• DFT-BASED FREQUENCY OFFSET ESTIMATORS FOR 16-APSK

      Rice, Michael; Redd, Bryan; Ebert, Jamison; Twitchell, Autumn; Brigham Young University, Dept Electrical and Computer Engineering (International Foundation for Telemetering, 2019-10)
      In this paper, we analyze several DFT-based frequency offset estimators for use with the 16-APSK digital modulation scheme. Even a small frequency offset between radio transmitters and receivers can cause phase information to be lost, so a system to align the phases is required to reliably demodulate PSK signals. These estimators have been adapted for 16-APSK from methods originally intended for use with QPSK and CPM. These methods consist of a coarse search and a fine search with an optional dichotomous search to improve accuracy. We analyze the estimator error variance and bit error rate associated with several methods of frequency estimation. These estimators exhibit small estimate error and variance and can provide bit error rates close to the ideal AWGN BER.
    • ON CARRIER FREQUENCY AND PHASE SYNCHRONIZATION FOR CODED 16-APSK IN AERONAUTICAL MOBILE TELEMETRY

      Rice, Michael; Redd, Bryan; Briceno, Ximena; Brigham Young University, Dept Electrical and Computer Engineering (International Foundation for Telemetering, 2019-10)
      This paper examines the problem of carrier phase and frequency estimation for coded 16-APSK in aeronautical mobile telemetry. Given the fact that coded systems tend to operate at lower signalto-noise ratios than uncoded systems, the synchronizer must operate at these lower signal-to-noise ratios. For a 30 kHz frequency offset and a 10 Mbit/s 16-APSK signal, the conventional phase lock loop (PLL) system does not achieve consistent lock to be a useful approach. Consequently, a blind feed-forward approach, based on the FFT, and an initialized feedback approach based on the PLL were examined. The feed-forward estimator is capable of achieving BER ideal performance for Eb/N0 ≥ 6 dB using 1024 symbols. The feedback estimator, initialized using a feed-forward estimate based on 1024 symbols is also capable of achieving BER ideal performance for Eb/N0 ≥ 6 dB. Both synchronizers require a sufficiently good blind estimate: the estimate based on 2014 symbols appears to be the minimum value to achieve good performance.