The serving cell specific SRS transmission bandwidths CSRS are configured by higher layers . The allowable values are given in subclause 5 . 5 . 3 . 2 of [ 3 ] . The serving cell specific SRS transmission sub - frames are configured by higher layers . The allowable values are given in subclause 5 . 5 . 3 . 3 of [ 3 ] . For a TDD serving cell , SRS transmissions can occur in UpPTS and uplink subframes of the UL / DL configuration indicated by the higher layer parameter subframeAssignment for the serving cell . When closed - loop UE transmit antenna selection is enabled for a given serving cell for a UE that supports transmit antenna selection , the index a ( nSRS ) , of the UE antenna that transmits the SRS at time nSRS is given bya ( nSRS ) = nSRS mod 2 , for both partial and full sounding bandwidth , and when frequency hopping is disabled ( i . e . ,