Telephonic communications – Echo cancellation or suppression – Disable or inhibit function
Reexamination Certificate
1999-08-26
2004-02-17
Tieu, Binh (Department: 2643)
Telephonic communications
Echo cancellation or suppression
Disable or inhibit function
C379S406050, C379S406080, C379S406120
Reexamination Certificate
active
06694019
ABSTRACT:
BACKGROUND
1. Field
The present invention relates to the field of communications. In particular, this invention relates to a communication device and method for detecting an infinite return loss condition and bypassing or temporarily halting operations of an echo canceller in response thereto.
2. General Background
During a two-way telephone conference, a caller sometimes can hear his or her own voice as a delayed echo. This phenomenon is referred to as “talker echo”. One cause for talker echo is the presence of signal reflections in a transmission path. Often, signal reflections occur at hybrid circuits. Generally speaking, a hybrid circuit is a transformer circuit that is designed for coupling together different types of transmission lines. It is commonplace for voice-based communication networks to be implemented with different types of transmission lines, and thus, necessities the need for echo cancelling techniques to mitigate or eliminate talker echo caused by signal reflections.
Besides talker echo, acoustic echo is an inherent problem in wireless handsets or headsets. The reason is that typical handsets and headsets continuously maintain their speaker (or earphone) and microphone in an active state. This creates an acoustic coupling between the speaker (or earphone) and the microphone. In addition, when applicable, acoustic echo may be caused by crosstalk in the handset or headset cord. Thus, echo cancellation techniques are also used to mitigate the effects of acoustic coupling.
Typically, echo cancellers are used to reduce or eliminate any type of echo. For example, to reduce echo caused by either signal reflections from a hybrid circuit or acoustic coupling, an echo canceller (i) simulates an estimated echo, and (ii) subtracts the estimate echo from outgoing voice data. During an “infinite return loss” (IRL) condition, however, the operations of conventional echo cancellers tend to create echo rather than reducing or eliminating echo. An IRL condition exists when the signal level of an incoming far-end signal exceeds the signal level of an outgoing near-end signal (including echo from hybrid reflection or acoustic coupling) by a substantial decibel level (e.g., forty or more decibels “dB”). For example, an IRL condition would likely occur with termination on a four-wire terminal device such as an Internet Protocol (IP) phone, in which case the echo canceller of the switching device effectively applies additional echo (e.g., the estimated echo) to the outgoing signal.
Hence, it would be desirable to provide a device and method that prevents unwanted echo from being generated when the IRL condition is identified. Also, it would be desirable to identify the IRL condition by monitoring signal levels associated with both an echo return loss (ERL) and an echo return loss residue (ERLE) threshold values. This avoids relying on computations based solely on delayed signals reflected from a hybrid circuit that can cause errand detection of the IRL condition.
SUMMARY
Briefly, the present invention relates to a communication device and method for detecting an infinite return loss (IRL) condition and either bypassing or temporarily halting operations of an echo canceller during this condition. This avoids the generation of unwanted echo. In one embodiment, the IRL condition is detected through analysis of both an echo return loss (ERL) and an echo return loss enhancement (ERLE). This improves reliability over conventional IRL condition computations because the IRL condition is not detected through computations based solely on delayed signals reflected from a hybrid circuit. This allows for better reliability and audio quality.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
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Blakely , Sokoloff, Taylor & Zafman LLP
Nortel Networks Limited
Tieu Binh
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