ECE537/6 #1Spring 2009 © , Richard A. Stanley ECE537 Advanced and High Performance Networks 6: WiMAX and More Professor Richard A. Stanley, P.E.

ECE537/6 #2 Overview of Tonight’s Class Student presentations/discussions on wireless network extensions Review of last time Issues in mobile networking implementations

ECE537/5 #3 Last time… Wireless networking is growing rapidly in importance There are many “special” considerations for wireless networking Unlike most wired networking, physical layer effects play a large in proper design of a network and its protocols

ECE537/5 #4 Summary Wireless networking adds many demands to both the design of network physical layer elements and to protocols Increasing demand for wireless networking will likely stretch our ability to provide robust networking that compares favorably with wired systems

ECE537/5 #5

ECE537/5 #6

ECE537/5 #7 WiMAX Introduction Goal: Provide high-speed Internet access to home and business subscribers, without wires. Base stations (BS) can handle thousands of subscriber stations (SS) Access control prevents collisions. Supports –Legacy voice systems –Voice over IP –TCP/IP –Applications with different QoS requirements

ECE537/5 #8 Some Possible Uses Connecting Wi-Fi hotspots to the Internet Wireless alternative to cable and DSL for “last mile” broadband access Providing telecommunications services Source of network connectivity as part of a business continuity plan or other survivability scheme Providing portable connectivity

ECE537/5 # 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

ECE537/5 #10 Applications of Standards

ECE537/5 # Network Architecture

ECE537/5 # Network Architecture (2)

ECE537/5 #13 Scope of Standards

ECE537/5 #14 IEEE Protocol Standards (1) StandardDescriptionStatus Fixed Broadband Wireless Access (10 – 63 GHz) Superseded Recommended practice for coexistenceSuperseded c-2002 System profiles for 10 – 63 GHz Superseded a-2003 Physical layer and MAC definitions for 2 – 11 GHz Superseded P802.16bLicense-exempt frequencies (Project withdrawn)Withdrawn P802.16d Maintenance and System profiles for 2 – 11 GHz (Project merged into ) Merged Air Interface for Fixed Broadband Wireless Access System (rollup of , a, c and P802.16d) Superseded P a Coexistence with 2 – 11 GHz and 23.5 – 43.5 GHz (Project merged into ) Merged Recommended practice for coexistence (Maintenance and rollup of and P a) Current f-2005Management Information Base (MIB) for Superseded

ECE537/5 #15 IEEE Protocol Standards (2) StandardDescriptionStatus /Cor Corrections for fixed operations (co-published with e-2005)Superseded e-2005Mobile Broadband Wireless Access SystemSuperseded k-2007Bridging of (an amendment to IEEE 802.1D)Current g-2007Management Plane Procedures and ServicesSuperseded P802.16iMobile Management Information Base (Project merged into )Merged Air Interface for Fixed and Mobile Broadband Wireless Access System (rollup of , /Cor 1, e, f, g and P802.16i) Current j-2009Multihop relayCurrent P802.16hImproved Coexistence Mechanisms for License-Exempt OperationIn progress P802.16mAdvanced Air Interface with data rates of 100 Mbit/s mobile & 1 Gbit/s fixedIn progress

ECE537/5 #16 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

ECE537/5 #17 Channel Characteristics GHz –Very weak multipath components (LOS is required) –Rain attenuation is a major issue –Single-carrier PHY 2-11 GHz –Multipath –NLOS (sometimes) –Single and multi-carrier PHYs

ECE537/5 #18 Wireless Performance (as of 2003) Source: S. Viswanathan, Intel

ECE537/5 #19 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

ECE537/5 #20 OFDM Basics Orthogonal Subcarriers Cyclic Prefix in Frequency Domain Cyclic Prefix in Time Domain

ECE537/5 #21 Equalizers 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

ECE537/5 #22 FFT Size Tradeoffs 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

ECE537/5 #23 OFDMA Scalability Supports s wide range of frame sizes (2-20 ms) Source: Intel “Scalable OFDMA Physical Layer in IEEE WirelessMAN”

ECE537/5 #24 Physical layer ”Burst single-carrier” modulation Allows use of directional antennas Allows use of two different duplexing schemes: –Frequency Division Duplexing (FDD) –Time Division Duplexing (TDD) Support for both full and half duplex stations

ECE537/5 #25 Half- and Full-Duplex

ECE537/5 #26 Time Division Duplexing (TDD)

ECE537/5 #27 Frequency Division Duplexing (FDD) Each transmitter / receiver pair operates on a separate frequency Advantages? Disadvantages?

ECE537/5 #28 TDMA Using both –TDM (Time Division Multiplexing) and –TDMA (Time Division Multiple Access) What is the difference? TDMTDMA

ECE537/5 #29 Physical layer Adaptive Data Burst Profiles –Transmission parameters (e.g. modulation and FEC settings) can be modified on a frame-by-frame basis for each SS. –Profiles are identified by ”Interval Usage Code” (Downlink IUC and Uplink IUC)

ECE537/5 #30 General Downlink Frame Structure Downlink Interval Usage Code (DIUC) indicates burst profile

ECE537/5 #31 TDD Downlink subframe

ECE537/5 #32 FDD burst framing

ECE537/5 #33 FDD Downlink subframe

ECE537/5 #34 General Uplink Frame Structure Uplink Interval Usage Code (UIUC) indicates burst profile

ECE537/5 #35 Uplink periods Initial Maintenance opportunities –Ranging –To determine network delay and to request power or profile changes. –Collisions may occur in this interval Request opportunities –SSs request bandwith in response to polling from BS. –Collisions may occur in this interval aswell. Data grants period –SSs transmit data bursts in the intervals granted by the BS. –Transition gaps between data intervals for synchronization purposes.

ECE537/5 #36 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)

ECE537/5 #37 Frame Structure – Another View

ECE537/5 #38 Media Access Control (MAC) Connection orienteded –Connection ID (CID), Service Flows(FS) Channel access: –UL-MAP –Defines uplink channel access –Defines uplink data burst profiles –DL-MAP –Defines downlink data burst profiles –UL-MAP and DL-MAP are both transmitted in the beginning of each downlink subframe (FDD and TDD).

ECE537/5 #39 Network Entry Process

ECE537/5 #40 Mac and Physical Layers The MAC is comprised of three sublayers. The Service Specific Convergence Sublayer (CS) provides any transformation or mapping of external network data, received through the CS service access point (SAP), into MAC SDUs received by the MAC Common Part Sublayer (MAC CPS) through the MAC SAP.

ECE537/5 #41 SDU and PDU SDU: service delivery unit PDU: packet delivery unit

ECE537/5 #42 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

ECE537/5 #43 PDU Transmission Source: R. Marks (NIST) IEEE Presentation

ECE537/5 #44 QoS Mechanism

ECE537/5 #45 Generic MAC Frame

ECE537/5 #46 Generic MAC Header

ECE537/5 #47 Generic Bandwidth Request

ECE537/5 #48 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

ECE537/5 #49 Key Management Messages (1)

ECE537/5 #50 Key Management Messages (2)

ECE537/5 #51 The QoS Object Model Scheduling type

ECE537/5 #52 Bandwidth request and allocation (1) SSs may request bw in 3 ways: –Use the ”contention request opportunities” interval upon being polled by the BS (multicast or broadcast poll). –Send a standalone MAC message called ”BW request” in an allready granted slot. –Piggyback a BW request message on a data packet.

ECE537/5 #53 Bandwidth request and allocation (2) BS grants/allocates bandwidth in one of two modes: Grant Per Subscriber Station (GPSS) Grant Per Connection (GPC) Decision based on requested bw and QoS requirements vs available resources. Grants are realized through the UL-MAP.

ECE537/5 #54 Unicast Polling 1.BS allocates space for the SS in the uplink subframe. 2.SS uses the allocated space to send a bw request. 3.BS allocates the requested space for the SS (if available). 4.SS uses allocated space to send data. Poll(UL-MAP) Request Alloc(UL-MAP) Data BSSS

ECE537/5 #55 4 Types of Scheduling Service Unsolicited Grant Service (UGS) –Real-time, periodic fixed size packets (e.g. T1 or VoIP) –Restrictions on bw requests (Poll-Me bit) –Slip Indicator (SI) Real-Time Polling Service (rtPS) –Real-time, periodic variable sizes packets (e.g MPEG) –BS issues periodic unicast polls. –Cannot use contention requests, but piggybacking is ok. Non-Real-Time Polling Service (nrtPS) –Variable sized packets with loose delay requirements (e.g. FTP) –BS issues unicast polls regularly (not necessarily periodic). –Can also use contention requests and piggybacking. Best Effort Service –Never polled individually –Can use contention requests and piggybacking

ECE537/5 #56 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

ECE537/5 #57 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 being receive and transmit antennas, respectively 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

ECE537/5 #58 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)

ECE537/5 #59 WiMAX Opportunities There is a work opportunity to create/enhance /WiMAX network level simulation Technical contributions characterizing performance and network capacity are much needed

ECE537/5 #60 Other Wireless Network Opportunities Is there anything magical about or ? Could we use wireless techniques to extend, say, Ethernet, without such protocols? Why would this be good / bad?

ECE537/5 #61Spring 2009 © , Richard A. Stanley Homework Examine the protocol set. How could you apply it to extend the range or usability of an existing network? What problems must be dealt with? What manner of training or other preparation must users have? Would be more appropriate for this application? Is this a “one size fits all” solution? Why or why not? Prepare a paper of approximately 1100 words describing your findings. Be prepared to discuss your findings with the class for minutes next week. You may use slides if you desire.

ECE537/5 #62Spring 2009 © , Richard A. Stanley Disclaimer Parts of the lecture slides contain original work of B. Jornar and Shyam Parekh and remain copyrighted materials by the original owner(s). The slides are intended for the sole purpose of instruction in computer networks at Worcester Polytechnic Institute.