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

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

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