LTE - PSS & SSS
Primary Synchronisation Signal (PSS):
PSS is the signal which is first decoded by the UE to access the LTE Cell. Lets see how the PSS is decoded & where exactly the PSS is transmitted.
1. PSS is always transmitted on 2 slots in every frame.
Slot 0 & Slot 10 will contain the PSS. i.e., 1st slots of Subframe 0 & Subframe 5.
Where it will be tranmitted in the Slots?
Its always on the last OFDM symbol of the slot. Which means, out of 7 OFDM symbols in a slot, 7th Slot will carry the PSS.
What UE will achieve by decoding PSS?
1. Subframe synchronisation.
2. Slot synchronisation.
3. Symbol synchronisation.
All three in the Time Domain.
4. To identify the center of the Channel BW in Frequency Domain,
5. To deduce the PCI from 3 available PCI's
Note: The PSS cannot be used to achieve radio frame synchronisation
Secondary Synchronisation Signal (SSS):
Once the PSS is decoded successfully the next task for the UE is to decode the SSS. So where SSS will come in Radio frame?
SSS will be carried in the 6th OFDM symbol of the Slot 0 & 10. Which means, like PSS, SSS also be tranmitted twice in a Radio Frame, exactly just before the PSS.
What UE will achieve by decoding SSS?
1. Radio Frame synchronisation.
2. To deduce one of the 168 PCI groups.
So at the End of SSS decoding, UE will come to know the Complete Cell ID.
RE Allocation's for PSS & SSS:
6 RB's are allocated for PSS & SSS irrespective of the Channel Bandwidth.
So Total RE's = 6 * 12 = 72 Resource Element's.
Out of this 72 RE's, 1st 5 & the Last 5 RE's are not used for Transmissions, i.e., DTX
In case of 1.4Mzh BW, only 6 RB's are present so PSS & SSS will occupy the entire BW.
What will happen if the Channel Bandwidth is 10 Mhz? Where PSS & SSS will occupy?
Since PSS & SSS will occupy the central channel BW, here it will occupy @ the center. IN 10Mhz BW, we have 50 RB's are present.
Total Subcarrier Freq's in 10Mhz = 50 * 12 = 600
So it will start from Subcarrier 264 & end at Subcarrier number 335. Remember the subcarriers starts with 0 to 500 here.
Pls find the Example Pic for PSS & SSS below.
Primary Synchronisation Signal (PSS):
PSS is the signal which is first decoded by the UE to access the LTE Cell. Lets see how the PSS is decoded & where exactly the PSS is transmitted.
1. PSS is always transmitted on 2 slots in every frame.
Slot 0 & Slot 10 will contain the PSS. i.e., 1st slots of Subframe 0 & Subframe 5.
Where it will be tranmitted in the Slots?
Its always on the last OFDM symbol of the slot. Which means, out of 7 OFDM symbols in a slot, 7th Slot will carry the PSS.
What UE will achieve by decoding PSS?
1. Subframe synchronisation.
2. Slot synchronisation.
3. Symbol synchronisation.
All three in the Time Domain.
4. To identify the center of the Channel BW in Frequency Domain,
5. To deduce the PCI from 3 available PCI's
Note: The PSS cannot be used to achieve radio frame synchronisation
Secondary Synchronisation Signal (SSS):
Once the PSS is decoded successfully the next task for the UE is to decode the SSS. So where SSS will come in Radio frame?
SSS will be carried in the 6th OFDM symbol of the Slot 0 & 10. Which means, like PSS, SSS also be tranmitted twice in a Radio Frame, exactly just before the PSS.
What UE will achieve by decoding SSS?
1. Radio Frame synchronisation.
2. To deduce one of the 168 PCI groups.
So at the End of SSS decoding, UE will come to know the Complete Cell ID.
RE Allocation's for PSS & SSS:
6 RB's are allocated for PSS & SSS irrespective of the Channel Bandwidth.
So Total RE's = 6 * 12 = 72 Resource Element's.
Out of this 72 RE's, 1st 5 & the Last 5 RE's are not used for Transmissions, i.e., DTX
In case of 1.4Mzh BW, only 6 RB's are present so PSS & SSS will occupy the entire BW.
What will happen if the Channel Bandwidth is 10 Mhz? Where PSS & SSS will occupy?
Since PSS & SSS will occupy the central channel BW, here it will occupy @ the center. IN 10Mhz BW, we have 50 RB's are present.
Total Subcarrier Freq's in 10Mhz = 50 * 12 = 600
So it will start from Subcarrier 264 & end at Subcarrier number 335. Remember the subcarriers starts with 0 to 500 here.
Pls find the Example Pic for PSS & SSS below.
No comments:
Post a Comment