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; and   receiving a random access response based on a Random Access-Radio Network Temporary Identifier (RA-RNTI),   wherein the random access preamble is transmitted on at least one time resource in a subframe,   wherein the subframe comprises at least one slot comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols,   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, and   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. 
     
     
       24. The method of claim 16, wherein the subframe comprises fourteen OFDM symbols. 
     
     
       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. A user equipment (UE) configured to perform random access for a cell, the UE comprising:
 a radio frequency (RF) unit;   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 control the RF unit to perform operations comprising:   transmitting, to a cell and via the RF unit, a random access preamble, and   receiving, via the RF unit, a random access response based on a Random Access-Radio Network Temporary Identifier (RA-RNTI),   wherein the random access preamble is transmitted on at least one time resource in a subframe,   wherein the subframe comprises at least one slot comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols,   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, and   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 UE 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 UE of claim 27, wherein the information regarding the plurality of configurations is received through system information. 
     
     
       29. A method of performing random access by a user equipment for a cell, the method comprising:
 transmitting, to a cell, a random access preamble; and   receiving a random access response based on a Random Access-Radio Network Temporary Identifier (RA-RNTI),   wherein the random access preamble is transmitted on at least one resource in a subframe,   wherein the subframe comprises a plurality of slots each comprising a plurality of orthogonal frequency division multiplexing (OFDM) symbols,   wherein a location of at least one among the plurality of OFDM symbols is aligned with a boundary of at least one slot among the plurality of slots in the subframe, and   wherein the RA-RNTI is calculated based on (i) a resource index among a plurality of resource indices in a time domain that are incremented at each slot boundary in the plurality of slots in the subframe in which the random access preamble is transmitted, and (ii) a frequency domain index for the random access preamble.   
     
     
       30. The method of claim 29, wherein the resource index is incremented at starting points of each slot in the plurality of slots in the subframe.