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References
• IEEE 802.16-2004 (802.16REVd)
• IEEE 802.16-2005 (802.16e)
• Intel’s Whitepapers, 2004 (http://www.intel.com/technology/itj/2004/volume08issue03/)
• “IEEE Standard 802.16: A Technical Overview of the WirelessMAN Air Interface for Broadband Wireless Access,” C. Eklund et al., IEEE Communication Magazine, June 2002
• “Broadband Wireless Access with 802.16/WiMax: Current Performance Benchmarks and Future Potential,” A. Ghosh et al., IEEE Communication Magazine, Feb 2005
• “Wireless Communication Standards: A Study of IEEE 802.11, 802.15, and 802.16,” T. Cooklev, 2004
802.16 Standards History
802.16a (Jan 2003)
• Extension for 2-11 GHz: Targeted for non-line-of-sight, Point-to-Multi-Point
applications like “last mile” broadband access
802.16 (Dec 2001)
• Original fixed wireless broadband air Interface for 10 – 66 GHz: Line-of-sight only, Point-to-
Multi-Point applications
802.16c (2002)
802.16 Amendment
WiMAX System Profiles
10 - 66 GHz
802.16REVd (802.16-2004)
(Oct 2004)
• Adds WiMAX System Profiles and Errata for 2-11 GHz
802.16e (802.16-2005)
(Dec 2005)
• MAC/PHY Enhancements to support
subscribers moving at vehicular speeds
• First standard based on proprietary implementations of DOCSIS/HFC
architecture in wireless domain
Physical Layer Summary
Designation Applicability MAC Duplexing
WirelessMAN-SC 10-66 GHz Licensed Basic TDD, FDD, HFDD
WirelessMAN-SC 2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
WirelessMAN-OFDM
2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz License-
exempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD
WirelessMAN-OFDMA
2-11 GHz Licensed Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz License-
exempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD
Channel Characteristics
• 10-66 GHz
– Very weak multipath components (LOS is required)
– Rain attenuation is a major issue
– Single-carrier PHY
• 2-11 GHz
– Multipath
– NLOS
– Single and multi-carrier PHYs
OFDMA Subchannels
• A subset of subcarriers is grouped together to form a subchannel
• A transmitter is assigned one or more subchannels in DL direction
(16 subchannels are supported in UL in OFDM PHY)
• Subchannels provide interference averaging benefits for aggressive frequency
reuse systems
Equalizers are avoided in OFDM
time
Cyclic Prefix Useful Symbol Time
time
Note: All signals & multipath over a
useful symbol time are from the same
symbol & add constructively (no ISI)
Note: dashed lines
represent multipath
Narrow bandwidth long symbol times all significant multipaths arrive within a symbol time minimizing ISI no equalization low complexity
Tx Signal
Rx Signal
Source: Lucent
Tradeoffs of FFT size
• The FFT size determines the number of sub-carriers in the specified bandwidth
• Larger FFT sizes lead to narrower subcarriers and smaller inter-subcarrier spacing
–More susceptibility to ICI, particularly in high Doppler
(Note: Doppler shift for 125 km/hr for operation at 3.5 GHz is v/λ = 35 m/sec/0.086 m = 408 Hz)
–Narrower subcarriers lead to longer symbol times less susceptibility to delay spread
• Smaller FFT sizes the opposite is true
Source: Lucent
OFDMA Scalability
• Supports s wide range of frame sizes (2-20 ms)
Source: Intel “Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN”
OFDMA TDD Frame Structure
• DL-MAP and UL-MAP indicate the current frame structure
• BS periodically broadcasts Downlink Channel Descriptor (DCD) and Uplink
Channel Descriptor (UCD) messages to indicate burst profiles (modulation and
FEC schemes)
Connections
• 802.16/WiMAX is connection oriented
• For each direction, a connection
identified with a 16 bit CID
• Each CID is associated with a Service
Flow ID (SFID) that determines the
QoS parameters for that CID
Management Messages
• Management messages are broadcast or sent on three CIDs in each direction: Basic, Primary, and Secondary
– Uplink Channel Descriptor
– Downlink Channel Descriptor
– UL-MAP
– DL-MAP
– DSA-REQ
– DSA-RSP
Scheduling Types and QoS
Scheduling Type Parameters
Unsolicited Grant Service
(UGS)
Max Sustained Traffic Rate,
Maximum Latency,
Tolerated Jitter
Real-Time Polling Service
(rtPS)
Max Sustained Traffic Rate,
Min Reserved Traffic Rate,
Committed Burst Size,
Maximum Latency, etc.
Non-real-time Polling Service
(nrtPS)
Committed Information Rate,
Maximum Information Rate
Best Effort (BE) Maximum Information Rate
• Extended rtPS was introduced in 802.16e that combines UGS and rtPS: This has
periodic unsolicited grants, but the grant size can be changed by request
Advanced 802.16 Features
• Multiple Input and Multiple Output (MIMO) – MIMO channel capacity is given by
C = B log2 det(I + SNR.HH*T/N)
where H is MxN channel matrix with M and N are receive and transmit antennas, resp.
• Hybrid-ARQ – For faster ARQ, combines error correction and
detection and makes use of previously received versions of a frame
• Adaptive Antenna System (AAS) – Enables directed beams between BS and SSs
WiBro (Wireless Broadband)
• WiBro is an early large-scale
deployment of 802.16 in South Korea
(Dec 2005)
• Demonstrates 802.16 performance as
compared to 3G/4G cellular
alternatives
• 3 operators have been licensed by the
government (each spending ~$1B)
WiMAX Opportunities
• There is a work opportunity to
create/enhance 802.16/WiMAX
network level simulation
– Contact [email protected]
• Technical contributions characterizing
802.16 performance and network
capacity are much needed