Random access procedure fallback

Patent metadata

Field	Value
Publication number	US-2020252973-A1
Application number	US-202016746704-A
Country	US
Kind code	A1
Filing date	Jan 17, 2020
Priority date	Feb 1, 2019
Publication date	Aug 6, 2020
Grant date	—

Abstract

This disclosure provides systems, methods and apparatus for wireless communications that support fallback from a 2-step to a 4-step random access procedures. A user equipment (UE) may establish a connection with a base station using a random access procedure. The random access procedure may be a 2-step random access procedure and reduce a number of handover exchange messages. The 2-step random access procedure may include the UE transmitting, to the base station, a first random access message including a preamble and a payload. In some implementations, the base station may receive the preamble but fail to receive or decode the payload. The random access procedure may utilize the received preamble information instead of performing retransmission of the first random access message. The base station may transmit a second random access message to the UE indicating, explicitly or implicitly, a fallback to a 4-step random access procedure for connection establishment.

First claim

1 . A method for wireless communication at a user equipment (UE), comprising:
transmitting, to a base station, a first random access message of a first random access procedure, the first random access message including a random access preamble and a connection request; monitoring a response window of a channel to receive a second random access message in response to the first random access message, the response window based at least in part on a configured timer; identifying a format of the second random access message based at least in part on the receiving, wherein the format of the second random access message indicates one of: the first random access procedure or a second random access procedure; and establishing a connection with the base station, based, at least in part, on the first random access message, the second random access message, and the indicated one of the first random access procedure or the second random access procedure.

2 . The method of claim 1 wherein identifying the format of the second random access message further comprises:
determining the second random access message comprises at least a random access response and a connection setup message for the first random access procedure.

3 . The method of claim 1 wherein identifying the format of the second random access message further comprises:
determining the second random access message comprises at least a preamble index and an uplink grant indicating a switch from the first random access procedure to the second random access procedure.

4 . The method of claim 3 , further comprising:
transmitting a third random access message based at least in part on the switch from the first random access procedure to the second random access procedure, the third random access message comprising a retransmission of the connection request; receiving a fourth random access message from the base station in response to the third random access message, the fourth random access message comprising a connection setup message in response to the connection request; and wherein establishing the connection is further based at least in part on the third random access message and the fourth random access message.

5 . The method of claim 1 , wherein monitoring the response window of the channel further comprises:
initiating the response window of the channel following the connection request.

6 . The method of claim 1 , wherein monitoring the response window of the channel further comprises:
initiating the response window of the channel following the random access preamble and prior to the connection request.

7 . The method of claim 1 , further comprising:
sensing the channel prior to at least one of the random access preamble or the connection request; and wherein the transmitting is based at least in part on sensing the channel, the transmitting spanning one or more physical uplink shared channel transmit occasions.

8 . The method of claim 1 , wherein:
the first random access procedure is a two-step random access procedure and the second random access procedure is a four-step random access procedure.

9 - 43 . (canceled)

44 . An apparatus for wireless communication at a user equipment (UE), comprising:
a processor, memory in electronic communication with the processor; and instructions stored in the memory and executable by the processor to cause the apparatus to: transmit, to a base station, a first random access message of a first random access procedure, the first random access message including a random access preamble and a connection request; monitor a response window of a channel to receive a second random access message in response to the first random access message, the response window based at least in part on a configured timer; identify a format of the second random access message based at least in part on the receiving, wherein the format of the second random access message indicates one of: the first random access procedure or a second random access procedure; and establish a connection with the base station based at least in part on the first random access message, the second random access message, and the indicated one of the first random access procedure or the second random access procedure.

45 . The apparatus of claim 44 , wherein the instructions to identify the format of the second random access message further are executable by the processor to cause the apparatus to:
determine the second random access message comprises at least a random access response and a connection setup message for the first random access procedure.

46 . The apparatus of claim 44 , wherein the instructions to identify the format of the second random access message further are executable by the processor to cause the apparatus to:
determine the second random access message comprises at least a preamble index and an uplink grant indicating a switch from the first random access procedure to the second random access procedure.

47 . The apparatus of claim 46 , wherein the instructions are further executable by the processor to cause the apparatus to:
transmit a third random access message based at least in part on the switch from the first random access procedure to the second random access procedure, the third random access message comprising a retransmission of the connection request; receive a fourth random access message from the base station in response to the third random access message, the fourth random access message comprising a connection setup message in response to the connection request; and wherein establishing the connection is further based at least in part on the third random access message and the fourth random access message.

48 . The apparatus of claim 44 , wherein the instructions to monitor the response window of the channel further are executable by the processor to cause the apparatus to:
initiate the response window of the channel following the connection request.

49 . (canceled)

50 . The apparatus of claim 44 , wherein the instructions are further executable by the processor to cause the apparatus to:
sense the channel prior to at least one of the random access preamble or the connection request; and wherein the transmitting is based at least in part on sensing the channel, the transmitting spanning one or more physical uplink shared channel transmit occasions.

51 . The apparatus of claim 44 , wherein:
the first random access procedure is a two-step random access procedure and the second random access procedure is a four-step random access procedure.

52 - 98 . (canceled)

99 . An apparatus for wireless communication at a user equipment (UE), comprising:
means for transmitting, to a base station, a first random access message of a first random access procedure, the first random access message comprising a random access preamble and a connection request; means for monitoring a response window of a channel to receive a second random access message in response to the first random access message, the response window based at least in part on a configured timer; means for identifying a format of the second random access message based at least in part on the receiving, wherein the format of the second random access message indicates one of: the first random access procedure or a second random access procedure; and means for establishing a connection with the base station based at least in part on the first random access message, the second random access message, and the indicated one of the first random access

Assignees

• Qualcomm Inc

Inventors

• Zhang Xiaoxia
• Sun Jing
• Akkarakaran Sony
• Islam Muhammad Nazmul
• Luo Tao

Classifications

• H04W76/10 Primary

  Connection setup · CPC title

• H04W74/0836

  with 2-step access · CPC title

• H04W74/0838

  using contention-free random access [CFRA] · CPC title

• H04W74/0833 Primary

  Random access procedures, e.g. with 4-step access · CPC title

• H04W36/0079

  in case of hand-off failure or rejection · CPC title