grants on a real-time periodic

basis

The SS does not need to send anyexplicit UL BW request

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rtPS: Real-time Polling Services

For rt-VBR-like services, e.g., MPEG video

The BS scheduler offers real-time, periodic, UL

BW request opportunities

The SS uses the offered UL BW req. opportunityto specify the desired UL BW grant

The SS cannot use contention-based BW req.

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ertPS: Extended-rtPS

Mainly Supports Voice Packets with

Silence Zone compressed

The variable sized packets and intervalmay be fixed or variable

Traffic parameters used are same as rtPS

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nrtPS: non-real-time polling services

For nrt-VBR-like services, such as,

bandwidth-intensive file transfer

The BS scheduler shall provide timely (ona order of a second or less) UL BW

request opportunities

The SS can use contention-based BW

request opportunities to send BW request

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BE: Best Effort

For best-effort traffic, e.g., HTTP,

SMTP

The SS uses the contention-based

BW request opportunities.

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Node Architecture and Their

Function

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WiMAX Nodes

There are basically two nodes in WiMAX

Subscriber Station (SS)

Base Station (BS)

SS: One side of SS connected to users

equipments (UE) and other side connected to

BS (or, each UE can also be directly used as

SS)

BS: One side of BS connected to SS and other

side to core network (i.e., outer world)

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BS & SS architectures of WiMAX

with Four Services

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WiMax BS & SS Nodes Architecture

with Four Services (Contd.)

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BS & SS Architecture supporting

with Five Services

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MAC Protocol

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Duplex Scheme Support

The duplex scheme is Usually specified byregulatory bodies, e.g., FCC (FederalCommunication Commission)

Time-Division Duplex (TDD) Downlink & Uplink time share the same RF channel

Dynamic asymmetry of Downlink an Uplink duration

does not transmit & receive simultaneously (low cost)

Frequency-Division Duplex (FDD) Downlink & Uplink on separate RF channels Full Duplexing (FDX): can Tx and Rx simultaneously;

Half-duplexing (HDX) SSs supported (low cost)

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A Frame in Case of WiMAX

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IEEE 802.16 MAC

OFDM PHY TDD Frame Structure

DL Subframe

Frame n-1

pre.

Time

Adaptive

Frame n Frame n+1

UL subframe

FCHDL

burst 1

DL

burst n

ULMAP

Broadcast Conrol msgs

...UL burst 1 UL burst m

DLMAP

DCDopt.

UCDopt.

...DL

burst 2

UL TDMADL TDM

pre. pre.

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IEEE 802.16 MAC addressing and

Identifiers

SS has 48-bit IEEE MAC address

BS has 48-bit base station ID

Not a MAC address 24-bit operator indicator

16-bit connection ID (CID)

32-bit service flow ID (SFID) 16-bit security association ID (SAID)

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IEEE 802.16 Reference Model and Protocol Stack

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MAC Protocol Sublayers

Convergence Sublayer: to support higher-layerprotocols

Common Part Sublayer (CPS): channelaccess, connection establishment andmaintenance, and QoS

Security Sublayer: Authentication, securekey exchange, and encryption

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MAC: Convergence Sublayer (CS)

Service specific CS does mapping or transformation of external network data,through service access point (SAP) Classify external service data unit (SDU) and associated them with proper service flow

connection identifier (CID)

Mainly it support two kinds SDU: ATM, Packet (Ethernet, IP, VLAN)

ATM Convergence Sub-Layer Support for VP/VC switched connections

Support for end-to-end signaling of dynamically created connections

Assigns channel ID (CID)

ATM payload header suppression

Full QoS support

Packet Convergence Sub-Layer Initial support for Ethernet, VLAN, IPv4, and IPv6

Payload header suppression

Full QoS support

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IEEE 802.16 MAC -- CS

Packet Convergence Sub-Layer

Functions: Classification: mapping the higher layer PDUs

(Protocol Data Units) into appropriate MACconnections

Payload header suppression (optional)

MAC SDU (Service Data Unit), i.e, CS PDU,formatting

Packet PDU(e.g., IP packet, Ethernet Packet)

PHSI

MAC SDU = CS PDU

Payload Header Suppression Index

Optional, Depending on upper layer

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MAC: Common Part Sublayer

(CPS)

Connection Oriented Protocol: assigns

connection ID (CID, of 16bit) identifies a

connection for each flow with peers MAC

Each service flow uniquely identified by 32

bit SFID for QoS parameters settings

(Delay, jitter, throughput, etc.)

BS grants the bandwidth allocation

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802.16 MAC CPS BW Request/Grant Mechanisms

Implicit requests (UGS): No actual requests BW request messages, i.e., BW req. header

Sends in either a contention-based BW req. slot or a regular UL allocation forthe SSe special B

Requests up to 32 KB with a single message Request

Incremental or aggregate, as indicated by MAC header

Piggybacked request (for non-UGS services only) Presented in Grant Management (GM) sub-header in a data MAC PDU of the

same UL connection

is always incremental

Up to 32 KB per request for the CID

Poll-Me bit Presented in the GM sub-header on a UGS connection

request a bandwidth req. opportunity for non-UGS services

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802.16 MAC CPS

-- Contention UL Access

Two types of Contention based UL slots Initial Ranging

Used for new SS to join the system

Requires a long preamble BW Request

Used for sending BW request

Short preamble

Collision Detection and Resolution Detection: SS does not get the expected response in a given

time

Resolution: a truncated binary exponential backoff window

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IEEE 802.16 MAC CPS

UL Sub-Frame Structure

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802.16 MAC CPS Ranging

Ranging is a process of acquiring the correct timing

offset, and PHY parameters, such as, Tx power

level, frequency offset, etc. so that the SS can

communicate with the BS correctly. BS performs measurements and feedback

SS performs necessary adjustments

Two types of Ranging: Initial ranging: for a new SS to join the system

Periodic ranging (also called maintenance ranging):

dynamically maintain a good RF link

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802.16 MAC CPS Automatic Repeat reQuest (ARQ)

A Layer-2 sliding-window based flow controlmechanism

Per connection basis

Only effective to non-real-time applications Uses a 11-bit sequence number field

Uses CRC-32 checksum of MAC PDU tocheck data errors

Maintain the same fragmentation structure forRetransmission

Optional

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802.16 MAC

Privacy Sub-layer (PS)

Two Major Functions:

Secures over-the-air transmissions

Protects from theft of service

Two component protocols:

Data encryption protocol

A client/server model based Key management

protocol (Privacy Key Management (PKM)

presents how BS distributes key to client SS)

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Scheduling services

Scheduling services represent the data

handling mechanisms supported by the MAC

scheduler for data transport on a connection Each connection is associated with a single

scheduling service

A scheduling service is determined by a set of

QoS parameters that quantify aspects of its

behavior

SS and BS has scheduler to schedule the

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