FDD in LTE

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Overview - FDD

The highest level view from 36.211 for FDD LTE is as follows. It only shows the structure of one frame in time domain. It does not show any structure in frequency domain.
Some of high level description you can get from this figure would be
i) Time duration for one frame (One radio frame, One system frame) is 10 ms. This means that we have 100 radio frame per second.
ii) the number of samples in one frame (10 ms) is 307200 (307.200 K) samples. This means that the number of samples per second is 307200 x 100 = 30.72 M samples.
iii) Number of subframe in one frame is 10.

iv) Number of slots in one subframe is 2. This means that we have 20 slots within one frame.


So one slot is the smallest structure in time domain ? No, if you magnify this frame structure one step further, you would get the following figure.
Now you see that one slot is made up of 7 small blocks called 'symbol'. (One symbol is a certain time span of signal that carry one spot in the I/Q constellation.).
And you see even smaller structures within a symbol. At the beginning of symbol you see a very small span called 'Cyclic Prefix' and the remaining part is the real symbol data.
There are two different type of Cyclic Prefix. One is normal Cyclic Prefix and the other is 'Extended Cyclic Prefix' which is longer than the Normal Cyclic Prefix. (Since the length of one slot is fixed and cannot be changed, if we use 'Extended Cyclic Prefix', the number of symbols that can be accomodated within a slot should be decreased. So we can have only 6 symbols if we use 'Extended Cyclic Prefix').


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