JPH10336104A - Base station for mobile communication - Google Patents

Abstract

(57) Abstract: A mobile communication base station capable of minimizing interference with communication of another base station and increasing the output power of the base station is realized. In order for a mobile station to receive a radio wave with a constant electric field strength based on a reception level of a radio wave from a mobile station measured by a receiver, how much radio wave of transmission output power is transmitted. Judgment is made as to whether to output the signal, and the output of the transmitter in the communication slot for performing communication with the mobile station is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a PHS (Personal
The present invention relates to control of transmission power of a base station in a mobile communication system of a microcell system using TDMA such as a Handy-phone System.

[0002]

2. Description of the Related Art PHS
Is a mobile communication system characterized by installing a large number of base stations covering a narrow area with a radius of several hundred meters, but recently by increasing the output of the base station within the range permitted by the Radio Law, It is required that one base station cover a wide area. Such a high-output type base station is in great demand in places where traffic is low, such as local stations and shopping centers.

[0003] However, if the output power of a base station is increased, radio waves reach the coverage area of another base station beyond the coverage area of the base station and interfere with the communication of the other base station. May give. If such interference occurs, within the coverage area of the other base station, the frame error rate in communication from the mobile station to the other base station increases, and voice quality and data transmission quality deteriorate. Become.

Conventionally, a base station that has suffered interference avoids interference by changing the frequency or time slot used for communication with the mobile station. However, such a passive avoidance method prevents communication. If there is no other channel to be allocated for communication from the base station to the mobile station, such as during congestion, communication cannot be performed, and a situation occurs in which communication is disconnected. Accordingly, it is an object of the present invention to realize a mobile communication base station capable of minimizing interference with communication of another base station and increasing the output power of the base station.

[0005]

SUMMARY OF THE INVENTION A mobile communication base station according to the present invention comprises a receiving level measuring means for measuring a receiving level of a radio wave from a mobile station, and a radio wave from the mobile station measured by the receiving level measuring means. In order for the mobile station to receive radio waves at a certain electric field strength based on the reception level of
And output control means for controlling the output of the transmitter in a communication slot for performing communication with the mobile station by determining how much radio wave of the transmission output power should be emitted. ).

[0006] According to the above configuration, the base station can estimate the level of the transmission output power of the mobile station within the range that does not affect the communication quality of the mobile station by estimating the reception level of the transmission radio wave of the mobile station. It is possible to control whether the output of the transmitter in the communication slot for performing communication with the mobile station is determined by determining whether the transmission is sufficient. The output control means estimates a distance to the moving body using correlation data that records a correlation between a radio wave arrival distance and a received electric field strength, and determines transmission output power based on the estimated distance. (Claim 2).

That is, when determining how far the transmission output power should be reduced, the distance to the mobile station is estimated from the reception level, and the mobile station at that distance receives radio waves with a constant electric field strength. Is based on how much radio wave of transmission output power should be emitted. It is preferable that the output control means sets the period T for controlling the output of the transmitter to the actual measurement period or longer by actually measuring the fluctuation period due to fading of the received radio wave.

[0008] When receiving a radio wave from a mobile station, the radio wave usually undergoes fluctuation due to fading since the mobile station is moving. This is because if the output of the transmitter is controlled more frequently than the fluctuation period due to fading, the communication quality is rather deteriorated. The output control means,
It is preferable that the output margin M when controlling the output of the transmitter is set in accordance with the actually measured fluctuation amount by measuring the fluctuation amount of the received radio wave due to fading (claim 4).

Conventionally, it is customary to give a predetermined margin to the transmission output power from the base station in advance. However, in reality, fading greatly varies depending on conditions such as time zones, so that an efficient system is constructed. In order to do so, a margin should be set according to the fluctuation due to the fading of the reception level during communication with the mobile object. Further, it is preferable that the output control means sets a cycle T for controlling the output of the transmitter based on past statistical data of a fluctuation cycle due to fading at each time at the start of a call (claim 5). Furthermore, it is preferable that the output control means sets the output margin M of the transmitter based on past statistical data of the amount of fluctuation due to fading at each time at the start of a call (claim 6).

At the start of a call, the data of the fading period and the fading depth are not sufficiently accumulated, so that the estimation is performed using statistical data. The output control means sets the rate of change of the transmission output power to 1
It is preferable to limit to dB / sec or less (claim 7). This is to prevent a sudden increase in transmission power.

The output control means may estimate the received electric field intensity from time-series data of the received electric field intensity for a predetermined time in the past (claim 8; see FIG. 4 (b)). This is because the reception electric field strength may fluctuate due to a temporary noise, but if such a fluctuation is suppressed, a rapid fluctuation of the transmission output power can be avoided.

When the output control means determines that the mobile station exists in the dead zone, it is preferable to set the transmission output power to the value before entering the dead zone (claim 9; FIG. 5 (c)).
reference). When the mobile station is in the dead zone, the received electric field strength becomes very small. However, if the transmission power is increased at this time, the transmission power becomes excessively large.

[0013]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Figure 1 shows the TDM
FIG. 2 is a diagram showing a transmission timing and a reception timing of a microcell system (1.9 GHz band) using A. The transmission timing and the reception timing are respectively composed of a control slot and a plurality of communication slots (three communication slots in FIG. 1) f ₁ , f ₂ , f ₃ (f indicates a frequency).

FIG. 2 is a block diagram showing the configuration of the mobile communication base station according to the present invention. Mobile communication base station 1
Are antennas 2 and 3 for diversity and antennas 2 and 3
An antenna switching unit 4 for switching between for transmission or reception;
It includes a transmitter 5, a TDMA controller 6, a base station controller 10, and a receiver 7. The receiver 7 has a function as "reception level measuring means" for measuring and outputting the reception level of the radio wave from the mobile station.

The base station control unit 10 controls the entire base station such as handover, outgoing call, incoming call, and the like, and the TDMA control unit 6 controls timing and communication data contents. Further, the base station control unit 10 has “correlation data between the radio wave arrival distance and the electric field strength”, and uses this “correlation data between the radio wave arrival distance and the electric field strength”,
The distance to the mobile station is estimated, and the data of this distance is passed to the reception electric field data processing unit 8.

The mobile communication base station 1 further includes a reception electric field data processing section 8 for estimating a distance to the mobile object based on a reception level of a radio wave from the mobile station measured by the receiver 7, A drive unit 9 for controlling the output of the transmitter based on the distance estimated by the data processing unit 8. Before the communication between the mobile communication base station 1 and the mobile station is secured, the reception electric field data processing unit 8 always monitors the reception electric field strength of the control slot from the mobile station,
When communication between the mobile communication base station 1 and the mobile station is secured, the received electric field strength of the communication slot from the mobile station being used is monitored, and the value is transmitted to the base station control unit 10. Furthermore, in order for a mobile station at that distance to receive radio waves with a certain electric field strength within a range where communication quality can be ensured, it is necessary to determine how much radio wave of transmission output power should be emitted. , The transmission output power with some margin M added thereto. This determination is made for each cycle T.

Hereinafter, the operation of the mobile communication base station 1 will be described in more detail. The function of performing the following operation may be realized by software in the base station control unit 10 or may be realized by being incorporated in the IC of the reception electric field data processing unit 8. The function of performing the following operation corresponds to the function of "output control means" described in the claims. The receiver 7 measures the reception electric field strength E for each slot at the reception timing shown in FIG. The measurement cycle is 5 msec. FIG. 3A shows a graph of the data of the received electric field strength E in a time series. As shown in FIG. 3A, the received electric field strength E includes large fluctuations A and B in addition to small fluctuations. The cause of this large variation is due to fading. In the PHS, the fading cycle is usually 0.1 sec, and the electric field strength drop ΔE is 10 dB or more.

Next, the reception electric field data processing unit 8 integrates the data of the reception electric field strength E received from the receiver 7,
Eliminate small fluctuations such as noise. 0.1 as the integration constant
About 10 sec to 10 sec is appropriate. The result of this processing is shown in FIG. In addition to the integration, for example, a process of digitizing data of the received electric field strength E and performing weighted averaging or a moving average may be performed. Hereinafter, such processing is collectively referred to as “smoothing”.

Further, the reception electric field data processing section 8
Aging effects A and B send out due to abnormal fluctuations
As shown in FIG. 3 (c), in order to prevent unnecessary increase of force,
Apply a limiter for fluctuations in electric field strength. That is, one time
Compare the point and the data at the time
The difference is converted to a predetermined value per second (for example, 1 dB).
/ Sec) or more, it is suppressed to a predetermined value. Ingredient
Physically, a certain time T ₁Of the received electric field strength E at
Value is adB, time T after that_Two(For example, after 10 seconds)
It is assumed that the integrated value obtained by the calculation is (a-12) dB. This and
And the rate of change per unit time is 1.2 dB / sec.
However, this is suppressed to 1.0 dB / sec by a limiter.
Time T_TwoOf Received Electric Field Strength E
The minute is (a-10) dB.

In this way, it is possible to obtain fluctuation data of the received electric field strength E as shown in FIG. Next, the received electric field data processing unit 8 inquires the base station control unit 10 about the distance to the partner mobile station corresponding to the received electric field intensity E, based on the fluctuation data of the received electric field intensity E subjected to the limiter. The base station controller 10 obtains the distance to the partner mobile station based on the aforementioned “correlation data between the radio wave arrival distance and the electric field strength” and the received electric field strength E, and provides it to the received electric field data processor 8. I do.

The received electric field data processing section 8 determines an output level to be transmitted based on the distance, issues an instruction to the driving section 9 and causes the driving section 9 to transmit at an output level corresponding to the distance from the partner mobile station. In the above embodiment, the base station control unit 10
Although the information on the distance is provided to the reception electric field data processing unit 8, the output level to be transmitted may be directly provided. The “correlation data between the radio wave arrival distance and the electric field strength” was held by the base station control unit 10, but was received by the received electric field data processing unit 8.
May have. Furthermore, the reception electric field data processing unit 8 may also have a calculation function for obtaining a distance and data therefor.

Further, the limiter is applied to the transmitter 5
It may be. That is, the data up to (b) of FIG. 3 is used as the control target data, and when a change instruction of 1 dB / sec is issued from the reception electric field data processing unit 8 in the driving unit 9, the output change is changed to 1 dB / sec. To keep. Next, a specific method of determining the cycle T and the margin M will be described.

When the state of the data of FIG. 3A is lower than the lower limit of the data of FIG. 3C by a predetermined value (for example, 10 dB) for more than a predetermined time (for example, 0.1 sec), 1 is counted. Depending on the number of counts in a predetermined time (usually a time selected from 10 seconds to 3 minutes, for example, 1 minute)
Obtain the fading cycle. The period T is set to avoid the effect of short-term fluctuations in electric field strength (fading).
Basically, it is determined to be the same as or longer than the fading period.

In the PHS, since the mobile station is assumed to be possessed by a walking person, the fading cycle is at most about 10 Hz. Also, the data in FIG. 3A is a predetermined value (for example, 10d) from the lower limit of the data in FIG.
B) The fading depth is obtained by calculating a numerical value when the low state continues for a predetermined time (for example, 0.1 sec) or more. The margin M is basically the same as the fading depth in order to avoid deterioration of communication quality,
It is determined to be a slightly larger value.

At the beginning of a call, there is a possibility that actual measured values of the received electric field intensity for a predetermined time have not been collected. In this case, the fading period and the fading depth are not determined from the fluctuation of the actual reception level.
In the past, it is accumulated as statistical data based on the reception level obtained at the time of communication at the time, and at the beginning of the call,
The cycle T and the margin M may be determined using the statistical data.

If the transmission output power thus determined exceeds the permitted upper limit (for example, 500 mW), the transmission output power is suppressed to the upper limit. If the determined transmission output power is below a certain lower limit (for example, 20 mW), the transmission output power is suppressed to the lower limit. This is because if it is reduced to this extent, the effect on the other base stations 1 can be neglected sufficiently, and if the transmission output power is too low, the communication quality with the mobile unit may be reduced.

To perform more advanced control, the base station controller 10 or the received electric field data processor 8 may have the following functions. FIG. 4 is a graph showing how the received electric field strength E varies when the mobile station gradually moves away from the base station. The swelling of the portion C in FIG. 4 (a) is due to the effects of fading and the like. Since such a case is assumed, the fluctuation of the received electric field strength after the smoothing is stored in a time series, and the fluctuation of the received electric field strength is stored from the time series data of the past predetermined time (about 10 seconds to 3 minutes). The rate may be calculated by the maximum likelihood estimation method or the like, and the next transmission output to be transmitted may be estimated from the variation rate. In short, the smoothed data of FIG. 3B is re-smoothed with a longer time constant.

It is assumed that the mobile station enters a dead zone. As shown in FIG. 5 (a), it is assumed that the decrease h of the received electric field strength is 10 dB or more and the reduced state continues. The received electric field strength after smoothing is as shown in Fig. 5 (b).
If the output power control described so far is performed based on this, the transmission output is increased as shown by the broken line in FIG. 5 (c). In this case, the transmission output becomes excessive.
As shown by the solid line in (c), when the state of intrusion into the dead zone shown in FIG. 5 (a) continues for a predetermined time T ₃ (about 10 seconds to 3 minutes), the received electric field intensity E ₁ before the electric field intensity decreases is obtained. Is controlled so as to obtain a transmission output according to the above. Thereby, when the mobile station comes out of the dead zone, communication can be performed with an appropriate output. The determination of invasion to the blind zone is made based on the frame error rate and the reception level of the received data.

If the state where the reception electric field strength is low continues for a long time (3 minutes to 10 minutes), it is recognized that the distance is far away, and the output is returned to the normal output control. The driving unit 9 controls the transmitter 5 so that the output power of the communication slot allocated to the mobile station of the communication partner is set to the power, so that when the mobile station is moving, the moving speed is reduced. Depending on,
When the mobile station moves fast, it can follow it, and when the mobile station moves slowly, it can follow it.

The output power in the channel used for the control slot is kept constant without control. The reason for this is
This is for securing a coverage area and securing synchronization with another base station. In the mobile communication base station according to the present invention, usually, one base station can simultaneously communicate with three or more mobile stations, but since the positions of the mobile stations have no correlation at all, each mobile station has It goes without saying that the transmission output power is controlled for each of the allocated communication slots f ₁ , f ₂ and f ₃ .

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the invention.

[0032]

As described above, according to the base station for mobile communication of the present invention, the base station does not affect the communication quality of the mobile station by inferring from the reception level of the radio wave transmitted from the mobile station. Within the range, it is possible to determine how much transmission output power of the radio wave is sufficient to control the output of the transmitter in a communication slot for communication with the mobile station. Therefore, interference between channels to other base stations in the vicinity can be prevented. For this reason, it is possible to suppress interference with other base stations.

[Brief description of the drawings]

FIG. 1 is a diagram showing a transmission timing and a reception timing of a microcell system using TDMA.

FIG. 2 is a block diagram showing a configuration of a mobile communication base station according to the present invention.

FIGS. 3A and 3B are graphs of a received electric field strength, where (a) shows raw data of the received electric field strength E, (b) shows data after smoothing, and (c) shows data after a limiter operation.

FIG. 4 is a graph showing how the received electric field strength E varies when the mobile station moves away from the base station;
(a) shows raw data of the received electric field strength E, and (b) shows data after smoothing.

FIG. 5 is a graph showing a state of a change in received electric field intensity E when a mobile station enters a dead zone, where (a) is raw data of received electric field intensity E, and (b) is data after smoothing. (C) is a graph of the transmission output when the output power is controlled.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base station for mobile communication 2, 3 Diversity antenna 4 Antenna switching part 5 Transmitter 6 TDMA control part 7 Receiver 8 Received electric field data processing part 9 Drive part 10 Base station control part

Claims (9)

[Claims] 1. A mobile communication base station used in a microcell mobile communication system using TDMA, comprising: a reception level measuring means for measuring a reception level of a radio wave from the mobile station; Based on the reception level of the radio wave from the mobile station measured by the measuring means, in order for the mobile station to receive the radio wave at a constant electric field strength, how much radio wave of the transmission output power should be emitted. A base station for mobile communication, comprising: output control means for determining and controlling the output of the transmitter in a communication slot for performing communication with the mobile station. 2. An output control means for estimating a distance to a moving body using correlation data in which a correlation between a radio wave arrival distance and a received electric field strength is recorded, and a transmission output based on the estimated distance. The power is determined.
A base station for mobile communication according to claim 1. 3. The output control means sets the period T for controlling the output of the transmitter to the actual measurement period or longer by actually measuring the fluctuation period due to fading of the received radio wave. The mobile communication base station according to claim 1. 4. An output control means for setting an output margin M for controlling the output of the transmitter by actually measuring the amount of fluctuation due to fading of the received radio wave and according to the actually measured amount of fluctuation. The mobile communication base station according to claim 1, wherein 5. The output control means, when setting a period T for controlling the output of the transmitter, at the start of a call, based on past statistical data of a fluctuation period due to fading at each time, based on past statistical data. The mobile communication base station according to claim 3, wherein a period T to be controlled is set. 6. An output control means for setting an output margin M for controlling the output of a transmitter at the start of a call based on past statistical data of the amount of fluctuation due to fading at each time. Machine output margin M
5. The mobile communication base station according to claim 4, wherein: 7. The output control means according to claim 1, wherein the rate of change of the transmission output power is limited to 1 dB / sec or less.
A base station for mobile communication according to claim 1. 8. The mobile communication base station according to claim 1, wherein the output control means estimates the received electric field intensity from time-series data of the received electric field intensity for a predetermined time in the past. 9. The mobile communication base according to claim 1, wherein the output control means sets the transmission output power to a value before invasion of the dead zone when it is determined that the mobile station exists in the dead zone. Bureau.