Local and remote echo canceling apparatus particularly adapted for use in a full duplex modem
US5418778A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Jul 28, 1993 |
| Grant date | May 23, 1995 |
| Priority date | — |
| Expiry date | Jul 28, 2013 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04B3/237
- WIPO fieldTelecommunications
- WIPO sectorElectrical engineering
Abstract
An echo cancellation apparatus is included in a variable rate modem. The echo cancellation apparatus includes a local echo canceler, a remote echo canceler and a quadrature echo canceler unit. The local and remote echo cancelers both operate to cancel echoes in a similar manner employing topped delay lines or transversal filters wherein the taps of each delay line are adjusted to accommodate both local and remote echo cancellation. The local echo canceler and the remote echo canceler share many programs in common. However, the remote echo canceler operates with a phase lock loop which essentially derives a signal obtained from the quadrature and local echo cancelers which signal is further correlated with the output residuals from the local echo canceler to develop samples applied to the remote echo canceler and to derive a frequency which is indicative of a offset carrier frequency to enable the remote echo canceler to cancel remote echoes. Remote echoes are due to frequency shifts occurring remote from the modem, such as those caused by changes in satellite positions or changes in frequency sources. The remote echo canceler operates to cancel echoes which are greater than 15 mill…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.