JPH10248078A - Speed detection system utilizing electric field strength in mobile communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a mobile station to make communication with a base station of a micro cell when the mobile station is moved at a low speed or comes at a standstill and to make communication with the base station of a macro cell when the mobile station is moved at a high speed in a mobile communication system adopting hierarchical cell structures where macro cells and micro cells are in coexistence. SOLUTION: In the case that a mobile station 1 makes a speech through a micro cell base station (A2), a reception section 21 always sends a strength of a signal from the mobile station 1 to a control section 23 as electric field information. The control section 23 calculates the electric field information and sends a median or a mean value of the electric field strength to a base station controller 5. The base station controller 5 calculates a change in the received electric field strength information and discriminates it to be a high speed movement when the change is large and hands over the base station (A2) to a macro cell base station (C4). The base station controller 5 discriminates it to be a low speed movement or a stop when the change is small and hands over the base station (A2) to a micro cell base station (B3) in the case that the mobile station 1 moves from the micro cell base station (A2) to the micro cell base station (B3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to mobile communication systems, and more particularly to channel switching (handover) in a digital cellular phone system having a hierarchical cell structure in which micro cells and macro cells are superimposed.

[0002]

2. Description of the Related Art A conventional channel switching method is applied to a system as shown in FIG. This system is composed of a plurality of microcells 12 and a macrocell 11 that covers the service area. The access to these two cells uses a common wireless interface, and the speed is about the walking speed or less. Mobile terminal 1 that moves with
6 communicates with the microcell base station 13, and the mobile terminal 15 moving at a speed higher than this speed communicates with the macrocell base station 14.

Each microcell base station transmits a radio control channel in synchronization with a radio control channel transmitted from the macrocell base station in a time-division manner.

On the other hand, a mobile terminal located in a macro cell repeatedly measures the reception level of the radio control channel of the micro cell base station, and according to the moving speed estimated from the speed at which the mobile terminal changes, the mobile terminal determines whether the mobile terminal is in the macro cell base station. Select a station or microcell base station to access.

In such a system, when a moving speed of a mobile terminal changes during communication, a method of automatically switching a base station during communication between a microcell base station and a macrocell base station is, for example, a special method. It is disclosed in Japanese Unexamined Patent Publication No. Hei 6-224828.

FIG. 8 shows another switching method.
As shown in the figure, the exchange 3, the indoor radio base station 2a, the outdoor radio base stations 2b and 2c, the radio base station under communication and the adjacent radio base station are indoor radio base stations or outdoor radio base stations. A mobile station 1 having a function of identifying a mobile station and a function of measuring a received electric field intensity of an adjacent radio base station and a change amount of a received electric field intensity per unit time. Regardless of the strength, if there is a wireless base station among the adjacent wireless base stations in which the received electric field intensity and the amount of change in the received electric field intensity per unit time both exceed the respective thresholds, the handover method required for the wireless base station (JP-A-7-203517) has also been proposed.

[0007]

On the other hand, if a method of estimating the moving speed from the speed at which the reception level from the base station fluctuates in a mobile terminal is applied to a currently operating system, a huge number of terminals are required. Must be remodeled. It is also known that the amount of change in the received electric field with respect to the moving speed is inversely proportional to the square to the fourth power of the distance between the base station and the mobile terminal. That is, it is necessary to reduce the weight for the amount of change at a high reception electric field and increase the weight at a low reception electric field.

[0008]

A feature of the present invention is that in a mobile communication having a hierarchical cell structure in which a macro cell and a micro cell are superimposed, a micro cell is first grasped from the viewpoint of effective use of frequency. The microcell base station constantly monitors the strength of the received electric field from the mobile station, and reports the median value of the received electric field to the base station controller at a preset cycle.

The base station controller calculates the difference between the value reported this time and the value reported last time, and calculates the amount of change. When calculating the amount of change, the base station controller prepares in advance a table of the received electric field and the correction coefficient for the amount of change, and performs the correction. If the amount of change after the correction exceeds a specified value, it is determined that the mobile station is moving at high speed, and handover is performed from the micro cell to the macro cell. On the other hand, when talking through the macro cell and moving little or not, the handover from the macro cell to the micro cell is performed because the fluctuation of the received electric field in the macro cell is smaller than a preset value. Do.

When stopping or moving at a low speed, capturing microcells enables effective use of the frequency in a high traffic area, while a mobile station moving at a high speed does not frequently switch channels and provides high quality communication. Can be secured.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows a hierarchical cell structure in which a macro cell and a micro cell are superimposed,
When the mobile station moves between these cells, the base station detects the moving speed. If the speed is high, the communication is performed through the macro cell, and if the speed is low, the communication is performed through the micro cell.

More specifically, as shown in FIG. 2, when the mobile station is moving in the direction from the microcell base station A to the microcell base station B, the mobile station always moves in the microcell base station A during a call. The intensity of the radio wave from the station 1 is monitored, and is transmitted from the receiving unit 21 to the control unit 23 as electric field information. The control unit 23 calculates the median value or the average value of the data in the cycle set in advance and sends the data to the base station controller 5.

The base station controller 5 calculates the amount of change in the electric field from the received electric field strength data and estimates the moving speed based on the magnitude of the change.

FIG. 3 is an example of a graph showing a change in electric field intensity. Since it is difficult to obtain the amount of change in the electric field strength from this graph, data is gathered to some extent and the median value is obtained.

FIG. 4 shows an example in which the median value is obtained every 1.8 seconds. When moving 20 km / h, the median value is obtained once every 10 m. FIG. 5 shows the absolute value of the difference between the median values. Here, the number of times that the amount of change exceeds a predetermined value is counted, and n and m are determined so that m out of n times are moved at high speed. At this time, the amount of change is weighted by the absolute value of the electric field intensity. This is because the propagation loss in mobile communication is almost linear when the distance axis is logarithmic at short distances, as is clear from the Okumura curve and the Hata formula. The amount of change is evaluated to be small, and the amount of change at a distant place (a place where the absolute value of the electric field strength is low) is largely evaluated. For example, the received electric field strength is approximated by the following equation as a function of distance. E (dBμV / m) = A−
B logR where E: reception electric field strength, A, B: frequency, transmission output,
A constant determined by the antenna height or the like, R: distance. The weighting based on the strength of the received electric field is corrected by the following equation.

Amount of change = Amount of change before correction × Amount of change when moving away from the wireless station by 10 m / B × (Electric field strength at that location−Electric field intensity assumed 10 m before) B: Frequency, Constant determined by transmission power, antenna height, etc.

If the amount of change in the electric field strength from the mobile station that is talking on the micro cell exceeds a predetermined value, it is determined that the mobile station is moving at a high speed, and the exchange switches over to the macro cell. Conversely, when talking in a macro cell, the change in the strength of the electric field from the mobile station is constantly monitored, but handover to the micro cell is performed only when the change is extremely small and continues for a long time. Let it.
This is to prevent frequent handover from a microcell to a macrocell or vice versa.

Next, the procedure of handover will be described with reference to the flowchart of FIG. First, when the mobile station is in a standby state, it waits in one of the macro cell and the micro cell depending on conditions such as the strength of radio waves from the base station. An outgoing / incoming call is made through the cell in the standby state, and a call is made through each of the macro cell and the micro cell. The receiving unit of the base station constantly monitors the strength of the electric field of the mobile station and sends the electric field information to the control unit. The controller processes this data and periodically sends it to the base station controller. The base station controller calculates the amount of change by taking the difference between the transmitted data and the immediately preceding data. The result is corrected. If the corrected amount of change continuously exceeds the specified value in the micro cell, it is determined that the micro cell is moving at a high speed, and handover to the macro cell is performed. In the macro cell, the corrected change amount is extremely small (smaller than a low value having a margin above the specified value).
If the mobile station has been kept for a long time, it is determined that the mobile station has stopped or is walking and handover to the micro cell is performed.

[0019]

According to the present invention, when a mobile station has a hierarchical cell structure in which a macro cell and a micro cell coexist, and the mobile station is performing a call through the base station of the micro cell, the strength of the radio wave from the mobile station at the base station side is reduced. In order to determine the moving speed based on the amount of change,
Since there is no need to perform speed detection on the mobile station side, a handover from a micro cell to a macro cell can be performed at high speed without modifying the mobile station.

Further, according to the present invention, when a mobile station is performing a call through a macro cell base station in a hierarchical cell structure in which a macro cell and a micro cell coexist, the base station side changes the intensity of radio waves from the mobile station. Since the moving speed is determined by the amount, there is no need to perform speed detection on the mobile station side.
The handover from the macro cell to the micro cell can be performed when the mobile station is at a low speed or stopped without any modification or the like.

Further, according to the present invention, the accuracy of speed detection can be made more accurate.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a hierarchical cell structure in which a macro cell and a micro cell are superimposed.

FIG. 2 shows an embodiment of a mobile communication system using the speed detection method of the present invention.

FIG. 3 is a diagram illustrating an example of a received electric field strength of a base station.

FIG. 4 is a diagram illustrating an example of a median value of a received electric field strength of a base station.

FIG. 5 is a diagram illustrating an example of a change amount of an electric field intensity.

FIG. 6 is a flowchart of a handover using the speed detection method of the present invention.

FIG. 7 is a diagram showing a conventional technique.

FIG. 8 is a diagram showing a conventional technique.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mobile station 2 microcell base station A 3 microcell base station B 4 microcell base station C 5 base station controller 21 receiving section of microcell base station A 22 transmitting section of microcell base station A 23 microcell base station A 31 Microcell base station B receiving section 32 Microcell base station B transmitting section 33 Microcell base station B controlling section 41 Macrocell base station C receiving section 42 Macrocell base station C transmitting section 43 Macrocell base station Control part of C

Claims (5)

[Claims] In a mobile communication having a hierarchical cell structure in which a macro cell and a micro cell coexist, when a mobile station is communicating via a base station of the micro cell, the base station of the micro cell is transmitted from the mobile station. A speed detection method that constantly monitors the strength of the radio wave and, when the amount of change in the strength of the radio wave is large, determines that the vehicle is moving at high speed and switches the channel from the micro cell to the macro cell. 2. Description of the Related Art In a mobile communication having a hierarchical cell structure in which a macro cell and a micro cell coexist, when a mobile station is communicating through a base station of the macro cell, the base station of the macro cell transmits radio waves from the mobile station. A speed detection method characterized in that the strength is constantly monitored, and when the change in the strength of the radio wave is small, it is determined that the mobile station is stopped or moving at a low speed, and the channel is switched from the macro cell to the micro cell. 3. The mobile station according to claim 1, wherein when the mobile station is performing a call through the base station of the macro cell, the base station of the macro cell also constantly monitors the intensity of the radio wave from the mobile station, and based on the monitoring result. And a switching from a macro cell to a micro cell channel. 4. The method according to claim 1, wherein weighting is performed on the amount of change in radio wave intensity. That is, when the radio wave is strong, the weight is reduced, and when the radio wave is weak, the weight is increased. A speed detection method characterized by correcting a speed detection error when moving far. 5. The handover from the microcell to the macrocell is performed when the amount of change in the electric field strength exceeds a certain prescribed value, and the handover from the macrocell to the microcell falls below a value considerably lower than the prescribed value. A speed detection method characterized in that the handover is not performed frequently between the micro cell and the macro cell even when the moving speed of the moving object changes variously by performing the process only when a certain period of time has elapsed and when the moving speed of the moving object changes in various ways.