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

WINLAB

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

2

XAdditional Rulingon Sep 23 2010

WINLAB

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

3

≈ ¢

≈ $

≈ $, votes

priceless

WINLAB

How much TV White Space is there in NJ?

TV Towers around NY City and Philadelphia Lots of white space spectrum available in NJ!

4

# of channels (fixed) vs. # of 5X5 sq. mi. grids

7 – 31 channels available per cell (42 – 186 MHz)

WINLAB

Radio Coverage

5

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

WINLAB

White Space Networks

6

Range of possible usage scenarios, with sweet spot in outdoor networks with medium range and speed

Bit-Rate

100 m

WINLAB

Sample Applications: Cellular Data Boost

7

“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

WINLAB

Sample Applications: Distribution/Backhaul

8

DISTRIBUTION AND BACKHAULUSING WHITE SPACE

WINLAB

Sample Applications: Long range V2V/Emergency Network

9

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

WINLAB10

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

WINLAB

Design Implications for White Space Networks

11

WINLAB

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

13

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.

2

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

14

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

14

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

15

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

16

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

WINLAB

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

WINLAB

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

WINLAB19

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?

WINLAB20

HOW WILL IT LOOK?

WINLAB

• 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

21

WINLAB

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

WINLAB

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

23

WINLAB

NJ TOWERS AT A GLANCE

• Towers in NJ, NY, DE & PA• Coverage can be 100km (r)

24

WINLAB

FCC’S PROTECTION RULE

Secondary White Space radio

25

AVAILABLE BANDWIDTH

CHANNEL AVAILABILITY INCLUDING ADJACENT CHANNEL EFFECT

26 WINLAB

AVAILABLE SPACE PER CHANNEL

24 25 26

AVAILABLE BANDWIDTH

TV tower coverageAdditional separation ringAvailable for possible useAvailable as White Spaces

25

AVAILABLE BANDWIDTH

27 WINLAB

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!

WINLAB

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

28

reuse factor (r) of 2 :

WINLAB

ACHIEVABLE CAPACITY DEMAND>><<

29

WINLAB

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

30

WINLAB

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)

31

US Census 2000 Our Approximation

WINLAB


• 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



32

WINLAB


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

33

WINLAB

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

WINLAB

AGGREGATING MULTIPLE FLOWS

35

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

WINLAB

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

36

WINLAB

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

37

WINLAB

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

38

WINLAB

WHITE SPACE: WHERE WILL WE GO?

• “Green” trumps “White”?

39

WINLAB

PILOT PROJECT: “BROADBAND TO BIVALVE”

40

WINLAB


• 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.

41

WINLAB


• 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

42

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

43

Acknowledgments

44

• 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

Documents

Backhauling in TV White Space