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Transcript of 80216
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802.16/WiMAXEECS 228a, Spring 2006
Shyam Parekh
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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
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Electromagnetic Spectrum
Source: LBL
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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 AmendmentWiMAX 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
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Applications of 802.16 Standards
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802.16 Network Architecture
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802.16 Network Architecture (2)
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Scope of 802.16 Standards
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Physical Layer SummaryDesignation 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
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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
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Wireless Performance(as of 2003)
Source: S. Viswanathan, Intel
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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
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OFDM Basics
Orthogonal Subcarriers
Cyclic Prefix in Frequency Domain Cyclic Prefix in Time Domain
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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
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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
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OFDMA Scalability
• Supports s wide range of frame sizes (2-20 ms)Source: Intel “Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN”
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Time Division Duplexing (TDD)
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General Downlink Frame Structure
• Downlink Interval Usage Code (DIUC) indicates burst profile
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General Uplink Frame Structure
• Uplink Interval Usage Code (UIUC) indicates burst profile
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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)
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Frame Structure – Another View
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Network Entry Process
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SDU and PDU
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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
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PDU Transmission
Source: R. Marks (NIST) IEEE Presentation
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QoS Mechanism
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Generic MAC Frame
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Generic MAC Header
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Generic Bandwidth Request
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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
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Key Management Messages (1)
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Key Management Messages (2)
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Scheduling Types and QoSScheduling 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
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Scheduling Classes
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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
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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)
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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