What is claimed is:1. A method for a user equipment (UE) performing random access to a network, the method performed by the UE and comprising:determining a predetermined number of downlink beams as candidate beams for the random access to the network by the UE;selecting a beam among the determined candidate beams based on a reception quality of the beam;after a random access is triggered, determining a next available random access preamble transmitting occasion for transmitting a random access preamble from among plural random access preamble transmitting occasions that correspond to the selected beam and that occur after the random access is triggered, the next available random access preamble transmitting occasion determined in consideration of a processing time of the UE, each of the plural random access preamble transmitting occasions being matched with a corresponding one of the candidate beams; andtransmitting the random access preamble on the determined next available random access preamble transmitting occasion.2. The method of claim 1, wherein, if a first random access procedure initiated by transmitting the random access preamble fails, the UE reselects another transmission beam from the candidate beams.3. The method of claim 2, wherein the UE reselects the another transmission beam as an earliest available candidate beam in time domain after a retransmission of the random access is triggered.4. The method of claim 1,wherein the candidate beams are selected from multiple beams, andwherein each of the multiple beams is associated with different random access preamble transmitting occasions for a beam sweeping.5. A user equipment (UE) performing random access to a network, the UE comprising:a processor configured to:determine a predetermined number of downlink beams as candidate beams for the random access to the network by the UE,select a beam among the determined candidate beams based on a downlink reception quality of the beam, andafter a random access is triggered, determine a next available random access preamble transmitting occasion for transmitting a random access preamble from among plural random access preamble transmitting occasions that correspond to the selected beam and that occur after the random access is triggered, the next available random access preamble transmitting occasion determined in consideration of a processing time of the UE, each of the plural random access preamble transmitting occasions being matched with a corresponding one of the candidate beams; anda transceiver connected to the processor and configured to transmit the random access preamble on the determined next available random access preamble transmitting occasion.6. The UE of claim 5, wherein, if a first random access procedure initiated by transmitting the random access preamble fails, the processor reselects another transmission beam from the candidate beams.7. The UE of claim 6, wherein the processor reselects the another transmission beam as an earliest available candidate beam in time domain after a retransmission of the random access is triggered.8. The UE of claim 5,wherein the candidate beams are selected from multiple beams, andwherein each of the multiple beams is associated with different random access preamble transmitting occasions for a beam sweeping.
