Method and apparatus for sharing spectrum between 3GPP LTE and NR in wireless communication system

1. A method performed by a wireless device operating in a wireless communication system, the method comprising:

receiving (i) a first physical random access channel (PRACH) configuration for a first uplink (UL) carrier and (ii) a second PRACH configuration for a second UL carrier, wherein the first UL carrier and a DL carrier linked to the first UL carrier belong to a first carrier band, and wherein the second UL carrier belongs to a second carrier band;

performing a reference signal received power (RSRP) measurement on the DL carrier;

selecting a UL carrier for a random access procedure, among the first UL carrier and the second UL carrier, based on a result of the RSRP measurement on the DL carrier; and

performing the random access procedure on the selected UL carrier based on a PRACH configuration for the selected UL carrier,

wherein, based on that the result of the RSRP measurement on the DL carrier is less than a threshold, the second UL carrier is selected as the UL carrier for the random access procedure,

wherein, based on that the result of the RSRP measurement on the DL carrier is not less than the threshold, the first UL carrier is selected as the UL carrier for the random access procedure,

wherein the method further comprises receiving a UL grant informing a UL carrier for a physical uplink shared channel (PUSCH) transmission, and

wherein, based on that the UL grant informs a carrier switching in the random access procedure such that the informed UL carrier for the PUSCH transmission is different from the second UL carrier selected for the random access procedure, the carrier switching is prohibited.

2. The method of claim 1 , wherein the first carrier band has a higher carrier than the second carrier band.

3. The method of claim 1 , wherein the first carrier band is a carrier band for a 5G new radio access technology (NR), and

wherein the second carrier band is a carrier band for a 4G long-term evolution (LTE).

4. The method of claim 1 , wherein the second UL carrier is supplemental UL carrier.

5. The method of claim 4 , wherein the supplemental UL carrier includes LTE UL resources and NR UL resources.

6. The method of claim 5 , wherein the LTE UL resources and the NR UL resources are multiplexed by time division multiplexing (TDM) and/or frequency division multiplexing (FDM).

7. The method of claim 5 , wherein a reference hybrid automatic repeat request (HARQ) timing based on frequency division duplex (FDD)-time division duplex (TDD) carrier aggregation (CA) is configured for the LTE UL resources.

8. The method of claim 1 , wherein a cell carrying a physical uplink control channel (PUCCH) is configured to one of the first UL carrier or the second UL carrier.

9. The method of claim 8 , wherein a physical uplink shared channel (PUSCH) transmission is performed in the cell carrying the PUCCH.

10. The method of claim 8 , wherein a PUSCH transmission is configured to a UL carrier that is different from a UL carrier to which the cell carrying the PUCCH is configured.

11. The method of claim 1 , further comprising receiving a DL tracking reference signal (RS) in the DL carrier.

12. The method of claim 1 , wherein the random access procedure carries data indicating a best beam.

13. The method of claim 1 , further comprising:

selecting a PRACH resource based on the PRACH configuration for the selected UL carrier,

wherein the PRACH resource is selected to indicate a best beam.

14. The method of claim 1 , wherein the wireless device is configured to communicate with at least one of a wireless device, a network, and/or autonomous vehicles other than the wireless device.

15. The method of claim 1 , wherein all uplink transmissions during the random access procedure are performed on the selected UL carrier based on that the second UL carrier is selected as the UL carrier for the random access procedure.

16. A wireless device configured to operate in a wireless communication system, the wireless device comprising:

a memory;

a transceiver; and

at least one processor, operably coupled to the memory and the transceiver, configured to:

control the transceiver to receive (i) a first physical random access channel (PRACH) configuration for a first uplink (UL) carrier and (ii) a second PRACH configuration for a second UL carrier, wherein the first UL carrier and a DL carrier linked to the first UL carrier belong to a first carrier band, and wherein the second UL carrier belongs to a second carrier band,

perform a reference signal received power (RSRP) measurement on the DL carrier,

select a UL carrier for a random access procedure, among the first UL carrier and the second UL carrier, based on a result of the RSRP measurement on the DL carrier; and

perform the random access procedure on the selected UL carrier based on a PRACH configuration for the selected UL carrier,

wherein, based on that the result of the RSRP measurement on the DL carrier is less than a threshold, the second UL carrier is selected as the UL carrier for the random access procedure,

wherein, based on that the result of the RSRP measurement on the DL carrier is not less than the threshold, the first UL carrier is selected as the UL carrier for the random access procedure,

wherein the at least one processor is further configured to control the transceiver to receive a UL grant informing a UL carrier for a physical uplink shared channel (PUSCH) transmission, and

wherein, based on that the UL grant informs a carrier switching in the random access procedure such that the informed UL carrier for the PUSCH transmission is different from the second UL carrier selected for the random access procedure, the carrier switching is prohibited.

17. The wireless device of claim 16 , wherein all uplink transmissions during the random access procedure are performed on the selected UL carrier based on that the second UL carrier is selected as the UL carrier for the random access procedure.