An upper bound on the bit-error probability (BEP) of a linear cyclic code over GF(2/sup l/) with hard-decision (HD) maximum-likelihood (ML) decoding on memoryless symmetric channels is derived. Performance results are presented for Reed-Solomon codes on GF(32), GF(64), and GF

In this paper the concept of differentially coherent detection of differentially phase-encoded QASK signals (DQASK) is described, and a receiver structure proposed. The remainder of the paper analyzes the performance of DQASK in the presence of a Gaussian noise environment with comparisons made to coherent detection of QASK.

The spread spectrum acquisition and tracking performance for the ShuttleS-band andKu-band communication links are analyzed and compared to test results. TheS-band link requirements are more severe than those of theKu-band links, hence, different despreader designs were developed for the two systems. TheS-band despreader acquires pseudonoise code lock by examining all possible code phases in half chip steps while theKu-band despreader acquires pseudonoise code lock by continuously sweeping a tau-jitter loop. Both despreaders employ a tau-jitter loop for code tracking. The code tracking performance is computed for the tau-jitter loop and compared to that of the more complex delay lock loop.

The false (sideband) lock problem in Shuttle Costas loop receivers, in the presencse of noise, is assessed in this paper. False lock margin is defined depending on symbol signal-to-noise ratio rather than in the absence of noise as reported earlier in [4], [5]. Closed form results are given when the arm filters of the Costas loop are one-pole Butterworth filters as used in the Shuttle receivers. However, the approach taken is also general enough to cover filters of arbitrary characteristics. As part of the development of the false lock margin, it is shown that the false lock phenomenon of the squaring loop is identical to that of the Costas loop.

Error correction coding techniques significantly improve performance of spread spectrum communication systems in environments containing jamming, multipath, and unregulated multiple access. This paper investigates the optimization of spread spectrum system performance for time-varying unknown interference. Noncoherent frequency hopping (FH) spread spectrum modulation, and hybrid FH-PN incorporating a direct sequence PN modulation on each hopped frequency are studied. For FH or FH-PN, the data modulations considered are differential phase-shift-keying (DPSK), differential quadriphase-quadriphase-shift-keying (DQPSK), and multiple-frequency-multiple-frequency-shift-keying (MFSK). Both block and convolutional error correction coding techniques are studied as a means of improving the spread spectrum performance.

For convolutional codes, thc variation of the minimum distance between nonmerging codewords with the lengths of those codewords is considered for all finite lengths. This is carried out in terms of a new distance parameter for convolutional codes do, the minimum average weight per branch over all cycles. Upper and lower bounds on do for binary convolutional codes of rate1/nare presented. The tradeoff betweend_{o}and the free distanced_{free}is obtained for small memory length codes.

Convolutional encoding with biphase modulation is an attractive combination of modulation/coding for the Gaussian channel, but a means of tracking carrier phase must be provided. The performance of combined sequential decoding and suppressed carrier (Costas loop) tracking in the receiver is difficult to analyze but can be obtained by computer simulations. Results of such simulations are presented in the form of a Pareto fit to the computation distributions for various tracking loop bandwidths and demodulator quantization (soft decisions). These distributions are applied to predict probability of error performance for typical decoder parameters (buffer size, speed factor). The anticipated advantage of quantized demodulation is observed. However, narrow tracking bandwidths are required, with sufficient interleaving to overcome effects of correlated phase perturbations due to noise.