Uplink transmission parameter selection for random access initial message transmission and retransmission
Methods, systems, and devices for wireless communication are described that provide for selecting different uplink transmission parameters for transmission or retransmission of a random access message. A user equipment (UE) may retransmit a random access message to a base station during a random access procedure if an initial transmission of the random access message was unsuccessfully received by the base station. The UE may select a different transmission beam, uplink resource, or transmission power for retransmission of the random access message. The selection may be based on path loss associated with synchronization signals or previous transmissions. The selection may also be based on a maximum number of retransmissions.
1. A method for wireless communication, comprising:
identifying a first uplink transmission beam for a random access procedure;
transmitting, to a base station, a random access message using the first uplink transmission beam;
selecting a second uplink transmission beam based at least in part on an absence of a random access response from the base station corresponding to the random access message transmitted using the first uplink transmission beam and a current path loss estimate, the second uplink transmission beam having a different transmission direction than the first uplink transmission beam;
determining a path loss difference between the current path loss estimate and a previous path loss estimate;
determining an uplink transmission power based at least in part on a power ramping counter value, the path loss difference satisfying a threshold path loss difference, and the selection of the second uplink transmission beam; and
retransmitting the random access message to the base station using the second uplink transmission beam and the determined uplink transmission power, wherein the power ramping counter value is based at least in part on a number of retransmissions of the random access message and a number of times an uplink transmission beam is selected based at least in part on the absence of the random access response.
2. The method of claim 1 , wherein determining the uplink transmission power further comprises
increasing the uplink transmission power by an additional amount, wherein the additional amount is based at least in part on the number of retransmissions.
3. The method of claim 2 , wherein:
the additional amount is a function of the power ramping counter value.
4. The method of claim 1 , wherein the power ramping counter value is equal to the number of retransmissions minus the number of uplink transmission beam changes.
5. The method of claim 1 , wherein determining the uplink transmission power further comprises:
maintaining the power ramping counter value based at least in part on the second uplink transmission beam being different than the first uplink transmission beam, wherein the uplink transmission power is based at least in part on the maintained power ramping counter value.
6. The method of claim 1 , wherein determining the uplink transmission power further comprises:
increasing the uplink transmission power by an additional amount, wherein the additional amount is equal to a power ramped amount associated with transmission of the random access message using the first uplink transmission beam.
7. The method of claim 1 , further comprising:
receiving, from the base station, a maximum retransmission number, wherein retransmitting the random access message is based at least in part on the maximum retransmission number.
8. The method of claim 7 , wherein the maximum retransmission number is associated with at least one of a total number of retransmission attempts of the random access message, a number of retransmission attempts of the random access message for each of a plurality of uplink transmission powers, a number of retransmission attempts of the random access message for each of a plurality of random access resources, or a number of retransmission attempts of the random access message for each combination of uplink transmission powers and random access resources.
9. The method of claim 1 , further comprising:
selecting a random access resource for retransmission of the random access message, the random access resource corresponding to a lowest uplink transmission power.
10. The method of claim 1 , wherein determining the uplink transmission power further comprises:
increasing the uplink transmission power by an additional amount based at least in part on determining that the path loss difference is greater than the threshold path loss difference.
11. The method of claim 1 , wherein determining the uplink transmission power further comprises:
maintaining the uplink transmission power based at least in part on determining that the path loss difference is less than the threshold path loss difference.
12. The method of claim 1 , wherein the previous path loss estimate is associated with the transmission of the random access message using the first uplink transmission beam.
13. The method of claim 1 , wherein the previous path loss estimate is associated with a previous retransmission of the random access message.