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The magnitude of the delay difference due to multihop wave propagation is such that it cannot be ignored compared to the inverse of the transmission speed, and it is capable of degrading transmission characteristics in TDMA digital mobile communications. It is known that adaptive equalizers are effective in preventing this problem; however, the traclung characteristics of such equalizers with respect to high-speed variations of mobile communications transmission paths are not adequate. This paper is an attempt to clarify the factors that degrade the tracking ability of such equalizers and to develop countermeasures to protect against them. Specifically, the fact that the equalizer cannot track a timevarying channel and evaporates when a decrease in the received signal level occurs due to the effects of wave propagation, etc., is a major contributor to the deterioration of equalization characteristics. This assertion is demonstrated analytically by simulations using the twowave Rayleigh model and the one-wave model in which the amplitude changes linearly with respect to time. In addition, to decrease the level of deterioration, a symbolselective double-directional equalizing system has been proposed; the efficacy of this system is demonstrated by simulation.

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