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Ashwini KumarKang Shin
University of Michigan
Aug-6-2009, ICCCN 2009, San Francisco
A Case Study of QoS Provisioning in TV-band Cognitive Radio Networks
Jianfeng Wang (presenter)Kiran Challapali
Philips Research
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Outline
• Introduction of TV Whitespace• System & QoS Model
• QoS-Provisioned DSA Protocol (QPDP) Overview• Distributed Reservation & Channel Access• Network & Spectrum Management
• Evaluation• Conclusion
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What is TV Whitespace
• TV Band Incumbents – TV, WM• TV bands only sparsely used today
(see graphic)• Fewer and fewer US households
rely on over-the-air TV (from FCC report)
– 33 % in 1994, 15 % in 2004 – Among these, on average only a
few channels watched• TV bands have nice propagation
characteristics for various applications
• FCC has taken steps on opening TV bands for unlicensed use
Source: New America Foundation
Source: FCC. Reported by New America Foundation
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White space regulatory milestones – US
Notice of Inquiry
?. 2009
2005
Oct. 2006
20042003
June 2008
Mar. 2007
Notice of Proposed Rule Making
Initial R & OandFurther NPRM
July 2007
Public Notice
Sep.2006
Report on Interference Rej. Cap. of DTV Rx’s
Field Tests Final rules in Federal Registry
Report on Sensing, Interference to DTVs & Other Radios
Nov. 2008
Final Rule and Order
Feb. 2009
Philips CompleteCR Demo @ FCC
Aug. 2008
Mar. 2008Sensing Proto Testing
Dec. 2008
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FCC 2nd Report and Order
• Personal/Portable TVBD (unlicensed) Devices
– Up to 100mW; limited to 40mW if operating in adjacent channels.
– Any channel between 21 and 51, except channel 37.
– Mode II device (Master device) must employ geo-location database to determine channel availability.
– Mode I device (Client device) operates under signaling control of Mode II device.
– All devices should also employ sensing mechanism to determine channel availability.
– Incorporate a dynamic frequency selection (DFS) mechanism and transmission power control (TPC) mechanism.
– Sensing only device operates <= 50mW.
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System & QoS Model
• Personal/portable TV band unlicensed devices equipped with one radio
• Cast study to provide HDTV streaming in home WLANs
• QoS met for multimedia traffic
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Cable/Internet AP(Residential Gateway)
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Design Challenge
• Complexity and overhead for coordinating sensing incumbents as low as -114dBm
– in personal/portable mobile environments
• Incumbents’ interference and interruption
• Stringent requirements of real-time multimedia traffic (e.g., HDTV streaming)
• Narrow channel-width (6 MHz) – Not much chance to use multiple contiguous channels
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Self coexistence issue
• Resource sharing and QP synchronization across neighboring networks
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QPDP Overview
• QPDP logically consists of Lower & Upper MAC
• Upper MAC• Spectrum management and
network management • Based on overlay master-slave
architecture
• Lower MAC• Slot reservation• Self-coexistence
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Distributed Reservation Access Based on WiMedia MAC
Upper MAC
Lower MAC
Overlay Master-Slave Operation
Spectrum Management
Function
Network Management
Function
QPDP MAC architecture
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QPDP Lower MAC functions
• Channel access follows time-recurring superframe structure– Each superframe consists of 256 MASs– MASs divided between BP, DSSP, SW
• Distributed beaconing and channel reservation – MASs reservations negotiated through beacons– BP merge for multiple network coexistence 10
Data/Sense/Sleep Period (DSSP)
…...
…...
mMASLength
Medium Access Slots (MASs)
Superframe m Superframe m+1Superframe m-1…... …...
...
Beacon Period (BP)
SignallingWindow
(SW)
…...
...
Adjustable
mBeaconSlotLength
Beacon Period (BP)
0 1 N 0 1 N
QP
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QPDP Upper MAC Functions
• Overlay master manages channel, sensing and device association
• Channel management made intelligent to reduce disruptions– Prioritized channel list– Backup channels– Channel-imaging
• Multi-level spectrum sensing to minimize overheads– Multiple short QPs within CDT– Long QPs scheduled on-demand
• Network entry & device discovery automated through boot-up scan and beacons
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Evaluation Setup
• To analyze QPDP performance w.r.t. QoS provisioning– Efficiency in supporting high data-rate, low error-rate & delay– Robustness in response to incumbent disruptions
• Simulations using OPNET Modeler• Home network setting, with HDTV streaming as multimedia
application
• Simulation parameters:– Sender-receiver pair, distance=30m– Exponential rayleigh multipath fading– Transmit power=30dbm, path loss factor=3– PHY based on OFDM: 128 FFT
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Results• Requirements of HDTV streaming achieved (~19.3 Mbps, <100ms
delay, BER<0.05) with proper setting • Impact of sensing schedule:
– FS-1 to FS-6: same long-term overhead , differ in short-term– Recovery is quick in both low & high-power incumbent case
130 10 20 30 40 500
0.5
1
1.5
2
2.5x 10
7
Time (s)
Thr
ough
put
(bit/
s)
FS-1
FS-2
FS-3
FS-4
FS-5
FS-6
Low Power Incumbent (iRxPr = -100.25dBm)
0 10 20 30 40 500
0.5
1
1.5
2
2.5x 10
7
Time (s)
T
hrou
ghpu
t (b
it/s)
High Power Incumbent (iRxPr = -40.25dBm)
FS-1
FS-2
FS-3
FS-4
FS-5
FS-6
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Results (contd.)
• Combining fast sensing with fine sensing performs better• Delay is sensitive to short-term sensing schedule
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0 10 20 30 40 500
0.5
1
1.5
2
2.5x 10
7
Time (s)
Thr
ough
put
(bit/
s)
ED + FS-1, iRxPr = -40.25dBm
ED + FS-2, iRxPr = -50.25dBm
ED + FS-3, iRxPr = -60.25dBm
ED + FS-4, iRxPr = -70.25dBm
ED + FS-5, iRxPr = -80.25dBm
ED + FS-6, iRxPr = -90.25dBm
FS-1, iRxPr = -40.25dBm
0 10 20 30 400.75
0.8
0.85
0.9
0.95
1
Delay (ms)
Cum
ulat
ive
Dis
trib
utio
n F
unct
ion
(CD
F)
FS-1
FS-2
FS-3
FS-4
FS-5
FS-6
High Power Incumbent (iRxPr = -40.25dBm)
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Results (contd.)• Fast incumbent detection and optimized channel-switch
minimizes traffic loss and sustains QoS• Packet aggregation very useful in sustaining QoS
155 10 15 20 25 301
1.5
2
2.5x 10
7
Time (s)
Th
rou
gh
pu
t (b
it/s)
MPDU size = 200Bytes
MPDU size = 400Bytes
MPDU size = 600Bytes
MPDU size = 800Bytes
MPDU size = 1000Bytes
MPDU size = 2000Bytes
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Conclusion
• Presented a system study of HDTV streaming over single TV channel
• Proposed QPDP incorporates both fine-grained and coarse-grained QoS mechanisms, including:
– Distributed beaconing and channel reservation– Overlay based Master-Slave based spectrum
management
• Results and discussions reveal the impact of key design parameters on QoS
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Backup Slides
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System Parameters
Parameter Value
Data Traffic Transmission Power (dBm)
20
Noise Power Spectrum Density (dBm)
-174
Noise figure (dB) 6
Implementation loss (dB) 6
Communication Distance (m) 30
Path loss exponent 3
HDTV traffic load (Mbps) 20
SDTV traffic load (Mbps) 6
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PHY-OFDM parameters
Parameter Value
Number of data subcarriers, ND 104
Number of pilot subcarriers, NP 4
Total number of subcarriers, NFFT 128
Inner coding rate 5/6
RS outer coding, t 5
Modulation 64-QAM
Preamble 4 sym
PHY+MAC header 1 sym
Symbol duration (µs) 21.25
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MAC Parameters
Parameter Value
Superframe length (µs) 110,592
mNumberMAS 256
mMASLength (µs) 432
mMaxBPLength (MAS) 5
Regular Quiet Period 1
mBeaconSlotLength (µs) 432
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UHF Band After Digital Switch Over in UK
Source: Ofcom ConsultationFeb. 16 2009
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Ofcom on TV White Space
• Released consultation on White Spaces on Feb. 16 2009, with comments due by May 01 2009. Awaiting next statement.
• Proposed parameters:
Source: Ofcom ConsultationFeb. 16 2009