How frame boundary is obtained by SSS?

Question

I know that slot-0 and slot-10 will be having different sequences in case of SSS. I want to know how these different sequences are being used in determining the boundary of the frame?

Answer 1

PSS and SSS are sent in subframe 0 (even subframe) and subframe 5 (odd subframe). From PSS, UE knows only the slot boundary. From PSS, UE cannot know whether it has read subframe 0 or 5 because PSS sequences are same for odd and even subframe. SSS has different sequences for odd and even subframes. So UE comes to know whether it has read subframe 0 or 5 so knows frame boundary.

Comments

I was not aware at that depth about PSS and SSS. Explained well. Can you please explain what different sequences are transmitted for SSS over subframe 0 and subframe 5. I know SSS can be any value in range of 1 to 167. If this is the case then how a particular chosen sequence becomes two different sequences ?

Answer 2

Hi bhagyashree,

As soon as you obtain an SSS you will come to know the slot no, If it is slot 10 then UE knows after 4 ms next frame will start, if it us 0th slot SSS then UE knows after 9 ms next frame will start, so by knowing SSS UE can decide the frame boundry (means starting and ending of frame).

Comments

Hi Jagan,

Is it possible to determine the same by PSS?

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Hi,
No, Because once you got PSS we can say Subframe boundry, where it starts and where it ends (without knowing frame number), But Frame boundry means It should know  when the Radio frame starts and ends (should know Radio frame number).

Answer 3

You can find explanation in 3GPP Rel 10 standard 36.211 Section 6.11.1 & 6.11.2. It involves zadoff-chu sequence generation.