JP2011018966A - Radio base station of mobile data communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve throughput of a terminal to be connected while putting, in an allowable range, a ratio of terminals involuntarily interrupting communication without intention during communication, in a mobile communication system.SOLUTION: This radio base station of a mobile data communication system includes: a storage device for storing a correspondence relationship between a date and a radio parameter; a control device for setting the ratio parameter on the date stored in the storage device; and a device for controlling radiation of radio waves from an antenna causing inter-cell interference with a cell of another radio base station in accordance with the radio parameter set by the control device. The radio parameter is a tilt angle or transmission power of the antenna.

Description

  The present invention relates to a radio base station in a mobile data communication system in which the throughput of data communication is determined by the radio signal reception quality of a terminal.

  Intercellular interference is a problem in cellular mobile communication systems that repeatedly use radio waves of the same frequency. In mobile communication systems up to the third generation, terminal reception quality (Reception SIR: Signal to Signal) is reduced against reception degradation of the mobile terminal (hereinafter referred to as terminal) due to distance attenuation, shadowing, fading, inter-cell interference, etc. The error rate of digital communication of voice and data is kept within a certain range by adaptive transmission power control (Transmission Power Control) based on the interference ratio. Therefore, the data rate of the terminal is almost constant everywhere in the cell.

  In mobile communication systems of 3.5 generations and beyond (1xEV-DO, HSDPA, LTE, etc.), a cell that specializes in data communication and uses a high data rate coding method for terminals with good reception quality. It has succeeded in improving the overall throughput. In this mobile communication system after the 3.5th generation, it is possible to improve the throughput by improving the reception quality of the terminal. For this purpose, a method of reducing inter-cell interference is effective. However, in the vicinity of the cell boundary or in the area where the most prominent reception path is shielded, it is necessary to overlap the cells so that the terminal can be handed over without communication interruption, and inter-cell interference is usually unavoidable. .

  Therefore, adjustment of inter-cell interference as conventional area optimization is performed by fixed radio parameter setting in which throughput and communication continuity are traded off.

  Patent Document 1 discloses that the tilt angle of an antenna is controlled in accordance with the amount of traffic from the viewpoint of adjusting the size of a service area.

JP-A-9-154168

  In data communication of mobile communication systems of 3.5 generations and beyond, the throughput depends on the radio wave reception quality of the terminal, so we want to improve throughput by reducing inter-cell interference, but reducing inter-cell interference There is a demerit that makes it easier for a mobile terminal to disconnect.

The technique described in Patent Document 1 does not consider appropriately adjusting inter-cell interference in order to reduce communication interruption of a moving terminal.
An object of the present invention is to improve the throughput of connected terminals while paying attention to the behavior of a subscriber having a mobile terminal and keeping the ratio of terminals that unexpectedly disconnect during communication within an allowable range. .

  The radio base station of the disclosed mobile communication system is set by a storage device that stores a correspondence relationship between date and time and a radio parameter, a control device that sets a radio parameter at the date and time stored in the storage device, and a control device. And an apparatus for controlling emission of radio waves from an antenna, which generates inter-cell interference with cells of other radio base stations according to the radio parameters.

  A desirable radio parameter of another aspect of the radio base station is the tilt angle of the antenna, and yet another aspect of the radio parameter is the transmission power of the antenna.

  According to the disclosed radio base station, the mobile communication system allows the ease of call disconnection to improve the throughput at a time when the occurrence of call disconnection is low, and at the time when the occurrence of call disconnection is high, The difficulty of disconnecting a call can be improved.

It is a table | surface which shows the relationship between a data rate and C / I. It is a conceptual diagram shown about the change of the influence range of the own cell by antenna tilt angle change. It is a figure explaining the case where the overlap between cells is large. It is a figure explaining the case where the overlap between cells is small. It is a block diagram which shows the structure of a wireless base station. 6 is a diagram showing a configuration example of a radio parameter time table in the configuration of the radio base station in FIG. 5. FIG. It is a flowchart of the control method of a radio | wireless parameter. It is a figure explaining the case where the cell of two radio base stations is interfering. It is the graph which illustrated the time change of the terminal connection number of two radio base stations. It is the graph which illustrated the time change of the communication disconnection rate of two radio base stations.

  Hereinafter, as an example, CDMA2000 1xEV-DO, which is a 3.5 generation mobile communication system, will be described. However, the present invention can be applied to a mobile communication system in which the Data Rate varies greatly depending on the degree of inter-cell interference.

In CDMA2000 1xEV-DO, which is a 3.5 generation mobile communication system, the radio base station changes the modulation system according to the received signal quality of the terminal. The data rate is determined as shown in FIG. 1 by C / I (the following formula) of the downlink signal reported by the terminal. Figure 1 shows the literature (P.Bender, P.Black, M.Grob, R.Padovani, N.Sindhushayana, and A.Viterbi, “CDMA / 1xEV-DO: A Bandwidth-Efficient High-Speed Wireless Data Service for Nomadic Users ”, IEEE Comm.Mag, July, 2000).
C / I = ΣS (k) / (No + ΣI (l) + ΣJ (m) + ΣK (n))
here,
・ S (k): Pilot power in demodulated multipath (including direct wave) among pilots of own cell ・ No: Thermal noise power density ・ I (l): Received power density of pilots in other cells (= interference) wave)
・ J (m): Power density of multipath components (including direct waves) that could not be demodulated among pilots of own cell ・ K (n): Power of interference wave by signals other than 1xEV-DO system in the band Density ・ k, l, m, n: Number of multipaths and sectors When there is an influence of interference waves from other radio base stations, C / I is about 0 dB or less, and the data rate is 921.6 kbps or less. Become. When there is one more interference wave, the C / I is further deteriorated by about 3 dB, and the data rate is 307.2 kbps to 614.4 kbps or less. When there is almost no influence of interference, C / I is almost determined by the ratio of the pilot power and noise power of the own cell, and the maximum Data Rate can be 2457.6 kbps.

  Since the radio waves emitted from the radio base station array antenna are directional, the range of the radio base station radio waves should be limited as shown in Fig. 2 by installing the array antenna at a high position and adding a depression angle. Is possible. This depression angle is generally called a tilt angle. The array antenna can change the tilt angle by an electronic method. The tilt angle can be increased, the own cell can be narrowed down, and the influence of interference on adjacent cells can be reduced. It is possible to reduce the tilt angle, expand the own cell, and increase the influence of interference with adjacent cells.

  The radio wave emitted from the radio base station can control its transmission power. By weakening the transmission power, it is possible to narrow down the own cell and reduce the influence of interference on adjacent cells. In this case, the C / I in the adjacent cell is improved, but the C / I in the own cell is deteriorated. Therefore, the transmission power of the cell itself for which C / I is desired to be improved is not weakened.

  In order for a terminal and a radio base station to be able to communicate, it is a condition that there exists a path (referred to as a communicable path) through which data communication can be performed between the radio base station and the terminal. In addition to direct waves, communicable paths include reflections and diffractions, and radio waves are blocked by various shielding objects such as buildings and features, so it is possible to communicate with points where there are paths that can communicate with wireless base stations. There is a point where a simple path does not exist. At a point where there is no path communicable with the radio base station, the terminal is unable to communicate, and communication is interrupted if the terminal enters that point while communicating. Such a point is called a deterioration point. Here, as shown in FIG. 3, if there are a radio base station B01 and a radio base station B02, and radio waves are irradiated from different directions in the same area, a path communicable with the radio base station B01, and a radio base station B02 The number of paths that can communicate with each other decreases. That is, the deterioration point decreases. When the tilt angle between the radio base station B01 and the radio base station B02 is set small as shown in FIG. 3 and the overlap between the cells is large, there are few deterioration points, and the radio base station B01 and the radio base station B02 as shown in FIG. When the tilt angle is set large and the overlap between cells is small, the deterioration points increase. At the boundary between cells, since there are few paths that are relatively far from both radio base stations and sufficient electric field strength can be obtained, it is necessary to prevent an increase in deterioration points due to the overlap between cells. Even when a local deterioration point is allowed, the overlap between cells is required to a minimum from the viewpoint of continuity of the communication service area.

  The reason why the terminal that is stationary is less likely to disconnect is because the terminal is communicating at a point where the terminal can communicate. On the other hand, the reason why the moving terminal often disconnects is nothing but the probability that the terminal passes through the deterioration point. Therefore, the terminal that is stationary has almost no change in the probability of communication interruption even if the number of deterioration points increases. A moving terminal is affected by an increase in the number of deterioration points, and the probability of communication interruption increases. As a result, when the overlap between cells is small, there are many deterioration points, and a mobile terminal frequently loses communication. When the overlap between cells is large, there are few deterioration points, and it is difficult for a moving terminal to disconnect communication. Regardless of the size of the overlap between cells, a stationary terminal that is not at the degradation point is less likely to be disconnected.

  In general, the number of mobile terminals is large during the daytime when there are many people going out, especially in the morning and evening commuting hours, and conversely at night when there are few people outside. Therefore, in the commuting time zone, by setting the tilt angle small and expanding the overlap between cells, the communication interruption of the moving terminal is reduced, and the other time zone, or especially at night when there are few outsiders In addition, by setting a large tilt angle and reducing the overlap between cells, the C / I of a stationary terminal can be improved and the throughput can be improved.

  From the aggregation of C / I data of downlink signals reported from terminals throughout the cell to the radio base station, it is possible to examine the degree of influence of throughput and inter-cell interference.

  In a time zone in which the number of communication interruptions is small relative to the number of terminal connections in the cell, the overlap between cells is sufficient, indicating that the number of communication interruptions is reduced. Conversely, in a time zone where the number of communication disconnections is large for the number of terminal connections, the overlap between cells is insufficient, indicating that it does not contribute much to the decrease in the number of communication disconnections.

  In a time zone in which the number of handovers related to the cell is large for the number of terminal connections in the cell, the overlap between cells is sufficient, indicating that the number of communication interruptions is reduced. Conversely, in a time zone where the number of handovers is small relative to the number of terminal connections, the overlap between cells is insufficient, indicating that it does not contribute much to the reduction in the number of communication interruptions.

  The degree of overlap between cells can be changed by changing the tilt angle or changing the transmission power, but the effects by time are the summation of C / I data of the downlink signal, the number of terminal connections, the number of communication interruptions The number of handovers can be obtained by time.

  Even in the time zone when there are many mobile and out-of-doors, even if C / I is improved by reducing the overlap between cells, the number of communication interruptions and the number of handovers cannot be ignored. Let's go. In such a time zone, in order to keep the number of communication interruptions within an allowable range, the overlap between cells is increased, that is, the tilt angle is decreased, so that the number of communication interruptions is decreased and the number of handovers is increased. Control that increases transmission power is effective.

  In the time zone when there are few mobile and out-of-doors, C / I can be improved by reducing the overlap between cells, and the number of communication interruptions will not increase so much. In such a time zone, control is effective in which the overlap between cells is reduced, that is, the tilt angle is increased or the transmission power is reduced, within a range where the number of communication interruptions is within an allowable range.

  From the execution result of such control, a setting pattern of radio parameters such as time-dependent tilt angle and transmission power is determined so that the best throughput can be obtained while keeping the number of communication interruptions within an allowable range. Based on this time-dependent radio parameter setting pattern, by controlling the radio base station so that the radio parameter setting value is determined at a predetermined date and time, the proportion of terminals that are disconnected is within an allowable range. It is possible to maximize the throughput of the terminal while keeping it within the range.

  Below, a more specific aspect is demonstrated. FIG. 5 is a block diagram showing a configuration of the radio base station.

  The radio base station includes a radio base station device D01, an array antenna AA01, a beam forming device E01, and a radio base station control device F01. The radio base station apparatus D01 inputs / outputs an RF signal by changing / amplifying transmission / reception data. The radio base station apparatus D01 accumulates the result of monitoring the number of connected terminals, the number of communication interruptions, and the number of handovers in the quality data acquisition unit G01, and C / I information of the downlink signal obtained from the received data from the terminal . The beam forming device E01 forms a gain characteristic pattern for emitting the RF signal input to the array antenna AA01 as a radio wave having directivity. The radio base station control device F01 has a radio parameter time table T01 in the storage device, and outputs a transmission power control signal to the radio base station device D01 according to the contents of the time table T01, thereby transmitting RF signal transmission power. And the tilt angle of the radio wave emitted from the array antenna AA01 is controlled by outputting a tilt angle control signal to the beam forming device E01.

  FIG. 6 is a diagram illustrating a configuration example of a radio parameter time table T01 in the configuration of the radio base station in FIG.

  The radio parameter time table T01 includes, for example, date / time information, transmission power, and tilt angle information. The radio parameter time table T01 is sorted in the order of date and time information, and constitutes a circulation table in which the schedule after the last row (date and time information) is the schedule of the first row. The first line of the radio parameter time table T01 means that the transmission power is controlled to be 40 dB and the tilt angle is 2 ° on Monday at 6:50:00, and the radio base station control device F01 follows Monday accordingly. The radio base station apparatus D01 and the beam forming apparatus E01 are controlled so that the transmission power is 40 dBm and the tilt angle is 2 ° at 6:50:00.

  FIG. 7 is a flowchart of a radio parameter control method according to the radio parameter time table T01 in the radio base station controller F01. A one-line schedule is read from the radio parameter time table T01 (step 70). Wait until the designated time indicated by the date and time information of the read schedule (step 72) .When the designated time comes, the designated transmission power is set in the radio base station apparatus D01, and the designated tilt angle is set in the beam forming apparatus E01 ( Step 74). The above processing is repeated.

Next, an example of determining information in the radio parameter time table T01 will be described using the case of FIG. 8 in which cells of two radio base stations interfere with each other. The radio base station B01 has a radio parameter time table T01, and the radio base station B02 has a radio parameter time table T02, and each controls the tilt angle according to time. At the initial stage, the contents of the radio parameter time table T01 and the radio parameter time table T02 are empty, and the initial radio parameters are set to satisfy the following conditions regardless of the time zone according to the conventional method And
Number of terminal connections per day for B01 station x1 ≥ Minimum number of terminal connections for B01 station X1
Number of terminal connections per day at station B02 x2 ≥ Minimum number of terminals connected at station B02 x2
B01 communication interruption rate l1 ≤ B01 station allowable communication interruption rate L1
B02 communication interruption rate l2 ≤ B02 station allowable communication interruption rate L2
(In the above, B01 station: radio base station B01, B02 station: radio base station B02)
here,
・ Communication loss rate: Number of communication interruptions / number of terminal connections (10 minutes)
・ Minimum number of terminals connected: Number of terminals connected to the station in a day set as an operation target ・ Allowable communication disconnection rate: Allowable limit of communication disconnection rate set as an operation target become that way.
(1A) Increase the tilt angle:
Due to area reduction, the number of terminal connections does not change or decreases. The communication interruption rate does not change or increases due to an increase in deterioration points.
(1B) Decreasing the tilt angle:
As the area expands, the number of terminal connections does not change or increases. The communication interruption rate does not change or decreases due to a decrease in deterioration points.
(2A) Decrease transmission power:
Due to area reduction, the number of terminal connections does not change or decreases. The communication interruption rate does not change or increases due to an increase in deterioration points.
(2B) Increase transmission power:
As the area expands, the number of terminal connections does not change or increases. The communication interruption rate does not change or decreases due to a decrease in deterioration points.

  Examples of the results of monitoring the number of connected terminals and the communication interruption rate by time are shown in FIG. 9 and FIG. From the graph of the communication interruption rate in FIG. 10, both the wireless base station B01 and the wireless base station B02 have a communication interruption rate that is significantly lower than the allowable communication interruption rates L1 and L2 depending on the time zone. It is possible to increase and reduce inter-cell interference.

  For example, in the time zone from 23:00 to 23:10, the wireless base station B01 and the wireless base station B02 are both set to increase the tilt angle because the communication disconnection rate is much lower than the allowable communication disconnection rates L1 and L2. Is possible. Therefore, the setting for increasing the tilt angles of the radio base station B01 and the radio base station B02 by 1 degree is set to the same time zone on the next day on the radio parameter time tables T01 and T02.

  The next day, the tilt angle is controlled at 23:00, but check the change in the number of terminal connections, communication disconnection rate and C / I due to it, the terminal connection number and communication disconnection rate are within the allowable range, Check if C / I is improving. If the number of connected terminals and the communication interruption rate are still within the allowable range and the C / I is improving, the setting for further increasing the tilt angle by one degree is set on the radio parameter time tables T01 and T02 on the next day. Set the time zone. Conversely, if the number of terminal connections and the communication disconnection rate exceed the allowable range, the settings of the previous day are restored.

  In this way, by repeating the steps of quality data confirmation, radio parameter time table setting, and radio parameter control, the radio parameter time table enables control of radio parameters that improve throughput for each time zone.

  Although the case where the tilt angle is changed has been described here, the same control can be performed when the transmission power is changed. The difference when changing the transmission power is that when the transmission power of the own station is weakened, the throughput in the adjacent cell is improved, but the throughput in the own cell deteriorates, so it is necessary to consider the overall effect. There is a point.

  According to the radio base station of the present embodiment, the mobile communication system allows the ease of call disconnection to improve the throughput when the call disconnection is low, and improves the throughput while the call disconnection occurs frequently. It is possible to improve the difficulty of disconnecting the call.

  AA01: Array antenna, B01: Radio base station 1, B02: Radio base station 2, D01: Radio base station device, E01: Beam forming device, F01: Radio base station control device, G01: Quality data acquisition unit, T01: Radio Parameter time table 1, T02: Radio parameter time table 2.

Claims (7)

A storage device for storing the correspondence between the date and time and the wireless parameters;
A control device for setting the wireless parameter at the date and time stored in the storage device;
A mobile communication device comprising: a device for controlling radio wave emission from an antenna that generates inter-cell interference with a cell of another radio base station in accordance with the radio parameter set by the control device; System radio base station. The radio base station of the mobile communication system according to claim 1, wherein the device that controls emission of radio waves is a beam forming device that changes a tilt angle of the antenna. The radio base station of a mobile communication system according to claim 1, wherein the device that controls emission of radio waves is a radio base station control device that changes transmission power of the antenna. The radio base station of the mobile communication system according to claim 1, further comprising a quality data acquisition unit that acquires the degree of inter-cell interference according to time. The radio base station of the mobile communication system according to claim 4, wherein the quality data acquisition unit acquires the number of terminal connections. 6. The radio base station of a mobile communication system according to claim 5, wherein the quality data acquisition unit further acquires a communication interruption number. Store the correspondence between date and time and wireless parameters in advance,
Set the wireless parameters at the stored date and time,
A method of controlling a radio base station of a mobile communication system, characterized by controlling emission of radio waves from an antenna that causes inter-cell interference with a cell of another radio base station according to the set radio parameter .

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