Method for performing uplink synchronization in wireless communication system and apparatus therefor

1. A method of performing uplink synchronization by a user equipment (UE) in a millimeter Wave (mmWave) based wireless communication system, the method comprising:

repeatedly transmitting a first type random access preamble through a plurality of coarse beams sequentially formed in different directions;

performing primary timing advance (TA) adjustment, based on a response of a base station to the repeated transmission of the first type random access preamble; and

transmitting a second type random access preamble through at least one fine beam having a smaller beam width than the coarse beams,

wherein a sequence of the second type random access preamble transmitted after the primary TA adjustment is configured to be shorter than a sequence of the first type random access preamble in a time domain.

2. The method according to claim 1 , wherein the first type random access preamble is transmitted in a unit of a subframe, and the second type random access preamble is transmitted in a unit of a predetermined symbol.

3. The method according to claim 1 ,

wherein the sequence of the second type random access preamble has a longer duration than a maximum channel delay spread of a mmWave in the time domain, and

wherein a sum of durations of the second type random access preamble, a guard time (GT) and a cyclic prefix (CP) are set to be equal to or shorter than a duration of 2 symbols.

4. The method according to claim 1 , wherein spacing of subcarriers in which the second type random access preamble is transmitted is set to a reciprocal of a duration of the second type random access preamble.

5. The method according to claim 1 , wherein the second type random access preamble satisfies a formula N DFT =f s *T SEQ , where N DFT denotes a Discrete Fourier Transform (DFT) size, f s denotes a sampling frequency, and T SEQ denotes a duration of the second type random access preamble.

6. The method according to claim 1 , further comprising:

performing secondary TA adjustment, based on a response of the base station to the transmission of the second type random access preamble.

7. The method according to claim 6 , wherein the UE performs only secondary TA adjustment again by transmitting the second type random access preamble when uplink asynchronization occurs due to communication path switching between Line of Sight (LoS) and non-LoS (NLoS).

8. The method according to claim 1 , further comprising:

receiving, through Radio Resource Control (RRC) signaling, at least one of a number of transmission times of the first type random access preamble, a number of transmission times of the second type random access preamble and a second type random access preamble transmission periodicity.

9. A user equipment (UE) performing uplink synchronization in a millimeter Wave (mmWave) based wireless communication system, the UE comprising:

a transmitter for transmitting a mmWave signal; and

a processor for controlling the transmitter,

wherein the processor is configured to control the transmitter to repeatedly transmit a first type random access preamble through a plurality of coarse beams sequentially formed in different directions, to perform primary TA adjustment, based on a response of a base station to the repeated transmission of the first type random access preamble and to transmit a second type random access preamble through at least one fine beam having a smaller beam width than the coarse beams, and

wherein a sequence of the second type random access preamble transmitted after the primary TA adjustment is configured to be shorter than a sequence of the first type random access preamble in a time domain.

10. The UE according to claim 9 , wherein the first type random access preamble is transmitted in a unit of a subframe, and the second type random access preamble is transmitted in a unit of a predetermined symbol.

11. The UE according to claim 9 ,

wherein the sequence of the second type random access preamble has a longer duration than a maximum channel delay spread of a mmWave in the time domain, and

wherein a sum of durations of the second type random access preamble, a guard time (GT) and a cyclic prefix (CP) are set to be equal to or shorter than a duration of 2 symbols.

12. The UE according to claim 9 , wherein spacing of subcarriers in which the second type random access preamble is transmitted is set to a reciprocal of a duration of the second type random access preamble.

13. The UE according to claim 9 , wherein the second type random access preamble satisfies a formula N DFT =f s *T SEQ , where N DFT denotes a Discrete Fourier Transform (DFT) size, f s denotes a sampling frequency, and T SEQ denotes a duration of the second type random access preamble.

14. The UE according to claim 9 , wherein secondary TA adjustment is performed, based on a response of the base station to the transmission of the second type random access preamble.

15. The UE according to claim 14 , wherein the processor performs only the secondary TA adjustment again by transmitting the second type random access preamble when uplink asynchronization occurs due to communication path switching between Line of Sight (LoS) and non-LoS (NLoS).

16. The UE according to claim 9 , further comprising:

a receiver for receiving, through Radio Resource Control (RRC) signaling, at least one of a number of transmission times of the first type random access preamble, a number of transmission times of the second type random access preamble and a second type random access preamble transmission periodicity.