JP2965057B2 - Method for monitoring interference state in base station of mobile communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile system in which a service area is divided into a plurality of zones, and a plurality of radio channels of different frequencies are repeatedly used in each zone throughout the service area so as to minimize interference. In a communication system, the present invention relates to a method of monitoring the interference state of radio waves performed by each base station, and particularly to monitoring the interference state of radio waves in a radio channel having the same frequency as the radio channel of the base station, and the interference state becomes worse than a specified value. The present invention relates to an interference monitoring method in an autonomous decentralized base station that switches to another frequency channel or stops operation when the operation is performed.

[0002]

2. Description of the Related Art In a mobile communication system, as shown in FIG. 1, a service area SA is divided into a plurality of zones Z ₁ , Z ₂ , Z ₃ ,.
Divided into Z _M, these zones Z _1, Z _2, ..., base station B to Z _{M
S 1, BS 2, ...,} BS M are provided, each of the zone Z _1, Z
_2, ..., for example, Z _M radio channel frequency f _1, f _2, f _3,
..., assign a f _6, as shown in FIG. In this case, as much as possible in consideration as radio waves in the same frequency of the radio channel does not interfere assigns the radio channel the same frequency f ₁ to a zone distant from one another, for example, as zones Z ₁ and Z _6, the entire service area , A plurality of channels of different frequencies are repeatedly used to increase the frequency utilization rate.

[0003] Such a frequency arrangement has conventionally been
The distance between radio base stations of the same frequency so that radio waves from each radio base station BS in a plurality of other zones using channels of the same frequency in each zone are sufficiently attenuated and mutual interference is allowable. And the transmission power were calculated.

[0004]

As described above, in the conventional system, the same set of frequencies f ₁ , f ₂ ,..., F ₆ is repeatedly used as much as possible in order to increase the use efficiency of radio waves as much as possible. In such a conventional system, when an unexpected new propagation path is generated or the existing propagation path is lost due to a change in the propagation environment of the radio wave, mutual interference of the same frequency radio waves from two radio base stations is caused. Sometimes occurred. Conventionally, to measure such interference,
Radio waves are radiated from each of the two radio base stations, the electric field strength in each case is measured, and the results of both measurements are comprehensively analyzed to determine the range affected by the radio waves of each base station. I was Even after the mobile communication system is in operation, the service area is expanded and base stations in new zones are created around it, some or all of the frequency allocation is changed, and large buildings and large towers are added. If the radio wave propagation environment changes, such as being made or being demolished, interference may occur or the interference may disappear. Therefore, in order to grasp the interference situation of the channel of each zone with the channel of another zone of the same frequency in each zone after the operation of the mobile communication system, the transmission of the radio wave of the base station in that zone is stopped. Had to do. In each case, the state of the radio wave was measured using a dedicated measuring device.

Conventionally, in order to know the interference state of radio waves in a certain zone, one of the other base stations using the same frequency is used.
Since electric field intensity measurement is performed by sequentially radiating radio waves, it takes time for the measurement and the determination of the interference situation. In particular, during operation, the electric field strength of radio waves from other base stations is measured in a region where radio waves from the base station in the zone are considered to have a sufficient reception electric field level, so that the base station in the zone is measured. It is necessary to stop transmission of radio waves, but since transmission of radio waves cannot be stopped frequently during operation, it takes a considerable amount of time to measure radio waves from other base stations. For this reason, the measurement cannot be performed in accordance with the change in the radio wave environment, and the measurement is considerably delayed, so that an area in an undesirable reception state in the zone may not be improved for a relatively long time. In addition, since radio waves are radiated only from one of a plurality of base stations of the same frequency that are considered to interfere with each other, the operation of the original mobile communication is deteriorated during that time.

Accordingly, an object of the present invention is to provide a method capable of easily and reliably monitoring an interference state even when a mobile communication system is in operation.

[0007]

According to the present invention, (a) the mobile station periodically measures the electric field strength and quality of the downlink radio wave from the radio base station, and (b) the measurement result. was reported to the radio base station, (c) the reported measurement results, pre
Whether the measurement result is abnormal compared to the determined reference characteristic
The radio base station statistically processes the result of the judgment to obtain data on the state of radio waves radiated from its own station. (D) The plurality of data are comprehensively evaluated, and the radio base station Monitoring the mutual interference between the transmitted radio wave and another radio wave of the same frequency.

According to the second aspect of the present invention, the quality is a bit error rate. According to the invention of claim 3, the downlink radio wave is a downlink control channel. According to the invention of claim 4, in the step (b), the base station requests the mobile station to transmit a measurement result, and in response to the request, the mobile station transmits the measurement result to the base station. I do.

According to the fifth aspect of the present invention, the above step
In (b), the mobile station voluntarily transmits the measurement result at a fixed period. According to the invention of 請 Motomeko 6, the reference characteristics in claim 1 is a characteristic determined based on the characteristic representing an ideal relationship between the field intensity and bit error rate, abnormal measurement result is compared with a reference characteristic It is determined whether or not the ratio is abnormal, and the ratio of abnormalities in the measurement results collected during a predetermined period is used as an index indicating the interference state.

According to the invention of claim 7, abnormal or not by comparing the claims the reference characteristic is divided into a plurality of electric field intensity area in claim 1, and measurement results determined error rate threshold for each region Is determined, and a weighted addition value of the ratio of the abnormality determination in each area is used as an index indicating the interference state.

[0011]

[Embodiment and Examples of the invention shows the mobile station MS a configuration example of the base station BS in one zone Z _i in the case of applying the invention to a mobile communication system of FIG. 1 in FIG. The base station BS of the zone Z _i to the radio transceiver 13, a processing unit 17, and a reference characteristic storage unit 18. The radio base station BS can perform two-way communication with the zone Z _j in the mobile station MS and the downlink radio wave to move (wave for mobile station) RW _D and uplink radio (radio waves for wireless base station) RW _U. Downlink radio RW _D to the base station BS transmits includes downlink control channels and downlink speech channels, uplink radio RW _U transmitted by the mobile station includes a different uplink control channel and an uplink communication channel of downlink radio frequency.

[0012] from the base station BS transmission receiver 13, it transmits the control signal and the call signal by the downlink control channel and downlink speech channels that zone Z _i is used. The control signal transmitted on the downlink control channel has a predetermined format including, for example, a call control signal relating to call processing, an identification signal for identifying a base BS, an identification signal for a surrounding zone, and a synchronization signal. As in the prior art, the mobile station MS is continuously or intermittently receiving the downlink control channel in the call waiting state. Upon receiving an incoming call signal for the mobile station MS through the control channel, it transmits a control signal acknowledging the reception signal to the base station BS through the uplink control channel, and further receives the downlink communication channel according to the instruction given from the base station BS through the downlink control channel. Then, the communication signal is transmitted through the uplink communication channel.

According to the present invention, the electric field strength (received signal level) and communication quality (eg, bit error rate BERR) of the downlink control channel received by each mobile station 14 in each zone are measured at desired intervals. They are transmitted to the base station through the uplink control channel, and the base station collects the field strength and communication quality data received from each mobile station over a desired period of time, statistically processes them and uses the channel used in the zone. Is analyzed, and when it is determined that the interference condition is worse than the prescribed condition, the used channel frequency in the zone is changed to another frequency. In order to execute such a method, the radio base station BS has an arithmetic processing unit 17,
A reference characteristic storage unit 18 is provided.

FIG. 3A shows a base station BS in a zone where there is no interference from a base station in another zone (ie, in an ideal state).
shows the curve E _a and B _a represents the relationship between the distance and the electric field strength and the bit error rate from _a, the horizontal axis represents distance and the vertical axis on the left field strength, the right vertical axis represents the bit error rate BERR . Ideal curve B _a of the ideal curve E _a and bit error rate of the electric field strength relative to the distance from the base station when there is no interference can be obtained by theoretical calculation. As the distance increases, the electric field strength decreases, and the bit error rate BERR gradually increases. When the electric field strength becomes smaller than a certain value (for example, 10 dbμV), the rate of increase (gradient) of the bit error rate BERR suddenly increases. Become. Bit error rate BERR size range (eg BERR <
0.1%, 0.1 ≦ BERR <0.3%, 0.3 ≦ BERR <1.0%, 1.0 ≦ BE
To the distance from the base station BS _a according to RR%), for example, error-free interval D _0, an error interval D ₁ of the small interval D ₂ moderate error, as the interval D ₃ error Univ Classify. Section D ₀ is a region that can talk without any trouble, the error of the section D ₁ is mainly due to fading, the error of the section D ₂ is mainly due to fading and noise. Errors section D ₃ is due to the decrease in S / N of the most received signal is a call difficult areas.

In the state without interference shown in FIG.
Examples of characteristics of the field intensity and bit error rate BERR relative to the distance from the base station BS _a in the case where the channel of the same frequency which is transmitted from the base station BS _b other zones away from the zone of _a exists as an interference radio wave Is shown in FIG. 3B. Curve E _b represents the field strength of the interference control channel from the base station BS _b. When such an interference channel exists, the base station BS
shows the electric field intensity curve E _b of the interference reception control channel from the base station BS _b in addition to the field strength of the desired reception control channel is lowered as shown by curve E _a as the distance from _a larger The curve B in FIG. 3B
_As shown in FIG. 3A, the frequency increases sharply from a position closer to the base station BSa than in the case of FIG. 3A. As a result, the error-free section D ₀ , the error small section D ₁ , and the error section D ₂ are shifted toward the base station BSa and shortened. On the other hand, the interval D ₃ error size is increased to the base station BS _a side.

When the mobile station MS is always in a call waiting state on the control channel of the visited zone, the mobile station MS repeatedly monitors the reception levels of the standby control channel and the control channels of the peripheral zones at regular intervals in order to detect a zone change. I have. In the present invention, the mobile station MS measures the bit error rate (BERR) of the control signal received on the standby control channel, and transmits it together with the reception level at that time to the base station BS through the uplink control channel. The control signal includes, for example, a synchronization word SW, a zone identification code (color code) as shown in FIG.
It has a predetermined format composed of repetition of CC and control data DATA. Although the control data DATA differs depending on the type of control signal, the synchronization word SW is predetermined in the system, and the identification code CC is determined for each zone. The measurement of the bit error rate BERR can be performed by detecting a known specific signal always included in the control signal, for example, any one of the synchronization word SW and the zone identification code CC or a desired combination thereof. The following method is possible as a method of transmitting the measured reception level and the bit error rate BERR to the base station.

(A) A dedicated signal format for reporting the measurement result is provided, and the measurement result is transmitted through the uplink control channel at each request of the base station, or the mobile station voluntarily sends the measurement result periodically. (b) Incorporate the measurement results into the existing predetermined control signals for various uplink control channels used in the current communication system and send them at the request of the base station, or voluntarily send them periodically. . The following method is an example of incorporating the measurement result into the control signal.

Incorporation into a position registration signal transmitted from the mobile station to the base station at fixed time intervals. -During communication, it is incorporated into a communication section control signal during communication performed in a time-division manner at a timing other than communication information. For example, in a personal digital cellular, in order to issue a transmission power control command to a mobile station, it is incorporated into a signal used to report the electric field strength of a downlink communication channel measured by the mobile station.

Incorporation into the call connection control signal. The method (a) has a disadvantage of increasing traffic since a new signal is provided. In contrast,
In the method (b), the measurement result is embedded in the conventional signal and transmitted, so that the increase in traffic is negligibly small.
And it can be easily implemented. When an interference control channel having the same frequency occurs in this way, the bit error rate of a received signal of a desired control channel increases, and communication quality deteriorates. This depends on the ratio of the electric field strengths of both channels that interfere with each other.

FIG. 5 shows reference characteristics representing the relationship between the electric field strength and the quality (bit error rate BERR), which serve as references for analyzing the interference state, and are stored in advance in the reference characteristic storage unit 18 in FIG. In FIG. 5, a straight line 5A represents the theoretical relationship between the electric field strength and the bit error rate BERR in an ideal state obtained by calculation in the case where there is no interference in FIG. 3A, and the straight line 5B is different from the theoretical relationship 5A in terms of fading and interference. It represents a permissible range predetermined in consideration of quality deterioration due to the influence. That is, the electric field strength measured by the mobile station (reception level E _RL )
Quality (BERR) it can be determined that does not receive any interference of a control channel from at least another zone if within region A ₁ below the straight line 5A of FIG. The measurement results show straight lines 5A and 5
If in a region surrounded by A ₂ and B it can be determined that the influence of fading and interference is an acceptable range. Measurement results can be determined that interference channel electric field strength which can not be ignored when it is in the area A ₃ of the above straight line 5B are present. Measurement points influence of interference is typically measured equal to or less than the allowable value is almost exist in a region A ₂ between the straight lines 5A and 5B, the area A ₁
Although intended to fall within considered not much, because it is not affected also interfere when there is measurement point enters an area A _1, in this example are a normal region A ₁ + A _2.

In the base station, the reference characteristics shown in FIG. 5 are stored in the reference characteristic storage unit 18 in advance, and the measurement results (E _RL , BERR) received from each mobile station are compared with the reference characteristics shown in FIG. Based on the data obtained by statistically processing the data of the comparison results (abnormal and normal judgment results) over a certain period of time, the influence of an interference channel from another zone on the channel used by that zone Is within an allowable range (a range in which the channel frequency does not need to be changed). Specifically, several methods are possible as follows.

(I) As a first method, for example, a reference characteristic case
The relation of the straight line 5B is stored in the storage section in advance, and the base station
Measurement results (E_RL, BERR)
Point (E _RL, BERR) is the area A in FIG._ThreeEnter or area A₁+ A_Two to go into
Is determined by the arithmetic processing unit 17. Area A_ThreeIf you enter
(Abnormal) and the measurement point (E_RL, BERR)
Count as normal points, area A₁+ A_Two No interference if entering
J). The arithmetic processing unit 17 operates for a certain period (for example, 1
Counts of all measurement points received over time)
Totals the abnormal point counts of all
Find the percentage of the number of points, and if the percentage is within the specified value,
The influence of the interference is determined to be within the allowable range. Greater than specified value
If so, it is determined that the effects of interference are not
Switch the channel frequency.

(II) As a second method, as shown in FIG. 6, the electric field strength in FIG.
₁ , R ₂ ,…, R ₅ and the error rate threshold for each of those regions
TH _1, TH _2, ..., decide in advance the TH _5. As each threshold value, for example, the average value of the straight line 5B in FIG. 5 in each of the divided areas is used. The arithmetic processing unit 17 of the base station determines the area to which the electric field strength ERL of the measurement point data (ERL, BERR) received from each mobile station belongs.
R _i (i = 1,..., 5) is determined and compared with a threshold value TH _{i of the} region,
Normal if less than or equal to the threshold value TH _i, is determined to be abnormal if greater than the threshold value. A ratio C _i of the number of measurement points determined to be abnormal to the number S _i of each measurement point in each of the regions R _{1 to} R _{5 over a} certain period is calculated. The average or simply the sum of these ratios C _i , i = 1,..., 5 is compared with a predetermined reference value. The average or the sum of the ratios C _i is calculated in the respective areas A _{1 to} A ₅
May be obtained by adding values weighted by weight coefficients W _{1 to} W ₅ determined in advance as ΣC _i W _i (i = 1,..., 5).

[0024] In method (II), instead of respectively using a fixed threshold value TH ₁ to TH ₅ for each region R ₁ to R _5, each of the regions R ₁
To R ₅ in dividing the reference line 5B of Figure 5, the measurement points belonging to each region R _i may determine whether or less are above the division reference line for that region. The above-mentioned statistical processing of the measurement by the mobile station and the measurement result by the base station is summarized as follows.

First, in the mobile station MS, as shown in FIG.
It is monitored whether or not the measurement timing has come (S ₁ ). In other words, the mobile station MS performs measurement periodically, but sets a timer, for example, and performs measurement each time the timer times out. This measurement interval, that is, the timer setting time,
For example, 1 minute, 5 minutes, or the like, a short set time can be set for a zone having a small area, and a relatively long set time can be set for a zone having a large area. Alternatively, a request for reporting a location registration signal is periodically sent from the radio base station BS to the mobile station MS as described above, but various methods may be used, such as measurement may be performed each time the request is received. be able to.

At the measurement timing, the electric field strength and quality (for example, bit error rate) of the downlink radio wave RW _D from the radio base station BS, usually the radio wave of the control channel for receiving the incoming call, are measured (S). ₂ ). The measurement result is reported on the uplink radio wave RW _U to the radio base station BS and the control channel for the normal call request (S ₃ ). This report may report the measurement result in addition to the report for the report request from the radio base station BS.

In the radio base station BS, as shown in FIG.
Wait for report of measurement result from mobile station MS (S_Four), Report
Each time it is received, the measurement result is compared with the reference characteristics.
Do (S_Five). That is, the reference characteristic in the reference characteristic storage unit 18 and
Comparison to determine whether the measurement point represented by the measurement result is abnormal.
And measure points and abnormal points. Next one period
For example, one hour has passed (S₆ ), Passed
If not, step S _Four Return to and receive more measurement data
To continue. Step S₆ Judge that a certain period has passed
All the measurement points and abnormalities collected during this period
Statistical processing of measured points determined as
Is determined whether or not is within the allowable range (S₇).

[0028]

As described above, according to the present invention, the mobile station measures the electric field strength and quality of the down-link radio wave and processes them in the radio base station. The state can be evaluated, and when the radio wave environment changes and the interference state changes, the change can be detected in a short time by following the change. For this reason, management control and artificial management via the central control device are not required.

In a mobile communication system in which the frequency (channel) of a radio wave radiated by a base station is autonomously determined, the validity of the radiated radio wave is autonomously determined. If a plurality of frequencies are allocated to the radio base station, when the occurrence of an abnormality is detected in the radio base station as described above, it is possible to autonomously switch to another frequency among the allocated frequencies, , A self-supporting wireless base station can be provided.

Since the measurement is performed by the mobile station, an abnormality in the service area (own zone) of the radio base station is detected from the user's standpoint, and the radio base station controls transmission power or directs the antenna. By controlling the direction or changing the propagation state of the downlink radio wave and knowing the result from the measurement result from the mobile station, it is possible to adjust to the optimum state.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of zone allocation and frequency allocation in a service area of a mobile communication system.

FIG. 2 is a block diagram showing a configuration example in a certain zone in mobile communication to which the method of the present invention is applied.

3A is a graph showing a theoretical curve representing a change in electric field strength and a bit error rate with respect to a distance from a base station in the absence of an interference wave; FIG. 3B is a graph showing a bit error rate when an interference wave is present in A; A graph showing a change.

FIG. 4 is a diagram showing an example of a format of a control signal.

FIG. 5 is a view showing an example of reference characteristics stored in a reference characteristic storage unit 18 of FIG. 2;

FIG. 6 is a graph for explaining an example of statistical processing of measurement results.

7A is a flowchart showing an example of a processing procedure in a mobile station in the method of the present invention, and FIG. 7B is a flowchart showing an example of a processing procedure in a radio base station.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kiyoto Nagata 2-1-1 Toranomon, Minato-ku, Tokyo NTT Mobile Communication Network Co., Ltd. (56) References JP-A-2-241249 ( JP, A) JP-A-5-284108 (JP, A) JP-A-5-308330 (JP, A) JP-A 8-88596 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , (DB name) H04Q 7/00-7/38 H04B 7/24-7/26 102

Claims (7)

(57) [Claims] 1. A method for monitoring an interference state in each zone of a mobile communication system in which a mobile station in each zone communicates through a base station in each zone in a service area, comprising the following steps: Each mobile station periodically measures the electric field strength and quality of the downlink radio wave emitted by the radio base station, (b) the mobile station reports each measurement result to the radio base station, and (c) the radio station The base station compares the measurement result reported from each mobile station with a predetermined reference characteristic and finds that the measurement result is abnormal.
It is determined whether or not it is, the result of the determination is collected over a predetermined period, and statistical processing is performed to obtain data on the interference state. (D) The data on the interference state is evaluated. An interference state between the emitted radio wave and another radio wave of the same frequency is determined. 2. The method according to claim 1, wherein the quality is a bit error rate. 3. The interference state monitoring method according to claim 1, wherein the downlink radio wave is a downlink control channel. 4. The interference state monitoring method according to claim 1, wherein the step (b) comprises the step of the base station requesting the mobile station to transmit a measurement result, and the step (b) responding to the request. Transmitting a measurement result from the mobile station to the base station. 5. The method according to claim 1, wherein the step (b) includes a step in which the mobile station voluntarily transmits the measurement result at a fixed period. 6. The interference state monitoring method according to claim 1 , wherein the reference characteristic is a characteristic determined in advance based on a characteristic representing a relationship between an ideal electric field strength and a bit error rate. Judge whether or not the bit error rate is degraded from the bit error rate defined by the reference characteristic, and judge whether or not it is abnormal, and judge whether the number of the measurement results within the certain period of time for the collected measurement results is abnormal. The ratio of the determined number of measurement results is used as an index indicating the interference state. 7. The interference condition monitoring method according to claim 1 , wherein the reference characteristic divides the electric field strength into a plurality of regions,
An error rate threshold determined based on an ideal characteristic representing a relationship between an ideal electric field strength and a bit error rate in each intensity region is determined as the reference characteristic, and the intensity region to which each of the measurement results belongs is determined. It is determined whether or not there is an abnormality by comparing with the threshold value of the intensity region, and the ratio of the number of measurement results determined to be abnormal to the number of measurement results belonging to the respective electric field intensity regions within the certain period is calculated. And weighting them with a predetermined weighting factor, and adding the respective weighted ratios to obtain an index representing the interference state.