Random-access response with analog beamforming
A system and method of Random-Access Response, RAR, messaging when a base station employs narrow beamforming. Multiple RAR messages are successively transmitted from the base station to a User Equipment, UE, before any response to a RAR message is received from the UE. Thus, despite any calibration mismatch between Uplink, UL, and Downlink, DL, beams in the beamformed system, a RAR message is not only received by the UE, but is received over the most-suitable DL beam for that UE. Each RAR message may contain a message-specific scheduling-delay indicator in the UL grant carried in the RAR message to provide an adjustable time delay for the UE's uplink transmission scheduled by the UL grant. Multiple RAR transmissions can schedule a single UL transmission at a specific time instance or different UL transmissions at different time intervals. The UE may report to the base station the best DL RAR transmission detected by the UE.
1. A method of processing a Random-Access Response (RAR) received by a User Equipment (UE) from a network entity, wherein the method comprises performing the following by the UE:
receiving one or more RAR messages from the network entity, wherein each RAR message includes a RAR message-specific time-delay indicator in a respective Uplink (UL) grant for the UE carried by the RAR message, wherein each RAR message-specific time-delay indicator specifies a UL time interval in which the UE is scheduled to transmit in the UL to the network entity;
detecting at least one of the one or more RAR messages; and
sending a response to the detected at least one of the one or more RAR messages during the UL time interval specified by the selected at least one RAR message.
2. The method of claim 1 , further comprising performing the following by the UE as part of sending the response:
processing the RAR message-specific time-delay indicator associated with the detected at least one RAR message to determine the UL time interval specified by the detected at least one RAR message in which the UE is scheduled to transmit to the network entity.
3. The method of claim 2 , wherein processing the RAR message-specific time-delay indicator includes performing the following by the UE:
using the RAR message-specific time-delay indicator associated with the selected at least one RAR message in a pre-defined formula to determine the UL time interval specified by the selected at least one RAR message.
4. The method of claim 1 , wherein detecting at least one of the one or more RAR messages includes performing one of the following by the UE:
from the received one or more RAR messages, detecting a RAR message having the largest received power;
from the received one or more RAR messages, detecting a successfully-received RAR message; and
from the received one or more RAR messages, detecting the at least one RAR message based on a pre-defined criterion.
5. The method of claim 1 , wherein sending the response to the detected at least one of the one or more RAR messages includes performing one of the following by the UE when the UL time interval specified by the detected at least one RAR message happens to be a reserved subframe:
send the response using another radio subframe that occurs before the reserved subframe; and
send the response using another radio subframe that occurs after the reserved subframe.