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Architecture and Protocol Design for Cognitive Radio Networks* Microsoft CR Summit, Jun 2008

Architecture and Protocol Design for Cognitive Radio Networks* Microsoft CR Summit, Jun 2008. Rutgers, The State University of New Jersey www.winlab.rutgers.edu Contact: Professor D. Raychaudhuri ray@winlab.rutgers.edu. *Collaborative project with Profs. Srini Seshan & Peter Steenkiste, CMU

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Architecture and Protocol Design for Cognitive Radio Networks* Microsoft CR Summit, Jun 2008

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  1. Architecture and Protocol Design for Cognitive Radio Networks*Microsoft CR Summit, Jun 2008 Rutgers, The State University of New Jersey www.winlab.rutgers.edu Contact: Professor D. Raychaudhuri ray@winlab.rutgers.edu *Collaborative project with Profs. Srini Seshan & Peter Steenkiste, CMU And Prof. Joe Evans, U Kansas

  2. BTS Cognitive Radio: Problem Scope Spectrum Allocation Rules (static) • Dense deployment of wireless devices, both wide-area and short-range • Proliferation of multiple radio technologies, e.g. 802.11a,b,g, UWB, 802.16, 3G femto, 4G, .. • New cognitive radio devices with programmable PHY/MAC • Available options include: • Agile radios (interference avoidance) • Dynamic centralized allocation methods • Distributed spectrum coordination (etiquette) • Collaborative ad-hoc networks Auction Server (dynamic) Spectrum Coordination Server (dynamic) INTERNET Dynamic frequency provisioning Short-range infrastructure mode network (e.g. WLAN) AP Spectrum Coordination protocols Etiquette policy Spectrum Coordination protocols Ad-hoc sensor cluster (low-power, high density) Collaborative ad-hoc networks MAC/PHY adaptation Scope of Cognitive Radio Protocol Stack Wide-area infrastructure mode network (e.g. 802.16)

  3. Unlicensed band + simple coord protocols Ad-hoc, Multi-hop Collaboration Internet Server-based Spectrum Etiquette “cognitive radio” schemes Protocol Complexity (degree of coordination) Radio-level Spectrum Etiquette Protocol Unlicensed Band with DCA (e.g. 802.11x) Agile Wideband Radios Internet Spectrum Leasing “Open Access” + smart radios Reactive Rate/Power Control UWB, Spread Spectrum Static Assignment Hardware Complexity Cognitive Radio: Design Space • Broad range of technology & related policy options for spectrum • Need to determine performance (e.g. bps/Hz or bps/sq-m/Hz) of different technologies taking into account economic factors such as static efficiency, dynamic efficiency & innovation premium Needs protocol support  unified framework called “CogNet”

  4. CogNet Protocol: Architectural Principles • Decentralized spectrum coordination as an integral part of protocol capabilities • “mutual observability” achieved via explicit exchange of spectrum information • Support for ad hoc network collaboration • Beacons that enable network bootstrapping and discovery without infrastructure support • Adaptive selection of PHY, MAC, routing methods • Control framework that enables on-the-fly selection of data path protocol components • Cross-layer control exchanged across protocol layers • Access to cross-layer information necessary for cross-layer adaptation • Logical separation of control & data for flexible design and low overhead • Minimize contention between control & data (…>>50% overhead in 802.11 networks!) • Efficient integration with the wired Internet • Aggregation of routing and cross-layer control information at boundary/gateway nodes

  5. Data Plane Global Control Plane Data Plane Control Plane Control API Application Data Transport Spectrum Mgmt - Bootstrap Path Discovery Establish Network ment MAC PHY “CogNet” Protocol Stack • Global Control Plane (GCP) • Common framework for spectrum allocation, PHY/MAC bootstrap, topology discovery and cross-layer routing • Data plane • Dynamically linked spectrum mgmt, PHY, MAC, Network modules and parameters as specified by control plane protocol Naming & Addres sing Control MAC Control PHY

  6. CogNet Protocol: Common Spectrum Coordination Channel (CSCC) • CSCC enables mutual observation between heterogeneous nodes to explicitly coordinate spectrum usage • CSCC function is an integral part of the CogNet global control plane (GCP) • Exchange of CSCC messages by an extra narrow-band (low bit-rate) radio • Periodically broadcast spectrum usage parameters to neighbors • Enables distributed algorithms for spectrum co-existence

  7. Message Type Flags Source Address IE length IE(1) IE(n) 1B 1B 6B 2B variable variable CogNet Protocol: Packet Format Generic GCP Packet:Ethernet packet format with control payload (consisting of variable length information elements) 0 8 16 24 31 Source MAC Address Message type Flags Source MAC Address (cont). . . . . . MAC Address IE length . . . Device Name and Description . . Type (8b) Channel(8b) Priority (8b) Price_bid(8b) Service Time . . . . . . Duration (32b) Tx Pwr (8b) Rx Pwr (8b) Example CSCC message used in WLAN-Bluetooth prototype at WINLAB

  8. CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT • Multi-radio node • 802.11a/b/g ad-hoc • WiFi infrastructure mode (AP to clients) • Bluetooth • 64kbps voice calls • File synchronization between PDAs, phones and laptops • Mouse/keyboard • Zigbee • Sensors • Potential WiMax • Aggregated web/email traffic to base stations GCP Coordination Range

  9. BT WiFi CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT (cont.)

  10. CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT (cont.) • UDP throughput results with and without interference from other BT/WiFi users • Throughput Drops by ~3-4x in the case of 802.11g nodes and by ~1.5-2x for bluetooth nodes in dense topologies with 4 wifi and 4 Bt links. Results Averaged over 5 different topologies & load conditions.  indicates the need for spectrum coordination

  11. CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT (cont.) Characteristics : • Each individiual in the room carries two radios bluetooth and wifi • Node density High • 28 radios in ~3000sqft • 14 Bluetooth radio • 14 Wifi radio

  12. CogNet Protocol: Beacon Format • Beacon format: (extended form of CSCC) • Short message, low-layer function • Link weight/metric calculation: • Estimate maximum supported data PHY rate • Direct link weight (proportional to achievable link rate) MAC Idle Ratio

  13. CogNet Protocol: Network Discovery • Obtain global awareness by aggregating local link states • Discover end-to-end paths with path weight • Use only one-hop broadcast for periodical update • Trade-off between network setup time and overhead • Link state aggregation message format • Flags: PR – Poll (0) / Response (1), UB – Unicast (0) / Broadcast (1) response required, FD – Forwarded or not, FU – Full or updated

  14. CogNet Protocol: Data Path Establishment • Hop-by-hop cross-layer parameter setup • Configure data plane and reserve radio resources by joint frequency/power/rate/bandwidth allocation • Unified message format for “up/down” hop setup

  15. CogNet Protocol: ns2 Simulation • Evaluation by ns-2 simulations • Bootstrap/Discovery: network setup time, overhead, theoretical end-to-end rate • DPE: joint F/P/R allocation success ratio, overhead • Naming/addressing: uniqueness of IP/Name • Ad hoc network – nodes randomly boot up Control Interface (802.11b) Data Interface (generic OFDM radio parameters)

  16. CogNet Protocol: Discovery & Path Setup Simulation Results Maximum and average network setup time (BSB interval 2sec, LSA interval 5sec, nodes randomly start [0, 4]sec) Theoretical max end-to-end rate averaged over the network Control overhead

  17. Control link CH1_CSMA Data path CH10_TDMA Slot = 5 Sender CH4_CSMA CH3_CSMA CH5_CSMA B Delay increase > 20% Request TDMA Switch CH2_CSMA A CH10_TDMA Slot = 3 CH1_CSMA CH10_TDMA Slot = 1 Receiver CogNet Protocol: Dynamic MAC Switching Using GCP Control • GCP offers control support necessary for MAC switching, for example from CSMA to TDMA • GCP messages carry state information needed by decentralized MAC switching algorithm at each node • GCP control used to set up TDMA schedule involving multiple nodes

  18. Node B Receiver Sender Node A Preferred Channel List Match channel Preferred Channel List CH3_CSMA Match channel Preferred Channel List CH5_CSMA Match channel CH1_CSMA Delay > 20% Request TDMA switch Request TDMA switch TDMA Join (Slot #1) Request TDMA switch TDMA Join (Slot #3) TDMA Join (Slot #5) CH10_TDMA (Slot #3) CH10_TDMA (Slot #1) CH10_TDMA (Slot #5) CogNet Protocol: Dynamic MAC Switching Using GCP Control (cont.) • GNU radio implementation currently in progress • Sample protocol exchange between nodes shown below

  19. CogNet Protocol: Future Work • Complete validation of key components • MAC switching, cross-layer routing protocols, adaptation algorithms, … • Complete baseline v1.0 protocol spec • Support for dynamic spectrum, bootstrap/discovery, MAC switching and cross-layer routing • End-to-end wired Internet integration issues • CR supernode and aggregation gateway details • Protocol implementation on GNU radio platform • GNU/ORBIT release planned for AY08-09  ORBIT upgrade to URSP2 • Experiments with adaptive wireless networks • Apply to dynamic networking scenarios (tactical, vehicular) and demonstrate value of coordination, cooperation and adaptation

  20. Suburban Urban ORBIT Radio Grid 300 meters Office 20 meters 500 meters 30 meters Future work: ORBIT Node Upgrade to CR • ORBIT radio grid testbed currently supports ~10 GNU radios and for ~100 low cost programmable radio boards • Plan to upgrade ~64 radio nodes with combination of GNU/USRP2 boards and WINLAB hardware platforms for higher performance evaluations; will include baseline CogNet stack Current ORBIT sandbox with GNU radio 400-node Radio Grid Facility at WINLAB Tech Center Planned upgrade (2007-08) Radio Mapping Concept for ORBIT Emulator URSP2 CR board Programmable ORBIT radio node

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