WO2018123025A1 - Base station, terminal, communication system, and communication method - Google Patents

Abstract

A first base station (120) is provided with a receiving unit (121) and a control unit (122). The receiving unit (121) receives, from a terminal (110) connected to a first cell of the local station, a value that indicates discrepancy between the wireless signal transmit timing of the terminal (110) and the reference timing of a second cell different from the first cell. The control unit (122) selects a handover method on the basis of the value received by the receiving unit (121) from a first handover method that includes a random access procedure and a second handover method that does not include at least a portion of the random access procedure. The control unit (122) exercises control for switching a connection destination of the terminal (110) to the second cell by the selected handover method.

Description

Base station, terminal, communication system and communication method

The present invention relates to a base station, a terminal, a communication system, and a communication method.

Conventionally, in 3GPP, specifications of mobile communication systems such as the third generation mobile communication system (3G), LTE corresponding to the 3.9th generation mobile communication system, LTE-Advanced corresponding to the fourth generation mobile communication system have been studied. ing. 3GPP is an abbreviation for 3rd Generation Partnership Project. LTE is an abbreviation for Long Term Evolution. In addition, studies on technologies relating to the fifth generation mobile communication system (5G) have also started. Also, for example, a technique is known in which a terminal performs handover without performing a random access procedure using RACH in order to reduce the time required for handover (see, for example, Patent Documents 1 and 2 below). RACH is an abbreviation for Random Access Channel (random access channel).

JP 2016-058884 A JP 2012-110005 A

However, in the above-described conventional technology, it is required to shorten the time required for handover. For example, if the transmission timing of the terminal with respect to the base station of the handover destination is deviated, the handover without performing the random access procedure may fail and the time required for the handover may not be shortened.

In one aspect, an object of the present invention is to provide a base station, a terminal, a communication system, and a communication method that can reduce the time required for handover.

In order to solve the above-described problems and achieve the object, in one embodiment, a terminal transmits a radio signal of its own terminal and a reference timing of a second cell different from the first cell to which the terminal is connected. A first handover method in which the base station of the first cell includes a random access procedure, and a second handover that does not include at least a part of the random access procedure. And a base station, a terminal, a communication system, and a communication method for performing control to switch the connection destination of the terminal to the second cell by a handover method selected based on the value transmitted by the terminal among the methods .

In another embodiment, the terminal may include a first handover method that includes a random access procedure and a second handover method that does not include at least a part of the random access procedure. Transmitting information indicating a handover method selected based on a value indicating a shift amount between a transmission timing and a reference timing of a second cell different from the first cell to which the terminal is connected; A base station, a terminal, a communication system, and a communication method are proposed in which the base station performs control to switch the connection destination of the terminal to the second cell by the handover method indicated by the information transmitted by the terminal.

In one aspect, the present invention has the effect of reducing the time required for handover.

FIG. 1 is a diagram illustrating an example of a communication system according to an embodiment. FIG. 2 is a sequence diagram illustrating an example of processing when the UE selects the HO method in the communication system according to the embodiment. FIG. 3 is a sequence diagram illustrating another example of processing when the UE selects the HO method in the communication system according to the embodiment. FIG. 4 is a sequence diagram illustrating an example of processing when the source eNB selects the HO method in the communication system according to the embodiment. FIG. 5 is a sequence diagram illustrating another example of processing when the source eNB selects the HO method in the communication system according to the embodiment. FIG. 6 is a flowchart illustrating an example of processing performed by the UE according to the embodiment. FIG. 7 is a flowchart illustrating an example of setting processing by the source base station according to the embodiment. FIG. 8 is a flowchart illustrating an example of the HO process performed by the source eNB according to the embodiment. FIG. 9 is a diagram illustrating an example of the UE according to the embodiment. FIG. 10 is a diagram illustrating an example of a hardware configuration of the UE according to the embodiment. FIG. 11 is a diagram illustrating an example of the eNB according to the embodiment. FIG. 12 is a diagram illustrating an example of a hardware configuration of the eNB according to the embodiment. FIG. 13 is a diagram illustrating an example of an event type definition according to the embodiment. FIG. 14 is a diagram illustrating an example of a measurement report according to the embodiment. FIG. 15 is a sequence diagram illustrating an example of a UE capability inquiry procedure in the communication system according to the embodiment. FIG. 16 is a sequence diagram illustrating an example of calculating the TA value of the target eNB by the UE according to the embodiment.

Hereinafter, embodiments of a base station, a terminal, a communication system, and a communication method according to the present invention will be described in detail with reference to the drawings.

(Embodiment)
(Communication system according to embodiment)
FIG. 1 is a diagram illustrating an example of a communication system according to an embodiment. As illustrated in FIG. 1, the communication system 100 according to the embodiment includes a terminal 110 and a first base station 120. The communication system 100 may further include a second base station 130. The first base station 120 is a base station apparatus that forms a first cell and can perform wireless communication with the terminal 110 using the first cell. The second base station 130 is a base station apparatus that forms a second cell different from the first cell and can perform wireless communication with the terminal 110 using the second cell. Each of the 1st base station 120 and the 2nd base station 130 is eNB (evolved Node B) as an example.

The terminal 110 is located in the first cell of the first base station 120 and the second cell of the second base station 130, and is a terminal device capable of wireless communication with the first base station 120 or the second base station 130. It is. The terminal 110 is a UE (User Equipment: user terminal) as an example. In the example illustrated in FIG. 1, the terminal 110 is connected to the first cell of the first base station 120 and performs wireless communication with the first base station 120.

For example, the terminal 110 includes a calculation unit 111, a transmission unit 112, and a control unit 113. The calculation unit 111 calculates a value indicating a deviation amount (a magnitude of deviation) between the transmission timing of the radio signal of the terminal (terminal 110) and the reference timing of the second cell, and calculates the calculated TA value. The data is output to the transmission unit 112. The value indicating the amount of deviation is, for example, a TA value. TA is an abbreviation for Timing Advance. For example, the calculation unit 111 calculates the TA value based on the reference signal transmitted by the second cell of the second base station 130. The calculation of the TA value will be described later.

For example, when the transmission timing of the radio signal of the terminal 110 to the second cell of the second base station 130 is not adjusted, the transmission timing of the radio signal of the terminal 110 serving as the reference of the TA value is determined by the terminal 110. Is a timing for transmitting a radio signal to the second cell. The reference timing of the second cell serving as a reference for the TA value is a timing for performing a reception process of a radio signal from the terminal 110 in the second cell of the second base station 130.

The transmission unit 112 wirelessly transmits a value indicating the amount of deviation output from the calculation unit 111 to the first base station 120 of the first cell. For example, the transmission unit 112 wirelessly transmits a value indicating the amount of deviation output from the calculation unit 111 to the first base station 120 together with the measurement result of the wireless quality in each terminal 110 of the first cell and the second cell. However, the transmission unit 112 may wirelessly transmit a value indicating the amount of deviation to the first base station 120 at an opportunity different from the transmission of the wireless quality measurement result.

The first base station 120 includes a receiving unit 121 and a control unit 122. The receiving unit 121 receives a value indicating the amount of deviation transmitted from the terminal 110 and outputs the received value to the control unit 122. Alternatively, the reception unit 121 may receive a value indicating a deviation amount together with the measurement result of the radio quality from the terminal 110 and output the received measurement result of the radio quality and a value indicating the deviation amount to the control unit 122.

The control unit 122, based on the value indicating the amount of deviation output from the reception unit 121, a first handover method including a random access procedure, a second handover method not including at least a part of the random access procedure, Select one of the following. Then, the control unit 122 performs control to switch the connection destination of the terminal 110 from the first cell of the first base station 120 to the second cell of the second base station 130 by the selected handover method.

For example, the control unit 122 determines whether to perform a handover for switching the connection destination of the terminal 110 to the second cell based on the measurement result of the radio quality output from the reception unit 121. Then, when the control unit 122 determines to perform handover for switching the connection destination of the terminal 110 to the second cell, the control unit 122 performs the handover method selected based on the value indicating the amount of deviation output from the reception unit 121 by the handover method. Control to switch the connection destination to the second cell is performed.

The random access procedure is a random access procedure executed between the terminal 110 and the second base station 130. For example, the random access procedure is a procedure in which the terminal 110 connects to the second base station 130 by transmitting and receiving radio signals between the terminal 110 and the second base station 130 using RACH.

The first handover method including a random access procedure is a handover in which the connection destination of the terminal 110 is switched to the second cell of the second base station 130 by executing the random access procedure between the terminal 110 and the second base station 130, for example. It is a method.

The second handover method that does not include at least a part of the random access procedure is, for example, a handover method that does not include a procedure for adjusting transmission timing from the terminal 110 to the second base station 130 among the random access procedures. is there. For example, the second handover method is a handover method in which the connection destination of the terminal 110 is switched to the second cell of the second base station 130 without executing a random access procedure between the terminal 110 and the second base station 130. is there. That is, the second handover method is a handover that does not use RACH, for example. As an example, the second handover method is a RACH-less (RACH-less) handover in 3GPP TR 36.881 or the like.

For example, the control unit 122 selects the second handover method when the amount of deviation indicated by the value output from the receiving unit 121 is equal to or less than a predetermined amount. As a result, when the amount of transmission timing deviation of the terminal 110 with respect to the second cell is small and there is a high possibility that the handover of the terminal 110 from the first cell to the second cell by the second handover method will be successful, the second handover method is used. A handover can be performed. For this reason, the time taken for the handover can be shortened.

Also, the control unit 122 selects the first handover method when the amount of deviation indicated by the value output from the receiving unit 121 is greater than a predetermined amount. As a result, when the amount of transmission timing deviation of the terminal 110 with respect to the second cell is large and the possibility that the handover of the terminal 110 from the first cell to the second cell by the second handover method is not likely to be successful, the first handover method is used. A handover can be performed. For this reason, failure of the handover can be suppressed and the time taken for the handover can be shortened.

Further, when the terminal 110 transmits a radio signal including a CP (Cyclic Prefix) when it is connected to the second cell to the second cell, the above-described predetermined amount compared with the amount of deviation is It can be an amount based on length (eg, CP length). As a result, it is possible to accurately determine the possibility of successful handover by the second handover method, select the handover method, and shorten the time required for the handover. The radio signal including the CP is, for example, an OFDM (Orthogonal Frequency Division Multiplexing) signal.

The control unit 113 of the terminal 110 performs control to switch the connection destination of the own terminal from the first cell to the second cell according to the control from the control unit 122 of the first base station 120. For example, when the control unit 113 of the first base station 120 is instructed to perform handover to the second cell by the first handover method, the control unit 113 performs handover to the second cell by the first handover method. In addition, when the control unit 113 is instructed to perform handover to the second cell by the second handover method from the control unit 122 of the first base station 120, the control unit 113 performs handover to the second cell by the second handover method.

As described above, the first handover method including the random access procedure and at least a part of the random access procedure are performed based on the amount of deviation between the radio signal transmission timing of the terminal 110 and the reference timing of the second cell. The second handover method not included is switched. Thereby, the time taken for the handover can be shortened.

Further, the transmission unit 112 of the terminal 110 may select one of the first handover method and the second handover method based on the amount of deviation output from the calculation unit 111. The handover method selection method by the terminal 110 is the same as the handover method selection method by the first base station 120 described above.

In this case, the transmission unit 112 wirelessly transmits information indicating the selected handover method to the first base station 120. For example, the transmission unit 112 wirelessly transmits information indicating the selected handover method to the first base station 120 together with the measurement results of the wireless quality in the terminals 110 of the first cell and the second cell. However, the transmission unit 112 may wirelessly transmit information indicating the handover method to the first base station 120 at an opportunity different from the transmission of the measurement result of the wireless quality.

The receiving unit 121 receives information indicating the handover method transmitted from the terminal 110, and outputs the received information to the control unit 122. Alternatively, the reception unit 121 may receive information indicating the handover method together with the measurement result of the radio quality from the terminal 110, and output the received measurement result of the radio quality and information indicating the handover method to the control unit 122.

The control unit 122 performs control to switch the connection destination of the terminal 110 from the first cell of the first base station 120 to the second cell of the second base station 130 by the handover method indicated by the information output from the reception unit 121. . For example, the control unit 122 determines whether or not to perform handover for switching the connection destination of the terminal 110 to the second cell based on the measurement result of the radio quality output from the reception unit 121. Then, when the control unit 122 determines to perform handover for switching the connection destination of the terminal 110 to the second cell, the control unit 122 changes the connection destination of the terminal 110 to the second cell by the handover method indicated by the information output from the reception unit 121. Perform switching control.

As described above, the terminal 110 may be configured to select the handover method. Also in this case, the time required for the handover can be shortened as in the configuration in which the handover method is selected in the first base station 120.

Also, the first selection method in which the handover method is selected in the first base station 120 and the second selection method in which the handover method is selected in the terminal 110 may be switchable. For example, the first base station 120 selects which of the first selection method and the second selection method is performed, and transmits information indicating the selected selection method to the terminal 110. The terminal 110 performs processing according to the selection method indicated by the information transmitted from the first base station 120.

Further, for example, the terminal 110 may select which of the first selection method and the second selection method is performed, and information indicating the selected selection method may be transmitted to the first base station 120. The first base station 120 performs processing according to the selection method indicated by the information transmitted from the terminal 110.

Although the case where the second cell is a cell formed by the second base station 130 different from the first base station 120 has been described in FIG. 1, the second cell is a cell formed by the first base station 120. It's okay. That is, the terminal 110 may be handed over from the first cell of the first base station 120 to the second cell of the first base station 120.

(Process when UE selects HO method in communication system according to embodiment)
FIG. 2 is a sequence diagram illustrating an example of processing when the UE selects the HO method in the communication system according to the embodiment. The terminal 110 illustrated in FIG. 1 can be realized by, for example, the UE 210 illustrated in FIG. The first base station 120 illustrated in FIG. 2 can be realized by the source eNB 220 illustrated in FIG. 2, for example. The second base station 130 illustrated in FIG. 2 can be realized by the target eNB 230 illustrated in FIG. 2, for example.

The UE 210 can perform wireless communication with each of the source eNB 220 and the target eNB 230. The source eNB 220 and the target eNB 230 can communicate with each other via an inter-base station interface such as an X2 interface between the source eNB 220 and the target eNB 230, for example.

In the communication system 100 according to the embodiment, for example, each step shown in FIG. 2 is executed. In the example illustrated in FIG. 2, a case where the source eNB 220 sets “Event Y” in which the UE 210 selects the HO (handover) method of the UE 210 to the UE 210 as the event type (EventType) will be described.

First, the source eNB 220 transmits an RRC reconfiguration (RRC Reconfiguration) designating “Event Y” as an event type to the UE 210 (step S201). RRC is an abbreviation for Radio Resource Control (Radio Resource Control). Next, UE210 transmits RRC reconfiguration complete (RRC Reconf comp) with respect to RRC reconfiguration transmitted by step S201 to the source eNB220 (step S202).

The target eNB 230 broadcasts a reference signal (Reference Signal) periodically to surrounding UEs including the UE 210 (step S203). Similarly, the source eNB 220 broadcasts reference signals periodically to surrounding UEs including the UE 210.

Next, it is assumed that the radio quality measured by the UE 210 is deteriorated and a predetermined measurement report (Measurement Report) is triggered (step S204). The measurement report opportunity is the timing at which the UE 210 reports the measurement result of the radio quality of each neighboring cell to the source eNB 220. For example, the timing of the measurement report may be the timing set by the source eNB 220 in the UE 210 or the timing set by the UE 210.

Next, the UE 210 calculates the TA value of the target eNB 230 based on the reference signal transmitted from the target eNB 230 in step S203 or the like (step S205). The TA value of the target eNB 230 is an adjustment value of the transmission timing of the UE 210 when the UE 210 transmits a signal to the target eNB 230. The TA value is, for example, information indicating a deviation in radio signal transmission timing by the UE 210 with respect to the reference timing of the target eNB 230. The transmission timing by the UE 210 is, for example, a default transmission timing by the UE 210 (reference timing of the UE 210). Or the transmission timing by UE210 may be the current transmission timing to source eNB220 by UE210.

Next, the UE 210 selects a HO method performed by the UE 210 based on the TA value calculated in step S205 (step S206). For example, the UE 210 selects RACH-less HO if the amount of transmission timing deviation (absolute value) indicated by the TA value is less than or equal to a threshold, and selects legacy HO if the amount of transmission timing deviation indicated by the TA value is greater than the threshold. . RACH-less HO is a HO (second handover method) in which at least a part of the RACH procedure (for example, transmission / reception of MSG1 to MSG4) is omitted. Legacy HO is HO (first handover method) using, for example, a RACH procedure (for example, transmission / reception of MSG1 to MSG4). For example, the length of the CP of the OFDM signal transmitted from the UE 210 to the target eNB 230 can be used as the threshold to be compared with the amount of deviation. In the example illustrated in FIG. 2, it is assumed that the UE 210 has selected RACH-less HO.

Next, the UE 210 transmits to the source eNB 220 a measurement report that includes the RACH less flag set to “on” and indicates the measurement result of the radio quality (step S207). The RACH less flag is flag information indicating that a RACH less HO is requested when “on” and a legacy HO is requested when “off”. The measurement result of the radio quality is a measurement result of the radio quality in the UE 210 for each cell of the source eNB 220 and the target eNB 230, for example. The radio quality is radio quality such as RSRP or RSRQ. RSRP is an abbreviation for Reference Signal Received Power (reference signal received power). RSRQ is an abbreviation for Reference Signal Received Quality (reference signal reception quality).

On the other hand, it is assumed that the source eNB 220 determines handover for switching the connection destination of the UE 210 from the source eNB 220 to the target eNB 230 based on the measurement result of the radio quality indicated by the measurement report received from the UE 210. In this case, the source eNB 220 transmits a handover request (Handover Request) requesting RACH-less HO to the target eNB 230 (step S208).

Next, the target eNB 230 transmits a handover request Ack (acknowledgment) for the handover request received in step S208 and the RACH-less HO parameter to the source eNB 220 (step S209). The RACH-less HO parameter is a parameter for the UE 210 to perform RACH-less HO to the target eNB 230. As an example, in the example of R2-1166604 of 3GPP, the RACH-less HO parameter includes ul-Grant and ul-SchedInterval.

Next, the source eNB 220 transmits the RRC reconfiguration instructing the RACH less HO to the target eNB 230 and the RACH less HO parameter received in step S209 to the UE 210 (step S210).

Next, the UE 210 transmits an RRC reconfiguration complete indicating the RACH-less HO to the target eNB 230 according to the RRC reconfiguration received in step S210 (step S211). Moreover, UE210 transmits RRC reconfiguration complete to the target eNB230 using the RACH less HO parameter received by step S210. For example, the UE 210 transmits a RRC reconfiguration complete to the target eNB 230 by calculating a subframe to which a grant to be used is assigned based on the RACH-less HO parameter.

In step S211, HO for switching the connection destination of the UE 210 from the cell of the source eNB 220 to the cell of the target eNB 230 is completed. In step S <b> 211, the UE 210 transmits the RRC reconfiguration complete to the target eNB 230 without executing the RACH procedure with the target eNB 230. That is, in the example illustrated in FIG. 2, the UE 210 can perform HO by omitting the RACH procedure.

FIG. 3 is a sequence diagram illustrating another example of processing when the UE selects the HO method in the communication system according to the embodiment. In the communication system 100 according to the embodiment, for example, each step shown in FIG. 3 is executed. In the example illustrated in FIG. 3, a case where the source eNB 220 sets “Event Y” in which the UE 210 selects the HO method of the UE 210 as the event type in the UE 210 will be described.

Steps S301 to S308 shown in FIG. 3 are the same as steps S201 to S208 shown in FIG. However, in the example illustrated in FIG. 3, it is assumed that the UE 210 selects the legacy HO in step S306. As an example, when the distance between the source eNB 220 and the target eNB 230 is long, the TA value calculated in step S305 becomes larger than the threshold, and the UE 210 selects the legacy HO.

In this case, in step S307, the UE 210 transmits to the source eNB 220 a measurement report indicating the measurement result of the radio quality including the RACH less flag in which “off” is set. In step S308, the source eNB 220 transmits a handover request requesting legacy HO to the target eNB 230.

Next to step S308, the target eNB 230 transmits a handover request Ack (acknowledgment) for the handover request received in step S308 to the source eNB 220 (step S309). Next, the source eNB 220 transmits RRC reconfiguration instructing HO (legacy HO) to the target eNB 230 to the UE 210 (step S310).

Next, the UE 210 executes a RACH procedure with the target eNB 230 according to the RRC reconfiguration received in step S310 (step S311). The RACH procedure in step S311 includes a procedure for adjusting the transmission timing of the UE 210 for the target eNB 230, for example. For example, the RACH procedure in step S311 includes transmission / reception of MSG1 to MSG4 in the RACH procedure. Transmission / reception of MSG1 to MSG4 will be described later.

The UE 210 can connect to the target eNB 230 by the RACH procedure in step S311. Next, UE210 transmits RRC reconfiguration complete to target eNB230 (step S312). By step S312, HO which switches the connection destination of UE210 from the cell of the source eNB220 to the cell of the target eNB230 is completed. That is, in the example illustrated in FIG. 3, the UE 210 can perform HO without omitting the RACH procedure.

(Transmission / reception of MSG1 to MSG4 in the RACH procedure)
An example of transmission / reception of MSG1 to MSG4 in the RACH procedure will be described. In the RACH procedure, the UE 210 and the target eNB 230 transmit / receive, for example, MSG1 to MSG4 using the RACH.

MSG1 (first message) is, for example, a random access preamble from the UE 210 to the target eNB 230 (Random Access Preamble). The target eNB 230 assigns C-RNTI based on MSG1 from the UE 210, determines transmission timing in the UE 210, and assigns uplink resources. C-RNTI is an abbreviation for Cell-Radio Network Temporary Identifier.

MSG2 (second message) is, for example, a random access response (Random Access Response) from the target eNB 230 to the UE 210. The random access response includes, for example, UL grant (uplink transmission permission), transmission timing (Timing Alignment information), CQI (Channel Quality Indicator) request, and the like.

MSG3 (third message) is, for example, a scheduled transmission from the UE 210 to the target eNB 230 (Scheduled Transmission). The scheduled transmission includes, for example, an RRC connection request (RRC Connection Request). For example, the UE 210 transmits MSG3 to the target eNB 230 using the UL grant included in MSG2.

MSG4 (fourth message) is, for example, contention resolution. The contention resolution is, for example, a response signal (Ack) from the target eNB 230 to the UE 210 for MSG3.

(Process when source eNB selects HO method in communication system according to embodiment)
FIG. 4 is a sequence diagram illustrating an example of processing when the source eNB selects the HO method in the communication system according to the embodiment. In the communication system 100 according to the embodiment, for example, each step shown in FIG. 4 is executed. In the example illustrated in FIG. 4, a case where the source eNB 220 sets “Event X” in which the source eNB 220 selects the HO method of the UE 210 as the event type in the UE 210 will be described.

First, the source eNB 220 transmits an RRC reconfiguration specifying “Event X” as an event type to the UE 210 (step S401). Steps S402 to S405 shown in FIG. 4 are the same as steps S202 to S205 shown in FIG. Following step S405, the UE 210 transmits a measurement report including the TA value calculated in step S405 and indicating the measurement result of the radio quality to the source eNB 220 (step S406).

Next, the target eNB 230 selects a HO method performed by the UE 210 based on the TA value included in the measurement report received in step S406 (step S407). The selection of the HO method by the target eNB 230 is the same as the selection of the HO method by the UE 210 described in step S206 of FIG. In the example illustrated in FIG. 4, it is assumed that the target eNB 230 has selected RACH-less HO. Steps S408 to S411 shown in FIG. 4 are the same as steps S208 to S211 shown in FIG.

FIG. 5 is a sequence diagram illustrating another example of processing when the source eNB selects the HO method in the communication system according to the embodiment. In the communication system 100 according to the embodiment, for example, each step shown in FIG. 5 is executed. In the example illustrated in FIG. 5, the case where the source eNB 220 sets “Event X” in which the source eNB 220 selects the HO method of the UE 210 as the event type in the UE 210 will be described.

First, the source eNB 220 transmits an RRC reconfiguration specifying “Event X” as the event type to the UE 210 (step S501). Steps S502 to S505 shown in FIG. 5 are the same as steps S302 to S305 shown in FIG. Following step S505, the UE 210 transmits a measurement report including the TA value calculated in step S505 and indicating the measurement result of the radio quality to the source eNB 220 (step S506).

Next, the target eNB 230 selects a HO method performed by the UE 210 based on the TA value included in the measurement report received in step S506 (step S507). The selection of the HO method by the target eNB 230 is the same as the selection of the HO method by the UE 210 described in step S206 of FIG. In the example illustrated in FIG. 5, it is assumed that the target eNB 230 has selected legacy HO. Steps S508 to S512 shown in FIG. 5 are the same as steps S308 to S312 shown in FIG.

(Processing by UE according to Embodiment)
FIG. 6 is a flowchart illustrating an example of processing performed by the UE according to the embodiment. UE210 concerning embodiment performs each step shown, for example in FIG. First, UE210 sets the measurement cell and measurement item of an own terminal (step S601). The measurement cell of the own terminal includes the cell of the source eNB 220 and the cell of the target eNB 230 to which the UE 210 is connected. The measurement items include, for example, radio quality and TA value. The radio quality includes, for example, RSRP or RSRQ.

Next, the UE 210 performs measurement based on the measurement cell and measurement items set in step S601 (step S602). Next, UE210 judges whether the report conditions of a measurement result are satisfy | filled (step S603). The measurement result reporting condition is, for example, that the current timing is a measurement report opportunity and the measurement result of the radio quality satisfies a predetermined condition. The measurement report trigger is a timing set periodically (for example, every second). The predetermined condition of the measurement result of the radio quality is, for example, that the radio quality of the own cell measured in step S601 is below the threshold, and the radio quality of the adjacent cell measured in step S601 is above the threshold. The own cell is a cell of the source eNB 220, for example. An adjacent cell is a cell of the target eNB 230, for example.

In step S603, when the report condition is not satisfied (step S603: No), the UE 210 returns to step S602. When the reporting condition is satisfied (step S603: Yes), the UE 210 determines whether or not “Event X” is set as the event type for the own terminal (step S604). The determination in step S604 can be made based on the event type specified in the RRC reconfiguration received by the UE 210 from the source eNB 220, for example.

In step S604, when “Event X” is set as the event type for the terminal (step S604: Yes), the UE 210 calculates the TA value of the neighboring cell (step S605). This neighboring cell is a neighboring cell for which, for example, the radio quality has been determined to exceed the threshold in step S604, and is, for example, the cell of the target eNB 230.

Next, the UE 210 transmits a report signal including the TA value calculated in step S605 to the source eNB 220 (step S606), and returns to step S602. The report signal is, for example, the above-described measurement report. The report signal may include information indicating the event type set in the UE 210.

In step S604, when “Event X” is not set as the event type in the own terminal and “Event Y” is set (step S604: No), the UE 210 calculates the TA value of the neighboring cell ( Step S607). The calculation of the TA value in step S607 is the same as the calculation of the TA value in step S605.

Next, the UE 210 determines whether or not the deviation amount indicated by the TA value calculated in step S605 is equal to or less than a threshold value (step S608). When the amount of deviation is less than or equal to the threshold (step S608: Yes), the UE 210 transmits a report signal including a RACH less flag set to “on” to the source eNB 220 (step S609), and returns to step S602. When the amount of deviation is not less than or equal to the threshold (step S608: No), the UE 210 transmits a report signal including a RACH less flag with “off” set to the source eNB 220 (step S610), and returns to step S602.

6, the UE 210 can select the HO method based on the TA value of the neighboring cell and request HO based on the selected method to the source eNB 220 by a report signal. Moreover, if there is an instruction for HO by RRC reconfiguration from the source eNB 220, the UE 210 performs HO according to the instruction.

Further, in step S604, when both “Event X” and “Event Y” are set as the event type in the own terminal, UE 210 reports both the TA value and the selected HO method to source eNB 220. May be. In this case, for example, the UE 210 calculates a TA value, selects a HO method based on the calculated TA value, and outputs a report signal including the RACH less flag corresponding to the selected method and the calculated TA value. Transmit to source eNB 220.

(Setting process by source base station according to embodiment)
FIG. 7 is a flowchart illustrating an example of setting processing by the source base station according to the embodiment. The source eNB 220 according to the embodiment executes, for example, each step illustrated in FIG. 6 for the UE 210 connected to the own cell. Each step shown in FIG. 6 is executed when the UE 210 attaches to the source eNB 220 as an example. However, the trigger for executing each step shown in FIG. 6 is not limited to this, and can be various triggers.

First, the source eNB 220 determines whether or not the UE 210 is compatible with RACH-less HO (step S701). The determination in step S701 can be made based on, for example, UE capability (UE Capability) transmitted from the UE 210 to the source eNB 220. The transmission of the UE capability from the UE 210 to the source eNB 220 will be described later (see, for example, FIG. 15).

In step S701, when the UE 210 does not support RACH-less HO (step S701: No), the source eNB 220 does not set “Event X” and “Event Y” as event types in the UE 210 (step S702). In this case, the source eNB 220 sets an event type that is different from “Event X” and “Event Y” and corresponds to the UE 210 to the UE 210. Then, the source eNB 220 ends a series of processes.

In step S701, when the UE 210 supports RACH-less HO (step S701: Yes), the source eNB 220 determines whether to set the event type for RACH-less HO to the UE 210 (step S703). The event type for RACH-less HO is, for example, “Event X” or “Event Y”. The determination in step S703 can be performed based on, for example, an arbitrary setting parameter in the source eNB 220.

If it is determined in step S703 that the event type for RACH-less HO is not set in the UE 210 (step S703: No), the source eNB 220 proceeds to step S702. When it is determined that the event type for RACH-less HO is set in the UE 210 (step S703: Yes), the source eNB 220 proceeds to step S704. That is, the source eNB 220 sets, for example, the event type determined to be set in the UE 210 among “Event X” and “Event Y” in the UE 210 (step S704), and ends the series of processes.

In step S704, for example, the source eNB 220 sets the event type by transmitting the RRC reconfiguration specifying the event type determined to be set among “Event X” and “Event Y” to the UE 210, for example. In step S704, the source eNB 220 may set both “Event X” and “Event Y” in the UE 210. In this case, for example, the source eNB 220 sets an event type by transmitting an RRC reconfiguration specifying “Event X” and “Event Y” to the UE 210.

(HO processing by the source eNB according to the embodiment)
FIG. 8 is a flowchart illustrating an example of the HO process performed by the source eNB according to the embodiment. The source eNB 220 according to the embodiment executes the steps illustrated in FIG. 8 together with the steps illustrated in FIG. 7 for the UE 210 connected to the own cell. First, the source eNB 220 determines whether or not a report signal has been received from the UE 210 (step S801), and waits until a report signal is received (step S801: No loop). The report signal is, for example, the above-described measurement report.

In step S801, when the report signal is received (step S801: Yes), the source eNB 220 determines whether or not the event type set in the UE 210 that has transmitted the report signal is “Event Y” (step S802). The determination in step S802 can be made based on information included in the report signal received in step S801, for example. Further, the source eNB 220 may store information indicating an event type set in the UE 210 in each step shown in FIG. 7 in a memory. In this case, the source eNB 220 can make the determination in step S802 based on the information stored in the memory.

In step S802, when the event type set in the UE 210 is “Event Y” (step S802: Yes), the source eNB 220 acquires a RACH less flag included in the received report signal (step S803). Next, the source eNB 220 determines whether or not the value of the RACH less flag acquired in step S803 is “on” (step S804).

In step S804, when the value of the RACH less flag is “on” (step S804: Yes), the source eNB 220 performs RACH less HO to the target eNB 230 for the UE 210 (step S805), and ends the series of processes. . In step S805, for example, the source eNB 220 acquires the RACH-less HO parameter from the target eNB 230 by transmitting a handover request for requesting the RACH-less HO of the UE 210 to the target eNB 230. Then, the source eNB 220 performs RACH-less HO by transmitting the RRC reconfiguration including the acquired RACH-less HO parameter and instructing the RACH-less HO to the target eNB 230 to the UE 210.

In step S804, when the value of the RACH less flag is not “on” (step S804: No), the source eNB 220 performs legacy HO to the target eNB 230 for the UE 210 (step S806), and ends a series of processes. In step S806, for example, the source eNB 220 transmits a handover request requesting legacy HO of the UE 210 to the target eNB 230, and obtains a response (Ack) from the target eNB 230. And source eNB220 implements legacy HO by transmitting RRC reconfiguration which instruct | indicates legacy HO to target eNB230 to UE210.

In step S802, when the event type set in the UE 210 is not “Event Y” but “Event X” (step S802: No), the source eNB 220 proceeds to step S807. That is, the source eNB 220 acquires the TA value included in the received report signal (step S807). Next, the source eNB 220 determines whether or not the deviation amount indicated by the TA value acquired in step S807 is equal to or less than a threshold value (step S808).

In step S808, when the deviation amount indicated by the acquired TA value is equal to or less than the threshold (step S808: Yes), the source eNB 220 performs RACH-less HO to the target eNB 230 for the UE 210 (step S809), The process ends. The implementation of RACH-less HO in step S809 is the same as the implementation of RACH-less HO in step S805.

In step S808, when the deviation amount indicated by the acquired TA value is not less than or equal to the threshold (step S808: No), the source eNB 220 performs legacy HO to the target eNB 230 for the UE 210 (step S810), and performs a series of processes. finish. The implementation of legacy HO in step S810 is the same as the implementation of legacy HO in step S806.

Also, when both “Event X” and “Event Y” are set in the UE 210, the source eNB 220 selects the HO method based on the TA value included in the report signal, for example. Alternatively, in this case, the source eNB 220 selects the HO method based on the RACH less flag included in the report signal. Alternatively, in this case, the source eNB 220 selects the HO method based on both the TA value and the RACH less flag included in the report signal.

(UE according to the embodiment)
FIG. 9 is a diagram illustrating an example of the UE according to the embodiment. For example, as illustrated in FIG. 9, the UE 210 according to the embodiment includes an antenna 901, an RF processing unit 910, a PHY / MAC processing unit 920, a control information setting unit 930, a user signal processing unit 940, an application, And a processing unit 950.

The antenna 901 receives a signal wirelessly transmitted from another wireless communication device (for example, the source eNB 220 or the target eNB 230), and outputs the received signal to the RF processing unit 910. In addition, the antenna 901 wirelessly transmits the signal output from the RF processing unit 910 to another wireless communication device.

The RF processing unit 910 performs an RF reception process on the signal output from the antenna 901. RF is an abbreviation for Radio Frequency. The RF reception processing by the RF processing unit 910 includes, for example, amplification, frequency conversion from the RF band to the baseband, conversion from an analog signal to a digital signal, and the like. The RF processing unit 910 outputs the signal subjected to the RF reception processing to the PHY / MAC processing unit 920.

Also, the RF processing unit 910 performs RF transmission processing on each signal output from the PHY / MAC processing unit 920. The RF transmission processing by the RF processing unit 910 includes, for example, conversion from a digital signal to an analog signal, frequency conversion from a baseband to an RF band, amplification, and the like. The RF processing unit 910 outputs the signal subjected to the RF transmission process to the antenna 901.

The PHY / MAC processing unit 920 performs physical layer (PHY) and MAC layer processing on the signal output from the RF processing unit 910. MAC is an abbreviation for Media Access Control (Media Access Control). Also, the PHY / MAC processing unit 920 outputs a control signal (C-Plane signal) among signals obtained by processing of the physical layer and the MAC layer to the control information setting unit 930. Also, the PHY / MAC processing unit 920 outputs a user signal (U-Plane signal) among signals obtained by processing of the physical layer and the MAC layer to the user signal processing unit 940.

Also, the PHY / MAC processing unit 920 performs MAC layer and physical layer processing on the control signal (C-Plane signal) output from the control information setting unit 930. The PHY / MAC processing unit 920 performs MAC layer and physical layer processing on the user signal (U-Plane signal) output from the user signal processing unit 940. Then, the PHY / MAC processing unit 920 outputs a signal obtained by processing the MAC layer and the physical layer to the RF processing unit 910.

The control information setting unit 930 performs processing based on the control signal output from the PHY / MAC processing unit 920, and outputs a control signal obtained by processing based on the control signal to the application processing unit 950. Further, the control information setting unit 930 performs processing based on the control signal output from the application processing unit 950 and outputs a control signal obtained by processing based on the control signal to the PHY / MAC processing unit 920.

For example, the control information setting unit 930 includes a measurement control unit 931, a TA measurement unit 932, and a call processing control unit 933. The measurement control unit 931 performs processing related to the measurement report transmitted by the UE 210. For example, the measurement control unit 931 acquires the RRC reconfiguration from the source eNB 220 included in the signal output from the PHY / MAC processing unit 920.

Then, when the acquired RRC reconfiguration specifies an event type related to TA measurement, the measurement control unit 931 instructs the TA measurement unit 932 to perform TA measurement, and displays the TA measurement result (TA value). Obtained from the TA measurement unit 932. The event type related to the TA measurement is, for example, “Event X” or “Event Y” described above.

When the RRC reconfiguration from the source eNB 220 specifies “Event X”, the control information setting unit 930 selects the HO method based on the TA value acquired by the measurement control unit 931. Then, the control information setting unit 930 outputs a measurement report including a RACH less flag indicating the selection result of the HO method to the PHY / MAC processing unit 920. In addition, when the RRC reconfiguration from the source eNB 220 designates “Event Y”, the control information setting unit 930 sends a measurement report including the TA value acquired by the measurement control unit 931 to the PHY / MAC processing unit 920. Output to.

The TA measurement unit 932 performs TA measurement in accordance with an instruction from the measurement control unit 931 and outputs a TA measurement result (TA value) to the measurement control unit 931. Further, the TA measurement unit 932 performs TA measurement in accordance with an instruction from the call processing control unit 933 and outputs a TA measurement result (TA value) to the call processing control unit 933. The TA measurement by the TA measurement unit 932 can be performed based on the timing of each reference signal in the own cell and the adjacent cell included in the control signal output from the PHY / MAC processing unit 920, for example. TA measurement (TA value calculation) by the TA measurement unit 932 will be described later.

The call processing control unit 933 controls call processing in the UE 210. For example, the call processing control unit 933 controls call processing in accordance with control from the application processing unit 950. In addition, for example, when controlling the RACH procedure by the UE 210, the call processing control unit 933 instructs the TA measurement unit 932 to perform TA measurement, and acquires the TA measurement result (TA value) from the TA measurement unit 932. May be. Further, the call processing control unit 933 may acquire the result of the TA measurement by the TA measurement unit 932 via the measurement control unit 931. Then, the call processing control unit 933 controls the RACH procedure using the acquired TA measurement result.

Further, the control information setting unit 930 may further include a radio quality measurement unit that measures radio quality for each cell around the UE 210. In this case, the control information setting unit 930 generates a measurement report indicating the radio quality measured by the radio quality measurement unit, and outputs the generated measurement report to the PHY / MAC processing unit 920.

The user signal processing unit 940 performs processing related to the user signal (U-Plane). For example, the user signal processing unit 940 includes an IP processing unit 941. The IP processing unit 941 performs IP processing on the user signal output from the PHY / MAC processing unit 920, and outputs the user signal subjected to the IP processing to the application processing unit 950. IP is an abbreviation for Internet Protocol. Also, the IP processing unit 941 performs IP processing of the user signal output from the application processing unit 950 and outputs the user signal subjected to the IP processing to the PHY / MAC processing unit 920.

Application processing unit 950 performs application processing executed in UE 210. For example, the application processing unit 950 performs application processing based on the control signal output from the control information setting unit 930 and the user signal output from the user signal processing unit 940. In addition, the application processing unit 950 outputs an uplink control signal obtained by the application processing to the control information setting unit 930. Further, the application processing unit 950 outputs an uplink user signal obtained by the application processing to the user signal processing unit 940.

The calculation unit 111 of the terminal 110 illustrated in FIG. 1 can be realized by the TA measurement unit 932, for example. The transmission unit 112 of the terminal 110 illustrated in FIG. 1 can be realized by the antenna 901, the RF processing unit 910, and the PHY / MAC processing unit 920, for example. The control unit 113 illustrated in FIG. 1 can be realized by the antenna 901, the RF processing unit 910, the PHY / MAC processing unit 920, and the call processing control unit 933, for example.

(Hardware configuration of UE according to embodiment)
FIG. 10 is a diagram illustrating an example of a hardware configuration of the UE according to the embodiment. The UE 210 illustrated in FIG. 9 can be realized by the wireless communication apparatus 1000, for example. 10 includes a processor 1001, a memory 1002, a user interface 1003, and a wireless communication interface 1004. The processor 1001, the memory 1002, the user interface 1003, and the wireless communication interface 1004 are connected by a bus 1009, for example. Further, the UE 210 may include a battery that supplies power to the processor 1001, the memory 1002, the user interface 1003, and the wireless communication interface 1004.

The processor 1001 is a circuit that performs signal processing, for example, a CPU (Central Processing Unit) that controls the entire wireless communication apparatus 1000. The memory 1002 includes, for example, a main memory and an auxiliary memory. The main memory is, for example, a RAM (Random Access Memory). The main memory is used as a work area for the processor 1001. The auxiliary memory is a non-volatile memory such as a magnetic disk or a flash memory. Various programs for operating the wireless communication apparatus 1000 are stored in the auxiliary memory. The program stored in the auxiliary memory is loaded into the main memory and executed by the processor 1001.

Further, the processor 1001 and the memory 1002 may be realized by a digital circuit such as an FPGA (Field Programmable Gate Array) or a DSP (Digital Signal Processor).

The user interface 1003 includes, for example, an input device that receives an operation input from the user, an output device that outputs information to the user, and the like. The input device can be realized by, for example, a key (for example, a keyboard), a microphone, a remote controller, or the like. The output device can be realized by, for example, a display or a speaker. Further, an input device and an output device may be realized by a touch panel or the like. The user interface 1003 is controlled by the processor 1001, for example.

The wireless communication interface 1004 is a communication interface that communicates with the outside of the wireless communication apparatus 1000 (for example, the source eNB 220 and the target eNB 230) wirelessly. The wireless communication interface 1004 is controlled by the processor 1001, for example.

The antenna 901 and the RF processing unit 910 illustrated in FIG. 9 are included in the wireless communication interface 1004, for example. The PHY / MAC processing unit 920, the control information setting unit 930, the user signal processing unit 940, and the application processing unit 950 illustrated in FIG. 9 can be realized by the processor 1001 and the memory 1002, for example.

(ENB according to the embodiment)
FIG. 11 is a diagram illustrating an example of the eNB according to the embodiment. Each of the source eNB 220 and the target eNB 230 according to the embodiment can be realized by the eNB 1100 illustrated in FIG. 11, for example. The eNB 1100 includes, for example, an antenna 1101, an RF processing unit 1110, a PHY / MAC processing unit 1120, a control information setting unit 1130, a user signal processing unit 1140, and a wired processing unit 1150.

The antenna 1101 receives a signal wirelessly transmitted from another wireless communication device (for example, the UE 210), and outputs the received signal to the RF processing unit 1110. The antenna 1101 wirelessly transmits the signal output from the RF processing unit 1110 to another wireless communication device.

The RF processing unit 1110 performs RF reception processing on the signal output from the antenna 1101. The RF reception processing by the RF processing unit 1110 includes, for example, amplification, frequency conversion from the RF band to the baseband, conversion from an analog signal to a digital signal, and the like. The RF processing unit 1110 outputs the signal subjected to the RF reception processing to the PHY / MAC processing unit 1120.

Also, the RF processing unit 1110 performs RF transmission processing on each signal output from the PHY / MAC processing unit 1120. The RF transmission processing by the RF processing unit 1110 includes, for example, conversion from a digital signal to an analog signal, frequency conversion from a baseband to an RF band, amplification, and the like. The RF processing unit 1110 outputs the signal subjected to the RF transmission process to the antenna 1101.

The PHY / MAC processing unit 1120 performs physical layer (PHY) and MAC layer processing on the signal output from the RF processing unit 1110. Also, the PHY / MAC processing unit 1120 outputs a control signal (C-Plane signal) among the signals obtained by the physical layer and MAC layer processing to the control information setting unit 1130. Also, the PHY / MAC processing unit 1120 outputs a user signal (U-Plane signal) out of signals obtained by physical layer and MAC layer processing to the user signal processing unit 1140.

Also, the PHY / MAC processing unit 1120 performs MAC layer and physical layer processing on the control signal (C-Plane signal) output from the control information setting unit 1130. Also, the PHY / MAC processing unit 1120 performs MAC layer and physical layer processing on the user signal (U-Plane signal) output from the user signal processing unit 1140. Then, the PHY / MAC processing unit 1120 outputs a signal obtained by processing the MAC layer and the physical layer to the RF processing unit 1110.

The control information setting unit 1130 performs processing based on the control signal output from the PHY / MAC processing unit 1120 and outputs the control signal obtained by the processing based on the control signal to the wired processing unit 1150. The control information setting unit 1130 performs processing based on the control signal output from the wired processing unit 1150, and outputs the control signal obtained by the processing based on the control signal to the PHY / MAC processing unit 1120.

For example, the control information setting unit 1130 includes a measurement control unit 1131 and a handover control unit 1132. The measurement control unit 1131 controls measurement and reporting of radio quality in the UE 210. For example, the above-described event type setting and report signal reception are performed by the measurement control unit 1131. The handover control unit 1132 performs HO control in the UE 210. For example, the handover control unit 1132 controls the determination of the implementation of HO and the determination of the HO method based on the report signal from the UE 210 described above based on the reception result of the report signal by the measurement control unit 1131.

The user signal processing unit 1140 performs processing related to the user signal (U-Plane). For example, the user signal processing unit 1140 includes an IP processing unit 1141. The IP processing unit 1141 performs IP processing on the user signal output from the PHY / MAC processing unit 1120, and outputs the user signal subjected to the IP processing to the wired processing unit 1150. The IP processing unit 1141 performs IP processing on the user signal output from the wired processing unit 1150 and outputs the user signal subjected to the IP processing to the PHY / MAC processing unit 1120.

The wired processing unit 1150 performs communication with a higher-level device of the core network to which the local station is connected, and communication between base stations by wire between the eNB 1100 and a different eNB. The host device of the core network includes, for example, MME, S-GW, P-GW and the like. MME is an abbreviation for Mobility Management Entity. S-GW is an abbreviation for Serving-Gateway. P-GW is an abbreviation for Packet data network-Gateway.

For example, transmission to the network side of the user signal received by the source eNB 220 from the UE 210 is executed by the wired processing unit 1150. Also, reception of a downlink user signal from the network side to the UE 210 is executed by the wired processing unit 1150. In addition, transmission / reception of the handover request to the adjacent base station and the RACH-less HO parameter described above is executed by communication between base stations of the wired processing unit 1150.

The receiving unit 121 of the first base station 120 shown in FIG. 1 can be realized by the antenna 1101, the RF processing unit 1110, and the PHY / MAC processing unit 1120, for example. The control unit 122 of the first base station 120 illustrated in FIG. 1 can be realized by the antenna 1101, the RF processing unit 1110, the PHY / MAC processing unit 1120, and the handover control unit 1132, for example.

(Hardware configuration of eNB according to embodiment)
FIG. 12 is a diagram illustrating an example of a hardware configuration of the eNB according to the embodiment. The eNB 1100 illustrated in FIG. 11 can be realized by the wireless communication device 1200 illustrated in FIG. 12, for example. The wireless communication device 1200 includes a processor 1201, a memory 1202, a wireless communication interface 1203, and a wired communication interface 1204. The processor 1201, the memory 1202, the wireless communication interface 1203, and the wired communication interface 1204 are connected by a bus 1209, for example.

The processor 1201 is a circuit that performs signal processing, and is, for example, a CPU that controls the entire wireless communication apparatus 1200. The memory 1202 includes, for example, a main memory and an auxiliary memory. The main memory is, for example, a RAM. The main memory is used as a work area for the processor 1201. The auxiliary memory is, for example, a nonvolatile memory such as a magnetic disk, an optical disk, or a flash memory. Various programs for operating the wireless communication device 1200 are stored in the auxiliary memory. The program stored in the auxiliary memory is loaded into the main memory and executed by the processor 1201. Further, the processor 1201 and the memory 1202 may be realized by a digital circuit such as an FPGA or a DSP.

The wireless communication interface 1203 is a communication interface that communicates with the outside of the wireless communication apparatus 1200 (for example, the UE 210) wirelessly. The wireless communication interface 1203 is controlled by the processor 1201. The wired communication interface 1204 is a communication interface that performs communication with the outside of the wireless communication device 1200 (for example, an adjacent base station or a higher-level device of the core network) by wire. The wired communication interface 1204 is controlled by the processor 1201, for example.

The antenna 1101 and the RF processing unit 1110 illustrated in FIG. 11 are included in the wireless communication interface 1203, for example. The PHY / MAC processing unit 1120, the control information setting unit 1130, and the user signal processing unit 1140 illustrated in FIG. 11 can be realized by the processor 1201 and the memory 1202, for example. The wired processing unit 1150 illustrated in FIG. 11 is included in the wired communication interface 1204, for example.

(Definition of event type according to the embodiment)
FIG. 13 is a diagram illustrating an example of an event type definition according to the embodiment. The information element 1300 shown in FIG. 13 is a ReportConfigEUTRA information element (information element) of the RRC message. It is represented by 1. ASN. 1 is an abbreviation for Abstract Syntax Notation One. The information element 1300 is an NR information element in which the definition of “Event X” is added to the ReportConfigEUTRA information element in 3GPP TS36.331 as an example. NR is an abbreviation for New Radio.

That is, the item 1301 (eventX) of the information element 1300 indicates the definition of “Event X” described above. Although the definition of “Event X” has been described, “Event Y” can be similarly defined in the information element 1300. Thereby, the source eNB 220 can set “Event X” and “Event Y” in the UE 210 by, for example, the RRC reconfiguration described above.

(Measurement report according to the embodiment)
FIG. 14 is a diagram illustrating an example of a measurement report according to the embodiment. The information element 1400 shown in FIG. 14 is a MeasResultEUTRA in the MeasResults information element. It is represented by 1. As an example, the information element 1400 is obtained by adding a TA value definition to the MeasResults information element in 3GPP TS36.331.

That is, the item 1401 (taResult) of the information element 1400 indicates the definition of the TA value described above. Although the definition of the TA value has been described, the RACH less flag can be similarly defined in the information element 1400. Thereby, UE210 can transmit the report signal (measurement report) containing the TA value mentioned above, or a RACH less flag, for example to source eNB220.

(UE capability inquiry procedure in the communication system according to the embodiment)
FIG. 15 is a sequence diagram illustrating an example of a UE capability inquiry procedure in the communication system according to the embodiment. For example, each step shown in FIG. 15 is executed as a UE capability inquiry procedure between the UE 210 and the source eNB 220. Each step shown in FIG. 15 is executed when the UE 210 attaches to the source eNB 220 as an example. However, the trigger for executing each step shown in FIG. 15 is not limited to this, and can be various triggers.

First, the source eNB 220 transmits a UE capability inquiry (Enquiry) signal for inquiring whether or not it supports RACH-less HO to the UE 210 (step S1501). Next, the UE 210 transmits UE capability information indicating whether or not the terminal itself supports RACH-less HO to the source eNB 220 (step S1502). According to the UE capability inquiry procedure shown in FIG. 15, the source eNB 220 determines whether or not the UE 210 supports RACH-less HO. When the UE 210 supports RACH-less HO, the source eNB 220 controls the RACH-less HO of the UE 210. It can be carried out.

(Calculation of TA value of target eNB by UE according to embodiment)
FIG. 16 is a sequence diagram illustrating an example of calculating the TA value of the target eNB by the UE according to the embodiment. When the UE 210 is connected to the source eNB 220, the UE 210 calculates the TA value of the target eNB 230, for example, by the process shown in FIG.

The source eNB 220 broadcasts a reference signal periodically to surrounding UEs including the UE 210 (step S1601). Similarly, the target eNB 230 broadcasts a reference signal periodically to surrounding UEs including the UE 210 (step S1602).

UE 210 detects the reception timing of each reference signal from source eNB 220 and target eNB 230 transmitted in steps S1601 and S1602 (step S1603). For example, the UE 210 detects the timing at which a signal having a predetermined pattern corresponding to the reference signal in the radio signal from the source eNB 220 is detected as the reception timing of the reference signal from the source eNB 220. Moreover, UE210 detects the timing which detected the signal of the predetermined pattern corresponding to a reference signal in the radio signal from target eNB230 as a reception timing of the reference signal from target eNB230.

Next, the UE 210 calculates the TA value of the target eNB 230 based on the difference between the reception timings detected in step S1603 (step S1604). For example, the UE 210 divides the difference between the reception timings detected in step S1603 by the time of one slot, sets the remainder as a reception time difference, and calculates the TA value of the target eNB 230 based on the calculated reception time difference.

The case where the transmission timing of the UE 210 to the source eNB 220 matches the reference timing of the source eNB 220 and the TA value of the source eNB 220 in the UE 210 is “0” will be described. In this case, the UE 210 derives the TA value corresponding to the calculated reception time difference as the TA value of the target eNB 230. That is, if the UE 210 has adjusted the transmission timing for the source eNB 220, the UE 210 can calculate the reception time difference based on each reception timing detected in step S1603 as the TA value of the target eNB 230.

Next, a case where the transmission timing of the UE 210 to the source eNB 220 does not match the reference timing of the source eNB 220 and the TA value of the source eNB 220 in the UE 210 is not “0” will be described. In this case, the UE 210 corrects the calculated reception time difference with the shift amount indicated by the TA value of the source eNB 220, and derives the TA value corresponding to the corrected reception time difference as the TA value of the target eNB 230.

As shown in FIG. 16, the UE 210 can calculate the TA value of the target eNB 230 based on the difference between the reception timing of the reference signal from the target eNB 230 and the reception timing of the reference signal from the source eNB 220. However, the calculation method of the TA value of the target eNB 230 by the UE 210 is not limited to the method illustrated in FIG. 16, and various calculation methods can be used.

Thus, according to the embodiment, the first handover method and the second handover method are based on the amount of deviation between the radio signal transmission timing of the terminal and the reference timing of the handover destination cell of the terminal. Can be switched. As a result, the first handover method and the second handover method can be switched according to the possibility of the successful handover of the terminal to the second cell by the second handover method. For this reason, the time taken for the handover can be shortened.

The amount of deviation between the terminal radio signal transmission timing and the terminal handover destination cell reference timing is, for example, the TA value of the target eNB 230 in the UE 210 described above. The first handover method is a handover method including a random access procedure, and an example is the above-described RACH-less HO. The second handover method is a handover method that does not include at least a part of the random access procedure, and an example is the above-described legacy HO.

Also, the first state in which the handover source base station selects the handover method and the second state in which the terminal selects the handover method may be switchable. As an example, the first state is a state in which the above-described “Event X” is set in the UE 210. As an example, the second state is a state in which “Event Y” described above is set in the UE 210.

As described above, according to the base station, the terminal, the communication system, and the communication method, the time required for the handover can be shortened.

For example, in order to shorten the time required for HO, RACH less HO that performs HO by omitting the RACH procedure by allocating resources in advance is scheduled to be introduced. In RACH-less HO, there is no timing for detecting a TA mismatch between the UE and the target eNB, so reconnection due to a TA mismatch may occur when the UE moves to the target eNB. When reconnection occurs, the time required for HO becomes longer due to the reconnection procedure.

Further, in 3GPP, T304 (50 [ms] or more) is defined as a UE timer used for determining to stop HO. T304 is set by eNB, for example. Further, for example, in 3GPP R2-166473, a process of setting a timer shorter than T304 and switching from RACH-less HO to legacy HO (HO performing RACH procedure) when the short timer expires has been proposed. However, even in this proposed process, when the UE cannot connect to the target eNB due to a TA mismatch, there is a problem that the RACH-less HO failure is repeated until the timer expires, and the time required for HO becomes long.

On the other hand, according to the above-described embodiment, a parameter related to RACH-less HO can be acquired from a downlink signal (for example, a reference signal) of the target eNB and can be used for selection of RACH-less HO. . That is, the HO method can be selected based on the timing information (for example, TA value) of the target eNB.

As a result, since the RACH-less HO or the legacy HO can be switched before the failure of the RACH-less HO, the failure of the RACH-less HO can be suppressed and the time taken for the HO can be shortened. it can. By shortening the time required for HO, for example, the time for which data communication of the UE is disconnected can be shortened. Further, for example, the amount of processing for HO in the UE and the target eNB can be reduced.

DESCRIPTION OF SYMBOLS 100 Communication system 110 Terminal 111 Calculation part 112 Transmission part 113,122 Control part 120 1st base station 121 Reception part 130 2nd base station 210 UE
220 source eNB
230 Target eNB
901, 1101 Antenna 910, 1110 RF processing unit 920, 1120 PHY / MAC processing unit 930, 1130 Control information setting unit 931, 1131 Measurement control unit 932 TA measurement unit 933 Call processing control unit 940, 1140 User signal processing unit 941, 1141 IP processing unit 950 Application processing unit 1000, 1200 Wireless communication device 1001, 1201 Processor 1002, 1202 Memory 1003 User interface 1004, 1203 Wireless communication interface 1009, 1209 Bus 1100 eNB
1132 Handover control unit 1150 Wired processing unit 1204 Wired communication interface 1300, 1400 Information element 1301, 1401 Item

Claims (15)

A receiving unit that receives, from the terminal, a value indicating the amount of deviation between a radio signal transmission timing of a terminal connected to the first cell of the local station and a reference timing of a second cell different from the first cell When,
The first handover method including a random access procedure and the second handover method not including at least a part of the random access procedure, and the handover method selected based on the value received by the receiving unit. A control unit that performs control to switch the connection destination of the terminal to the second cell;
A base station comprising: The base station according to claim 1, wherein the value indicating the amount of deviation is a TA (Timing Advance) value. The control unit selects the second handover method when the amount of deviation indicated by the value is equal to or less than a predetermined amount, and selects the first handover method when the amount of deviation indicated by the value is greater than the predetermined amount. The base station according to claim 1 or 2, characterized in that The terminal transmits a radio signal including a cyclic prefix to the second cell when the connection destination of the terminal is switched to the second cell,
The control unit selects the second handover method when the amount of deviation indicated by the value is less than or equal to a predetermined amount based on the length of the cyclic prefix, and when the amount of deviation indicated by the value is greater than the predetermined amount Selects the first handover method,
The base station according to claim 3. A base station capable of switching between a first state and a second state,
In the first state, the receiving unit receives a value indicating the amount of deviation from the terminal, and the control unit connects the terminal by a handover method selected based on the value received by the receiving unit. Control to switch the second cell to the second cell,
In the second state, the receiving unit receives, from the terminal, information indicating a handover method selected by the terminal based on a value indicating the shift amount among the first handover method and the second handover method, The control unit performs control to switch the connection destination of the terminal to the second cell by a handover method indicated by the information received by the reception unit;
The base station according to any one of claims 1 to 4, wherein: A calculation unit that calculates a value indicating the amount of deviation between the transmission timing of the radio signal of the own terminal and the reference timing of the second cell different from the first cell to which the own terminal is connected;
A transmission unit for transmitting the value calculated by the calculation unit to the base station of the first cell;
The base station selects the first handover method including a random access procedure and the second handover method not including at least a part of the random access procedure based on the value transmitted by the transmission unit. A control unit that performs control to switch the connection destination of the terminal to the second cell by a method;
A terminal comprising: A terminal capable of switching between a first state and a second state,
In the first state, the transmission unit transmits the value calculated by the calculation unit to the base station, and the control unit selects the base station based on the value transmitted by the transmission unit. In this way, control is performed to switch the connection destination of the terminal to the second cell,
In the second state, the transmission unit transmits information indicating a handover method selected based on the value calculated by the calculation unit among the first handover method and the second handover method to the base of the first cell. The control unit performs control to switch the connection destination of the terminal to the second cell by the selected handover method according to control from the base station,
The terminal according to claim 6. A terminal that transmits a value indicating the amount of deviation between the transmission timing of the radio signal of the own terminal and the reference timing of the second cell different from the first cell to which the own terminal is connected;
The first cell base station, the first handover method including a random access procedure, and the second handover method not including at least a part of the random access procedure, and transmitted by the terminal. A base station that performs control to switch the connection destination of the terminal to the second cell by a handover method selected based on a value;
A communication system comprising: The base station
A value indicating the amount of deviation between the transmission timing of the radio signal of the terminal connected to the first cell of the local station and the reference timing of the second cell different from the first cell is received from the terminal,
The first handover method including a random access procedure, the second handover method not including at least a part of the random access procedure, and the connection method of the terminal by the handover method selected based on the received value Control to switch to the second cell;
A communication method characterized by the above. The device
Calculate a value indicating the amount of deviation between the transmission timing of the radio signal of the own terminal and the reference timing of the second cell different from the first cell to which the own terminal is connected,
Transmitting the calculated value to the base station of the first cell;
The first handover method including a random access procedure, and the second handover method not including at least a part of the random access procedure, and the method selected by the base station based on the transmitted value. Control to switch the connection destination to the second cell;
A communication method characterized by the above. Of the first handover method including a random access procedure and the second handover method not including at least a part of the random access procedure, transmission of a radio signal of a terminal connected to the first cell of the own station A receiving unit that receives from the terminal information indicating a handover method selected by the terminal based on a value indicating a shift amount between a timing and a reference timing of a second cell different from the first cell;
A control unit that performs control to switch the connection destination of the terminal to the second cell by a handover method indicated by the information received by the reception unit;
A base station comprising: A calculation unit that calculates a value indicating the amount of deviation between the transmission timing of the radio signal of the own terminal and the reference timing of the second cell different from the first cell to which the own terminal is connected;
A handover method selected based on the value calculated by the calculation unit among a first handover method including a random access procedure and a second handover method not including at least a part of the random access procedure is shown. A transmitter for transmitting information to the base station of the first cell;
A control unit that performs control to switch the connection destination of the terminal to the second cell by the selected handover method according to the control from the base station;
A terminal comprising: Of the first handover method including the random access procedure and the second handover method not including at least a part of the random access procedure, the transmission timing of the radio signal of the own terminal and the own terminal are connected A terminal that transmits information indicating a handover method selected based on a value indicating a deviation amount between a reference timing of a second cell different from the first cell, and
A base station of the first cell that performs control to switch the connection destination of the terminal to the second cell by a handover method indicated by the information transmitted by the terminal;
A communication system comprising: The base station
Of the first handover method including a random access procedure and the second handover method not including at least a part of the random access procedure, transmission of a radio signal of a terminal connected to the first cell of the own station Receiving from the terminal information indicating a handover method selected by the terminal based on a value indicating a deviation amount between a timing and a reference timing of a second cell different from the first cell;
Control to switch the connection destination of the terminal to the second cell by the handover method indicated by the received information,
A communication method characterized by the above. The device
Calculate a value indicating the amount of deviation between the transmission timing of the radio signal of the own terminal and the reference timing of the second cell different from the first cell to which the own terminal is connected,
Information indicating a handover method selected based on the calculated value among a first handover method including a random access procedure and a second handover method not including at least a part of the random access procedure. To the cell base station,
In accordance with control from the base station, control to switch the connection destination of its own terminal to the second cell by the selected handover method,
A communication method characterized by the above.

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