JP2995065B2 - Transmission power control method in mobile communication system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to transmission power control in a mobile communication system, and more particularly to transmission power when a mobile station moving at a high speed and a mobile station moving at a low speed are mixed. It relates to a control method.

[Conventional technology]

A transmission power control technique often used in conventional mobile communication will be described by taking a car phone system as an example.

Variations in the radio wave propagation characteristics of land mobile communications such as mobile phone systems include fluctuations that occur in short intervals, so-called instantaneous fluctuations,
There are short section median fluctuations in which the median of the fluctuations occurs for a relatively long time, and long section fluctuations in which the median of the short section median fluctuation curve changes for a longer time.
Since the long section fluctuation corresponds to the distance from the base station, it is also called a distance characteristic. In the case of the car telephone system, the instantaneous variation follows a Rayleigh distribution, and the variation of the median of a short section follows a lognormal distribution.

FIG. 1 is a diagram showing an example of a configuration of a conventional transmission power control system in an automobile telephone system, wherein 1 is a receiver, and 2 is a CP.
U and 3 represent transmitters.

In FIG. 1, a receiver 1 of a base station or a mobile station includes:
Reads the reception level of the partner station reported from the partner station
Output to The CPU 2 determines the difference between the reception level of the partner station reported from the receiver 1 and the required reception power level (control setting value), and specifies the transmission power to the transmitter 3 so as to eliminate the difference. The transmitter 3 performs an operation of setting the transmission power to a value specified by the CPU.

The receiver 1 measures the reception level of the own station and notifies the transmitter 3 of the measurement. The transmitter 3 performs an operation of notifying the reception level of its own station to the partner station.

2A and 2B are diagrams showing an operation example of the conventional transmission power control method, in which FIG. 2A shows a state before transmission power control is performed, and FIG. 2B shows a state after transmission power control is performed.

In the figure, reference numeral 4 denotes a short-term median fluctuation of the reception level,
5 is an instantaneous fluctuation of the reception level, 6 is a control cycle of the transmission power control, 7 is a control set value of the transmission power control, 8 is an average value of the reception level within the control cycle of the transmission power control, and 9 is after the transmission power control is performed. Indicates the reception level of the data.

In the conventional transmission power control method, the reception side measures the reception level 8 obtained by averaging the reception levels during the control cycle 6 of the transmission power control and notifies the other station of the measurement. And the control setting value 7 are calculated, and the transmission power is specified to the transmitter so that the difference becomes zero.

[Problems to be solved by the invention]

In the conventional transmission power control method as described above, attention is paid only to short-term fluctuations with a slow fluctuation cycle, and instantaneous fluctuations with a relatively fast fluctuation cycle are not considered. However, in recent years, in the mobile telephone system, in addition to the on-vehicle mobile device mounted on a car and used, a portable mobile device that can communicate while walking has been used. Mobile stations that move at low speeds have been mixed. For this reason, the conventional transmission power control method in which the control cycle related to the transmission power control is constant has the following disadvantages.

FIG. 3 is a diagram showing an example of a case where the conventional transmission power control is performed when the mobile station moves at a high speed.

In the figure, (a) is before transmission power control is performed, and (b) is
Indicates the transmission power control after execution, 6 indicates the control cycle of the transmission power control, 7 indicates the control setting value of the transmission power control, 10 indicates the short-term median fluctuation of the reception level, and 11 indicates the control cycle of the transmission power control. , 12 indicates the reception level after the transmission power control is performed.

As the mobile station moves at a high speed, the fluctuation cycle of the short-term median value fluctuation of the reception level and the control cycle of the transmission power control approach each other (FIG. 3 shows an example in which the fluctuation cycle is about twice the control cycle). In this case, the reception level 12 after the conventional transmission power control is performed on the reception level 10 is higher than the average reception level 11 when the transmission power control is not performed when the oscillation level is set. However, the fluctuation of the reception level is rather large.

FIG. 4 is a diagram showing an example of a case where conventional transmission power control is performed when the mobile station moves at a low speed.

In the figure, (a) is before transmission power control is performed, and (b) is
Indicates the transmission power control after execution, 6 indicates the control cycle of the transmission power control, 7 indicates the control setting value of the transmission power control, 13 indicates the short-term median fluctuation of the reception level, and 14 indicates the control cycle of the transmission power control. , 15 indicates the reception level after the transmission power control is performed.

The mobile station moves at a low speed, and the fluctuation cycle of the instantaneous fluctuation of the reception level and the control cycle of the transmission power control are approaching (FIG. 4 shows an example in which the fluctuation cycle is about twice the control cycle).
In the case, the reception level 15 after the conventional transmission power control is performed on the reception level 13 is smaller than the short-term median fluctuation 13 of the reception level when the oscillation level is set and the transmission power control is not performed. On the contrary, the fluctuation of the reception level becomes large.

As described above, in the conventional transmission power control, since the control cycle of the transmission power control is constant, there is a disadvantage that the reception level fluctuates rather depending on the moving speed of the mobile station.

The present invention has been made in consideration of the above-described conventional problems, and has been made in consideration of the above-described problems. Therefore, even when a mobile station that moves at a high speed and a mobile station that moves at a low speed are mixed, transmission that can ensure high-quality communication is performed. It is intended to provide power control means.

[Means for solving the problem]

According to the present invention, the above objects are achieved by the means as set forth in the claims.

That is, according to the present invention, a service area is constituted by a wireless zone of a base station, and the transmission power of the base station or the mobile station is changed during communication between the mobile station moving within the service area and the base station. In a mobile communication system configured as possible, means for estimating the moving speed of the mobile station to at least one of the base station and the mobile station,
Means for setting a time interval at which the transmission power should be changed based on the result obtained by the means, and the transmission power is set for each of the set time intervals in accordance with the estimation result of the moving speed of the mobile station. This is a transmission power control method for increasing or decreasing.

[Action]

In the conventional transmission power control, the transmission power is set so as to eliminate the difference between the average value of the reception level averaged within the control cycle of the transmission power control and the control set value of the transmission power control.

However, in this method, as described above, when the control cycle of the transmission power control and the fluctuation cycle of the reception level approach each other, the oscillation state occurs and the amplitude of the reception level fluctuation may be rather increased. On the other hand, in the present invention, the moving speed of the mobile station is estimated to estimate the moving speed of the mobile station, and the control amount of the transmission power is changed according to the moving speed of the mobile station.

That is, for example, a part of the difference between the average value of the reception level averaged within the control cycle of the transmission power control and the control set value of the transmission power control is used as the control amount to control the transmission power.

By employing such a method, the oscillation state can be suppressed even when the fluctuation cycle of the reception level and the control cycle of the transmission power control approach, and high-quality communication can be ensured.

〔Example〕

FIG. 5 is a diagram showing a configuration of a transmission power control system according to one embodiment of the present invention, wherein 22 is a receiver, 23 is a moving speed detection circuit, 24 is a CPU, 25 is a transmitter, and 26 is an antenna. It represents.

In the figure, a receiver 22 of a base station or a mobile station reads a reception level reported from a partner station and outputs it to a CPU 24. Further, it outputs the envelope level to the moving speed detection circuit 23.

The moving speed detecting circuit 23 estimates the moving speed of the mobile station from the envelope level and reports the estimated moving speed to the CPU 24. The CPU 24 determines the difference between the reception level of the partner station reported by the receiver 22 and the set value of the transmission power control, determines the control amount, and instructs the transmitter 25 on the transmission power.

Further, a transmission power control cycle corresponding to the moving speed of the mobile station is determined from the moving speed estimated value of the mobile station from the moving speed detecting circuit 23, and designated to the receiver 22. The receiver 22 measures the average value of the subsequent reception levels according to the transmission power control cycle specified by the CPU 24, and reports the average value to the transmitter 25. The transmitter 25
The reception level reported from the receiver 22 is reported to the partner station.

Further, the reception level of the partner station from the receiver 22 is also output in the designated transmission power control cycle, so that the subsequent transmitter 25
At the control cycle interval of the transmission power control with respect to.

FIG. 6 is a diagram showing an example of the configuration of the moving speed detection circuit 23 shown in FIG. 5, in which 27 denotes an HPF, 28 denotes a comparator, and 29 denotes a counter.

In the figure, the envelope level from the receiver is passed through a high-pass filter (HPF) 27 to remove the DC component, compared with a threshold level in a comparator 28, and the result is counted by a counter 29. I do. The moving speed of the mobile station is estimated from the counting result.

Hereinafter, the operation of the embodiment will be described for a case where the mobile station moves at a high speed and a case where the mobile station moves at a low speed.

FIG. 7 is a diagram illustrating an example in which the transmission power control of the present invention is performed when the mobile station moves at a high speed,
(A) shows before transmission power control is performed, and (b) shows after transmission power control is performed.

In the figure, 7 is a control set value of the transmission power control, 10 is a short-term median variation of the reception level, 16 is a control cycle of the transmission power control, 17 is an average value of the reception level in the control cycle of the transmission power control, Reference numeral 18 indicates the reception level after the transmission power control is performed.

The control cycle 16 of the transmission power control is a value set as the control cycle of the transmission power control according to the moving speed of the mobile station by estimating the moving speed of the mobile station (the control cycle 16 of the transmission power control).
Is a case where it is set to one fifth of the control cycle 6 of the transmission power control in FIG. 3, that is, one tenth of the fluctuation cycle of the reception level 10.)

The reception level 18 after performing the transmission power control shown in FIG. 7 (b) (estimating the moving speed of the mobile station and setting the control period of the transmission power control according to the moving speed of the mobile station, the transmission power control is performed). As shown in FIG. 3, the reception level after the transmission power control is performed, the reception level does not become larger than the reception level 10 before the transmission power control is performed. It fluctuates at a level very close to the control set value 7 of the power control.

As described above, by performing the transmission power control of the present invention, the fluctuation of the reception level after performing the transmission power control, which is a drawback of the conventional transmission power control, increases when the mobile station moves at a high speed. Since the phenomenon can be prevented, even when the mobile station moves at a high speed, the reception level can be kept constant and high quality communication can be secured.

FIG. 8 is a diagram showing an example in which the transmission power control of the present invention is performed when the mobile station moves at a low speed,
(A) shows before transmission power control is performed, and (b) shows after transmission power control is performed.

In the figure, 7 is a control set value of the transmission power control, 13 is a short-term median fluctuation of the reception level, 19 is a control cycle of the transmission power control, 20 is an average value of the reception level within the control cycle of the transmission power control, Reference numeral 21 denotes a reception level after the transmission power control is performed.

The control cycle 19 of the transmission power control is a value set as the control cycle of the transmission power control according to the moving speed of the mobile station by estimating the moving speed of the mobile station (the control cycle 19 of the transmission power control).
Is eight times the control period 6 of the transmission power control in FIG. 4, that is, four times the fluctuation period of the reception level 13).

The reception level 19 after the execution of the transmission power control shown in FIG. 8 (b) (the transmission speed control is performed by estimating the moving speed of the mobile station and setting the control period of the transmission power control according to the moving speed of the mobile station) As shown in FIG. 4, the reception level after the transmission power control is not changed as much as the reception level 13 before the transmission power control is performed, unlike the reception level 15 after the conventional transmission power control is performed. In addition, the average value 20 of the reception level in the control cycle of the transmission power control can be set to a level very close to the control setting value 7 of the transmission power control.

As described above, by performing the transmission power control of the present invention, the fluctuation of the reception level after performing the transmission power control, which is a drawback of the conventional transmission power control, increases when the mobile station moves at a low speed. Since the phenomenon can be prevented, even when the mobile station moves at a low speed, the reception level can be kept constant to ensure high-quality communication.

As described above, according to the method of performing the transmission power control by setting the control period and the control amount of the transmission power control according to the moving speed of the mobile station by estimating the moving speed of the mobile station of the present invention,
High quality communication can always be performed even if the moving speed of the mobile station changes.

In the above embodiment, the case where the moving speed of the mobile station is estimated based on the reception level of the signal from the partner station has been described, but the method of estimating the moving speed of the mobile station is as follows.
However, the present invention is not limited to this. For example, a method may be employed in which the mobile station notifies the base station of information on its own moving speed, and the base station estimates the moving speed of the mobile station.

〔The invention's effect〕

As described above, according to the method of the present invention, regardless of the moving speed of a mobile station, it is possible to perform transmission power control that can ensure high-quality communication while maintaining a constant reception level. . The present invention can be applied to all mobile communication systems that perform transmission power control, especially when performing communication with a mobile station in which the moving speed of the mobile station is low or high. Very effective.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing a configuration example of a conventional transmission power control system in an automobile telephone system, FIG. 2 is a diagram showing an operation example of a conventional transmission power control system, and FIG. FIG. 4 is a diagram showing an example of a case where the conventional transmission power control is performed when the station moves at a high speed. FIG. 4 is an example of a case where the conventional transmission power control is performed when the mobile station moves at a low speed. FIG. 5 is a diagram showing a configuration of a transmission power control system according to an embodiment of the present invention.
FIG. 7 is a diagram showing an example of the configuration of a moving speed detection circuit, FIG. 7 is a diagram showing an example in which the transmission power control of the present invention is performed when the mobile station moves at a high speed, and FIG. FIG. 9 is a diagram illustrating an example of a case where transmission power control according to the present invention is performed when the mobile terminal moves at a low speed. 1,22… Receiver, 2,24 …… CPU, 3,25 …… Transmitter, 4…
... Short-term median fluctuation of reception level, 5... Instantaneous fluctuation of reception level, 6... Control cycle of transmission power control, 7... Control set value of transmission power control, 8. Average reception level, 9: reception level after transmission power control is performed, 10: short-term median fluctuation of reception level, 11:
Average value of the reception level within the control cycle of the transmission power control, 12 ...
... reception level after transmission power control, 13 ... short-term median fluctuation of reception level, 14 ... average value of reception level within control cycle of transmission power control, 15 ... reception level after transmission power control, 16 ...... Control cycle of transmission power control, 17 ... average value of reception level within control cycle of transmission power control, 18 ... reception level after execution of transmission power control, 19 ... control cycle of transmission power control, 20 ... ... Average value of the reception level within the control cycle of the transmission power control, 21...
Moving speed detection circuit, 26: Antenna, 27: High-pass filter, 28: Comparator, 29: Counter

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Seigura Onoe 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Takanori Utano 1-16-1 Uchisaiwaicho, Chiyoda-ku, Tokyo No. Nippon Telegraph and Telephone Corporation (56) References JP-A-61-135241 (JP, A) JP-A-60-52128 (JP, A) JP-A-64-32727 (JP, A) JP-A-1- 305733 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H04Q 7/00-7/38

Claims (1)

(57) [Claims] 1. A service area is defined by a wireless zone of a base station, and the transmission power of the base station or the mobile station may be changed during communication between the mobile station moving within the service area and the base station. In a mobile communication system configured as possible, at least one of a base station and a mobile station estimates a moving speed of the mobile station, and the transmission power should be changed based on a result obtained by the means. Means for setting a time interval, wherein the transmission power is increased or decreased at each set time interval according to the estimation result of the moving speed of the mobile station.