Backhauling in TV White Space
description
Transcript of Backhauling in TV White Space
WINLAB
Backhauling in TV White Space
Narayan B. Mandayam
(joint work with Cyrus Gerami, Larry Greenstein, Ivan Seskar)
WINLAB, Rutgers University
IEEE Distinguished Lecture1
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What is White Space?
TV Band Devices: Fixed or Portable Max. Fixed antenna height = 30m, Portable < 3m
Permissible channels (6MHz each)
Transmit Restrictions Protected region around primary TV transmitters Sense and avoid protected devices TX power:
Fixed:30 dBm (6dBi antenna gain) = 4W EIRP, Co- and Adjacent-channel not allowed
Portable: 20 dBm (no antenna gain) = 100mW, Co-channel not allowed, Adjacent = 16 dBm
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XAdditional Rulingon Sep 23 2010
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What is “Really” White Space?
Economist Markets, Property
Regulator/Politician Social Good
Engineer New Technology, Cognitive Radios
Folks who are “out there” Free speech, Bill of Rights
Communication/Information Theorist W
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≈ ¢
≈ $
≈ $, votes
priceless
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How much TV White Space is there in NJ?
TV Towers around NY City and Philadelphia Lots of white space spectrum available in NJ!
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# of channels (fixed) vs. # of 5X5 sq. mi. grids
7 – 31 channels available per cell (42 – 186 MHz)
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Radio Coverage
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Prime spectrum with a wide range of applications ~50-200 MHz available depending on TV transmitter density Power constraints result in achievable bit-rate profile for fixed-
fixed, fixed-mobile, and mobile-mobile ~5 Mbps @ 2Km range for LOS fixed-mobile ~3-5x WiFi range for non-LOS services, e.g. ~50 Mbps @ 250m
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White Space Networks
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Range of possible usage scenarios, with sweet spot in outdoor networks with medium range and speed
Bit-Rate
100 m
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Sample Applications: Cellular Data Boost
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“Cellular data boost” network can be used to offload fast-growing cellular traffic using dual-mode radio Mesh network of outdoor white space hot spots; backhaul data to existing
BTS Intended for transport of non-real time data such as mail, content,
facebook … Potential for ~2-5x capacity boost depending on % coverage & service mix
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Sample Applications: Distribution/Backhaul
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DISTRIBUTION AND BACKHAULUSING WHITE SPACE
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Sample Applications: Long range V2V/Emergency Network
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Long-range V2V useful for traffic control/warnings, geographic apps, p2p content, etc. Supplements short-range 802.11p/DSRC
V2V links (from mandated car radios?) can be used to form a high capacity emergency backup network using ad hoc mesh between cars and fixed AP’s
Application requirements well matched with WS range/bit-rate properties
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GENIE NODE
Central spectrum manager
Service Provision Device
Provides end-user service
Relay and Wireless Access Devices
Provides relay/connectivity support
Core Network
GENIE NODE
TV 1
Game Console Game
Controller Laptop
Lin
k C
Lin
k B
Access Point
TV 2
Wireless HDMI
TVWS Database
Sample Applications: Cognitive Digital Home
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Design Implications for White Space Networks
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WS Building Blocks: NC OFDMA PHY
NC OFDMA approach used to opportunistically fill spectrum
Allows for flexible spectrum sharing for secondary coexistence
Center freq White Space
Primary
freq
Min. tones needed for freq. synchronization
Case for Noncontiguous OFDMA - I
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1
2
3
A
B
C
X
• Three available channels
• Node A transmits to node C via node B.
• Node B relays node A’s data and transmits its own data to node C.
• Node X, an external and uncontrollable interferer, transmits in channel 2.
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If we use max-min rate objective and allocate channels, node B requires two channels; node A requires one channel
Scheduling options for Node A and Node B?
Case for Noncontiguous OFDMA - II
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2
A
C
3
B
• Transmission in link BC suffers interference in channel 2
1 2
#1: Contiguous OFDM
X
2
A
C
B
• Spectrum fragmentation limited by number of radio front ends
1 3
2
#2: Multiple RF front ends
X
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2
A
C
B
2
1 3
#3: Non-Contiguous OFDM (NC-OFDMA)
Nulled Subcarrier
X
NC-OFDM accesses multiple fragmented spectrum chunks
with single radio front end
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2
A
AP
B
2
1 3
Non-Contiguous OFDM
Nulled Subcarrier
Serial toParallel IFFT Parallel
to Serial D/A
X
X[1] X[3]X[1]
X[3]
0
x[1]x[2]x[3]
X[2] =
NC-OFDM accesses multiple fragmented spectrum chunks
with single radio front end
• Node B places zero in channel 2 and avoids interference
• Node A, far from the interferer node X, uses channel 2.
• Both nodes use better channels.
• Node B spans three channels, instead of two.• Sampling rate increases.
Modulation
NC-OFDM Operation
Resource Allocation in NC-OFDMABenefits:Avoids interference, incumbent usersUses better channelsEach front end can use multiple fragmented spectrum chunks
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Challenges:Increases sampling rate
Increases ADC & DAC power Increases amplifier power
Increases peak-to-average-power-ratio (PAPR)
Develop centralized, distributed and hybrid algorithms for carrier and forwarder selection, power control
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WS Building Blocks: NC OFDMA MAC
NC OFDMA offers the possibility of a simple FDMA MAC instead of CSMA or TDMA (..CSMA may still be used for end-user access)
Simplifies ad hoc network operation and avoid classical mesh self interference and exposed node problems
Requires a cooperative access policy (i.e. not greedy, and with some form of congestion backpressure)
LINK 1
freq
LINK 2 LINK 3
rate r1 rate r2 rate r3
Rates r1, r2, r3 periodically adjusted via cooperative procedures
f1
f2
f3
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Architectures for Secondary Coexistence
WS MobileAccess Protocol
WS APw/ backhaul
Secondary System A Secondary System B
freq
Secondary A Spectrum
Secondary BSpectrum
Secondary co-existence an important requirement for WS Various schemes possible depending on system model
Completely autonomous, using performance feedback only Common coordination channel Common Internet based spectrum server
Common Coordination Channel (optional)
Internet
Spectrum Server (optional)
Controlinformation
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3G
WIFI
FIBERBACKHAULNETWORK
DISTRIBUTION AND BACKHAULUSING WHITE SPACE
OUTLINE• The Proposed System• First order Methodology• Achievable Capacity• Traffic Demand• How many cells would need fiber?• Aggregating Flows• Conclusion and Future Directions• White Space: Where are we? Where do we go?
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HOW WILL IT LOOK?
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• NJ as case study• Proximity to NY & Philly• Highest population density• WINLAB in NJ!
• Cells of 5 mi X 5 mi• total 307
• Antenna (base-station) in each• FCC’s max allowed height=30 m• FCC’s max TX power=4 W
• Based on fixed devices rules of FCC
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WHAT WILL IT DO?
Internet user
Wifi
Fiber
4 sector antennas
Antenna coverage
Wireless Distribution and Backhaul
Use of Sector antennas for more concentrated transmission
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CAN WHITE SPACES BE USED?
ACHIEVABLE CAPACITY DEMAND (PER CELL) (PER CELL)
>><<Use Radio
Use Fiber
Resources used:
FIRST ORDER CRITERION
FCC rules Propagationmodels
NJ pop statisticsCensus 2000
Internet usage statistics
Internet traffic survey
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NJ TOWERS AT A GLANCE
• Towers in NJ, NY, DE & PA• Coverage can be 100km (r)
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FCC’S PROTECTION RULE
Secondary White Space radio
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AVAILABLE BANDWIDTH
CHANNEL AVAILABILITY INCLUDING ADJACENT CHANNEL EFFECT
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AVAILABLE SPACE PER CHANNEL
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AVAILABLE BANDWIDTH
TV tower coverageAdditional separation ringAvailable for possible useAvailable as White Spaces
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AVAILABLE BANDWIDTH
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25 BANDWIDTH DATABASE
X
• Repeat this for each cell and you get bandwidth database
• Each channel is 6 MHz• 7 – 31 channels available per cell
(42 – 186 MHz)
• No islands• Similar channels available in
neighboring cells INTERFERENCE!
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FREQUENCY REUSE PLANNING
• SNR at cell-2 = 19 dB
• SNR at cell-4 = 5 dB– Interference
• 14 dB isolation for r=2
• Median path loss: ITU terrain model for LOS• Obstruction height:15m for sparse population and 30m for dense population
• 1% outage with 8 dB shadowing variance
AVAILABLE BANDWIDTH
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reuse factor (r) of 2 :
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ACHIEVABLE CAPACITY DEMAND>><<
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LET’S CONSIDER ONE CELL
• 54 MHz (9 channels) available• 27 MHz usable (reuse)• Spectral Efficiency: 6.23 bps/Hz (path loss and population and building heights)• Max Achievable Capacity:
~168 Mbps ~75.7 GB/hour
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ACHIEVABLE CAPACITY DEMAND>><<
• Pop/sq mi pop/cell• 3 people per household• 74.2% have internet internet clients/cell• 18MB/hr (Cisco Survey) 90 MB/hr (5 times more) 126 MB/hr (7 times more) 180 MB/hr (10 times more)
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US Census 2000 Our Approximation
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LET’S CONSIDER ONE CELL
• Cell pop: 8750• Cell households: 2917• Cell internet connections: 2164• Cell traffic using α = 30% : 18 MB/hr/link: 11.7 GB/hr
90 MB/hr/link: 58.4 GB/hr
126 MB/hr/link: 81.8 GB/hr
180 MB/hr/link: 116.9 GB/hr
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LET’S CONSIDER ONE CELL
ACHIEVABLE CAPACITY DEMAND>><<α = 30% & 18 MB/hr/link : 75.7 > 11.7 α = 30% & 90 MB/hr/link : 75.7 > 58.4
α = 30% & 126 MB/hr/link : 75.7 < 81.8 α = 30% & 180 MB/hr/link : 75.7 < 116.9
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18MB 20 63 7090MB 70 117 137
126MB 80 135 141180MB 91 139 155
per hour
α = 10%
α = 30%
α = 50%
HOW MANY CELLS NEED FIBER?(OUT OF 307)
18 MB/hr 90MB/hr 126 MB/hr 180 MB/hr
Cells requiring fiber connection34
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AGGREGATING MULTIPLE FLOWS
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FIBER
Proposed Solution:• Use Excess Capacity for
aggregation• Excess Capacity =
Achievable Capacity - Demand
• Clustering• Plant more fiber at
cluster heads• Plant cluster heads in
high capacity cells to route traffic through
• Detailed routing study
CLUSTERCLUSTER HEAD
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EXAMPLE OF AGGREGATION • Group cells into clusters (illustrated in figure)• Have 1 fiber connected cell in each cluster
• If in each cluster:
Excess Capacity > Total Demand X (2 or 3)
Then: 1 fiber per cluster is sufficient!
Else: Add 1 fiber to cluster
After calculations for α = 30% & 126 MB/h:
WORST CASE REQUIRES 10 MORE FIBER CELLS
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CONCLUSIONS AND FUTURE WORK• Feasibility study of a distribution plan in NJ
– First order study promising in spite of conservative assumptions on traffic and propagation
– system more cost effective than a fiber layout– Most effective in rural areas (where it’s needed)
• No prior high speed internet connectivity• No fiber infrastructure• More bandwidth available and better propagation
• Same methodology for other states/regions
• Further issues that need to be studied:• Detailed routing strategies• Cost/benefit analysis
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WHITE SPACE: WHERE ARE WE TODAY?
• Database Testing and Trials– Google, Microsoft, Spectrum Bridge, Telcordia, etc.– No TVBDs and services rolled out yet!
• Wireless Service Providers and TV Broadcasters still continue to resist• Service providers want more licensed spectrum• Broadcasters worry about interference
• FCC working on next round of spectrum auctions• Reverse Auctions, Repackaging and Incentive Auctions
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WHITE SPACE: WHERE WILL WE GO?
• “Green” trumps “White”?
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PILOT PROJECT: “BROADBAND TO BIVALVE”
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PILOT PROJECT: “BROADBAND TO BIVALVE”
• Set up WiFi Hotspots in Bivalve, NJ • Backhaul to Bridgeton, NJ where Internet (T1) connectivity
exists • Use “Fixed Towers” and available TV White Space to provide
backhaul as shown in exemplary figure– Could reuse water towers or weather towers as feasible for
installing radios– Towers requires power supply
• The set-up will also serve as a “research testbed” for protocol and application development to benefit rural areas
• If an ISP partner is available, mobile hotspot service could be provided along the way to farms, etc.
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PILOT PROJECT: “BROADBAND TO BIVALVE”
• Hardware: Radio Router Node based on currently available second generation ORBIT platform– Multiple radio interfaces: 802.11 (wifi), 802.16
(wimax), LTE, ZigBee, Bluetooth, CRKit (whitespace capable)
• Software: Whitespace Routing Protocol optimized for throughput– Local (hotspot) support– Caching capabilities
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References• C. Gerami, N. B. Mandayam, and L. J. Greenstein, “Backhauling in TV white spaces,” Proceedings of
IEEE GLOBECOM 2010, December 2010• O. Ileri and N. B. Mandayam. Dynamic spectrum access models: Toward an engineering perspective
in the spectrum debate. IEEE Communications Magazine, 46(1):153-160, January 2008.• D. Zhang, R. Shinkuma, N. B. Mandayam, “Bandwidth Exchange: An Energy Conserving Incentive
Mechanism for Cooperation” in IEEE Transactions on Wireless Communications, vol. 9, No. 6, pp. 2055-2065, June 2010
• D. Zhang and N. B. Mandayam, “Bandwidth Exchange for Fair Secondary Coexistence in TV White Space,” in Proceedings of International ICST Conference on Game Theory for Networks (GameNets), Shanghai, April 2011
• M. N. Islam, N. B. Mandayam, and S. Kompella. Optimal resource allocation in a bandwidth exchange enabled relay network. In Proc. IEEE MILCOM’2011, pages 242–247, November 2011
• C. Raman, R. Yates, N. B. Mandayam, ”Scheduling Variable Rate Links via a Spectrum Server” in Proceedings of IEEE DySpan 2005, November 2005, Baltimore, MD
• D. Raychaudhuri, N. B. Mandayam, J. B. Evans, B. J. Ewy, S. Seshan, and P. Steenkiste. Cognet: an architectural foundation for experimental cognitive radio networks within the future internet. In Proc. ACM MobiArch’ 2006
• N. Krishnan, R. D. Yates, N. B. Mandayam, J. S. Panchal, “Bandwidth Sharing for Relaying in Cellular Systems” in IEEE Transactions on Wireless Communications, vol. 11, No. 1, pp. 117-129, January 2012
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Acknowledgments
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• U.S. National Science Foundation
• Office of Naval Research
• IEEE COMSOC• Debi Siering• WINLAB Collaborators: Cyrus Gerami, Larry Greenstein,
Nazmul Islam, Ivan Seskar, Dipankar Raychaudhuri