- This topic has 3 replies, 3 voices, and was last updated 9 years, 4 months ago by alistu.
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July 22, 2015 at 8:31 am #22639Dhananjay PatelParticipant
I am working on OFDM system whose design is attached here with. I have certain query to make:
1. What is the significance of these global parameters:
Sequence length
Samples per bit
Guard Bits
Symbol rate
Number of samples2. What is the use of position array in OFDM block.
3. What is the relationship between the number of sub carrier, position array, number of FFT point
4. How to decide the roll of rate of the LP cosine filter?
5. Also in my input and output constellation, I am finding a huge difference, kindly let me know the reason behind it.
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July 24, 2015 at 4:40 am #22687Ashu vermaParticipant
Hello Dhanjay
I try to explain the points and question you raised about the parameters of OFDM
First of all, sequence length is the no. of bits transmit and the sequence length is directly relates to the word length that you can set from PRBS. In the case of OFDM the sequence length is long.
Samples per bit are the instants to sample the the one bit and total sampling freq. is your bit rate x sample per bits.Sample per bit in the case of OFDM are chosen to be less due to long sequence length which results into high no. of samples.
Gaurd bits are used to reduce ISI in the OFDM system.
Symbol rate quantifies the number of symbols transmitted per second.
No. of sample=Seq. length x Sample per bit
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July 24, 2015 at 4:43 am #22688Ashu vermaParticipant
In the addition to the above points,for the FFT points go to the link i have given below
For Understanding of Lp cosine filter and roll of factor visit the given link
https://en.wikipedia.org/wiki/Raised-cosine_filterFor the last one,can you attach the system setup screen shot along with constellation diagrams as i am not able to open the file you have attached.
Hope you got your all answers
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July 24, 2015 at 5:16 am #22690alistuParticipant
Hi Dhananjay,
I believe I gave you the answer for some of the questions you have asked above in the forum below:
Your constellation on receiver side looks strange! After all, you have only sent 4 symbols but you are receiving more!
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