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) [ ] –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) [ ] –Large-scale MANET using low-cost cognitive radios –Multiple wideband ( 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 2

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 Primary on f4

Enabling CR MANETs 4

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) 5

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 6

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 7

Exploiting CR-enabled MANETs 8

E2E Throughput and Latency 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 9 S D D Proc Queueing Wait for access Backoff Retransmission Physical MAC/ Link Network Forwarding Queuing Packet CUT-THRU using Orthogonal channels

Make your own topology 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 10 Can do or Can do or ( and ) Can’t do if or Topology Is a controllable parameter Constraints Routes Network Layer Create Negotiate Get the topology that best matches the need

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 11