Aerospace Engineering and Engineering Mechanic

Heath, Robert

Humphreys, Todd

Pesyna, Ken

Wesson, Kyle

English

Texas ScholarWorks

GPS-assistedFemtocellSynchronizationandLocalizationThroughTightly-CoupledOpportunisticNavigationKEN PESYNA, KYLE WESSON, ROBERT HEATH, AND TODD HUMPHREYSTHE PROBLEMFemtocells must be synchronized with the cellularnetwork and also be self-locatable• GPS is typically used to achieve this• Problem: GPS signals attenuate 30–50 dB in-doorsFEMTOCELL REQUIREMENTSSynchronization Requirements:Standard Time FrequencyCDMA2000 10 µs 100 ppbGSM N/A 100 ppbWiMAX 1 µs (TDD) 8 ppmLTE 3 µs (TDD) 250 ppbWCDMA 2.5 µs (TDD) 250 ppbTD-SCDMA 2.5 µs 100 ppbLocation Requirements: E911, Spectrum LicensingSOLUTIONS1. Cellular Network Listen2. Precision Time Protocol (IEEE 1588)3. Global Positioning System (GPS)GPS SEARCH SPACEGPS acquisition includes a 2-dimensional searchover frequency (doppler) and code-phase (time)STANDALONE GPS LIMITATIONS1. Large searchspace2. Femtocell clocklimits coherentintegration timeUnstable OscillatorPhasor RotationReIm∫ ∫ ∫ ∫∫ ∫ ∫ ∫∫ ∫ ∫ ∫∫ ∫ ∫ ∫Code Phase [µs]Frequency [Hz]-500 500-60006000TCON-ENABLED FEMTOCELLTightly-Coupled Opportunistic Navigation(TCON) is a strategy for exploiting the frequencystability, transmit location, and timing infor-mation of non-GPS “signals of opportunity” toassist GPS-synchronized femtocells in weak-signalenvironments. A femtocell can use TCON to:1. Constrain its search space2. Increase its coherent integration time–> frequency stability transferSIGNALS OF OPPORTUNITYFREQUENCY STABILITY TRANSFER MODELFrequency stability transfer is the exercise of compensating for the local oscillator’s phase instability byapplying phase corrections derived from a tightly coupled stable aiding signal:RotationAccumulationIntermediate AccumulationFinal   DespreadScale*S S ′ S ′′km = argmaxk |F [k]|S ′′ = F [km]∑(·)(fGNSSfAID)F = FFT[S ′1, S′2, ..., S′NS]∆φ[j]∆φAID[j]rGPS[n]CGPS[n]ejθ[n] “Tight Coupling” implies that∆φAID[j] is traceable to thesame clock used to downmixand sample rGPS[n].RESULTS: CDMA-BASED TCON FOR FEMTOCELLSMean and Standard Deviation of CDMA Frequency Error Mean and Standard Deviation of CDMA Timing OffsetCarrier Freq. [Mhz] Mean [Hz] Std. Dev. [Hz]Verizon 1935 0.006 0.012Sprint 1952.5 -0.001 0.038Cricket 1977.5 0.100 0.058Carrier Freq. [Mhz] Mean [µs] Std. Dev. [µs]Cricket 1977.5 3.773 0.031Verizon 1935 2.968 0.016Sprint 1952.5 40.745 0.03510−1 100 101 10200.10.20.30.40.50.60.70.80.91time  [sec]<C2 coh>  Verizon 1935 MhzSprint 1952.5 MhzCricket 1977.5 MhzOCXOTCXO10−1 100 101 102−10−50510152025trackingacquisitiontime  [sec]SNR  [dB]  Verizon 1935 MhzSprint 1952.5 MhzCricket 1977.5 MhzOCXOTCXOMean-squared coherence of the TCXO-, OCXO-, Pre-detection SNR for TCXO-, OCXO-, and CDMA-generatedand CDMA-driven carrier phase estimates carrier phase estimates for an assumed C/N0 = 5 dB-Hz.CONCLUSIONBy harnessing the frequency and time informationof CDMA signals, a TCON-enabled femtocell canacquire and track GPS signals down to 5 dB-Hz.This would allow the synchronization and localiza-tion of femtocells in 90% of residences.REFERENCES[1] K.M. Pesyna, K.D. Wesson, R.W. Heath, T.E. Humphreys.“Extending the Reach of GPS-assisted Femtocell Synchro-nization and Localization Through Tightly-Coupled Oppor-tunistic Navigation” to appear in the IEEE 2nd Intl. Workshipon Femtocell Networks, Globecom, December 20111

GPS-assisted Femtocell Synchronization and Localization Through Tightly-Coupled OpportunisticNavigation

https://repositories.lib.utexas.edu/bitstream/2152/63332/2/tconFemto2011.pdf

GPS-assisted Femtocell Synchronization and Localization Through Tightly-Coupled OpportunisticNavigation

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