Building Efficient Spectrum-Agile Devices for Dummies

Building Efficient Spectrum-Agile Devices for DummiesEugene Chai, Kang G. ShinUniversity of Michigan Ann ArborJeongkeun JK Lee, Sung-Ju Lee, Raul EtkinHewlett Packard Labs Palo Alto

1Why Fast Spectrum Shaping?2

Median Channel Availability = 3 seconds, approx300MHz~1GHzWhat about allocation over time?Using measurement traces from RWTH Aachen University:2How Can We Do This?3Option 1: Commercial Off-The Shelf (COTS) DevicesMAC: Incompatible preamblesPHY: Monolithic spectrumOption 2: Software Defined RadiosFPGA: ComplexSoftware: Slow3Our Solution: Rodin4PHYMACNETTRANSAPPMACCOTSSDRHybrid ArchitecturePer-Frame Spectrum ShapingSpectrum-Agile PreambleRodin4EmptyEmptyRodin: Spectrum Shaping5FrequencyTimeEmptyEmptyEmptyRodin detects interference and reshapes next frame5Rodin: Spectrum Shaping6Rodin splits a monolithic spectrum into two subbands:

From COTSTo Channel6Rodin: Filter Design7

Problem: Frequency offset between devices7Our Solution: Rodin8PHYMACNETTRANSAPPMACCOTSSDRHybrid ArchitecturePer-Frame Spectrum ShapingSpectrum-Agile PreambleRodin8Rodin: Spectrum AgreementWhy is spectrum agreement hard?This is the actual spectrum allocationABEmptyBAEmptyFrequencyThis is what the receiver seesOccupiedOccupiedEmptyOccupiedOccupiedEmptyFrequencyThe receiver does not know which subbands are assigned to each transmitter If a transmitter uses M out of N total subbands, the number of possible combinations is9

9Rodin: Spectrum AgreementP1EmptyP4EmptyP2P3Frequency

Solution: I-FOP (In-Front Of Preamble)10I-FOPCOTS PreambleDataComposite Rodin FrameTransmitter10Rodin: Spectrum AgreementSolution: I-FOP (In-Front Of Preamble)11P1XP4XP2P3FrequencyTimePN Sequences P1,,P4OrderArrival TimeReceiverI-FOPCOTS PreambleDataComposite Rodin Frame11Rodin: Spectrum Agreement12P1XP4XP2P3FrequencyTime

P1P2

P3

P4

P4P1

P2

P3Receiver searches for P1,, P4 in each subband simultaneouslyReceiver12Rodin: Spectrum Agreement13Device AddressingReceiver ComplexityPreamble CollisionAssociation frame with an association preamble addressSame PN sequences; same order; same transmit instant Parallel search over multiple subbands in hardware13Our Solution: Rodin14PHYMACNETTRANSAPPMACCOTSSDRHybrid ArchitecturePer-Frame Spectrum ShapingSpectrum-Agile PreambleRodin14How Does Rodin Compare?15Picasso (SIGCOMM 2012)WiFi-NC (NSDI 2012)Spectrum Virtualization Layer (DySpan 2012)Jello (NSDI 2010)Concurrent operations over sub-channelsSoftware layer between standard PHY and channelFlow-based spectrum allocation15Evaluation16Spectrum ShapingI-FOPThroughput16Implementation & EvaluationSpectrum ShapingFPGA and Matlab implementations10MHz COTS signal split into two 5MHz subbands separated by 10MHzInterference BW is 2.5, 5 and 10MHz17Parameters

17Evaluation: Spectrum ShapingExperiment 1: Spectrum shaping vs no spectrum shaping. No interference.Spectrum shaping does not distort the signal18

18

Evaluation: Spectrum ShapingExperiment 2: Spectrum shaping with interferenceRodin can avoid interference effectivelyWithout shapingWith shapingError Vector Magnitude19Implementation & Evaluation20I-FOPImplemented using WARPLab and Matlab5 WARP devices placed throughout an office20MHz channel with 8 subbandsPreamble consists of 4 sequences transmitted over 4 subbands20Evaluation: I-FOPExperiment 3: I-FOP under varying SIR levelsWe randomly select 3 devices as transmitter, receiver and interfererDetection ratio increases with increasing preamble sequence length21

Preamble LengthDelay (microsec)371.8733.651135.5621Simulations22

Experiment 4: Transmission opportunities in 1.5GHz spectrum band centered at 5.25GHzMore transmit opportunities with smaller subband bandwidth22Where do we go from here?23Spectrum Agile NetworksHow well do current protocols work under spectrum agility?Whitespace NetworksWhat happens if we change the operating frequency?Integrated Hybrid PlatformCan we build a more integrated device?23Conclusions24Hybrid ArchitecturePer-Frame Spectrum ShapingSpectrum-Agile PreambleRodin is the key to enabling large scale spectrum agile networks24

Questions?2525