Adaptive Wireless Networks Using Cognitive Radios as a Building Block

Transcription

1 Adaptive Wireless Networks Using Cognitive Radios as a Building Block MobiCom 2004 Keynote Speech Sept 29, Philadelphia D. Raychaudhuri Professor ECE Dept & Director, WINLAB Rutgers University ray@winlab.rutgers.edu 1

2 Talk Outline Introduction: the future wireless network and related R&D challenges Dynamic spectrum management & cognitive radio concepts Cognitive radio technologies: selected results Coexistence of and in unlicensed bands CSCC spectrum etiquette Adaptive networks and ad-hoc self-organization Cognitive radio hardware Concluding remarks 2

3 Introduction 3

4 Introduction: Future Wireless Network Scenario Custom Mobile Infrastructure (e.g. GSM, 3G) BTS Public Switched Network (PSTN) BSC MSC GGSN, etc. WLAN Access Point Internet (IP-based) Generic mobile infrastructure BTS Infostation cache Growing role for fast, low-cost short-range radios Heterogeneous systems with multiple radio standards (3G, 4G, WLAN, UWB..) Self-organizing ad-hoc access networks Increasing use of unlicensed spectrum and dynamic sharing methods Uniform IP core network Wide range of applications ( ubiquitous wireless services ) High-speed data & VOIP WLAN Hot-Spot CDMA, GSM or 3G radio access network High-speed data & VOIP Voice (legacy) Ad-hoc network extension Relay node Broadband Media cluster (e.g. UWB or MIMO) VOIP (multi-mode) Today Future Low-tier clusters (e.g. low power sensor) 4

5 Introduction: Wireless Technology Trends Pervasive systems Primary Applications Telephony; PC/LAN VOIP, H264, HTTP, etc. Location-aware services Telephony; Multimedia; Mobile Internet Sensor net applications, Embedded wireless devices Telephony; Multimedia; Mobile Internet Sensor Nets Network Architecture Cellular networks Ethernet + WLAN Mobile IPv6, etc. IP-based networks for both Cellular & WLAN Beyond IP networks (e.g. content aware routing) Self-organizing multi-hop IP+ Layer 7 overlay infrastructure net; Ad-hoc low-tier networks Radio Technology 2G/CDMA & TDMA ~1 Mbps WLAN ~1 Mbps 3G/WCDMA ~10-54 Mbps WLAN Cross-layer techniques ~100 Mbps+ 4G/OFDM, & WLAN; ~500 Mbps UWB, etc Higher speed, OFDM Very wideband signals New spectrum policies ~ ~ Cognitive radio ~2010+ Adaptive Radio Networks 5

6 Introduction: Key Technologies for Future Wireless Systems New radios for heterogeneous access Low-power sensor radios High-speed WLAN and 4G/ Faster 4G cellular, , etc. Spectrum-sharing for dense networks Dynamic spectrum/cognitive radio for frequency coordination Spectrum etiquette protocols Ad-hoc wireless networks Self-organizing networks capable of scaling organically Discovery, MAC and routing protocols for reliable ad-hoc services Pervasive computing software Dynamic binding of application agents and sensors Real-time orchestration of sensors and actuators Focus of this talk 6

7 Dynamic Spectrum Management & Cognitive Radio 7

8 Motivation for Dynamic Spectrum and Cognitive Radio Techniques: Static allocation of spectrum is inefficient Slow, expensive process that cannot keep up with technology Spectrum allocation rules that encourage innovation & efficiency Free markets for spectrum, more unlicensed bands, new services, etc. Anecdotal evidence of WLAN spectrum congestion Unlicensed systems need to scale and manage user QoS Density of wireless devices will continue to increase ~10x with home gadgets, ~100x with sensors/pervasive computing Interoperability between proliferating radio standards Programmable radios that can form cooperating networks across multiple PHY s 8

9 Spectrum Management: Frequency allocation today Source: FCC website 9

10 Spectrum Management: Policy Concepts Unlicensed bands with spectrum etiquette More ISM/U-NII bands with simple coordination rules Property Rights Fee simple ownership with non-interference easements Spectrum clearinghouse Packets are sent with access tokens with pricing determined by congestion Open access No coordination rules, technology expected to evolve towards co-existence Cognitive radio bands Agile/smart radios capable of adaptive strategies for interference avoidance 10

11 Spectrum Management: Problem Scope Spectrum Coordination Server (dynamic) BTS Etiquette policy Short-range ad-hoc net INTERNET Dynamic frequency provisioning Spectrum Allocation Rules (static) Auction Server (dynamic) Spectrum Coordination protocols Spectrum Coordination protocols Wide-area infrastructure mode network (e.g ) AP Short-range infrastructure mode network (e.g. WLAN) Ad-hoc sensor cluster (low-power, high density) Dense deployment of wireless devices, both wide-area and shortrange Proliferation of multiple radio technologies, e.g a,b,g, UWB, , 4G, etc. How should spectrum allocation rules evolve to achieve high efficiency? Available options include: Agile radios (interference avoidance) Dynamic centralized allocation methods Distributed spectrum coordination (etiquette) Collaborative ad-hoc networks 11

12 Cognitive Radio: Definitions The term cognitive radio used to denote new generation of adaptive wireless devices capable of dynamic spectrum coordination Baseline capability includes spectrum scanning and frequency agility Fast adaptation of transmitted signal to fit into changing radio environment Capable of higher-layer spectrum etiquette or negotiation protocols May also participate in ad-hoc networks formed with other cognitive radios Interoperability with multiple radio technologies based on SDR capabilities 12

13 Cognitive Radio: R&D Status Policy and technology R&D on cognitive radio still at an early stage. Recent activities include: FCC notice of rulemaking for specific underlay data services in UHF TV bands More general notice of proposed rulemaking on new unlicensed cognitive bands Software defined cognitive radios developed at Vanu Inc., GNU/Utah XG policy framework being developed by DARPA System studies and prototyping at Mitre, Rutgers/WINLAB, Stevens, others. New National Science Foundation research initiative ( NeTS ProWIN ), 2004 Cognitive radio has the potential for significant improvements in spectrum efficiency, performance and interoperability between unlicensed band services 13

14 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 Protocol Complexity (degree of coordination) Unlicensed band + simple coord protocols Internet Internet Server-based Server-based Spectrum Spectrum Etiquette Etiquette Unlicensed Unlicensed Band Band with DCA with DCA (e.g x) (e.g x) Ad-hoc, Ad-hoc, Multi-hop Multi-hop Collaboration Collaboration Radio-level Radio-level Spectrum Spectrum Etiquette Etiquette Protocol Protocol cognitive radio schemes Internet Internet Spectrum Spectrum Leasing Leasing Static Static Assignment Assignment Reactive Reactive Rate/Power Rate/Power Control Control UWB, UWB, Spread Spread Spectrum Spectrum Agile Agile Wideband Wideband Radios Radios Open Access + smart radios Hardware Complexity 14

15 Cognitive Radio: Reactive Algorithms Reactive (autonomous) methods may be used to avoid interference via: Frequency agility: dynamic channel allocation by scanning Power control: power control by interference detection and scanning Time scheduling: MAC packet re-scheduling based on observed activity B C Frequency agility A&B s spectrum band D D D C D D C&D s spectrum band A Range with Power Control Range with Power Control Range without Power Control Scheduling Range without Power Control 15

16 Cognitive Radio: Limitations of Reactive Schemes Reactive schemes (without explicit coordination protocols) suffer from certain limitations: Near-far problems possible at the receiver Inability to predict future behavior of other nodes Only detects transmitters, not receivers, but interference is a receiver property C B D s agile radio waveform without coordination protocol D A s agile radio waveform A A cannot hear D Coverage area of D Y with coordination Coverage area of A Hidden Terminal Problem 16

17 Cognitive Radio: Spectrum Policy Server Internet-based Spectrum Policy Server can help to coordinate wireless networks Needs connection to Internet even under congested conditions (...low bit-rate OK) Some level of position determination needed (..coarse location OK?) Spectrum coordination achieved via etiquette protocol centralized at server Internet Internet Spectrum Policy Server WLAN operator A AP1 Access Point (AP2) WLAN operator B Etiquette Protocol AP1: type, loc, freq, pwr AP2: type, loc, freq, pwr BT MN: type, loc, freq, pwr Master Node Wide-area Cellular data service Ad-hoc Bluetooth Piconet 17

18 Cognitive Radio: Common Spectrum Coordination Channel (CSCC) Common spectrum coordination channel (CSCC) can be used to coordinate radios with different PHY Requires a standardized out-of-band etiquette channel & protocol Periodic tx of radio parameters on CSCC, higher power to reach hidden nodes Local contentions resolved via etiquette policies (..independent of protocol) Also supports ad-hoc multi-hop routing associations CH#N : : CH#N-1 CH#N-2 CSCC RX range for X Ad-hoc net B Ad-hoc net A Frequency CH#2 CH#1 CSCC X Ad-hoc Piconet Master Node Y CSCC RX range for Y 18

19 Adaptive Wireless Networks: Ad-Hoc Collaboration Cognitive radios can organize themselves into a multi-hop adaptive network in order to achieve better system performance Multi-hop collaboration can increase spectrum efficiency, reduce power consumption and potentially also improve throughput Cognitive radio scans for active nodes and executes discovery algorithm Bootstrapped PHY to selected nodes adapts to high bit-rate, low power/range Control protocol between nodes used to negotiate ad-hoc network parameters and to exchange routing tables End-to-end routed path From A to F PHY A C Bootstrapped PHY & control link PHY B PHY C B D D E Control (e.g. CSCC) Multi-mode radio PHY Ad-Hoc Discovery & Routing Capability AA Adaptive Wireless Network Node ( functionality can be quite challenging!) F 19

20 Adaptive Wireless Network: Simple cellular/wlan example Multi-mode (cellular, WLAN) or cognitive radio capable of ad-hoc association can be used to improve cellular srevices System may also include provisioned radio forwarding nodes Radio paths (single or multi-hop) selected adaptively based on current cellular radio link quality and proximity to other nodes BTS To wired network Ad-Hoc Cluster n Dual-Mode Mobile Forwarding Node Ad-Hoc Cluster 1 Dual-Mode Mobile (relay node) To wired network Ad-Hoc Cluster 2 20

21 Cognitive Radio Techniques: Selected Research Results 21

22 Reactive Schemes: Case study of & 16 in shared unlicensed band b(~500m) and a (~10Km) coexist by applying reactive schemes to avoid interference Dynamic Frequency Selection (DFS): Radio Scans each channel and calculates interference power level Typical scanning interval is averaged 100ms Choose the channel with least interference for communication Power Control (PC): The receiver senses interference power level and calculates the minimum required transmit power and feedback to the transmitter The transmitter uses minimum transmit power for communication 22

23 & 16 Co-Existence: Simulation Parameters a b Traffic Type UBR (Poisson arrival), UDP packet, 512 Bytes datagram MAC protocol TDMA IEEE BSS mode Channel Model AWGN, two ray ground propagation model, no fading Bandwidth/channels 20 MHz / 4 non-overlapping chs 22MHz / 11 overlapping chs Bit Rate 13Mbps 2Mbps Radio parameters OFDM (256-FFT, QPSK) DSSS (QPSK) Background Noise -174 dbm/hz Rx Noise Figure 9 db 9 db Receiver Sensitivity -80dBm (@BER 10^-6) -82dBm (@BER 10^-5) Antenna Height BS 15m, SS 1.5m 1.5m Tx Power/Max range 33dBm / 3.2Km 20dBm / 500m Default channel Channel 1 : centered at 2412GHz Channel 1 : centered at 2412GHz Available channels 4 (non-overlap) 12 (overlapping) 23

24 & 16 Co-Existence: Power Control Results Observations: throughput can improve up to 3 times at the expense of throughput degradation < 10% (e.g. at D=2.5Km) If two systems are too near to each other, power control may not work DL Throughput (Kbps) Both PC OFF Both PC ON BS-SS Distance (meters) 4 links for hotspot, each has Poisson arrival with mean 3ms hotspot is 3Km away from BS hotspot Average Link throughput (Mbps) Both PC OFF Both PC ON BS-SS Distance (meters) Down Link Throughput Average Link Throughput 24

25 CSCC Spectrum Etiquette Protocol CSCC( Common Spectrum Coordination Channel) can enable mutual observation between neighboring radio devices by periodically broadcasting spectrum usage information Service channels Edge-of-band coordination channel 25

26 CSCC: Protocol Stack CSCC-PHY: 1Mbps b with 10 mw power (~100 m range) CSCC-MAC: Simple periodic broadcast with randomization (100ms~seconds) to eliminate repeated collisions 26

27 CSCC: Packet Format Dest addr Src addr Type IE length IE(1) IE(n) 6B 6B 2B 2B 2B 2B CSCC-PKT: A standard Ethernet packet format with control payload (consisting of variable length information elements) CSCC radio (802.11) MAC Address (48bits) MAC Address Device Name and Device Name and Description (64bits) and Description Type (8b) Channel(8b) Priority (8b) Price_bid(8b) Service Time Duration (32b) Tx Pwr (8b) Rx Pwr (8b) CSCC packet used in WLAN-Bluetooth prototype at WINLAB 27

28 CSCC: Proof-of-Concept Experiments WLAN-BT Scenario Different devices with dual mode radios running CSCC d=4 meters are kept constant Priority-based etiquette policy 28

29 CSCC: Experimental Parameters WLAN nodes Bluetooth nodes Mobility Static without mobility BT1 static, BT2 position varies Traffic Model 100M bytes data by TCP 1.5M bytes data using Stop-and-wait scheme MAC protocol IEEE b at 11Mbps Bluetooth ACL data link Data card Cisco Aironet 350 series DS (at channel #1) Ericsson BT w/ USB (hopping over whole band) CSCC MAC IEEE & periodic announcements at 1Mbps CSCC card Cisco Aironet 350 series DS (at channel #11) 29

30 CSCC Results: Throughput Traces Observations: WLAN session throughput can improve ~35% by CSCC coordination BT session throughput can improve ~25% by CSCC coordination WLAN = high priority 65 Bluetooth = high priority WLAN Throughput (Mbps) CSCC on CSCC off Bluetooth Throughput (Kbps) CSCC on CSCC off Time (Seconds) WLAN session with BT2 in initial position Time (Seconds) BT session with BT2 in initial position 30

31 Adaptive Wireless Networks: Ad-hoc Discovery and Self-Organization Spectrum etiquette channel used to initiate discovery and network bootstrap Expanded beacon signals transmitted by each radio in CSCC Note that each link may use a different PHY/MAC -> cognitive radio switches between links dynamically, while using mutually agreed routing protocol B s beacon (may be in CSCC) B s transmission range End-to-end routed path From A to D PHY B (~100 Mbps) B Control connection A C s beacon (may be in CSCC) C D D PHY A (~50 Mbps) Data path C s transmission range Node ID PHY spec Tx power MAC spec Neighbor table Routing bootstrap. Example of Beacon Payload 31

32 Adaptive Networks: Ad-hoc Discovery Protocol Implementation WINLAB s SOHAN based ad-hoc prototype demonstrates aspects of self-organization that can be extended to cognitive radio Internet Self-organized ad-hoc network AP coverage area Forwarding Node (FN) MN Low-tier (e.g. sensor) Mobile Node (MN) FN MN AP MN FN FN MN MN AP Access Point (AP) MN MN FN coverage area MN Low-tier access links (AP/FN Beacons, MN Associations, Data) Ad-hoc infrastructure links between FNs and APs (AP/FN Beacons, FN Associations, Routing Exchanges, Data) AP Source MAC Broadcast MAC Node ID Packet Type Cluster ID Sequence Number Node Type FN Scan all channels Find minimum delay links to AP Set up routes to AP Send beacons Forward SN data Hops To AP Transmit Power FN Assoc Channel 2 Transmit Power Required: 1mW Beacon Beacon Channel 4 Transmit Power Required: 4mW SN Scan all channels Associate with FN/AP Send data Beacon Frame Format 32

33 Adaptive Networks: Discovery Algorithm Performance Results NS-2 extended to support Hierarchical net with APs, FNs, MNs Multiple interfaces Multiple channels Distributed and optimal centralized algorithms 2 APs, 4 FNs, 10 SNs CBR traffic of 64 byte packets 1000 m x 1000 m area 1 Mbps radios..significant reductions in routing overhead & energy used 33

34 Adaptive Networks: Ad-Hoc Routing/Discovery Implementation Protocol stack at each layer 34

35 Adaptive Networks : SOHAN Experimental Results Experimental Setup Packet delivery ratio Gains in system capacity and per-user throughput achievable relative to WLAN BSS mode or comparable flat ad-hoc mesh, particularly when FN s use multiple radio channels... 35

36 Cognitive Radio: Hardware Platforms Next-generation software-defined radio supporting fast spectrum scanning, adaptive control of modulation waveforms and collaborative network processing Facilitates efficient unlicensed band coordination and multi-standard compatibility between radio devices Megarray Connector- 244 Configurable I/O pins XC2V6000 FPGA TMS320C BaseT Ethernet MPC8260 Bell Laboratories Software Defined Radio (Baseband Processor) Courtesy of Dr. T. Sizer 36

37 Cognitive Radio: Hardware Platforms Vanu Inc. SDR programmable radio based on commodity processors. Supports multiple standards on handheld device. Vanu Inc. Software Defined Radio Source: 37

38 Cognitive Radio: Hardware Platform Requirements include: Agile radio I/O Software defined modem Network Processor ~Ghz spectrum scanning, - Etiquette policy processing - PHY layer adaptation (per pkt) - Ad-hoc network discovery Wakeup Clock Mgmt - Multi-hop routing ~100 Mbps+ radio A/D D/A Packet Buffer DRAM) radio A/D D/A Baseband FPGA Baseband Processor Core (DSP) Packet FPGA radio A/D D/A SRAM Host (CR Strategies) Local ethernet drop WINLAB s network centric concept for cognitive radio prototype (..under development in collaboration with GA Tech & Lucent Bell Labs) 38

39 Concluding Remarks 39

40 Concluding Remarks: ORBIT Testbed Open-access next-generation wireless network testbed being developed at Rutgers for NSF network research testbeds (NRT) program Large scale radio grid emulator for evaluating new concepts for future wireless networks, e.g. ad-hoc networks, cognitive radio protocols,... Also, outdoor field trial network with open-interface 3G & WLAN for realworld application work Research User of Testbed ns-2+ scripts & code downloads Global Internet Global Internet Static radio node Emulator Mapping Firewall High Speed Net Mobility Server Open API 3G BTS ORBIT radio node Radio link emulation Wired routers Open API Access Point (802.11b) 3G access link Ad-hoc link End-user devices 1. Radio Grid for Lab Emulation 2. Field Trial Network 40

41 Concluding Remarks: ORBIT Radio Grid 41

42 ORBIT: Field Trial System Lucent Base Station Router with IP interface Open API a,b,g ORBIT radio node 42

43 Concluding Remarks Future wireless networks need ~ x increases in density and bit-rate of radios motivates better spectrum coordination methods Spot shortages of spectrum will occur if present static allocation is continued significant improvement achieved with dynamic allocation Cognitive radio technologies can be characterized in terms of the combination of hardware complexity and level of protocol coordination Possible cognitive radio schemes include Agile radio with interference avoidance Spectrum etiquette protocols: spectrum server, CSCC.. Adaptive networks via ad-hoc collaboration Early technical results now available for some of these methods, but very different complexity factors and market implications 43

44 Concluding Remarks Future research areas in cognitive radio include: New concepts and algorithms for agile radio and spectrum etiquette protocols Architecture and design of adaptive wireless networks based on cognitive radios Detailed evaluation of large-scale cognitive radio systems using alternative methods Spectrum measurement and field validation of proposed methods Cognitive radio hardware and software platforms User-level field trials of emerging cognitive radios and related algorithms/protocols may also be useful to gain experience Controlled testbed experiments comparing different co-existence methods Large-scale spectrum server trial for x coordination Experimental deployments in proposed US FCC cognitive radio band Success with cognitive radio technologies should lead to major improvements in spectrum efficiency, performance and interoperability 44