Hello Experts,
Can someone explain in detail role of Semi Persistent Scheduling in 4G/5G?
SPS in 5G is used for VoNR.
For 4G we have SPS feature for VoLTE.
Thanks @ankgitm.
But could you please explain it little more? Or share some reading for more details?
Do you have specific query?
Just wanted to understand SPS role in general, by hearing from experts experience.
Every DL/UL resource assighnmemt/grant requires CCEs to transmit DCI format.
If buffer data to transmit is large enough we can afford to use required CCE.
But if buffer data to transmit is small and repetitive scheduling required, required CCEs are used again and again for scheduling smaller data.
E.g. VoLTE.
This is wastage of PDCCH resources.
In such cases SPS can be used.
In SPS scheduling grant is given only once, and UE has to use same resources again and again for transmitting or receiving VoLTE packets.
So CCE usage also reduced drastically.
This help mainly in congested cells where scheduling cannot be done due to lack of CCEs.
This is just rough concept… there are many things involve in detail algorithm.
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I trialed this feature.
During VoLTE time it increases drastically VoLTE call drop rate.
VoLTE most of features are useless!
Below are useful:
- RoHC
- TTI bundling
- qci1 specific reestablishment
- qci1 specific handover threshold
- VoLTE coverage boosting
TTI bundling also not usefull in congested networks, VoLTE drop due to reconfig timeout in poor radio condition.
For customer selling it’s used, very hot buzz word.
I remember for TTI bundling improvement 6 months i struggled. 
Same here. We applied many if and buts for activating TTIB.
Somehow VoLTE drop avoided but TTIB gain disappeared. 
Was its activation BLER based or SINR based, that you have tried?
It is basically based on Supportable TBS by UE, i.e. based on UL channel condition.
If UEs supportable TBS is less tham threshold, TTIB is setup.