Wireless Networks Spring 2007 WiMAX: Broadband Wireless Access

Wireless Networks Spring Standards Development  Use wireless links with microwave or millimeter wave radios o GHz o a extension to 2-11 GHz  Use licensed spectrum (unlicensed too in a)  Metropolitan in scale  Provide public network service to fee- paying customers  Point-to-multipoint architecture with rooftop or tower-mounted antennas

Wireless Networks Spring Standards Development  Provide efficient transport of heterogeneous traffic supporting QoS  Capable of broadband transmissions (2- 75 Mbps) o Accommodate both continuous and bursty traffic  Mobile extensions: e

Wireless Networks Spring 2007 IEEE Protocol Architecture

Wireless Networks Spring 2007 Protocol Architecture  Physical layer functions: o Encoding/decoding of signals o Preamble generation/removal o Bit transmission/reception  Medium access control layer functions: o On transmission, assemble data into a frame with address and error detection fields o On reception, disassemble frame, and perform address recognition and error detection o Govern access to the wireless transmission medium

Wireless Networks Spring 2007 Protocol Architecture  Convergence layer functions: o Encapsulate PDU framing of upper layers into native MAC/PHY frames o Map upper layer’s addresses into addresses o Translate upper layer QoS parameters into native MAC format o Adapt time dependencies of upper layer traffic into equivalent MAC service

Wireless Networks Spring 2007 IEEE 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 Harsher environment demands more robust profiles o Favorable environment allows efficient profiles

Wireless Networks Spring 2007 IEEE Frame Format  Header - protocol control information o Downlink header – used by the base station o Uplink header – used by the subscriber to convey bandwidth management needs to base station o 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, 16- QAM or 64-QAM

Wireless Networks Spring 2007 Physical Layer: Downlink  Continuous downstream mode o For continuous transmission (audio/video) o Simple TDM scheme is used for channel access o Frequency division duplex (FDD)  Burst downstream mode o For bursty transmission (IP-based traffic) o DAMA-TDMA scheme for channel access o 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 16- bit 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 Subscriber station monitors downlink quality o Requests a new profile o Granted if base station judges possible  Uplink profile change o Base station monitors the uplink signal quality o 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 Grant per connection (GPC) o 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 No need to request bandwidth for services that generate fixed units of data periodically o 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