WiMAX for Broadband Wireless Access

WiMAX for Broadband Wireless Access

By:Karim M. El DefrawyICSUCI-2005

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

What is WiMAX?

Worldwide Interoperability for Microwave Access (WiMAX) is the common name associated to the IEEE 802.16a/REVd/e standards.

These standards are issued by the IEEE 802.16 subgroup that originally covered the Wireless Local Loop technologies with radio spectrum from 10 to 66 GHz.

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


Coverage range up to 50km and speeds up to 70Mbps(shared among users).


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

IEEE 802.16 MAC -- Highlights

WirelessMAN: Point-to-Multipoint and optional mesh topology

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

Reference Model

Adaptive PHY

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

Adaptive Burst Profiles

Burst profile: Modulation and FEC On DL, multiple SSs can associate the

same DL burst On UL, SS transmits in an given time slot

with a specific burst Dynamically assigned according to link

conditions Burst by burst Trade-off capacity vs. robustness in real time

Duplex Scheme Support

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

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

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 1DL

burst n

ULMAP

Broadcast Conrol msgs

...UL burst 1 UL burst m

DLMAP

DCDopt.

UCDopt.

...DLburst 2

UL TDMADL TDM

pre. pre.

IEEE 802.16 MAC – OFDM PHY FDD Frame 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.

FDD MAPs Time Relevance

frame

Broadcast

Full Duplex Capable User

Half Duplex Terminal #1

Half Duplex Terminal #2

UPLINK

DOWNLINK

DL MAP

UL MAP

DL MAP

UL MAP

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)

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

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 layerprotocol

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)

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

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

IEEE 802.16 MAC – CPS-- MAC Management Connections

Each SS has 3 management connections in each direction: 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 mgmt

messages 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

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; Primary mgmt connection; Broadcast connection; and initial ranging connections

• 41 MAC mgmt msgs specified in 802.16• The TLV (type/length/value) encoding scheme is used in MAC

mgmt 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

IEEE 802.16 MAC – CPS – MAC PDU Transmission

MAC PDUs are transmitted in PHY Bursts The PHY burst can contain multiple FEC

blocks MAC PDUs may span FEC block

boundaries Concatenation Packing Segmentation Sub-headers

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

IEEE 802.16 MAC – CPS – MAC PDU Fragmentation

FEC block1

OFDMsymbol

1

PHY Burst

Pre.

MAC SDU

OFDMsymbol

n1

......

FEC FEC Blockm1

......

MAC SDUseg-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 SDUseg-2

MAC SDUseg-3

FSH

FSH

FragmentationSub-Header

(8 bits)

FSH

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 orseg n

Variable sizeMSDUs or MSDUsegments, e.g.,IP packets, on

the sameconnection

PackingSub-Heder

(16 bits)

IEEE 802.16 MAC – CPS 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 throughput 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 not

active Active: the required resources committed by the BS

IEEE 802.16 MAC – CPS – Uplink Service Classes

UGS: Unsolicited Grant Services rtPS: Real-time Polling Services nrtPS: Non-real-time Polling

Services BE: Best Effort

IEEE 802.16 MAC – CPS – Uplink Services: UGS

UGS: Unsolicited Grant ServicesFor CBR or CBR-like services, e.g.,

T1/E1.The BS scheduler offers fixed size

UL BW grants on a real-time periodic basis.

The SS does not need to send any explicit UL BW req.

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.

IEEE 802.16 MAC – CPS – Uplink Services: nrtPS

nrtPS: non-real-time polling services 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.

IEEE 802.16 MAC – CPS – Uplink Services: BE

BE: Best EffortFor best-effort traffic, e.g., HTTP,

SMTP.The SS uses the contention-based

BW request opportunities.

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, maintaining QoS and service-level agreements

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

Off- loading base station’s work Requires intelligent subscriber station to redistribute the

allocated BW among connections

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 a regular 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

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 backoff

window

IEEE 802.16 MAC – CPS UL Sub-Frame Structure

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

IEEE 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.

IEEE 802.16 MAC – CPS – Automatic Repeat reQuest (ARQ)

A Layer-2 sliding-window based flow control mechanism.

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 check

data errors. Maintain the same fragmentation structure for

Retransmission. Optional.

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 Key Management, or PKM)

IEEE 802.16 MAC – PS -- Security Associations

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

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

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

IEEE 802.16 MAC – PS -- Data Encryption

Use DES (Data Encryption Standard) in CBC (Cipher Block Chaining) mode with IV (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.

IEEE 802.16 MAC – one big item is out of scope

Scheduler

Questions ??

References

IEEE802.16-2004 Alcatel White Paper: WiMAX, making

ubiquitous high-speed data services a reality

Intel White Paper: Understanding WiMAX and 3G for Portable/Mobile Broadband Wireless

WiMAX Forum: www.wimaxforum.com http://en.wikipedia.org/wiki/WiMax

IEEE 802.16 MAC – commonly used terms

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

WiMAX for Broadband Wireless Access

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