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What is Semi Persistent Scheduling in LTE?

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Want to understand what is Semi persistent Scheduling in LTE.

posted Jul 14, 2013 by Salil Agrawal

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1 Answer

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There are 3 types of LTE scheduling used like Persistent, Semi- Persistent and Dynamic. Every scheduling has its own important based on type of data transmission. I mean sometimes data bur sty in nature or less bur sty.

Depend on your application these scheduling algorithms are used. Normally Dynamic scheduling is used, In which when UE need to send data it send SR(Scheduling request) to Enodeb and then ENodeb allocates resources to UE and inform through DCI(Downlink Control information) over PDCCH channel. If I talk about VoLTE, voice packet size if less but comes at regular interval. so to avoid every time Scheduling Request towards EnodeB, which is a overhead since packets come at regular interval, EnodeB while setting up bearer with qci 1 (which is used for Voice) also perform SPS config towards UE. So In this way Enodeb reduces signalling overhead.

I don't have much clarity about Persistent scheduling.

answer Jul 14, 2013 by Vimal Kumar Mishra
In case of semi persistent scheduling, eNB can assign predefined chunk of radio resources for VoIP users with interval of 20ms. Therefore, UE is not required to request resources each TTI, saving control plan overhead. This scheduling is semi-persistent in the sense that eNB can change the resource allocation type or location if required for link adaptation or other factors.

You can read about all the three types of scheduling in this link
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0 votes

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.