• DIFFERENTIAL ENCODING REVEALED: AN EXPLANATION OF THE TIER-1 DIFFERENTIAL ENCODING IN IRIG 106

      Rice, Michael; Brigham Young University (International Foundation for Telemetering, 2007-10)
      IRIG 106-04 specifies differential encoding for use with the interoperable Tier-1 modulations to deal with phase and delay-axis ambiguities associated with PLL-based carrier phase synchronization. The origins of the differential encoding have been shrouded in the mists of an unavailable technical report and a mysterious connection to previous published work in the open literature. This paper removes the mystery by showing that the differential encoding rule results from encoding bit-by-bit transitions in the phase trajectory of an offset QPSK modulated carrier.
    • A HIGH-ACCURACY AND LOW-COMPLEXITY CARRIER-OFFSET-FREQUENCY ESTIMATOR

      Rice, Michael; Palmer, Joseph; Brigham Young University (International Foundation for Telemetering, 2007-10)
      A single-tone frequency estimator for a non-uniformly sampled sinusoid is proposed. A nonuniformly sampled sinusoid may be generated from the received training sequences of a telemetry link. The frequency of the sinusoid matches the carrier-frequency-offset (CFO) of the received signal, and estimation of this quantity allows a receiver to compensate for the CFO. The performance bounds of this type of estimator have been investigated in the literature, though little work has been published on practical algorithms. The estimator proposed in this paper is a generalization of phase-increment estimators previously described in the literature. It exhibits a low computational complexity yet converges to theoretical bounds at high SNR. The paper argues that a periodic training sequence structure, combined with the new estimator, allows for a high-accuracy and lowcomplexity CFO compensator.
    • THE IMPLEMENTATION OF AN IRREGULAR VITERBI TRELLIS DECODER

      Rice, Michael; Lavin, Christopher; Brigham Young University (International Foundation for Telemetering, 2007-10)
      The Viterbi algorithm has uses for both the decoding of convolutional codes and the detection of signals distorted by intersymbol interference (ISI). The operation of these processes is characterized by a trellis. An ARTM Tier-1 space-time coded telemetry receiver required the use of an irregular Viterbi trellis decoder to solve the dual antenna problem. The nature of the solution requires the trellis to deviate from conventional trellis structure and become time-varying. This paper explores the architectural challenges of such a trellis and presents a solution using a modified systolic array allowing the trellis to be realized in hardware.
    • An Optimum Detector for Space-Time Trellis Coded Differential MSK

      Rice, Michael; Dang, Xiaoyu; Brigham Young University (International Foundation for Telemetering, 2007-10)
      The accuracy of channel estimation plays a crucial role in the demodulation of data symbols sent across an unknown wireless medium. In this work a new analytical expression for the channel estimation error of a multiple input multiple output (MIMO) system is obtained when the wireless medium is continuously changing in the temporal domain. Numerical examples are provided to illustrate our findings. Space-time (ST) coding using Continuous Phase Modulation (CPM) has spectral advantages relative to linear modulations. In spite of the spectral benefits, Space-Time Trellis Codes (STTC) using the CPM implementation of Minimum Shift Keying (MSK) scheme has inherent inphase and quadrature interference, when the received complex baseband signal is the input into the matchfilter to remove the shaped sinusoid pulses. In this paper a novel optimum transmitting and detecting structure for STTC-MSK is proposed. Treating the Alamouti scheme as an outer code, each STTC MSK waveform frame is immediately followed by the orthogonal conjugate waveform frame at the transmit side. At the receiver first orthogonal wave forming is applied, then a new time-variant yet simple trellis structure of the STTC-MSK signals is developed. This STTC-MSK detector is absolutely guaranteed to be I/Q interference-free and still keeps a smaller computation load compared with STTC-QPSK. Simulations are made over quasi-static AWGN fading channel. It is shown that our detector for ST-MSK has solved the I/Q interference problem and has around 2.8 dB gain compared with the Alamouti Scheme and 3.8 dB gain for bit error rate at 5 X 10^(-3) in a 2 by 1 Multiple Input Single Output system.
    • TURBO-CODED APSK FOR TELEMETRY

      Shaw, Christopher; Rice, Michael; Brigham Young University (International Foundation for Telemetering, 2007-10)
      This paper considers the use of Amplitude-Phase Shift Keying (APSK) for a telemetry system. Variable rate turbo codes are used to improve the power efficiency of 16- and 32-APSK. We discuss compensation techniques for power amplifier nonlinearities. Simulation results show the improved spectral efficiency of this modulation scheme over those currently defined in telemetry standards.
    • A WIDEBAND CHANNEL MODEL FOR SHF-BAND TELEMETRY OVER WATER

      Rice, Michael; Lei, Qiang; Brigham Young University (International Foundation for Telemetering, 2007-10)
      Data recorded during multipath channel sounding experiments, conducted off the coast of Pt. Mugu Naval Air Station at 8.0 GHz was used to model the multipath interference at SHF band over water. The modeling results show that a three ray model consisting of line-of-sight propagation and two reflected propagation paths is a good fit for the measured channel frequency responses. The properties of the multipath reflections are determined by geometry and sea state. For calm seas, the first reflection is a large amplitude short-delay reflection whereas for rough seas, the first reflection has a smaller amplitude and longer delay. The second reflection has a smaller amplitude and larger delay when the sea is calm.