Rach procedures using multiple prach transmissions

Abstract

Techniques are described herein to improve a link budget of physical random access channel (PRACH) transmissions used during a random access (RACH) procedure. The link budget of a PRACH transmission associated with the RACH procedure may be improved by transmitting multiple PRACH transmissions. The multiple PRACH transmissions may be combined to achieve some combining gain. Each retransmission of a PRACH transmission may be done at a higher power level than the previous PRACH transmission. If UE receives an indication that a target base station failed to successfully decode the PRACH transmission, the UE may retransmit the PRACH transmission but at a higher power level than the initial PRACH transmission. PRACH transmissions may be distributed across multiple slots. PRACH transmissions may be distributed across multiple frequency sub-bands in the same slot or across frequency sub-bands in the different slots.

What is claimed is: 
     
         1 . A method for wireless communication, comprising:
 receiving a transmission schedule that indicates that a physical random access channel (PRACH) transmission of a random access channel (RACH) procedure is a first type of PRACH transmission and indicating a fixed timing between a first time associated with a transmission of the PRACH transmission and a second time associated with a retransmission of the PRACH transmission;   selecting a first location for control information in the PRACH transmission and a second location for payload information in the PRACH transmission;   transmitting the PRACH transmission at the first time including the control information and the payload information;   detecting a failure to receive a random access response (RAR) message responsive to the PRACH transmission within a time period; and   retransmitting the PRACH transmission at the second time including the control information and the payload information based at least in part on the fixed timing and the first type of PRACH transmission.   
     
     
         2 . The method of  claim 1 , further comprising:
 mapping the PRACH transmission and the retransmission of the PRACH transmission to one or more uplink-centric slots, wherein each of the one or more uplink-centric slots comprises at least the control information and the payload information of the PRACH transmission or the control information and the payload information of the retransmission of the PRACH transmission.   
     
     
         3 . The method of  claim 1 , wherein receiving the transmission schedule further comprises:
 receiving the transmission schedule including a plurality of PRACH transmission opportunities associated with the RACH procedure, wherein the plurality of PRACH transmission opportunities are associated with the fixed timing, wherein transmitting the PRACH transmission and the retransmission of the PRACH transmission is based at least in part on the transmission schedule.   
     
     
         4 . A method for wireless communication, comprising:
 receiving, as part of a random access channel (RACH) procedure, a first physical random access channel (PRACH) transmission at a first reception time, the first PRACH transmission including a first control information at a first location in the first PRACH transmission and a first payload information at a second location in the first PRACH transmission, wherein the first location in the first PRACH transmission of the first control information and the second location in the first PRACH transmission of the first payload information correspond to a first type of PRACH transmission;   identifying that the first PRACH transmission failed to be successfully decoded;   receiving a second PRACH transmission at a second reception time according to a fixed timing, the second PRACH transmission including a second control information at a first location in the second PRACH transmission and a second payload information at a second location in the second PRACH transmission, wherein the first location in the second PRACH transmission of the second control information and the second location in the second PRACH transmission of the second payload information correspond to the first type of PRACH transmission; and   generating a combined PRACH control message including a combination of the first PRACH transmission and the second PRACH transmission.   
     
     
         5 . The method of  claim 4 , further comprising:
 extracting data that is common to both the first PRACH transmission and the second PRACH transmission based at least in part on the fixed timing.   
     
     
         6 . The method of  claim 4 , further comprising:
 initiating a contention-free random access procedure, wherein generating the combined PRACH control message is based at least in part on initiating the contention-free random access procedure.   
     
     
         7 . The method of  claim 4 , wherein receiving the first PRACH transmission and the second PRACH transmission comprises:
 receiving a common message portion present in both the first PRACH transmission and the second PRACH transmission, the common message portion including the first control information of the first PRACH transmission and the second control information of the second PRACH transmission.   
     
     
         8 . The method of  claim 7 , wherein the second PRACH transmission is a retransmission of the first PRACH transmission. 
     
     
         9 . The method of  claim 7 , wherein receiving the common message portion further comprises:
 receiving the first control information at the first location in the first PRACH transmission and the second control information at the first location in the second PRACH transmission, wherein generating the combined PRACH control message is based at least in part on the first location in the first PRACH transmission of the first control information being the same as the first location in the second PRACH transmission of the second control information.   
     
     
         10 . The method of  claim 4 , further comprising:
 receiving a number of PRACH transmissions being equal to or greater than a threshold number of PRACH transmissions; and   terminating the RACH procedure.   
     
     
         11 . The method of  claim 4 , further comprising:
 initiating the RACH procedure to establish a communication link between a user equipment (UE) and a cell of a base station; and   transmitting a PRACH transmission schedule having a plurality of PRACH transmission opportunities, wherein generating the combined PRACH control message is based at least in part on the PRACH transmission schedule.   
     
     
         12 . The method of  claim 4 , wherein:
 the first PRACH transmission or the second PRACH transmission are mapped into one or more self-contained uplink slots, wherein each of the one or more self-contained uplink slots comprises at least the first control information and the first payload information of the first PRACH transmission or the second control information and the second payload information of the second PRACH transmission.   
     
     
         13 . The method of  claim 4 , wherein:
 the first PRACH transmission and the second PRACH transmission are based at least in part on an outer loop power control.   
     
     
         14 . The method of  claim 4 , wherein:
 a second transmission power of the second PRACH transmission is greater than a first transmission power of the first PRACH transmission.   
     
     
         15 . The method of  claim 4 , further comprising:
 identifying that the second PRACH transmission failed to be successfully decoded; and   receiving a third PRACH transmission.   
     
     
         16 . The method of  claim 4 , wherein receiving the first PRACH transmission and the second PRACH transmission comprises:
 receiving the first PRACH transmission during a first uplink slot and the second PRACH transmission during a second uplink slot different from the first uplink slot.   
     
     
         17 . An apparatus for wireless communication, comprising:
 a processor;   memory coupled with the processor; and   instructions stored in the memory and executable by the processor to cause the apparatus to:
 receive a transmission schedule that indicates that a physical random access channel (PRACH) transmission of a random access channel (RACH) procedure is a first type of PRACH transmission and indicating a fixed timing between a first time associated with a transmission of the PRACH transmission and a second time associated with a retransmission of the PRACH transmission; 
 select a first location for control information in the PRACH transmission and a second location for payload information in the PRACH transmission; 
 transmit the PRACH transmission at the first time including the control information and the payload information; 
 detect a failure to receive a random access response (RAR) message responsive to the PRACH transmission within a time period; and 
 retransmit the PRACH transmission at the second time including the control information and the payload information based at least in part on the fixed timing and the first type of PRACH transmission. 
   
     
     
         18 . The apparatus of  claim 17 , wherein the instructions are further executable by the processor to cause the apparatus to:
 map the PRACH transmission and the retransmission of the PRACH transmission to one or more uplink-centric slots, wherein each of the one or more uplink-centric slots comprises at least the control information and the payload information of the PRACH transmission or the control information and the payload information of the retransmission of the PRACH transmission.   
     
     
         19 . The apparatus of  claim 17 , wherein the instructions to receive the transmission schedule are further executable by the processor to cause the apparatus to:
 receive the transmission schedule including a plurality of PRACH transmission opportunities associated with the RACH procedure, wherein the plurality of PRACH transmission opportunities are associated with the fixed timing; and   transmit the PRACH transmission and the retransmission of the PRACH transmission based at least in part on the transmission schedule.   
     
     
         20 . An apparatus for wireless communication, comprising:
 a processor;   memory coupled with the processor; and   the processor and the memory configured to:
 receive, as part of a random access channel (RACH) procedure, a first physical random access channel (PRACH) transmission at a first reception time, the first PRACH transmission including a first control information at a first location in the first PRACH transmission and a first payload information at a second location in the first PRACH transmission, wherein the first location in the first PRACH transmission of the first control information and the second location in the first PRACH transmission of the first payload information correspond to a first type of PRACH transmission; 
 identify that the first PRACH transmission failed to be successfully decoded; 
 receive a second PRACH transmission at a second reception time based at least in part on a fixed timing, the second PRACH transmission including a second control information at a first location in the second PRACH transmission and a second payload information at a second location in the second PRACH transmission, wherein the first location in the second PRACH transmission of the second control information and the second location in the second PRACH transmission of the second payload information correspond to the first type of PRACH transmission; and 
 generate a combined PRACH control message including a combination of the first PRACH transmission and the second PRACH transmission. 
   
     
     
         21 . The apparatus of  claim 20 , wherein the processor and the memory are further configured to:
 extract data that is common to both the first PRACH transmission and the second PRACH transmission based at least in part on the fixed timing.   
     
     
         22 . The apparatus of  claim 20 , wherein the processor and the memory are further configured to:
 initiate a contention-free random access procedure, wherein generating the combined PRACH control message is based at least in part on initiating the contention-free random access procedure.   
     
     
         23 . The apparatus of  claim 20 , wherein the instructions to receive the first PRACH transmission and the second PRACH transmission are executable by the processor to cause the apparatus to:
 receive a common message portion present in both the first PRACH transmission and the second PRACH transmission, the common message portion including the first control information of the first PRACH transmission and the second control information of the second PRACH transmission.   
     
     
         24 . The apparatus of  claim 23 , wherein the second PRACH transmission is a retransmission of the first PRACH transmission. 
     
     
         25 . The apparatus of  claim 23 , wherein the instructions to receive the common message portion are further executable by the processor to cause the apparatus to:
 receive the first control information at the first location in the first PRACH transmission and the second control information at the first location in the second PRACH transmission, wherein generating the combined PRACH control message is based at least in part on the first location in the first PRACH transmission of the first control information being the same as the first location in the second PRACH transmission of the second control information.   
     
     
         26 . The apparatus of  claim 20 , wherein the instructions are further executable by the processor to cause the apparatus to:
 receive a number of PRACH transmissions being equal to or greater than a threshold number of PRACH transmissions; and   terminate the RACH procedure.   
     
     
         27 . The apparatus of  claim 20 , wherein the instructions are further executable by the processor to cause the apparatus to:
 initiate the RACH procedure to establish a communication link between a user equipment (UE) and a cell of a base station; and   transmit a PRACH transmission schedule having a plurality of PRACH transmission opportunities, wherein generating the combined PRACH control message is based at least in part on the PRACH transmission schedule.   
     
     
         28 . The apparatus of  claim 20 , wherein:
 the first PRACH transmission or the second PRACH transmission are mapped into one or more self-contained uplink slots, wherein each of the one or more self-contained uplink slots comprises at least the first control information and the first payload information of the first PRACH transmission or the second control information and the second payload information of the second PRACH transmission.   
     
     
         29 . The apparatus of  claim 20 , wherein:
 a second transmission power of the second PRACH transmission is greater than a first transmission power of the first PRACH transmission.   
     
     
         30 . The apparatus of  claim 20 , wherein the instructions to receive the first PRACH transmission and the second PRACH transmission are executable by the processor to cause the apparatus to:
 receive the first PRACH transmission during a first uplink slot and the second PRACH transmission during a second uplink slot different from the first uplink slot.