Download NIST_Wimax_Module

NS-2 NIST add-on
IEEE 802.16 model
(MAC+PHY)
Miray Kas
28 Jan 2008
Outline
MAC Layer overview
 Basic Data about PHY Layer
 List of Available/Unavailable Features
 Available Features

 Convergence
Sublayer
 MAC Common Part
 PHY Layer

Comments on Unavailable Features
Basic Data on IEEE 802.16
Standards (1)
Basic Data on IEEE 802.16
Standards (2)
Why NS-2 & WiMAX

Ns-2:
 De

facto Standard for Simulation of Networks
Not so many WiMAX modules available:
 NIST
Most reliable
 Only one that has mobility functionality

 Chang
Gung University Taiwan
 State University of Campinas Brazil
ns-2 vs. ns-3 environment
ns-2 since 1996
 ns-3 in progress, no initial alpha release
 ns-3 : Rewrite of core simulator

 802.11
PHY cleanup
 ns-2 integration with ns-3
 tools to parse output data (tcpdump and Ethereal)
 (Dynamic) Calendar Queue
 NIST WiMAX ns-2 port to ns-3
Main Features of WiMAX Module

PHY:
 OFDM

MAC:
 PMP
mode
 TDD
Builds on ns2 legacy code
 Implemented in C++

Convergence Sublayer




Classifying higher layer PDUs into appropriate
connections
Delivering resulting CS PDUs to MAC SAP
associated with the service flow.
Suppressing / Rebuilding payload header
information
Used for Internet Protocol (IP)
Point-to-Point Protocol (PPP)
Ethernet (IEEE 802.3)
Convergence Sublayer
Convergence Sublayer
Convergence Sublayer
MAC Sublayer - Addressing &
Connection


Initialization of BS
 Initial
Ranging( )
 Padding(
)
 Broadcast(
)
 Adaptive Antenna System(

Initialization of SS
 Initial
Ranging(
 Padding(
)
 Broadcast(
)
)
During network entry, following are set up:
 Basic
CID(
)
 Primary CID(
)
 Secondary CID(
 Data CIDs
Exchange time urgent MAC mng. msg
Longer delay tolerant MAC mng. msg
) DHCP, TFTP, SNMP
Current model supports only one
)
MAC PDU Format
Fixed Length
0 or more sub-headers
0 or more fragments
 Virtual PHY header : Used to carry physical
information such as frequency, modulation…
HT = 1
Mutually Exclusive
HT = 0
Construction & Transmission of
MAC PDUs

3 steps:
 Receive,
classify, put in the connection queue
 Scheduling
 Transmission

Construction:
 Fragmentation
& Packing
 CRC calculation
Scheduler

Service Flow classes are implemented
 UGS,

Current one does not use service classes
 Best

Effort Scheduler with Round-Robin algorithm
Allows custom implementations
 One

nrtPS, rtPS, BE
default for SS and BS each
Replace current one by a TCL command
 $mac
set-scheduler $scheduler
Scheduler
QoS

Structure supports Service Flows
 ertPS
not implemented
Scheduler does not use them
 No Admission Control during creation of flows

 Accept

all requests from MSs
List of flows in each SS
 Static
 Stored
by ServiceFlowHandler
Contention Resolution
BS has full control on downlink
 Collisions possible in uplink

 Initial
Ranging Request
 Bandwidth Request
BS decides contention slots
 Binary exponential backoff window

 SS
decides how many minislots to defer
Contention Slot
Contention Request
TDD
Uplink transmissions occur after downlink transmissions
at each frame
Frame Structure
Network Entry & Initialization

Steps:
 Scan
downlink channel
 Obtain transmit parameters
 Initial ranging
 Registration

Following can be configured:
 Timers
to perform channel scanning
 Frequency of the DCD/UCD messages
 Parameters for initial ranging (backoff window size
& # of slots per frame)
 Channel allocation
Network Entry
Scanning

Related to Handover procedure

When link quality weakens MS scans to
find another BS

Send MOB-SCN_REQ to current BS to
request scanning interval
Scanning
Scanning Modes

Without association
 MS

attempts itself
Association Level 0 – w.o. Coordination
 Target

BS has no information about scanning MS
Association Level 1 – with Coordination
 Serving

BS negotiates with target BS
Association Level 2 – Network Assisted
 Not
implemented yet.
Scanning

WiMAXCtrlAgent
 Extends Agent

Has three functions:
 Exchange
 Trigger
DCD/UCD info btw. BSs
sending of NBR-ADV msg. to MSs
 Synchronize
BSs (serving & target)
Ranging

Definition
 A mechanism
to allow an SS to maintain link
quality by adjusting its 1-) Transmission power
2-) Modulation

Uplink Ranging = Initial Ranging + Periodic Ranging

Downlink Ranging = No periodic ranging
Ranging (Current Situation in the Module)

No algorithm to make use of ranging capabilities

Periodic ranging not implemented

CDMA request not implemented

Only to add latency to the network entry

Mechanism implemented not applicable to
OFDMA
Timers









WimaxFrameTimer
WimaxRxTimer
WimaxDCDTimer
WimaxUCDTimer
WimaxRngIntTimer
WimaxLostDLMAPTimer
WimaxLostULMAPTimer
DLTimer
ULTimer
Mobility
Extensions









WimaxT1Timer
WimaxT2Timer
WimaxT3Timer
WimaxT6Timer
WimaxT9Timer
WimaxT12Timer
WimaxT16Timer
WimaxT17Timer
WimaxT21Timer
WimaxMobNbrAdvTimer
WimaxScanIntervalTimer
WimaxRdvTimer
WimaxT44Timer
PHY Layer

Only OFDM is implemented
OFDMA
 WirelessMAN-SC
 WirelessMAN-SCa
 WirelessHUMAN

Missing Yet!!!
PHY Layer

Configurable parameters (TCL):
 Transmission power
 Cyclic Prefix
 Frequency
 Frequency bandwidth
 Modulation

Computed values:
 Sampling frequency
 OFDM symbol time duration
 Xmission time of a packet acc. to its size and modulation
 Max packet size for a given modulation and # of available
OFDM symbols
PHY Layer

Default:
 OFDM_BPSK_1_2

modulation
 OFDM_IDLE

Supported Modulations:
States:
 OFDM_IDLE
 OFDM_SEND
 OFDM_RECV
 OFDM_RX2TX
 OFDM_TX2RX
PHY Layer
Available/Unavailable Features
Open to Improvement

WirelessMAN-OFDMA physical layer

ARQ (Automatic Repeat Request)

Error Correction

Service Flow and QoS scheduling

Call Admission Control

Periodic ranging and power adjustments
Will be Still Missing…
ATM Convergence Sublayer
 Mesh Mode
 Physical Layers

 WirelessMAN-SC
 WirelessMAN-SCa
 WirelessHUMAN
Frequency Division Duplexing (FDD)
 Authentication
