Wimax Entry Overview

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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)

Intels 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: CurrentPerformance Benchmarks and Future Potential, A. Ghosh etal., IEEE Communication Magazine, Feb 2005

Wireless Communication Standards: A Study of IEEE802.11, 802.15, and 802.16, T. Cooklev, 2004
http://www.intel.com/technology/itj/2004/volume08issue03/http://www.intel.com/technology/itj/2004/volume08issue03/


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Electromagnetic Spectrum

Source: LBL


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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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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 subchannelA 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 auseful symbol time are from the samesymbol & add constructively (no ISI)

Note:dashed linesrepresent multipath

Narrow bandwidth long symbol times all significant multipaths arrive within a symboltime 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 andsmaller inter-subcarrier spacingMore susceptibility to ICI, particularly in high Doppler

(Note: Doppler shift for 125 km/hr for operation at 3.5GHz is v/= 35 m/sec/0.086 m = 408 Hz)

Narrower subcarriers lead to longer symbol timesless 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 structureBS periodically broadcasts Downlink Channel Descriptor (DCD) and UplinkChannel 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 connectionidentified with a 16 bit CID

Each CID is associated with a ServiceFlow ID (SFID) that determines theQoS 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 broadcastor 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 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


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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 log2det(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 anddetection 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-scaledeployment of 802.16 in South Korea(Dec 2005)

Demonstrates 802.16 performance ascompared to 3G/4G cellularalternatives

3 operators have been licensed by thegovernment (each spending ~$1B)


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WiMAX Opportunities

There is a work opportunity tocreate/enhance 802.16/WiMAXnetwork level simulation

Contact [email protected]

Technical contributions characterizing802.16 performance and network

capacity are much needed
mailto:[email protected]:[email protected]

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