I have a query about application of pulse-shaping filters to a impulse/symbol train, for let's say a QPSK modulated signal. Can the symbol train be be oversampled above the symbol rate? If so, are the samples in between symbols zeroed or identical to the preceding symbol? If it is the former, does that mean that simple diagrams such as this are not quite right since the phase is only modulated at one point and not throughout the duration of the symbol? If it is the latter, does this cause inter-symbol interference? Thanks