So I'm pretty confused about something.While studying DFT windowing, I saw how rectangular window has lowest bandwidth compared to Hanning window( which is basically raised cosine), but higher side-lobes. But in all pulse shaping filter tutorials, apart from minimizing ISI they describe how the bandwidth of the rectangular pulse is almost twice the raised cosine pulse ( for alpha=0). What am I doing wrong? This seems very contradictory to me. In both cases windowing and pulse shaping we are looking are the frequency response aren't we??Im obviously making some very basic mistake, please enlighten me.

# FFT Windowing and Transmit Pulse Shaping

Started by ●August 11, 2010

Reply by ●August 11, 20102010-08-11

On 8/11/2010 3:55 PM, Zeph80 wrote:> So I'm pretty confused about something.While studying DFT windowing, I saw > how rectangular window has lowest bandwidth compared to Hanning window( > which is basically raised cosine), but higher side-lobes. > But in all pulse shaping filter tutorials, apart from minimizing ISI they > describe how the bandwidth of the rectangular pulse is almost twice the > raised cosine pulse ( for alpha=0). > What am I doing wrong? This seems very contradictory to me. In both cases > windowing and pulse shaping we are looking are the frequency response > aren't we??Im obviously making some very basic mistake, please enlighten > me.English is evidently not your first language. Basically, you are confusing the bandwidth of a pulse with the selectivity of a filter. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������

Reply by ●August 11, 20102010-08-11

>On 8/11/2010 3:55 PM, Zeph80 wrote: >> So I'm pretty confused about something.While studying DFT windowing, Isaw>> how rectangular window has lowest bandwidth compared to Hanning window( >> which is basically raised cosine), but higher side-lobes. >> But in all pulse shaping filter tutorials, apart from minimizing ISIthey>> describe how the bandwidth of the rectangular pulse is almost twice the >> raised cosine pulse ( for alpha=0). >> What am I doing wrong? This seems very contradictory to me. In bothcases>> windowing and pulse shaping we are looking are the frequency response >> aren't we??Im obviously making some very basic mistake, pleaseenlighten>> me. > >English is evidently not your first language. Basically, you are >confusing the bandwidth of a pulse with the selectivity of a filter. > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >Could you please elaborate? In both cases aren't we considering the DFT of the same time domain waveform?

Reply by ●August 11, 20102010-08-11

On 8/11/2010 4:38 PM, Zeph80 wrote:>> On 8/11/2010 3:55 PM, Zeph80 wrote: >>> So I'm pretty confused about something.While studying DFT windowing, I > saw >>> how rectangular window has lowest bandwidth compared to Hanning window( >>> which is basically raised cosine), but higher side-lobes. >>> But in all pulse shaping filter tutorials, apart from minimizing ISI > they >>> describe how the bandwidth of the rectangular pulse is almost twice the >>> raised cosine pulse ( for alpha=0). >>> What am I doing wrong? This seems very contradictory to me. In both > cases >>> windowing and pulse shaping we are looking are the frequency response >>> aren't we??Im obviously making some very basic mistake, please > enlighten >>> me. >> >> English is evidently not your first language. Basically, you are >> confusing the bandwidth of a pulse with the selectivity of a filter.> Could you please elaborate? In both cases aren't we considering the DFT of > the same time domain waveform?What cases? A pulse shaped like a raised cosine in the time domain has much less "splatter" -- broadband energy -- than a rectangular pulse of the same width. What has that to do with windowing the data fed to a DFT routine? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������

Reply by ●August 11, 20102010-08-11

>On 8/11/2010 4:38 PM, Zeph80 wrote: >>> On 8/11/2010 3:55 PM, Zeph80 wrote: >>>> So I'm pretty confused about something.While studying DFT windowing,I>> saw >>>> how rectangular window has lowest bandwidth compared to Hanningwindow(>>>> which is basically raised cosine), but higher side-lobes. >>>> But in all pulse shaping filter tutorials, apart from minimizing ISI >> they >>>> describe how the bandwidth of the rectangular pulse is almost twicethe>>>> raised cosine pulse ( for alpha=0). >>>> What am I doing wrong? This seems very contradictory to me. Inboth>> cases >>>> windowing and pulse shaping we are looking are the frequency response >>>> aren't we??Im obviously making some very basic mistake, please >> enlighten >>>> me. >>> >>> English is evidently not your first language. Basically, you are >>> confusing the bandwidth of a pulse with the selectivity of a filter. > >> Could you please elaborate? In both cases aren't we considering the DFTof>> the same time domain waveform? > >What cases? A pulse shaped like a raised cosine in the time domain has >much less "splatter" -- broadband energy -- than a rectangular pulse of >the same width. What has that to do with windowing the data fed to a DFT >routine? > >Jerry >-- >Engineering is the art of making what you want from things you can get. >����������������������������������������������������������������������� >Ok, I think you did not understand my question. However I think I realizemy mistake. Case 1: I'm comparing the DFT of a rectangular window and a hanning (raised cosine window). Case 2: Then I'm comparing the frequency domain of a rectangular pulse to a raised cosine shaped pulse . I thought that case 1 and case 2 should have the same results I think the mistake is that even though the Hanning window is called raised cosine, its really a truncated raised cosine compared to the shaped raised cosine pulses used to transmit data.

Reply by ●August 11, 20102010-08-11

On Aug 11, 12:55=A0pm, "Zeph80" <surabhi_talwar@n_o_s_p_a_m.hotmail.com> wrote:> So I'm pretty confused about something.While studying DFT windowing, I sa=w> how rectangular window has lowest bandwidth compared to Hanning window( > which is basically raised cosine), but higher side-lobes.These windows are applied in the time domain.> But in all pulse shaping filter tutorials, apart from minimizing ISI they > describe how the bandwidth of the rectangular pulse is almost twice the > raised cosine pulse ( for alpha=3D0).Shaping filter specifications are in the frequency domain.> =A0What am I doing wrong? This seems very contradictory to me. In both ca=ses> windowing and pulse shaping we are looking are the frequency response > aren't we??No.>...Dale B. Dalrymple

Reply by ●August 11, 20102010-08-11

On Wed, 11 Aug 2010 16:01:45 -0500, "Zeph80" <surabhi_talwar@n_o_s_p_a_m.hotmail.com> wrote:>>On 8/11/2010 4:38 PM, Zeph80 wrote: >>>> On 8/11/2010 3:55 PM, Zeph80 wrote: >>>>> So I'm pretty confused about something.While studying DFT windowing, >I >>> saw >>>>> how rectangular window has lowest bandwidth compared to Hanning >window( >>>>> which is basically raised cosine), but higher side-lobes. >>>>> But in all pulse shaping filter tutorials, apart from minimizing ISI >>> they >>>>> describe how the bandwidth of the rectangular pulse is almost twice >the >>>>> raised cosine pulse ( for alpha=0). >>>>> What am I doing wrong? This seems very contradictory to me. In >both >>> cases >>>>> windowing and pulse shaping we are looking are the frequency response >>>>> aren't we??Im obviously making some very basic mistake, please >>> enlighten >>>>> me. >>>> >>>> English is evidently not your first language. Basically, you are >>>> confusing the bandwidth of a pulse with the selectivity of a filter. >> >>> Could you please elaborate? In both cases aren't we considering the DFT >of >>> the same time domain waveform? >> >>What cases? A pulse shaped like a raised cosine in the time domain has >>much less "splatter" -- broadband energy -- than a rectangular pulse of >>the same width. What has that to do with windowing the data fed to a DFT >>routine? >> >>Jerry >>-- >>Engineering is the art of making what you want from things you can get.>>Ok, I think you did not understand my question. However I think I realize >my mistake. >Case 1: I'm comparing the DFT of a rectangular window and a hanning (raised >cosine window). >Case 2: Then I'm comparing the frequency domain of a rectangular pulse to >a raised cosine shaped pulse . >I thought that case 1 and case 2 should have the same results >I think the mistake is that even though the Hanning window is called raised >cosine, its really a truncated raised cosine compared to the shaped raised >cosine pulses used to transmit data.A Raised Cosine window for a DFT is not the same as a Raised Cosine response for a pulse shape. This is an unfortunate overloading of the terminology "Raised Cosine", as the raising of the cosine is used differently and does different things in each case. So they are not expected to be the same. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.abineau.com

Reply by ●August 11, 20102010-08-11

>On Wed, 11 Aug 2010 16:01:45 -0500, "Zeph80" ><surabhi_talwar@n_o_s_p_a_m.hotmail.com> wrote: > >>>On 8/11/2010 4:38 PM, Zeph80 wrote: >>>>> On 8/11/2010 3:55 PM, Zeph80 wrote: >>>>>> So I'm pretty confused about something.While studying DFTwindowing,>>I >>>> saw >>>>>> how rectangular window has lowest bandwidth compared to Hanning >>window( >>>>>> which is basically raised cosine), but higher side-lobes. >>>>>> But in all pulse shaping filter tutorials, apart from minimizingISI>>>> they >>>>>> describe how the bandwidth of the rectangular pulse is almost twice >>the >>>>>> raised cosine pulse ( for alpha=0). >>>>>> What am I doing wrong? This seems very contradictory to me. In >>both >>>> cases >>>>>> windowing and pulse shaping we are looking are the frequencyresponse>>>>>> aren't we??Im obviously making some very basic mistake, please >>>> enlighten >>>>>> me. >>>>> >>>>> English is evidently not your first language. Basically, you are >>>>> confusing the bandwidth of a pulse with the selectivity of a filter. >>> >>>> Could you please elaborate? In both cases aren't we considering theDFT>>of >>>> the same time domain waveform? >>> >>>What cases? A pulse shaped like a raised cosine in the time domain has >>>much less "splatter" -- broadband energy -- than a rectangular pulse of>>>the same width. What has that to do with windowing the data fed to a DFT>>>routine? >>> >>>Jerry >>>-- >>>Engineering is the art of making what you want from things you can get. > >>>Ok, I think you did not understand my question. However I think Irealize>>my mistake. >>Case 1: I'm comparing the DFT of a rectangular window and a hanning(raised>>cosine window). >>Case 2: Then I'm comparing the frequency domain of a rectangular pulseto>>a raised cosine shaped pulse . >>I thought that case 1 and case 2 should have the same results >>I think the mistake is that even though the Hanning window is calledraised>>cosine, its really a truncated raised cosine compared to the shapedraised>>cosine pulses used to transmit data. > >A Raised Cosine window for a DFT is not the same as a Raised Cosine >response for a pulse shape. This is an unfortunate overloading of >the terminology "Raised Cosine", as the raising of the cosine is used >differently and does different things in each case. > >So they are not expected to be the same. > > >Eric Jacobsen >Minister of Algorithms >Abineau CommunicationsThanks, I guess I was not communicating my question well. You're the only one who understood my question and mistake. Thanks, again!>http://www.abineau.com >

Reply by ●August 11, 20102010-08-11

Jerry Avins wrote:> On 8/11/2010 4:38 PM, Zeph80 wrote: >>> On 8/11/2010 3:55 PM, Zeph80 wrote: >>>> So I'm pretty confused about something.While studying DFT windowing, I >> saw >>>> how rectangular window has lowest bandwidth compared to Hanning window( >>>> which is basically raised cosine), but higher side-lobes. >>>> But in all pulse shaping filter tutorials, apart from minimizing ISI >> they >>>> describe how the bandwidth of the rectangular pulse is almost twice the >>>> raised cosine pulse ( for alpha=0). >>>> What am I doing wrong? This seems very contradictory to me. In both >> cases >>>> windowing and pulse shaping we are looking are the frequency response >>>> aren't we??Im obviously making some very basic mistake, please >> enlighten >>>> me. >>> >>> English is evidently not your first language. Basically, you are >>> confusing the bandwidth of a pulse with the selectivity of a filter. > >> Could you please elaborate? In both cases aren't we considering the >> DFT of >> the same time domain waveform? > > What cases? A pulse shaped like a raised cosine in the time domain has > much less "splatter" -- broadband energy -- than a rectangular pulse of > the same width. What has that to do with windowing the data fed to a DFT > routine? > > JerryJerry, Oh, I'd say "everything"! :-) Rectangular window vs. raised cosine window..... Fred

Reply by ●August 11, 20102010-08-11

Fred Marshall <fmarshall_xremove_the_xs@xacm.org> wrote:>Jerry Avins wrote:>> A pulse shaped like a raised cosine in the time domain has >> much less "splatter" -- broadband energy -- than a rectangular pulse of >> the same width. What has that to do with windowing the data fed to a DFT >> routine?>Jerry,>Oh, I'd say "everything"! :-)I'd tend to agree. And it depends upon why you are applying a DFT. If you are trying to estimate the relative amplitudes and phases of expected components within the passband of a signal, often there is no windowing applied first. If instead you are trying to find out how much unwanted energy there is in the stopband, outside of the signal of interest, you pretty much have to apply a window. (The above is of course a very broad generalization, to which there are many exceptions, but I think it holds up pretty often.) Steve