9-16-05 karim hassib - wimax (1)

8/2/2019 9-16-05 Karim Hassib - WiMAX (1)

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WiMAX for Broadband Wireless Access

By:

Karim M. El Defrawy

ICS

UCI-2005


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Outline

What is WiMAX

802.16 Introduction

802.16 MAC Highlights 802.16 Reference Model

MAC Convergence Sub-Layer (CS)

MAC Common Part Sub-Layer (CPS)

MAC Privacy Sub-Layer (PS)

Questions


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What is WiMAX?

Worldwide Interoperability forMicrowave Access (WiMAX) is thecommon name associated to the IEEE

802.16a/REVd/e standards.

These standards are issued by the IEEE802.16 subgroup that originally coveredthe Wireless Local Loop technologieswith radio spectrum from 10 to 66 GHz.


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IEEE 802.16 -- Introduction

IEEE 802.16 (2001) Air Interface for Fixed Broadband Wireless Access System MAC and

PHY Specifications 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

topology support, 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?) Amendment to 802.16-2004 MAC Modifications for limited mobility


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Coverage range up to 50km and speeds up to70Mbps(shared among users).


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Source: WiMAX, making ubiquitous high-speed data services a reality, White Paper, Alcatel.


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IEEE 802.16 MAC -- Highlights

WirelessMAN: Point-to-Multipoint and optional meshtopology

Connection-oriented Multiple Access: DL TDM & TDMA, UL TDMA;UL OFDMA

& TDMA, DL OFDMA & TDMA (Optional) PHY considerations that affect the MAC

Duplex: TDD, FDD, FDX FDD BS and SS, HDX FDD SS Adaptive burst profiles (Modulation and FEC) on both DL

and UL

Protocol-independent core (ATM, IP, Ethernet) Flexible QoS offering (CBR, rt-VBR, nrt-VBR, BE) Strong security support


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Reference Model


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Adaptive PHY

Source: Understanding WiMAX and 3G for Portable/Mobile Broadband Wireless, Technical White

Paper, Intel.


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Adaptive Burst Profiles

Burst profile: Modulation and FEC

On DL, multiple SSs can associate thesame DL burst

On UL, SS transmits in an given time slotwith a specific burst

Dynamically assigned according to linkconditions

Burst by burst

Trade-off capacity vs. robustness in real time


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Duplex Scheme Support

The duplex scheme is Usually specified byregulatory bodies, e.g., FCC

Time-Division Duplex (TDD)

Downlink & Uplink time share the same RF channel Dynamic asymmetry

does not transmit & receive simultaneously (lowcost)

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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IEEE 802.16 MACOFDM PHY TDDFrame Structure

DL Subframe

Frame n-1

pre.

Time

Adaptive

Frame n Frame n+1

UL subframe

FCHDL

burst 1DL

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 MACOFDM PHY FDDFrame Structure

DL Subframe

Frame n-1

pre.

Time

BroadcastControl Msgs

Frame n Frame n+1

UL subframe

FCHDL

burst 1DL

burst k...

DL TDMA

UL burst 1 UL burst m

DLburst 2

DLburst n

DLburst k+1

...

DL TDM

...

UL TDMA

DLMAP

ULMAP

DCDopt.

UCDopt.

pre.pre.

UL MAP for nextMAC frame UL

burstspre. pre.


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FDD MAPs Time Relevance

frame

Broadcast

Full Duplex Capable User

Half Duplex Terminal #1

Half Duplex Terminal #2

UPLINK

DOWNLINK

DL

MAP ULMAPDL

MAP ULMAP


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IEEE 802.16 MAC addressing andIdentifiers

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 MAC Convergence Sub-Layer (CS)

ATM Convergence Sub-Layer: Support for VP/VC switched connections Support for end-to-end signaling of

dynamically created connections

ATM 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 MAC

connections 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 IndexOptional, Depending on upper layer

protocol


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IEEE 802.16 MAC -- CPS MAC PDU Format

CRC(optional)MAC PDU payload (optional)

Generic MACHeader

(6 bytes)

LENmsb(3)

HT

CID msb (8)LEN lsb (8)

Generic MAC Header Format(Header Type (HT) = 0)

BW Req. Header Format(Header Type (HT) =1)

msb lsb

EC

Type (6 bits)rsv

CI

EKS(2)

rsv

HCS (8)CID lsb (8)

BW Req.msb (8)

HT

CID msb (8)BWS Req. lsb (8)

EC

Type (6 bits)

HCS (8)CID lsb (8)


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IEEE 802.16 MAC -- CPS-- Three Types of MAC PDUs

Data MAC PDUs HT = 0 Payloads are MAC SDUs/segments, i.e., data

from upper layer (CS PDUs)

Transmitted on data connections Management MAC PDUs

HT =0 Payloads are MAC management messages or

IP packets encapsulated in MAC CS PDUs

Transmitted on management connections BW Req. MAC PDUs

HT =1; and no payload, i.e., just a Header


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IEEE 802.16 MAC -- CPS Data Packet Encapsulations

PHSI

MAC PDU

Ethernet Packet

Ethernet Packet

Packet PDU(e.g., Ethernet)

CS PDU(i.e., MAC SDU)

HT

FEC block 1

CRCMAC PDU Payload

OFDMsymbol

1

PHY Burst(e.g., TDMA burst)

PreambleOFDMsymbol

2

OFDMsymbol

n

......

FECFEC Block 2 FEC block m

......FEC Block 3


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IEEE 802.16 MAC CPS-- MAC Management Connections

Each SS has 3 management connections in eachdirection:

Basic Connection:

short and time-urgent MAC management messages

MAC mgmt messages as MAC PDU payloads Primary Management connection:

longer and more delay tolerant MAC mgmtmessages

MAC mgmt messages as MAC PDU payloads

Secondary Management Connection: Standard based mgmt messages, e.g., DHCP,

SNMP, etc

IP packets based CS PDU as MAC PDU payload


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IEEE 802.16 MAC CPS MAC Management Messages

MAC mgmt message format:

MAC mgmt msg payloadmgmtmsgHD

8 bits

MAC mgmt msg can be sent on: Basic connections; Primarymgmt connection; Broadcast connection; and initial rangingconnections

41 MAC mgmt msgs specified in 802.16

The TLV (type/length/value) encoding scheme is used in MACmgmt msg, e.g., in UCD msg for UL burst profiles,

(type=1, length=1, value=1) QPSK modulation

(type=1, length=1, value=2) 16QAM modulation

(type=1, length=1, value=3) 64QAM modulation


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IEEE 802.16 MAC CPS MAC PDU Transmission

MAC PDUs are transmitted in PHY Bursts

The PHY burst can contain multiple FECblocks

MAC PDUs may span FEC blockboundaries

Concatenation

Packing

Segmentation

Sub-headers


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IEEE 802.16 MAC CPS MAC PDU Concatenation

MAC PDU 2

HT

FEC block 1

CRCMAC PDU Payload

OFDMsymbol

1

PHY Burst(e.g., TDMA burst)

PreambleOFDMsymbol

2

OFDMsymbol

n

......

FECFEC Block 2 FEC block m

......FEC Block 3

MAC PDU 1

HT CRCMAC PDU Payload ......

MAC PDU k

HT CRCMAC PDUPayload

Multiple MAC PDUs are concatenated into the same PHY burst


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IEEE 802.16 MAC CPS MAC PDU Fragmentation

FEC block1

OFDMsymbol

1

PHY Burst

Pre.

MAC SDU

OFDMsymbol

n1

......

FECFEC Block

m1......

MAC SDU

seg-1

HT CRCMAC PDU PayloadHT CRC

MAC PDUPayload

A MAC SDU can be fragmented into multiple segments, eachsegment is encapsulated into one MAC PDU

FEC block1

OFDMsymbol

1

PHY Burst

Pre.OFDMsymbol

n2

......

FEC Blockm2

......

HT CRCMAC PDUPayload

MAC SDU

seg-2

MAC SDU

seg-3

FSH

FSH

FragmentationSub-Header

(8 bits)

FSH


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IEEE 802.16 MAC CPS MAC PDU Packing

MACSDU 1

Fixed size MSDUs, e.g., ATMCells, on the same connection

HT CRCMAC PDU Payload

HT CRC

Packing with fixed size MAC SDUs (no packing sub-header is needed)

......

PSH

MACSDU 2

MACSDU k

Packing with variable size MAC SDUs (Packing Sub-Heade is neeeded)

PSH ...... PSH

MAC SDU orseg. 1 MAC SDU or seg 2

MAC SDU or

seg n

Variable sizeMSDUs or MSDUsegments, e.g.,

IP packets, onthe sameconnection

Packing

Sub-Heder(16 bits)


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IEEE 802.16 MAC CPSQoS

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, andthroughput assurances

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

Three types of service flows Provisioned: controlled by network management system

Admitted: the required resources reserved by BS, but notactive Active: the required resources committed by the BS


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IEEE 802.16 MAC CPS Uplink Service Classes

UGS: Unsolicited Grant Services

rtPS: Real-time Polling Services

nrtPS: Non-real-time PollingServices

BE: Best Effort


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IEEE 802.16 MAC CPS Uplink Services: UGS

UGS: Unsolicited Grant Services

For CBR or CBR-like services,

e.g., T1/E1. The BS scheduler offers fixed size

UL BW grants on a real-timeperiodic basis.

The SS does not need to send anyexplicit UL BW req.


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IEEE 802.16 MAC CPS Uplink Services: rtPS

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.opportunity to specify the desired UL

BW grant. The SS cannot use contention-based

BW req.


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IEEE 802.16 MAC CPS Uplink Services: nrtPS

nrtPS: non-real-time pollingservices

For nrt-VBR-like services, such as,bandwidth-intensive file transfer.

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

request opportunities. The SS can use contention-based BW

req. opportunities to send BW req.


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IEEE 802.16 MAC CPS Uplink Services: BE

BE: Best Effort

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

SMTP. The SS uses the contention-based

BW request opportunities.


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IEEE 802.16 MAC CPS Bandwidth Grant

BW grants are per Subscriber Station:

Allows real-time reaction to QoS need, i.e., SS may re-distribute bandwidth among its connections, maintainingQoS and service-level agreements

Lower overhead, i.e., less UL-MAP entries compare to grantper connection

Off- loading base stations work

Requires intelligent subscriber station to redistribute the

allocated BW among connections


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IEEE 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 aregular UL allocation for the SS;he 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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IEEE 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 req

Short preamble

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

in a given time

Resolution: a truncated binary exponential backoffwindow


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IEEE 802.16 MAC CPSUL Sub-Frame Structure

Source: http://www.cygnuscom.com/pdf/WP_PN_Article.pdf


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IEEE 802.16 MAC CPS Ranging

Ranging is a process of acquiring thecorrect timing offset, and PHYparameters, 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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IEEE 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 to checkdata errors.

Maintain the same fragmentation structure for

Retransmission. Optional.


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IEEE 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 KeyManagement, or PKM)


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IEEE 802.16 MAC PS-- Security Associations

A set of privacy information, e.g.,encryption keys, used encryptionalgorithm

Three types of Security Associations (SAs) Primary SA: established during initial registration

Static SA: provisioned within the BS

Dynamic SA: dynamically created on the fly

Identified by a 16-bit SAID Connections are mapped to SAs


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IEEE 802.16 MAC PS

-- Multi-level Keys and Their Usage

Public Key Contained in X.509 digital certificate Issued by SS manufacturers Used to encrypt AK

Authorization Key (AK) Provided by BS to SS at authorization Used to derive KEK

Key Encryption Key (KEK) Derived from AK

Used to encrypt TEK Traffic Encryption Key (TEK)

Provided by BS to SS at key exchange Used to encrypt traffic data payload


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IEEE 802.16 MAC PS-- Data Encryption

Use DES (Data Encryption Standard) inCBC (Cipher Block Chaining) mode withIV (Initialization Vector).

CBC IV is calculated from IV parameter in TEK keying info; and PHY synchronization field in DL-MAP.

Only MAC PDU payload (including sub-headers) is encrypted.

MAC PDU headers are unencrypted. Management messages are

unencrypted.


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IEEE 802.16 MAC one big item is out of scope

Scheduler


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Questions ??


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References

IEEE802.16-2004

Alcatel White Paper: WiMAX, makingubiquitous high-speed data services a

reality Intel White Paper: Understanding WiMAX

and 3G for Portable/Mobile BroadbandWireless

WiMAX Forum: www.wimaxforum.com

http://en.wikipedia.org/wiki/WiMax


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IEEE 802.16 MAC commonly usedterms

BS Base Station SS Subscriber Station, (i.e., CPE) DL Downlink, i.e. from BS to SS UL Uplink, i.e. from SS to BS

FDD Frequency Division Duplex TDD Time Division Duplex TDMA Time Division Multiple Access TDM Time Division Multiplexing OFDM Orthogonal Frequency Division

Multiplexing OFDMA - Orthogonal Frequency Division Multiple

Access QoS Quality of Service

9-16-05 karim hassib - wimax (1)

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