Cyclic Prefix and Zero padding

[paresh_saxena]

I am recently reading OFDM, I am wondering if any body can tell me in which technology we use cyclic prefix and in which we use zero padding. For example I want to know that what we use in Wimax, LTE, DVB-T, IEEE 802.11 and ADSL ? thank you very much.

 

[pappu_sam]

Cyclic Prefix and Zero padding are the techniques used to avoid IBI(Inter Block Interference) in OFDM.

one way to avoid IBI(Inter Block Interference) is we insert (L-1) or more zeros in place of overlap. By doing this only those L-1 number of blocks will be affected and we can recover the required information blocks. This is called zero padding method, another and most practical way to avoid IBI is Cyclic prefix, instead of padding with zeros at the end we take last L-1 samples and copy it in the beginning of every block. This is cyclically repeated so it is called cyclic prefix.

OFDM is used in all application as said by you............

 

[paresh_saxena]

thank u very much, I know the concept of cyclic prefix and zero padding. I want to know that in technologies like Wimax, LTE, DVB-T, IEEE 802.11 and ADSL, we use cyclic prefix or zero padding?? Any material also in this reference will be very helpful.

 

[remembervin]

They all use cyclic prefix !

 

[jmpac]

Hi, paresh_saxena:

In all familiar COFDM transmission methods (DAB, DVB-T, ISDB-T, WLAN, ADSL), both cyclic prefix (also called guard interval) and zero-padding (unused subcarriers set to zero) are being used.

The guard interval cannot be used for eliminating fading: there is nothing that can be done against fading apart from adding error protection to the data stream by means of upstream FEC (forward error correction) and distributing the data stream as uniformly as possible over all COFDM subcarriers in the transmission channel.

As the cyclic prefix (guard interval) is useful, viewed in the time domain, to avoid intersymbol interference due to echoes, the unused zero-information carriers helps for preventing adjacent channel crosstalk, by facilitating the filtering of the shoulders of the COFDM spectrum (frequency domain), and for adapting the bit capacity per symbol to the input data structure.

Regards.