WiMAX:%20Broadband%20Wireless%20Access

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WiMAX Broadband Wireless Access
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802.16 Standards Development

• Use wireless links with microwave or millimeter
  wave radios
• 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 fee-paying
  customers
• Point-to-multipoint architecture with rooftop or
  tower-mounted antennas

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802.16 Standards Development

• Provide efficient transport of heterogeneous
  traffic supporting QoS
• Capable of broadband transmissions (2-75 Mbps)
• Accommodate both continuous and bursty traffic
• Mobile extensions 802.16e

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IEEE 802.16 Protocol Architecture
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Protocol Architecture

• Physical layer functions
• Encoding/decoding of signals
• Preamble generation/removal
• Bit transmission/reception
• Medium access control layer functions
• 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

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Protocol Architecture

• Convergence layer functions
• Encapsulate PDU framing of upper layers into
  native 802.16 MAC/PHY frames
• Map upper layers 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

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IEEE 802.16 Services

• Digital audio/video multicast
• Digital telephony
• ATM
• Internet protocol
• Bridged LAN
• Back-haul
• Frame relay

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Burst Profiles

• Each subscriber station negotiates a burst
  profile with the base station
• Burst profiles decided based on QoS needs and
  channel conditions
• Harsher environment demands more robust profiles
• Favorable environment allows efficient profiles

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IEEE 802.16.1 Frame Format

• Header - protocol control information
• 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

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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

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Physical Layer Downlink

• Continuous downstream mode
• For continuous transmission (audio/video)
• Simple TDM scheme is used for channel access
• Frequency division duplex (FDD)
• Burst downstream mode
• 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)

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Medium Access Control (MAC)

• Connection-oriented
• 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

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Radio Link Control

• Power control and paging
• Transition among burst profiles
• Downlink burst profile change
• Subscriber station monitors downlink quality
• Requests a new profile
• Granted if base station judges possible
• Uplink profile change
• Base station monitors the uplink signal quality
• Specifies the new profiles usage code when
  granting subscriber bandwidth in a frame

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Bandwidth Requests Grants

• Two kinds of subscribers
• 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

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Requesting Bandwidth

• Unsolicited grants
• 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

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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

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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