802.16/WiMAX EECS 228a, Spring 2006 Shyam Parekh

References IEEE (802.16REVd) IEEE (802.16e) Intel’s Whitepapers, 2004 ( “IEEE Standard : 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 /WiMax: Current Performance Benchmarks and Future Potential,” A. Ghosh et al., IEEE Communication Magazine, Feb 2005 “Wireless Communication Standards: A Study of IEEE , , and ,” T. Cooklev, 2004

Electromagnetic Spectrum Source: LBL

Standards History a (Jan 2003) Extension for 2-11 GHz: Targeted for non- line-of-sight, Point-to-Multi-Point applications like “last mile” broadband access (Dec 2001) Original fixed wireless broadband air Interface for 10 – 66 GHz: Line-of-sight only, Point-to- Multi-Point applications c (2002) Amendment WiMAX System Profiles GHz REVd ( ) (Oct 2004) Adds WiMAX System Profiles and Errata for 2-11 GHz e ( ) (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

Applications of Standards

Network Architecture

Network Architecture (2)

Scope of Standards

Physical Layer Summary DesignationApplicabilityMACDuplexing WirelessMAN-SC10-66 GHz LicensedBasicTDD, FDD, HFDD WirelessMAN-SC2-11 GHz LicensedBasic, (ARQ), (STC), (AAS) TDD, FDD WirelessMAN-OFDM 2-11 GHz LicensedBasic, (ARQ), (STC), (AAS) TDD, FDD 2-11 GHz License- exempt Basic, (ARQ), (STC), (DFS), (MSH), (AAS) TDD WirelessMAN-OFDMA 2-11 GHz LicensedBasic, (ARQ), (STC), (AAS) TDD, FDD 2-11 GHz License- exempt Basic, (ARQ), (STC), (DFS), (MSH), (AAS) TDD

Channel Characteristics 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

Wireless Performance (as of 2003) Source: S. Viswanathan, Intel

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

OFDM Basics Orthogonal Subcarriers Cyclic Prefix in Frequency DomainCyclic Prefix in Time Domain

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 WirelessMAN”

Time Division Duplexing (TDD)

General Downlink Frame Structure Downlink Interval Usage Code (DIUC) indicates burst profile

General Uplink Frame Structure Uplink Interval Usage Code (UIUC) indicates burst profile

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)

Frame Structure – Another View

Network Entry Process

SDU and PDU

Connections /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

PDU Transmission Source: R. Marks (NIST) IEEE Presentation

QoS Mechanism

Generic MAC Frame

Generic MAC Header

Generic Bandwidth Request

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

Key Management Messages (1)

Key Management Messages (2)

Scheduling Types and QoS Scheduling TypeParameters 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 e that combines UGS and rtPS: This has periodic unsolicited grants, but the grant size can be changed by request

Scheduling Classes

Advanced Features Multiple Input and Multiple Output (MIMO) –MIMO channel capacity is given by C = B log 2 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 in South Korea (Dec 2005) Demonstrates 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 /WiMAX network level simulation –Contact Technical contributions characterizing performance and network capacity are much needed