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How the Symbols sent in a slot with perfect timing in LTE ???

+5 votes
125 views

Each carrier in LTE is 15khz so in a calculation i found that useful symbol time = 1/15khz = 66.6 mircosec

wrt to this
Each symbol duration is calculated like this
Normal Cyclic Prefix length = 4.69 microsec --- so each symbol in this = 66.6 + 4.69 = 71.29 microsec
Extended Cyclic Prefix length = 16.67 microsec ----so each symbol in this = 66.6 + 16.67 = 83.27 microsec

So Normal cyclic prefix Slot (7 symbols) duration = 71.29 * 7 = 499.03 microsec(0.49903 millis)
and Extended cyclic prefix Slot (6 symbols) duration = 83.27 * 6 = 499.63 microsec (0.49963 millis)

But slot duration is fixed as 0.5 ms ...

So does this slight difference creates any problem ???
How real time it works ???

posted Feb 24, 2014 by Amit Sharma

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1 Answer

+5 votes

I may not have satisfied answer here, but I would like to correct/add some information for the question.

Each carrier in LTE is 15khz so in a calculation i found that useful symbol time = 1/15khz = 66.6666 micro sec
wrt to this
Normal Cyclic Prefix:
Normal Cyclic Prefix length = 4.6875 micro sec. This length applies for symbol 1,2,3,4,5,6 but not for symbol 0.
- For Symbol 0, Cyclic Prefix length = 5.2083 micro sec.(please refer OFDM baseband signal generation section in 3GPP spec 36.211 in which OFDM parameters table mentions about cyclic prefix length)
- so 6 symbol out of 7 has length = 66.6666 + 4.6875 = 71.3541 micro sec
- But for symbol 0, length = 66.6666 + 5.2083 = 71.8749 micro sec
- So total lengh in case of Normal Cyclic Prefix is 71.8749 + (6 * 71.3541) = 499.9995 micro sec(0.4999995)

Extended Cyclic Prefix:
Extended Cyclic Prefix length = 16.6666 micro sec ----so each symbol in this = 66.6666 + 16.6666 = 83.3332 micro sec
and Extended cyclic prefix Slot (6 symbols) duration = 83.3332 * 6 = 499.992 micro sec (0.4999992 millis)

I hope it helps !!

answer Apr 20, 2016 by Bhaskar Kalaria
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