What to do next after Channel Estimation, when number of estimated channels (Antenna Ports) is smaller than number of antennas?

I'm reading example NR Channel Estimation Using CSI-RS and I have a question about the estimated channel.

While the true channel has the size (300,14,4,4) - (N_subcarrier, N_symbol, N_receiveAntenna, N_transmitAntenna), the estimated channel has the size (300,14,4,2) - (N_subcarrier, N_symbol, N_receiveAntenna, N_transmitAntennaPort) - the system consists of 4-antenna transmitter and 4-antenna receiver.

There is also a line in the example that:

H_err = (H_est - H_actual(:,:,:,1:size(H_est,4)));

which it calculates the errors between estimated channel and true channel over dimension (300,14,4,2) (the first 2 (300,14,4,1) matrice of true channel).

So my question is, how about the other 2 matrice of true channel? Do we need to estimate them also? if yes, how can we do that?

If no (as the antenna ports are different to actual/physical antennas, as I read from many other sites), can you explain the relationship between antenna ports of actual/physical antenna? If the antenna ports and physical antennas have no relationship, how can we evaluate our estimated channel (in this example we have 4 true channels (for 4 physical antennas), but we just have 2 channels (for 2 antenna ports)). As in the code above, is it the error between estimated-channel-for-the-2-antenna-ports and actual-channel-of-the-first-2-antennas?

Thank you in advance for your clarification.

Answer 1

[Divyanshu]

Hello @Thien Hieu,

Antenna ports are logical entities which are mapped to physical antennas which in turn are used for transmitting and receiving reference signals.

And one antenna port can be mapped to one or more physical antennas based on requirements and system configuration. Therefore in the example NR Channel Estimation Using CSI-RS the estimated channel is configured with only 2 antenna ports and the estimation of other 2 matrices of true channel is not required.

Yes the error is calculated between 2 antenna ports and the corresponding physical antennas they are mapped to.

For more details, you can actually read the reference attached in 'References' section of above example documentation.

[Thien Hieu]

Thank you for you response