Abstract: A TDM/TDMA (Time Division Multiplex/Time Division Multiple Access) multidirection multiplex communication system of the type using a demand assignment protocol. The system has a multiframe arrangement in which each unit frame is constituted by a frame synchronization signal, a connection control signal for setting up radio channels, N conversation channels, and a single additional bit transmission channel shared by the N conversation channels. When N unit frames are combined in a multiframe format by a frame synchronization signal, N additional bit transmission channels are provided in total.

Abstract: A deman assignment TDMA communication system includes first and second time division multiplexed (TDM) transmitting channels for establishing a broadcast channel from the central station to the terminal stations and a pair of first and second TDM receiving channels for establishing channels from the terminal stations to the central station on an as needed basis. A polling circuit transmits a polling signal on a common time slot of the broadcast channel for polling the terminal stations and periodically shifting the polled station to the next to permit each of the terminal stations to send an acknowledgment to the central station on a common time slot of the established channels. A fault identification circuit is provided for detecting the presence and absence of the acknowledgment at the central station and determining therefrom the location of a fault.

Abstract: In a multidirection multiplex communication system of the demand assign type including a central station and a plurality of subscriber stations cooperating therewith, a maintenance poling signal assigned to a maintenance time slot of a frame is sent from the central station to a subscriber station not requested to send an information signal, the subscriber station inserts a maintenance burst signal in a time slot of a frame corresponding to the maintenance poling signal and sends back the maintenance burst signal. The central station extracts the timing signal transmitted from the subscriber station out or the maintenance burst signal and compares the extracted timing signal with the reference timing signal in the central station to form a time difference signal. After inserting the time difference signal in the maintenance frame the central station sends back the time difference signal to the subscriber station.

Abstract: A baseband switching device for switching between first and second redundant channels is provided with the capability of adjusting the phase and polarity of the data signals in each channel to be equal so that data will continue without interruption when switching from one channel to another.

Abstract: A carrier recovery apparatus for phase modulated waves including phase-locked loops is operable to prevent false locks. The apparatus includes a clock recovery circuit which generates a signal in response to a modulated carrier, a first phase comparator responsive to the modulated carrier and the output of a VCO, a second phase comparator responsive to the first phase comparator and the clock signal, and a control device for superimposing the low frequency component of the output of the second phase comparator on the output of the first phase comparator or a loop filter which controls the VCO.

Abstract: A demodulator for PSK-FM double modulated carrier signals in which the carrier signal is 2.sup.N phase modulated by a main signal and frequency modulated by a sub-signal. A clock component is extracted from the received double-modulated carrier signal and the carrier signal sampled in accordance therewith. The amplitude of the output of the sampling gate is limited prior to frequency multiplication by 2.sup.N. A frequency modulated component is then demodulated from the multiplied signal.