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Ram Ramanathan Principal Scientist BBN Technologies Cambridge, MA

Challenges in Enabling and Exploiting Opportunistic Spectrum MANETs An Industry Perspective NSF “Beyond Cognitive Radio” Workshop June 13-14, 2011. Ram Ramanathan Principal Scientist BBN Technologies Cambridge, MA. Cognitive Radio at BBN. DARPA neXt Generation Communications (XG) [2003-2005]

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Ram Ramanathan Principal Scientist BBN Technologies Cambridge, MA

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  1. Challenges in Enabling and Exploiting Opportunistic Spectrum MANETsAn Industry PerspectiveNSF “Beyond Cognitive Radio” WorkshopJune 13-14, 2011 Ram Ramanathan Principal Scientist BBN Technologies Cambridge, MA

  2. Cognitive Radio at BBN • DARPA neXt Generation Communications (XG) [2003-2005] • Spectrum Agility: Cross-layer MANET protocols for dynamic spectrum access • Policy Agility: Framework for machine-readable policies and reasoning • DARPA Wireless Network after Next (WNaN) [2008 - ] • Large-scale MANET using low-cost cognitive radios • Multiple wideband (0.9 - 6 GHz) tunable transceivers per node • Opportunistic Spectrum Access (OSA): dynamic sensing and allocation, evacuation, reconstitution, policy conformance • Scalable routing, Disruption tolerant network, content-based… • 100 node mobile network demonstration last year

  3. OSA Model • Primaries and Secondaries • Secondaries can use spectrum, conforming to interference policy • Spectrum overlay access • Sense and transmit on unoccupied frequencies to each of transceivers • Dynamic, distributed, frequency assignment algorithm • Evacuate immediately to another frequency if primary is sensed Primary on f1 7 6 4 7 4 2 6 1 2 1 2 3 1 5 5 Primary on f4 3 5

  4. Enabling CR MANETs

  5. Challenges in Sensing • Sheer number of channels (up to 1000) to sense • Detection/classification takes time • Need to evacuate quickly (200 ms) • Prioritization, multiple detectors etc. • Sensing with CSMA/CA • Need secondary MANET nodes to be “quiet” when sensing • No dedicated slot like in TDMA • Detector more sensitive, so large “quiet” radius • Collaborative sensing • Team formation, collaboration overhead • Linking nodes by fiber (static networks)

  6. Allocation and Evacuation • Allocation and Use • Some frequencies are inherently “clearer” than others • Cross-channel interference cannot be ignored • choice of frequency to use depends upon frequencies assigned to other transceivers in same node and neighboring nodes • Wide range of frequencies => wide range in range! • Evacuating a frequency • Jammers vs Primaries • Coordinating evacuation, ripple effects • Unified view of primaries, interference, noise • MAC protocol that simply moves to the clearest frequency and transmits

  7. Tools to help enable CR • Multiple Hypothesis testing • Dynamic probabilities of multiple hypothesis of primaries on each channel • Can be used with cooperative sensing as well • Artificial Intelligence in CR • Why: Human engineers cannot predict and design for all contingencies • Distributed planning and optimization to organize and coordinate • Machine learning to observe prior experience and modify behavior • Machine learning to rapidly update models • Scenario: Network trained in a desert can learn how to perform well under water • BBN work showing promise

  8. Exploiting CR-enabled MANETs

  9. E2E Throughput and Latency 1011011011 10101101111111 1011111011101 • End to end throughput in excess of per transceiver data rate via multiple frequency-orthogonal paths • Challenge: Cross-layer solution for assignment and multipath route generation • Full duplex possible • Challenge: Picking non-interfering channels, isolation • Cut-through routing possible • Can reduce E2E latency dramatically • Challenge: New radio architecture S D Forwarding Queuing Proc Proc Network CUT-THRU using Orthogonal channels D Queueing Wait for access Backoff Retransmission Proc MAC/ Link Proc Proc Proc Physical Packet Packet

  10. Make your own topology Can do or Can do or ( and ) Can’t do if or Get the topology that best matches the need • Sensing, allocation, etc. can be controlled by the network layer • Throw in power control, beamforming etc… a general architecture for controlling the topology with a global viewpoint Constraints Topology Is a controllable parameter Network Layer Create Negotiate Routes

  11. Summary • Several challenges in enabling a large scale real-world CR MANET.. • Sensing: scalability, “quieting” in CSMA, collaborative sensing • Allocation: channel interference, no control channel, evacuation • Multiple hypothesis and AI • … but perhaps more challenging is to go beyond and make sure we fully exploit what we get • True multipath routing • Full duplex, cut through • Topology by design • Acknowledgments: Chip Elliott, Karen Haigh, Jason Redi and others at BBN

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