Pulse-Shaping Flashcards
Would you prefer raised cosine or root raised cosine pulse-shape at the transmitter, if you are not allowed to use an equaliser at the receiver and you want a simple clock synchronisation? Justify your answer and give also the related parameter of the pulse-shape. (2021)
What happens if you transmit a signal at high modulation rate through a band-limited channel?
Creates ISI
What happens to the (frequency) spectrum of the signal which is sharp rectangular, in the time domain? Theoretically, what’s the advantage of a sinc shaped pulse?
A sinc shape. There is no ISI.
What is theoretically the best pulse shaping filter and what are the drawbacks of it? What is the alternative?
Theoretically, the best pulse shaping filter would be the sinc filter, but it cannot be implemented precisely. Raised-cosine filters are then used.
What is the trade off for using raised-cosine filters?
The tradeoff of smaller sidelobes for a slightly larger spectral width.
What is the roll-off factor? Describe the effects of the roll-off filter when it is zero and one on the spectrum.
Roll-off factor is a measure of the excess bandwidth of the filter i.e. the bandwidth beyond the Nyquist bandwidth of 1/2T
When the roll-off factor is zero, it turns into a rectangular shape which corresponds to a sinc shape. When the roll-off factor is one, the shape of the spectrum is a pure raised cosine.
Describe the application of a Nyquist filter.
A Nyquist filter has the ability to eliminate ISI, as it’s impulse response is zero for all nT, except n=0.
Therefore, if the transmitted waveform is correctly sampled at the receiver, the original symbol values can be recovered completely.
