Cognitive Radio: Ten Years of Experimentation and · PDF fileCognitive radio (CR), in its original meaning, is a wireless communication paradigm utilizing all ... versal Software Radio

INTRODUCTION

Cognitive radio (CR), in its original meaning, isa wireless communication paradigm utilizing allavailable resources more efficiently with the abil-ity to self-organize, self-plan, and self regulate[1]. In its narrow, however far more popularizeddefinition, CR-based technology aims to combatscarcity in radio spectrum using dynamic spec-trum access (DSA) [2]. DSA technologies arebased on the principle of opportunistically usingavailable spectrum segments in a somewhatintelligent manner.

Implementation and experimentation workhas ramped up in the latter half of the decade.Because of the complexities involved in design-ing and developing CR systems [3, 4], moreemphasis has been placed on the development ofhardware platforms for full experimentation andtesting of CR features. Since 1999, the first timethe term cognitive radio was used in a scientificarticle [1], numerous different platforms andexperimental deployments have been presented.These CR testbeds differ significantly in theirdesign and scope. It is now appropriate to askhow mature these platforms are, what has been

learned from them, and if any trends from theanalysis of functionalities provided by these plat-forms can be identified. This article answersthese questions.

This article has three main sections and con-tributions. First, we present a primer on thecommon systems being used for CR researchand development. The following section focuseson overviews of the key events in recent yearsthat have helped progress the field of CR andDSA technologies. We then present insightsgained from these experiences and look ahead athow the community can grow in the comingyears. We conclude in the final section.

CR IMPLEMENTATION:PLATFORMS AND SYSTEMS

We briefly review the most popular existinghardware and software radio systems, dividingthese platforms into two headings. First, we dealwith reconfigurable software/hardware systems,where the majority of the radio functionality,like modulation/coding/medium access control(MAC) and other layer processing, is performedin software. The burden in terms of processingand functionality on the radio frequency (RF)front-end is intended to be minimal in thesecases. Second, we take a look at composite sys-tems comprising a combination of purely soft-ware and hardware-based signal processingelements (e.g., field-programmable gate arrays[FPGAs]).

RECONFIGURABLESOFTWARE/HARDWARE PLATFORMS

We begin by focusing on three research-orientedsystems: OSSIE, GNU Radio, and Iris.

OSSIE — The Open Source SCA Implementa-tion::Embedded (OSSIE) project is an opensource software package for SDR development[5]. OSSIE was developed at Virginia Tech, andhas become a major Linux-based open sourceSDR software kit, sponsored by the U.S. Nation-

IEEE Communications Magazine • March 20112 0163-6804/11/$25.00 © 2011 IEEE

This material is based onwork supported by ScienceFoundation Ireland underGrant no. 03/CE3/I405 aspart of CTVR at the Uni-versity of Dublin, TrinityCollege, Ireland.

ABSTRACT

The year 2009 marked the 10th anniversaryof Mitola and Maguire Jr. introducing the con-cept of cognitive radio. This prompted an out-pouring of research work related to CR,including the publication of more than 30 specialissue scientific journals and more than 60 dedi-cated conferences and workshops. Although thetheoretical research is blooming, with manyinteresting results presented, hardware and sys-tem development for CR is progressing at aslower pace. We provide synopses of the com-monly used platforms and testbeds, examinewhat has been achieved in the last decade ofexperimentation and trials relating to CR, anddraw several perhaps surprising conclusions.This analysis will enable the research communityto focus on the key technologies to enable CR inthe future.

COGNITIVE RADIO NETWORKS

Przemyslaw Pawelczak, University of California, Los Angeles

Keith Nolan and Linda Doyle, University of Dublin, Trinity College

Ser Wah Oh, Institute for Infocomm Research

Danijela Cabric, University of California, Los Angeles

Cognitive Radio: Ten Years ofExperimentation and Development

PAWELCZAK LAYOUT 2/1/11 4:01 PM Page 2

IEEE Communications Magazine • March 2011 3

al Science Foundation (NSF) and the Joint Tac-tical Radio System (JTRS), among others.OSSIE implements an open source version ofthe Software Communication Architecture(SCA) development framework supporting SDRdevelopment initiated by the U.S. Departmentof Defense, and it supports multiple hardwareplatforms. Further information is available athttp://ossie.wireless.vt.edu. OSSIE is mostly usedat Virginia Tech.

GNU Radio — Arguably, the software definedradio (SDR) system with the most widespreadusage is the open source GNU Radio project(http://www.gnuradio.org). It supports hardware-independent signal processing functionalities.Beginning in 2001 as a spin-off of the Mas-sachusetts Institute of Technology’s (MIT’s)PSpectra code originating from the Spec-trumWare project, the GNU Radio software wascompletely rewritten in 2004. Signal processingblocks are written in C and C++, while the sig-nal flow graphs and visualization tools are main-ly constructed using Python. GNU Radio iscurrently one of the official GNU projects hav-ing strong support from the international devel-opment community. A wide range of SDRbuilding blocks are available, including onescommonly used to build simple CR-like applica-tions (e.g., energy detection). The GNU Radioproject prompted the development of the Uni-versal Software Radio Peripheral (USRP) hard-ware by Ettus Research LLC, described later.

Iris — Iris is a dynamically reconfigurable soft-ware radio framework developed by the Univer-sity of Dublin, Trinity College. This is ageneral-purpose processor-based rapid prototyp-ing and deployment system. The basic buildingblock of Iris is a radio component written inC++, which implements one or more stages of atransceiver chain. Extensible Markup Language(XML) is used to specify the signal chain con-struction and characteristics. These characteris-tics can be dynamically reconfigured to meetcommunications criteria. Iris works in conjunc-tion with virtually any RF hardware front-endand on a wide variety of operating systems.

A wide range of components have beendesigned for Iris that are focused on CR-like sys-tems. Multiple sensing components ranging fromsimple energy detection to more sophisticatedfilter bank and feature-based detection compo-nents are available. A suite of components fordynamically shaping and sculpting waveforms tomake best use of available white space, or com-ponents that enable frequency rendezvousbetween two systems on frequencies that are notknown a priori, have also been developed. Fordevelopment purposes Iris can also interfacewith Matlab. Iris is predominantly used by thedevelopment group at the University of Dublin,Trinity College.

RF Front-Ends — GNU Radio and Iris aredesigned to carry out the majority of signal pro-cessing in software. However, each systemrequires a minimal hardware RF front-end.

USRP — The most commonly used RF front-

end, especially in the research world, is the Uni-versal Software Radio Peripheral (USRP). TheUSRP is an inexpensive RF front-end and acqui-sition board with open design and freely avail-able documentation and schematics. The USRPis highly modular; a range of different RF daugh-terboards for selected frequency ranges may beconnected.

Two types of USRP are available. USRP 1.0contains four high-speed analog-digital convert-ers (ADCs) supporting a maximum of 128Msamples/s at a resolution of 14 bits with 83 dBspurious-free dynamic range, an Altera CycloneFPGA for interpolation, decimation, and signalpath routing, and USB 2.0 for the connectioninterface. USRP 2.0 replaces the Altera FPGAwith a Xilinx Spartan 3-2000 FPGA, gigabit Eth-ernet, and an ADC capable of 400 Msamples/swith 16-bit resolution. The reader is directed tohttp://wwww.ettus.com for further information.

Other RF Front-Ends — A limited number ofother RF front-ends are also available for usewith these systems. These include the Scaldioflexible transceiver from IMEC, Belgium(http://www2.imec.be/ be en/research/green-radios/cognitive-radio.html), and the MaynoothAdaptable Radio System from the National Uni-versity of Ireland, Maynooth [6].

COMPOSITE SYSTEMSThe boundary between hardware and softwareframeworks (or platforms) is not as straightfor-ward as might be assumed. The emphasis inreality is on reconfigurability. A number of com-posite platforms exist which have both softwareand hardware components that can be used tofacilitate CR systems. Composite systems differfrom reconfigurable software/hardware plat-forms in that composite systems contain all therequired components (dedicated hardware andsoftware, documentation, ready-made softwarepackages and modules, etc.) that allow for imme-diate CR development.

Iris began life on a general-purpose processorbut has also migrated to an FPGA platform. Onthe FPGA platform, components can be run insoftware on the PowerPC and/or in hardware onthe FPGA logic. The main Iris framework runson the PowerPC with many of the componentsmentioned above in the FPGA logic.

BEE — The Berkeley Emulation Engine (BEE)and its successor BEE2 are two hardware plat-forms developed by the University of Californiaat Berkeley Wireless Research Center. BEE2consists of five Xilinx Vertex-II Pro VP70FPGAs in a single compute module with 500giga-operations/s. These FPGAs can parallelizecomputationally intensive signal processing algo-rithms even for multiple radios. In addition todedicated logic resources, each FPGA embeds aPowerPC 405 core for minimized latency andmaximized data throughput between micropro-cessor and reconfigurable logic. To support pro-tocol development and interfaces between othernetworked devices, the PowerPC on one of theFPGAs runs a modified version of Linux and afull IP protocol stack. Since FPGAs run at clockrates similar to those of the processor cores, sys-

Composite systems

differ from

reconfigurable

software/hardware

platforms in that

composite systems

contain all the

required components

(dedicated hardware

and software, docu-

mentation, ready

made software pack-

ages and modules,

etc.) that allow for

immediate CR

development.


IEEE Communications Magazine • March 20114

tem memory, and communication subsystems, alldata transfers within the system have tightlybounded latency and are well suited for real-time applications. In order to interface this real-time processing engine with radios and otherhigh-throughput devices, multigigabittransceivers (MGTs) on each FPGA are used toform 10 Gb/s full-duplex links. Eighteen suchinterfaces per BEE2 board are available, allow-ing 18 independent radio connections in an arbi-trary network configuration. The BEE2 withnetwork and Simulink capabilities can be usedfor experimenting with CRs implemented onreconfigurable radio modems and in the pres-ence of legacy users or emulated primary users.Further information is available at http://bee2.eecs.berkeley.edu.

WARP — The Wireless Open-Access ResearchPlatform (WARP) (http://warp.rice.edu) fromRice University, Houston, Texas, is a completehardware and software SDR design. WARPhardware is very similar in approach to USRP. Amotherboard serves as an acquisition board,while daughterboards serve as data collectionboards. As of December 2009, two versions ofmotherboards were available. The version 2.2motherboard is connected to a PC via a gigabitEthernet interface. Motherboard processing isperformed by a Xilinx Virtex-II Pro FPGA. Fourindependent motherboards can be connected atthe same time. ADCs operating at 65 Msam-ples/s with 14-bit resolution are available. Soft-ware development for WARP is multilayered. Itranges from low-level very-high-speed integratedcircuit hardware description language (VHDL)coding to Matlab modeling. Xilinx Matlab exten-sions for VHDL are available, and the code forWARP is widely open. As of December 2009, 21demo implementations of different wirelessfunctionalities using WARP originated fromRice University itself, while 17 are from otherinstitutions around the world.

KUAR — The Kansas University Agile Radio(KUAR) was an experimental hardware plat-form intended for the 5.25–5.85 GHz unlicensednational information infrastructure (UNII) fre-quency band with a tunable range of 30 MHz[7]. It featured a Xilinx Virtex II Pro P30 FPGA

with embedded PC for signal processing, fourindependent interfaces between the FPGA andembedded PC, and used an ADC with 105Msamples/s and 14-bit resolution. The KUARapproach allows split processing between theembedded PC platform and FPGA. KUAR usesmodified GNU Radio software to implement itssignal processing features.

Other Platforms — Many other custom SDRplatforms are available that are unique in bothhardware and software design. However, weneed to emphasize that these platforms simplyprovide appropriate hardware and software forthe digital processing required, integrated withan RF front-end. Hence, the user of these prod-ucts does not need to look for a standalone RFfront. Some commercial platforms such as theLyrtech solutions (http://www.lyrtech.com)among others also exist but are not consideredin this article. The summary of described compo-nents, along with additional parameters, is pre-sented in Table 1.

OTHER SYSTEMSIn addition to the software-centric and compos-ite systems described in this article, it is impor-tant to note that several standalone componentshave also been developed. The need for spec-trum sensing, an important aspect of CR func-tionality, has been a driver for this developmentwork. Examples include Rockwell Collins,IMEC, and sensing devices from the Institute forInfocomm Research (I2R), Singapore, which isaddressed later in this article.

Finally, there are some well known DSA-focused SDR platforms that are not used direct-ly in CR experimentation at the moment. Themost prominent ones include the JapaneseNational Institute of Information and Communi-cations Technology SDR Platform [6, Sec. 3.3],FlexRadio and PowerSDR used mainly for ama-teur radio work (http://www.flex-radio.com), andSoftRock kits (http://www.dspradio.org).

BUILDING CR AND DSA SYSTEMS:EXPERIMENTATION AND TRIALS

Following the brief synopses of the key systems

Table 1. Summary of popular development solutions for CR, see also [6, Table 2].

USRP2 KUAR WARP BEE2

RF bandwidth (MHz) 100 30 40 64

Frequency range (GHz) DC-5 (non continuous) 5.25–5.85 2.4–2.5 (4.9–5.87) 2.39–2.49

Processing architecture FPGA FPGA FPGA FPGA

Connectivity gigabit Ethernet USB/Ethernet gigabit Ethernet Ethernet

No. of antennas 2 2 4 18

ADC performance 400 MS/s, 16 bit 105 MS/s, 14 bit 125 MS/s, 16 bit 64 MS/s, 12 bit

Community support yes no (defunct) yes no

In addition to the

software-centric and

composite systems

described in this

article, it is important

to note that several

stand-alone compo-

nents have also been

developed. The need

for spectrum sens-

ing, an important

aspect of CR func-

tionality, has been a

driver for this devel-

opment work.



enabling SDR and CR development, we proceedto the second main part of this article. We startwith describing the experimental results of multi-ple platform interactions during recent SDR,CR, and DSA-focused conferences.

OVERVIEW OF IMPORTANT CR EXPERIMENTSConference Demonstrations — In the latterpart of the last decade, some independent con-ference venues featured demonstration sessions.The information relating to these events formsour starting point. We focus mostly on thedemonstrations presented at IEEE DySPAN andSDR Forum (now Wireless Innovation Forum)conferences, which are the most recognized andlargest directly related events in the community.

A demonstration track was first established inthe IEEE DySPAN conference series in 2007.Since that year there have been a total of 22demonstrations. The SDR Forum annual techni-cal symposium, run by the SDR Forum since1996, organized their first demonstration track in2007. The demonstrations presented that yearcomprised only SDR platforms and developmentkits for engineers. In 2008 real demonstrationswere presented. In total, 12 demo platformswere shown, among them three that were relatedto DSA. During the 2009 SDR Forum confer-ence event, 10 demonstrations were presented,among them three related to DSA systems.Important demos presented outside of these twovenues are also included in this survey. TheAssociation for Computing Machinery (ACM)MobiCom ’09 included only one CR-like demofrom RWTH, Aachen University, Germany. In2008 ACM MobiCom featured one CR demofrom Microsoft Research, China. ACM SIG-COMM ’09 included one demonstration fromthe University of Dublin, Trinity College.

The survey data for this article were collectedas follows. From the publicly available data oneach demonstration, we have extracted informa-tion related to the waveforms used, frequencyranges, form of spectrum sensing, transmit orreceive capabilities, control channel usage, typeof application used, sponsoring body, and num-ber of developers. We focused only on actualdemonstrations, ignoring demos that were eitherpresenting development frameworks only, orbased on SDR and reconfigurable platforms thatwere not related to CR or DSA systems. In total,we have identified 41 relevant demonstrations.For detailed information on each demonstrationplatform the reader is referred to the respectiveconference proceedings. The data are as follows:• IEEE DySPAN ’10:

–Wright State University, Army Research,United States: “Spectrally Modulated Spec-trally Encoded Platform”; sponsored byinternal funds–University of Dublin, Trinity College, Ire-land, European Union (EU): “OFDMPulse-Shaping for DSA; Multi-CarrierCDMA for DSA”; both sponsored by Sci-ence Foundation Ireland–Institute for Infocomm Research, Singa-pore: “Communication in TV WhiteSpaces”; sponsored by Singapore Agencyfor Science, Technology and Research–IMEC, Belgium, EU: “Wideband Spec-

trum Sensor”; sponsored by internal funds–RWTH, Germany, EU: “Policy Engine forHome Networks”; sponsored by GermanResearch Foundation and EU ARAGORNProject; “OFDM Adaptation Based onSpectrum Sensing”; sponsored by GermanResearch Foundation; “DecomposableMAC Framework”; sponsored by GermanResearch Foundation and EU 2PARMAproject–Communications Research Center, Cana-da: “WiFi Network with Spectrum Sens-ing”; sponsored by internal funds–University of Notre Dame, United States:“Primary User Traffic Pattern Detection”;sponsored by U.S. National Science Foun-dation and National Institute of Justice

• SDR Forum ’09:–University of Oulu, Finland, EU: “MobileAd Hoc Network with Opportunistic CRMAC”; sponsored by internal funds–IMEC, Belgium, EU: “Wideband Spec-trum Sensor”; (also IEEE DySPAN ’10),sponsored by internal funds–University of Piraeus, Greece, Alcatel-Lucent, Germany, EU: “Dynamic RadioAccess Technique Re-Configuration”; spon-sored by the EU E2R Project

• ACM MobiCom ’09:–RWTH, Germany, EU: “CR Capacity Esti-mation”; sponsored by German ResearchFoundation and EU ARAGORN project

• ACM SIGCOMM ’09:–University of Dublin, Trinity College, Ire-land, EU: “An FPGA-Based AutonomousAdaptive Radio”; sponsored by ScienceFoundation Ireland

• SDR Forum ‘08:–University of Dublin, Trinity College, Ire-land, EU: “Cyclostationary SignatureEmbedding and Detection” (see IEEE DyS-PAN ‘07); sponsored by Science Founda-tion Ireland–Shared Spectrum Company, United States:“XG Radio”; sponsored by DARPA XGProgram–Virginia Tech, United States: “MultinodeCR Testbed”; sponsorship informationunknown

• ACM MobiCom ’08:–Microsoft Research, China: “WiFi Net-work on TV Bands”; sponsored by internalfunds

• IEEE DySPAN ’08:–TU Delft, University of Twente, Nether-lands: “Non-Continuous OFDM with Spec-trum Sensing”; sponsored by Dutch AAFFreeband Program–Philips Research, United States: “IEEE802.11a with Frequency Adaptation”; spon-sored by internal funds–Adaptrum, United States: “Wireless Micro-phone Detection”; sponsored by internalfunds–University of Dublin, Trinity College, Ire-land, EU: “Cyclostationary SignatureEmbedding and Detection” (also SDRForum ‘08); “Point to Point DSA Link withSpectrum Sensing”; both sponsored by Sci-ence Foundation Ireland

In the latter part of

the last decade,

some independent

conference venues

featured demonstra-

tion sessions. The

information relating

to these events

forms our starting

point. We focus

mostly on the

demonstrations pre-

sented at the IEEE

DySPAN and SDR

Forum (now Wireless

Innovation Forum)

conferences.



–Virginia Tech, United States: “Heteroge-neous Cooperative Multinode DSA net-work”; sponsored by U.S. National Instituteof Justice, National Science Foundation,and DARPA–Institute for Infocomm Research, Singa-pore: “Transmission over TV WhiteSpaces”; sponsored by the Singapore Agen-cy for Science, Technology and Research–Motorola, United States: “WiFi-LikeOperation in TV Bands”; sponsored byinternal funds–Omesh Networks, United States: “ZigBee-Based Self-Configured Network”; spon-sored by internal funds–Rockwell Collins, United States: “Spec-trum Sensor and Signal Classifier”; spon-sored by the DARPA XG Program–Shared Spectrum Company, United States:“XG Radio”; sponsored by the DARPAXG Program–University of South Florida, United States:“Spectrum Sensing with Feature Detec-tion”; sponsored by internal funds–University of Utah, United States: “HighResolution Spectrum Sensing”; sponsoredby internal funds

• IEEE DySPAN ’07:–Shared Spectrum Company, United States:“XG Radio”; sponsored by the DARPAXG Program–Motorola, United States: “WiFi-Like Net-work in Licensed Bands”; sponsored byinternal funds–Virginia Tech, United States, University ofDublin, Trinity College, Ireland, EU: “Cog-nitive Engine-Based Radio Reconfigura-tion”; sponsored by Science FoundationIreland

–University of Dublin, Trinity College, Ire-land, EU: “Cyclostationary SignatureEmbedding and Detection” (also SDRForum ’08); sponsored by Science Founda-tion Ireland–University of Kansas, United States:“KUAR Presentation”; sponsored by theU.S. National Science Foundation,DARPA, and the Department of the Interi-or National Business Center–QinetiQ, United Kingdom: “SpectrumMonitoring Framework”; sponsored byinternal funds–SRI International, United States: “PolicyReasoner Combined with SSC XG Radios”;sponsored by the DARPA XG Program–University of Dublin, Trinity College, Ire-land, EU: “Extensions to XG Policy Lan-guage”; sponsored by Science FoundationIreland–University of Twente, Netherlands, EU:“Spectrum Monitoring Device”; sponsoredby the Dutch Adaptive Ad Hoc Free BandWireless Communications (AAF) Program

IEEE DySPAN ‘07 — During the first ever trialof its kind during IEEE DySPAN ’07, QinetiQ(a U.K. Ministry of Defense contractor) andShared Spectrum Company carried out a simul-taneous transceiver operation test in the UHFband. Data from the evaluation are not publical-ly available as it was considered proprietaryinformation. However, it was found that theShared Spectrum Company’s detect-and-avoidsystem could coexist with a very fast hopping sin-gle-carrier system in the same frequency band.Further information regarding the demonstra-tions is available at http://www.ieee-dyspan.org/2007. A wireless trial licence was issued by theCommission for Communications Regulation(Comreg) in Ireland for multiparty trials in thiscase. Further information is available at http://www.testandtrial.ie.

IEEE DySPAN ‘08 — IEEE DySPAN ’08 fea-tured 13 live demonstrations comprising Tx/Rxand Rx-only systems. A special temporaryauthority license was issued by the FCC for the482–500 MHz frequency range, allowing multi-ple companies and academic institutions to occu-py and interfere with each other for the durationof the event. The University of Dublin — TrinityCollege, Shared Spectrum Company (using XGnodes), I2R, University of Utah, Stevens Insti-tute of Technology, OMESH Networks, VirginiaTech, and Motorola demonstrated DSAtransceiver systems. Adaptrum, Philips, the Uni-versity of South Florida, Anritsu, RockwellCollins, and TU Delft carried out signal detec-tion and analysis work using these transmissionsources. This location features several high-power analog TV transmitters in the immediatevicinity. The trials demonstrated that DSA sys-tems and networks could be established andmaintained even in close proximity to thesehigh-power TV services and even in Chicago’sextremely crowded RF environment. Furtherinformation is available at http://www.ieee-dys-pan.org/2008.

Figure 1 is an example waterfall plot obtained

Figure 1. Measurement results example from IEEE DySPAN '08. In the water-fall plot the narrowband signal is a FM transmission and the broadband signalis an XG radio. The waterfall spans approximately 60 seconds of measure-ment.



using an Anritsu MS2721B handheld analyzerinside the conference demo room spanningapproximately 1 min. The wideband signal isShared Spectrum Company’s orthogonal fre-quency-division multiplexing (OFDM) signalfrom the XG nodes. This was operating on a dono harm basis and simply vacated any channelwhere the received signal level from a non-XGsignal exceeded –90 dBm. In one scenario, a nar-rowband FM signal modulated with a 1 kHz sinewave was swept up and down in the frequencyband to serve as a potential interferer to XG. Itis clearly seen that the XG signal did move to avacant channel. This proved that DSA is possibleeven in the shadow of extremely powerful adja-cent channel TV transmissions. However, thisalso demonstrated the weakness of an energydetection do no harm approach. As an exampleof a simple denial of service attack demonstra-tion, it was possible to trigger the XG signal tochange channels as the detection system wasenergy-threshold-based. In some cases the XGand narrowband source appear on the same fre-quency. This is because the transmitted power ofthe narrowband interferer was reduced, and didnot exceed the XG system detection threshold.

IEEE DySPAN ‘10 — IEEE DySPAN ’10 fea-tured 10 demonstrations of DSA systems. Whilesome of the demonstrations possessed the capa-bility to transmit, as was the case with the Uni-versity of Notre Dame and CommunicationsResearch Centre Canada devices, all of themused license-exempt bands only. Two demos, onefrom RWTH, Aachen University, and one fromUniversity of Dublin, Trinity College, demon-strated the capability of non-contiguous OFDMtransmission end effective subcarrier suppressiontechniques, again showing the demonstrationusing the license-exempt channels only.

Key Commercial Experimentation and Trials— This section presents brief overviews of keycommercial trials and experimentation work car-ried out in recent years that have broken newground and helped influence the direction of CRand DSA research.

DARPA XG Experimentation — DARPA XGradio was manufactured by Shared SpectrumCompany in the early 2000s [8]. It is an imple-mentation of a DSA system using interferencedetection and avoidance techniques. A policyengine is used for frequency selection and access.The XG radio uses the IEEE 802.16 physicallayer, with a 1.75 MHz bandwidth OFDM signaland 20 dBm transmit power. All nodes in thenetwork use a common frequency, despite theavailability of more channels at a certain pointof time.

One of the most interesting field trial resultswere presented in [8] by the Defense AdvancedResearch Projects Agency (DARPA) XG pro-gram. The DARPA XG trial was presumably thefirst private CR system trial ever. On August15–17, 2006 the U.S. Department of Defense’sDARPA demonstrated the capabilities of XGradios to work on a CR-like basis. Tests wereperformed at different locations in Virginia. Sixmobile nodes were involved in the demonstra-

tions, and as the authors claim, a demonstrationwas successful, proving that the idea of listenbefore talk communication equipped with policy-based reasoning in radio access is fully realiz-able. The system demonstrated very shortchannel abandon times of less than 500 ms (i.e.,the time during which the device ceased commu-nication at a certain channel and vacated it) andshort reestablishment times (i.e., less than 200ms) given the lack of pre-assigned frequencies.The reestablishment time is the time taken forthe device to select a new channel and resumecommunications.

The channel abandon goal of 500 ms wasmostly met, and problems were mostly due tosoftware and IEEE 802.16 modem glitches. Dur-ing the experiment U.S. Department of Defenseradios were operating in the 225–600 MHzrange, and XG radios were selecting unused fre-quency channels in this range (i.e., one out of sixpossible), where the number of all possible chan-nels to select was an implementation choice.

Experiences from Spectrum Sensing in theTV Bands — The most prominent hardwaretrial for spectrum sensing thus far has been theFCC field trial conducted in 2008 by the Officeof Engineering and Technology (OET). Fivehardware prototypes from Adaptrum, I2R Singa-pore, Microsoft Corporation, Motorola Inc., andPhilips Electronics North America were submit-ted for examination. The tests covered TV sig-nals and Part 74 wireless microphone signals, ina laboratory controlled environment as well asthe actual field. All devices supported sensing ofTV signals, while the I2R, Microsoft, and Philipsdevices also supported wireless microphonesensing.

TV Sensing Laboratory Test: In general, alldevices exhibited good sensitivities (better thanthe –114 dBm threshold established by the FCC[9]) in the laboratory single channel test. ThePhilips device in particular achieved the bestsensitivity in clean signal environment while theMicrosoft device had the best performance incaptured signal tests. Most devices were able tomaintain good sensitivities when the adjacentchannel power was within manageable levels forthe devices [10, Table 3-1] for adjacent channeltest results. However, the sensitivities were notdetermined in some cases due to insufficientselectivity, receiver desensitization, or devicemalfunction. From the measurable detectionthresholds, the I2R device threshold was betterthan –114 dBm for all cases except for one whenthe N + 1 adjacent signal level is at –28 dBm.The Philips device exhibited the best perfor-mance at low adjacent signal level of –68 dBm.Nevertheless, the future spectrum sensing hard-ware development should tackle the issues oflack of receiver selectivity and receiver desensiti-zation, especially when the adjacent channelshave high powers.

TV Sensing Field Test: Four test conditions(Table 2) were considered by the FCC [10]. Twoof these test conditions involved the white spacedevice (WSD) operating within the service con-tour of a station assigned to the channel. Forcondition I, the broadcast signal was viewable ona representative consumer TV, and for condition

In some cases, the

XG and narrowband

source appear on

the same frequency.

This is because the

transmitted power of

the narrowband

interferer was

reduced, and did not

exceed the XG

system detection

threshold.


II, the broadcast signal was not viewable on arepresentative consumer TV. For condition II,we note that there is no mechanism to deter-mine whether a TV signal actually exists in themeasurement locations.

All devices, under condition I tests, met theintended probability of detection of over 90 per-cent for ATSC channels. The geolocationdatabase approach from Motorola was able toidentify occupied channels with 100 percentaccuracy. For identification of unoccupied chan-nels, the I2R device exhibited the best perfor-mance, but not with complete reliability.Ironically, the geolocation-database-basedapproach did not exhibit the best performance inthis aspect, presumably due to incomplete infor-mation in the database. This shows that spec-trum sensing alone works to some degree, butthe performance could be further enhancedespecially in the identification of unoccupiedchannels. Combining a geolocation databasewith spectrum sensing may be a better optiondepending on the specific deployment scenarioin mind.

Wireless Microphone Test: The field tests forwireless microphone sensing were performedwith the I2R and Philips devices at two locations.The Philips device reported all of the channelson which the microphones were designated totransmit as occupied whether the microphonewas transmitting or not. The I2R device indicat-ed several channels as available even when themicrophones were on. The wireless microphonefield tests at first glance did not seem to giveconvincing results in the capability of the submit-ted WSDs to detect wireless microphone signalsreliably. Nevertheless, the White Space Coalition(WSC) later found out that the wireless micro-phone operators were improperly transmittingsignals on many channels occupied by TV broad-cast signals within the protected TV service con-tours during the field trials [11]. Even so, thereis so far no comprehensive trial that proves theacceptable performance of wireless microphonesignal detection. As an alternative, the WSCproposed to use beacons for protecting wirelessmicrophone signals.

OBSERVATIONS FROMCR PLATFORMS’ INTERACTIONS

We now proceed to the third and final part ofthis article. We focus on the many interestingconclusions that may be drawn from the obser-vation of the development progress of demon-stration platforms for CR-like systems andnetworks presented earlier. Some of these mayseem to be surprising and contradict the com-mon feeling about the way these networks areevolving. We also suggest recommendations tohelp the community evolve faster and advancethe field of research. These are summarizedbelow.

THERE ARE PRACTICALLY NO COMPREHENSIVECR DEMONSTRATION PLATFORMS

Almost all testbeds presented publicly are moreor less focused on DSA functionality. From thesurveyed demos there is not a single one thatpresents at least a feature of CR that has beenproposed in [1], like artificial intelligence (AI)usage in spectrum selection. We presume thatthe field is not mature enough to provide mean-ingful demonstrations with AI features. Themore exciting AI functionality tends to lenditself better to scenarios involving networks, dis-tributed resources, and higher-plane functionali-ty featuring teamwork and collaboration [12].

We encourage open collaboration betweenresearch groups to help progress toward compre-hensive demonstrations better linked to real-world scenarios. The IEEE DySPANdemonstrations series provided a glimpse ofwhat value could be generated from these col-laborative activities. Further public dissemina-tion of outcomes from these activities in theform of website content and publicly availablevideos would significantly increase the visibilityand impact of this work. This in turn wouldincrease the prospects of collaboration and jointproject opportunities with external groupsaround the world.


Table 2. Probabilities of proper channel classification.

PrototypeATSC channels NTSC channels

UnoccupiedCondition I Condition II Condition I Condition II

Adaptrum 91% 51% 89% 30% 75%

I2R 94% 30% 25%1 10%1 81%

Motorola (geolocation) 100% 100% 100% 100% 71%

Motorola (sensing) 90% 48% — — 64%

Philips 100% 92% 100% 100% 15%

Note: 1 I2R’s white space device did not support NTSC but was tested by the FCC for NTSC anyway.

We encourage open

collaboration

between research

groups to help

progress toward

comprehensive

demonstrations bet-

ter linked to real-

world scenarios. The

IEEE DySPAN

demonstrations

series provided a

glimpse of what

value could be

generated from

these collaborative

activities.



OPEN SDR PLATFORMS DOMINATE THERESEARCH MARKET

As seen in Fig. 2a, the majority of demonstra-tions use GNU Radio and either the USRP ordedicated RF front-ends. This demonstrates thatopen source SDR development kits and openhardware platforms are proving to be the mostaccessible university research platform for DSA-related research. On the other hand, other opensource software components supporting develop-ment of CR-like systems, such as WARP, Iris,and OSSIE, described earlier, are mostly used bythe universities that developed them.

Open sourcing is a valuable means of enticingnew users, supporting a wide range of develop-ment ecosystems, and increasing the impact of aresearch platform. Research institutions areencouraged to explore this option. Additionalopportunities in the form of bespoke develop-ment work, greater employment opportunitiesfor the researchers involved, and the prospectsof a development lifetime not restricted by theduration of the project are potential indirectoutcomes from this approach.

MANY TESTBEDS ARE NOT DSA IN THESTRICT MEANING OF THE TERM

Surprisingly, the majority of platforms enablingreal-world communication and presented in thepast couple of years are designed to work inlicense-exempt bands, where no requirements onprimary user protection are present. However,certain issues (e.g., the interference impact ofsecondary opportunistic usage on primary users,and adjacent channel and dynamic range issues)simply cannot be analyzed properly unlessdeployed in a frequency band with active real-world incumbents. In addition to these technicalconstraints, market mechanisms and economicdrivers including light licensing and incentiveauction schemes cannot be properly trialed inlicense-exempt bands.

Spectrum regulators can provide wireless testand trial licensing options to help facilitateexperiments in non-license-exempt spectrum thatmore closely meet real-world incumbent scenar-ios. The Commission for Communications Regu-lation (Comreg) in Ireland, the Office ofCommunications (Ofcom) in the United King-dom, and the FCC (through their special tempo-rary authority license mechanism) are examplesof regulators that offer these options. Weencourage research groups to avail of theseopportunities where possible.

OFDM IS TYPICALLY THEDESIGN CHOICE FOR WAVEFORMS

Referring to Fig. 2b, the majority of waveformsused have been OFDM-based (includingDARPA XG). In addition, some prototypes arebased on IEEE 802.11 standards where OFDMis a standard spectrum access scheme. USRP-based testbeds use OFDM to implement non-contiguous forms of this spectrum access scheme,which allows for the dynamic notching and shap-ing of subcarriers to accommodate detectedincumbent frequency user activity. Some other

demonstrations not using OFDM are available,like recent University of Dublin, Trinity Collegedemonstrations with multicarrier code-divisionmultiple access (MC-CDMA).

Single-carrier (SC) waveform-based researchshould continue. SC schemes can alleviate theneed for highly linear power amplifiers andbackoff as is the case for OFDM, thus helpingreduce the cost of user terminals. Single-carrierfrequency-division multiple access (SC-FDMA)is a variant of OFDM being used for Long TermEvolution (LTE) and LTE-Advanced terminals,the successor to High Speed Download PacketAccess (HSPDA). The research community cantherefore stand to potentially benefit from

Figure 2. Current status of CR demonstration platforms presented in this arti-cle: a) hardware platforms used; b) waveforms used; c) types of signal detec-tion used (OTS: off the shelf, SC: single carrier, SMSE: spectrally modulatedspectrally encoded).

(a)

Dedicated

6

0

Num

ber

8

10

4

2

12

USRP IRIS 802.11 OTS SDR KUAR WARP

(c)

Energy0

Num

ber

5

20

10

15

Other Cyclostationarity Feature

(b)

OFDM

6

0

Num

ber

8

10

4

2

12

802.11 xPSK MC-CDMA SMSE SC 802.15.4 802.16



extending their existing OFDM-based work totarget SC-FDMA, carrier aggregation, and otherrelated LTE-based technologies.

ENERGY DETECTION IS THEMOST POPULAR SIGNAL DETECTION METHOD

Energy detection is used by the majority of thesystems addressed in this article to detect thepresence of other users in a band of interest.Energy detection offers a greater detectionspeed and less computational complexity thancyclostationary feature analysis, for example.However, this comes at a cost. Energy detectionis not highly regarded for accuracy in low signal-to-noise ratio cases, as noted earlier. Amongthose demos enabling energy detection only, afew enable cooperation in spectrum sensing.However, it was found during the DySPANdemonstrations that this method is suboptimaland easy to abuse. There are many other inter-esting and more reliable sensing approaches inexistence in the literature, including cyclostation-ary feature analysis [13, 14] and filter bank tech-niques [15], which lend themselves toimplementation on a variety of the platformsmentioned in this article (Fig. 2c).

GEOLOCATION AND SENSING ARE NEEDED FORMAXIMUM RELIABILITY BUT AT A COST

The FCC WSD tests demonstrated that a combi-nation of geolocation and sensing yielded thebest results in condition I and II tests. However,the ability to sense signals down to the estab-lished thresholds may have implications in termsof significantly higher terminal costs than if ageolocation database approach was used on itsown.

Cost is a major factor influencing the marketadoption of WSD-based technologies. Furtherreal-world trials are required to determinewhether sensing and the associated costs can besignificantly reduced if geolocation-basedapproaches can be employed to meet the regula-tory guidelines. The outcomes of this work wouldalso help shape regulatory policy in terms of astance that balances the need for primary userprotection, and helping new markets to emergeand evolve. These factors would in turn help toincrease the market adoption prospects of newwhite space-based technologies.

LACK OF APPROPRIATE RF FRONT ENDSA key bottleneck in CR experimentation hasalways been (and we believe continues to be) theavailability of appropriate frequency-agile RFfront-ends that can easily be coupled with theparts of the CR that carry out the digital pro-cessing — be they pure software systems likeGNU Radio or a mix of hardware and softwarelike the BEE. The USRP has been the most suc-cessful product to do just this, especially in termsof accessibility for researchers (Fig. 2a).

We have approached the stage where out-of-the-laboratory tests are now required to signifi-cantly progress the field of research. The RFfront-end requirements must therefore evolve tosupport this work. Increased transmit power, fre-quency range coverage, smaller form factors,

increased support for add-on modules, anincreased range of interfaces, weatherproofhousings, and more adaptable power sourcefacilities are key to facilitating this shift in focus.The research community needs to engage withlarge equipment vendors to demonstrate ideasand prototype solutions to promote developmentof new RF front-ends in sufficient quantities toprovide for larger-scale research and commercialactivities.

SMALL AND CENTRALIZED SYSTEMS ARE THEDESIGN CHOICE FOR MOST OF THE PLATFORMS

Designers have full control over their platformswith a centralized approach. This avoids theneed for a control channel (19 out of 28 sur-veyed platforms focusing on networking had nocontrol channel enabled); however, it means sac-rificing the flexibility of the design. Most demoshave two nodes, some have three, and there area few that might have a few more. Thus, testbedsare small and not of a substantial enough size toreally explore or uncover networking issues.There is much less focus on cognitive networks,and when a network focus is present the scenar-ios typically target single-digit numbers of nodesand centralized scenarios.

The time to increase the scope of the researchvision has now arrived. The research communityis urged to expand their testbed plans to exam-ine larger-scale and distributed multinode sce-narios over wider geographical areas.Collaborative efforts are now beginning to focuson this more, however. Key activities in Europe,for example, include the European ScienceFoundation’s European Cooperation in Scienceand Technology (COST) IC0902 and COST-IC0905 (COST-TERRA) projects, which focuson applying CR across layers, devices, and net-works, and developing a harmonized techno-eco-nomic framework for CR and DSA acrossEurope. Further information on these is avail-able at http://cost-terra.org and http://newyork.ing.uniroma1.it/IC0902.

NO DRAMATIC INCREASE IN THE NUMBER OFAVAILABLE CR AND NETWORK PROTOTYPES

The number of papers presented including cog-nitive radio as a keyword increases exponentiallyevery year. However, every year IEEE DySPANhas received a similar number of demonstrationsubmissions. IEEE DySPAN ’07, ’08, and ’10received 13, 15, and 12 submissions, respectively.

More industry-led research is now required toincrease the number of prototype systems fromthe small set of systems focused on long-termresearch-only concept ideas.

ONLY ONE THIRD OF THEPRESENTED DEMOS ARE FROM THE UNITED

STATES

Although the United States still dominates inresearch and development of CR-like systems,due to worldwide interest almost 60 percent ofthe demos are from Canada, the EU, and Asia.

Cost is a major factor

in influencing the

market adoption of

WSD-based tech-

nologies. Further

real-world trials are

required to deter-

mine whether sens-

ing and the

associated costs can

be significantly

reduced if geoloca-

tion-based approach-

es can be employed

to meet the regula-

tory guidelines.



UNIVERSITIES DOMINATE THEDEMONSTRATION MARKET

As an emerging technology, DSA-based systemsare the basis for patent generation and otherintellectual property protection endeavors. Thisis one of the reasons why publicly viewable com-mercial offerings appear to be slow to emerge.On the other hand, university-created prototypesand research publications concerning these tendto emerge more quickly and involve public dis-semination of the work through academic publi-cations to help build the research profile andstatus of the research group and academic insti-tution.

MORE EMPHASIS IS NEEDED ONREPORTING FAILURES

The development path of an emerging technolo-gy includes failures as well as successes. In manycases, the reasons why a particular DSA or CRapproach was not successful can be perhaps evenmore important than the small number of sce-narios where the system does live up to itsclaims. While some technical reports focus onproblems associated with DSA-related systemslike [10], research publications tend not to focuson this valuable information. By reporting thereasons approaches may not work, the researchcommunity can avoid repeating the same mis-takes and evolve faster.

EACH DEMONSTRATION WAS DEVELOPED BY ASMALL NUMBER OF PEOPLE

Thanks in part to ready-made SDR systems,available documentation, and, in the case ofUSRP, an active community of developers, thenumber of people involved in demonstrationscan be limited. For the case of surveyed demosfrom the previous section, the average numberof developers is approximately three.

ABSENCE OF IEEE 802.22 DEMONSTRATIONSInterestingly among all presented demonstra-tions, not a single one implemented the IEEE802.22 protocol stack. Although some compo-nents for IEEE 802.22 have already been devel-oped (e.g., the spectrum sensing module of [16]),none of the universities and companies havefocused on these networks. Not only are demosand testbeds for IEEE 802.22 missing; there isalso a lack of literature on WRAN networks thatdirectly take into account specifications of thestandard to evaluate its performance [3, 4].

CONCLUSIONSIn this article we have presented a survey ofstate-of-the-art hardware platforms and testbedsrelated to CR concepts. We broke this workdown into three sections. First, we present aprimer on the common systems being used forCR research and development. Synopses of thekey events in recent years that have helpedprogress the field of CR and DSA technologiesfollow this. Finally, we present insights gainedfrom these experiences in an attempt to help thecommunity grow further and faster in the com-

ing years.

ACKNOWLEDGMENTSThe authors would like to thank Rahman DoostMohammady and Jörg Lotze for providing initialdata for the demonstration survey.

REFERENCES[1] J. Mitola III and G. Q. Maguire, Jr., “Cognitive Radio:

Making Software Radios More Personal,” IEEE PersonalCommun., vol. 6, no. 4, Aug. 1999, pp. 13–18.

[2] J. Hoffmeyer et al., “Definitions and Concepts forDynamic Spectrum Access: Terminology Relating toEmerging Wireless Networks, System Functionality, andSpectrum Management,” IEEE 1900.1-2008, Oct. 2,2008.

[3] F. Granelli et al., “Standardization and Research in Cog-nitive and Dynamic Spectrum Access Networks: IEEESCC41 Efforts and Other Activities,” IEEE Commun.Mag., vol. 48, no. 1, Jan. 2010, pp. 71–79.

[4] Q. Zhao and B. M. Sadler, “A Survey of Dynamic Spec-trum Access: Signal Processing, Networking, and Regu-latory Policy,” IEEE Signal Process. Mag., vol. 24, no. 3,May 2007, pp. 79–89.

[5] C. R. Aguayo González et al., “Open-Source SCA-BasedCore Framework and Rapid Development Tools EnableSoftware-Defined Radio Education and Research,” IEEECommun. Mag., vol. 47, no. 10, Oct. 2009, pp. 48–55.

[6] R. Farrell, M. Sanchez, and G. Corley, “Software-DefinedRadio Demonstrators: An Example and Future Trends,”Hindawi Int’l. J. Digital Multimedia Broadcasting, 2009.

[7] G. J. Minden et al., “KUAR: A Flexible Software-DefinedRadio Development Platform,” Proc. IEEE DySPAN,Dublin, Ireland, Apr. 17–20, 2007.

[8] M. McHenry et al., “XG Dynamic Spectrum Access FieldTest Results,” IEEE Commun. Mag., vol. 45, no. 6, June2007, pp. 51–57.

[9] FCC, “Second Report and Order and MemorandumOpinion and Order, in the Matter of ET Docket no. 08-260 and ET Docket no. 02-380,” tech. rep., Nov. 14,2008; http://hraunfoss.fcc.gov/edocspublic/attach-match/FCC-08-260A1.pdf.

[10] S. K. Jones et al., “Evaluation of the Performance ofPrototype TV-Band White Space Devices Phase II,” FCCTech. Rep., Oct. 15, 2008; http://hraunfoss.fcc.gov/edocs public/attachmatch/DA-08-2243A3.pdf.

[11] Harris Wiltshire & Grannis LLP, “Ex Parte Filing inResponse to FCC ET Docket Nos. 04-186, 02-380,” Aug.19, 2008, Philips, in the name of the White SpaceCoalition.

[12] K. E. Nolan and L. E. Doyle, “Teamwork and Collabora-tion in Cognitive Wireless Networks,” IEEE WirelessCommun., vol. 14, no. 4, Aug. 2007, pp. 22–27.

[13] A. Tkachenko, D. Cabric, and R. W. Brodersen, “Cyclo-stationary Feature Detector Experiments using Recon-figurable BEE2,” Proc. IEEE DySPAN ‘07, Dublin, Ireland,Apr. 17–20, 2007.

[14] P. D. Sutton, K. E. Nolan, and L. E. Doyle, “Cyclosta-tionary Signatures in Practical Cognitive Radio Applica-tions,” IEEE JSAC, vol. 26, no. 1, Jan. 2008, pp. 13–24.

[15] B. Farhang-Boroujeny and R. Kempter, “MulticarrierCommunication Techniques for Spectrum Sensing andCommunication in Cognitive Radios,” IEEE Commun.Mag., vol. 46, no. 4, Apr. 2008, pp. 80–85.

[16] J. Park et al., “A Fully Integrated UHF-Band CMOSReceiver with Multi-Resolution Spectrum Sensing(MRSS) Functionality for IEEE 802.22 Cognitive RadioApplications,” IEEE J. Solid-State Circuits, vol. 44, no. 1,Jan. 2009, pp. 258–68.

BIOGRAPHIESPRZEMYSLAW PAWELCZAK [S’03, M‘10] ([email protected])received his M.Sc. degree from Wroclaw University of Tech-nology, Poland, in 2004 and his Ph.D. degree from DelftUniversity of Technology, The Netherlands. From 2004 to2005 he was a staff member of Siemens COM SoftwareDevelopment Center, Wroclaw, Poland. During fall 2007 hewas a visiting scholar at the Connectivity Laboratory, Uni-versity of California, Berkeley. Since 2009 he has been apostdoctoral researcher at the Cognitive ReconfigurableEmbedded Systems Laboratory, University of California, LosAngeles. His research interests include cross-layer analysisof opportunistic spectrum access networks. He is a Vice-Chair of the IEEE SCC41 Standardization Committee. He

Interestingly, among

all presented

demonstrations, not

a single one

implemented the

IEEE 802.22 protocol

stack. Although

some components

for IEEE 802.22 have

already been

developed (see the

spectrum sensing

module of [16]),

none of the

universities and

companies have

focused on these

networks.



was a coordinator and an organizing committee memberof cognitive radio workshops collocated with IEEE ICC in2007, 2008, and 2009. Since 2010 he has been a co-chairof the demonstration track of IEEE DySPAN. He was therecipient of the annual Telecom Prize for Best Ph.D. Stu-dent in Telecommunications in The Netherlands in 2008awarded by the Dutch Royal Institute of Engineers.

KEITH NOLAN ([email protected]) received his Ph.D. degreein electronic engineering from the University of Dublin,Trinity College, Ireland, in 2005. He is a research fellowwith the Telecommunications Research Centre (CTVR) atthe University of Dublin, Trinity College. He has served asorganizer, chair, and co-chair of demonstrations for IEEEDySPAN symposia, and on numerous TPCs for conferencesconcerning cognitive radio and dynamic spectrum accesstechnologies. He currently serves on the management com-mittee for COST Actions IC0902 and IC0905 (COST-TERRA),and is also a technical co-author of the IEEE P1900.1 stan-dard.

LINDA DOYLE ([email protected]) is a member of faculty in theSchool of Engineering, University of Dublin, Trinity College.She is currently director of CTVR, a national research centerthat is headquartered in Trinity College and based in fiveother universities in Ireland. CTVR carries out industry-informed research in the area of telecommunications, andfocuses on both wireless and optical communication sys-tems. She is responsible for the direction of CTVR as wellas running a large research group that is part of the cen-ter. Her research group focuses on cognitive radio, recon-figurable networks, spectrum management andtelecommunications, and digital art.

SER WAH OH [SM] ([email protected]) obtained hisB.Eng. from the University of Malaya, Malaysia, in 1996,and Ph.D. and M.B.A. degrees from Nanyang TechnologicalUniversity (NTU), Singapore, in 1999 and 2010, respective-ly. He is currently a research scientist and project managerat the Institute for Infocomm Research (I2R), Singapore. Heoversees TV white space activities in I2R, and is currentlylooking into application of TV white space on the smartgrid. In 2008 he successfully led a team of researchers tocontribute TV white space technologies to the field trialconducted by the U.S. FCC, which resulted in subsequentapproval of TV white space in the United States. He waspreviously in charge of algorithm development for 3GWCDMA over a software-defined radio platform. At thesame time, he also serves as technical adviser for Rohde &Schwarz and ComSOC Technologies. From 2005 to 2008 heconcurrently held the position of adjunct assistant profes-sor in NTU. Prior to I2R, he was a technical manager atSTMicroelectronics in charge of teams in the Singapore andBeijing R&D Centers. He was responsible for 3G WCDMAand TD-SCDMA physical layer development. He is also arecipient of the 2010 Ernst & Young Cash Prize Award asthe Top MBA Graduate, the 2009 Institution of EngineersSingapore Prestigious Engineering Achievement Award,and the IEEE ICT 2001 Paper Award. He has served asDemo Chair, Publicity Chair, and Track Chair, and on theTPCs for various conferences and seminars. He has pub-lished over 30 papers and several invited papers, and holdsfour U.S. patents with several pending.

DANIJELA CABRIC ([email protected]) received a Dipl. Ing.degree from the University of Belgrade, Serbia, in 1998and an M.Sc. degree in electrical engineering from the Uni-versity of California, Los Angeles, in 2001. She received herPh.D. degree in electrical engineering from the Universityof California, Berkeley, in 2007, where she was a memberof the Berkeley Wireless Research Center. In 2008 shejoined the Faculty of Electrical Engineering at the Universityof California, Los Angeles as an assistant professor. Her keycontributions involve the novel radio architecture, signalprocessing, and networking techniques to implement spec-trum-sensing functionality in cognitive radios. She has writ-ten three book chapters and over 25 major journal andconference papers in the fields of wireless communicationsand circuits and embedded systems. Her book, CognitiveRadios: System Design Perspective, was published bySpringer in 2010. She was awarded a Samueli Fellowshipin 2008 and an Okawa Foundation research grant in 2009.


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