Title page for ETD etd-05032011-133905


Type of Document Master's Thesis
Author Steiner, Michael Paul
Author's Email Address mstein02@vt.edu
URN etd-05032011-133905
Title Spectrum Sensing and Blind Automatic Modulation Classification in Real-Time
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Bose, Tamal Committee Chair
Hasan, S. M. Shajedul Committee Member
Reed, Jeffrey Hugh Committee Member
Keywords
  • implementation
  • blind classification
  • cumulant
  • modulation classificaiton
  • real-time
  • spectrum sensing
Date of Defense 2011-04-28
Availability unrestricted
Abstract
This paper describes the implementation of a scanning signal detector and automatic modulation classification system. The classification technique is a completely blind method, with no prior knowledge of the signal’s center frequency, bandwidth, or symbol rate. An energy detector forms the initial approximations of the signal parameters. The energy detector used in the wideband sweep is reused to obtain fine estimates of the center frequency and bandwidth of the signal. The subsequent steps reduce the effect of frequency offset and sample timing error, resulting in a constellation of the modulation of interest. The cumulant of the constellation is compared to a set of known ideal cumulant values, forming the classification estimate.

The algorithm uses two platforms that together provide high speed parallel processing and flexible run-time operation. High-rate spectral scanning using an energy detector is run in parallel with a variable down sampling path; both are highly pipelined structures, which allows for high data throughput. A pair of processing cores is used to record spectral usage and signal characteristics as well as perform the actual classification.

The resulting classification system can accurately identify modulations below 5 dB of signal-to-noise ratio (SNR) for some cases of the phase shift keying family of modulations but requires a much higher SNR to accurately classify higher-order modulations. These estimates tend toward classifying all signals as binary phase shift keying because of limits of the noise power estimation part of the cumulant normalization process. Other effects due to frequency offset and synchronization timing are discussed.

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