A radio communication system for simultaneous telecommunication between a calling station and a called station, in which an aural signal to be transmitted from the calling station is divided by sampling pulses in the form of clock pulses of low frequency and is then suitably compressed with respect to the time axis to produce periodic signal-free time regions in the compressor output, so that an aural signal similarly compressed with respect to the time axis and transmitted from the called station can be received within these signal-free time regions. The received aural signal is expanded with respect to the time axis so that the original aural signal output of the microphone in the called station can be reproduced and applied to the speaker in the calling station. A zero cross synchronizing circuit is connected to the compressor to attain zero cross synchronization of the time-divided compressed aural signal and such aural signal is applied to the transmitter.
Receivers synchronize to signals sequentially transmitted from several transmitters prior to receiving signals simulcast by the transmitters. The relative delay differential of the received sequential signals is measured and used to determine the optimal sampling positions for the simulcast signals.
Prior to each voice activity period, the transmitter supplies a digital preamble for coding the speech signal levels and during these periods high frequency signals modulated in substantially constant amplitude, but transmits nothing other than said preamble and said periods. On reception, a signal detector and logic elements control a switch to obtain only speech signals at the input of an attenuator. The preamble decoding circuit controls the attenuation value of the attenuator in order to resupply to the receiver output signals of the same relative level as those applied to the transmitter input.
In radio communication system in which single frequency simultaneous transmission and reception is performed, a speech audio signal is divided by a predetermined time interval. A transmission time and a reception time are allotted in the predetermined time. A time-compressed signal is transmitted during the transmission time, and a time-compressed signal transmitted from other transceiver is received during the reception time and it is decompressed to the original length. The transmission time and the reception time are alternately repeated to transmit and receive the audio signals substantially simultaneously by a single frequency, and the audio signal is reproduced from the received signal. When communication with a telephone set is to be established, a DTMF signal is used as a dialing signal to call the telephone set from the transceiver. The DTMF signal is time-compressed and then transmitted along with the speech signal. A transmission timing of the DTMF signal is controlled, and the generated DTMF signal is temporarily stored in a memory. When the transmission of the DTMF signal can be completed before the transmission time is switched to the reception time is determined, and if it can, the DTMF signal is read from the memory and transmitted.
A multichannel duplex radio system for cordless telephone in which digital information is sent between the two ends. The data is divided into blocks which are transmitted in a fraction of the original block length. The other time slots are used for the duplex return path and for other similar equipment operating nearby. A direct conversion radio receiver is used in which the local oscillator signal is modulated for transmission.
A method of connecting audio information between a base telephone unit which is stationary and a portable unit associated therewith, the method involving dividing the communication time for audio information into first and second periods. During each first period, transmitting audio information from one of the units to the other over a radio channel and during each second period transmitting in reverse direction. The duration of the periods is a function of which transmitter is active at a given time.
