JPH08237729A - Method for monitoring interference state in base station of mobile communication system - Google Patents

Abstract

PURPOSE: To allow the system to trace a change in a radio wave environment and an interference state in a short time and to detect the state of change by allowing a mobile station to measure the electric field strength and quality of an outgoing radio wave and allowing a base station to process the radio wave. CONSTITUTION: A radio base station BS makes two-way communication with a mobile station MS moving in a zone by means of an outgoing radio wave RWD and an incoming radio wave RWU. The radio wave RWD includes an outgoing control and speech channel and the radio wave RWU includes an incoming call and speech channel different from an outgoing frequency. The mobile station MS measures the reception level and speech quality of the received outgoing control channel at a desired interval and sends them to the base station BS through the incoming control channel of the incoming radio wave RWU. The base station BS collects the data for a desired period, an arithmetic processing section 17 applies statistic processing to the data to analyze the interference state of the operating channel of the zone, and when it is deteriorated from a specified state of a reference characteristic storage section 18, the operating channel frequency in the zone is revised into other frequency. Thus, management control and artificial management by a central controller are not required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention divides a service area into a plurality of zones and uses a plurality of radio channels of different frequencies repeatedly in each zone over the entire service area so as to avoid interference as much as possible. In a communication system, the present invention relates to a method of monitoring the radio wave interference state performed by each base station, and in particular, it monitors the radio wave interference state of a radio channel of the same frequency as the radio channel of the base station and the interference state deteriorates below a specified value. In this case, the present invention relates to an interference monitoring method in an autonomous distributed base station that switches to a channel of another frequency or stops operation.

[0002]

2. Description of the Related Art In a mobile communication system, a service area SA is divided into a plurality of zones Z ₁ , Z ₂ , Z ₃ , ..., As shown in FIG.
Divided into Z _M, these zones Z _1, Z _2, ..., base station B to Z _M
S ₁ , BS ₂ , ..., BS _M are provided, and the respective zones Z ₁ , Z
₂ , ..., Z _M , for example, radio channel frequencies f ₁ , f ₂ , f ₃ ,
…, Assign f ₆ as shown. In this case, the entire service area should be allocated so that radio waves of the same frequency as possible do not interfere with each other and radio channels of the same frequency f ₁ are allocated to zones that are separated from each other, such as zones Z ₁ and Z _6. The frequency utilization rate is increased by repeatedly using a plurality of channels having different frequencies.

In the past, such frequency arrangement has been
The distance between radio base stations of the same frequency so that the radio waves from each radio base station BS of a plurality of other zones that use the same frequency channel as that zone are sufficiently attenuated and mutual interference is tolerable. And the transmission power were calculated.

[0004]

As described above, in the conventional system, the frequencies f ₁ , f ₂ , ..., F ₆ of the same group are repeatedly used as much as possible in order to improve the utilization efficiency of radio waves as much as possible. In such a conventional system, when a new propagation path unexpectedly occurs or the existing propagation path disappears due to changes in the propagation environment of radio waves, mutual interference of radio waves of the same frequency from two radio base stations. May occur. In order to measure such interference, conventionally,
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. Was there. Even after the mobile communication system is in operation, the service area is expanded to create base stations in new zones around it, some or all of the frequency allocation is changed, large buildings and large towers When the radio wave propagation environment changes, such as when it is created or demolished, interference may occur or the interference may disappear. Therefore, after entering the operation of the mobile communication system, in order to grasp the interference situation by the channel of the other zone of the same frequency with respect to the channel of that zone in each zone, stop the transmission of the radio wave of the base station of that zone. Had to do. Moreover, in any case, the state of the radio wave is measured using a dedicated measuring device.

Conventionally, one of other base stations that use the same frequency to know the interference state of radio waves in a certain zone 1
Since the electric field strength is measured by sequentially radiating radio waves from the beginning, it takes time to measure the electric field strength and judge the interference situation. In particular, the measurement during operation measures the electric field strength of the radio waves from other base stations within the area where the radio waves from the base stations in that zone are considered to have sufficient reception electric field levels. It is necessary to stop the transmission of radio waves, but it is not possible to frequently stop the transmission of radio waves during operation, so it took a considerable time to measure the radio waves from other base stations. Therefore, the measurement cannot be performed following the change in the radio wave environment, which causes a considerable delay, and an area in an unfavorable reception state in the zone may not be improved for a relatively long time. Also, since radio waves are radiated only from one base station among a plurality of same frequency base stations that are considered to interfere with each other, the original operation of mobile communication deteriorates during that time.

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

[0007]

According to the invention of claim 1, (a) the mobile station periodically measures the electric field strength and the quality of the downlink radio wave from the radio base station, and (b) the measurement result. To the above-mentioned radio base station, (c) statistically processing the reported measurement results at the above-mentioned radio base station to obtain the radio wave state data radiated from the own station, and (d) comprehensively combining the plurality of data. And monitoring mutual interference between the radio wave emitted by the radio base station and another radio wave having the same frequency.

According to the invention of claim 2, 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 the measurement result, and in response to the request, the mobile station transmits the measurement result to the base station. To do.

According to the invention of claim 5, the above steps
In (b), the mobile station voluntarily transmits the measurement result at a constant cycle. According to the invention of claim 6, the above step (c)
Compares the measurement result with the reference characteristic to determine whether or not there is an abnormality. According to the invention of claim 7, in claim 6, the reference characteristic is a characteristic determined based on a characteristic representing an ideal relationship between the electric field strength and the bit error rate, and whether the measurement result is abnormal by comparing with the reference characteristic. It is determined whether or not, and the ratio of abnormalities in the measurement results collected during the predetermined period is used as an index indicating the interference state.

According to the eighth aspect of the present invention, the reference characteristic is divided into a plurality of electric field intensity regions in the sixth aspect, and an error rate threshold value determined for each region is compared with a measurement result to determine whether or not there is an abnormality. Or not, and the weighted addition value of the ratio of abnormality determination in each area is used as an index representing the interference state.

[0011]

FIG. 2 shows a configuration example of a base station BS and a mobile station MS in one zone Z _i when the present invention is applied to the mobile communication system of FIG. The base station BS in the zone Z _i has a wireless transmission / reception device 13, an arithmetic 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. The downlink radio wave RW _D transmitted by the base station BS includes a downlink control channel and a downlink speech channel, and the uplink radio wave RW _U transmitted by the mobile station includes an uplink control channel and an uplink speech channel having different frequencies from the downlink radio wave.

The base station BS transmits a control signal and a call signal from the receiving device 13 through the downlink control channel and the downlink call channel used by the zone Z _i . The control signal transmitted on the downlink control channel has a predetermined format including, for example, a call control signal for processing a call, an identification signal for identifying the base BS, an identification signal for the surrounding zone, and a synchronization signal. As in the conventional case, the mobile station MS is in a call waiting state and continuously or intermittently receives the downlink control channel. When an incoming call signal for the mobile station MS is received through the control channel, a control signal that acknowledges it is transmitted to the base station BS through the uplink control channel, and the downlink communication channel is received according to an instruction given from the base station BS through the downlink control channel. Then, the call signal is transmitted through the upstream call channel.

According to the present invention, the electric field strength (received signal level) of the downlink control channel received by each mobile station 14 in each zone and the speech quality (for example, the bit error rate BERR) are measured at desired intervals, They are transmitted to the base station through the uplink control channel, and the base station collects the electric field strength and communication quality data received from each mobile station for a desired period, statistically processes them and uses the zone's used channel. When the interference state is judged to be worse than the specified state, the channel frequency used 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 when there is no interference from a base station of another zone in one zone (that is, 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 . The ideal curve E _{a of the} electric field strength and the ideal curve B _a of the bit error rate with respect to the distance from the base station when there is no interference can be theoretically calculated. The electric field strength decreases as the distance increases, and the bit error rate BERR increases little by little. 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 magnitude range (eg BERR <
0.1%, 0.1 ≦ BERR <0.3%, 0.3 ≦ BERR <1.0%, 1.0 ≦ BE
RR%) to the distance from the base station BS _a , for example, an error-free section D ₀ , a small error section D ₁ , an intermediate error section D ₂ , and a large error section D ₃ . Divide. The section D ₀ is an area where communication is possible without any trouble, the error in the section D ₁ is mainly due to fading, and the error in the section D ₂ is mainly due to fading and noise. The error in the section D ₃ is almost due to the decrease of the S / N of the received signal, and it is the area where the call is difficult.

For the interference-free state of FIG. 3A, the base station BS
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. The curve E _b represents the electric 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 Curve B in FIG. 3B
_As shown in _a , as compared with the case of FIG. 3A, it rapidly increases from a position closer to the base station BSa. As a result, the error-free section D ₀ , the small error section D ₁ , and the middle-error section D ₂ are shifted to the base station BSa side and become shorter. On the other hand, the error large section D ₃ 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 zone in which it is located, 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 to detect zone transition. There is. 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 to the base station BS through the uplink control channel together with the reception level at that time. The control signal is, for example, as shown in FIG. 4, a sync word SW, a zone identification code (color code)
It has a predetermined format formed by repeating CC and control data DATA. The control data DATA varies depending on the type of control signal, but the synchronization word SW is predetermined in the system, and the identification code CC is fixed for each zone. The measurement of the bit error rate BERR can be performed by detecting a known specific signal that is 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 methods can be used to send the measured reception level and 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 sent through the uplink control channel at each request of the base station, or the mobile station voluntarily sends the measurement result. (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 each request of the base station or voluntarily and periodically. . The following method is an example of incorporating the measurement result into the control signal.

It is incorporated in the position registration signal transmitted from the mobile station to the base station at regular intervals. -Incorporate into the in-communication wireless section control signal that is performed in a time-divisional manner at timings other than communication information during communication. For example, in a personal digital cellular system, in order to issue a transmission power control command to a mobile station, it is incorporated into a signal used for reporting the electric field strength of a downlink communication channel measured by the mobile station.

Incorporated in the call connection control signal. The above method (a) has a disadvantage that traffic is increased because a new signal is provided. In contrast,
Method (b) incorporates the measurement results into the conventional signal and transmits it, so the increase in traffic is negligible.
And it can be easily implemented. When the interference control channel of the same frequency is generated, the bit error rate of the received signal of the desired control channel increases and the communication quality deteriorates. This depends on the ratio of the electric field strengths of both channels interfering with each other.

FIG. 5 is a reference characteristic showing the relationship between the electric field strength and the quality (bit error rate BERR), which is the reference for the interference state analysis, and is stored in advance in the reference characteristic storage unit 18 of FIG. In FIG. 5, the straight line 5A represents the theoretical relationship between the electric field strength and the bit error rate BERR in the ideal state obtained by calculation in the case where there is no interference in FIG. 3A, and the straight line 5B represents the theoretical relationship 5A with respect to fading and interference. It represents a predetermined allowable range in consideration of quality deterioration due to influence. That is, the electric field strength measured by the mobile station (reception level E _RL )
If the quality (BERR) is within the area A ₁ below the straight line 5A in FIG. 5, it can be determined that at least no control channel interference from other zones is received. Measurement results are straight lines 5A and 5
If it is within the area A ₂ surrounded by B, it can be determined that the influence of fading or interference is within an allowable range. When the measurement result is within the area A ₃ above the straight line 5B, it can be determined that there is an interference channel having a field intensity that cannot be ignored. If the influence of interference is below the allowable value, the measurement points that are normally measured are almost in the area A ₂ between the straight lines 5A and 5B, and the area A ₁
It is thought that there are not many things inside, but even if there is a measurement point that enters area A ₁ , it is not affected by interference, so in this example area A ₁ + A ₂ is normal.

Therefore, in the base station, the reference characteristics shown in FIG. 5 are stored in advance in the reference characteristics storage unit 18, and the measurement results (E _RL , BERR) received from each mobile station are compared with the reference characteristics shown in FIG. The influence of interference channels from other zones on the channel used in that zone, based on the results obtained by statistically processing the data of their comparison results (abnormality and normal determination results) over a certain period. Is within an allowable range (a range in which the change of the channel frequency is unnecessary) is determined. Specifically, several methods are possible as follows.

(I) As a first method, for example, a reference characteristic case
The relationship of the straight line 5B is stored in advance in the storage unit, and the base station
Measurement result (E_RL, BERR), the measurement
Point (E _RL, BERR) is the area A in FIG.₃Enter or area A₁+ A₂ to go into
The arithmetic processing unit 17 determines whether or not. Area A₃If you enter
(Abnormal) and the measurement point (E_RL, BERR)
Counted as a normal point, area A₁+ A₂ If there is no interference (correct
Always). The arithmetic processing unit 17 has a fixed period (for example, 1
Count value of all measurement points received over time and
Accumulated count values of abnormal points of
Calculate the percentage of the number of points, and if the percentage is within the specified value,
It is determined that the influence of Wataru is within the allowable range. Greater than the specified value
If so, it is determined that the effect of interference is unacceptable, and
Switch the channel frequency.

(II) As a second method, as shown in FIG. 6, the electric field strength shown in FIG. 5 is applied to a region R for each predetermined width (for example, 20 dbμV).
₁ , R ₂ , ..., R ₅ and the error rate threshold for each of those areas
Predetermine TH ₁ , TH ₂ ,…, TH ₅ . As each threshold value, for example, the average value of the straight line 5B in FIG. 5 in each divided area is used. The arithmetic processing unit 17 of the base station is a region to which the electric field strength ERL of the measurement point data (ERL, BERR) received from each mobile station should belong.
R _i (i = 1, ..., 5) is determined and compared with the threshold value TH _{i of the} region,
If it is less than or equal to the threshold TH _i , it is determined to be normal, and if greater than the threshold, it is determined to be abnormal. The ratio C _i of the number of measurement points determined to be abnormal to the number of measurement points S _{i in} each of the regions R _{1 to} R _{5 over a} fixed period is calculated. The average value or simply the total value of these ratios C _i , i = 1, ..., 5 is compared with a predetermined reference value, and if larger than that, it is determined that the influence of the interference channel is unacceptable. The average or sum of the proportions C _i is the respective areas A _{1 to} A ₅
However, the values weighted by the predetermined weighting factors W _{1 to} W ₅ may be added and calculated 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
It is also possible to divide the reference straight line 5B of FIG. 5 by ~ R ₅ and determine whether the measurement point belonging to each region R _i is above or below the division reference straight line of that region. The statistical processing of the measurement by the mobile station and the measurement result by the base station described above is summarized as follows.

First, in the mobile station MS, as shown in FIG. 7A,
The measurement timing is monitored (S ₁ ). That is, the mobile station MS periodically measures, but sets a timer, for example, and measures each time the timer times out. This measurement interval, that is, the set time of the timer,
For example, it may be set to 1 minute, 5 minutes, or the like, and a short setting time may be set in a zone having a small area and a relatively long setting time may be set in a zone having a large area. Alternatively, as described above, the radio base station BS periodically sends a request for reporting the location registration signal to the mobile station MS, but measurement may be performed each time the request is received. be able to.

At the measurement timing, the electric field strength of the downlink radio wave RW _D from the radio base station BS, usually the radio wave of the control channel for receiving an incoming call, and its quality (eg bit error rate) 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 the measurement result report from the mobile station MS (S_Four), Report
Each time it is received, the measurement result is compared with the reference characteristic.
Do (S_Five). That is, if the reference characteristic in the reference characteristic storage unit 18
Compare and determine whether the measurement point indicated by the measurement result is abnormal.
The measurement points and the abnormal points. Next one
For example, it is determined whether one hour has passed (S₆ ), Passed
If not, step S _Four Return to and receive more measurement data
To continue. Step S₆ It is judged that a certain period has passed in
All measurement points and abnormalities collected during this fixed period
The influence of interference channel is obtained by statistically processing the measurement points determined to be
Is determined to be 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 downlink radio wave, and the radio base station processes the electric field strength and the quality of the downlink radio wave. The state can be evaluated, and when the radio wave environment changes and the interference state changes, the change state can be detected by following this change in a short time. Therefore, there is no need for management control or artificial management via the centralized control device.

In the mobile communication system in which the frequency (channel) of the radio wave radiated by the base station is autonomously determined, the validity of the radiated radio wave is autonomously determined. If a plurality of frequencies are assigned to the radio base station, and the abnormality occurrence is detected in the radio base station as described above, it is possible to autonomously switch to another frequency among the assigned frequencies. It is possible to provide a self-supporting operation type wireless base station without the provision of the above.

Since the measurement is carried out 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 side controls the transmission output or directs the antenna. It is possible to adjust to the optimum state by controlling the direction, changing the propagation state of the downlink radio wave, and knowing the result from the measurement result from the mobile station.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of zone arrangement and frequency arrangement 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.

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

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

5 is a diagram showing an example of reference characteristics stored in a reference characteristic storage section 18 of FIG.

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

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyoto Nagata 2-10-1 Toranomon, Minato-ku, Tokyo NTT Mobile Communications Network Co., Ltd.

Claims (8)

[Claims] 1. A method of 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, including the following steps: (a) 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 The base station collects the measurement results reported from each mobile station over a predetermined period, statistically processes them as data on the interference state, and (d) evaluates the data on the interference state, and then the radio base station. The state of interference between the radio wave emitted by and other radio waves of the same frequency is determined. 2. The interference state monitoring 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) includes a step in which the base station requests the mobile station to transmit a measurement result, and the step in response to the request. The mobile station transmits the measurement result to the base station. 5. The interference condition monitoring method according to claim 1, wherein the step (b) includes a step in which the mobile station voluntarily transmits the measurement result at a constant cycle. 6. The interference condition monitoring method according to claim 1, wherein the step (c) comprises a step of comparing the measurement result with a predetermined reference characteristic to determine whether or not the measurement result is abnormal. Including. 7. The interference state monitoring method according to claim 6, wherein the reference characteristic is a characteristic previously determined based on a characteristic representing a relationship between an ideal electric field strength and a bit error rate, and each measurement result is It is determined whether it is abnormal by judging whether it is deteriorated from the bit error rate specified by the reference characteristic, and it is determined whether the collected measurement results are abnormal with respect to the number of measurement results within the certain period. The ratio of the determined number of measurement results is used as an index representing the interference state. 8. The interference state monitoring method according to claim 6, wherein the reference characteristic divides the electric field intensity into a plurality of regions,
The error rate threshold value determined based on the ideal characteristic representing the relationship between the ideal electric field strength and the bit error rate in each intensity region is determined as the above reference characteristic, and the intensity region to which each measurement result belongs is determined. , It is determined whether or not it is abnormal by comparing with the threshold of the strength region, the ratio of the number of measurement results determined to be abnormal to the number of measurement results belonging to each electric field strength region within the certain period The method further includes a step of obtaining, weighting them with a predetermined weighting coefficient, adding respective weighted proportions, and obtaining the weighted rate as an index representing the interference state.