• High Data Rate Coding for the Space Station Telemetry Links

      Lumb, D. R.; Viterbi, A. J.; NASA; Linkabit Corp. (International Foundation for Telemetering, 1971-09)
      This paper summarizes a study of coding systems for high data rates with potential application to the space station telemetry links. Among the approaches considered were convolutional codes with sequential, Viterbi and cascaded Viterbi decoding. It was concluded that a high-speed (.40 Mbps) sequential decoding system best satisfies the requirements for the assumed growth potential and specified constraints. Trade-off studies leading to this conclusion will be reviewed. Some sequential (Fano) algorithm improvements will be discussed as well as real-time simulation results.
    • L-/S-Band Calibration Error Analysis

      Taylor, Ralph E.; NASA (International Foundation for Telemetering, 1971-09)
      A statistical error analysis is performed to determine the degree of uncertainty encountered when calibrating steerable receiving antennas with the solar calibration method. The analysis considers the propagation of precision error indexes. It is shown that a worst-case one-sigma (1σ) uncertainty of ±0.8 dB in system noise temperature occurs for a solar calibration at L-band. Somewhat better precision can be achieved by monitoring the antenna gain-to-noise temperature (G/T) ratio at a station; a worst-case uncertainty of ±0.5 dB (1σ) can be realized. An error analysis is made of a method to determine absolute antenna gain based upon solar flux density. The uncertainty in this type measurement is ±0.7 dB (1σ) at L- and S-band frequencies.
    • Performance Results for a Hybrid Coding System

      Hoffman, L. B.; NASA (International Foundation for Telemetering, 1971-09)
      Computer simulation studies of the hybrid pull-up bootstrap decoding algorithm hive -been conducted using a constraint length 24, nonsystematic, rate 1/2 convolutional code for the symmetric channel with both binary and 8-level quantized outputs. Computational performance was used to measure the effect of several decoder parameters and determine practical operating constraints. Results reveal that the track length may be reduced to 500 information bits with small degradation in performance. The optimum number of tracks per block was found to be in the range of 7 to 11. An effective technique was devised to efficiently allocate computational effort and identify reliably decoded data sections. Long simulations indicate that a practical bootstrap decoding configuration has a computational performance about 1.0 dB better than sequential decoding and an output bit error rate about 2.5 x10⁻⁶ near the R(comp) point.