Presentation on theme: "Compressive Data Gathering for Large-Scale Wireless Sensor Networks"— Presentation transcript:
1Compressive Data Gathering for Large-Scale Wireless Sensor Networks Chong Luo, Feng Wu, Jun Sun and Chang Wen ChenMobicom’09, Beijing, China
2Outline Background Compressive Data Gathering Conclusion Compressive sensing theoryNew research opportunitiesCompressive Data GatheringThe first complete design to apply CS theory for sensor data gatheringConclusion
3Compressive SensingIf an N-dimensional signal is K-sparse in a known domain Ψ, it can be recovered from M random measurements by:
4New Research Opportunities Compressive Sensing HallmarksData Communications ResearchUniversalSame random projection op. for any compressible signalDemocraticPotentially unlimited number of measurementsEach measurement carries the same amount of informationAsymmetricalSimple encoding, most processing at decoderRandom linear network codingAchieves multicast capacityFountain codea.k.a. rateless erasure codePerfect reconstruction from N(1+ε) encoding symbolsDistributed source codinge.g. Slepian-Wolf codingBlind encoding, joint decodingIt is not hard to find many similarities between CS and Data communication topics..
5From Compressive Sensing to Compressive Data Gathering The asymmetrical property makes CS a perfect match for wireless sensor networksCompressive SensingCompressive Data GatheringSample-then-compressSample-with-compressionCompress-then-transmitCompress-with-transmissionThe long-established paradigm for digital data acquisition is to uniformly sample data at its Nyquist rate, and then compress the data before storage or transmission. CS shifts this paradigm by directly acquiring compressed data, turning sample-then-compress process into sample-with-compression process.
6Data Gathering in WSNs Challenges Global communication cost reduction Energy consumption load balancing
8Is Reconstruction Possible? FactsSensor readings exhibit strong spatial correlationsAccording to CS theoryReconstruction can be achieved in a noisy setting by solving:M<<N
9Practical Problem 1 Solution: Abnormal readings compromise data sparsitySolution:Signal d1Representation of d1 in DCT domainSignal in time domainRepresentation in DCT domainSignal d2Representation of d2 in time domain7-sparseOvercomplete basis
10Practical Problem 2If a signal is not sparse in any intuitively known domainvalue2y11Φd72051519312101417841613189t16
11Universal SparsityCS-based data representation and recovery is optimal in exploiting data sparsityEncoderThe same random projection operationDecoderSelect and design representation basis ΨReorder signal d to make it sparse in a known domainNeither transform-based compression nor distributed source coding is able to exploit these special types of data sparsityData collection and transmission order can be totally different from the recovery order. This flexibility is especially important for wireless multi-hop networks, in which transmitting data back and forth consumes a lot of energy.
12Network Capacity GainTheorem: In a wireless sensor network with N nodes, CDG can achieve a capacity gain of N/M over baseline transmission, given that sensor readings are K-sparse, and M = c1K.Mathematical proofSimulation verification
13Example 1 CTD data from NOAA N=1000, K≈40 M=100 Recon. Precision 99.2% Comm. Reduction5Capacity Gain10Only 40 coefficients (4.0%) are larger than 0.2
14Example 2 Temperature data from data center 498 temperature sensorssensor readings exhibit little spatial correlationsReorder sensors according to their readings at t0
15Utilizing Temporal Correlation Sensor readings at t0 + Δt are sparse as wellTemperatures do not change violently with time∆t=30min
16ConclusionCompressive Sensing is an emerging field which may bring fundamental changes to networking and data communications researchOur ContributionsThe first complete design to apply CS theory to sensor data gatheringCDG exploits “universal sparsity”CDG improves network capacityFuture WorkBring innovations to LDPC, NC, DSC, and Fountain code through CS theory