Itt Manufacturing Enterprises, Inc.

Itt Corporation

Bryan S Majkrzak

Marvin A Epstein

Joseph M Fine

Peter Cummiskey

Gary V Blois

John Bertrand

Richard Kim

There is disclosed in a frequency hopping digital communications system having a transmitter for transmitting a data signal via a noisy transmission path, and a receiver responsive to the transmitted signal for receiving the same, a method for removing bias in the data signal at the receiver comprising the steps of: forming a sample amplitude histogram from the received data signal samples for a given hop frequency; correlating the amplitude histogram against a stored reference amplitude histogram to obtain a correlated output signal having a peak correlation position; determining the position difference between the peak correlation position and the correlation center position to provide an offset signal corresponding to the difference and indicative of an estimated bias offset value; and applying the estimated bias offset value to the received signal samples in response to the offset signal to obtain an output signal indicative of an unbiased received data signal.

Method for removing bias in a frequency hopping digital communication

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 milliseconds in delay, as compared to local echoes, which are canceled by the local echo canceler responding to echoes which are delayed 15 milliseconds or less.

Local and remote echo canceling apparatus particularly adapted for use

Growing community of inventors

Clifton, NJ, United States of America

Bryan S Majkrzak