In DL FUSC, the mapping of pilots is done first. Then , the remaining subcarriers are used to define the data carriers which inturn is grouped to form subchannels. But , i find that there are 2 variable and constant pilot set. I am eager to know the reason/use of the 2 variable and constant pilot set used in Downlink FUSC. Any ideas ?
I understand that in FUSC (DL), Certain number of the active tones are pilot and their location in the spectrum is based on some algorithm (predefined). That is, scattered pilots are inserted at pre-determined intervals/duration in the time- frequency. Is it something as below ?
1) Variable pilot set - This is based on Channel condition, Multipath delay spread and Doppler. Useful for channel estimation.
2) Constant pilot set - This is not dependent on the Channel condition / Doppler. It is just based on the OFDM symbol duration and subcarrier spacing.
Is there any link / doc in internet that talks in detail about these. I searched the internet, but i did not get any link. I am eager to know the reason/advantage for variable/constant pilot set. Any ideas ?