Abstract: A modulation circuit is used in GMSK modulation system. The system includes I-channel and Q-channel ROM look-up tables, each preprogrammed for generating a representative digital waveform based on an input data stream and a clock signal. Each digital waveform is converted to an analog signal for subsequent radio frequency (RF) modulation. Each ROM is addressed by an interpolation counter controlled by a clock signal, by a data shift register receiving input data at a rate corresponding to the clock signal, and by an quadrant register, also receiving the input data, for specifying the phase of the data signal with respect to the clock signal. Additionally, a signal indicates a time at which synchronization to the system clock is required and such synchronization requires synchronizing at a non-integer bit interval time, and in response to that signal, the address of the ROMs is adjusted in order to modify the phase of the data signal so that it is consistent with the system clock requirement.

Abstract: A time division multiple access (TDMA) radio system conveying a quadrature phase shift keying (QPSK) modulated data signal is disclosed. In order to overcome multipath distortion and phase variation introduced by the radio channel, a synchronizing poriton of a TDMA timeslot is transmitted in only one vector of the QPSK modulation. The system utilizes the one vector synchronizing portion to develop a channel profile estimate which is applied to the received message portion of the QPSK data signal to compensate for the multipath distortion and phase variation during one TDMA timeslot.

Abstract: A method and apparatus for phase-coherently demodulating a multipath-impaired time division multiple access QPSK data timeslot is disclosed. A quadrature separator generates multipath-impaired intermediate signals which, during a predetermined synchronizing sequence for the timeslot, are applied to a pair of synchronizing correlators to generate quadrature multipath profiles. These profiles then are used to modify subsequently received QPSK timeslot signals at the separator outputs to coherently construct multipath compensated I and Q channel data.