Why SRS is sent last?

Hi All.

Why SRS is being sent in last only?

Why we can’t send SRS symbols in starting any specific reason?

Why SRS is sent last

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Just my opinion: you need to prioritize data channel symbols first to improve efficiency and latency perhaps.

But sending SRS at first or last will not impact much the quality of SRS.

It can also simply the design for basestation, by comparision to sending it any specific other slot could harden the processing of BTS.

It’s on Uplink from UE and eNB to be decoded.

SRS is always transmitted in the last OFDM symbol in a subframe which is based on srs-ConfigIndex.

Frequency domain resource selection for SRS transmission.

There are two types of SRS, wide band SRS and narrow band SRS.

Wide band SRS doesn’t necessarily over the entire system bandwidth but on the entire bandwidth of interest, whereas narrow band SRS allows the UE to do frequency hopping between transmissions for efficient TX.

Thanks all…

Point is, I have never seen SRS being sent in starting. Why?

Yes always last.

But I am sharing my opinion, also interference could be a reason, for instance first smybol of data channel assigned to DMRS.

I don’t think there is universal reason perhaps sombody else could figure out…

Because SRS is used for estimating channel in UL, and channel reciprocity is then used to apply those coefficients in DL.

And in case of high mobility channel will change quickly.

Sending SRS in last will make sure that there is minimal gap between time of channel estimation and applying it in DL.

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If slot config is DDDSU and S slot configures for 10:2:2 (10 DL, 2 guard, 2 SRS).

SRS is 1st UL transmission.