Use of DS/SS signaling to mitigate Rayleigh fading in a dense scatterer environment

The issues discussed are summarised by a minimal checklist which should be applied to any DS/SS link architecture for use in a dense scatterer environment. For effective mitigation of fading the chip interval T, should be at most equal to the RMS delay spread Δ, indeed preferably much smaller. For minimal intersymbol interference the symbol duration T_s should be much longer than Δ. On a fast-moving antenna platform the distance traversed by the antenna during one symbol interval should be much less than 0.38 λ. Otherwise, coherent symbol correlation becomes difficult, and a high irreducible error rate may result. The so-called mean bit error rates are just that. They are probabilistic means over the full range of antenna travel. If the antenna tends to remain stationary or travel very slowly, then perhaps it is more meaningful to speak of the maximum (or worst-case) error rate over a specified large fraction of all antenna locations. The chip stream should be as random as possible; that is, the chip values should be statistically uncorrelated. A chip-matched filter, adaptive to the continual metamorphoses of the arriving chip pulse shape and the mean chip arrival time, is essential to symbol detection at those frequently occurring antenna locations where the received power is a minimum, dispersion is a maximum, and the chip pulses arrive with essentially zero mean value. Such situations crop up roughly once per wavelength of antenna travel. In DPSK signaling the matched filter could be as simple as a single time delay of duration T_s