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Wireless LAN Overview

Wireless LAN Overview. Sunggeun Jin 2005-10-17. Outline. IEEE802.16 MAC IEEE802.11 MAC. IEEE802.16 (a, e, Wibro). Original goal alternative to cabled access network to provide network access to buildings it came from DOCSIS spec. Amendments IEEE802.16a for fixed service subscribers

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Wireless LAN Overview

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  1. Wireless LAN Overview Sunggeun Jin 2005-10-17

  2. Outline • IEEE802.16 MAC • IEEE802.11 MAC

  3. IEEE802.16 (a, e, Wibro) • Original goal • alternative to cabled access network • to provide network access to buildings • it came from DOCSIS spec. • Amendments • IEEE802.16a • for fixed service subscribers • IEEE802.16e • for movable service subscribers • Feature • FDD or TDD • TDD as to Wibro • TDM, TDMA, OFDM, OFDMA • OFDM/OFDMA for Wibro

  4. Protocol Layers of IEEE802.16 - Transformation of external network data into MAC SDUs ; - Payload header suppression - System Access - Bandwidth Allocation - Connection set - up - Connection maintenance - QoS - Authentication - Secure key exchange - Encryption

  5. System operations BS CD • BS access inf. • Burst Profile • Power Control MAP • BW allocations • Frame Information Transmit Initial Ranging Code Transmit BW-Req. Code CD/MAP SS trying to access to BS UL Data Transmit Periodic Ranging Code DL Data Requesting BW allocation SS performing periodic ranging Data transmission service

  6. Initial Ranging • timing and frequency offset adjustments • obtaining management CID

  7. CIDs Basic CID Primary Management CID Secondary Management CID Transport CID1 Transport CID2 • Management Connection • Basic CID • Short, Urgent MAC Messages • Primary Management CID • Longer, More Delay Tolerant MAC Messages • Secondary Management CID • Delay Tolerant, Standard-Based Management Messages • E.g., : DHCP, TFTP, SNMP • Transport Connection • Multiple CIDs exist • BS assigns them to SS • Data transmission

  8. MAP and frame structure Frame in case of TDD Frames in case of FDD

  9. IEEE802.11 • Application overview • Wireless Ethernet with compatible speed • Enable (indoor) wireless and mobile high-speed networking • Functional overview • Runs at unlicensed bands at 2.4GHz and 5GHz • Connectionless MAC and multiple PHYs • Supports up to 11 and/or 54 Mbps within >100 m range

  10. 802.11 Reference Model

  11. Two Modes • Infrastructure mode • Infrastructure Basic Service Set  BSS • An access point (AP) and multiple stations (STAs) • Every transmission is with AP; no peer-to-peer communication

  12. Two Modes cont. • Ad hoc mode • Independent Basic Service Set  IBSS • Multiple stations (STAs), and no AP • Peer-to-peer communication only

  13. Two Coordination Functions • Mandatory Distributed Coordination Function (DCF) • For distributed contention-based channel access • Optional Point Coordination Function (PCF) • For centralized contention-free channel access

  14. Distributed Coordination Function (DCF) • Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) • similar to IEEE 802.3 Ethernet CSMA/CD

  15. Carrier-Sense Mechanisms • Physical carrier-sense • Provided by PHY, and depends on PHY • Clear Channel Assessment (CCA) by PHY • Virtual carrier-sense • Provided by MAC via Network Allocation Vector (NAV) counter • Each frame carries Duration value in the header • Any correctly received frame updates NAV if the new NAV is larger • Assumes busy channel if non-zero NAV irrespective of CCA!

  16. Stop-and-Wait ARQ • Receiver of a directed frame returns an ACK • If ACK not received, sender retransmits after another back-off

  17. References • Carl Eklund and et al, “IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access,” IEEE Comm. Mag. Jun. 2002 • IEEE802.11 tutorial material presented by Sunghyun Choi, Seoul Natl. Univ. • IEEE802.16 tutorial material presented by Samsung • IEEE802.16 tutorial material presented by ETRI

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