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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 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 • IEEE802.16e • for movable service subscribers • Feature • FDD or TDD • TDD as to Wibro • TDM, TDMA, OFDM, OFDMA • OFDM/OFDMA for Wibro
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
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
Initial Ranging • timing and frequency offset adjustments • obtaining management CID
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
MAP and frame structure Frame in case of TDD Frames in case of FDD
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
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
Two Modes cont. • Ad hoc mode • Independent Basic Service Set IBSS • Multiple stations (STAs), and no AP • Peer-to-peer communication only
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
Distributed Coordination Function (DCF) • Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) • similar to IEEE 802.3 Ethernet CSMA/CD
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!
Stop-and-Wait ARQ • Receiver of a directed frame returns an ACK • If ACK not received, sender retransmits after another back-off
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