Consider a point-to-point communication system, in which the receiver reports an incorrect SNR (deliberate/undeliberate) to the transmitter. Is there a way for the transmitter to verify this? (In HARQ systems, I guess the ACK/NACK feedback can reveal something, but I am not an expert in the field.)
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\$\begingroup\$ Neither transmitter nor receiver are in any position to determine SNR (signal to noise ratio). \$\endgroup\$– Andy akaCommented Sep 9 at 12:28
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\$\begingroup\$ @Andyaka I think the transmitter typically sends a pilot signal, based on which the receiver measures the SNR and reports it back. Isn't it so? \$\endgroup\$– BenCommented Sep 9 at 12:52
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\$\begingroup\$ Unless you specifically provide a training model for the transmitter to understand appropriate SNR, I don't see how the transmitter would automatically know what's considered tolerable. \$\endgroup\$– ColinCommented Sep 9 at 13:27
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1\$\begingroup\$ the transmitter has no means of knowing what sources of noise the receiver is getting, or the channel attenuation the signal is passing through, so is doubly ignorant of the receiver SNR. \$\endgroup\$– Neil_UKCommented Sep 9 at 18:23
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Is there a way for the transmitter to verify this? (In HARQ systems, I guess the ACK/NACK feedback can reveal something, but I am not an expert in the field.)
Your viewpoint is correct! LTE and 5G systems rely on CQI reports from the receiver to the transmitter to adjust the modulation and coding scheme (MCS). These CQI reports are based on the measured SNR at the receiver. But.. how LTE and 5G verify the effectiveness of the CQI and other link quality reports. These commercial communications use HARQ mechanisms via ACK/NACK feedback. If there’s a mismatch between reported CQI and frequent NACKs, the transmitter can infer that the reported SNR is inaccurate.
The ETSI documentation for 3GPP TS 36.213, section 7 cover how CQI reporting and HARQ work.
