Why do we do oversampling in raised cosine?

The purpose of Oversampling in raised cosine filter is to narrow the spectral content of the transmitted sequence. An oversampling factor is chosen such that the available bandwidth becomes entirely occupied with the signal.

1. What is the purpose of oversampling?
2. Why do we use raised cosine?
3. Why do you need upsampling before pulse shaping?
4. How does oversampling reduce noise?

What is the purpose of oversampling?

Oversampling is capable of improving resolution and signal-to-noise ratio, and can be helpful in avoiding aliasing and phase distortion by relaxing anti-aliasing filter performance requirements. A signal is said to be oversampled by a factor of N if it is sampled at N times the Nyquist rate.

Why do we use raised cosine?

Raised cosine filters are used for pulse shaping, where the signal is upsampled. Therefore, we also need to specify the upsampling factor.

Why do you need upsampling before pulse shaping?

Pushing the sample rate out by upsampling provides room to shape the spectrum as needed for transmit mask as well as matching. The same thing can be seen in the time domain. Shaping the eye pattern can only be done if there are more than one sample per symbol. That clear up some confusion.

How does oversampling reduce noise?

Oversampling is a cost-effective process of sampling the input signal at a much higher rate than the Nyquist frequency to increase the SNR and resolution (ENOB) that also relaxes the requirements on the antialiasing filter.