>On Mon, 08 Feb 2016 06:46:29 -0600, "mohitdaksh" <111830@DSPRelated>
>wrote:
>
>>Hello,
>>
>>I am studying implementation of a BPSK modulator and demodulator for
radio
>>applications and I am very confused.
>>
>>From what I have read, in the transmitter section, the binary data is
>>given to a BPSK mapper, which maps to bits to one symbol ( 0 =cos(wt),
>>1=-cos(wt) ).
>>
>>But I had read we are doing pulse shaping because we cannot transmit
>>square pulses through the channel, but we are not sending square waves
>>anyway so where does pulse shaping come into picture?
>
>There are several different ways of looking at this, one of which
>Tauno already alluded to, where you first creat the NRZ bit stream
>with +/-1 values, filter it, and then mix it up to IF/RF with an
>oscillator.
>
>From that perspective it's easy to see that the spectrum of the NRZ
>bit stream has a sinx/x shape (the transform of the rectangular
>pulses).
>
>It is essentially the same thing if you look at it the way you
>mentioned, where a 1 is -cos(wt) and a 0 is cos(wt). In that case
>you have a tone (the cos(wt)), multiplied by the NRZ bit stream, still
>with +/-1 values. The resulting spectrum is then the convolution of
>the tone and the sinx/x shape of the NRZ stream.
>
>So either perspective gets you to exactly the same place.
>
>The pulse shaping filter provides a number of benefits, one being that
>the transmit spectrum is then better contained to a much narrower
>region than the original sinx/x shape, so that the spectrum can be
>used more efficiently by other signals without interference.
>
>
>Eric Jacobsen
>Anchor Hill Communications
>http://www.anchorhill.com
Thanks Eric and Tauno
---------------------------------------
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Reply by Eric Jacobsen●February 8, 20162016-02-08
On Mon, 08 Feb 2016 06:46:29 -0600, "mohitdaksh" <111830@DSPRelated>
wrote:
>Hello,
>
>I am studying implementation of a BPSK modulator and demodulator for radio
>applications and I am very confused.
>
>From what I have read, in the transmitter section, the binary data is
>given to a BPSK mapper, which maps to bits to one symbol ( 0 =cos(wt),
>1=-cos(wt) ).
>
>But I had read we are doing pulse shaping because we cannot transmit
>square pulses through the channel, but we are not sending square waves
>anyway so where does pulse shaping come into picture?
There are several different ways of looking at this, one of which
Tauno already alluded to, where you first creat the NRZ bit stream
with +/-1 values, filter it, and then mix it up to IF/RF with an
oscillator.
From that perspective it's easy to see that the spectrum of the NRZ
bit stream has a sinx/x shape (the transform of the rectangular
pulses).
It is essentially the same thing if you look at it the way you
mentioned, where a 1 is -cos(wt) and a 0 is cos(wt). In that case
you have a tone (the cos(wt)), multiplied by the NRZ bit stream, still
with +/-1 values. The resulting spectrum is then the convolution of
the tone and the sinx/x shape of the NRZ stream.
So either perspective gets you to exactly the same place.
The pulse shaping filter provides a number of benefits, one being that
the transmit spectrum is then better contained to a much narrower
region than the original sinx/x shape, so that the spectrum can be
used more efficiently by other signals without interference.
Eric Jacobsen
Anchor Hill Communications
http://www.anchorhill.com
Reply by Tauno Voipio●February 8, 20162016-02-08
On 8.2.16 14:46, mohitdaksh wrote:
> Hello,
>
> I am studying implementation of a BPSK modulator and demodulator for radio
> applications and I am very confused.
>
> From what I have read, in the transmitter section, the binary data is
> given to a BPSK mapper, which maps to bits to one symbol ( 0 =cos(wt),
> 1=-cos(wt) ).
>
> But I had read we are doing pulse shaping because we cannot transmit
> square pulses through the channel, but we are not sending square waves
> anyway so where does pulse shaping come into picture?
You change the bits so that a 0 becomes -1 and an 1
becomes +1, shape the stream of (-1, +1) and multiply
the carrier (cos(wt)) with the shaped modulating signal.
--
-TV
Reply by mohitdaksh●February 8, 20162016-02-08
Hello,
I am studying implementation of a BPSK modulator and demodulator for radio
applications and I am very confused.
From what I have read, in the transmitter section, the binary data is
given to a BPSK mapper, which maps to bits to one symbol ( 0 =cos(wt),
1=-cos(wt) ).
But I had read we are doing pulse shaping because we cannot transmit
square pulses through the channel, but we are not sending square waves
anyway so where does pulse shaping come into picture?
---------------------------------------
Posted through http://www.DSPRelated.com