Spectrum Agile RadioTeam 4Jim KileDon LittleSamir Shah

Structure of PresentationDefinition, why?, and evolutionBackground conceptsWhite space, measurementsRegulatory environmentWireless standardsImplementations

Spectrum Agile Radio (SAR)Use of a licensed radio band by other than the license holders on a non-interfering basis.

WHY?Wireless LANs & MANsPalmPocketPCBlackberryCell phoneWearable computingOther consumer electronics

Evolution of DevicesNecessary radio spectrum will not be available in the future

HOW?Almost all radio bands suitable for wireless communications have been allocatedPreliminary studies indicate that much of the radio spectrum is not in useFor a significant amount of timeAt large numbers of locations

Definition Radio resourcesRadio frequency bandsCan be used/occupiedFor certain durationIn a certain areaCalled footprint

Definition Primary UsersConventional legacy usersRightful ownersHardware and protocols have strict priority on spectrum accessShould not be required to retrofit to meet secondary user access needs

Definition Secondary usersSpectrum-agile devicesSense environmentAdapt to appropriateFrequencyPowerTransmission schemesOpportunistically access unused spectrum vacated by idle primaries

Definition Rules for CoexistenceWhen a primary user is using the bandSecondary users are not allowed to co-existChannel availability of secondary users determined by the activities and properties of primary users

Definition Opportunistic Spectrum UtilizationUsage by Secondary UsersOn a non-interfering basisBand not usedUsed in deterministic patternCURRENTLY ILLEGAL

DefinitionSpectrum Agile RadioCommunicates using available radio resourcesLicensed to OTHER radio servicesWithout interfering with the operation of licensed radio devices

Spectrum Agile Radio

Definition: White SpaceAlmost all of the radio spectrum has been allocatedBut, there are areas of the radio spectrum not currently in use by primary userA band is counted as white space when:Wider than 1 MHz andRemains unoccupied for 10 minutes or longerSignificance?Resource is scarceProvides an opportunity for dynamic spectrum usage

White Space Example

White Space Example Even in the unlicensed spectrumReturn

Measuring Spectrum White SpaceWhy?Understand the amount of under-utilized spectrumConditions30 MHz to 3,000 MHz (3 GHz)Use a worse case locationDowntown Washington, DCBoth government and commercial spectrum useSeveral hour duration during high use periods

Spectrum Measurement RequirementsElevated locationHigher detection probabilityEliminates line of site obstacles Use of high quality RF equipmentDetection sensitivity

Whitespace EstimateStudy conducted in June 2003 by the Shared Spectrum CompanyWhat constitutes white space for this estimate?Bands 1MHz wideUnoccupied for 10 minutes or longer

62% white space in the licensed spectrum

Regulatory EnvironmentBandwidth is a natural resourceHeavily regulatedExpensiveA 3 GHz mobile communications band costs $17 Billion!In the U. S., almost all bandwidth is allocated (licensed)

Regulatory Environment- U. S. FCC ModelsLicensed primary user modelSet aside for exclusive useExamples: TV and radioUnlicensed non-exclusive use modelSet aside for non-exclusive useExamples: ISM band applications such as Wireless LAN (802.11) or BluetoothRepresents a small fraction of the total bandwidth available

Regulatory Environment circa 1940Dumb device assumptionTightly regulated to prevent interferenceExample: Television VHF/UHF band channel allocationNo way to share inefficiently used spectrum

Regulatory Environment TodayFast processing power and intelligent radiosNew technology which is more tolerant to interference Spread spectrumSpectrum agile radio

Regulatory Environment TodayIntroducing underlays/noise floor rightsDeveloping a noise temperature measureDevices measure the level of interference and transmit accordingDevelopment of co-existence modesAllow multiple uses of a spectrum (spectrum agile radio SAR)

Regulatory EnvironmentSpectrum policy task forceSetup by Chairman Michael Powell in June 2002Headed by Paul KolozdyPurposeConduct a comprehensive review of spectrum policyModernize spectrum management and utilization rulesCommand and control consumer-orientedSubmitted findings and recommendations in December 2002

Regulatory Environment Spectrum Policy Task Force[T]he time is ripe for spectrum policy reform. Increasing demand for spectrum-based services and devices are straining longstanding, and outmoded, spectrum policies. While the Commission has recently made some major strides in how spectrum is allocated and assigned in some bands . . . spectrum policy is not keeping pace with the relentless spectrum demands of the market.

Regulatory EnvironmentSpectrum policy task forceFindingsSpectrum access versus scarcityNew methods as a solution to access Interference tolerance Need to define rights and responsibilityRecommendationsModernizing the regulator modelIncrease access to spectrum through the time dimensionNew inferences management standardsLegislative recommendations

Regulatory EnvironmentFCC 2005 Rule ChangesMarch 2005, FCC adopts rule changes for smart radiosAllows sharing spectrum with primary users without causing harmful interferenceRegulate emission characteristics rather than the type of serviceAllows rapid development of new applicationsUnencumbered by regulatory delays

Regulatory EnvironmentFCC 2005 Rule Change PrinciplesProvide reasonable security measures to prevent unauthorized software modifications affect the RF operating parametersManufacturer to supply a high level operational description of the software that controls the radios RF characteristicsA description of the software security measures employed to prevent unauthorized modifications

Regulatory EnvironmentFCC 2005 Rule Change Principles contdManufacturers to market radios that have the hardware-based capability to transmit outside authorized United States frequency bandsRequired software controls to limit operation to authorized frequency bands when used in the United States.

Regulatory Environment FCC 2005Commission concluded thatTechnical measures that cognitive radios can employ will allow a reliable secondary use of licensed spectrumMaintains Availability of the spectrum Rapid reversion to the licensee when neededSaw no need to adopt any particular technical model for interruptible spectrum leasing

Defense Advanced Research Projects Agency (DARPA)Working on developing new technologiesAllow multiple radio systems to share the spectrum through adaptive mechanismsNeXt Generation communications (XG) programIdentify behaviors versus detailed descriptionsDynamically align rules with technologies for future radio systems

DARPANeXt Generation communications (XG) program concepts (continued)Abstract behaviors, protocols, and a policy language Flexibility, long-term impact, and the need for regulatory approval

US ArmyAdaptive Spectrum Exploitation (ASE)Real-time spectrum management in the battlefieldTactical battlefield spectrum managementImportance of spectrum planningDynamic apportionmentDynamic interference resolution

Spectrum Agile RadioSalient FeaturesRules for radios as opposed to rules for services/applicationsRadio regulators will continue to decide policy that specify behaviors of these radiosSpectrum sharing, interference management, and coordination between users, based on radio environment awarenessReal-time measurements, dissemination and opportunity identification

Spectrum Agile RadioSalient FeaturesAwareness of primary and secondary usageRadio behaviors influenced by evolving policiesPolicies set by regulatorsPolicies for wireless network managementExamples:For U-NII bands, using etiquette as discussed in Wi-FiFor hospitals

IEEELAN/MAN Standards SeriesLocal Area Network standardsMetropolitan Area Network standardsTask Groups (TGs) to develop extensionsIEEE 1900 Next Generation Radio StandardsIEEE 802.22 Wireless Regional Area NetworksIEEE 802.11 Wireless Local Area Networks802.11h Spectrum Managed 802.11a802.11k Physical measurement of wireless energy

IEEE 1900 Next Generation Radio StandardsEstablished in the first quarter 2005IEEE Communications Society (ComSoc)IEEE Electromagnetic Compatibility (EMC) SocietyDevelop supporting standardsNext generation radioAdvanced spectrum management

IEEE 802.22 Wireless Regional Area NetworksWorking Group on Wireless Regional Area NetworksDevelop standard for spectrum agile radio-based air interfaceLicense-exempt devices on a non-interfering basisSpectrum allocated to TV Broadcast Service

IEEE 802.11 Wireless Local Area NetworksCurrent wireless LAN standard802.11h Spectrum Managed 802.11a 802.11k Physical measurement wireless energy

IEEE 802.11h Spectrum Managed 802.11a Resolve interference issues 802.11a in 5 GHz bandMilitary radar systemsMedical devicesSatellite communicationsTransmit Power Control (TPC)Dynamic Frequency Selection (DFS)

IEEE 802.11h Dynamic Frequency Selection (DFS)Detects the presence/type of other devices on a channelRequires quiet periodsResponds based upon type of device identifiedWhen radar is identifiedDevices MUST change channelsWill coexist with other 802.11 traffic

IEEE 802.11kWireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Radio Resource Management of Wireless LANs Final approval of this amendment is targeted for January 2007Defines measurement framework

IEEE 802.11kWhere?IEEE 802.11 wireless local area networks operate in the unlicensed 2.4 GHz Industrial, Scientific and Medical (ISM )4.9 GHz (Japan)5 GHz Unlicensed National Information Infrastructure (UNII) bands

IEEE 802.11kWhy?Enable more accurate and efficient operation of Wireless LANsOptimize radio environmentsMore devices can coexistReduce wireless network traffic congestion

IEEE 802.11kHow?Enhanced measurements and diagnosticsMedium sensing measurement requests and reportsCollects spectrum usage patterns

IEEE 802.11kWhat?Provides information about other radio systems on a channelCould be 802.11 devicesCould be non-802.11 radiators such as a microwaveCan derive operational parameters for 802.11 stations

IEEE 802.11kStandardsRadio resource measurements not standardizedStandardized frame formatsRequest for a specific measurement One radio device to anotherReport of such a measurementResponse to the request

IEEE 802.11k What do you want to know?Is channel suitable for use?Percent busyNon-802.11 signalsPatterns of these Non-802.11 signals

IEEE 802.11k Clear Channel Assessment (CCA)Logical function found within physical layersDetermines the current state of use of wireless mediumAids in contention avoidanceProcess that determines if the device can transmit on the channel

IEEE 802.11kClear Channel AssessmentReportsChannel Load ReportNoise Histogram ReportMedium Sensing Time Histogram Report

IEEE 802.11k Channel Load ReportPercentage of time the medium is busy during the measurement period

IEEE 802.11k Noise Histogram ReportSamples non-802.11 energySamples medium only when CCA indicates that no 802.11 signal is presentReports noise and other non-802.11 signals

IEEE 802.11k Medium Sensing Time HistogramHistogram of busy and idle time observedAssesses spectrum usage pattern of other radio devicesShows pattern of medium usage so that medium can be shared

SummarySpectrum Agile GoalsIdentify spectrum not used by primary users (spectrum white spaces).Transmit in white spaces with appropriate power levelsDo not cause interference to primary usersDetect the transmission of other secondary devicesShare some or all of the channels occupied by other secondariesReduce own blocking probability

Identify Spectrum Hidden Node ProblemReceivers are passive and their presence cannot be detected directlyInterference is caused at the receiversAgile radios have to detect primary signal at thresholds that are under signal levels of primary devicesFor example, directional antenna

Identify Spectrum PowerHigher the transmit power employed by the spectrum agile radioFurther away that it must be able to detect a television transmitter

Identify Spectrum TimeframeSensing approaches must assess signal presence quicklyWideband of spectrum must be sensed possibly one channel at a timeDifferent primary usersDifferent transmission characteristics

Identify Spectrum How?Energy Detection ApproachFeature Detection Approach

Identify Spectrum Energy Detection ApproachWireless device measures RF energy in the channelSense the presence of a primary if energy is above thresholdCannot arbitrarily lower the threshold Result in non-detection because of Signal/Noise Ratio

Energy Detection ApproachDisadvantagesNot be able to distinguishOther secondary usersShare the mediumPrimary usersRequire movement to another channel

Identify Spectrum Feature Detection ApproachUsed in the military to detect the presence of weak signalsUses cyclostationary signal processing to detect the presence of primariesProcess exhibits cyclostationarity if its statistics vary periodically with timeCan be detected at very low signal-to-noise ratios (SNR)

Identify Spectrum ImplementationCollocated Sensing ArchitectureSingle Radio Sensing Architecture Dual Radio Sensing ArchitectureSensor Network ArchitectureAgile Radio Policy

Identify Spectrum Collocated Sensing ArchitecturesSensing function and the data transmission collocated in a single deviceAgile radio itself responsible for sensing spectrum usageSingle radio sensing architectureDual radio sensing architecture

Single Radio Sensing Architecture AdvantagesSingle radio Both sensing and data transmissionCompletely distributed Simple to implement with less equipmentLonger battery life

Single Radio Sensing Architecture DisadvantagesLost transmit opportunity costsRadio has to reserve time for sensingDecreasing time to transmit/receive dataSignificant processing overhead Obtain measurement resultsCompare with past resultsEstimate how channel is going to behave in the future

Single Radio Sensing Architecture Disadvantages contdImposes limitation on MAC layer designCollision - MAC has no means to determine causeTransmission by another agile radio deviceChannel errorPrimary userDoes not overcome hidden node problem

Dual Radio Sensing Architecture AdvantagesTwo radiosOne is exclusively dedicated for sensingOther is dedicated for data transmissionRemoves Lost transmit opportunity costs

Dual Radio Sensing Architecture DisadvantagesAdditional complexity Additional power constraintsCost per device likely higherDoes not overcome hidden node problem

Identify Spectrum Sensor Network ArchitectureTwo complementary networks Sensing networkOne or more operational networks

Identify Spectrum Sensor Network Architecture

Sensor Network Architecture Operational NetworksResponsible for traditional data transmissionOpportunistic use of the spectrumAccept the information about sensor networkChannel to useWhen to useHow long to use

Sensor Network Architecture Sensor NetworkSeparate network fully dedicated to spectrum sensingDeployed in the desired target areaCommunicate the results to sink nodeSink node makes the information available to operational networks

Sensor Network ArchitectureAdvantagesNumerous measurements made Provide needed location diversity to identify multipath fadingNo Lost transmit opportunity costs Reduces power requirements for the Operational Network

Sensor Network Architecture AdvantagesSensors InexpensiveSmall form factorVery energy efficient

Sensor Network ArchitectureAdditional BenefitsCan be designed to serve a wide and evolving range of purposesOffer new measurement capabilities for older, regulated bandsLocalizing illegal emittersSpatial diversity allows this feature

Identify Spectrum Agile Radio PolicyFCC identifies licensed band with white spaceFCC assigns policies for use of bandPolicies published in machine-understandable form

Agile Radio PolicyAdvantagesAutonomous spectrum managementAuthority for radio regulation and spectrum management remains with Federal Communications Commission (FCC)No need to sense the medium with additional equipmentNo Lost transmit opportunity costs

Agile Radio Policy DistributionPolicies are published in a machine-readable formPolicies are available for download from FCC serversAgile radio devices obtain updates of policies from serversPolicies could be made available through memory devices such as flash cards

Agile Radio Policy Distribution contdAfter update local information baseDisseminate updates to other agile radio devicesDevices that belong to different networks may coordinate sharing of radio resources with the help of spectrum etiquette

Identify Spectrum One Proposed Architecture

Opportunity IdentifierDetermines opportunity bandsSenses available white spaceEstimates white spaces durationPasses results to Opportunity Manager

Policy InteractionUnderstands policies set by regulatory bodyInterpretation passed to Opportunity Manager

Opportunity ManagerCore of this architectureRequests measurements in target bandsDetermines if particular band is an opportunityPasses parameters to the flexible PHYResponsible to map traffic to the MAC queue to these opportunities

Flexible PHY LayerTakes inputs from Opportunity ManagerShapes waveforms so that they comply with transmission policies set by regulation

Overall SummaryMore radio spectrum will be available to support new devicesNew technologies will be required to make use of the spectrumLots of research opportunities

References

[1]"RADIO RESOURCE MANAGEMENT SPEC FOR IEEE 802(R) WIRELESS LANs PASSES MILESTONE", http://standards.ieee.org/announcements/pr_p820.html.

[2]Testimony of Dr. Paul Kolodzy Former Director of the Spectrum Policy Task Force Federal Communications Commission.

[3]J. A. Hoffmeyer, "Regulatory and standardization aspects of DSA technologies - global requirements and perspective", p. 700, 2005.

[4]S. Mangold, Z. Zhun, K. Challapali and C. Chun-Ting, "Spectrum agile radio: radio resource measurements for opportunistic spectrum usage", vol. 6, p. 3467, 2004.

[5]N. Sai Shankar, C. Cordeiro and K. Challapali, "Spectrum agile radios: utilization and sensing architectures", p. 160, 2005.

[6]L. Xin and W. Wei, "On the characteristics of spectrum-agile communication networks", p. 214, 2005.

1) The six vertexes 1-6 represent six different secondary users. 2) There are three frequency bands, namely A, B, and C, which are communication channels that are opportunistically available to the secondary users.3) Four (active) primary users I-IV are present, using bands C, B, C, A, respectively. The footprint of a primary user is represented by the dashed circle centered at it. For instance, Node 5 is within the footprints of primary users II and III, who use channels B and C, respectively. Therefore, channels B and C are not available at Node 5 while channel A is.4) Because of location differences, each node may have access to a different set of channels. In our figure, the available channels are (A,B) at vertex 1, (A,C) at vertex 2, etc. The resource allocationproblem is how they should share these channels.For my part of the talk, I will be discussing the concepts of spectrum white space, describe the past and current regulatory environment and current government research areas, and introduce the concept of spectrum agile radios.

White space. In the three papers upon which this presentation is based, white space in the radio spectrum refers to bands that are wider than 1MHz and unoccupied for 10 minutes or longer.

Although almost all of the radio spectrum has been allocated, studies by the Shared Spectrum Company, for example indicates that 62% percent of unused space below 3GHz band even in the most crowded area near downtown Washington, DC, where both governmental and commercial spectrum usage are intensive.

The large portion of white space indicates that opportunistic or dynamic spectrum usage may significantly mitigate the spectrum scarcity. One paper focused on what they call opportunistic spectrum utilization.

In the presented graphic, the spectrum is represented on the x axis, power on the y axis, and time on the z axis. The blue areas represent multi-carrier transmissions. In the white areas, there are sporadic transmissions (called non-contiguous on the diagram). The non-contiguous transmissions contribute to the amount of white space available. The availability of this white space changes with the amount of transmission activity within the spectrum opportunity area.

This is in the licensed band.This particular example shows both the licensed and unlicensed spectrum. Though it is not considered a part of agile radio, there is also white space in the unlicensed spectrum. This is merely a follow-on example to show that white space exists all over the spectrum. It gives another visual view of usage that may be easier for individuals to understand.One of the key requirements which serve as a premise for agile radio is that there is white space available for its use. In case it hasnt been properly defined, agile radio is designed to switch frequencies from one band to another based upon the traffic detected from other agile radios or the primary carrier.

Several studies were undertaken to determine the amount of white space that is available in a typical heavily used metropolitan area to understand how much of the spectrum was under-utilized (if any).

The conditions were put in place such that a worst-case scenario was identified. This called for test in downtown areas (e.g. Washington, DC with both government and commercial spectrum use or New York during the Republican Convention in 2004). Also, the duration of the test would have to be for several hours to understand the ebbs and flows of information across the spectrum.

How do you measure the spectrum?

There are two primary requirements:The location that is measuring the spectrum should be elevated. The reason for this is to improve the detection probability for transmissions since the idea is to determine the overall white space of the licensed spectrum.The equipment used must be of high quality. This is due to the inherent sensitivity required and found in high quality equipment. Again, this will assist in determining the overall white space of the licensed spectrum.In one study by Shared Spectrum Company, it was found that only 38% of the licensed spectrum was in use in the heavily crowded downtown Washington DC area where there are both government and commercial users.

Conditions:Only bands greater than or equal to 1MHz wide were counted if they were unoccupied for 10 minutes or longer.The study was conducted in a heavily populate area. This constitutes the worse case scenario. Other areas would presumably have higher white space percentages, though this hasnt been studied.

Conclusions:There is opportunity in the licensed spectrum for additional transmission capacity based upon the current utilization.

Radio spectrum is considered a natural resource and is, therefore, heavily regulated. In the United States, this regulation is by the Federal Communications Commission (FCC). This means that the allocation of bandwidth is both centralized and tightly controlled. It also means that it is expensive!!

A 3 GHz mobile communications band license can cost $17 Billion dollars (with a B).As noted earlier, almost all of the bandwidth in the United States has been allocated and/or licensed.Two types of models: Licensed primary user and Unlicensed Non-exclusive users

Licensed primary users include TV, radio, cell phone, etc.Unlicensed non-exclusive includes unlicensed uses. A good example is in the ISM band where 802.11 Wireless LAN and Bluetooth transmissions reside.

Definition and original use of ISM: The industrial, scientific and medical (ISM) radio bands were originally reserved internationally for non-commercial use of RF electromagnetic fields for industrial, scientific and medical purposes.

This unlicensed non-exclusive use model area represents only a small fraction of the total bandwidth available can recall from the whitespace discussionDumb devices. Devices that cannot tolerate interference from other devices. If you just take a look at an old TV and use a blender at the same time, you can see the impact interference can have on a transmission. It is worthwhile to note that there are still instances of interference today put your cell phone near your computer monitor while it is transmitting or near an improperly shielded telephone.

The FCC and other governments tightly regulated the spectrum in part to prevent such interference. A perfect example of this is with the TV VHF band where not only is the band allocated, but the frequencies upon which each channel can transmit are also allocated in 6 KHz increments to prevent interference. This 6 KHz frequency band is divided into two parts to cover the audio and the video. Interestingly, with the advent of digital transmissions, the entire 6 KHz band is not needed. Some stations have elected to send multiple transmissions within their band allotment.Much of the regulatory environment has centered on introducing regulations that permit equipment to tolerate and adapt to interference and ensure that it does not interfere with other equipment.

Underlays/noise floor rights refers to the amount of signal leakage Purpose:

To conduct a comprehensive review of spectrum policyIdentify recommendations to modernize the rules that guide how the nations spectrum is managed and utilizedTo move from a command and control structure to a more consumer-oriented structure.This is a quote from the final report issued by the spectrum policy task force for the FCC.Increasing demand is straining longstanding and outmoded policies.Spectrum policy is not keeping pace with the demands of the market.Key findings

Access. Some spectrum bands are heavily used, but many are not in use in all geographic areas or are used only part of the time. Opportunities for spectrum-based services or devices to operate in the resulting white spaces including both those that result from variability in the operations of existing spectrum users over time and those that result from the geographic separation of existing spectrum users.

Technology. Technological advances are contributing to the increased diversity of spectrum-based consumer applications and greater consumer demand for spectrum-based services, technological advances such as the increased use of digital technologies and the development of software-defined radios are providing some potential answers to current spectrum policy challenges. These technological advances enable spectrum rights to be parceled as a function of time, in addition to the currently-used parameters of frequency and geographic area. Also, they allow systems to be much more tolerant of interference than in the past.

Rights and Responsibilities. Spectrum rights and responsibilities are not always clearly defined users need more certainty. In addition, the rights and responsibilities that are defined need to better reflect more market-based models and policies.

Recommendations

Migrate toward more flexible, consumer-oriented policies. The Task Force recommends that the Commission evolve its spectrum policy toward more flexible and market-oriented spectrum policies that will provide incentives for users to migrate to more technologically innovative and economically efficient uses of spectrum. Specific recommendations include: Provide incentives for efficient spectrum use by both licensed and unlicensed users through flexible rules and facilitating secondary markets. This would enable spectrum users to make fundamental choices about how they use spectrum, taking into account market factors such as consumer demand, availability of technology and competition.Clearly and exhaustively define spectrum users rights and responsibilities.Investigate rule changes that promote more flexible power limits in rural or less congested areas. Adopt quantitative standards to provide interference protection: interference temperature. The Task Force recommends the creation of a quantitative standard for acceptable interference that provides both greater certainty for licensees and greater access to unused spectrum for unlicensed operators. Specifically, the Task Force recommends that, on a going forward basis, the Commission adopt a new metric the interference temperature to quantify and manage interference. The Commission could use the interference temperature metric to establish maximum permissible levels of interference on a band-by-band basis, thus placing a limit on the noise environment in which receivers would be required to operate. To the extent, however, that the interference temperature in a particular band is not reached, users who emit energy below that temperature could operate more flexibly with the interference temperature serving as the maximum cap on the potential RF energy they could introduce into the band. Improve access through the time dimension. The Task Force found that new technological developments now permit the Commission to increasingly consider the use of time, in addition to frequency, power and space, as an added dimension permitting more dynamic allocation and assignment of spectrum usage rights. This would provide access to unused or underused spectrum through time-sharing of spectrum between multiple users and lead to more efficient use of the spectrum resource.

Shift from command and control model to exclusive and commons models. The Task Force recommends that the Commission base its spectrum policy on a balance of three spectrum rights models: an exclusive use approach, a commons approach and, to a more limited degree, a command-and-control approach. While the command-and-control model currently dominates todays policy, the Task Force recommends altering the balance to provide greater use of both the exclusive use and commons models throughout the radio spectrum and limiting the use of the command-and-control model to those instances where there are compelling public policy reasons, such as some public safety applications. To the extent feasible, more spectrum should be identified for both licensed and unlicensed uses under flexible rules and existing spectrum that is subject to more restrictive command-and-control regulation should over time be transitioned to these models.The rules changes are key because they begin to open the door for spectrum agile radio implementation. The change was one of paradigm: regulate the emission characteristics rather than the type of service. It is thought that this will allow the rapid development of new applications which would be unencumbered by regulatory delays. The commission concluded that changes could be made to their rules about the use of the licensed spectrum because The technology that so-called spectrum agile radios can employ will allow a secondary use of the scarce spectrum resource while maintaining the availability of the spectrum and permit the original licensee to use their allocated spectrum when it is needed.DARPA is a research agency of the defense department. They currently have underway a program called neXt Generation Communications (or XG for short)The purpose of the program is to develop new technologies that allow multiple radio systems to share the licensed and unlicensed spectrum through adaptive mechanismsOne principle of the research is to identify behaviors rather than detailed descriptions of a standardized protocol or a set of different standardized protocols. It is thought that this will allow regulators and industry to dynamically align future requirements and rules for spectrum usage with existing and emerging technologies for future radio systems in essence, aside from making better use of the existing spectrum, they are looking to make sure that the methodology and rule base do not become obsolete.The U. S. Army has been investing in Adaptive Spectrum Exploitation research. This involves the management of the communications spectrum in real-time on the battlefield. Managing the spectrum is not new for the military. In the past, their technical battlefield spectrum management system focused on the importance of planning the spectrum, apportioning it, and ensuring there was no interference. ASE seeks to make these operations dynamic.Reminder: Primary = Licensed (the owner); Secondary = unlicensed in the licensed space.

U-NII Band. Unlicensed National Information Infrastructure. An FCC regulatory domain for 5-GHz wireless devices. UNII bands are 100 MHz wide and divided into four channels when using 802.11a OFDM modulation.

For hospitals, the example refers to the various pieces of equipment that exist in the health care domain and must communicate with each other.What is Cyclostationarity? Stated simply, a process exhibits cyclostationarity if its statistics vary periodically with time. Note the relationship between this description and that of a stationary process, where the statistics do not vary at all with time.

A simple example of this would be the dice-rolling analogy that is used so much in statistics. If I roll a (fair) six-sided die a thousand times every day, I would expect that the mean score for each day to be the same (i.e. 3.5). Therefore my process is stationary - the statistics don't vary with time.

Now consider what would happen if I had two dice, one of which has six sides, and the other nine. I use the six-sided die on Sundays, Mondays, Tuesdays and Wednesdays, and the nine-sided die for the rest of the week. Clearly I would expect to get a mean of 3.5 on the days where I used a six-sided die, and a mean of 5 on the days where I used the nine-sided die. Therefore my statistics do vary with time - so they aren't stationary. In fact, they vary periodically (i.e. weekly), and the process is said to be cyclostationary.

Wow. But who cares? A very good question to ask at this point is about the advantages of this. Basically, the main use of this technique comes from a second definition of a cyclostationary process - a cyclostationary signal is one which has correlation between areas in it's spectrum.

This makes it possible to discriminate between two completely overlapping signals. For example, if I receive two signals from antennas which are very close together (or indeed both transmitted from the same antenna) which use the same carrier frequency, it isn't possible to separate them using traditional methods. However, using the cyclic statistics, I can.

Taking this a step further produces great improvements in direction finding. This is because two targets which are very close to each other "blur" together, so that DF equipment is fooled into thinking there is only one target, lying somewhere between the two. One method for dealing with this is to filter out the frequencies of one transmitter. However, if the two transmitters are using the same frequency band, this isn't possible - unless cyclostationarity is used. By using a time-variant filter, it is possible to remove unwanted targets, however closely they overlap - either spatially or spectally. What is Cyclostationarity?

Stated simply, a process exhibits cyclostationarity if its statistics vary periodically with time. Note the relationship between this description and that of a stationary process, where the statistics do not vary at all with time.

A simple example of this would be the dice-rolling analogy that is used so much in statistics. If I roll a (fair) six-sided die a thousand times every day, I would expect that the mean score for each day to be the same (i.e. 3.5). Therefore my process is stationary - the statistics don't vary with time.

Now consider what would happen if I had two dice, one of which has six sides, and the other nine. I use the six-sided die on Sundays, Mondays, Tuesdays and Wednesdays, and the nine-sided die for the rest of the week. Clearly I would expect to get a mean of 3.5 on the days where I used a six-sided die, and a mean of 5 on the days where I used the nine-sided die. Therefore my statistics do vary with time - so they aren't stationary. In fact, they vary periodically (i.e. weekly), and the process is said to be cyclostationary.

Taking the similarity between stationarity and cyclostationarity one step further we come up the notion of a process which shows wide-sense (weak) cyclostationarity, in other words only the mean and autocorrelation of the process vary periodically.

Wow. But who cares?

A very good question to ask at this point is about the advantages of this. Basically, the main use of this technique comes from a second definition of a cyclostationary process - a cyclostationary signal is one which has correlation between areas in it's spectrum.

This makes it possible to discriminate between two completely overlapping signals. For example, if I receive two signals from antennas which are very close together (or indeed both transmitted from the same antenna) which use the same carrier frequency, it isn't possible to separate them using traditional methods. However, using the cyclic statistics, I can.

Taking this a step further produces great improvements in direction finding. This is because two targets which are very close to each other "blur" together, so that DF equipment is fooled into thinking there is only one target, lying somewhere between the two. One method for dealing with this is to filter out the frequencies of one transmitter. However, if the two transmitters are using the same frequency band, this isn't possible - unless cyclostationarity is used. By using a time-variant filter, it is possible to remove unwanted targets, however closely they overlap - either spatially or spectally.