* Multipath causes multiple copies of the transmitted signal to be received. Each copy is at a fixed time offset but at random amplitude and phase.
* If multipath copies from adjacent symbols arrive at the receiver at the same time this creates inter-symbol interference and loss of performance
The received signal is only pure after the last ray arrives and before the first ray disappears
This reduces the useful symbol length by 15% being the difference in path delay – also known as the delay spread
Adding the cyclic prefix (CP)
* The useful symbol length can be restored by extending the length of each symbol by copying the end of the symbol to the start (cyclic prefix)
* Provided the length of this cyclic prefix is at least as long as the significant multipath then the receiver can sample the signal from the start of the cyclic prefix and completely avoid interference from the adjacent symbols at the expense of a proportional decrease in system capacity
