A digital radio receiver (7) is arranged to receive and process data frames, each data frame comprising (i) a plurality of identical synchronization sequences; (ii) identification data different from the synchronization sequences; and (iii) convolution-encoded message data. An initial-synchronization section of the receiver (7) uses the plurality of synchronization sequences in a received data frame to perform a frequency-synchronization or symbol-timing-synchronization operation. A frame-synchronization section determines frame-synchronization information by correlating at least a part of the received identification data against reference identification data stored in a memory. A convolution-decoding section uses the frame-synchronization information to decode the message data.

A communication device of the disclosure includes a phase synchronizer, a first modulator, and a detector. The phase synchronizer generates a second signal on a basis of a first signal received from a communication partner. The first modulator is able to modulate the first signal on a basis of the second signal. The detector detects that synchronization between the first signal and the second signal is lost.

A receiver circuit includes a quadrature signal generator to generate an in-phase (I) signal and a quadrature (Q) signal from a local oscillator signal and an IQ phase sense and control circuit to generate a phase adjustment code responsive to a phase error between quadrature signals generated by a plurality of mixers. The receiver circuit also includes a phase corrector to adjust a phase difference between the I and Q signals from the quadrature signal generator to generate corrected I and Q signals to be provided to the plurality of mixers.

A receiver circuit includes a quadrature signal generator to generate an in-phase (I) signal and a quadrature (Q) signal from a local oscillator signal and an IQ phase sense and control circuit to generate a phase adjustment code responsive to a phase error between quadrature signals generated by a plurality of mixers. The receiver circuit also includes a phase corrector to adjust a phase difference between the I and Q signals from the quadrature signal generator to generate corrected I and Q signals to be provided to the plurality of mixers.

A receiver circuit includes a quadrature signal generator to generate an in-phase (I) signal and a quadrature (Q) signal from a local oscillator signal and an IQ phase sense and control circuit to generate a phase adjustment code responsive to a phase error between quadrature signals generated by a plurality of mixers. The receiver circuit also includes a phase corrector to adjust a phase difference between the I and Q signals from the quadrature signal generator to generate corrected I and Q signals to be provided to the plurality of mixers.

A local oscillator outputs a local oscillation signal. A orthogonal detector subjects a received signal to orthogonal detection by using the local oscillation signal so as to output an I-phase baseband signal and a Q-phase baseband signal. A first HPF and a second HPF reduce a direct current component of each of the I-phase baseband signal and the Q-phase baseband signal. A demodulator demodulates the I-phase baseband signal and the Q-phase baseband signal output from the first HPF and the second HPF. A distribution detector detects an unevenness in a distribution of the I-phase baseband signal and the Q-phase baseband signal with the reduced direct current component. When the distribution detector detects an unevenness in the distribution, the distribution detector changes a status of the first HPF and the second HPF.

A method for detecting useful signals in an overall signal. Each useful signal may be affected with a frequency drift. In the detection phase, frequency spectra for detecting the overall signal for multiple detection time windows are calculated and useful signals according to the detection frequency spectra are detected. In the estimation phase, for each useful signal detected: the frequency of the overall signal for multiple frequency drift values is reset. In the estimation phase, for each useful signal detected, a frequency spectrum is calculated for the estimation of the overall signal for each frequency drift value over an estimation time window having the useful signal detected and of a duration higher than the detection time window. In the estimation phase, for each useful signal detected, the frequency drift is estimated affecting the useful signal detected according to the estimation frequency spectra.

A spatial position-dependent I/Q domain modulation method, dual domain modulation method and multiple access communication method are provided. The methods eliminate the dependence of physical layer secure communication on channel state information, and realize the function that a receiver at an expected position can communicate normally, while an eavesdropper at other positions cannot receive a signal or can only receive a wrong signal. The security capability of a wireless communication system is improved from the spatial dimension. The multiple access communication method can realize the distinguishing of multiple users according to precise spatial position points. Even if a plurality of users are located in the same sector in an angular domain, as long as the spatial positions of these users are different, the method can be used to perform multiple access communication, thereby further improving the spatial multiplexing rate of the system and increasing the system capacity.

A receiver is presented, such that the receiver may be configured to receive transmissions in accordance with a continuous waveform and to relock quickly on a received transmission when the transmitter is switched or a change in the waveform parameters is made. The receiver may be configured to support reception of a shared channel and/or of a channel allocated for SCPC usage and may be modified while used (e.g., dynamic SCPC). In addition, a satellite communication system is presented, the satellite communication system comprising at least one receiver in accordance with the above-described receiver. The satellite communication system may be configured to utilize the receiver's characteristics for at least the purpose of achieving a highly efficient return link channel.

A local oscillator outputs a local oscillation signal. A orthogonal detector subjects a received signal to orthogonal detection by using the local oscillation signal so as to output an I-phase baseband signal and a Q-phase baseband signal. A first HPF and a second HPF reduce a direct current component of each of the I-phase baseband signal and the Q-phase baseband signal. A demodulator demodulates the I-phase baseband signal and the Q-phase baseband signal output from the first HPF and the second HPF. A distribution detector detects an unevenness in a distribution of the I-phase baseband signal and the Q-phase baseband signal with the reduced direct current component. When the distribution detector detects an unevenness in the distribution, the distribution detector changes a status of the first HPF and the second HPF.