I am new here. I hope I can get help.
I want to ask a question regarding digital communication.
Does anyone know what are pulse shaping used for? Are they used for ISI mitigation or for something else? Also what is the receiver side of this operation is it matched filter?
Answer
As you've told the main goal of pulse shaping filter is to restrict signal bandwidth in the transmitter while in receiver you should place the matched filter to maximize SNR. In the practical modems pulse shaping filter in the transmitter and matched filter in the receiver are usually the same in terms of frequency response. The task is to choose filters to minimize ISI (not all TX-RX filters pairs satisfy this condition while if even maximizing SNR value). From the theory is known raised cosine filter satisfy ISI condition. You can read about this filter here. Let's place such a filter in TX and RX side:
$H_{system} = H_{Tx} * H_{Rx}$
We can see the total response of the system is no longer raised cosine. So the root raised cosine filter was proposed. The main idea is
$H_{rrc} = \sqrt{H_{rc}}$, so for our system
$H_{system} = H_{Tx} * H_{Rx} = H_{rrc} * H_{rrc} = (\sqrt{H_{rc}})^2 = H_{rc}$
By doing this we can minimize ISI and maximize SNR if the filter bandwidth is closely matched to signal's one. So it is very practical and widely used in digital modems (especially single carriers (SC) modems).
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