Abstract: A complex multiplier 5 complex-multiplies base band signals x and y obtained from a receive signal by local oscillation signals c and s, to output complex detection signals p and q. A phase difference detecting portion 7 outputs the amount of the detected phase difference corresponding to the phase difference between the phase of the receive signal and the phase of the local oscillation signals. A loop filter 8 emphasizes its DC component. A local oscillation portion 6 outputs local oscillation signals having a frequency corresponding to the amount of the detected phase difference. A region judging portion 9 judges which of regions on a complex plane is one to which the base band signals belong, and outputs a region signal. A most frequent region judging portion 10 judges which of the regions is one in which the base band signals are concentrated most frequently upon input of the region signal a predetermined number of times.

Abstract: A rectangular to phase converter (201) includes a first converter circuit (201B) which limits signals to a predetermined level. A phase selector (259) selects a relative phase from the limited signals. According to one aspect of the invention, input rectangular coordinate signals are mapped to the first quadrant in a first quadrant mapping circuit (201A) before the first quadrant signals are limited and the relative phase signal is returned to the original quadrant by an original quadrant mapping circuit (260).

Abstract: In a signal processor for processing a multilevel signal, a partial response equalizer is provided having a first predetermined number of reference amplitudes. The equalizer receives the multilevel signal and detects a significant instant of amplitude transition of the multilevel signal with respect to the reference amplitudes and produces a signal representative of the amplitude at the detected significant instant. The amplitude representative signal assumes one of a second predetermined number of amplitudes including spontaneously generated amplitudes, the second predetermined number being greater than the first predetermined number of the reference amplitudes. A maximum likelihood estimator, connected to the equalizer, have transition states and a state transition rule which determines one of the states with respect to decision thresholds greater in number than the first predetermined number and equal to or smaller than the second predetermined number.

Abstract: A complex baseband signal as long as one period of PN signal is divided into three sequences. The three partial signals are input to three correlators which then calculate the correlations between the three partial signals and three partial PN signals. The squares of the absolute values of outputs from the three partial correlators are summed and the peak of the resultant summed signal is detected, thereby performing initial acquisition and tracking of synchronization of PN signal. Outputs from the three partial correlators are added together by an adder for generating a correlation signal used for data demodulation. Since partial correlation signals output from three partial correlators have a phase difference corresponding to a frequency offset, and error signal corresponding to the frequency offset is provided by performing complex conjugate product operations on the partial correlation signals.