Adaptive transmit levels for modems operating over cellular

Abstract

Abstract The strength of a local echo signal is used to dynamically adjust the transmit signal level of a modem. In particular, the modem provides a transmit signal to a local loop of a public switched telephone network (PSTN). This local loop couples the modem to, for example, a central office. The amount of reflected energy from the central office, i.e., echo, received by the modem is inversely proportional to the amount of energy actually getting through to the central office. If the magnitude of the local echo signal is small, which indicates that most of the transmit signal energy is reaching the equipment of the central office, then the signal level of the transmit signal is lowered. Conversely, if the magnitude of the local echo signal is large, which indicates that most of the transmit signal energy is being back reflected from the central office, then the signal level of the transmit signal is raised. This use of the local echo signal to adjust the transmit signal level helps avoid situations where the signal level of the modem may be either "too hot" or "too cold," either of which may result in a concomitant loss of data through the communications system.

Inventors

• 👤 Robert E. Scott

Bibliographic Details