FPGA Central

Hi, any insight to these queries?

1) Which come first at the transmitter - cyclic prefix or pulse
shaping? Reason I ask this is if cyclic prefix is done first, won't
the pulse shaping destroy the structure?

2) Which pulse shapes are used - RC or RRC? Is a corresponding matched
filtering required at the receiver? Reason I ask this is some
literature seem to imply that a matched filter is not necessary at the
receiver.

Thanks!

ckian...@gmail.com wrote:
> Hi, any insight to these queries?
>
> 1) Which come first at the transmitter - cyclic prefix or pulse
> shaping? Reason I ask this is if cyclic prefix is done first, won't
> the pulse shaping destroy the structure?
>
pulse shaping comes first at the transmitter and then comes CP(always
the last step).

> 2) Which pulse shapes are used - RC or RRC? Is a corresponding matched
> filtering required at the receiver?
RRC. Yes a corresponding matched filter is required to maximize the
SNR and make use of the "information in the pulse shape" i.e. which
sample to weight more or less.

> Reason I ask this is some
> literature seem to imply that a matched filter is not necessary at the
> receiver.
Mention the literature you are referring to or the context in which
they said so.

Ubaid Abdullah
http://dspdotcomm.blogspot.com

On Mar 31, 5:34*pm, Ubaid Abdullah <ubaidabdul...@gmail.com> wrote:
> ckian...@gmail.com wrote:
> > Hi, any insight to these queries?
>
> > 1) Which come first at the transmitter - cyclic prefix or pulse
> > shaping? Reason I ask this is if cyclic prefix is done first, won't
> > the pulse shaping destroy the structure?
>
> pulse shaping comes first at the transmitter and then comes CP(always
> the last step).
>
> > 2) Which pulse shapes are used - RC or RRC? Is a corresponding matched
> > filtering required at the receiver?
>
> RRC. Yes a corresponding matched filter is required to maximize the
> SNR and make use of the "information in the pulse shape" i.e. which
> sample to weight more or less.
>
> > Reason I ask this is some
> > literature seem to imply that a matched filter is not necessary at the
> > receiver.
>
> Mention the literature you are referring to or the context in which
> they said so.
>
> Ubaid Abdullahhttp://dspdotcomm.blogspot.com

For example, there isn't a matched filter in Figure 1 of "Peak-To-
Average Power Ratio of Single Carrier FDMA Signals with Pulse
Shaping". I thought maybe there is but not shown. In section 3 of the
paper, it is mentioned that RC pulse is used. Since PAPR should be
computed before any matched filtering (am I right?), it seemed to
imply that RC pulse is used at the transmitter pulse shaping and hence
no matched filtering at the receiver.

> Since PAPR should be
> computed before any matched filtering (am I right?), it seemed to
> imply that RC pulse is used at the transmitter pulse shaping and hence
> no matched filtering at the receiver.

I dont think so. PAPR is a parameter of importance for power
amplifier. That means we are interested in the PAPR of the final
waveform that comes out of your DAC. You will compute PAPR for the
signal that is input to the PA not at any other stage of the
transmitter.

Using RC pulse shaping at the transmitter doesn't imply that you
shouldn't use matched filtering at the receiver. You should perceive
matched filtering as a device that filters the out-of-band noise at
the receiver and applies weights to the samples. You always need
something for this job whatever the pulse shaping filter you use at
the transmitter.

Ubaid Abdullah
http://dspdotcomm.blogspot.com

On Mar 31, 8:11*pm, Ubaid Abdullah <ubaidabdul...@gmail.com> wrote:
> > Since PAPR should be
> > computed before any matched filtering (am I right?), it seemed to
> > imply that RC pulse is used at the transmitter pulse shaping and hence
> > no matched filtering at the receiver.
>
> I dont think so. PAPR is a parameter of importance for power
> amplifier. That means we are interested in the PAPR of the final
> waveform that comes out of your DAC. You will compute PAPR for the
> signal that is input to the PA not at any other stage of the
> transmitter.
>
> Using RC pulse shaping at the transmitter doesn't imply that you
> shouldn't use matched filtering at the receiver. You should perceive
> matched filtering as a device that filters the out-of-band noise at
> the receiver and applies weights to the samples. You always need
> something for this job whatever the pulse shaping filter you use at
> the transmitter.
>
> Ubaid Abdullahhttp://dspdotcomm.blogspot.com

I agree with you. But is there any reason to use a RC instead of RRC?
What matched filter should one use to maintain ISI free and still
filter the out-of-band noise?

On Apr 1, 6:48*am, ckian...@gmail.com wrote:
> On Mar 31, 8:11*pm, Ubaid Abdullah <ubaidabdul...@gmail.com> wrote:
>
>
>
> > > Since PAPR should be
> > > computed before any matched filtering (am I right?), it seemed to
> > > imply that RC pulse is used at the transmitter pulse shaping and hence
> > > no matched filtering at the receiver.
>
> > I dont think so. PAPR is a parameter of importance for power
> > amplifier. That means we are interested in the PAPR of the final
> > waveform that comes out of your DAC. You will compute PAPR for the
> > signal that is input to the PA not at any other stage of the
> > transmitter.
>
> > Using RC pulse shaping at the transmitter doesn't imply that you
> > shouldn't use matched filtering at the receiver. You should perceive
> > matched filtering as a device that filters the out-of-band noise at
> > the receiver and applies weights to the samples. You always need
> > something for this job whatever the pulse shaping filter you use at
> > the transmitter.
>
> > Ubaid Abdullahhttp://dspdotcomm.blogspot.com
>
> I agree with you. But is there any reason to use a RC instead of RRC?
> What matched filter should one use to maintain ISI free and still
> filter the out-of-band noise?

You have two requirements for a communication system design.

i). Zero ISI
ii). Implementation of a matched filter at the receiver.

A raised cosine filter is one that is designed to produce zero ISI.
But, this zero ISI is needed before detection of the symbols or after
matched filtering. If you implement raised cosine filter at the
transmitter, the overall response of transmitting raised cosine filter
and matched filter doesn't produce zero ISI. That's why RC filter is
broken down into two parts each with an RRC response. In this case, we
will implement RRC filter at the transmitter and the same filter at
the receiver as matched filter to get the overall RC response. This
gives us zero ISI prior to detection and fulfills both the
requirements stated above.

Ubaid Abdullah
http://dspdotcomm.blogspot.com

On Apr 1, 1:50*pm, Ubaid Abdullah <ubaidabdul...@gmail.com> wrote:
> On Apr 1, 6:48*am, ckian...@gmail.com wrote:
>
>
>
> > On Mar 31, 8:11*pm, Ubaid Abdullah <ubaidabdul...@gmail.com> wrote:
>
> > > > Since PAPR should be
> > > > computed before any matched filtering (am I right?), it seemed to
> > > > imply that RC pulse is used at the transmitter pulse shaping and hence
> > > > no matched filtering at the receiver.
>
> > > I dont think so. PAPR is a parameter of importance for power
> > > amplifier. That means we are interested in the PAPR of the final
> > > waveform that comes out of your DAC. You will compute PAPR for the
> > > signal that is input to the PA not at any other stage of the
> > > transmitter.
>
> > > Using RC pulse shaping at the transmitter doesn't imply that you
> > > shouldn't use matched filtering at the receiver. You should perceive
> > > matched filtering as a device that filters the out-of-band noise at
> > > the receiver and applies weights to the samples. You always need
> > > something for this job whatever the pulse shaping filter you use at
> > > the transmitter.
>
> > > Ubaid Abdullahhttp://dspdotcomm.blogspot.com
>
> > I agree with you. But is there any reason to use a RC instead of RRC?
> > What matched filter should one use to maintain ISI free and still
> > filter the out-of-band noise?
>
> You have two requirements for a communication system design.
>
> i). Zero ISI
> ii). Implementation of a matched filter at the receiver.
>
> A raised cosine filter is one that is designed to produce zero ISI.
> But, this zero ISI is needed before detection of the symbols or after
> matched filtering. If you implement raised cosine filter at the
> transmitter, the overall response of transmitting raised cosine filter
> and matched filter doesn't produce zero ISI. That's why RC filter is
> broken down into two parts each with an RRC response. In this case, we
> will implement RRC filter at the transmitter and the same filter at
> the receiver as matched filter to get the overall RC response. This
> gives us zero ISI prior to detection and fulfills both the
> requirements stated above.
>
> Ubaid Abdullahhttp://dspdotcomm.blogspot.com

That is correct, which brings us back to my second question above that
the pulse shaping function at the transmitter should not be a RC
filter, but the paper seems to imply that it is.

How do one deal with the filter delay if cyclic prefix is added after
pulse shaping?

In addition, in a scheme that uses a known seq (PN1) as the cyclic
prefix for symbol sync, e.g. [PN1|Data|PN2] where PN1 = PN2 and [Data|
PN2] is the FFT block, the starting symbols of PN1 after matched
filtering would not be right because of the filter delay, isn't it?