How to estimate channel quality using Sounding Referance Signal in 5G

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KISHORE K E R 2020-4-13

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评论： KISHORE K E R 2020-5-19

I know the symbols at the receiver side of SRS .But I dont know how to estimate channel quality with the received symbols.Can you explain what exactly channel quality means? and what is the approach to find channel quality

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Answer 1

Sriram Tadavarty 2020-4-26

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Hi Kishore,

Sounding reference signals are uplink physical signals used by user equipment (UE) for uplink channel sounding, including synchronization and CSI estimation. CSI comprises channel quality indicator (CQI), rank indicator (RI), and precoder matrix indicator (PMI). Channel sounding is basically to estimate the channel.

For more details of the concept, look at the video here and example here.

Hope this helps.

Thanking you.

Regards,

Sriram

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Sriram Tadavarty 2020-5-8

Hi Kishore,

I didnt get the notification for your comment. Sorry for that.

In the standard, there is no procedure stated for the CSI reporting with SRS, as stated for CSI-RS.

As i see, SRS is the uplink counterpart for CSI-RS, which BS uses to perform the channel estimation and define the resource blocks to the UE where there is better channel.

The PMI configuration and reporting is done with codebooks used for the PUSCH. Since, that defines the choice of PMI through SRI indicator based on the transmission scheme used for PUSCH.

In terms of channel reciprocity, this can be indicated in the context when there are both the links. Channel recciporcity is best applied in TDD systems. The example uses only a single link (i.e. uplink), and compares the SINR loss for the estimated PMI. This metric provides the insights of how well the same can be used in case of channel reciprocity. It can be seen in the example that the estimated PMI in the slots where SRS is not transmitted applies the previous estimate, implies this can be used to show some form of the reciprocity, when used the DL transmission in those slots (where there is no SRS transmission).

Hope this helps.

Regards,

Sriram

Sriram Tadavarty 2020-5-18

Hi Kishore,

The CDM lengths used in the example are based on the structure of SRS configured. It tells about the spread in frequency domain and time domain as a two element vector [FD TD], that can be used for better channel estimation. You can turn off this by directly placing [1 1], if needed.

The spread depends on different antenna ports. If there is only single antenna port, there is no spreading leading to [1 1]. For two antenna ports, the frequency location will vary in each port, leading to [2 1]. Similarly for four antenna ports, it depends on the cyclic shifts leading to either [2 1] or [4 1].

Hope this helps.

Regards,

Sriram

KISHORE K E R 2020-5-19