BigBandwidth: Challenges it Poses in Wireless System Design

Wade Trappe

[1]

WINLAB[2]

Setting the Stage: How did we get here? The Spectrum Debate.

Open Access (Commons)– [Noam, Benkler, Shepard, Reed …]

Triumph of Technology Agile wideband radios will dynamically share a commons Success of 802.11 vs 3G

Spectrum Property Rights– [Coase, Hazlett, Faulhaber+Farber]

Triumph of Economics Owners can buy/sell/trade spectrum Flexible use, flexible technology, flexible divisibility, transferability A spectrum market will (by the force of economics) yield an efficient solution

What everyone agreed on (a few years ago): Spectrum use is inefficient FCC licensing has yielded false scarcity

Overview

WINLAB

•Source: FCC website

Setting the Stage: Frankly, spectrum allocation is complex…

Overview

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Maximum Amplitudes

Frequency (MHz)A

mpl

idue

(dB

m)

•Heavy Use

•Sparse Use

•Heavy Use

•Medium Use

•Less than 6% Occupancy

FCC measurement shows that occupancy of approximately 700 MHz of spectrum below 1 GHz is less than 6~10%

~ 13% spectrum opportunities utilized in New York City during 2004 Political Convention to nominate U.S. Presidential Candidate

•Atlanta

•NewOrleans

•SanDiego

•Frequency

•Time

Setting the Stage: This complex utilization has yielded poor spectral efficiency.

Overview

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Research themes that have emerged from mobile ad hoc and/or sensor networks research: Hierarchical Network Architecture wins

– Capacity scaling, energy efficiency, increases lifetimes, facilitates discovery

Cooperation wins– Achievable rates via information theoretic relay and broadcast channels

“Global” awareness and coordination wins– Space, time and frequency awareness and coordination beyond local measurements

Efficient operation requires radios that can:– Cooperate; Collaborate; Discover; Self-Organize into hierarchical networks

What everyone agrees on now:– Spectrum use is inefficient, FCC licensing has yielded false scarcity

Possible middle ground?– Dynamic spectrum access– Short-term property rights– Spectrum use driven by both technology and market forces

Cognitive Radios with ability to incorporate market forces?– Microeconomics based approaches to spectrum sharing– Pricing and negotiation based strategies

Setting the Stage: A spectrum debate emerged, driven by research themes.

Overview

WINLAB[6]

Setting the Stage: Fast forward… Bandwidth Everywhere But What are We to Do?

2011 State of the Union address, the President emphasized the objective of improving economic development through a proposed “National Broadband Initiative” – Double the amount of wireless spectrum available for mobile broadband

– Bring high-speed wireless services to roughly 98% of Americans within a few years.

The FCC has opened up large chunks of spectrum– In the 300MHz to 400MHz band for unlicensed use– National Broadband Plan: To open up 500 MHz in next 10

years

Bandwidth + CR Technologies + Coexistence Issues + Economics + ….. = Many unsolved problems that need to be tackled

Overview

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And now… What will you hear today?

Today’s agenda will include talks that address many questions associated with the using spectrum

1. Large spectrum chunks that are severely under-utilized They must be found to be used!

2. Spectrum opportunities/risks must be shared How to make this information available?

3. Users may lease rights to use spectrum How to trade spectrum rights?4. Abuse of spectrum is likely to happen How to detect and understand what

is going on in the spectrum?5. Possibility to use wide bandwidth itself How to efficiently model these

channels?6. RADAR and commercial wireless interfere How to coordinate and

coexist?7. How can we find the best radio strategies to use spectrum, cooperatively and

competitively?[7]

Overview

WINLAB

Project aims to develop a distributed network service to support dynamic spectrum assignment– Overlay or integrated network protocol to support spectrum data interchange– Geographic multicasting within region of interest– Enables a range of possible coordination algorithms (fully distributed)

•AP

•Internet

•Distributed Spectrum Coordination •Algorithm Software (runs on all radio devices)

•Aggregate Spectrum•Updates Between Routers

•Radio Coverage• Region A

•Region B

•Region C

•Region D

•Spectrum Use Update (from Radios)•Spectrum Occupancy Map (from Routers)

•Geo-cast Spectrum •Update Service

DSA can benefit from a network service that shares spectrum information, interference, etiquette, etc.

Appetizer…

WINLAB

Scenario-based channel emulator studied to facilitate performance evaluation of tactical radios in complex, broadband environments

Current RF matrix implementations for emulating channels are not able to support the challenging requirements of many tactical waveforms:

– Dynamics: Many scenarios will involve communicators moving very rapidly (e.g. communications involving jets)

– Broadband: It is desirable to emulate channels up to 250MHz of bandwidth

– Multi-party communications: It is desirable to be able to study the performance of an N-to-N communication setting

WINLAB collaborated with dBm and DSCI on a Navy STTR grant to design an N-to-N broadband RF channel emulator

– Approach involves implementation using an FPGA architecture

– WINLAB provided methods to reduce computational complexity while maintaining emulation fidelity

dBm Single Channel Emulator

Appetizer…

WINLAB

Management of RF Network and Tasking Infrastructure (MARTI)

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• A distributed system executing on participating RF devices that performs reception, transmission and local processing tasks on behalf of RadioMap applications:

• Without manual intervention • Subject to available resources and limited

impact on the primary mission of the device. • Software that intelligently assigns tasks to RF

devices and collects results on behalf of applications.

• Trading off probability of success and overhead

• Provides standardized mechanisms for tasking• Provides standardized reporting mechanisms

and formats• Modularity and Layering

• Any RF device should be able to perform tasks for any application without customizing

• MARTI infrastructure• RF Devices,• Applications.

Appetizer…

WINLAB

•WINLAB WINC2R System•RST SDR System•USRP2

•USRP

•RICE WARP Platform•U. Of Colorado

Unveiling a new cognitive radio platform…Appetizer…

WINLAB

Big Bandwidth: Finding Anomalous Needles in the Spectrum Haystack

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•Research Goals: The goal is to develop tools that can facilitate the detection of improper usage of radio spectrum.

•Develop Algorithms and Hardware for a Single-Scanner. The project explores how a single scanner:

•Should allocate its scanning strategy to best detect an unknown signal.•Develop sub-Nyquist techniques that allow digital scanning of wide bandwidths•Develop RF photonic scanning that allows for scanning of wide bandwidths

•Develop Algorithms for Multiple-Scanners. Multiple sensors allows for coordinated scanning. The project will examine how scanning should be allocated across sensors to detect anomalous transmissions.

Frequency

Appetizer…

WINLAB

Big Bandwidth will involve a coordinated algorithm and hardware development effort (examples)

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•A Single Sensor Scanning in Time and Frequency. •Rationale: By understanding platform limitations, we may scan smaller chunks of spectrum and sequentially adjust the scanning band versus time in a manner to better detect the Invader.•Technical Approach: The impact of practical parameters, such as scanning bandwidth, dwell time, switching time on detection performance will be explored. Arrive at relationships between probability of detection versus the invader’s time and bandwidth used and versus scanning bandwidth, dwell time, and switching time for different scanning strategies.

scan

scan

scan

scan

t

1

Time

x

Ts: switching time

Invader

Ts

Ts

Tsscan

y

0

scan

scan

scan

scan

t

1

Time

x

Ts: switching time

Invader

Ts

Ts

Tsscan

y

0bandwidth bandwidth

ττ

•Improving Scanning Bandwidth using RF Photonics. •Rationale: By redesigning the scanning platform through use of RF photonic circuitry, significantly more bandwidth can be scanned at any instance, thereby ensuring that few, if any, spectro-temporal gaps are left unexplored.•Technical Approach: Full-bandwidth RF signals undergo electrical-to-optical (EO) conversion. Fast-tuned narrowband optical filters and optical filterbanks will be applied to the resulting optical signal to infer RF spectral behavior.

Appetizer…

WINLAB[14]

Sensor-assisted anomaly detection can be used to detect manipulation and exploitation

Network Structure for Anomaly Detection– Primary (authorized) transmitter is

stationary– Distributed detection by a network of

sensors that collaborate locally.

Significance Testing– Test statistic T: a measure of observed data– Acceptance Region Ω: we accept the null

hypothesis if T Ω– Significance level : probability of false

alarm

When a channel is dedicated to a singleauthorized user we can try to distinguish between single and multiple transmissions

– Formulate a decision statistic that captures the characteristics of the received power in the normal case

[14]

Appetizer…