Managing small data transmission in unlicensed radio frequency band by wireless device

A method for managing a small data transmission (SDT) by a wireless device using an unlicensed radio frequency band of a cellular wireless network, the method comprising:

• by the wireless device while in an inactive state:
• determining uplink (UL) data is available for transmission to the cellular wireless network;
• determining validity of a timing advance (TA) value most recently received from the cellular wireless network;
• acquiring downlink (DL) timing synchronization during a DL timing synchronization occasion within a time range of a configured grant SDT (CG-SDT) occasion;
• transmitting a portion of the UL data to the cellular wireless network during the CG-SDT occasion, when the unlicensed radio frequency band is available for transmission;
• when the unlicensed radio frequency band is not available for transmission:
• i) delaying transmission of the portion of the UL data to a subsequent CG-SDT occasion, or
• ii) discarding the portion of the UL data.

An apparatus configurable for operation in a wireless device, the apparatus comprising one or more processors coupled to a memory storing instructions that, when executed by the one or more processors, configure the wireless device to manage a small data transmission (SDT) while in an inactive state using an unlicensed radio frequency band of a cellular wireless network by:

• determining uplink (UL) data is available for transmission to the cellular wireless network;
• performing a first timing advance (TA) validation procedure to determine validity of a TA value most recently received from the cellular wireless network;
• when the TA value is determined to be valid:
• attempting to acquire downlink (DL) timing synchronization during one or more timing synchronization occasions within a time range of a configured grant SDT (CG-SDT) occasion;
• when DL timing synchronization is successfully acquired during at least one DL timing synchronization occasion within the time range of the CG-SDT occasion:
• determining whether the unlicensed radio frequency band is unoccupied using a listen before talk (LBT) procedure in advance of the CG-SDT occasion;
• and
• transmitting a first portion of the UL data to the cellular wireless network during the CG-SDT occasion, when the LBT procedure indicates the unlicensed radio frequency band is available for transmission;
• and
• when acquisition of DL timing synchronization fails in all DL timing synchronization occasions in advance of the CG-SDT occasion:
• i) delaying transmission of the first portion of the UL data to a subsequent CG-SDT occasion, or
• ii) discarding the first portion of the UL data.