opportunistic spectrum access: challenges, architecture, protocols c. santivanez, r. ramanathan...
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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
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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
Fre
quen
cy
Time
Fre
quen
cy
Time
Fre
quen
cy
Time
Fre
quen
cyTime
Fre
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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• Spectrum policy is simply outdated– FCC Spectrum Policy Task Force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
44
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
ccu
pa
tion
(x
100
KH
z)B
W O
ccu
pa
tion
(x
100
KH
z)
Time
Time
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