# 5G Positioning via Position Reference Signal

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I am styding the Position Reference Signal via 3GPP .Do you know the definition of PRS repetition factor time gap in 3GPP38.214,I have no dieas how PRS distribution on difference system frame and slots.

Sriram Tadavarty on 5 Jan 2021
Edited: Sriram Tadavarty on 5 Jan 2021
Hi there,
PRS repetition time gap is the slot offset between two consecutive repetition indices of all the PRS resources in a PRS resource set.
In simple words, it is the time difference of a PRS resource and the repetition instance of the same PRS resource.
Consider a PRS resource set has only one PRS resource and that PRS resource has a repetition factor of 2. Assuming PRS resource set period is 8 slots and then PRS resource starts at an offset of 2 slots (slot #2). As the PRS resource repetition is 2, there will be two instances of PRS resource in the PRS resource set period. The first instance is at slot #2, since it is at an offset of 2 slots. Now, we need to figure out at which slot in the 8 slot period, is the repetition of first instance should be. This is known with the help of PRS repetition factor time gap.
If the PRS repetition factor time gap for the above example is 4, then the repetition of first instance is at a gap of (4-1) slots with respect to the first instance. Implies gap of 3 slots from slot #2, which is slot #6. See the below illustration with code comments.
% Consider one frame of 15 kHz SCS (i.e., 10 slots), PRS resource set period is 8 with slot offset as 0
%
% |<----------------------------------- Frame --------------------------------------->|
% | slot#0 | slot#1 | slot#2 | slot#3 | slot#4 | slot#5 | slot#6 | slot#7 |sl#8 |sl#9 |
% |<---------------------- PRS resource set period ---------------------->|<--- ......
%
% |<-- PRS Offset ->| |<--- PRS time gap - 1 --->|
% | Res1 | | Res1Rep|
% Res1 is the first instance of PRS resource
% Res1Rep is the repetition instance of same PRS resource
% PRS Offset is the offset of PRS resource with respect to the slot offset of PRS resource set (slot #0 here).
% The gap between the first instance and the repetition instance of the PRS resource is (PRS time gap - 1).
The illustration above indicates only the PRS presence in the slot. But, the actual transmission of PRS in a slot also depends on the muting configuration.
Hope this helps.
Regards,
Sriram
Edit: Changed the illustration to look better in the answer.
##### 2 CommentsShowHide 1 older comment
Noor Mohammedali on 1 Sep 2021
Hello Sriram,
Thank you for your expleantion, help me to understand it better.
I have one question, Do you have an idea how can i create PRS resources like Res1, Res2 and Res3?
Thanks,