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What is SRS and where is it physically mapped? Explain.

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What is SRS and where is it physically mapped? Explain.
posted Dec 5, 2014 by Sridharan P

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1 Answer

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SRS means Sounding Reference Signal, it is reference signal for eNodeB (sent by the UE) to figure out the channel quality of uplink path for each subsections of frequency region.

Why SRS is required?
ENodeB often allocates only a partial section of full system bandwidth for a specific UE and at a specific time. So it would be good to know which section across the overall bandwidth has better channel quality comparing to the other region. In this case, Network can allocate the specific frequency region which is the best for each of the UEs. (If we always have to use full bandwidth, we may not need this kind of reference signal since there is no choice even when there is a better or worse spots within the bandwidth).

How often UE transmit SRS ?
It depends on the configuration set by the signaling message (SIB2, RRC Connection Setup, RRC Connection Reconfiguration etc), but UE can transmit it every two subframes at the most and every 32 frame (320 subframe) at the least (10 bit signaling parameter srs-ConfigIndex tells UE of the periodicity of SRS transmission and the period can be 2,5,10,20,40,80,160,320 ms). Actually there is an option in which UE does not transmit SRS at all.

Credit: http://www.sharetechnote.com/html/Handbook_LTE_SRS.html

answer Dec 5, 2014 by Salil Agrawal
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One question came out and want to get answer for that just to avoid assumptions what I have.
A multiple MBMS services are being transmitted over the air through eNodeBs belong to one MBSFN Area. Here I considered all the eNodeBs belongs to that particular MBSFN area have maximum six sub frames of a radio frame to broadcast the content and all eNodeBs are doing.
In between some of the eNodeBs belong to same MBSFN Area get congested and out of 6 sub frames only two subframes are being used in those eNodeB.
My first question where exactly things will be affected ?
Another question, MBMS-GW will be sending data in same speed with same SYNC information. Since few eNodeBs are congested then how data will be transmitted ? Segmentation at eNodeB RLC may affect User experience since UE combines the data in MBMS case from all the neighboring eNodeBs and get better result in term of quality.
If one eNodeB is sending data without segmentation and the other one is sending with segmentation then How UE RLC will behave and what will be the user experience ?

Please ignore these question if segmentation and reassembling is not applicable for MBMS data transmission at RLC.

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