The main theme of this workshop is to elucidate medium access control (MAC) layer operation and cross-layer system and network design techniques for providing Quality-of-Service (QoS) in wireless broadband networks, and to put it in the context of military communications. We will use the IEEE 802.16 standard as an example for the rich feature set it presents, and the flexibility it provides for...
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Elements of Cross-Layer System Elements of Cross-Layer System and Network Design for QoS-and Network Design for QoS-
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OFDM Basics
If coherence bandwidth signal bandwidth
Signal experiences frequency-selective fading
Split transmission b/w into large number of sub-carriers
Create N sub-carriers with bandwidth
Symbol time (delay spread)
No inter-symbol interference (ISI)
Overlapping bands possible, if sub-carriers are orthogonal
N
WW
N
1 1N m
N c
T TW W
WcW
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OFDM Symbol in the Frequency Domain
. . .
Ideal sampling positions(in frequency domain)
N Sub-carriers
Frequency
sf
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OFDMA Explained
OFDM: PHY layer technique
OFDMA: multiple-access scheme
User occupies subset of sub-carriers (traffic channels)
Sub-carriers assigned to a particular user may change over time
11
2 2
2
33
33
Frequency
Time
User 3
User 2
User 1
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Metanoia, Inc.Critical Systems Thinking™
OFDMA Explained
OFDM: PHY layer technique
OFDMA: multiple-access scheme
User occupies subset of sub-carriers (traffic channels)
Sub-carriers assigned to a particular user may change over time
Time
23
11
2 233
3Frequency 1
12
2 233
33
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Pre
am
ble
ULMAP
DLMAP
FCH
DL Burst #1
DL Burst #3
DL Burst #4
DL Burst #2
DL Burst #6
DL Burst #7
DL Burst #5
OFDM Symbol Number
Su
b-c
han
ne
l L
og
ical
Nu
mb
er
Downlink Subframe
ULMAP
(cont.)
0 1 3 5 7 9 . . . . . . N-1
1
S-1
SS+1
Ns
802.16 OFDMA Frame Structure
Guard
0 . . . . . . . . . M-1
Uplink SubframeR
an
gin
g
ACKCH
Fast Feedback (CQICH)
UL Burst #1
UL Burst #2
UL Burst #3
UL Burst #4
UL Burst #5
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Opportunistic OFDMA
Total sum capacity is maximized …
… if throughput in each sub-carrier is maximized
Schedule each sub-carrier to user with best channel gain
Optimum power allocation
Water-filling
Proportional fairness can be extended to OFDMA
Select users with largest ratio of instantaneous data rate to average data rate
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OFDMA Scheduling in IEEE 802.16
Users allocated groups of sub-carriers (sub-channels)
Smallest allocation unit – a slot
Single sub-channel, spanning over 1 to 3 OFDM symbols
Subscriber stations (SSs)
Perform channel-quality measurements
Send feedback to Base Station (BS)
Fast feedback channel (CQICH) allocated
MAC sub-header
DL MAP
Implementation Issues in Implementation Issues in Protocols and AlgorithmsProtocols and Algorithms
Metanoia, Inc.Critical Systems Thinking™
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System Design Issues
End-to-end QoS is a must for growing multimedia applications
Access network is the usual bottleneck – more so, if wireless!
Provisioned & perceived QoS may differ markedly for wireless
Must address fading and interference
Wireless QoS thus requires:
Connection-oriented service
Implies a centralized coordinated MAC
Cross-layer based resource allocation
Adaptive MAC
Adaptive PHY
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Wi-Max Protocol Implementation Model
Service-SpecificConvergence
Sublayer
Service-SpecificConvergence Sublayers
MAC Common PartSublayer
Security Sublayer
Physical Layer(PHY)
MAC Common PartSublayer
Security Sublayer
PHY Layer
MAC SAP
PHY SAP
CS SAP
NetworkMgt. Sys.
Data/Control Plane Management Plane
MAC
PHY
TuningLayer
Mapping Layer
IP QoS
Mapping Layer
Mapping Layer
Realizes cross-layer functions
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Implications …
WiMAX has many options and features
Requires a mapping and tuning layer for translating provider managed services finally to bit/packet-level QoS
Mapping and tuning layer must integrate with service provisioning platform
Requires a unified implementation framework
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802.16 Challenges in Practice
Fluctuating channel Adaptive modulation based on link quality
Link quality fluctuation between very high to very low SNR lead to wide variation in data rates
May affect pkt level performance
TCP and BS scheduler Inappropriate scheduling may lead to time-outs
BW grants need to take into account congestion window
TCP over OFDM Interactions of TCP over OFDM and fading channel not yet fully
understood
OFDMA Performance degrades due to Doppler spread
Future of WiMax and Future of WiMax and Applicability to Military Applicability to Military
CommunicationsCommunications
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Metanoia, Inc.Critical Systems Thinking™IEEE 802.16j Mobile Multi-hop
Relay for Military Mesh Network
Network Elements
MMR BS
Relay Station (RS)
Fixed RS (FRS)
Nomadic Relay Station (NRS)
Typical military environment …
RS pre-planned
Antenna heights less than in a commercial env.
Redundant routes between RS and MMR-BS
Support for NRS
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Features of 802.16e
PHY Layers
OFDMA 2048, 1024, 512 FFT modes
STC, MIMO
Extensions for H-ARQ
MAC
Handover support
Power management
Multi-zone frame structure
Frame partitioned into multiple zones
Different sub-channelization schemes supportable in each zone
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Mobile Broadband Standardization
Various standards (all based on OFDMA + MIMO)
802.16e
802.16m
3GPP Long Term Evolution (LTE)
3GPP UMB
802.20
IMT-Advanced
May harmonize various projects
Global low-cost 4G standard may emerge based on OFDMA
Thank You!Thank You!Questions?Questions?
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Glossary and ReferencesGlossary and References
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GlossaryAAS Adaptive Antenna Systems
ABR Available Bit Rate
ACK Acknowledgement
ADSL Assymetrical Digital Subscriber Line
AMC Adaptive Modulation and Coding
ARQ Automatic Repeat Request
ATM Asynchronous Transfer Mode
AWGN Additive White Gaussian Noise
BE Best Effort
BER Bit Error Rate
BoD Bandwidth-on-Demand
bps bits per second
BPSK Binary Phase Shift Keying
BS Base Station
BSN Block Sequence Number
BWA Broadband Wireless Access
CAC Connection Admission Control
CBR Constant Bit Rate
CDMA Code Division Multiple Access
CH Channel
CI CRC Indicator
CID Connection Identifier
CINR Carrier to Interference plus Noise Ratio
CLP Cell Loss Priority
CLR Cel Loss Ratio
CoS Class-of-Service
CPS Common Part Sublayer
CQICH Channel Quality Indicator Channel
CRA Contention Ratio Algorithm
CRC Cyclic Redundancy Check
CRC Contention Ratio Calculator
CS Convergence Sublayer
CSA Contention Slot Allocator
CSMA/CA Carrier Sense Multiple Access/Collision Avoidance
DA-FDRR Demand-Aware Fair Deficit Round Robin
DC Direct Current
DCD Downlink Channel Descriptor
Diffserv Differentiated Services
DIUC Downlink Interval Usage Code
DL Downlink
DOCSIS Data Over Cable Service Interface Specification
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GlossaryDRR Deficit Round Robin
DSL Digital Subscriber Line
EC Encryption Control
EKS Encryption Key Sequence
EV-DO EVolution Data Optimized
FDD Frequency Division Duples
FDMA Frequency Division Multiple Access
FEC Forward Error Correction
FFSH Fast-Feedback Allocation Sub-Header
FFT Fast Fourier Transform
FIFO First-In First-Out
FSH Fragmentation Sub-Header
FSN Fragment Sequence Number
FTP File Transfer Protocol
FUSC Full Usage of Sub-Channels
GBN Go-Back-N
GFR Generic Frame Rate
GMSH Grant Management Sub-Header
GSM Global System for Mobile Communications
HARQ Hybrid ARQ
HCS Header Check Sequence
H-FDD Half Frequency Division Duplex
HT Header Type
HTTP Hyper-Text Transfer Protocol
IFFT Inverse Fast Fourier Transform
IFS Inter-Frame Spacing
Intserv Integrated Services
IP Internet Protocol
ISI Inter-Symbol Interference
KHz Kilohertz
LAN Local Area Network
LEN Length
LOS Line-of-Sight
MAC Media Access Control
MAN Metopolitan Area Network
MHz Megahertz
MIMO Multi-Input Multi-Output
MPDU MAC Protocol Data Unit
MPLS Multi-Protocol Label Switching
MSDU MAC Service Data Unit
NACK Negative Acknowledgement
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Glossary
NFS Network File System
NLOS Non Line-of-Sight
nrt-PS Non Real-Time Polling Service
O-DRR Opportunistic Deficit Round Robin
OFDM Orthogonal Frequency Division Multiplexing
OFDMA Orthogonal Frequency Divison Multiple Access
O-FUSC Optional-Full Usage of Sub-Channels
O-PUSC Optional-Partial Usage of Sub-Channels
PAR Project Authorization Request
PCR Peak Cell Rate
PDU Protocol Data Unit
PER Packet Error Rate
PHSI Payload Header Suppression Index
PHSI Payload Header Suppression
PHY Physical Layer
PM Poll Me
PSH Packing Sub-Header
PTI Payload Type Indicator
PUSC Partial Usage of Sub-Channels
QAM Quadrature Amplitude Modulation
QoS Quality-of-Service
QPSK Quadrature Phase Shift Keying
Rcv Receive
Rcvr Receiver
REQ Request
RNG Ranging
RSP Response
RSSI Received Signal Strength Indicator
Rsv Reserved
rt-PS Real-Time Polling Service
Rv Reserved
Rx Receiver
SAP Service Access Point
SC Single Carrier
SCR Sustainable Cell Rate
SDU Service Data Unit
SFID Service Flow ID
SI Slip Indicator
SINR Signal to Interference plus Noise Ratio
SNMP Simple Network Management Protocol
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GlossarySNR Signal to Noise Ratio
S-OFDMAScalable Orthogonal Frequency Division Multiple Access
SR Selective Repeat
SS Subscriber Station
TC Traffic Category
TCP Transmission Control Protocol
TDD Time Division Duplex
TDMA Time Division Multiple Access
TFTP Trival File Transfer Protocol
TLV Type-Length-Value
Tx Transmitter or Transmit
UBR Unspecified Bit Rate
UCD Uplink Channel Descriptor
UF-DRR Uniformly Fair Deficit Round Robin
UGS Unsolicited Grant Service
UIUC Uplink Interval Usage Code
UL Uplink
VBR Variable Bit Rate
VCI Virtual Circuit Identifier
VOD Video-on-Demand
VoIP Voice-over-IP
VPI Virtual Path Identifier
WDRR Wireless Deficit Round Robin
WG Working Group
Wi-Fi Wireless Hi-Fidelity
WLAN Wireless LAN
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References and Readings (1) [FaL02] H. Fattah and C. Leung, “A Efficient Scheduling Algorithm for Packet
Cellular Networks,” in Proc. VTC, vol. 4, pp. 2419-2423, September 2002.
[GWA05] A. Ghosh, G. R. Walter, J. G. Andrews, and R. Chen, “Broadband Wireless Access withWiMax/8O2.16: Current Performance Benchmarks and Future Potential,” IEEE Commun. Magazine, vol. 45, pp. 129-136, February 2005.
[IEEE04] LAN/MAN Standards Committee, “IEEE Standards for Local and Metropolitan Area Network: Part 16: Air Interface for Fixed Broadband Wireless Access Systems,” IEEE Computer Society and IEEE Microwave Theory and Techniques Society, May 2004.
[IEEE05] LAN/MAN Standards Committee, “IEEE Standards for Local and Metropolitan Area Network: Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems (Amendments for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands),” IEEE Computer Society and IEEE Microwave Theory and Techniques Society, September 2005.
[RBS06a] H. Rath, A. Bhorkar, and V. Sharma, “An Opportunistic Deficit Round Robin (O-DRR) Uplink Scheduling Scheme for Wi-Max Networks,” Proc. IETE Int’l Conf. on Next-Generation Networks (ICNGN’06), Mumbai, 9-11 February, 2006.
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References and Readings (2)
[RBS06b] H. Rath, A. Bhorkar, and V. Sharma, “An Opportunistic Uplink Scheduling Scheme to Achieve Bandwidth Fairness and Delay for Multiclass Traffic in Wi-Max (IEEE 802.16) Broadband Wireless Networks,” to appear IEEE Globecom’06, San Francisco, CA, 27 Nov. – 1 Dec. 2006.
[ShV96] M. Shreedhar and G. Varghese, “Efficient Fair Queueing Using Deficit Round Robin,” IEEE/ACM Trans. on Networking, vol. 4, no. 3, pp. 375-385, June 1996.
[SRK03] S. Shakkottai, T. S. Rappaport, and P. C. Karlsson, “Cross Layer Design for Wireless Networks,” IEEE Commun. Magazine, vol. 41, no. 10, pp. 74-80, October 2003.
[Vam06] N. Vamaney, “Scheduling in IEEE 802.16 Metropolitan Area Networks,” M. Tech. Dissertation, Dept. of Electrical Engineering, IIT Bombay, September 2006.