Transcript ECE537-Class 6_2009 - Worcester Polytechnic Institute

ECE537 Advanced and High
Performance Networks
6: WiMAX and More
Professor Richard A. Stanley, P.E.
Spring 2009
© 2000-2009, Richard A. Stanley
ECE537/6 #1
Overview of Tonight’s Class
• Student presentations/discussions on
wireless network extensions
• Review of last time
• Issues in mobile networking
implementations
ECE537/6 #2
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 #3
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 #4
ECE537/5 #5
ECE537/5 #6
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 #7
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 #8
802.16 Standards History
• First standard based on proprietary implementations of DOCSIS/HFC
architecture in wireless domain
802.16
(Dec 2001)
• Original fixed wireless broadband air Interface
for 10 – 66 GHz: Line-of-sight only, Point-toMulti-Point applications
802.16c
(2002)
802.16 Amendment
WiMAX System Profiles
10 - 66 GHz
802.16a
(Jan 2003)
802.16REVd
(802.16-2004)
(Oct 2004)
802.16e
(802.16-2005)
(Dec 2005)
• Extension for 2-11 GHz: Targeted for nonline-of-sight, Point-to-Multi-Point
applications like “last mile” broadband access
• Adds WiMAX System Profiles and Errata for
2-11 GHz
• MAC/PHY Enhancements to support
subscribers moving at vehicular speeds
ECE537/5 #9
Applications of 802.16 Standards
ECE537/5 #10
802.16 Network Architecture
ECE537/5 #11
802.16 Network Architecture (2)
ECE537/5 #12
Scope of 802.16 Standards
ECE537/5 #13
IEEE 802.16 Protocol Standards (1)
Standard
802.16-2001
Description
Status
Fixed Broadband Wireless Access (10–63 GHz)
Superseded
802.16.2-2001
Recommended practice for coexistence
Superseded
802.16c-2002
System profiles for 10–63 GHz
Superseded
802.16a-2003
Physical layer and MAC definitions for 2–11 GHz
Superseded
P802.16b
License-exempt frequencies (Project withdrawn)
Withdrawn
P802.16d
Maintenance and System profiles for 2–11 GHz
(Project merged into 802.16-2004)
Merged
802.16-2004
Air Interface for Fixed Broadband Wireless Access System
(rollup of 802.16-2001, 802.16a, 802.16c and P802.16d)
Superseded
P802.16.2a
Coexistence with 2–11 GHz and 23.5–43.5 GHz
(Project merged into 802.16.2-2004)
Merged
802.16.2-2004
Recommended practice for coexistence
(Maintenance and rollup of 802.16.2-2001 and P802.16.2a)
Current
802.16f-2005
Management Information Base (MIB) for 802.16-2004
Superseded
ECE537/5 #14
IEEE 802.16 Protocol Standards (2)
Standard
802.16-2004/Cor
1-2005
Description
Status
Corrections for fixed operations (co-published with 802.16e-2005)
Superseded
802.16e-2005
Mobile Broadband Wireless Access System
Superseded
802.16k-2007
Bridging of 802.16 (an amendment to IEEE 802.1D)
802.16g-2007
Management Plane Procedures and Services
P802.16i
Current
Superseded
Mobile Management Information Base (Project merged into 802.16-2009)
Merged
802.16-2009
Air Interface for Fixed and Mobile Broadband Wireless Access System
(rollup of 802.16-2004, 802.16-2004/Cor 1, 802.16e, 802.16f, 802.16g
and P802.16i)
Current
802.16j-2009
Multihop relay
Current
P802.16h
Improved Coexistence Mechanisms for License-Exempt Operation
In progress
P802.16m
Advanced Air Interface with data rates of 100 Mbit/s mobile & 1 Gbit/s fixed
In progress
ECE537/5 #15
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
2-11 GHz Licensed
Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz Licenseexempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD
2-11 GHz Licensed
Basic, (ARQ),
(STC), (AAS)
TDD, FDD
2-11 GHz Licenseexempt
Basic, (ARQ),
(STC), (DFS),
(MSH), (AAS)
TDD
WirelessMAN-OFDM
WirelessMAN-OFDMA
ECE537/5 #16
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 (sometimes)
– Single and multi-carrier PHYs
ECE537/5 #17
Wireless Performance
(as of 2003)
Source: S. Viswanathan, Intel
ECE537/5 #18
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 #19
OFDM Basics
Orthogonal Subcarriers
Cyclic Prefix in Time Domain
Cyclic Prefix in Frequency Domain
ECE537/5 #20
Equalizers Avoided in OFDM
Narrow bandwidth  long symbol times  all significant multipaths arrive
within a symbol time minimizing ISI  no equalization  low complexity
Tx Signal
time
Cyclic Prefix
Note: All signals & multipath over a
useful symbol time are from the same
symbol & add constructively (no ISI)
Useful Symbol Time
Rx Signal
time
Note: dashed lines
represent multipath
Source: Lucent
ECE537/5 #21
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 #22
OFDMA Scalability
• Supports s wide range of frame sizes (2-20 ms)
Source: Intel “Scalable OFDMA Physical Layer in IEEE 802.16 WirelessMAN”
ECE537/5 #23
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 #24
Half- and Full-Duplex
ECE537/5 #25
Time Division Duplexing (TDD)
ECE537/5 #26
Frequency Division Duplexing
(FDD)
• Each transmitter / receiver pair operates on
a separate frequency
• Advantages?
• Disadvantages?
ECE537/5 #27
TDMA
• Using both
– TDM (Time Division Multiplexing) and
– TDMA (Time Division Multiple Access)
• What is the difference?
TDM
TDMA
ECE537/5 #28
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 #29
General Downlink Frame Structure
• Downlink Interval Usage Code (DIUC) indicates burst profile
ECE537/5 #30
TDD Downlink subframe
ECE537/5 #31
FDD burst framing
ECE537/5 #32
FDD Downlink subframe
ECE537/5 #33
General Uplink Frame Structure
• Uplink Interval Usage Code (UIUC) indicates burst profile
ECE537/5 #34
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 #35
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
ECE537/5 #36
FEC schemes)
Frame Structure – Another View
ECE537/5 #37
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 #38
Network Entry Process
ECE537/5 #39
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 #40
SDU and PDU
SDU: service delivery unit
PDU: packet delivery unit
ECE537/5 #41
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
ECE537/5 #42
PDU Transmission
Source: R. Marks (NIST) IEEE Presentation
ECE537/5 #43
QoS Mechanism
ECE537/5 #44
Generic MAC Frame
ECE537/5 #45
Generic MAC Header
ECE537/5 #46
Generic Bandwidth Request
ECE537/5 #47
Management Messages
• Management messages are broadcast or
sent on three CIDs in each direction: Basic,
Primary, and Secondary
–
–
–
–
–
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Uplink Channel Descriptor
Downlink Channel Descriptor
UL-MAP
DL-MAP
DSA-REQ
DSA-RSP
ECE537/5 #48
Key Management Messages (1)
ECE537/5 #49
Key Management Messages (2)
ECE537/5 #50
The QoS Object Model
ECE537/5 #51
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 #52
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 #53
Unicast Polling
BS
SS
Poll(UL-MAP)
1. BS allocates space for the SS in
the uplink subframe.
Request
Alloc(UL-MAP)
Data
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.
ECE537/5 #54
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 #55
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
Committed Information Rate,
(nrtPS)
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
ECE537/5 #56
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 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 #57
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)
ECE537/5 #58
WiMAX Opportunities
• There is a work opportunity to
create/enhance 802.16/WiMAX network
level simulation
• Technical contributions characterizing
802.16 performance and network capacity
are much needed
ECE537/5 #59
Other Wireless Network
Opportunities
• Is there anything magical about 802.11 or
802.16?
• Could we use wireless techniques to extend,
say, Ethernet, without such protocols?
• Why would this be good / bad?
ECE537/5 #60
Homework
• Examine the 802.16 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
802.11 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 510 minutes next week. You may use slides if you desire.
Spring 2009
© 2000-2009, Richard A. Stanley
ECE537/5 #61
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.
Spring 2009
© 2000-2009, Richard A. Stanley
ECE537/5 #62