Message 2 of a two-step random access procedure and coexistence with four-step random access procedure

A method for wireless communication at a network entity:

• receiving an uplink request message from a user equipment, UE;
• identifying that the uplink request message is a first message of a two-step random access channel, RACH, procedure, wherein the first message includes a group random access radio network temporary identifier;
• sending a physical downlink control channel comprising an indication of resources of a broadcast or a multicast physical downlink shared channel on which a downlink response intended for the UE to the uplink request message is to be received, wherein sending the physical downlink control channel is based at least in part on the group random access radio network temporary identifier, wherein the downlink response intended for the UE includes an uplink grant indicating resources for transmission by the UE of a confirmation message that confirms the UE received the downlink response intended for the UE, wherein the broadcast or multicast physical downlink shared channel is configured to provide a plurality of downlink responses to a corresponding plurality of UEs that includes the UE;
• and
• sending the plurality of downlink responses, including the downlink response intended for the UE, to the plurality of UEs via the broadcast or multicast physical downlink shared channel, wherein the plurality of downlink responses are multiplexed at a media access control layer, the downlink response intended for the UE being a second message of the two-step RACH procedure.

An apparatus for wireless communication at a user equipment, UE, comprising:

• means for identifying that the UE is to use a two-step random access channel, RACH, procedure, the two-step RACH procedure including an uplink request message and a downlink response;
• means for sending, as a first message, of the two-step RACH procedure, the uplink request message to a base station;
• means for determining a group random access radio network temporary identifier;
• means for receiving, from the base station, a physical downlink control channel comprising an indication of resources of a broadcast or multicast physical downlink shared channel on which the downlink response is to be received;
• means for decoding the physical downlink control channel based at least in part on the group random access radio network temporary identifier;
• means for decoding the broadcast or multicast physical downlink shared channel in accordance with the indication received on the physical downlink control channel, the broadcast or the multicast physical downlink shared channel being configured to provide downlink responses for multiple UEs;
• means for identifying that downlink responses for multiple UEs, including a downlink response intended for the UE, are included within the broadcast or multicast physical downlink shared channel and multiplexed at a media access control layer;
• means for receiving the downlink response intended for the UE on the broadcast or multicast physical downlink shared channel, the downlink response intended for the UE being a second message of the two-step RACH procedure;
• means for identifying an uplink grant in the downlink response intended for the UE, the uplink grant indicating resources for transmission by the UE of a confirmation message that confirms the UE received the downlink response intended for the UE on the broadcast or multicast physical downlink shared channel;
• and
• means for transmitting the confirmation message based at least in part on the uplink grant.

An apparatus for wireless communication at a network entity, comprising:

• means for receiving an uplink request message from a user equipment, UE;
• means for identifying that the uplink request message is a first message of a two-step random access channel, RACH, procedure, wherein the first message includes a group random access radio network temporary identifier;
• means for sending a physical downlink control channel comprising an indication of resources of a broadcast or multicast physical downlink shared channel on which a downlink response intended for the UE to the uplink request message is to be received, wherein the physical downlink control channel is based at least in part on the group random access radio network temporary identifier, wherein the downlink response intended for the UE includes an uplink grant indicating resources for transmission by the UE of a confirmation message that confirms the UE received the downlink response intended for the UE, wherein the broadcast or multicast physical downlink shared channel is configured to provide a plurality of downlink responses to a corresponding plurality of UEs that includes the UE;
• and
• means for sending the plurality of downlink responses, including the downlink response intended for the UE, via the broadcast or multicast physical downlink shared channel, wherein the plurality of downlink responses are multiplexed at a media access control layer, the downlink response intended for the UE being a second message of the two-step RACH procedure.

An apparatus for wireless communication at a user equipment, UE, comprising:

• a processor,
• memory coupled with the processor;
• and
• instructions stored in the memory and executable by the processor to cause the apparatus to:
• identify that the UE is to use a two-step random access channel, RACH, procedure, the two-step RACH procedure including an uplink request message and a downlink response;
• send, as a first message of the two-step RACH procedure, the uplink request message to a base station;
• determine a group random access radio network temporary identifier;
• receive, from the base station, a physical downlink control channel comprising an indication of resources of a broadcast or multicast physical downlink shared channel on which the downlink response is to be received;
• decode the physical downlink control channel based at least in part on the group random access radio network temporary identifier;
• decode the broadcast or multicast physical downlink shared channel in accordance with the indication received on the physical downlink control channel, the broadcast or multicast physical downlink shared channel being configured to provide downlink responses for multiple UEs;
• and
• identify that downlink responses for multiple UEs, including a downlink response intended for the UE, are included within the broadcast or multicast physical downlink shared channel and multiplexed at a media access control layer;
• receive the downlink response intended for the UE on the broadcast or multicast physical downlink shared channel, the downlink response intended for the UE being a second message of the two-step RACH procedure;
• identify an uplink grant in the downlink response intended for the UE, the uplink grant indicating resources for transmission by the UE of a confirmation message that confirms the UE received the downlink response intended for the UE on the broadcast or multicast physical downlink shared channel;
• and
• transmit the confirmation message based at least in part on the uplink grant.

An apparatus for wireless communication at a base station network entity:

• a processor,
• memory coupled with the processor;
• and
• instructions stored in the memory and executable by the processor to cause the apparatus to:
• receive an uplink request message from a user equipment, UE;
• identify that the uplink request message is a first message of a two-step random access channel, RACH, procedure, wherein the first message includes a group random access radio network temporary identifier;
• send a physical downlink control channel comprising an indication of resources of a broadcast or a multicast physical downlink shared channel on which a downlink response intended for the UE to the uplink request message is to be received, wherein sending the physical downlink control channel is based at least in part on the group random access radio network temporary identifier, wherein the downlink response intended for the UE includes an uplink grant indicating resources for transmission by the UE of a confirmation message that confirms the UE received the downlink response intended for the UE, wherein the broadcast or multicast physical downlink shared channel is configured to provide a plurality of downlink responses to a corresponding plurality of UEs that includes the UE;
• and
• send the plurality of downlink responses, including the downlink response intended for the UE, to the plurality of UEs via the broadcast or multicast physical downlink shared channel, wherein the plurality of downlink responses are multiplexed at a media access control layer, the downlink response intended for the UE being a second message of the two-step RACH procedure.