Digital Signal Processors
Digital Network Echo Cancellers
Processor
StarCore鈩?Family of Digital Signal
Processors from Freescale
Introduction
Freescale echo cancellation solutions
include a set of network echo cancellers
for various market requirements and
applications. Equipped with Freescale
technologies, the solutions offer
carrier-class echo cancellation service for
packet telephony networks. The echo
cancellers are designed to cover up to
128 ms echo path delay with one 24 ms
moving window. This 24 ms window is
sufficient to handle the multi-reflective echo
paths in G.168 (2002) and others that are
expected to be encountered in the network.
The echo path delay of the echo canceller
is runtime configurable, from 8 ms up to
128 ms, so users may choose a proper
configuration to meet the need of echo path
configurations (or spans) and the resource
budget in per channel data memory and
processing load million cycles per
second (MCPS).
Features
Freescale Semiconductor鈥檚* echo cancellation
solutions are robust, field-proven
implementations with more than 15 years
global deployment into Tier 1 carrier-class
telecommunications infrastructure products.
The echo cancellers are based on normalized
LMS adaptive algorithms and have the
following major features:
> Rapid initial convergence rate
(echo cancelled within 50 ms)
> Far-reaching and stable infinite
convergence depth
> Intelligent near-end talk signal
detection mechanism
> Adaptive nonlinear processor with
optional comfort noise matching
FREESCALE ECHO CANCELLER BLOCK DIAGRAM
> Innovative mechanism for near-end
background noise handling
Sin (signal from near end)
Echo
Delay
HPF
+
+
Error
Signal
Sout (signal to far end)
Nonlinear
Processor
> Effective background processing for
divergence prevention
> Runtime configurable echo-span
coverage from 8 ms up to 128 ms
-
Echo
Estimate
Double
Talk
Detector
Adaptive
Filter
Echo
Canceller
Controller
Hybrid
Echo
> Fast mid-call convergence
(i.e., re-convergence upon hybrid
change in the middle of a call)
> Four configurable comfort noise
matching levels
> Smart handling of signaling tones
Rin (signal from far end)
Near End
Pure
Delay
Estimator
Delay
Delay
HPF
Rout (signal to near end)
Freescale IPs
The echo cancellers are ITU-T G.168
(2000/2002) compliant, and systematically
evaluated with Freescale voice quality
evaluation techniques and by
independent expert groups.
*The Semiconductor Products Sector of Motorola, Inc. became Freescale Semiconductor, Inc. in 2004.
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