Re: Excess bandwidth in constellation modulator

[Md. Atiqur Rahman]

Thank you for your reply with the details.

I do already read from the GNU Radio tutorial but wasn't fully sure.

The equation now clear, just want to make sure one point from you.

After the modulation(e.g qpsk) signal upconverted to RF, then the signal bandwidth still will be the same?

Thank you again.

On Wed, Feb 26, 2020 at 12:31 AM Moses Browne Mwakyanjala <address@hidden> wrote:

I saw your post on the gnuradio mailing list. 

The constellation modulator block uses a Square-Root Raised-Cosine filter with occupied bandwidth (double-sided a.k.a passband) given by BW = (1 + alpha)Rs, where Rs is the symbol rate. The bit rate for M-ary linear modulation is given by Bit Rate = Rs*Log(M)base2. Thus, for BPSK you will achieve Bit Rate = Rs, and for QPSK it will be Bit Rate = 2 * Rs. 

The transmission over-the-air is called passband, which for the SRRC filter is given as described above. 

You could read more on the SRRC filter from this Wikipedia article:

https://en.wikipedia.org/wiki/Root-raised-cosine_filter

You could get more information here:

https://wiki.gnuradio.org/index.php/Tutorials

Good luck. 

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Sincerely,

Md Atiqur Rahman