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

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

Answer 1

[Sriram Tadavarty]

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

[KISHORE K E R]

Thank you Sriram. I saw that example earlier.But the confusing thing is how are you going to estimate CQI and RI.In the downlink,for CSI RS you have the look up table for CQI and RI.From that you can estimate the CSI reports.But in the uplink side you dont have any look up table.Can you give me the approach for estimating CQI and RI ?

Thank you,

Regards,

Kishore.

[KISHORE K E R]

Hi Sriram,

The channel estimated in the given example will support for channel reciprocity.If supports,can you explain it.If not,what modifications have to do to achieve channel reciprocity?

Thanking you,

Regards

Kishore

[Sriram Tadavarty]

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

[KISHORE K E R]

Hi Sriram,

Thank you for response.The information you haved provided is useful for me.But again I have a doubt that in the example ,used CDM lengths.But i didn't those CDM lengths values in standards.Can you explain that how you have taken or if it is present in standards ,please direct me to that standards.

Regards

Kishore

[Sriram Tadavarty]

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]

Hi Sriram,

Thank you for your help.

Regards

Kishore