Telephone echo on a satellite voice channel: practical suppression method In a geostationary satellite voice link where long round-trip delay causes audible echo to the telephone user, which technique is commonly used in practice to remove or greatly reduce the echo?

Introduction / Context:
Geostationary links have a one-way delay of roughly 240 ms, leading to a round-trip delay near 480 ms. This delay makes hybrid reflections and impedance mismatches audible as echo in telephony. Echo control is therefore essential for user comfort.

Given Data / Assumptions:

• Long GEO satellite propagation delay.
• Two-wire/four-wire hybrids in telephony can reflect part of the signal.
• Goal: suppress audible echo at the talker’s ear.

Concept / Approach:
Echo suppressors and echo cancellers detect the presence of far-end speech and attenuate or subtract the echo path. Modern systems use adaptive echo cancellers that model the echo path and remove the delayed replica of the talker’s own speech.

Step-by-Step Solution:
Identify the echo source: hybrid reflections and impedance mismatch.Recognize long GEO delays exacerbate echo audibility.Apply an echo suppressor/canceller which monitors speech activity and attenuates or cancels the echo path adaptively.Result: echo power is reduced to inaudible levels.

Verification / Alternative check:
Telecom standards and satellite telephony deployments universally specify echo control for long-delay circuits; field experience confirms their effectiveness.

Why Other Options Are Wrong:
Vocoder/Multiplexer: Compression or multiplexing does not inherently cancel echo.
“Digital techniques”: Too vague; echo requires specific cancellation algorithms.
Higher IF bandwidth: Unrelated to echo delay/reflection.

Common Pitfalls:
Confusing noise reduction with echo cancellation; they solve different problems.

Final Answer:
An echo suppressor (or echo canceller)