What is the difference between persistent scheduling and semi persistent scheduling?

Question

In case of UE specific data transmission MAC layer allocates radio resources on dynamic basis. When we say dynamic resource allocation it means in each TTI (subframe) different amount of data is sent over the over considering various factor QCI, amount of data buffered at RLC and available radio resource.
What about the MBMS data transmission. MBSFN subrames are fixed in radio frame for the MBMS data transmission. Is there really need of any dynamic resources allocation for the MBMS data comes from RLC layer or it is persistent since required modulation and coding other parameters are already known at the time of bearer establishment and these parameters does not change throughout the data transmission of MBMS data.

Answer 1

I wonder if your question is more about semi-persistent scheduling in the first place.

In LTE the "opposite" of semi-persistent scheduling is NOT persistent scheduling. Persistent scheduling is not really an option for users. Technically you could say that the MIB and SIBs are persistently scheduled meaning they are always they are always going to have a scheduled allocation.

For dedicated signaling to individual users, there are resource grants given for a single subframe. This is the most common.

The only other alternative is a semi-persistent grant. Called SEMI meaning partly, because a truly persistent (permanent for all time) grant is just not done. As the first answer suggests, there are many way to configure this resource grant in terms of how long it is good for.

It was invented to support VOLTE, voice over LTE, to ensure that people talking on the phone, would have access to PHY resources on a somewhat continuous basis. For more information read about voice codecs and jitter.

My apologies if this is obvious, but the way you phrased the question made me think that I shouldn't take the question literally.

Good luck.

Answer 2

Persistent Scheduling ::: The amount of data scheduled for all 'N' subframes are fixed.

Semipersistent Scheduling ::: The amount of data scheduled for every 'N' frames are fixed but in next period The amount of data scheduled may be varies. This SPS period is configured by RRC.

For example : For SPS Period 80ms, The amount of data (ex: 50bits) scheduled for all subframes 1-80ms, in next interval 81-160 the amount of data scheduled in every ms may be variey to 70bits.