Tài liệu Broadband wireless access

WiMAX: Broadband Wireless Access Wireless Networks Spring 2007 802.16 Standards Development  Use wireless links with microwave or millimeter wave radios o o     10-66 GHz 802.16a extension to 2-11 GHz Use licensed spectrum (unlicensed too in 802.16a) Metropolitan in scale Provide public network service to feepaying customers Point-to-multipoint architecture with rooftop or tower-mounted antennas Wireless Networks Spring 2007 802.16 Standards Development   Provide efficient transport of heterogeneous traffic supporting QoS Capable of broadband transmissions (275 Mbps) o  Accommodate both continuous and bursty traffic Mobile extensions: 802.16e Wireless Networks Spring 2007 IEEE 802.16 Protocol Architecture Wireless Networks Spring 2007 Protocol Architecture  Physical layer functions: o o o  Encoding/decoding of signals Preamble generation/removal Bit transmission/reception Medium access control layer functions: o o o On transmission, assemble data into a frame with address and error detection fields On reception, disassemble frame, and perform address recognition and error detection Govern access to the wireless transmission medium Wireless Networks Spring 2007 Protocol Architecture  Convergence layer functions: o o o o Encapsulate PDU framing of upper layers into native 802.16 MAC/PHY frames Map upper layer’s addresses into 802.16 addresses Translate upper layer QoS parameters into native 802.16 MAC format Adapt time dependencies of upper layer traffic into equivalent MAC service Wireless Networks Spring 2007 IEEE 802.16 Services        Digital audio/video multicast Digital telephony ATM Internet protocol Bridged LAN Back-haul Frame relay Wireless Networks Spring 2007 Burst Profiles   Each subscriber station negotiates a burst profile with the base station Burst profiles decided based on QoS needs and channel conditions o o Harsher environment demands more robust profiles Favorable environment allows efficient profiles Wireless Networks Spring 2007 IEEE 802.16.1 Frame Format  Header - protocol control information o o o   Downlink header – used by the base station Uplink header – used by the subscriber to convey bandwidth management needs to base station Bandwidth request header – used by subscriber to request additional bandwidth Payload – either higher-level data or a MAC control message CRC – error-detecting code Wireless Networks Spring 2007 Physical Layer: Uplink      Stations transmit in in their assigned allocation specified in an initial map Uplink sub-frame may also contain contention-based allocations for initial system access Uses a DAMA-TDMA technique Error correction uses Reed-Solomon codes Modulation scheme based on QPSK, 16QAM or 64-QAM Wireless Networks Spring 2007 Physical Layer: Downlink  Continuous downstream mode o o o  For continuous transmission (audio/video) Simple TDM scheme is used for channel access Frequency division duplex (FDD) Burst downstream mode o o o For bursty transmission (IP-based traffic) DAMA-TDMA scheme for channel access FDD with adaptive modulation, frequency shift division duplexing (FSDD), time division duplexing (TDD) Wireless Networks Spring 2007 Medium Access Control (MAC)  Connection-oriented o   All services inherently connectionless mapped to a connection Connections referenced using a 16bit connection identifier (CID) Management channels and transport channels for contracted services Wireless Networks Spring 2007 Radio Link Control    Power control and paging Transition among burst profiles Downlink burst profile change o o o  Subscriber station monitors downlink quality Requests a new profile Granted if base station judges possible Uplink profile change o o Base station monitors the uplink signal quality Specifies the new profile’s usage code when granting subscriber bandwidth in a frame Wireless Networks Spring 2007 Bandwidth Requests & Grants  Two kinds of subscribers o o    Grant per connection (GPC) Grant per subscriber (GPSS) Both classes request bandwidth per connection for QoS guarantees For GPC, bandwidth explicitly guaranteed to connection For GPSS, bandwidth aggregated into a single grant for SS Wireless Networks Spring 2007 Requesting Bandwidth  Unsolicited grants o o    No need to request bandwidth for services that generate fixed units of data periodically Negotiated at connection setup time Send a bandwidth request MAC packet Piggyback request within MAC data packet Polling by base station Wireless Networks Spring 2007 MAC Management Messages       Uplink and downlink channel descriptor Uplink and downlink access definition Ranging request and response Registration request, response and acknowledge Privacy key management request and response Dynamic service addition request, response and acknowledge Wireless Networks Spring 2007 MAC Management Messages      Dynamic service change request, response, and acknowledge Dynamic service deletion request and response Multicast polling assignment request and response Downlink data grant type request ARQ acknowledgment Wireless Networks Spring 2007