FPGA Central

Hello.
Who knows how matched filter can be realized if sample rate is not
integer multiple of symbol rate?
In book of Meyr "Digital Communications Recievers" matched filter is
placed before controlled interpolation. What is the impulse response
of fiter matched for example with rectangular transmit filter or
raised cosine filter in that case? In Matlab I can calculate filter
impulse response only if sample rate is integer multiple of symbol
rate.
Thanks.
Pavel Schukin.

Pavel.Schukin@gmail.com wrote:

> Hello.
> Who knows how matched filter can be realized if sample rate is not
> integer multiple of symbol rate?

I know. But I won't tell you.

> In book of Meyr "Digital Communications Recievers" matched filter is
> placed before controlled interpolation. What is the impulse response
> of fiter matched for example with rectangular transmit filter or
> raised cosine filter in that case? In Matlab I can calculate filter
> impulse response only if sample rate is integer multiple of symbol
> rate.

Just another illustration of the mental harm done by MatLab.

VLV

">> Hello.
>> Who knows how matched filter can be realized if sample rate is not
>> integer multiple of symbol rate?
>
> I know. But I won't tell you.
>

VLV, you can at least point him in the right direction and I'm curious too

On 7 Feb, 17:43, "Pavel.Schu...@gmail.com" <Pavel.Schu...@gmail.com>
wrote:
> What is the impulse response
> of fiter matched for example with rectangular transmit filter *or
> raised cosine filter in that case?

Window functions in a matched filter? That's a new one.
How does that work?

Rune

On Feb 19, 4:15 am, Rune Allnor <all...@tele.ntnu.no> wrote:
> On 7 Feb, 17:43, "Pavel.Schu...@gmail.com" <Pavel.Schu...@gmail.com>
> wrote:
>
> > What is the impulse response
> > of fiter matched for example with rectangular transmit filter or
> > raised cosine filter in that case?
>
> Window functions in a matched filter? That's a new one.
> How does that work?
>
> Rune

If the signal was generated by windowing, as all finite signals are,
don't you try to match the window?

Dale B. Dalrymple
http://dbdimages.com

On 19 Feb, 18:10, dbd <d...@ieee.org> wrote:
> On Feb 19, 4:15 am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > On 7 Feb, 17:43, "Pavel.Schu...@gmail.com" <Pavel.Schu...@gmail.com>
> > wrote:
>
> > > *What is the impulse response
> > > of fiter matched for example with rectangular transmit filter *or
> > > raised cosine filter in that case?
>
> > Window functions in a matched filter? That's a new one.
> > How does that work?
>
> > Rune
>
> If the signal was generated by windowing, as all finite signals are,
> don't you try to match the window?

Not explicitly. The way I know the matched filter, you
try and match the impulse response. How the impulse is
found is a separate issue. If a non-rectangular window
function was used somewhere it would be part of the
impulse response already and not need explicit handling.

Rune

On Thu, 7 Feb 2008 08:43:27 -0800 (PST), "Pavel.Schukin@gmail.com"
<Pavel.Schukin@gmail.com> wrote:

>Hello.
>Who knows how matched filter can be realized if sample rate is not
>integer multiple of symbol rate?

Resampling filters, like Farrow filters, are often used.

>In book of Meyr "Digital Communications Recievers" matched filter is
>placed before controlled interpolation. What is the impulse response
>of fiter matched for example with rectangular transmit filter or
>raised cosine filter in that case?

An integrate-and-dump filter in the receiver matches rectangular
pulses from the transmitter.

> In Matlab I can calculate filter
>impulse response only if sample rate is integer multiple of symbol
>rate.
>Thanks.
>Pavel Schukin.
Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

On Feb 19, 9:29 am, Rune Allnor <all...@tele.ntnu.no> wrote:
> On 19 Feb, 18:10, dbd <d...@ieee.org> wrote:
>
>

> > On Feb 19, 4:15 am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > On 7 Feb, 17:43, "Pavel.Schu...@gmail.com" <Pavel.Schu...@gmail.com>
> > > wrote:
>
> > > > What is the impulse response
> > > > of fiter matched for example with rectangular transmit filter or
> > > > raised cosine filter in that case?

> > > Window functions in a matched filter? That's a new one.
> > > How does that work?

> > > Rune
>
> > If the signal was generated by windowing, as all finite signals are,
> > don't you try to match the window?
>
> Not explicitly. The way I know the matched filter, you
> try and match the impulse response. How the impulse is
> found is a separate issue. If a non-rectangular window
> function was used somewhere it would be part of the
> impulse response already and not need explicit handling.
>
> Rune

Rune

You are the only one to suggest any explicit handling of windowing.
The OP mentioned it as part of the transmit function which produces
the impulse response. It was my point that windows are implicit in all
finite responses, a fact that is better dealt with by understanding
the consequences than by a knee-jerk reaction on seeing the word:
windowing. The confusion about windowing comes from thinking that it
is something we can do, or not, explicitly after the impulse response
is determined.

Dale B. Dalrymple

On 19 Feb, 21:52, dbd <d...@ieee.org> wrote:
> On Feb 19, 9:29 am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
>
>
>
>
> > On 19 Feb, 18:10, dbd <d...@ieee.org> wrote:
>
> > > On Feb 19, 4:15 am, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> > > > On 7 Feb, 17:43, "Pavel.Schu...@gmail.com" <Pavel.Schu...@gmail.com>
> > > > wrote:
>
> > > > > *What is the impulse response
> > > > > of fiter matched for example with rectangular transmit filter *or
> > > > > raised cosine filter in that case?
> > > > Window functions in a matched filter? That's a new one.
> > > > How does that work?
> > > > Rune
>
> > > If the signal was generated by windowing, as all finite signals are,
> > > don't you try to match the window?
>
> > Not explicitly. The way I know the matched filter, you
> > try and match the impulse response. How the impulse is
> > found is a separate issue. If a non-rectangular window
> > function was used somewhere it would be part of the
> > impulse response already and not need explicit handling.
>
> > Rune
>
> Rune
>
> *You are the only one to suggest any explicit handling of windowing.

You are right. I didn't understand (and still don't) why and
how the terms 'rectangular' or 'raised cosine' appear in
a discussion about matched filters. Are these impulse repsonses
or transfer functions?

Rune

Thank you very much Eric for you valuable input. I had a feeling a
fractional filter approach would be most likely method.

Thanks again.

"Eric Jacobsen" <eric.jacobsen@ieee.org> wrote in message
news:398mr35cmvrbepvn6qjoj072guuphkp3pe@4ax.com...
> On Thu, 7 Feb 2008 08:43:27 -0800 (PST), "Pavel.Schukin@gmail.com"
> <Pavel.Schukin@gmail.com> wrote:
>
>>Hello.
>>Who knows how matched filter can be realized if sample rate is not
>>integer multiple of symbol rate?
>
> Resampling filters, like Farrow filters, are often used.
>
>>In book of Meyr "Digital Communications Recievers" matched filter is
>>placed before controlled interpolation. What is the impulse response
>>of fiter matched for example with rectangular transmit filter or
>>raised cosine filter in that case?
>
> An integrate-and-dump filter in the receiver matches rectangular
> pulses from the transmitter.
>
>> In Matlab I can calculate filter
>>impulse response only if sample rate is integer multiple of symbol
>>rate.
>>Thanks.
>>Pavel Schukin.
> Eric Jacobsen
> Minister of Algorithms
> Abineau Communications
> http://www.ericjacobsen.org

On Feb 19, 1:07 pm, Rune Allnor <all...@tele.ntnu.no> wrote:

....
> You are right. I didn't understand (and still don't) why and
> how the terms 'rectangular' or 'raised cosine' appear in
> a discussion about matched filters. Are these impulse repsonses
> or transfer functions?
>
> Rune

Rune

It seemed to me that the windows were applied in the poster's
transmission processing while generating the signal to be transmitted
and then hopefully matched in the receiver. That would make them part
of the impulse response to a symbol at the transmitter output. That
would make them part of the transmission processing 'transfer
function' from symbol to impulse response.

I guess that means the answer is yes.

Dale B. Dalrymple

On 20 Feb, 07:04, dbd <d...@ieee.org> wrote:
> On Feb 19, 1:07 pm, Rune Allnor <all...@tele.ntnu.no> wrote:
>
> ...
>
> > You are right. I didn't understand (and still don't) why and
> > how the terms 'rectangular' or 'raised cosine' appear in
> > a discussion about matched filters. Are these impulse repsonses
> > or transfer functions?
>
> > Rune
>
> Rune
>
> It seemed to me that the windows were applied in the poster's
> transmission processing while generating the signal to be transmitted
> and then hopefully matched in the receiver.

...as is not unheard of...

> That would make them part
> of the impulse response to a symbol at the transmitter output.

...which brings us back to my first question: Why are they
treated explicitly? If they are the transmitted impulses
then there is no need to mention their specific forms,
everything is already taken care of in the general theory
of matched filters.

> That
> would make them part of the transmission processing *'transfer
> function' from symbol to impulse response.

If the windows are viewed as weight functions applied to some
other 'raw' input signal (like if they are used to ease the
load on a transmitter at high powers) the matched filter is
trying to detect the wrong pulse shape. The filter should try
and match what is actually transmitted rather than the 'raw'
pulse shapes that are fed to the transmitter stages.

I just don't understand the OP's question.

Rune

On Tue, 19 Feb 2008 13:07:11 -0800 (PST), Rune Allnor
<allnor@tele.ntnu.no> wrote:

>On 19 Feb, 21:52, dbd <d...@ieee.org> wrote:
>> On Feb 19, 9:29 am, Rune Allnor <all...@tele.ntnu.no> wrote:
>>
>>
>>
>>
>>
>> > On 19 Feb, 18:10, dbd <d...@ieee.org> wrote:
>>
>> > > On Feb 19, 4:15 am, Rune Allnor <all...@tele.ntnu.no> wrote:
>>
>> > > > On 7 Feb, 17:43, "Pavel.Schu...@gmail.com" <Pavel.Schu...@gmail.com>
>> > > > wrote:
>>
>> > > > > *What is the impulse response
>> > > > > of fiter matched for example with rectangular transmit filter *or
>> > > > > raised cosine filter in that case?
>> > > > Window functions in a matched filter? That's a new one.
>> > > > How does that work?
>> > > > Rune
>>
>> > > If the signal was generated by windowing, as all finite signals are,
>> > > don't you try to match the window?
>>
>> > Not explicitly. The way I know the matched filter, you
>> > try and match the impulse response. How the impulse is
>> > found is a separate issue. If a non-rectangular window
>> > function was used somewhere it would be part of the
>> > impulse response already and not need explicit handling.
>>
>> > Rune
>>
>> Rune
>>
>> *You are the only one to suggest any explicit handling of windowing.
>
>You are right. I didn't understand (and still don't) why and
>how the terms 'rectangular' or 'raised cosine' appear in
>a discussion about matched filters. Are these impulse repsonses
>or transfer functions?
>
>Rune

I think you guys are on the wrong channel.

He's talking about a communication system where the "matched filter"
is the pulse shaping filter. Root Raised Cosine is a very common
matched filter that is applied to both the transmit and recieve pulses
to get a Raised Cosine frequency response.

The "rectangular" reference means unfiltered NRZ pulses, i.e.,
rectangular symbols.

Hope that helps...



Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org

On 21 Feb, 06:05, Eric Jacobsen <eric.jacob...@ieee.org> wrote:

> He's talking about a communication system where the "matched filter"
> is the pulse shaping filter. * Root Raised Cosine is a very common
> matched filter that is applied to both the transmit and recieve pulses
> to get a Raised Cosine frequency response.
>
> The "rectangular" reference means unfiltered NRZ pulses, i.e.,
> rectangular symbols.

Does 'matched filter' mean something else in this application
than I think it does? If you have a 'raw' symbol and apply a
window function to it, a 'classical' matched filter which
looks for the 'raw' symbol will not preform very well at all.

My experience with matched filters is with certain types
of sonars, where the system has to be tuned to what will
be *recieved*. Frequency-dependent scattering and absorption
effects mess up broad-band pulses to the extent that the
matched filters at the recievers miss the reflections
altogether. When we see that happen, we need to adjust
the bandwidth of the transotted pulse so as to minimize
the degrading scattering and absorption effects.

Rune

On Thu, 21 Feb 2008 02:12:55 -0800 (PST), Rune Allnor
<allnor@tele.ntnu.no> wrote:

>On 21 Feb, 06:05, Eric Jacobsen <eric.jacob...@ieee.org> wrote:
>
>> He's talking about a communication system where the "matched filter"
>> is the pulse shaping filter. * Root Raised Cosine is a very common
>> matched filter that is applied to both the transmit and recieve pulses
>> to get a Raised Cosine frequency response.
>>
>> The "rectangular" reference means unfiltered NRZ pulses, i.e.,
>> rectangular symbols.
>
>Does 'matched filter' mean something else in this application
>than I think it does? If you have a 'raw' symbol and apply a
>window function to it, a 'classical' matched filter which
>looks for the 'raw' symbol will not preform very well at all.

The meaning is the same, but I think the terminology has resulted in
some confusion.

In the communications case Raised Cosine describes the frequency
response of the aggregate filter, not any windowing function that is
applied anywhere. The "match" part of the filtering is so that the
point where the receiver is sampling the symbol has no InterSymbol
Interference from adjacent symbols. This is the classical sense of
"matched filtering" in that the filter is matched to the symbol
response shape at that sample point. i.e., the energy sampled at
that point is maximizing the energy related to that symbol and
minimizing energy from other, adjacent symbols, or anything not
correlated with that pulse shape.

Generally, in order to limit the transmit spectrum to something
reasonable to minimize the occupied channel bandwidth, the transmit
filter shapes the spectrum to something with a reasonably flat top and
reasonably steep sides. Matching the receiving filter to the
spectral shape of the transmitted energy maximizes the received energy
while rejecting adjacent channel energy or adjacent noise. Performing
both of those function AND the zero-InterSymbol Interference function
is very often done by making the composite of the transmit and receive
filters a Raised Cosine shape in the frequency domain, and then
factoring it into two Root Raised Cosine filters so that half is done
at transmit and half at recieve.

If the channel is dispersive or otherwise adds distortion, a channel
equalizer inverts only the channel response, so that the matched pulse
filters still produce zero-ISI. A few people have built architectures
where a stupendous equalizer automatically seeks a zero-ISI solution
regardless of what was transmitted and what the channel response was,
so that it "matches" the received pulse shape. IMHO that's a more
complicated system than it needs to be, but it does work.

So the "raw" symbol is "windowed by a roughly sinx/x shape that has,
typically, a Root Raised Cosine frequency response. If the NRZ
rectangular pulses are left unfiltered and transmitted, which wastes a
lot of bandwidth, an integrate-and-dump filter in the receiver is the
"matched" filter for that situation.

The function of a "matching" filter that results in zero-ISI is
typically referred to as a Nyquist filter. There are an infinite
number of Nyquist filter shapes or matched pairs.

>My experience with matched filters is with certain types
>of sonars, where the system has to be tuned to what will
>be *recieved*. Frequency-dependent scattering and absorption
>effects mess up broad-band pulses to the extent that the
>matched filters at the recievers miss the reflections
>altogether. When we see that happen, we need to adjust
>the bandwidth of the transotted pulse so as to minimize
>the degrading scattering and absorption effects.
>
>Rune

Yup. In a comm system the channel equalizer performs that function of
correcting for the static or dynamic channel effects. The nature and
complexity of the equalizer depends on the expected channel
characteristics, which differ widely between short range, long range,
fixed or mobile systems.

One might get away with no equalizer at all in a satellite comm
system, or need a really big, gnarly equalizer for a mobile broadband
system that needs to work in an urban environment.



Eric Jacobsen
Minister of Algorithms
Abineau Communications
http://www.ericjacobsen.org