Opportunistic Spectrum Access: Opportunistic Spectrum Access: Challenges, Architecture, Challenges, Architecture,

ProtocolsProtocols

C. Santivanez, R. Ramanathan (presenter), C. Partridge, R. Krishnan, M. Condell, S. Polit

Internetwork Research Department

BBN Technologies, Cambridge, MA

(ramanath@bbn.com)

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OutlineOutline

• Introduction and motivation

• Spectrum Agility

• Policy Agility

• A simple system for opportunistic spectrum access

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Opportunistic Spectrum AccessOpportunistic Spectrum Access

TIME

FR

EQ

UE

NC

Y

PRIMARY 1

PRIMARY 2

PRIMARY 3

PRIMARY 4

HOLE

SECONDARY

WALL

• Basic idea– Sense the spectrum you want to transmit in– Look for “holes” or “opportunities” in time and frequency– Transmit so that you don’t interfere with the licensees

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Problem StatementProblem Statement

• Given– a set of possibly mobile nodes

comprising a wireless network– the hole/wall characteristics as a

function of time for each node– a set of constraints on the spatial

reuse of frequencies– [a set of capacity demands per link]

• dynamically control access (xmt/rcv, beam, power etc.) on each frequency such that

– network capacity is maximized– constraints are honored– [capacity demands are met]

Time

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Time

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quen

cy

Time

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cy

Time

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cyTime

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Why Opportunistic Spectrum AccessWhy Opportunistic Spectrum Access

• Current “static” spectrum allocation strategy is wasteful

– Huge opportunities exist in time, frequency and space

– Apparent spectrum scarcity

• Deployment difficulty– Allocating spectrum for overseas

military operations– Using WiFi in different countries in

conformance with the country’s policy

• Spectrum policy is simply outdated– FCC Spectrum Policy Task Force

Maximum Amplitudes

Frequency (MHz)

Amplidue (dBm)

Heavy Use

Sparse Use

Heavy Use

Medium Use

Less than 6% OccupancyLess than 6% Occupancy

Maximum Amplitudes

Frequency (MHz)

Amplidue (dBm)

Heavy Use

Sparse Use

Heavy Use

Medium Use

Less than 6% OccupancyLess than 6% Occupancy

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OSA in the Wireless Internet: DriversOSA in the Wireless Internet: Drivers

• Need for more capacity– 2G, 3G, 4G……

• Waveform Diversity– Beamforming, MIMO, UWB, OFDM, Spectrum-adaptive/heteromorphic …..

• Software/Agile/Cognitive Radios– JTRS, Vanu Inc., GNU Radio ……

• Secondary markets, FCC Spectrum Policy, ….

Current trends point to a need for and capability to do opportunistic access as a key part of next generation Wireless Internet architecture

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OSA ChallengesOSA Challenges

• Spectrum Agility– How do we identify holes (opportunities) ?– How can we access those opportunities?– How do we prevent interfering with primary users?

• Policy Agility– How do we control access to be in conformance with regulatory policies?– How can we effect a change in node behavior in accordance with policy changes?– How do we support multiple (concurrent) policy authorities

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Next …..Next …..

• Introduction and motivation

• Spectrum Agility

• Policy Agility

• A simple system for opportunistic spectrum access

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Spectrum Agility ComponentsSpectrum Agility Components

Opportunity Awareness

Determine spectrum opportunities and usage constraints, based on sensing, and policy information

Opportunity Use

Transmit packet in accordance withopportunity assignment, adjust parameters as per constraints

Usage constraints

Per-packetassignment

Opportunity Allocation

Determine how the available opportunities are shared on an instant-by-instant basis

OpportunityInfo, andconstraints

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Challenge: Opportunity AwarenessChallenge: Opportunity Awareness

• Wideband sensing– Problem: Sense energy/ receive signatures over a large portion of the spectrum

(e.g. entire U-NII indoor band (5.15 - 5.25 GHz (100 MHz))– Current wireless receiving technology receives/transmits over much smaller

chunks (e.g. each channel in 802.11b is about 22 MHz)– An alternative: Primaries log their current/planned use, secondaries access this

database

• Opportunity Identification– Problem: Based on sensing, decide whether or not to use a slice of spectrum– Interference occurs at receivers, but you can only sense transmitters– Hidden transmitters

• Opportunity Dissemination– Problem: Share opportunities with other nodes to coordinate use of spectrum– Opportunity dissemination can be bandwidth intensive– Chicken-and-egg: Which channel do we use to disseminate opportunities?

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Challenges: Opportunity Allocation/UseChallenges: Opportunity Allocation/Use

• Allocation– Problem: Channel access over

dynamically changing holes– CSMA/CA: Need to acquire floor over

a common channel set– TDMA: Assign time slots over each

available frequency

• Use– Problem: Implementing the allocation– Waveforms that can use

discontiguous portions of the spectrum– Dynamically adapt waveform to

required PSD– Adjust beamforming, data rate,

modulation, spreading …

RTS (3,4,5)

CTS (3,4)

1,2,3,4,5

1,2

1,2,3,4,5

5,6

4,5,6,7

3,4,5,6

1,2,3,4

X Y

Z

A

DC

B

E

1,2,3

2,3,4,5

3,4,52,3,4

1,2,3,4,5

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4

3 5

5

4

3

2

1

S1 S2 S3 S4

A-D

B-E A-DB-EA-D

B-E

C-D

B-C

B-C

C-D C-DC-D

B-CB-C

A-CA-CA-C

B-EA-D

A-D

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Next …..Next …..

• Introduction and motivation

• Spectrum Agility

• Policy Agility

• A simple system for opportunistic spectrum access

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Policy AgilityPolicy Agility

FCC Rule BookHardwired policy

Canned behaviors:few/fixed modesof operation

Limited or no programmability(e.g. ASICs)

Agile behaviors: numerous modes of operation

Dynamic Policy

Machine-Readable Policies

Highly Programmable, fast, low power devices (e.g FPGAs)

Policy agility is necessary to exploit the emerging agility of devices and allow in-situ policy-based control of radio behaviors

Policy agility is necessary to exploit the emerging agility of devices and allow in-situ policy-based control of radio behaviors

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Machine Understandable PoliciesMachine Understandable Policies

OSA node

OSA node

Machine-readable Policies

SpectrumPolicies

Policy Repository

Internet

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Benefits of policy agilityBenefits of policy agility

• Adaptation to policies changing over time– Allows development of technology in advance of policies

• Adaptation to policies changing over geography– E.g., use a new smart card when in a new country

• Self-checking policies– Implications of policy interactions can be worked out in advance– Consistency checking at the logical level

• Sub-policy management– Secondary markets: Overarching policy, sub-policy – allow primary user to develop

sub-policies for secondary users

• Radio system capabilities based policies– E.g. two different policies depending on whether a radio system can detect certain

waveforms or not

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Challenges: Policy AgilityChallenges: Policy Agility

• A language for policy expression– Inheritance, Reification (rules about rules), Inference (derivable rules),

Extensibility, Scalability, Declarative

• An ontology for policies– What are the “primitive” objects underlying policies?– What are the inter-relationships between the primitive objects

• Reasoning about policies– Conformance: Is this usage permitted by policy?– Constraints: What is the range of parameters for this particular usage?– Searches: Here are my specs, my needs. Give me the usage.

• BBN has developed an initial ontology and a policy language based on OWL (Semantic Web Language)

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Next …..Next …..

• Introduction and motivation

• Spectrum Agility

• Policy Agility

• A simple system for opportunistic spectrum access

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A policy-aware OSA systemA policy-aware OSA system

Transmit

SystemStrategyReasoner

OSAcapableDevice

PolicyConformance

Reasoner

Sense

DeviceConfiguration

SystemPolicy

RegulatoryPolicy

Ask for transmission opportunities

Return transmission opportunities

Ask for usage validity

Allow/Deny

Rest of talk

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Upper Layer

To PCR

Spectrum Agility: Components Spectrum Agility: Components

OpportunityIdentification

Kernel

- ND- HIP- RMAC

TRANSCEIVER

XG Opportunity API

XG Transceiver API

My HIANbr list, nbr HIAs

My IDLE CHANNEL, my HIA, pathloss

Information Flow

Control Flow

FFT

To SSR

ND-HIPSense Interface

- Waveform selection- Idle Channel Selection

OSAAdaptationLayer

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Sense InterfaceSense Interface

Hole Information Array (HIA)

11 11 00 00 00 11 00 00 11 11

Frequency (KHz)Frequency (KHz)

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IDLE Channel SelectionIDLE Channel Selection

11 11 00 00 00 11 00 00 11 11My_HIAMy_HIA

11 00 00 00 00 11 11 00 00 11Nbr_1_HIANbr_1_HIA

00 11 11 00 00 00 11 00 11 11Nbr_2_HIANbr_2_HIA

11 11 00 00 00 11 00 11 11 11Nbr_3_HIANbr_3_HIA

Idle Idle ChannelChannel

– IDLE Channel (freq., rate, waveform) is not the XG Coordination Channel

– While node listen to IDLE Channel MUST be reachable by all 1-hop neighbors.

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– Communication with neighbors may then switch to a more favorable channel.

– E.g. RTSs need to be sent using a nbr IDLE channel, while DATA packet may be sent using one of the channels below:

11 11 00 00 00 11 00 00 11 11My_HIAMy_HIA

11 00 00 00 00 11 11 00 00 11Nbr_1_HIANbr_1_HIA

00 11 11 00 00 00 11 00 11 11Nbr_2_HIANbr_2_HIA

11 11 00 00 00 11 00 00 11 11My_HIAMy_HIA

Point to Point opportunity to Point to Point opportunity to Nbr 2Nbr 2

Point to point opportunity to Nbr Point to point opportunity to Nbr 1 1

IDLE Channel Selection (contd.)IDLE Channel Selection (contd.)

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Spectrum UtilizationSpectrum UtilizationB

W O

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(x

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Time

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Zoom

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Concluding RemarksConcluding Remarks

• Opportunistic Spectrum Access de-bunks the “spectrum scarcity” myth and a promising technology for Wireless Internet

• Realizing true opportunistic spectrum access requires solving not only the spectrum agility problem but also the policy agility problem

• There is plenty of “low hanging fruit” that can be harvested with a relatively simple set of mechanisms

– We presented one such system, that incorporates both spectrum and policy agility– Showed an order of magnitude gain in capacity

• Future research to target “higher hanging fruit”– Dealing with rapidly changing hole information in a large network– Constructing a coordination channel “on the fly”– Theoretical capacity bounds of OSA

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ResourcesResources

• Much of this work was based on the DARPA XG Program– Phase I: BBN project “Medium Access Control for XG (X-MAC)”– Phase 2: BBN project “XG Architecture and Protocols (XAP)”

• Documents– “The XG Vision”, version 2.0, http://www.ir.bbn.com/projects/xmac/vision.html

– “The XG Policy Language Framework”, version 1.0, http://www.ir.bbn.com/projects/xmac/vision.html

• Web sites– http://www.ir.bbn.com/projects/xmac/index.html– http://www.darpa.mil/ATO/programs/xg/index.htm