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

2 Cognitive Radio: Problem Scope Spectrum Allocation Rules (static) INTERNET BTS Auction Server (dynamic) Spectrum Coordination Server (dynamic) AP Ad-hoc sensor cluster (low-power, high density) Short-range infrastructure mode network (e.g. WLAN) Collaborative ad-hoc networks MAC/PHY adaptation Wide-area infrastructure mode network (e.g ) Dense deployment of wireless devices, both wide-area and short- range Proliferation of multiple radio technologies, e.g a,b,g, UWB, , 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 Etiquette policy Spectrum Coordination protocols Spectrum Coordination protocols Dynamic frequency provisioning Scope of Cognitive Radio Protocol Stack

3 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 Hardware Complexity Protocol Complexity (degree of coordination) Reactive Rate/Power Control Reactive Rate/Power Control Agile Wideband Radios Agile Wideband Radios Unlicensed Band with DCA (e.g x) Unlicensed Band with DCA (e.g x) Internet Server-based Spectrum Etiquette Internet Server-based Spectrum Etiquette Ad-hoc, Multi-hop Collaboration Ad-hoc, Multi-hop Collaboration Radio-level Spectrum Etiquette Protocol Radio-level Spectrum Etiquette Protocol Static Assignment Static Assignment Internet Spectrum Leasing Internet Spectrum Leasing cognitive radio schemes UWB, Spread Spectrum UWB, Spread Spectrum Open Access + smart radios Unlicensed band + simple coord protocols Cognitive Radio: Design Space 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 networks!) Efficient integration with the wired Internet Aggregation of routing and cross-layer control information at boundary/gateway nodes

5 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 Control PHY Control MAC Naming & Addres sing

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 CogNet Protocol: Packet Format Message Type FlagsSource Address IE length IE(1)IE(n) 1B 6B2Bvariable Generic GCP Packet: Ethernet packet format with control payload (consisting of variable length information elements)... Duration (32b) Service Time...Price_bid(8b)Priority (8b) Channel(8b)Type (8b).... Device Name and Description IE length... MAC Address Source MAC Address (cont) Tx Pwr (8b)Rx Pwr (8b) Example CSCC message used in WLAN-Bluetooth prototype at WINLAB Message typeFlags Source MAC Address

8 CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT Multi-radio node a/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/ traffic to base stations GCP Coordination Range

9 CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT (cont.) Data Radio Service PHY Type IEEE g (Atheros AR5212) Bluetooth (USB Dongle) Frequency MHz MHz Modulation OFDM (256 FFT) QAM FHSS Transmit Power 18dBm4dBm (~10m) (class 2) 20dBm (~100m) (class 1) PHY Rate 1M-54Mbps AutoRate Upto 1Mbps (class 2) Upto 4Mbps (class 1) Data session Pareto ON/OFF variable rate CBR: 5 sec random session Constant audio streaming (64, 128,320,512, 1024kbps) BT WiFi

10 CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT (cont.) Throughput Drops by ~3-4x in the case of g 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 UDP throughput results with and without interference from other BT/WiFi users

11 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 CogNet Protocol: Validating GCP-based Spectrum Coordination on ORBIT (cont.)

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) Control overhead Theoretical max end-to-end rate averaged over the network

17 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 Control link Data path Sender Receiver CH1_CSMA CH2_CSMA CH4_CSMA CH3_CSMA CH5_CSMA CH1_CSMA Delay increase > 20% Request TDMA Switch A B CH10_TDMA Slot = 1 CH10_TDMA Slot = 3 CH10_TDMA Slot = 5

18 CogNet Protocol: Dynamic MAC Switching Using GCP Control (cont.) SenderNode A Node B Receiver Preferred Channel List Match channel CH3_CSMA Delay > 20% Preferred Channel List Match channel CH5_CSMA Preferred Channel List Match channel CH1_CSMA TDMA Join (Slot #3) TDMA Join (Slot #1) TDMA Join (Slot #5) CH10_TDMA (Slot #3) CH10_TDMA (Slot #1) CH10_TDMA (Slot #5) Request TDMA switch 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 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 Urban 300 meters 500 meters Suburban 20 meters ORBIT Radio Grid Office 30 meters Radio Mapping Concept for ORBIT Emulator 400-node Radio Grid Facility at WINLAB Tech Center Programmable ORBIT radio node URSP2 CR board Planned upgrade ( ) Current ORBIT sandbox with GNU radio