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In General, SRS is a reference signal transmitted by the UE. It is measured by the BTS to estimate UL channel propagation, and this, in general, can be used for many other functions, Such as DL Propagation Channel Estimation in TDD System.
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The UE transmits the Sounding Reference Signal(SRS) according to the instructions provided by the BTS and is used by the BTS to measure the UL propagation channel from the SRS.
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An SRS Transmission can occupy 1, 2, or 4 symbols in the time domain; these symbols can be located at the last six symbols of a UL Slot.
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An SRS Transmission can occupy up to 272 RBs in the frequency domain, but an individual UE does not transmit the SRS on every subcarrier but select specific SCs based on transmission comb type(TC).
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NR SRS is more flexible than 4G; for example, 4G SRS occupies one symbol and uses transmission comb type 2 only, while NR occupies up to 4 symbols and uses transmission comb type 2 or 4.
*Transmission Comp will be shared in different posts, but it controls how the UE will transmit SRS in the frequency domain; for example, TX Comb 2 means an individual UE transmits on every second subcarrier.
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