NS-2 NIST add-onIEEE 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 SublayerMAC Common PartPHY 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 TaiwanState 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 cleanupns-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:PHY:

OFDM

MAC:MAC: PMP modeTDD

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 BSInitialization of BS Initial Ranging( ) Padding( ) Broadcast( ) Adaptive Antenna System( )

Initialization of SSInitialization of SS Initial Ranging( ) Padding( ) Broadcast( )

During network entry, following are set up:During network entry, following are set up: Basic CID( ) Exchange time urgent MAC mng. msg Primary CID( ) Longer delay tolerant MAC mng. msg Secondary CID( ) DHCP, TFTP, SNMP Data CIDs Current model supports only one

MAC PDU Format

0 or more sub-headers0 or more sub-headers

0 or more fragments0 or more fragments

Fixed LengthFixed Length

Virtual PHY header : Used to carry physical information such as frequency, modulation…

Mutually ExclusiveMutually Exclusive

HT = 1

HT = 0

Construction & Transmission of MAC PDUs 3 steps:

Receive, classify, put in the connection queueSchedulingTransmission

Construction:Fragmentation & PackingCRC calculation

Scheduler Service Flow classes are implemented

UGS, nrtPS, rtPS, BE

Current one does not use service classes Best Effort Scheduler with Round-Robin algorithm

Allows custom implementations One default for SS and BS each

Replace current one by a TCL command $mac set-scheduler $scheduler

Scheduler

QoS

Structure supports Service FlowsertPS 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

StaticStored by ServiceFlowHandler

Contention Resolution BS has full control on downlink Collisions possible in uplink

Initial Ranging RequestBandwidth 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 transmissionsat 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 DCD/UCD info btw. BSs

Trigger sending of NBR-ADV msg. to MSs

Synchronize BSs (serving & target)

Ranging

DefinitionA 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

WimaxT1Timer WimaxT2Timer WimaxT3Timer WimaxT6Timer WimaxT9Timer WimaxT12Timer WimaxT16Timer WimaxT17Timer WimaxT21Timer

WimaxMobNbrAdvTimerWimaxScanIntervalTimerWimaxRdvTimerWimaxT44Timer

Mobility Mobility ExtensionsExtensions

PHY Layer

Only OFDM is implemented

OFDMA WirelessMAN-SC WirelessMAN-SCa WirelessHUMAN

Missing Yet!!!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:Default:

OFDM_BPSK_1_2 modulation OFDM_IDLE

Supported Modulations:Supported Modulations:

States: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