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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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Presentation Transcript
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…
slide16

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
slide23
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
slide28
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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