Device and method of handling random access procedure

1. A communication device of handling a random access procedure, comprising:

a storage unit, for storing instructions of:

determining a first coverage enhancement (CE) level;

selecting at least one first random access preamble from a first preamble group corresponding to the first CE level;

performing the random access procedure according to the at least one first random access preamble with a network;

determining a second CE level for performing the random access procedure, if the random access procedure is performed unsuccessfully;

selecting at least one second random access preamble from a second preamble group; and

performing the random access procedure according to the at least one second random access preamble with the network;

wherein the second preamble group comprises at least one subgroup, and a first one of the at least one subgroup is corresponding to the first CE level, and a second one of the at least one subgroup is corresponding to the second CE level; and

a processing circuit, coupled to the storage unit, configured to execute the instructions stored in the storage unit.

2. The communication device of claim 1 , wherein the first CE level is determined according to a downlink (DL) measurement result.

3. The communication device of claim 2 , wherein the DL measurement result comprises information of reference signal received power (RSRP).

4. The communication device of claim 1 , wherein the communication device determines that the random access procedure is performed unsuccessfully, if the at least one first random access preamble is retransmitted for a first maximum number of retransmission attempts.

5. The communication device of claim 4 , wherein the first maximum number of the retransmission attempts is determined according to the first CE level.

6. The communication device of claim 1 , wherein the instruction of performing the random access procedure according to the at least one first random access preamble with the network comprises:

performing the random access procedure according to the at least one first random access preamble with a first number of repetitions with the network;

increasing a counter, if a random access response message is not received from the network; and

determining a number of retransmission attempts according to the counter.

7. The communication device of claim 6 , wherein the communication device determines that the random access procedure is performed unsuccessfully, if the number of retransmission attempts is larger than a first maximum number of retransmission attempts.

8. The communication device of claim 7 , wherein the first maximum number of the retransmission attempts is determined according to the first CE level.

9. The communication device of claim 6 , wherein the first number of the repetitions is determined according to the first CE level.

10. The communication device of claim 1 , wherein the second preamble group is corresponding to the second CE level, if a radio resource control (RRC) request message has not been transmitted by the communication device.

11. The communication device of claim 1 , wherein the second preamble group is corresponding to the second CE level, if a radio resource control (RRC) re-establishment message has not been transmitted by the communication device.

12. The communication device of claim 1 , wherein the second preamble group is corresponding to the second CE level, if a cell radio network temporary identifier (C-RNTI) medium access control (MAC) control element has not been transmitted by the communication device.

13. The communication device of claim 1 , wherein the second preamble group is corresponding to the first CE level, if a RRC request message is transmitted by the communication device.

14. The communication device of claim 13 , wherein the at least one first random access preamble and the at least one second random access preamble is the same or different.

15. The communication device of claim 1 , wherein the second preamble group is corresponding to the first CE level, if a RRC re-establishment message is transmitted by the communication device.

16. The communication device of claim 1 , wherein the second preamble group is corresponding to the first CE level, if a cell radio network temporary identifier (C-RNTI) medium access control (MAC) control element is transmitted by the communication device.

17. The communication device of claim 1 , wherein a configuration configuring the at least one subgroup is broadcasted by the network, or is transmitted in a radio resource control (RRC) message by the network.