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

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)

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  1. NS-2 NIST add-onIEEE 802.16 model (MAC+PHY) Miray Kas 28 Jan 2008

  2. 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

  3. Basic Data on IEEE 802.16 Standards (1)

  4. Basic Data on IEEE 802.16 Standards (2)

  5. 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

  6. 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

  7. Main Features of WiMAX Module • PHY: • OFDM • MAC: • PMP mode • TDD • Builds on ns2 legacy code • Implemented in C++

  8. 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)

  9. Convergence Sublayer

  10. Convergence Sublayer

  11. Convergence Sublayer

  12. 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

  13. 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…

  14. HT = 1 HT = 0 Mutually Exclusive

  15. Construction & Transmission of MAC PDUs • 3 steps: • Receive, classify, put in the connection queue • Scheduling • Transmission • Construction: • Fragmentation & Packing • CRC calculation

  16. 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

  17. Scheduler

  18. 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

  19. 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

  20. Contention Slot

  21. Contention Request

  22. TDD • Uplink transmissions occur after downlink transmissions • at each frame

  23. Frame Structure

  24. 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

  25. Network Entry

  26. 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

  27. Scanning

  28. 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.

  29. 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)

  30. 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

  31. 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

  32. 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

  33. PHY Layer • Only OFDM is implemented • OFDMA • WirelessMAN-SC • WirelessMAN-SCa • WirelessHUMAN Missing Yet!!!

  34. 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

  35. PHY Layer • States: • OFDM_IDLE • OFDM_SEND • OFDM_RECV • OFDM_RX2TX • OFDM_TX2RX • Default: • OFDM_BPSK_1_2 modulation • OFDM_IDLE • Supported Modulations:

  36. PHY Layer

  37. Available/Unavailable Features

  38. 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

  39. 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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