cordless telephony 2 (CT2)
Cordless Telephony 2 (CT2) is a variant of the CT1 cordless telephone standard developed in England. CT2 was the first digital standard; thanks to digitization, it is significantly superior to the CT1 analog system in terms of its security and interception properties.
The CT2 system operates in the frequency range from 864.1 MHz to 868.1 MHz, with 40 100 kHz wide duplex channels, and uses time division multiplex as the transmission method. Duplex transmissiontakes place on one and the same carrier frequency, alternating between uplink and downlink transmission at millisecond intervals. Between the switchovers, the transmitter is blanked.
For speech coding, CT2 uses Adaptive Delta Pulse CodeModulation( ADPCM) at 32 kbit/s according to G.721. GPSK is used as the modulation. The transmitting power of the hearing aid is max. 10 mW; the range is 200 m. CT2 can be set up as a single-cell and multi-cell network and therefore offers all the advantages of multi-cell networks, such as roaming, handover, calls within a radio cell and across radio cells, call forwarding, and much more.
In addition to pure voice transmission, data can also be transmitted at low transmission rates of 2400 bit/s. With special modems, this speed can be increased to 9.6 kbps.
Logical sub-channels are defined in the CT2 system: the B channel is used for voice transmission and the possibility of data transmission with modem. The D channel is the signaling channel, which is used for connection setup and disconnection, handover and charge transmission, and the SYN channel is used for synchronization of stations.