Phase Distortion Study.
Abstract
This is the Final Report of a 9 month study of channel distortions on digital data transmission over the DSCS. Computer simulations and supporting analysis were developed for evaluating the degradation for QPSK/FDMA and QPSK/TDMA. Emphasis was placed on the use of adaptive equalization to correct severe phase distortion and alleviate intersymbol interference due to narrow bandwidth filtering. Several equalizer configurations and control strategies were developed for interfacing with present modems. Error correction coding was shown to significantly reduce degradation due to adjacent channel interference and intermodulation produced by channel saturation and AM/PM coversion. The study also investigated techniques for improved bandwidth utilization. For FDMA, the spacing between adjacent signals is reduced, and for TDMA, a higher signaling rate is enabled by narrowband equalized filters. With conventional QPSK, data transmission at 2 bps/Hz becomes feasible. Duobinary demodulation of QPSK achieves 3 bps/Hz at no increase in E sub b/N sub o through use of a maximum-likelihood demoduation technique and appropriate channel equalization. Performance is shown to be good even for saturating channels, and the rate-1/2 coding gain is comparable to that for the memoryless channel.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 20, 1976
- Accession Number
- ADA068351
Entities
People
- C. L. May
- C. R. Cahn