White-Space Networking

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White-Space Networking. Nick Feamster CS 6250 Fall 2011. (slides from Rohan Murty ). Motivation. Bandwidth becoming scarcer and more valuable Increased demands on wireless applications Users demand higher performance Dynamically accessing multiple channels can increase spectrum efficiency - PowerPoint PPT Presentation

Text of White-Space Networking

White-Space Networking

White-Space NetworkingNick FeamsterCS 6250Fall 2011(slides from Rohan Murty)MotivationBandwidth becoming scarcer and more valuableIncreased demands on wireless applicationsUsers demand higher performanceDynamically accessing multiple channels can increase spectrum efficiencyOur goal is to support multiple transmissions and increase performance by mitigating interference


Higher FrequencyWi-Fi (ISM)Broadcast TV3

dbmFrequency-60-100White spaces470 MHz700 MHzWhat are White Spaces?40 MHz7000 MHz


ISM (Wi-Fi)7004702400518025005300 are Unoccupied TV ChannelsWhite Spaces54-90170-216Wireless Mic

TV Stations in America50 TV Channels

Each channel is 6 MHz wideFCC Regulations*Sense TV stations and Mics Portable devices on channels 21 - 514The Promise of White Spaces50 MHz7000 MHz


ISM (Wi-Fi)700470240051802500530054-90174-216Wireless Mic

More SpectrumLonger RangeUp to 3x of 802.11gat least 3 - 4x of Wi-Fi5White Spaces Spectrum AvailabilityDifferences from ISM(Wi-Fi)6

FragmentationVariable channel widths1234512345Each TV Channel is 6 MHz wide Use multiple channels for more bandwidthSpectrum is Fragmented6White Spaces Spectrum AvailabilityDifferences from ISM(Wi-Fi)7

FragmentationVariable channel widths12345Location impacts spectrum availability Spectrum exhibits spatial variationCannot assume same channel free everywhere12345Spatial Variation

TVTowerWhite Spaces Spectrum AvailabilityDifferences from ISM(Wi-Fi)8

FragmentationVariable channel widthsIncumbents appear/disappear over time Must reconfigure after disconnectionSpatial VariationCannot assume same channel free everywhere

1234512345Temporal VariationSame Channel will not always be freeAny connection can bedisrupted any timeChannel Assignment in Wi-Fi9Fixed Width Channels

Optimize which channel to use


Spectrum Assignment in WhiteFi10

12345Spatial Variation BS must use channel iff free at clientFragmentation Optimize for both, center channel and width12345Spectrum Assignment ProblemGoalMaximize ThroughputIncludeSpectrum at clientsAssignCenter ChannelWidth&10Accounting for Spatial Variation11



Use widest possible channelIntuition13452Limited by most busy channelBut Carrier Sense Across All Channels

All channels must be freeBS(2 and 3 are free) = BS(2 is free) x BS(3 is free)Tradeoff between wider channel widths and opportunity to transmit on each channel12Discovering a Base Station13

Can we optimize this discovery time?12345

Discovery Time = (B x W) 12345How does the new client discover channels used by the BS? BS and Clients must use same channelsFragmentation Try different center channel and widths13SIFT, by example14


10 MHz5 MHzSIFTPattern match in time domainDoes not decode packetsDataACKSIFS14