# System Frame Number in LTE Specifications

What exactly is System Frame Number in LTE specifications? What is the use of it?

I have read that it is a 10 bit number and used for synchronization purposes. But it's not clear how it helps for synchronization. Any help is appreciated.

• Where have you read that? Context makes answering such questions easier, usually. As far as 20s of Googling yielded, the SFN is simply a counter with no meaning, aside from being a counter – probably helpful if someone needs to keep frames in order. – Marcus Müller Mar 10 '17 at 9:34
• Yeah, I tried google searching and some books also. (sharetechnote.com/html/Handbook_LTE_SFN.html) . I want to know where exactly it is placed in the Resource Block? How this additional field will help synchronizing? I have already got general idea about it. I want more details and hence I'm asking help from you guys. – spectre Mar 10 '17 at 15:21
• "How will that field help synchronizing" probably not at all. You still keep claiming it does - but that's not what the resource you've pointed you says. It's just the counter that you keep to know where you are. – Marcus Müller Mar 10 '17 at 15:29
• First thing is, the resource I mentioned is just an example. I'm not keeping it as a reference. I want to know how SFN works. Answers/Comments which makes sense are welcome. – spectre Mar 14 '17 at 10:36
• It doesn't "work". It's just a counter. – Marcus Müller Mar 14 '17 at 10:47

Nonetheless, SFN does help physical layer protocol synchronization, i.e. synchronization in term of scheduling, between DL physical channels and UL physical channels (just from release 13 for cat-M or NB-IOT UE with long repetition), or synchronization between UL physical channels (for CQI reporting, SRS scheduling, ...). For more details you can take a look at specfication 36.213 all version, the scheduling of SRS, CQI, ... all depend on $$n_f$$ which is SFN, i.e. absolute SFN modulo 1024.