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IEEE 802.16/a/d/e/m (WiMAX)
Dr. Debabrata Das
IIIT-Bangalore
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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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