| 摘要 |
The supervisory signal of a derived channel data reporting system is used as a primary, data communicating signal. The data communicating signal can be implemented as a single tone, or as plural tones having a frequency (e.g., from 200 Hz to 300 Hz) which is capable of being transmitted by existing telephone network equipment, including digital transmission equipment, and an attenuated level. As an alternative, the data reporting signal can be implemented at a reduced frequency (e.g., at an audible frequency of less than 150 Hz) to be compatible with existing, high-speed modems. Such operation can be achieved in a simplex mode, or in a half-duplex or full-duplex mode, as preferred. The data reporting signal can further be implemented in such a way that multiple applications can be supported by a single telephone line or switchboard grouping, by using different signals to avoid interference between multiple subscriber terminal units associated with the system. The data rate achievable with the data reporting signal can be increased to transmit increased amounts of data by increasing the bit rate of the communicating signal, preferably using modulation techniques such as quaternary phase shift keying (QPSK), 8-phase shift keying or discrete multi-tone (DMT) modulation, to yield multiple bits per baud while maintaining a low channel baud rate. |
