How does UE become aware of UL frequency in LTE

The UL Tx-Rx frequency separation is dependent on the EUTRA Operating Band in LTE therefore the UE has to be told of the UL frequency by the NW. Unlike in UTRAN, the UE can compute the UL freq since the Tx-Rx separation is fixed.

The SIB2 contains the UL freq information:

SystemInformationBlockType2

freqInfo                         SEQUENCE {

       ul-CarrierFreq                   ARFCN-ValueEUTRA             OPTIONAL,  -- Need OP

       ul-Bandwidth                     ENUMERATED {n6, n15, n25, n50, n75, n100}

The default separation is defined in 36.101

Default UE TX-RX frequency separation (source 3GPP TS 36.101)

E-UTRA Operating Band	TX - RX carrier centre frequency separation
1	190 MHz
2	80 MHz.
3	95 MHz.
4	400 MHz
5	45 MHz
6	45 MHz
7	120 MHz
8	45 MHz
9	95 MHz
10	400 MHz
11	48 MHz
12	30 MHz
13	-31 MHz
14	-30 MHz
17	30 MHz
18	45 MHz
19	45 MHz
20	-41 MHz
21	48 MHz
22	100 MHz
23	180 MHz
24	-101.5 MHz
25	80 MHz