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Cyclic prefix in OFDM....

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mashhur

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cyclic prefix

Hi all members!

I want to ask about cyclic prefix and guard period. What is the difference between them?
Among the symbols OFDM usually use cyclic prefix and some tutorials show it is equal to guard period, however, other books explain them in different. So, unfortunately I couldn't get the main distinguish argue.

Could somebody help me?

Thanks in advance!

Added after 4 hours 6 minutes:

Ok, finally I found the answer for my question myself. If it involves, somebody can find out :

The cyclic prefix, which is transmitted during the guard interval, consists of the end of the OFDM symbol copied into the guard interval, and the guard interval is transmitted followed by the OFDM symbol. The reason that the guard interval consists of a copy of the end of the OFDM symbol is so that the receiver will integrate over an integer number of sinusoid cycles for each of the multipaths when it performs OFDM demodulation with the FFT.
 

cyclic prefix in ofdm

hello friend i have some thesis that simulate the OFDM using matlab if u need.
 

cyclic prefix wiki

could you please attach it?

Thanks a lot!
 

symbol ofdm

Hi Dear,

see these attached files
 

cyclic prefix

by the way : all from the internt
 

guard interval cyclic prefix

this cyclic prefix is one block in OFDM. whether iam right. i need to know coding for basic OFDM structure and to reduce PAPR. please aya make me favour iam waiting for your reply.
 
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    sapra

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ofdm cyclic prefix

hi gayathri123,

please enjoy my group on yahoo. i hope some body can help you regarding the PAPR.

**broken link removed**


The programs for the basic OFDM was included in the above attachements.


Best Wishes
 

why to use cyclic prefix?

also see this file
 

hi, could any one tell me wht should be the length of Cyclic Prefix(CP) in accordance to symbol/block length.
Is there any relation between or just any length is good?

---------- Post added at 07:41 ---------- Previous post was at 07:35 ----------

I am stuck with one more problem:
when I would convolute serial data stream x(n) with channel h(k) length would be n+k+1...
now first question is that can length of data stream and channel be different or should be same.
second is that after convolution I have addition bits what to do with these extra bits...because i need exact same number of bits for maintaining the number of blocks and blocks.
and further to demodulation and BER
Kindly put some insights on this topic
 

varindernew said:
hi, could any one tell me wht should be the length of Cyclic Prefix(CP) in accordance to symbol/block length.
Is there any relation between or just any length is good?
Click to expand...


CP length can be 10-25% of Symbol period

---------- Post added at 18:25 ---------- Previous post was at 18:20 ----------
mashhur said:
The cyclic prefix, which is transmitted during the guard interval, consists of the end of the OFDM symbol copied into the guard interval, and the guard interval is transmitted followed by the OFDM symbol. The reason that the guard interval consists of a copy of the end of the OFDM symbol is so that the receiver will integrate over an integer number of sinusoid cycles for each of the multipaths when it performs OFDM demodulation with the FFT.
Click to expand...

Do we need guard interval in ODFM? I think we can just use cyclic prefix only?
 

mazdaspring said:
CP length can be 10-25% of Symbol period

---------- Post added at 18:25 ---------- Previous post was at 18:20 ----------



Do we need guard interval in ODFM? I think we can just use cyclic prefix only?
Click to expand...


The Cyclic prefix in OFDM is sometimes called Guard Interval so that in some references you found in the block diagram of the OFDM system the three letters (GII) which it means Guard Interval Insertion (CP insertion).

Regarding its length, it depends on the channel you will use so that it is between 8-25% of the symbol length.

Regards
 

thanx for replying,
i think Gaurd interval and CP is same thing and used interchangeably...

---------- Post added at 04:35 ---------- Previous post was at 04:33 ----------

i just read that length of CP should be less then delay spread of channel model.
I am using Power line communication channel and I have the channel model of it, but I dont know from where could I check the information about delay spread.
could anyone help me with this.
 

Guard Interval is sometimes synonyms with CP, however, some references consider that the Guard Interval (GI) is an empty period attached to the OFDM symbol (this removes ISI but looses orthogonality), while CP is a copy of the OFDM symbol terminating samples pasted at the beginning of the symbol, this keeps orthogonality
and removes ISI.
 

As I know, CP converts the linear convolution into circular convolution. What maintains orthogonality between sub-carriers is the separation between these sub-carriers, not what this separation is.
 

Cyclic prefix is set of symbols inserted to the OFDM signal in order to provide aguard time to prevent inter block interference(IBI) due to multipath propagation.In general CP is a copy of the last part of the block which is added at the start of each block .Mainly there are two reasons

1.CP acts as a guard time.
2. concerts linear convolution to circular convolution
 

hello friend i have some thesis that simulate the OFDM using matlab if u need.
 

Dear sz-aiden,
please upload the thesis for us to share. It will be grateful to you.
 

Re: guard interval cyclic prefix

gayathri123 said:
this cyclic prefix is one block in OFDM. whether iam right. i need to know coding for basic OFDM structure and to reduce PAPR. please aya make me favour iam waiting for your reply.
Click to expand...
yes, i can help u out in explanation as well as coding my id is er.projectdeveloper@gmail.com

---------- Post added at 05:02 ---------- Previous post was at 04:58 ----------

yes, i can help u out contact at er.projectdeveloper.com
 

Re: guard interval cyclic prefix

I'm realizing an HDL-synthesizable (thrugh hdllib library) dvb-t model. I'm having problem with Cyclic Prefix (or Guard Interval) and Pilot insertion too.
The problem is that, if my input is a stream of data, these block should operate with a sample frequency higher than input or
1)i will loose data when i insert pilot/cyclic prefix/zero pad before iFFT
2)saturate eventually FIFO/RAM used to store input value when inserting.
Other ways like "frame based" to insert these values are not supported in hdl code generation.
 

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