JP4645322B2 - Mobile communication system and cell radius determination method in the system - Google Patents

Description

  The present invention relates to a mobile communication system and a cell radius determination method in the system, and more particularly to a mobile communication system used for cellular mobile communication and a cell radius determination method in the system.

  In the conventional cell design, the cell arrangement, transmission power, etc. are finally determined by actually measuring the electric field strength in the cell. However, in recent years, small base stations have been developed and the installation of base stations has become easier.

  On the other hand, as an example of this type of mobile communication system, an invention for detecting the position of a mobile station based on a transmission / reception time difference (delay amount) in communication with a communicating base station is disclosed (for example, Patent Documents). 1).

  As another example, an invention is disclosed in which the base station apparatus compares the reception level of the common control channel with a threshold value to determine the position of the mobile station (see, for example, Patent Document 2).

  In addition, as another example, an invention is disclosed in which a reach value (cell radius) of a common channel signal is optimized by setting a lower limit value for the transmission power value of the common channel signal (see, for example, Patent Document 3). ).

JP 2002-159034 (paragraph 0077, FIG. 4) JP 2002-345013 A (paragraphs 0061, 0097, 0098, FIG. 3, FIG. 5, FIG. 7) JP 2003-143069 A (paragraph 0035)

  However, in the case of the above-mentioned small base station, there is a possibility that many installations are performed in places where it is difficult to measure electric field strength or in buildings. It is difficult to apply determination of cell arrangement, transmission power, and the like by measuring electric field strength to such a base station.

  On the other hand, in Patent Documents 1 to 3 described above, the position detection of the mobile station, the comparison between the reception level and the threshold value, and the optimization of the cell radius are described. It is not intended to control the above, and all of its purpose, configuration, action and effect are completely different from those of the present invention.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a mobile communication system capable of autonomously controlling a cell radius regardless of electric field strength measurement and a cell radius determination method in the system.

In order to solve the above problems, a mobile communication system according to the present invention is a mobile communication system including a plurality of base station apparatuses forming each cell and a base station control apparatus for controlling the plurality of base station apparatuses, The base station control device includes: propagation delay acquisition means for acquiring the uplink propagation delay of the mobile device measured at each base station device from each base station device; and downlink common control obtained by the mobile device from each base station Reception information acquisition means for acquiring channel reception power from the mobile station, and transmission power control means for controlling the downlink common control channel transmission power of each base station apparatus, wherein the transmission power control means is a propagation at a cell boundary. A delay is compared with the uplink propagation delay of the mobile station, and when the difference is smaller than a predetermined value, it is determined that the mobile station exists at the cell boundary, and the transmission power control means further comprises: If the mobile station is determined to exist in the cell boundary, that compares the downlink common control channel reception power between, their difference to control the downlink common control channel transmission power of each base station apparatus to be smaller Features.

A cell radius determination method according to the present invention is a cell radius determination method in a mobile communication system including a plurality of base station devices forming each cell and a base station control device for controlling the plurality of base station devices. The base station control device includes a propagation delay acquisition step of acquiring the uplink propagation delay of the mobile device measured by each base station device from each base station device, and the downlink common obtained by the mobile device from each base station. A reception information acquisition step of acquiring a control channel reception power from the mobile device, and a transmission power control step of controlling a downlink common control channel transmission power of each base station apparatus, wherein the transmission power control step includes: The propagation delay is compared with the uplink propagation delay of the mobile station, and when the difference is smaller than a predetermined value, it is determined that the mobile station exists at the cell boundary, and In the transmission power control step, when it is determined that the mobile station is present at the cell boundary, the downlink common control channel received powers are compared with each other so that the difference therebetween is reduced. Control channel transmission power is controlled .

  In the present invention, the received power of the downlink common control channel of an adjacent cell near the cell boundary is measured by measuring the position of the mobile station at the time of handover using the uplink propagation delay measured by the base station apparatus. Compare. Based on the result, the transmission power of the downlink common control channel of each base station apparatus is controlled, and the cell radius is adjusted autonomously.

  According to the present invention, since the above configuration is included, the cell radius can be autonomously controlled regardless of the measurement of the electric field strength.

  That is, the first effect of the present invention is that the cell radius can be autonomously adjusted by measuring the received power of the downlink common control channel near the boundary of the adjacent cell using the mobile device in operation.

  The second effect is that since the cell radius can be autonomously changed, it is easier to install a large number of small base stations or to install a base station in an area where traffic is not convenient.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The present invention relates to a cellular mobile communication. Here, a W-CDMA (Wideband-Code Division Multiple Access) system will be described as an example.

  FIG. 1 is a block diagram of a first embodiment of a mobile communication system according to the present invention. Referring to the figure, a mobile communication system according to the present invention includes a base station controller (hereinafter referred to as “RNC”) 1, a base station device (hereinafter referred to as “BTS-X”) 2, A station apparatus (hereinafter referred to as “BTS-Y”) 3, a cell 4, a cell 5, and a mobile device (hereinafter referred to as “UE”) 8 are configured.

  RNC1 is connected to BTS-X2 and BTS-Y3 via Iubs 6 and 7 which are RNC-BTS interfaces. In FIG. 1, two BTSs, namely BTS-X2 and BTS-Y3, are connected to RNC1.

  Each BTS forms cell 4 and cell 5. The cell radius of each cell is substantially determined by the transmission power of the downlink common control channel of each BTS. The UE 8 communicates with the BTS-X 2 when located in the cell 4, and communicates with the BTS-Y 3 when located in the cell 5.

  Here, consider that the UE 8 moves from the cell 4 to the cell 5. The situation at this time will be described with reference to FIG. FIG. 2 is a diagram schematically showing how the UE 8 moves on a straight line from the cell 4 to the cell 5 in FIG. Reference numeral 9 denotes a boundary between the cell 4 and the cell 5. dxB is a propagation delay between the BTS-X2 and the UE8 when the UE8 exists at the cell boundary 9 (one way), and dyB is a propagation delay between the BTS-Y3 and the UE8 when the UE8 exists at the cell boundary 9 (one way) ). When UE8 is closer to BTS-X2 than cell boundary 9, propagation delay dx between BTS-X2 and UE8 is dx <dxB, and propagation delay dy> dyB between BTS-Y3 and UE8. When UE8 is closer to BTS-Y3 than cell boundary 9, the propagation delay dx between BTS-X2 and UE8 is dx> dxB, and the propagation delay dy between BTS-Y3 and UE8 is dy <dyB. .

  FIG. 3 is a sequence chart showing the operation of the first embodiment of the mobile communication system according to the present invention. In the figure, functions added to the RNC 1 in the present invention will be described. Here, it is assumed that the UE 8 performs handover from the BTS-X2 cell (cell 4) to the BTS-Y3 cell (cell 5).

  First, when the UE 8 decides to hand over from the cell 4 to the cell 5, the RNC 1 has a function of transmitting an uplink propagation delay report request 12 to the handover source and destination BTS-X2 and BTX-Y3. This request includes an ID (Identification) for identifying the user (User), a reporting cycle, and a measurement start time. Each received BTS performs measurement according to the designation and sends a measurement report for each designated reporting cycle. An uplink propagation delay report 13 is transmitted to RNC1. The uplink propagation delay report 13 includes the measured uplink propagation delay and measurement time. Here, BTS-X2 reports uplink propagation delay dx (n) (n is a positive integer), and BTS-Y3 reports uplink propagation delay dy (n).

  When the UE 8 decides to hand over from the cell 4 to the cell 5, the RNC 1 has a function of transmitting a downlink common control channel reception level report request 15 to the UE 8. This request includes the BTS type, reporting period, and measurement start time. The UE 8 receiving this report request measures the received power of the downlink common control channel according to the designation, and transmits the result to the RNC 1 by the downlink common control channel received power report 11. This report includes the received power and measurement time of the downlink common control channel for each BTS type. Here, the received power of the downlink common control channel reports Sx (n) that is a measured value of BTS-X2, and Sy (n) that is a measured value of BTS-Y3.

  When the RNC 1 determines that the UE 8 is present at the cell boundary 9 from the reported dx (n) and dy (n), it performs an averaging process of Sx (n) and Sy (n) (described later). 4 and FIG. 5). When the designated sample number averaging process is performed, the cell radius is autonomously controlled by controlling the transmission power of the downlink common channel of each BTS as follows.

  In the following description, Sref is the reference received power of the downlink common control channel at the cell boundary 9, Px is the transmission power of the downlink common control channel of BTS-X2, and Py is the transmission power of the downlink common control channel of BTS-Y3. , Pd indicate change steps when changing Px, Py, respectively. M is a positive integer.

(1) When Sx (m)> Sy (m) and Sy (m) <Sref Py <−Py + Pd: That is, the cell 5 is enlarged.
(2) When Sx (m)> Sy (m) and Sx (m)> Sref Px <−Px−Pd: That is, the cell 4 is reduced.
(3) When Sx (m) <Sy (m) and Sx (m) <Sref Px <−Px + Pd: That is, the cell 4 is expanded.
(4) When Sx (m) <Sy (m) and Sy (m)> Sref Py <-Py-Pd: That is, the cell 5 is reduced.
(5) Other than the above Cells 4 and 5 are not changed.

  Next, details of the operation of the first embodiment will be described. In FIG. 1, consider that UE 8 hands over from cell 4 to cell 5. When the UE 8 is in the cell 4 (before the handover), the UE 8 communicates information (UplaneData) 10 via the BTS-X2 before the handover as shown in FIG.

  When the UE 8 moves to the cell 5 to be handed over to the cell 5, the RNC 1 transmits an uplink propagation delay report request 12 to the BTS-X2 and BTX-Y3 that are the handover source and the destination. Further, the RNC 1 transmits a downlink common control channel reception level report request 15 to the UE 8.

  When each BTS and UE8 receive the respective report requests, each BTS performs measurement according to the designation, and transmits measurement reports dx (n) and dy (n) as uplink propagation delay reports 13 to the RNC 1 for each designated reporting period. To do. Further, the UE 8 measures the reception power of the downlink common control channel of each BTS according to the designation, and transmits the result to the RNC 1 as the downlink common control channel reception power report 11 as Sx (n) and Sy (n).

  Here, when the RNC 1 receives these measurement reports, the RNC 1 once performs the processes as shown in FIGS. 4 and 5 are flowcharts showing an example of a processing procedure in the RNC 1.

  First, when receiving the uplink propagation delay report 13 from the BTS-X2 (step 17), the RNC 1 compares the propagation delay dx (n) between the BTS-X2 and the UE 8 with the propagation delay dxB at the cell boundary 9, and the difference is the cell. It is determined whether it is smaller than the boundary determination range dr (step 18). If the difference is greater than or equal to dr, the UE 8 determines that it does not exist at the cell boundary 9 and exits the process without doing anything (in the case of “N” in step 18). If the difference is smaller than dr, the UE 8 determines that it exists at the cell boundary 9 (in the case of “Y” in step 18), and the received power of the downlink common control channel at the cell boundary is Sx (m) < -RSx (m-1) + (1-r) Sx (n) and moving average processing are performed (step 19).

  At this time, Sx (n) uses a report value at the same time as dx (n). Here, r is a forgetting factor. Further, the counter Ctx indicating the average number of samples is counted up (step 20). Similarly, the process shown in FIG. 5 is performed on the uplink propagation delay report 13 reported from the BTS-Y3 to update Sy (m) and Cty.

  The processing shown in FIGS. 4 and 5 is performed by the RNC 1 every time the uplink propagation delay report 13 is received from each BTS. These processes are performed for all the UEs and the average value is calculated. That is, Sx (m) and Sy (m) are updated by acquiring Sx (n) and Sy (n) from all UEs that perform handover between the cells 4 and 5.

  Each time the UE 8 hands over from the cell 4 to the cell 5, the average value of the received power of the downlink common control channel transmitted from each BTS at the current cell boundary 9 is obtained by continuing the processing of FIG. 4 and FIG. It will be. Further, Sx (m) and Sy (m) obtained here are materials for determining whether the cell radii of the cells 4 and 5 are as expected. That is, since it is ideal that Sx (m) = Sy (m) at the cell boundary 9, if Sx (m)> Sy (m), the transmission power of the downlink common control channel of BTS-Y3 If Sx (m) <Sy (m), it means that the transmission power of the downlink common control channel of BTS-X2 is insufficient.

  FIG. 6 is a flowchart showing a procedure (first embodiment) of a process for changing the transmission power of the downlink common control channel in the RNC 1. Referring to the figure, following the above operation, RNC 1 constantly monitors whether Ctx and Cty are sufficiently averaged, and downlink common control that determines the cell radius when Ctx and Cty exceed the preset average number of samples TB, respectively. A process of changing the transmission power of the channel is started (step 25).

  After confirming that Ctx and Cty have exceeded the average number of samples TB, Sx (m) and Sy (m) are compared, and if they are the same, nothing is done and the process exits (in the case of “=” in step 26). Here, when comparing Sx (m) and Sy (m), if Sx (m) −Sy (m)> Sr, then Sx (m)> Sy (m) (in the case of “>” in step 26) ), If Sy (m) −Sx (m)> Sr, it is determined that Sx (m) <Sy (m) (when “<” in step 26), and | Sx (m) −Sy (m) If | = <Sr, it is determined that Sx (m) = Sy (m) (when “=” in step 26). Here, Sr is a reception level determination range, and a stable operation can be expected without frequent change by giving a range to the determination value.

  When the result of comparing Sx (m) and Sy (m) is Sx (m)> Sy (m) (when “>” in step 26), the transmission power of the downlink common control channel of BTS-Y3 is It means that there is not enough. Therefore, first, Sy (m) is compared with the reference received power Sref (step 30).

  Sref is the reference received power of the downlink common control channel at the cell boundary 9. Even if it is determined that Sx (m)> Sy (m), if it is equal to or higher than the reference reception power, it is not necessary to increase the transmission power Py of the downlink common control channel of BTS-Y3, and the process proceeds to the next process (step 30) If “≧”).

  If Sy (m) <Sref (“<” in step 30), it is determined that Py is insufficient, and Py is increased as Py <−Py + Pd (step 31). Here, Pd is a step of increasing Py. However, Py is controlled within the range of Py <Pymax × kpy. Pymax is the maximum value of Py, and kpy indicates a ratio of power that can be allocated to the downlink common control channel in the maximum transmission power of BTS-Y3.

  If Py is changed, Sx (m) and Sy (m) need to be counted again, so Ctx, Cty, Sx (m), and Sy (m) are cleared (step 32).

  If Sx (m)> Sy (m) and Sy (m) is greater than or equal to Sref (“≧” in step 30), it can be determined that Sx (m) is too large (in step 27). In the case of “>”), in that case, it is considered that the transmission power Px of the downlink common control channel of the BTS-X2 is decreased in order to decrease Sx (m).

  In that case, Px is lowered as Px <-Px-Pd (step 28). If Px is changed, Sx (m) and Sy (m) need to be counted again, so Ctx, Cty, Sx (m), and Sy (m) are cleared (step 29).

  On the other hand, if Sx (m) <Sy (m) as a result of comparing Sx (m) and Sy (m) (“<” in step 26), transmission of the downlink common control channel of BTS-X2 It means that there is not enough power. First, Sx (m) is compared with the reference received power Sref (step 33).

  Sref is the reference received power of the downlink common control channel at the cell boundary 9. Even if it is determined that Sx (m) <Sy (m), if Sx (m) is equal to or higher than the reference reception power, it is not necessary to increase the transmission power Px of the downlink common control channel of BTS-X2, so the next processing (If “≧” in step 33).

  If Sx (m) <Sref (“<” in step 33), it is determined that Px is insufficient, and Px is increased as Px <−Px + Pd (step 34). Here, Pd is an increase step of Px. However, Px is controlled within the range of Px <Pxmax × kpx. Pxmax is the maximum value of Px, and kpx indicates a ratio of power that can be allocated to the downlink common control channel in the maximum transmission power of BTS-X2.

  If Px is changed, Sx (m) and Sy (m) must be counted again, so Ctx, Cty, Sx (m), and Sy (m) are cleared (step 35).

  If Sx (m) <Sy (m) and Sx (m) is greater than or equal to Sref (“≧” in step 33), it can be determined that Sy (m) is too large (in step 36, “ >>).

  In that case, it is considered that the transmission power Py of the downlink common control channel of BTS-Y3 is decreased in order to decrease Sy (m). In that case, Py is lowered as PY <-PY-PD (step 37).

  If Py is changed, Sx (m) and Sy (m) need to be counted again, so Ctx, Cty, Sx (m), and Sy (m) are cleared (step 38).

  According to the first embodiment, the cell radius can be autonomously controlled by controlling Px and Py as described above.

  In the first embodiment, it is considered that the cell radius is controlled by controlling the transmission power of the downlink common control channel of two cells at the cell boundary 9. However, in practice, there are usually a plurality of BTSs (cells) around one BTS (cell), and this may increase downlink interference in cells other than the currently considered cell. Absent.

  FIG. 7 is a diagram showing a case where a plurality of BTS-Y1 to BTS-Y6 exist around BTS-X. In the figure, the case where six cells are adjacent to each other around BTS-X is considered, but the present invention does not particularly limit the number of adjacent cells.

  In this case, the reception level of the downlink common control channel near the boundary of each cell is defined as follows.

  For BTS-X and BTS-Y1, the reception power of the downlink common control channel of BTS-X is Sxy1 (m), and the reception power of the downlink common control channel of BTS-Y1 is Sy1x (m).

  For BTS-X and BTS-Y2, the reception power of the downlink common control channel of BTS-X is Sxy2 (m), and the reception power of the downlink common control channel of BTS-Y2 is Sy2x (m).

  For BTS-X and BTS-Y3, the reception power of the downlink common control channel of BTS-X is Sxy3 (m), and the reception power of the downlink common control channel of BTS-Y3 is Sy3x (m).

  For BTS-X and BTS-Y4, the reception power of the downlink common control channel of BTS-X is Sxy4 (m), and the reception power of the downlink common control channel of BTS-Y4 is Sy4x (m).

  For BTS-X and BTS-Y5, the reception power of the downlink common control channel of BTS-X is Sxy5 (m), and the reception power of the downlink common control channel of BTS-Y5 is Sy5x (m).

  For BTS-X and BTS-Y6, the reception power of the BTS-X downlink common control channel is Sxy6 (m), and the reception power of the BTS-Y2 downlink common control channel is Sy6x (m).

  Each of the above Sxyn (m) and Synx (m) is obtained when a handover across the boundary of each cell is performed in the same manner as in FIGS. 4 and 5 (n is 1 to 6). Counters Ctxyn and Ctynx indicating the average number of samples are also counted up (n is 1 to 6). Here, Ctxyn is a counter indicating the average number of samples when Sxn (m) of the neighboring cell BTS-Yn of BTS-X in FIG. 7 is obtained, and Ctynx is the neighboring cell BTS-X of BTS-Yn in FIG. It is a counter which shows the average sample number at the time of calculating | requiring Synx (m).

  Here, only BTS-Yn (n is 1-6) which is an adjacent cell of BTS-X is described, but in actuality, adjacent cells BTS-X, BTS-Y2, BTS-Y6,. BTS-Y1 is Sy1x (m), Sy1y2 (m), Sy1y6 (m) ... Sy1 (*) (m), Cty1x, Cty1y2, Cty1y6 ... Cty1 (*) Holds the measurement results. The same applies to the other BTS-Yn.

  FIG. 8 is a flowchart showing a procedure (second embodiment) for changing the transmission power of the downlink common control channel in the RNC 1. Hereinafter, an example of the operation of the second embodiment will be described with reference to FIG.

  The operation related to BTS-X will be described based on the measurement result. The RNC 1 performs the following processing when the counters Ctxyn and Ctyn (*) indicating the average number of samples in the adjacent cells all exceed TB (step 39).

  (1) If Sxyn (m)> Synx (m) (“>” in step 40) and Sxyn (m)> Sref (“>” in step 41), Px <−Px−Pd is performed (step 42) The BTS-X cell is reduced.

  (2) When Sxyn (m) <Synx (m) (“<” in step 40) and Sxyn (m) <Sref (“<” in step 44), Px <−Px + Pd and Px <Pxmax × kpx (Step 45), the cell of BTS-X is expanded.

  (3) In other cases, the BTS-X cell is not changed.

  Sref is the reference received power of the downlink common control channel at the cell boundary 9, Px is the transmission power of the downlink common control channel of BTS-X2, Pd is the change step when changing Px, and n is the change step of the adjacent cell. Numbers, here BTS-Y1 to BTS-Y6 1 to 6, respectively, are shown.

  Further, when the processing of (1) or (2) is performed, Ctxyn, Sxyn (m), Ctynx, Synx (m), which are measurement results so far, are cleared (steps 43 and 46). That is, the measurement result regarding BTS-X of the adjacent cell is cleared.

  According to the second embodiment, it is possible to reduce downlink interference in each cell even when a plurality of BTSs (cells) exist around one BTS (cell).

1 is a configuration diagram of a first embodiment of a mobile communication system according to the present invention. It is the figure which showed typically a mode that UE8 moved on the straight line from the cell 4 of FIG. 1 to the cell 5. FIG. It is a sequence chart which shows operation | movement of 1st Example of the mobile communication system which concerns on this invention. It is a flowchart which shows an example of the procedure of the process in RNC1. It is a flowchart which shows an example of the procedure of the process in RNC1. It is a flowchart which shows the procedure (1st Example) of the change process of the transmission power of the downlink common control channel in RNC1. It is a figure which shows the case where several BTS-Y1 to BTS-Y6 exist around BTS-X. It is a flowchart which shows the procedure (2nd Example) of the change process of the transmission power of the downlink common control channel in RNC1.

Explanation of symbols

1 Base station controller (RNC)
2 Base station equipment (BTS-X)
3 Base station equipment (BTS-Y)
4 cell 5 cell 8 mobile station (UE)

Claims (4)

A mobile communication system including a plurality of base station devices forming each cell, and a base station control device that controls the plurality of base station devices,
The base station controller is
Propagation delay acquisition means for acquiring the uplink propagation delay of the mobile device measured in each base station device from each base station device ,
A reception information acquiring unit that the mobile station acquires the downlink common control channel reception power obtained from each of the base stations from the mobile station,
Transmission power control means for controlling the downlink common control channel transmission power of each base station device,
The transmission power control means compares the propagation delay at the cell boundary with the uplink propagation delay of the mobile station, and determines that the mobile station exists at the cell boundary when the difference is smaller than a predetermined value,
Further, the transmission power control means compares the downlink common control channel received powers when it is determined that the mobile station is present at the cell boundary, and the downlink common stations of the base station apparatuses reduce the difference therebetween. A mobile communication system, characterized by controlling control channel transmission power . The transmission power control means performs a moving average process on the downlink common control channel received power when it is determined that the mobile station is present at the cell boundary, and based on the processing result, the transmission power control means The mobile communication system according to claim 1, wherein the control channel transmission power is controlled. A cell radius determination method in a mobile communication system including a plurality of base station devices forming each cell and a base station control device for controlling the plurality of base station devices, wherein the base station control device A propagation delay acquisition step of acquiring the uplink propagation delay of the mobile device measured by the device from each base station device; and the mobile device acquires the downlink common control channel received power obtained from each base station from the mobile device. A reception information acquisition step, and a transmission power control step for controlling the downlink common control channel transmission power of each of the base station devices. In the transmission power control step, a propagation delay at a cell boundary and an uplink propagation delay of the mobile device If the difference is smaller than a predetermined value, it is determined that the mobile station is present at the cell boundary, and the transmission power control step further includes When it is determined that a mobile station exists at the cell boundary, the downlink common control channel received powers are compared with each other, and the downlink common control channel transmission power of each base station apparatus is controlled so that the difference therebetween is reduced. A cell radius determination method characterized by:   The transmission power control step performs a moving average process of the downlink common control channel received power when it is determined that the mobile station is present at the cell boundary, and the downlink common station of each base station apparatus based on the processing result 4. The cell radius determination method according to claim 3, wherein control channel transmission power is controlled.

Images