IEEE 802.16 WiMAX
高雄大學資工系
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IEEE 802.16
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IEEE 802.16 standardizes the air interface
and related functions associated with
wireless local loop
Wireless local loop


use of a wireless communications link for “
last
mile / first mile”telephone/broadband
connection
officially called WirelessMAN in IEEE
WiMAX
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Worldwide Interoperability for Microwave
Access
Commercial name used by the industry
alliance called the WiMAX Forum
IEEE 802.16 Family
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802.16 (2001): the first standard
802.16a (2003): provide “
last mile”fixed
broadband access
802.16d (802.16-2004): superseded the
earlier 802.16 documents
802.16e-2005: addresses mobility (Mobile
WiMAX)
Network Architecture
Three kinds of Devices
•
•
•
Subscriber Station (SS)
Base Station (BS)
Mobile Subscriber Station (MSS): 802.16e2005 only
Network Architecture–PMP Topology
(Point-to-MultiPoint)
Network Architecture–Mesh Topology
IEEE 802.16 Reference Model
IEEE 802.16 Reference Model
Convergence Sublayer (CS)
- Classification of the higher-layer
protocol PDU into the appropriate
connection
-
Suppression of payload header
information
-
Delivery of the resulting CS PDU to
the MAC SAP associated with the
service flow for transport to the peer
MAC SAP
-
Receipt of the CS PDU from the peer
MAC SAP
-
Rebuilding of any suppressed
payload header information
IEEE 802.16 Reference Model
MAC Common Part
Sublayer (MAC CPS)
- System Access
- Bandwidth Request/Allocation
- Connection establishment/Maintenance
-
Quality of Service (QoS)
Power saving mechanisms
Handover mechanism
IEEE 802.16 Reference Model
Security Sublayer
- Authentication
- secure key exchange
- Encryption
IEEE 802.16 Reference Model
Physical Layer
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WirelessMAN-SC
WirelessMAN Single Carrier
WirelessMAN-SCa
WirelessMAN Single Carrier Access
WirelessMAN-OFDM
WirelessMAN Orthogonal
Frequency Division Multiplexing
WirelessMAN-OFDMA
WirelessMAN Orthogonal
Frequency Division Multiple Access
WirelessHUMAN
Wireless High-speed Unlicensed
Metropolitan Area Network
MAC Protocol Data Unit –
MAC PDU Formats
Each MAC PDU consists of three
components
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A fixed-length Generic MAC Header
A variable length Payload
A CRC ( Cyclic Redundancy Check )
MAC header
Payload
6 Byte
variable
Management Message
4 Byte
MAC Layer Functions
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Support for integrated voice/data
connections
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Fragmentations
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Various level of QoS settings
Fragmentation and reassemble
Retransmissions

Using ARQ (Automatic Repeat Request)
Two Types of MAC Header
HT
EC
TYPE
BR
CID
HCS
Bandwidth Request MAC Header
HT
EC
TYPE
RSV
CI
EKS
RSV
Generic MAC Header
LEN
CID
HCS
Generic MAC Header
HT（Header Type）--- 1 bit
Generic MAC Header shall be set to zero
EC（Encryption Control）--- 1 bit
Specify if the payload is encrypted
0=Payload is not encrypted
1=Payload is encrypted
TYPE --- 6 bits
Indicates the subheader and special payload types present
in
the message payload
Generic MAC Header
HT (Header Type) --- 1 bit (1 for Generic MAC Header)
EC (Encryption Control) --- 1 bit (1: encrypted)
RSV (Reserved) --- 1 bit
shall be set to zero
CI (CRC Indicator) --- 1 bit
1 = CRC is present
0 = No CRC is included
EKS (Encryption Key Sequence) --- 2 bits
LEN (Length) --- 11 bits
Header + Payload + CRC
CID (Connection Identifier) --- 16 bit
HCS (Header Check Sequence) --- 8 bits
Used to detect errors in the header
Bandwidth Request MAC Header
HT (Header Type) --- 1 bit (0 for Bandwdith Request MAC
Header)
EC (Encryption Control) --- 1 bit (always 0, indicating no
encryption)
TYPE: Indicates the request is incremental or aggregate
000 = for incremental
001 = for aggregate
BR (Bandwidth Request) --- 19 bits
The number of bytes of uplink bandwidth requested by SS.
CID (Connection Identifier) --- 16 bits
Indicates the connection for which UL Bandwidth is requested
HCS (Header Check Sequence) --- 8 bits
Used to detect errors in the header
Channel Access
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Uplink (SS  BS)
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TDMA
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DAMA (demand assigned multiple access)
Downlink (BS  SS)
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TDM (Time Division Multiplexing)
Duplexing can be FDD or TDD
Frame Structure
Frame (n-1)
Frame n
Frame (n+1) Frame (n+2)
Time
DL PHY
DU
Contention
slot for initial
ranging
Contention
Slot for BW
request
DL Subframe
Preamble
DLFP
UL PHY
PDU
From SS#1
…
UL PHY
PDU
From SS#k
UL Subframe
FCH
DL burst #1
Broadcast msgs
Eg. DL-MAP, UL-MAP, DCD, UCD
FCH: Frame Control Header
DLFP: Downlink Frame Prefix
DCD: Downlink Channel Descriptor
DL burst #2
…
DL burst #N
Regular MAC
PDUs
MAC msg 1
(MAC PDU-1)
…
MAC msg N
Pad
(MAC PDU-N)
UCD: Uplink Channel Descriptor
MAC Header
Frame Structure ----- TDD (DL)
MAC Msg Payload
CRC
FCH (Frame Control Header)
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DLFP (Downlink Frame Prefix)
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specifies the modulation type and number of symbols
associated with one or several downlink bursts that
follow the FCH
The modulation and coding used in the first downlink
burst immediately following the FCH is specified in
the RateID. The RateID is a 4-b code.
The Downlink Interval Usage Code (DIUC) is a 4-b
code similar to the RateID and is used for identifying
the profiles of the other bursts in the downlink.
The DLFP also includes an 8-b Header Check
Sequence (HCS)
DL Subframe
UL Subframe
UIUC and DIUC specify the profile (modulation, coding) used in each burst
Frame (n-1)
Frame n
Frame (n+1) Frame (n+2)
Time
DL PHY
PDU
Contention
slot for initial
ranging
DL Subframe
Contention
Slot for BW
request
UL PHY
PDU
From SS#1
…
UL Subframe
Preamble
MAC msg 1
(MAC PDU-1)
…
MAC Header
Frame Structure ----- TDD (UL)
UL burst #1
MAC msg N
Pad
(MAC PDU-N)
MAC Msg Payload
CRC
UL PHY
PDU
From SS#k
Network Entry and Initialization
Network Entry Procedure—PMP mode
Phases
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Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Network Entry Procedure
--- Scan for the Downlink Channel
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On initialization or after signal loss, SS shall
acquire a DL channel
The SS shall have nonvolatile storage in which
the last operational parameters are stored and
shall first try to acquire this DL channel
If fails , the SS begins to continuously scan the
possible channels for the DL frequency band of
operation until it finds a valid DL signal
Network Entry Procedure:
Establish PHY synchronization
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Identifying the carrier center frequency
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Acquiring the preamble
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Reading the FCH (Frame Control Header)
Network Entry Procedure:
Establish MAC synchronization
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The SS achieves MAC synchronization once it
has received at least one DL-MAP message.
An SS MAC remains in synchronization as long
as it continues to successfully receive the DLMAP and DCD messages for its channel.
If the Lost DL-MAP Interval has elapsed without
a valid DL-MAP message or the T1 Interval has
elapsed without a valid DCD message, an MS
shall try reestablish synchronization
Frame (n-1)
Frame n
Frame (n+1) Frame (n+2)
Time
DL PHY
DU
Contention
slot for initial
ranging
Contention
Slot for BW
request
DL Subframe
Preamble
DLFP
UL PHY
PDU
From SS#1
…
UL PHY
PDU
From SS#k
UL Subframe
FCH
DL burst #1
Broadcast msgs
Eg. DL-MAP, UL-MAP, DCD, UCD
(MAC PDU-1)
Frame Structure ----- TDD (DL)
…
DL burst
#N
Regular MAC
PDUs
MAC msg 1
MAC Header
DL burst #2
…
MAC msg N
Pad
(MAC PDU-N)
MAC Msg Payload
CRC
Network Entry Procedure—PMP mode
Phases
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

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Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Network Entry Procedure—PMP mode
Phases









Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Network Entry Procedure
--- Perform Ranging
Purpose
The process by which the SS and BS maintain of RF
communication link between them
How
RNG-REQ / RNG-RSP MAC management message
Special CDMA code modulated message
Ranging Procedures
A.
B.
C.
D.
Initial Ranging
Periodic Ranging
Contention Ranging
Non-Contention Ranging
Network Entry Procedure
--- Perform Ranging
Initial Ranging
•Acquire correct transmission parameters (Power adjustment, timing
offset estimation, and synchronization) to communicate with the BS
Periodic Ranging
•To maintain uplink communication with the BS
•Adjust transmission parameters
Contention Ranging
•Required by the SS to access the system for the first time
•No dedicated connection resources assigned to the SS
Non-Contention Ranging
•Regulated by the BS to allow the SS to finish system access earlier
when dedicated channel is provided
•Polled initial ranging
Frame (n-1)
Frame n
Frame (n+1) Frame (n+2)
Time
DL PHY
PDU
Contention
slot for initial
ranging
DL Subframe
Contention
Slot for BW
request
UL PHY
PDU
From SS#1
…
UL Subframe
Preamble
MAC msg 1
(MAC PDU-1)
…
MAC Header
Frame Structure ----- TDD (UL)
UL burst #1
MAC msg N
Pad
(MAC PDU-N)
MAC Msg Payload
CRC
UL PHY
PDU
From SS#k
Network Entry Procedure—PMP mode
Phases









Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Initialization Procedure
--- Negotiate Basic Capabilities
Purpose
The SS informs the BS of its basic capabilities
How
SBC-REQ / SBC-RSP management message
•SBC-REQ stands for SS Basic Capabilities Request
•SBC-RSP stands for SS Basic Capabilities Response
Procedure
1. After completion of ranging ,the BS will wait for SBC-REQ
message transmitted by the SS
2. If SBC-REQ message are not received within T9 ,the BS
shall release and age out Basic and Primary Management
CIDs
Network Entry Procedure—PMP mode
Phases
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


Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Initialization Procedure
--- Authorization & Key Exchange
Purpose
For authorization procedure
How
PKM ( Privacy Key Management ) Protocol
•PKM-REQ /PKM-RSP management message
Initialization Procedure --Registration
Purpose
The process by which the SS is allowed entry into network
and becomes manageable
How
REG-REQ / REG-RSP management message
Procedure
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SS sends a REG-REQ message to the BS
BS responds with a REG-RSP message, including
secondary management CID if the SS is managed SS
A managed SS shall establish secondary management
connection and configure its IP connectivity
A unmanaged SS shall set up provisioned connections
Network Entry Procedure—PMP mode
Phases
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




Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Initialization Procedure
--- Establish IP Connectivity
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
SS and BS shall negotiate IP version during
REG REQ/RSP exchange if the SS is managed.
After registration, SS shall invoke DHCP
mechanisms (on SS’
s Secondary management
Connection) to obtain an IP address and any
other parameters for IP connectivity.
Initialization Procedure
--- Establish Provisioned Connection
Purpose
Create a provisioned service flow
Procedure
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The BS shall send DSA-REQ message to the SS to set
up connections for pre-provisioned service flows
belonging to the SS
The SS responds with DSA-RSP messages to the BS
Network Entry Procedure—PMP mode
Phases
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







Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Initialization Procedure
--- Establish Time of day
Purpose
For retrieving Time-stamping logged events
Procedure
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The protocol by which the time of day shall retrieved is
defined in IETF RFC 868
Establishment of time of day shall be performed on the
SS’
s Secondary management Connection
Network Entry Procedure—PMP mode
Phases
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




Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections
Initialization Procedure
--- Transfer Operational parameters

When the configuration file is successfully
downloaded, the SS shall notify the BS by
transmitting a TFTP-CPLT message on SS’
s
Primary management connection
(The BS shall response a TFTP-RSP message. TFTPRSP stands for Config File TFTP Complete Response)
Network Entry Procedure—PMP mode
Phases









Scan for DL channel and establish synchronization
with the BS
Obtain transmit parameters (form UCD message)
Perform initial ranging
Negotiate basic capabilities
Authorize MS and perform key exchange
Establish IP connectivity
Establish time of day
Transfer operational parameters
Set up connections <= Final Step!
How to set up contention?
Contention Resolution Algorithm
(1/2)
1. Contention resolution is based on a truncated
binary exponential back-off
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The initial back-off window and maximum back-off
window are controlled by the BS
These values are as part of the UCD message and
power-of-two. E.g. 4 for (0, 15) window; 10 for (0,1023)
2. The SS shall randomly select a number of
contention within its back-off window
3. The random value is the number of contention
transmission opportunities that the SS shall
defer before transmitting
Contention Resolution Algorithm
(2/2)
4. After a contention transmission, the SS waits
for a Data Grant Burst Type IE in a subsequent
map ( or waits for a RNG-RSP message for
initial ranging).
5. Once received, the contention resolution is
complete
6. The SS shall consider the connection
transmission lost if no data grant had been
given within T16 (or T3 for initial ranging)

The SS shall increase its back-off window by a
factor of two, as long as it is less than the maximum
back-off
Frame
2 TxOP
SS1 send
BW Request
第一次Initial Ranging 要競爭,先聽UL-MAP
知道每個frame 有2個TXOP 及CWmin,
CWmax
再用random back-off 搶,並等回應
SS2 send
BW Request
SS3 send
BW Request
Assume that
1. Three SS (SS1,SS2 and SS3) compete to send BW Request
2. The Broadcast Request IE = 2 transmission opportunities (the Broadcast
Request IE is part of UL-MAP determined by BS)
3. The initial back-off window is 0 to 15
4. The random values for each SS are: 2 (SS1), 3 (SS2) and 5 (SS3)
How does BS allocate
bandwidth to SS?
Five QoS Levels
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Unsolicited Grant Service (UGS):
used for real-time data with fixed packet size and periodic arrivals
(T1/E1, VoIP).
Extended Real-time Polling Service (ertPS):
used for real-time data with variable-sized packets and periodic
arrivals (VoIP with silence suppression).
Real-time Polling Service (rtPS):
used for near real-time data with variable-sized packets and periodic
arrivals (MPEG).
Non-real-time Polling Service (nrtPS):
used for delay tolerant traffic requiring some minimum data rate
(FTP).
Best Effort (BE):
used for streams with no rate guarantees (HTTP).
Classification and CID Mapping
IEEE 802.16 QoS Architecture
Proposed architecture to provide QoS
in IEEE 802.16 standards
Unicast Polling
Multicast and Broadcast Polling