National Instruments Corporation

Sartaj Chaudhary

Vijaya Yajnanarayana

Baijayanta Ray

I Zakir Ahmed

Utkarsh Gupta

System and methods and memory media for identifying a rogue base station. A receiver captures an input signal that includes a mixture of the rogue station's transmission and the transmission of a victim base station. The victim station's transmission is removed from the mixture. A plurality of channel signals are extracted from the residual signal. The channel signals are analyzed which of them are 'valid', i.e., contain a GMSK-modulated GSM signal. The 'valid' channel signals are low pass filtered and then analyzed to determine which of them corresponds to the beacon channel. Information identifying the rogue base station is extracted from the beacon channel.

Identifying rogue GSM base stations by intercepting downlink beacon channels

A computer-implemented system and method for blind demodulation of an offset QPSK input signal, involving repeatedly performing a set of operations, including: (a) applying a phase correction to the input signal based on an estimate of a carrier phase offset of the input signal to obtain a first modified signal; (b) shifting a quadrature component of the first modified signal by half a symbol period relative to an inphase component to obtain a second modified signal; (c) extracting a first sequence of symbols from the second modified signal, where the extraction includes estimating a symbol timing offset from the second modified signal; (d) performing hard-decision demodulation on the first sequence of symbols to obtain a second sequence of reference symbols; (e) computing a phase difference between the first sequence of symbols and second sequence of reference symbols; and (f) updating the carrier phase offset estimate using the phase difference.

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Mumbai, India

Sartaj Chaudhary