JP5102649B2 - Wireless terminal and cell selection method - Google Patents

Description

  The present invention relates to a radio terminal and a cell selection method for selecting a registered cell, which is a cell for performing location registration, in a radio communication system having a plurality of cells.

  Conventionally, a radio terminal measures the reception quality of a signal received from a radio base station (cell) (radio quality in a radio section) and selects a cell (hereinafter referred to as a registered cell) where the radio terminal performs location registration according to the radio quality. The technology to do is known.

  Specifically, in a radio communication system, a radio base station manages one or a plurality of cells. The wireless terminal performs location registration in one of a plurality of cells. A cell in which a wireless terminal has already performed location registration is referred to as a serving cell. A cell provided in the vicinity of the serving cell is referred to as a peripheral cell. The wireless terminal compares the reception qualities of signals received from the serving cell and the neighboring cells, and selects an appropriate cell as a registered cell from the plurality of cells.

  By the way, when a registered cell is simply selected according to reception quality, a case is assumed in which a cell provided on the side opposite to the traveling direction of the wireless terminal is selected as a registered cell. In such a case, the reception quality of a signal received from a cell newly selected as a registered cell immediately deteriorates. Therefore, reselection of registered cells may occur frequently.

On the other hand, a technique for selecting a registered cell based on a frequency shift amount (Doppler frequency) in addition to reception quality has been proposed (for example, Patent Document 1). Specifically, the frequency of the signal received by the wireless terminal from the cell provided in the traveling direction of the wireless terminal becomes higher as the wireless terminal moves. On the other hand, the frequency of the signal received by the wireless terminal from the cell provided on the side opposite to the traveling direction of the wireless terminal decreases as the wireless terminal moves. Therefore, in selecting a registered cell, a cell having the best reception quality is selected from cells whose frequency deviation is higher than a predetermined threshold.
JP 2002-204182 A

  By the way, in general, in order to prevent frequent registration cell selection, registration cell selection is performed when a condition for selecting a registration cell over a predetermined period is satisfied. Is called.

  Here, the predetermined period is a fixed length regardless of the moving speed of the wireless terminal. On the other hand, in the case where the wireless terminal is moving at high speed, the cell with the best reception quality frequently fluctuates at the timing when the registered cell is selected. Accordingly, there may be a case where the timing of selecting the registered cell cannot follow the change in the cell having the best reception quality, and the optimum cell is not selected as the registered cell.

  On the other hand, in the case where the wireless terminal is moving at a low speed, the cell having the best reception quality at the timing of selecting the registered cell is the registered cell even if the frequency deviation amount is lower than the predetermined threshold. Is preferably selected. In other words, the condition that “the frequency deviation amount is higher than the predetermined threshold value” inhibits the selection of the optimum cell.

  Therefore, the present invention has been made to solve the above-described problem, and an object of the present invention is to provide a radio terminal and a cell selection method capable of selecting an optimum cell as a registered cell.

  The wireless terminal according to the first feature selects a registered cell that is a cell for performing location registration in a wireless communication system having a plurality of cells. The wireless terminal receives from a serving cell reception quality which is a reception quality of a signal received from a serving cell which is a cell where the location registration has already been performed, and a neighboring cell which is a cell provided around the serving cell. A measurement unit (reception quality measurement unit 12) that measures reception quality of neighboring cells that is reception quality of a signal to be received; and a serving cell shift amount that is a frequency shift amount of a signal received from the serving cell; An acquisition unit (frequency shift amount acquisition unit 13) that acquires a shift amount of a peripheral cell that is a shift amount of a frequency of a signal received from the peripheral cell, and a moving speed that is a speed at which the wireless terminal moves. Based on the detection unit (movement speed detection unit 14) to detect, the serving cell reception quality, the neighboring cell reception quality, the serving cell deviation amount, the neighboring cell deviation amount, and the movement speed, the registration Cell selection part for selecting cells (cell selection 154) and a.

  According to this feature, the wireless terminal selects a registered cell based on the moving speed in addition to the reception quality and the frequency shift amount. Therefore, in the case where the wireless terminal is moving at a high speed, the timing of selecting a registered cell can be made to follow the fluctuation of the cell with the best reception quality. On the other hand, in the case where the wireless terminal is moving at a low speed, even if the frequency deviation amount is a cell lower than a predetermined threshold, a cell having good reception quality at the timing of selecting a registered cell is registered. Can be selected. That is, an optimum cell can be selected as a registered cell.

  In the first feature, the cell selection unit determines whether a selection condition for selecting the registered cell is satisfied based on the serving cell reception quality, the neighboring cell reception quality, and the moving speed. Determination unit (determination unit 155). The determination unit advances the timing at which the selection condition is satisfied when the movement speed is higher than a predetermined movement speed.

  In the first feature, the radio terminal determines whether a reception quality difference, which is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality, is smaller than a predetermined reception quality difference ( A start condition determination unit 151), a continuation condition determination unit (continuation condition determination unit 152) that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration, and the movement A continuation condition changing unit (condition changing unit 153) that shortens the predetermined duration when the speed is higher than a predetermined moving speed is further provided. The determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration.

  In the first feature, the radio terminal determines whether a reception quality difference, which is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality, is smaller than a predetermined reception quality difference ( A start condition determination unit 151), a continuation condition determination unit (continuation condition determination unit 152) that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration, and the movement The apparatus further includes a start condition changing unit (condition changing unit 153) that increases the predetermined reception quality difference when the speed is higher than the predetermined moving speed. The determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration.

  In the first feature, the wireless terminal includes a start condition determining unit that determines whether a reception quality difference, which is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality, is smaller than a predetermined reception quality difference; A continuation condition determination unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration, and when the movement speed is higher than a predetermined movement speed, and And a continuation condition changing unit that shortens the predetermined duration when the frequency shift amount is a positive value. The determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration.

  In the first feature, the wireless terminal includes a start condition determining unit that determines whether a reception quality difference, which is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality, is smaller than a predetermined reception quality difference; A continuation condition determination unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration, and when the movement speed is higher than a predetermined movement speed, and And a start condition changing unit that increases the predetermined reception quality difference when the frequency shift amount is a positive value. The determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration.

  In the first feature, the wireless terminal includes a start condition determining unit that determines whether a reception quality difference, which is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality, is smaller than a predetermined reception quality difference; A continuation condition determination unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration, and when the movement speed is higher than a predetermined movement speed, and And a continuation condition changing unit that extends the predetermined duration when the frequency shift amount is a negative value. The determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration.

  In the first feature, the wireless terminal includes a start condition determining unit that determines whether a reception quality difference, which is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality, is smaller than a predetermined reception quality difference; A continuation condition determination unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration, and when the movement speed is higher than a predetermined movement speed, and And a start condition changing unit that reduces the predetermined reception quality difference when the frequency shift amount is a negative value. The determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration.

  In the first feature, the cell selection unit performs a first selection process when the movement speed is higher than a predetermined movement speed, and performs a second selection process when the movement speed is lower than the predetermined movement speed. . The first selection process is a process of selecting the registered cell based on the reception quality from cells in which the frequency deviation amount is higher than a predetermined deviation amount. The second selection process is a process of selecting the registered cell based on the reception quality without considering the frequency shift amount.

  In the first feature, the first selection process selects the registered cell based on the reception quality from cells in which the frequency deviation amount is higher than the predetermined deviation amount over a certain period. It is processing.

  In the cell selection method according to the second feature, in a radio communication system having a plurality of cells, a radio cell selects a registration cell, which is a cell in which location registration is performed. The cell selection method includes: a serving cell reception quality which is a reception quality of a signal received by the wireless terminal from a serving cell which is a cell where the location registration has already been performed; and a cell provided around the serving cell. Measuring the reception quality of the neighboring cell, which is the reception quality of the signal received by the wireless terminal from the neighboring cell, and the shift amount of the frequency of the signal received by the wireless terminal from the serving cell. Step B for obtaining a serving cell deviation amount and a neighboring cell deviation amount that is a frequency deviation amount of a signal received by the wireless terminal from the neighboring cell, and a moving speed that is a speed at which the wireless terminal moves And detecting the registered cell based on the serving cell reception quality, the neighboring cell reception quality, the serving cell deviation amount, the neighboring cell deviation amount, and the moving speed. Including D

  ADVANTAGE OF THE INVENTION According to this invention, the radio | wireless terminal and cell selection method which enable selection of the optimal cell as a serving cell can be provided.

  Hereinafter, a wireless communication system according to an embodiment of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

  However, it should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Therefore, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

[First Embodiment]
(Configuration of wireless communication system)
Hereinafter, the configuration of the wireless communication system according to the first embodiment will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a wireless communication system according to the first embodiment.

  As illustrated in FIG. 1, the wireless communication system includes a wireless terminal 10 and a plurality of wireless base stations 20 (wireless base stations 20a to 20d).

  The wireless terminal 10 is a terminal such as a mobile phone or a PDA, and has a function of performing wireless communication with the wireless base station 20. The wireless terminal 10 performs location registration of its own terminal on the network side and performs wireless communication with the wireless base station 20.

  The radio base station 20 manages an area 21 composed of a single cell or a plurality of cells. The area 21 is a range where radio waves transmitted from the radio base station 20 reach.

  For example, the radio base station 20a manages the area 21a, and the radio base station 20b manages the area 21b. The radio base station 20c manages the area 21c, and the radio base station 20d manages the area 21d.

  It should be noted that “cell” is basically used as a term indicating an area where the wireless terminal 10 is located. It should also be noted that the “cell” may be used as a function for communicating with the wireless terminal 10.

  Hereinafter, a cell in which the wireless terminal 10 performs location registration is referred to as a registered cell. A cell in which the wireless terminal 10 has already registered its location is referred to as a serving cell. A cell provided in the vicinity of the serving cell is referred to as a peripheral cell.

  It should be noted that the first embodiment assumes a case where a registered cell is selected when the wireless terminal 10 moves from the point A toward the point B.

(Configuration of wireless terminal)
Hereinafter, the configuration of the wireless terminal according to the first embodiment will be described with reference to the drawings. FIG. 2 is a block diagram illustrating a configuration of the wireless terminal 10 according to the first embodiment.

  As illustrated in FIG. 2, the wireless terminal 10 includes a reception unit 11, a reception quality measurement unit 12, a frequency shift amount acquisition unit 13, a moving speed detection unit 14, a control unit 15, and a transmission unit 16. Have.

  The receiving unit 11 receives various signals from the radio base station 20d. The various signals are, for example, control signals such as pilot signals and data signals. Specifically, the receiving unit 11 receives a signal from the serving cell. The receiving unit 11 receives signals from neighboring cells.

  The reception quality measuring unit 12 measures the reception quality of the signal received from the serving cell (hereinafter, serving cell reception quality). The reception quality measurement unit 12 measures the reception quality of signals received from neighboring cells (hereinafter referred to as neighboring cell reception quality).

  The reception quality is, for example, SIR (Signal to Interference Ratio), SNR (Signal to Noise Ratio), SINR (Signal to Interference Noise Ratio), or the like.

  The frequency shift amount acquisition unit 13 acquires the frequency shift amount of the signal received from the serving cell (hereinafter referred to as the serving cell shift amount). Further, the reception quality measurement unit 12 acquires the frequency shift amount of the signal received from the neighbor cell (hereinafter, the neighbor cell shift amount).

  Here, it should be noted that the frequency shift amount of the signal received from the cell provided in the traveling direction of the radio terminal 10 increases as the radio terminal 10 moves. On the other hand, it should be noted that the frequency shift amount of the signal received from the cell provided on the side opposite to the traveling direction of the radio terminal 10 decreases as the radio terminal 10 moves.

  The moving speed detector 14 detects a moving speed that is the speed at which the wireless terminal 10 moves. The moving speed detection unit 14 detects the moving speed using, for example, a speed sensor or an acceleration sensor.

  The control unit 15 comprehensively controls the wireless terminal 10. In the following, the configuration necessary for the description of the first embodiment will be mainly described. Specifically, the control unit 15 has a function of selecting a registered cell.

  As illustrated in FIG. 3, the control unit 15 includes a start condition determination unit 151, a continuation condition determination unit 152, a condition change unit 153, and a cell selection unit 154.

  The start condition determination unit 151 determines whether or not the reception quality difference, which is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality, is smaller than the predetermined reception quality difference. Here, the predetermined reception quality difference is a threshold (Time to Trigger activation threshold) that defines the minimum reception quality that should be satisfied by a cell selected as a registered cell.

  The continuation condition determining unit 152 determines whether or not the duration for which the reception quality difference is within the predetermined reception quality difference is longer than the predetermined duration. The predetermined duration is a threshold (Time to Trigger) that defines a duration in which the state where the minimum reception quality is satisfied should be continued.

  The condition changing unit 153 shortens the predetermined duration (threshold value) when the moving speed is higher than the predetermined moving speed. The condition changing unit 153 increases the predetermined reception quality difference (threshold value) when the moving speed is higher than the predetermined moving speed.

  The cell selection unit 154 selects a registered cell based on the serving cell reception quality, the neighboring cell reception quality, the serving cell deviation amount, the neighboring cell deviation amount, and the moving speed. Specifically, the cell selection unit 154 includes a determination unit 155 that determines whether a selection condition for selecting a registered cell is satisfied based on the serving cell reception quality, the neighboring cell reception quality, and the moving speed. Have. Here, the selection condition is that the duration in which the reception quality difference is within the predetermined reception quality difference is longer than the predetermined duration. That is, the determination unit 155 determines that the selection condition for selecting a registered cell is satisfied when it is determined that the duration is longer than the predetermined duration.

  As described above, the reception quality difference is a value obtained by subtracting the neighboring cell reception quality from the serving cell reception quality. Further, the predetermined reception quality difference (threshold) and the predetermined duration (threshold) are changed depending on the moving speed of the wireless terminal 10.

  That is, it should be noted that the determination unit 155 determines whether the selection condition is satisfied based on the serving cell reception quality, the neighboring cell reception quality, and the moving speed.

  More specifically, the cell selection unit 154 performs the first selection process when the movement speed is higher than the predetermined movement speed, and performs the second selection process when the movement speed is lower than the predetermined movement speed.

  The first selection process is a process of selecting a cell that satisfies a selection condition from cells whose frequency deviation amount is higher than a predetermined deviation amount (threshold value). In the first selection process, it is preferable to select a cell that satisfies the selection condition from cells whose frequency deviation amount is higher than the predetermined deviation amount over a certain period. The second selection process is a process of selecting a cell that satisfies the selection condition without considering the frequency shift amount.

  The cell selection unit 154 generates a measurement result (Measurement Report) including a cell identifier for identifying a cell selected by the first selection process or the second selection process. The measurement result preferably includes the reception quality corresponding to the cell identifier in addition to the cell identifier.

  The transmission unit 16 transmits various signals to the radio base station 20d. The various signals are, for example, control signals and data signals. Specifically, the transmission unit 16 transmits a signal to the serving cell. Moreover, the transmission part 16 transmits a signal to a neighboring cell.

  For example, the transmission unit 16 transmits the measurement result generated by the cell selection unit 154 to the network side via the serving cell (or neighboring cell).

(Wireless terminal operation)
Hereinafter, the operation of the wireless terminal according to the first embodiment will be described with reference to the drawings. 4 to 6 are flowcharts showing the operation of the wireless terminal 10 according to the first embodiment.

  As shown in FIG. 4, in step 10, the wireless terminal 10 determines whether or not the moving speed that is the speed at which the wireless terminal 10 moves is higher than a predetermined moving speed (threshold). When the moving speed is higher than the predetermined moving speed, the radio terminal 10 proceeds to the process of step 11. On the other hand, when the moving speed is not higher than the predetermined moving speed, the radio terminal 10 proceeds to the process of step 14.

  In step 11, the radio terminal 10 has a frequency deviation amount higher than a predetermined deviation amount (threshold value) among the serving cell and the neighboring cells based on the serving cell deviation amount and the neighboring cell deviation amount. Determine if there is a cell. The radio terminal 10 manages a cell having a frequency deviation amount higher than a predetermined deviation amount (threshold value) as a candidate cell of a registered cell.

  If there is such a cell, the radio terminal 10 proceeds to the process of step 12. On the other hand, when there is no such cell, the radio terminal 10 proceeds to the process of step 14.

  In Step 12, the radio terminal 10 is in a state in which the frequency deviation amount is higher than the predetermined deviation amount (threshold value) among the candidate cells of the registered cell based on the serving cell deviation amount and the neighboring cell deviation amount. Determines whether there is a cell that continues for a certain period of time. The radio terminal 10 manages, as a registered cell candidate cell, a cell in which a state in which the frequency deviation amount is higher than a predetermined deviation amount (threshold value) continues for a certain period. That is, the radio terminal 10 excludes cells whose frequency deviation amount is higher than the predetermined deviation amount (threshold value) for a certain period from the registered cell candidate cells.

  When there is such a cell, the radio terminal 10 proceeds to the process of step 13. On the other hand, when there is no such cell, the radio terminal 10 proceeds to the process of step 14.

  In step 13, the wireless terminal 10 changes the predetermined reception quality (threshold value) and the predetermined deviation amount (threshold value). Specifically, the radio terminal 10 shortens the predetermined duration (threshold) and increases the predetermined reception quality difference (threshold).

  In step 14, the wireless terminal 10 performs a selection process (A) for determining whether or not the selection condition is satisfied. Details of the selection process (A) will be described later (see FIG. 5).

  In step 15, the wireless terminal 10 performs a selection process (B) for determining whether or not the selection condition is satisfied. Details of the selection process (B) will be described later (see FIG. 6).

  The selection process (A) and the selection process (B) are processes for selecting cells that satisfy the selection condition. That is, the selection process (A) and the selection process (B) are processes for selecting a cell in which the duration in which the reception quality difference is within the predetermined reception quality difference is longer than the predetermined duration.

  First, the selection process (A) will be described with reference to FIG. As shown in FIG. 5, in step 20, the radio terminal 10 determines that the reception quality difference is within the predetermined reception quality difference between the serving cell and the neighboring cell based on the serving cell reception quality and the neighboring cell reception quality. Determine if there is a cell. The radio terminal 10 manages a cell whose reception quality difference is within a predetermined reception quality difference as a candidate cell of a registered cell.

  If there is such a cell, the radio terminal 10 proceeds to the process of step 21. On the other hand, when there is no such cell, the wireless terminal 10 ends the series of processes.

  In step 21, the radio terminal 10 determines whether or not there is a cell having a duration in which the reception quality difference is within the predetermined reception quality difference among the candidate cells of the registered cell longer than the predetermined duration. The radio terminal 10 manages cells whose duration is longer than the predetermined duration as registered cell candidate cells. That is, the radio terminal 10 excludes cells whose duration is shorter than the predetermined duration from the candidate cells for registered cells.

  If there is such a cell, the radio terminal 10 proceeds to the process of step 22. On the other hand, when there is no such cell, the wireless terminal 10 ends the series of processes.

  In step 22, the radio terminal 10 transmits a measurement result (Measurement Report) including at least a cell identifier for identifying a cell whose duration is longer than the predetermined duration (that is, a candidate cell of a registered cell) to the network side.

  Next, the selection process (B) will be described with reference to FIG. As shown in FIG. 6, in step 30, the radio terminal 10 determines that the reception quality difference is a predetermined reception quality difference (after expansion) among the candidate cells of the registered cell based on the serving cell reception quality and the neighboring cell reception quality. It is determined whether or not there is a cell inside. The radio terminal 10 manages a cell whose reception quality difference is within a predetermined reception quality difference (after expansion) as a candidate cell of a registered cell. That is, the radio terminal 10 excludes a cell whose reception quality difference is not within the predetermined reception quality difference (after expansion) from the candidate cells of the registered cell.

  If there is such a cell, the radio terminal 10 proceeds to the process of step 31. On the other hand, when there is no such cell, the wireless terminal 10 ends the series of processes.

  In step 31, the radio terminal 10 determines whether or not there is a cell having a duration in which the reception quality difference is within the predetermined reception quality difference longer than the predetermined duration (after shortening) among the candidate cells of the registered cell. . The radio terminal 10 manages a cell whose duration is longer than a predetermined duration (after shortening) as a candidate cell of a registered cell. That is, the radio terminal 10 excludes a cell whose duration is shorter than a predetermined duration (after shortening) from the candidate cells of registered cells.

  If there is such a cell, the radio terminal 10 proceeds to the process of step 22. On the other hand, when there is no such cell, the wireless terminal 10 ends the series of processes.

  In step 32, the radio terminal 10 sends a measurement result (Measurement Report) including at least a cell identifier for identifying a cell (that is, a candidate cell of a registered cell) whose duration is longer than a predetermined duration (after shortening) to the network side. Send.

(When the selection conditions are met)
Hereinafter, the timing when the selection condition according to the first embodiment is satisfied will be described with reference to the drawings. FIG. 7 is a diagram for explaining the timing at which the selection condition according to the first embodiment is satisfied. In FIG. 7, the vertical axis indicates the reception quality of signals received by the wireless terminal 10 from each cell (cell A and cell B), and the horizontal axis indicates time.

  As described above, the selection condition is that the duration in which the reception quality difference is within the predetermined reception quality difference is longer than the predetermined duration. The predetermined reception quality difference (Time to Trigger start threshold) is increased when the moving speed of the wireless terminal 10 is higher than the predetermined moving speed. The predetermined duration (Time to Trigger) is shortened when the moving speed of the wireless terminal 10 is higher than the predetermined moving speed.

  In FIG. 7, the following four cases will be described with examples.

(1) Case where the predetermined reception quality difference (Time to Trigger start threshold) is not increased and the predetermined duration (Time to Trigger) is not shortened (2) The predetermined reception quality difference (Time to Trigger start threshold) is The case where the predetermined duration (Time to Trigger) is not expanded and the predetermined duration (Time to Trigger) is shortened (3) The predetermined reception quality difference (Time to Trigger start threshold) is widened and the predetermined duration (Time to Trigger) is shortened Case (4) Case where the predetermined reception quality difference (Time to Trigger start threshold) is widened and the predetermined duration (Time to Trigger) is shortened As shown in FIG. The starting timing of the duration in which the reception quality difference is within the predetermined reception quality difference is It is between _{t 2.} Therefore, the expiration time of a predetermined duration is the time t _6. Thus, the timing of selection condition is satisfied, the time t _6.

In case (2), similarly to the case (1), counting the timing duration reception quality difference is within a predetermined reception quality difference is the time t _2. Expiration time of a predetermined duration, for a predetermined duration is shortened, the time t _4. Thus, the timing of selection condition is satisfied, the time t _4.

In case (3), the start timing of the duration in which the reception quality difference is within the predetermined reception quality difference is time t ₁ because the predetermined reception quality difference is expanded. Expiration time of a predetermined duration is the time t _5. Thus, the timing of selection condition is satisfied, the time t _5.

In the case (4), as in the case (3), the start timing of the duration in which the reception quality difference is within the predetermined reception quality difference is the time t ₁ because the predetermined reception quality difference is enlarged. The expiration timing of the predetermined duration is time t ₃ because the predetermined duration is shortened. Thus, the timing when the selection condition is satisfied is time t ₃ .

  In the cases (2) to (4), the timing at which the selection condition is satisfied is earlier than in the case (1). That is, when the moving speed of the wireless terminal 10 is higher than the predetermined moving speed, the timing at which the selection condition is satisfied is advanced compared to the case where the moving speed of the wireless terminal 10 is lower than the predetermined moving speed.

(Function and effect)
According to the first embodiment, the radio terminal 10 selects a registered cell based on the moving speed in addition to the reception quality and the frequency shift amount. Therefore, in the case where the radio terminal 10 is moving at a high speed, the timing of selecting a registered cell can be made to follow the fluctuation of a cell with good reception quality. On the other hand, in the case where the wireless terminal 10 is moving at a low speed, a cell with good reception quality is registered at the timing of selecting a registered cell even if the frequency deviation amount is lower than a predetermined threshold. It can be selected as a cell. That is, an optimum cell can be selected as a registered cell.

  Specifically, the wireless terminal 10 advances the timing at which the selection condition is satisfied when the moving speed is higher than a predetermined moving speed. Therefore, it is possible to make the timing of selecting a registered cell follow the fluctuation of a cell with good reception quality.

  When the moving speed is lower than the predetermined moving speed, the radio terminal 10 selects a registered cell based on the reception quality without considering the frequency shift amount. Therefore, even in a cell whose frequency deviation is lower than a predetermined threshold, a cell with good reception quality can be selected as a registered cell at the timing of selecting a registered cell.

[Second Embodiment]
The second embodiment will be described below with reference to the drawings. In the following, differences between the first embodiment and the second embodiment will be mainly described.

  Specifically, in the first embodiment described above, when the moving speed is higher than the predetermined moving speed, the wireless terminal 10 expands the predetermined reception quality difference (Time to Trigger start threshold) and increases the predetermined duration (Time to Trigger).

  On the other hand, in the second embodiment, the radio terminal 10 considers not only the moving speed but also the frequency shift amount (the cell shift amount and the neighbor cell shift amount), and the predetermined reception quality. Change the difference and the predetermined duration. The radio terminal 10 manages a predetermined reception quality difference and a predetermined duration for each of a plurality of cells (a serving cell and a neighboring cell).

(Wireless terminal operation)
Hereinafter, operations of the wireless terminal according to the second embodiment will be described with reference to the drawings. FIG. 8 is a flowchart showing the operation of the radio terminal 10 according to the second embodiment. FIG. 8 is a flowchart showing the details of step 13 (change of threshold value) described above.

  As shown in FIG. 8, in step 131, the radio terminal 10 determines whether or not the frequency shift amount of the signal received from the change target cell that is one of the registered cell candidate cells is a negative value. To do. If the frequency shift amount is a negative value, the radio terminal 10 proceeds to the process of step 132. That is, when the radio terminal 10 is away from the change target cell, the radio terminal 10 proceeds to the process of step 132. On the other hand, when the frequency shift amount is a positive value, the radio terminal 10 proceeds to the process of step 133. That is, when the radio terminal 10 is approaching the change target cell, the radio terminal 10 proceeds to the process of step 133.

  In step 132, the radio terminal 10 determines whether there is a cell with better reception quality than the change target cell among the candidate cells of the registered cell. If there is a cell with better reception quality than the change target cell, the radio terminal 10 proceeds to the process of step 134. On the other hand, when there is no cell with better reception quality than the change target cell, the radio terminal 10 proceeds to the process of step 133.

  In step 133, the radio terminal 10 increases the predetermined reception quality difference (Time to Trigger activation threshold) and shortens the predetermined duration (Time to Trigger) for the change target cell.

  In step 134, the radio terminal 10 reduces the predetermined reception quality difference (Time to Trigger activation threshold) and extends the predetermined duration (Time to Trigger) for the change target cell.

  In addition, the process of step 131-step 134 is performed about all the candidate cells of a registration cell by selecting the change object cell in order from the candidate cells of a registration cell.

  Thus, when the moving speed is higher than the predetermined moving speed and the frequency shift amount is a positive value, the wireless terminal 10 increases the predetermined reception quality difference (Time to Trigger start threshold) and The duration (Time to Trigger) is shortened. That is, when approaching the change target cell at high speed, the radio terminal 10 advances the timing at which the selection condition for selecting the change target cell as the registered cell is satisfied.

  On the other hand, when the moving speed is higher than the predetermined moving speed and the frequency shift amount is a negative value, the radio terminal 10 reduces the predetermined reception quality difference (Time to Trigger start threshold) and continues the predetermined period. The period (Time to Trigger) is extended. That is, when the radio terminal 10 is moving away from the change target cell at high speed, the radio terminal 10 delays the timing at which the selection condition for selecting the change target cell as the registered cell is satisfied.

[Other Embodiments]
Although the present invention has been described with reference to the above-described embodiments, it should not be understood that the descriptions and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the embodiment described above, when the moving speed is higher than the predetermined moving speed, the wireless terminal 10 changes both the predetermined reception quality difference (Time to Trigger start threshold) and the predetermined duration (Time to Trigger). This embodiment is not limited to this. Specifically, when the moving speed is higher than the predetermined moving speed, the radio terminal 10 may shorten the predetermined duration without changing the predetermined reception quality difference. When the moving speed is higher than the predetermined moving speed, the wireless terminal 10 may expand the predetermined reception quality difference without changing the predetermined duration.

  Even if the moving speed is higher than the predetermined moving speed, the wireless terminal 10 does not need to change both the predetermined reception quality difference (Time to Trigger start threshold) and the predetermined duration (Time to Trigger). Good. That is, the process of step 13 shown in FIG. 4 may be omitted.

  In the above-described embodiment, when the moving speed is higher than the predetermined moving speed, the wireless terminal 10 does not continue the state where the frequency deviation amount is higher than the predetermined deviation amount (threshold value) for a certain period. The cells are excluded from the registered cell candidate cells, but the present embodiment is not limited to this. Specifically, the radio terminal 10 does not have to exclude a cell whose frequency deviation amount is higher than a predetermined deviation amount (threshold value) for a certain period from the registered cell candidate cells. Good. That is, the process of step 12 shown in FIG. 4 may be omitted.

It is a figure which shows the structure of the radio | wireless communications system which concerns on 1st Embodiment. It is a block diagram which shows the structure of the radio | wireless terminal 10 which concerns on 1st Embodiment. It is a block diagram which shows the structure of the control part 15 which concerns on 1st Embodiment. It is a flowchart which shows operation | movement of the radio | wireless terminal 10 which concerns on 1st Embodiment. It is a flowchart which shows operation | movement of the radio | wireless terminal 10 which concerns on 1st Embodiment. It is a flowchart which shows operation | movement of the radio | wireless terminal 10 which concerns on 1st Embodiment. It is a figure for demonstrating the timing with which the selection conditions which concern on 1st Embodiment are satisfy | filled. It is a flowchart which shows operation | movement of the radio | wireless terminal 10 which concerns on 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Wireless terminal, 11 ... Reception part, 12 ... Reception quality measurement part, 13 ... Frequency shift amount acquisition part, 14 ... Movement speed detection part, 15 ... Control part, DESCRIPTION OF SYMBOLS 16 ... Transmission part, 20 ... Wireless base station, 21 ... Area, 151 ... Start condition determination part, 152 ... Continuation condition determination part, 153 ... Condition change part, 154 ... -Cell selection unit, 155 ... determination unit

Claims (10)

In a wireless communication system having a plurality of cells, a wireless terminal for selecting a registered cell that is a cell for performing location registration,
The serving cell reception quality that is the reception quality of the signal received from the serving cell that is the cell that has already performed the location registration, and the signal received from the neighboring cell that is a cell provided around the serving cell. A measurement unit that measures reception quality of neighboring cells, which is reception quality;
An acquisition unit that acquires a serving cell deviation amount that is a frequency deviation amount of a signal received from the serving cell and a neighboring cell deviation amount that is a frequency deviation amount of a signal received from the neighboring cell. When,
A detection unit that detects a moving speed that is a speed at which the wireless terminal moves;
A cell selection unit that selects the registered cell based on the serving cell reception quality, the neighboring cell reception quality, the serving cell deviation amount, the neighboring cell deviation amount, and the moving speed ;
The cell selection unit includes a determination unit that determines whether a selection condition for selecting the registered cell is satisfied based on the serving cell reception quality, the neighboring cell reception quality, and the moving speed. And
The determination unit advances a timing at which the selection condition is satisfied when the moving speed is higher than a predetermined moving speed . A start condition determination unit that determines whether or not a reception quality difference that is a value obtained by removing the neighboring cell reception quality from the serving cell reception quality is smaller than a predetermined reception quality difference;
A continuation condition determining unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration;
A continuation condition changing unit that shortens the predetermined duration when the moving speed is higher than a predetermined moving speed;
The wireless terminal according to claim 1 , wherein the determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration. A start condition determination unit that determines whether or not a reception quality difference that is a value obtained by removing the neighboring cell reception quality from the serving cell reception quality is smaller than a predetermined reception quality difference;
A continuation condition determining unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration;
A start condition changing unit for expanding the predetermined reception quality difference when the moving speed is higher than a predetermined moving speed;
The wireless terminal according to claim 1 , wherein the determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration. A start condition determination unit that determines whether or not a reception quality difference that is a value obtained by removing the neighboring cell reception quality from the serving cell reception quality is smaller than a predetermined reception quality difference;
A continuation condition determining unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration;
A continuation condition changing unit that shortens the predetermined duration when the moving speed is higher than a predetermined moving speed and the frequency shift amount is a positive value;
The wireless terminal according to claim 1 , wherein the determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration. A start condition determination unit that determines whether or not a reception quality difference that is a value obtained by removing the neighboring cell reception quality from the serving cell reception quality is smaller than a predetermined reception quality difference;
A continuation condition determining unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration;
When the moving speed is higher than a predetermined moving speed, and when the shift amount of the frequency is a positive value, further comprising a start condition changing unit that expands the predetermined reception quality difference,
The wireless terminal according to claim 1 , wherein the determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration. A start condition determination unit that determines whether or not a reception quality difference that is a value obtained by removing the neighboring cell reception quality from the serving cell reception quality is smaller than a predetermined reception quality difference;
A continuation condition determining unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration;
A continuation condition changing unit for extending the predetermined duration when the moving speed is higher than a predetermined moving speed and the frequency shift amount is a negative value;
The wireless terminal according to claim 1 , wherein the determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration. A start condition determination unit that determines whether or not a reception quality difference that is a value obtained by removing the neighboring cell reception quality from the serving cell reception quality is smaller than a predetermined reception quality difference;
A continuation condition determining unit that determines whether or not a duration in which the reception quality difference is within a predetermined reception quality difference is longer than a predetermined duration;
A start condition change unit that reduces the predetermined reception quality difference when the moving speed is higher than a predetermined moving speed and the frequency shift amount is a negative value;
The wireless terminal according to claim 1 , wherein the determination unit determines that the selection condition is satisfied when it is determined that the duration is longer than a predetermined duration. The cell selection unit performs a first selection process when the movement speed is higher than a predetermined movement speed, and performs a second selection process when the movement speed is lower than the predetermined movement speed,
The first selection process is a process of selecting the registered cell based on the reception quality from cells whose frequency deviation amount is higher than a predetermined deviation amount.
The radio terminal according to claim 1, wherein the second selection process is a process of selecting the registered cell based on the reception quality without considering the frequency shift amount. The first selection process is a process of selecting the registered cell based on the reception quality from cells whose frequency deviation amount is higher than the predetermined deviation amount over a certain period. The wireless terminal according to claim 8 . In a wireless communication system having a plurality of cells, a cell selection method for selecting a registered cell, which is a cell in which a wireless terminal performs location registration,
From a serving cell reception quality that is a reception quality of a signal received by the wireless terminal from a serving cell that is a cell that has already performed the location registration, and from a neighboring cell that is a cell provided around the serving cell Measuring a neighboring cell reception quality which is a reception quality of a signal received by the wireless terminal; and
A serving cell deviation amount which is a frequency deviation amount of a signal received by the wireless terminal from the serving cell and a neighboring cell deviation which is a frequency deviation amount of a signal received by the wireless terminal from the neighboring cell. Step B for obtaining a transfer amount;
Detecting a moving speed which is a speed at which the wireless terminal moves; and
Step D of selecting the registered cell based on the serving cell reception quality, the neighboring cell reception quality, the serving cell deviation amount, the neighboring cell deviation amount and the moving speed ,
The step D includes a step of determining whether a selection condition for selecting the registered cell is satisfied based on the serving cell reception quality, the neighboring cell reception quality, and the moving speed,
In the determining step, when the moving speed is higher than a predetermined moving speed, the timing at which the selection condition is satisfied is advanced .

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