kopia lustrzana https://github.com/proto17/dji_droneid
Updated Home (markdown)
rodzic
fe48a18350
commit
e87ecf5276
17
Home.md
17
Home.md
|
@ -250,6 +250,19 @@ According to the LTE spec, the first OFDM symbol should use the long cyclic pref
|
|||
|
||||
So, lets check to see if this math works out. From the MATLAB plot earlier the OFDM symbol seemed to end (far right of the white box) around sample number `9,760`. Assuming that each symbol after the first is `2048 + 144` or `2192` samples, the end of the previous OFDM symbol should be `9760 - 2192` or `7,568`
|
||||
|
||||
![Screenshot from 2022-04-12 22-35-22](https://user-images.githubusercontent.com/4240543/163088581-9057c90a-8254-4b88-a12d-b22b2b2ef08d.png)
|
||||
![image](https://user-images.githubusercontent.com/4240543/163088695-9665d928-1fc7-471f-a7f0-45e0423b6e5c.png)
|
||||
|
||||
The mouse cursor is roughly at `7,568` and that does look like the very beginning of the OFDM symbol from earlier. Subtracting `2,192` again gives `5,376`
|
||||
|
||||
![image](https://user-images.githubusercontent.com/4240543/163088951-f9382be1-d93b-4bf2-b0fc-1fbf47403806.png)
|
||||
|
||||
Moving back again by `2,192` gives `3,184`
|
||||
|
||||
![image](https://user-images.githubusercontent.com/4240543/163089050-a253c005-717e-46d7-abab-aa410e177093.png)
|
||||
|
||||
For the next symbol the cyclic prefix length should be 160, so we need to subtract `2048 + 160` or `2208` which gives `3184 - 2208` or `976`
|
||||
|
||||
![image](https://user-images.githubusercontent.com/4240543/163089256-8a6ebdf9-6ee9-4665-8b68-b8213c91ca6e.png)
|
||||
|
||||
And that brings us back to the very beginning of the burst! We can assume that a rough starting sample for the burst is `976`. We will have to refine this value further in order to demodulate, but it's a starting point, and validates the expected cyclic prefix and FFT size assumptions.
|
||||
|
||||
The
|
Ładowanie…
Reference in New Issue