RF

LTE Channels

Look through the constellations and control channel(CCH) and Share Channel(SCH) configuration.. and see how the constellation changes depending on the configuration.

Why only pictures ? It is to give you something to think about.

All of these example are from the measurement result of the transmitted from a LTE Network emulator transmitting with full Resource Block allocation across all the subframes. If you see the first three example, they are all MCS 9 which is QAM. Why the constellation are different from each other ? Even in the same example, why slot 0 constellation is different from other slots ? Why are there some additional dots (constellation) in slot 5 and 6 ?

Try to correlate the map explained at Frame Structure-Downlink with the constellation shown here. If you can freely pull up the channel map and these constellation in your brain and draw correlation line between the map and the constellation, you are in a good position to understand the physical entity of LTE signal. Practice ! Practice ! Practice.

CCH = Single, SCH = Single, MCS = 9 (QAM)

The seven constellation corresponds to the first slot of a sub frame. (Can you pull up the channel map in your brain ? If not, see the channel map again). Symbol 1 corresponds to the control channel (PDCCH) (In LTE, control channel in each subframe can use maximum 3 symbols, but for this tutorial I configured the number of slots for the control channel to be 1. So in this constellation, only symbol 1 is for control channel and all the other symbols are for data (PDSCH) (of course, small portions of these parts are used for Sync channel and PBCH).

In symbol 5 and 6, you see a couple of other dots (constellation) which look different from the other symbols (symbol 2-4). What would they are ? We would need further study to figure out exactly what they are, but just based on the channel map poping up in your brain now.. you would see these strage looking dots would come from Primary Sync, Secondary Sync). You don't have to know everything at once, just try to accumulate knowledge one by one.

The constellations shown above is for symbol 7-13. These are all for PDSCH (data) and I configured all the slot with the same data format, so you don't see any differences among these constellations.

This is very brief explantion of the constellation of one subframe (subframe 1) of LTE downlink signal. It may sound too superficial, but trying to explain the other constellations listed below in the way I explanined here would allow you to be more familiar to LTE PHY signals.

CCH = SFBC, SCH = Single, MCS = 9 (QAM)

CCH = Single, SCH = MIMO, MCS = 9 (QAM)

CCH = SFBC, SCH = MIMO, MCS = 23 (64QAM)