Ns 2 nist add on ieee 802 16 model mac phy
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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.

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Ns 2 nist add on ieee 802 16 model mac phy

NS-2 NIST add-onIEEE 802.16 model (MAC+PHY)

Miray Kas

28 Jan 2008


Outline
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




Why ns 2 wimax
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 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
Main Features of WiMAX Module

  • PHY:

    • OFDM

  • MAC:

    • PMP mode

    • TDD

  • Builds on ns2 legacy code

  • Implemented in C++


Convergence sublayer
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)





Mac sublayer addressing connection
MAC Sublayer - Addressing & Connection

  • Initialization of SS

    • Initial Ranging( )

    • Padding( )

    • Broadcast( )

  • Initialization of BS

    • Initial Ranging( )

    • Padding( )

    • Broadcast( )

    • Adaptive Antenna System( )

  • 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
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

HT = 0

Mutually Exclusive


Construction transmission of mac pdus
Construction & Transmission of MAC PDUs

  • 3 steps:

    • Receive, classify, put in the connection queue

    • Scheduling

    • Transmission

  • Construction:

    • Fragmentation & Packing

    • CRC calculation


Scheduler
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



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
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




TDD

  • Uplink transmissions occur after downlink transmissions

  • at each frame



Network entry initialization
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



Scanning
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 modes
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.


Scanning2
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
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
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
Timers

  • WimaxT1Timer

  • WimaxT2Timer

  • WimaxT3Timer

  • WimaxT6Timer

  • WimaxT9Timer

  • WimaxT12Timer

  • WimaxT16Timer

  • WimaxT17Timer

  • WimaxT21Timer

  • WimaxFrameTimer

  • WimaxRxTimer

  • WimaxDCDTimer

  • WimaxUCDTimer

  • WimaxRngIntTimer

  • WimaxLostDLMAPTimer

  • WimaxLostULMAPTimer

  • DLTimer

  • ULTimer

  • WimaxMobNbrAdvTimer

  • WimaxScanIntervalTimer

  • WimaxRdvTimer

  • WimaxT44Timer

Mobility

Extensions


Phy layer
PHY Layer

  • Only OFDM is implemented

  • OFDMA

  • WirelessMAN-SC

  • WirelessMAN-SCa

  • WirelessHUMAN

Missing Yet!!!


Phy layer1
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 layer2
PHY Layer

  • States:

    • OFDM_IDLE

    • OFDM_SEND

    • OFDM_RECV

    • OFDM_RX2TX

    • OFDM_TX2RX

  • Default:

    • OFDM_BPSK_1_2 modulation

    • OFDM_IDLE

  • Supported Modulations:




Open to improvement
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
Will be Still Missing…

  • ATM Convergence Sublayer

  • Mesh Mode

  • Physical Layers

    • WirelessMAN-SC

    • WirelessMAN-SCa

    • WirelessHUMAN

  • Frequency Division Duplexing (FDD)

  • Authentication


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