Cyclic prefix & Ex Cyclic Prefix

[saurabh]

Hi,Can any one explain, what is the benefit of Ex Cyclic prefix over Cyclic prefix and which condition we required and what would be impact on capacity.thanksSaruabh

[Weiland86]

Everything is related to the symbol period on OFDM and the Spread delay of the channel, i do not remeber exacty the numbers involved in but basically is as follow in order to mitigate ISI inter symbol interference and Frequency selective channels ofdm increase the symbol period using low bandwidth channels (15khz) and using cyclic prefix this under normal environment, well if the coverage of the cell is too large (here is the trick after certain number of kilometers cyc prefix lenght is not enough to guarantee low ISI) so what lte does is consider a extended cyc pref in order to increse period symbol even more than before and thus mitigate ISI and frequency selective channels under that circunstances.


when use extended cyc prefix well when the coverage of the cell is too large (research about the distance this is not so difficult is a very simple formulation) the impact on capacity i do not have exact numbers but basically if your period symbol is now larger than before and not because is transmitting more information... actually increasing the cyc pref (extended) increase the repeated part of the actual information contained in the symbol, so the overhead in the symbol also increases reducing the payload.


This is just the general idea for obtained accurate numbers based on what i have said just research a little bit... information must be there



BR,
Weiland

[jayk]

In Normal CP there are 7 symbols in slot while Extended CP has 6 symbols per slot. Normal CP achieves better system performance in case of small multi path delay scenario while Extended CP in large multi path delay scenario.