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 10-66 GHz
o 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
Wireless Networks Spring 2007
802.16 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: 802.16e
Wireless Networks Spring 2007
IEEE 802.16 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 802.16 MAC/PHY
frames
o Map upper layer’s addresses into
802.16 addresses
o Translate upper layer QoS parameters
into native 802.16 MAC format
o 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 Harsher environment demands more robust
profiles
o Favorable environment allows efficient profiles
Wireless Networks Spring 2007
IEEE 802.16.1 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