Forums

Re: Training sequences in hybrid echo cancellers

Started by Maurice Givens February 14, 2002
The hybrid is not connected until the connection is made when the called
is off hook. Therefore, the called party would hear the training
sequence. This is considered annoying and unacceptable by the carriers. Maurice Givens
(one of those G.168 authors)

On Tue, 12 Feb 2002 11:59:43 +0000 "Sudarini Pushparajah"
<> writes:
> Hi,
> I understand that this echocancel group consist of people who
> are
> involved in compiling the ITU-G.168 standard. My question is
> addressed to
> these members in particular.
>
> I am working on network echo cancellers. Hybrid echo paths have a
> typical
> active region of 5ms-7ms (G.168) and when a call is made, the hybrid
> echo
> path is formed and remains pretty much the same throughout the call.
>
> My question is this;
> Why can't we use a training sequence across the hybrid echo path at
> the
> beginning of every call?. Training sequences are used in mobile
> communication systems to identify channel characteristics
> successfully. We
> could also use this idea in network echo cancellation to measure the
> hybrid
> echo path. From this measurement, we could identify the active
> region of
> the echo path then, we could use a 5ms-7ms adaptive echo canceller
> instead
> of the usual 64ms adaptive echo canceller (i.e., reducing the
> complexity of
> the echo canceller). Furthermore, the echo cancellers can be made to
> become
> very robust to double talk situations.
>
> Therefore, why don't we include an agreed training sequence into all
> the
> network echo cancellers?. Please let me know all your opinions on
> this
> issue.
>
> Thanks
> Sudarini > _________________________________________________________________
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