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In this paper the frame timing acquisition which is important for Time Division Duplex (TDD) mode of transmission in Direct Sequence Spread Spectrum (DS-SS) communications is studied.In TDD DS-SS system Frame timing and base station signal must be obta.ined in presence of interference from other mobile users. It is shown that acquisition of non-continuous TDD signals is possible after transniission of few acquisition bursts. Computer simulation technique are used to eva.luate the performmce of this method.

It has been considered impossible to demodulate a fast frequency-hopping (FFH) spread-spectrum signal coherently in a frequency selective fading channel as a result of difficulties with making the receiver local oscillator track the phase of a received signal that lacks phase continuity. This paper proposes a coherent demodulator for both FFH-PSK (phase-shift keying) and FFH-FSK (frequency-shift keying) signal employing a method in which the received signal is noncoherently downconverted and phase-adjusted by an adaptive algorithm.Computer-simulations show that performance is better than in the case of noncoherent demodulators and that the interference-rejection effect of the adaptive algorithm produces strong protection against interferences from other CDMA users.