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Message from discussion Looking for FIR 17 taps coef shaping filter for V32 implementation
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Clay S. Turner  
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 More options Aug 26 1999, 3:00 am
Newsgroups: comp.dsp
From: "Clay S. Turner" <cstur...@peachnet.campuscwix.net>
Date: 1999/08/26
Subject: Re: Looking for FIR 17 taps coef shaping filter for V32 implementation
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Hello Louis,
        The RRC is different from the RC.  In fact two RRC convolved yield a RC
response.  This is usually implemented by putting a RRC in the
transmitter and another RRC in the receiver.  This will give you a
little bit of advantage over using a RC in the transmitter and a
brickwall filter in the receiver.

The RRC impulse response is given by:

h(t) =     pi^2      4at cos(t(a+b))+pi sin(t(b-a))
       ----------- * ------------------------------
        pi(a-b)-4a         t(16t^2 a^2 - pi^2)

where a and b are defined as in the RC post

As you can see by the formula, this is different from the RC impulse
response.

Clay S. Turner

Louis Croisez wrote:

> I thanx you all for your prompt reply to my question!

> Following the advise of Grant Griffin, I have downloaded SCOPEFIR. It gaves me all filter coef that I needed.
> I have seen that there is no major difference between Root Raised Cosine Pulse Shaping (RRCPS) filter and the Raised Cosine Pulse Shaping (RCPS) filter.

> Allan, you seem to prefer RRC instead of RC: why ?
> Also, what Rx matched filter are you talking about ?
> All I know is what I have read in the ITU V32 standard and in some other sources (analog and TI application notes). They all talk about RCPS filter and not about Root RCPS filters.

> --Louis Croisez

> Allan Herriman <allan.herriman.hates.s...@fujitsu.com.au> wrote in message news:37c4941e.3339838@newshost.fujitsu.com.au...
> | On Wed, 25 Aug 1999 18:36:41 +0200, "Louis Croisez"
> | <croi...@hotmail.com__nospam> wrote:
> |
> | >Hi everybody,
> | >I am working on a V32 digital modem implementation.
> | >I would like to get the 17 taps FIR coeficients of the Raised Cosine Pulse
> | >Shaping filter (TX part of V32 modem).
> |
> | (I don't have V.32 handy.)  Why does it use Raised Cosine filtering
> | and not Root Raised Cosine filtering in the Tx filter?  What does it
> | say to use for the Rx filter?  [If we use RC for the Tx, the Rx
> | matched filter will be a brickwall lowpass.]
> |
> | Allan.


 
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