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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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IEEE 802.16 -- Introduction
Coverage range up to 50km and speeds up to70Mbps(shared among users).
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IEEE 802.16 -- Introduction
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