Cyclic prefix vs. guard interval. Why use one over the other? I'm currently studying some OFDM techniques, and have found that in order to avoid Inter-Symbol Interference (ISI), there needs to be some space in between symbols. Lets assume this length to be $\mu$. This can either be done by adding a cyclic prefix to the beginning of the OFDM symbol, or by adding a simple guard interval (no transmission). 

It seems to me like a cyclic prefix is typically used, but I'm not sure why this is used over a guard interval. using a guard interval would save power, and since the first $\mu$ points of the received signal will be ignored anyways, wouldn't it be better to save power? I'm not sure what the advantages of using a cyclic prefix are. Thanks for any insight!
A silent  guard interval would likely increase PAPR (peak to average power), which requires a sender capable of more dynamic range (without clipping or generating power supply noise, etc.)

A long enough cyclic prefix prevents multipath echoes from one symbol interfering with the portion of the next symbol after the prefix.  And a symbol interfering with itself from only its own multipath echo can be modeled as a flat fading channel, which may be easier to equalize or to error correct over a far wider range of multipath channel responses.