Method and terminal for random access to small cell

Abstract

The present invention relates to a method for random access to a small cell by means of a terminal. The method can include the steps of: receiving a plurality of settings for a random access preamble; selecting one of the plurality of settings; and transmitting the random access preamble according to the one selected setting. Here, a resource on which the random access preamble can be transmitted can be provided in plurality in one subframe, and the preamble transmitted on each resource is distinguishable.

What is claimed is: 
     
       1. A method for performing random access by a user equipment for a cell, the method comprising:
 receiving, via the cell, a plurality of configurations for a random access preamble;   selecting one of the plurality of configurations;   transmitting, via the cell, the random access preamble according to a selected configuration; and   receiving a random access response including a Random Access-Radio Network Temporary Identifier (RA-RNTI),   wherein the random access preamble is transmitted according to the selected configuration on at least one resource in a subframe including a plurality of resources on which the random access preamble is capable of being transmitted,   wherein the random access preamble transmitted on the at least one resource is uniquely distinguishable, and   wherein the RA-RNTI is calculated based on an index of the subframe and a location index of the at least one resource in the subframe on which the random access preamble is transmitted according to the selected configuration.   
     
     
       2. The method of  claim 1 , wherein locations of the plurality of resources are aligned with a boundary of the subframe. 
     
     
       3. The method of  claim 1 , wherein locations of the plurality of resources are aligned with a boundary of each slot in the subframe. 
     
     
       4. The method of  claim 1 , wherein locations of the plurality of resources are aligned with a boundary of a group of Orthogonal Frequency Division Multiple Access (OFDMA) or Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbols in the subframe. 
     
     
       5. The method of  claim 4 , wherein a length of the random access preamble transmitted on the resource is shorter than a length of 3 OFDMA or SC-FDMA symbols in case of normal Cyclic Prefix (CP), and is shorter than a length of 2 OFDMA or SC-FDMA symbols in case of extended CP. 
     
     
       6. The method of  claim 1 , wherein the plurality of configurations are received through system information. 
     
     
       7. The method of  claim 1 , wherein the plurality of configurations include a configuration of format 0 to 4 for a Physical Random Access Channel (PRACH) preamble and a configuration of a new format for the PRACH preamble which is designed to support coverage of the cell. 
     
     
       8. The method of  claim 7 , wherein the new format is generated based on format 4 for the PRACH preamble which is designed to support cell coverage of 1.4 km. 
     
     
       9. The method of  claim 7 , wherein when the one of the plurality of configurations is selected, the user equipment selects a configuration of the new format which is designed to support the coverage of the cell. 
     
     
       10. The method of  claim 1 , wherein the subframe is downlink subframe. 
     
     
       11. The method of  claim 1 , wherein the cell is a pico cell, a femto cell, a Home (e)NodeB or a Closed Subscriber Group (CSG) cell. 
     
     
       12. A user equipment (UE) for performing random access for a cell, the UE comprising:
 a radio frequency (RF) unit configured to receive, via the cell, a plurality of configurations for random access preamble; and   a processor configured to control the RF unit to:
 select one of the plurality of configurations, 
 transmit, via the cell, the random access preamble according to the selected configuration, and 
 receive a random access response including a Random Access-Radio Network Temporary Identifier (RA-RNTI), 
 wherein the random access preamble is transmitted according to the selected configuration on at least one resource in a subframe including a plurality of resources on which the random access preamble is capable of being transmitted, 
 wherein the random access preamble transmitted on the at least one resource is uniquely distinguishable, and 
 wherein the RA-RNTI is calculated based on an index of the subframe and a location index of the at least one resource in the subframe on which the random access preamble is transmitted according to the selected configuration. 
   
     
     
       13. The UE of  claim 12 , wherein locations of the plurality of resources are aligned with a boundary of the subframe. 
     
     
       14. The UE of  claim 12 , wherein locations of the plurality of resources are aligned with a boundary of each slot in the subframe. 
     
     
       15. The UE of  claim 12 , wherein locations of the plurality of resources are aligned with a boundary of a group of Orthogonal Frequency Division Multiple Access (OFDMA) or Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbols in the subframe. 
     
     
       16. A method of performing random access by a user equipment for a cell, the method comprising:
 transmitting, to a cell, a random access preamble on at least one time resource in a subframe; and   receiving downlink control information (DCI) with a cyclic redundancy check (CRC) scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI),   wherein the subframe comprises at least one slot comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols,   wherein the RA-RNTI is calculated based on (i) a first index related to the subframe, (ii) a second index of the at least one time resource in the subframe on which the random access preamble is transmitted, and (iii) a third index for a frequency domain location of the random access preamble.   
     
     
       17. The method of claim 16, wherein a length of the random access preamble transmitted on the at least one time resource is shorter than a length of 3 OFDMA or SC-FDMA symbols in case of normal Cyclic Prefix (CP), and is shorter than a length of 2 OFDMA or SCFDMA symbols in case of extended CP. 
     
     
       18. The method of claim 16, further comprising:
 receiving, from the cell, information regarding a plurality of configurations for the random access preamble; and   selecting a configuration among the plurality of configurations,   wherein the random access preamble is based on the selected configuration.   
     
     
       19. The method of claim 18, wherein the information regarding the plurality of configurations is received through system information. 
     
     
       20. The method of claim 18, wherein the plurality of configurations comprises a configuration of format 0 to 4 for a Physical Random Access Channel (PRACH) preamble and a configuration of a new format for the PRACH preamble which is designed to support coverage of the cell. 
     
     
       21. The method of claim 20, wherein the new format is generated based on format 4 for the PRACH preamble which is designed to support cell coverage of 1.4 km. 
     
     
       22. The method of claim 20, wherein based on the configuration among the plurality of configurations being selected, the user equipment selects a configuration of the new format which is designed to support the coverage of the cell. 
     
     
       23. The method of claim 16, wherein the subframe is downlink subframe and comprises fourteen OFDM symbols. 
     
     
       24. The method of claim 16, wherein a location of at least one among the plurality of OFDM symbols is aligned with a boundary of the at least one slot in the subframe. 
     
     
       25. The method of claim 16, wherein the at least one slot in the subframe comprises a plurality of slots that are indexed by slot numbers. 
     
     
       26. An apparatus for a user equipment (UE) configured to perform random access for a cell, the UE comprising:
 at least one processor; and   at least one computer memory that is operably connectable to the at least one processor and that has stored thereon instructions which, when executed, cause the at least one processor to perform operations comprising:   transmitting, to a cell, a random access preamble on at least one time resource in a subframe, and   receiving downlink control information (DCI) with a cyclic redundancy check (CRC) scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI),   wherein the subframe comprises at least one slot comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols,   wherein the RA-RNTI is calculated based on (i) a first index related to the subframe, (ii) a second index of the at least one time resource in the subframe on which the random access preamble is transmitted, and (iii) a third index for a frequency domain location of the random access preamble.   
     
     
       27. The apparatus of claim 26, wherein the operations further comprise:
 receiving, via the cell, information regarding a plurality of configurations for the random access preamble; and   selecting a configuration among the plurality of configurations,   wherein the random access preamble is based on the selected configuration.   
     
     
       28. The apparatus of claim 27, wherein the information regarding the plurality of configurations is received through system information. 
     
     
       29. The apparatus of claim 26, wherein a location of at least one among the plurality of OFDM symbols is aligned with a boundary of the at least one slot in the subframe. 
     
     
       30. A method of receiving a random access preamble, the method performed by a base station and comprising:
 receiving, from a user equipment (UE), a random access preamble on at least one time resource in a subframe; and   transmitting downlink control information (DCI) with a cyclic redundancy check (CRC) scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI),   wherein the subframe comprises at least one slot comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols,   wherein the RA-RNTI is calculated based on (i) a first index related to the subframe, (ii) a second index of the at least one time resource in the subframe on which the random access preamble is transmitted, and (iii) a third index for a frequency domain location of the random access preamble.   
     
     
       31. The method of claim 30, further comprising:
 transmitting information regarding a plurality of configurations for the random access preamble.   
     
     
       32. The method of claim 30, wherein a location of at least one among the plurality of OFDM symbols is aligned with a boundary of the at least one slot in the subframe. 
     
     
       33. An apparatus for a base station of receiving a random access preamble, the base station comprising:
 at least one processor; and   at least one computer memory that is operably connectable to the at least one processor and that has stored thereon instructions which, when executed, cause the at least one processor to perform operations comprising:
 receiving, from a user equipment (UE), a random access preamble on at least one time resource in a subframe; and 
 transmitting downlink control information (DCI) with a cyclic redundancy check (CRC) scrambled by a Random Access-Radio Network Temporary Identifier (RA-RNTI), 
   wherein the subframe comprises at least one slot comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols,   wherein the RA-RNTI is calculated based on (i) a first index related to the subframe, (ii) a second index of the at least one time resource in the subframe on which the random access preamble is transmitted, and (iii) a third index for a frequency domain location of the random access preamble.   
     
     
       34. The apparatus of claim 33, wherein the operations further comprise:
 transmitting information regarding a plurality of configurations for the random access preamble.   
     
     
       35. The apparatus of claim 33, wherein a location of at least one among the plurality of OFDM symbols is aligned with a boundary of the at least one slot in the subframe.