Cryptography – Cryptanalysis
Patent
1995-10-12
1998-11-24
Cangialosi, Salvatore
Cryptography
Cryptanalysis
380 49, 375216, 4557761, 455425, H04L 900
Patent
active
058418628
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL ART
The present invention relates to a mobile radio communications apparatus, such as a land mobile radiotelephone, a hand-held telephone unit and a cordless telephone unit and, more in particular, to a mobile radio communications apparatus for use as a mobile unit in a cellular radio communications system adapted to wirelessly transmit a communication signal between a base station and the mobile unit.
BACKGROUND ART
A mobile radio communications apparatus adopting a dual mode system has been recently proposed in place of a mobile radio communications system adapted to wirelessly transmit a communication signal in a conventional analog system. Here, a dual mode is intended to mean an analog/digital combined mode.
The analog mode is of such a type as to transmit a speech signal and data through, for example, the FM modulation of a carrier with an analog speech signal and data at a transmitter and to receive a modulated carrier by a receiver coming from the transmitter and to reproduce an analog speech signal and data through FM demodulation. In the analog mode, a frequency-division multiple access (FDMA) system is used as an access system between the base station and the mobile unit.
A digital mode, on the other hand, is of such a type as to, through the encoding of a speech signal and data at a transmitter, transmit a carrier digitally modulated with an encoded signal, for example, in a .pi./4 shifted DQPSK (.pi./4 shifted, differentially encoded quadrator phase shift keying) system and to receive a demodulated signal by a receiver coming from the transmitter and reproduce a speech signal and data after the digital demodulation of the received data and decoding of a demodulated signal. In the digital mode, a time-division multiple access (TDMA) system is used in an access system between the base station and the mobile unit.
FIG. 1 is a view showing one practical example of this type of a system. This system includes a control station CS connected by a cable circuit line CL to a cable communications network NW, a plurality of (for example, three) base stations BS1, BS2 and BS3 connected by corresponding cable circuit lines CL1 to CL3 to the control station CS, and a great number of mobile units PS1, PS2, . . . . The base stations BS1, BS2 and BS3 create circular radio zones E1, E2 and E3 each of a predetermined radius. The mobile units PS1, PS2, . . . are connected to the base stations BS1, BS2 and BS3 of the radio zones E1, E2 and E3, via a radio speech communication channel, to which their own mobile units belong. As the radio speech communication channel, there are two types: an analog speech communication channel by the FDMA system and a digital radio communication channel by the TDMA system.
In the system as set out above, the connection of a radio link between the mobile unit and the base station is performed as set out below. With a power supply in an ON state, that is in a normal state, the base stations BS1, BS2 and BS3 broadcast control information to those mobile units in the respective radio zones via control channels called "paging channels". The control information contains information such as a service capacity possessed by the base station and the service capability contains information of a communication mode and so on.
At the time of turning on a power source and finishing communications, the mobile unit sequentially scans the control channels called "the paging channels" of the base units BS1, BS2 and BS3 and detects, out of these control channels, a control channel whose electric field strength received is the greatest. Thereafter, the mobile unit is set in a standby state in that control channel. When, in the standby state, a calling operation is made or a called signal is reached from the base station via the control channel, the mobile unit sends a calling signal to the base station via the control channel. At that time, if any desired communication mode is entered as a designated mode at the mobile unit, a request to set a communication mode is informed to the base unit
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Kanbara Masatomo
Obayashi Arata
Tanaka Masayuki
Cangialosi Salvatore
Kabushiki Kaisha Toshiba
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