Lte downlink frame ( ofdm and pilots )

[eng_ana1982]

I work in channel coding so i used lte phy layer downlink for one ofdm symbole
i have now module OFDMA CONTAINS OF
1-B.W = 20MHZ
2-SUBCARRIER = 1201 ( INCLUDE DC)
THE IFFT IS 2048 OK

THE PROBLEM IS HOW CAN I DISTRBUITE THE PILOTS IN THIS FRAME

PLZ HELP ME AND IF YOU WANT TO KNOW MORE I WILL TELL YOU

 

[jmpac]

Hi,

Scalable OFDMA (SOFDMA) is introduced in the IEEE 802.16e Amendment to support scalable channel bandwidths from 1.25 to 20 MHz. The scalability is supported by adjusting the FFT size while fixing the sub-carrier frequency spacing at 10.94 kHz. Thus, useful symbol time is 91.4 microseconds (cyclic prefix not included). Sample rate is 22.4 MHz and the number of subchannels is 32. The zero-information carriers are in the edge of the channel for preventing crosstalk with adjacent channels, and some of your 1201 subcarriers are pilot carriers which must be placed periodically.

Regards.

 

[eng_ana1982]

Hi,
thanks for your care and cooperation, i ask about how can i distribute the pilots in frame ok
and about the guard ( zero information ) is it at the starting of the frame and the end of the frame or not ?
and how many pilots i used how can i determined it ?

 

[jmpac]

Don't confuse guard interval (cyclic prefix) with the zero-information carriers.
Zero-carriers are for preventing crosstalk with adjacent channels, but also for adapting the bit capacity per symbol to the input data structure.

The guard interval must be seen only in the time domain; it must be longer than the longest echo delay time of the transmission system. it's at the beginning of the symbol, and it's not empty! Usually, the end of the symbol is put into this time interval so that the receiver is then able to use the autocorrelation function, in order to find the beginning and the end of the area within the symbols not affected by inter-symbol interference due to echoes.

For your 20 MHz | 2048 FFT system I'd employ:
368 zero-information carriers.
560 pilot carriers.
1120 information carriers.

Regards.

 

[eng_ana1982]

Hi,
you say that your design is
For your 20 MHz | 2048 FFT system I'd employ:
368 zero-information carriers.
560 pilot carriers.
1120 information carriers

so how u determined these numbers and i do not understand that
if LTE ( 3GPP) who determined this or me plz explain to me

 

[jmpac]

Type in google 802.16 and you'll find some document explaining how the number of subcarriers must be selected, depending on your channel bandwidth and FFT points.