• Comparison of Viterbi and Sequential Decoding with a Noisy Carrier Reference

      Hofman, L. B.; Lumb, D. R.; NASA Ames Research Center (International Foundation for Telemetering, 1974-10)
      Performance of convolutionally encoded telemetry systems with Viterbi decoding or sequential decoding is well understood for the additive white Gaussian noise channel with coherent detection of bi-phase-shift-keyed signals. Significant degradation from ideal performance can occur due to correlated noise resulting from low signal-to-noise ratios in the receiver carrier tracking phase-locked loop. Performance at the lower telemetry data rates on the two Pioneer Jupiter deep space probes provides examples of the effect of correlated noise on a sequential decoding system. Performance degradation needs to be quantified as a function of carrier signal-to-noise ratio (P(c)/N(o)2B(lo)) and carrier-tracking- loop-bandwidth-to-symbol-rate ratio (B(l)/R(s)) in order to provide design and analysis information on such effects. Analytical modeling is extremely difficult, particularly where B(l)/R(s) is neither very large nor very small.
    • A Computer-Controlled, On-Board Data Acquisition System for Wind-Tunnel Testing

      Finger, Herbert J.; Cambra, Joseph M.; NASA Ames Research Center (International Foundation for Telemetering, 1974-10)
      A computer-controlled data acquisition system has been developed for the 40x80-Foot Wind Tunnel at Ames Research Center. The system, consisting of several small "on-board" units installed in the model and a data-managing, data-displaying ground station, is capable of sampling up to 256 channels of raw data at a total sample rate of 128,000 samples/sec. Complete signal conditioning is contained within the on-board units. The sampling sequence and channel gain selection is completely random and under total control of the ground station. Outputs include a bar-graph displays digital-to-analog converters, and digital interface to the tunnel's central computer, an SEL 840MP. The system can be run stand-alone or under the control of the SEL 840MP.
    • Some Simulation Results for Convolutional Codes Over a PCM/FM Fading Channel

      Grant, T. L.; Hofman, L.; NASA Ames Research Center (International Foundation for Telemetering, 1974-10)
      NASA is now actively planning entry probe missions for the outer planets. Such an entry probe requires a new telemetry link design. A probable modulation for this link is a continuous phase, narrow-band FSK (or PCM/FM), and this paper reports on simulations which can be used to estimate convolutional code performance with mild fading on such a channel. Simulated decoding has been performed for a range of signal-to-noise ratios on the PCM/FM channel with various fading characteristics.