Terminal apparatus, and control method for performing handover having enhanced communication efficiency

Patent metadata

Field	Value
Publication number	US-12464569-B2
Application number	US-202519018124-A
Country	US
Kind code	B2
Filing date	Jan 13, 2025
Priority date	Feb 10, 2023
Publication date	Nov 4, 2025
Grant date	Nov 4, 2025

Abstract

A base station apparatus performs, for a currently connected terminal apparatus, setting of a radio resource control (RRC) layer for another base station apparatus that is a destination candidate for a handover by the terminal apparatus from the base station apparatus, instructs the terminal apparatus to transmit a random access preamble to the other base station apparatus via a physical downlink control channel (PDCCH) order without handover to the other base station apparatus being performed, and transmits, to the terminal apparatus, a command instructing for handover to the other base station apparatus in response to the terminal apparatus being in a state for handover to the other base station apparatus.

First claim

What is claimed is:

1 . A terminal apparatus comprising:
a receiving unit configured to receive, from a currently connected base station apparatus, a setting of a radio resource control (RRC) layer for another base station apparatus that is a destination candidate for a handover by the terminal apparatus from the base station apparatus and to receive, from the base station apparatus, a physical downlink control channel (PDCCH) order instructing the terminal apparatus to transmit a random access preamble to the other base station apparatus without handover to the other base station apparatus being performed; a transmitting unit configured to transmit the random access preamble to the other base station apparatus according to the instruction; and a performing unit configured to perform handover to the other base station apparatus in a case where a command instructing for a handover to the other base station apparatus is received from the base station apparatus, wherein the receiving unit receives, from the base station apparatus, a sequence unique to the terminal apparatus used by the terminal apparatus when generating the random access preamble and information for identifying radio resources that can be used when transmitting the random access preamble, and the transmitting unit generates the random access preamble using the sequence unique to the terminal apparatus and transmits the random access preamble using radio resources identified via the information, and in a case where a signal requesting for retransmission of the random access preamble is received from the base station apparatus, the transmitting unit retransmits the random access preamble, and in a case where a signal requesting for retransmission of the random access preamble is not received from the base station apparatus or the other base station apparatus, the transmitting unit does not retransmit the random access preamble.

2 . The terminal apparatus according to claim 1 , wherein
the receiving unit receives an instruction to transmit the random access preamble to a plurality of the other base station apparatuses via one PDCCH.

3 . The terminal apparatus according to claim 1 , wherein
the receiving unit receives, from the base station apparatus or the other base station apparatus, a value (TA value) of a timing advance identified by the other base station apparatus on a basis of the random access preamble transmitted by the terminal apparatus.

4 . The terminal apparatus according to claim 3 , further comprising:
a retaining unit configured to retain the TA value, wherein the transmitting unit transmits a predetermined uplink signal to the other base station apparatus in response to an effective period of the TA value ending or an update period of the TA value arriving.

5 . The terminal apparatus according to claim 4 , wherein
in a case where the transmitting unit is instructed to transmit the random access preamble from the base station apparatus in response to the effective period of the TA value ending or the update period of the TA value arriving, the transmitting unit transmits the random access preamble to the other base station apparatus as the predetermined uplink signal.

6 . The terminal apparatus according to claim 4 , wherein
the transmitting unit transmits, at predetermined periods or in response to an instruction to transmit a sounding reference signal (SRS) from the other base station apparatus, the SRS to the other base station apparatus at a transmission timing determined using the TA value as the predetermined uplink signal.

7 . The terminal apparatus according to claim 4 , wherein
the retaining unit ends retention of the TA value in response to a wireless quality between the terminal apparatus and the other base station apparatus being equal to or less than a predetermined level.

8 . The terminal apparatus according to claim 1 , wherein
the transmitting unit repeatedly transmits the random access preamble at predetermined periods until a transmission stop instruction for the random access preamble is received from the base station apparatus and stops transmitting the random access preamble in response to the transmission stop instruction being received.

9 . The terminal apparatus according to claim 1 , wherein
the receiving unit receives, from the base station apparatus, a group of sequences that can be used when generating the random access preamble to be transmitted to the other base station apparatus, and the transmitting unit uses one sequence selected from the group of sequences to generate the random access preamble and transmits the random access preamble to the other base station apparatus.

10 . The terminal apparatus according to claim 9 , wherein
the receiving unit receives a response to the random access preamble from the base station apparatus or the other random access preamble, the transmitting unit transmits a first message including identification information of the terminal apparatus to the other base station apparatus in a case where the response is received, and the receiving unit receives a second message including identification information of the terminal apparatus with respect to the first message from the base station apparatus or the other base station apparatus.

11 . The terminal apparatus according to claim 10 , wherein
the receiving unit receives, from the base station apparatus, a notification of at least one of a timing for transmitting, from the other base station apparatus, the response to the random access preamble by the terminal apparatus and a timing for transmitting, from the other base station apparatus, the second message.

12 . The terminal apparatus according to claim 1 , wherein
the transmitting unit repeatedly retransmits the random access preamble at predetermined periods in response to an instruction to transmit the random access preamble, the receiving unit receives a transmission stop for the random access preamble from the base station apparatus, and the transmitting unit stops transmitting the random access preamble in response to receiving the transmission stop instruction.

13 . A control method executed by a terminal apparatus comprising:
receiving, from a currently connected base station apparatus, a setting of a radio resource control (RRC) layer for another base station apparatus that is a destination candidate for a handover by the terminal apparatus from the base station apparatus and receiving, from the base station apparatus, a physical downlink control channel (PDCCH) order instructing the terminal apparatus to transmit a random access preamble to the other base station apparatus without handover to the other base station apparatus being performed; transmitting the random access preamble to the other base station apparatus according to the instruction; and performing handover to the other base station apparatus in a case where a command instructing for a handover to the other base station apparatus is received from the base station apparatus, wherein in the receiving, a sequence unique to the terminal apparatus used by the terminal apparatus when generating the random access preamble and information for identifying radio resources that can be used when transmitting the random access preamble are received from the base station apparatus, and in the transmitting, the random access preamble is generated using the sequence unique to the terminal apparatus and the random access preamble is transmitted using radio resources identified via the information, and in a case where a signal requesting for retransmission of the random access preamble is received from the ba

Assignees

• Kddi Corp

Inventors

• Takeda Hiroki
• Li Yanwei
• Hong Jungyeon
• Takaku Yoshitaka
• Ohseki Takeo

Classifications

• H04W72/23

  in the downlink direction of a wireless link, i.e. towards a terminal · CPC title

• H04W76/38

  triggered by timers · CPC title

• H04W36/0055

  Transmission or use of information for re-establishing the radio link · CPC title

• H04W56/0045

  compensating for timing error by altering transmission time · CPC title

• H04W74/0833 Primary

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