Mô tả:
WiMAX: Broadband Wireless Access
Wireless Networks Spring 2007
802.16 Standards Development
Use wireless links with microwave or
millimeter wave radios
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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)
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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:
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Encoding/decoding of signals
Preamble generation/removal
Bit transmission/reception
Medium access control layer functions:
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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:
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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
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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
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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
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For continuous transmission (audio/video)
Simple TDM scheme is used for channel access
Frequency division duplex (FDD)
Burst downstream mode
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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
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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
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Subscriber station monitors downlink quality
Requests a new profile
Granted if base station judges possible
Uplink profile change
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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
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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
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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
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