JPH10215218A - Power controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the power controller by which the effect of non-uniform traffic in the CDMA system is suppressed and the opportunity of hand-off associated with movement along a cell border is reduced. SOLUTION: A base station in a mobile radio communication system adopting the CDMA system is provided with control means 1-6 for pilot signal power of an outgoing channel and with control means 11-16 for incoming channel reception object power. The non-uniformity of traffic is coped with by controlling the pilt signal power so as to increase/decrease a cell coverage and the speech quality is kept constant by controlling the reception object power. Furthermore, in order to reduce number of times of hand-off, a pilot signal power update interval is selected longer than a reception object power update interval or the pilot signal power is controlled only when the number exceeds a permissible range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power control apparatus, and more particularly, to a code division multiple access (Code Division Multiple Access).
Access, hereinafter referred to as CDMA) mobile radio system.

[0002]

2. Description of the Related Art As a prior art in such a field, there are the following documents. “Performance of SIR Based Power
Control in the Presence of Non-uniform Traffic Dis
tribution, ”T. Dohi, M. Sawahashi and F. Adachi, I
EEE ICUPC'95. One effective means for increasing the number of accommodated mobile stations in a mobile radio communication system is a microcell system. In the micro-cell method, cells are subdivided and 1
Shrink the area covered by the cell. The narrower the cell area,
It is expected that the frequency use efficiency will increase and the number of accommodation stations will increase. However, as the cell area becomes smaller, the environment (high-rise buildings, roads, etc.) and population distribution of the place are greatly affected,
The traffic volume (the total number of mobile stations and the data volume) covered by one cell is not uniform for each cell. Traffic non-uniformity reduces the efficiency of the system.

In recent years, spread spectrum systems have been applied.
CDMA communication systems are receiving attention. In the CDMA system, since all mobile stations use the same frequency band, transmission power control in the uplink is an essential technology. That is, the mobile station controls the transmission power so that the reception power from each mobile station is always equal in the base station. Even in the CDMA system, uneven traffic reduces system efficiency. The communication quality SIR of the uplink in the CDMA system is shown as follows.

SIR = S / (A.S + B) (1)

[0005] S is the signal power, for example, the target power of the mobile station radio wave received by the base station in transmission power control. A indicates the number of other mobile stations in the own cell, and B indicates the total amount of interference from adjacent cells. When the number of mobile stations in the own cell increases or interference from adjacent cells increases due to uneven traffic, the quality SIR deteriorates. Conversely, when the traffic volume is small, the SIR is considerably better than the guaranteed value of the quality, but the efficiency of the entire system decreases.

As a method for coping with non-uniform traffic in the CDMA system, there is a method of controlling a target reception power of transmission power control in the uplink according to communication quality. This principle is shown in FIG. The target power received from the mobile station at each of the base stations BS0 and BS1 is defined as TPR0 and TPR1. The transmission power required for the mobile station to achieve the target reception power TPR0 is TM0, and the transmission power required for achieving the TPR1 is TM1 and TM2. Here, the relationship between the mobile station transmission power and the target reception power is approximately given by the following equation.

TPR = TM × (r-k power) (2)

[0008] Here, r represents the distance between the mobile station and the base station, and k is a propagation attenuation coefficient and takes a value of 3 to 4. It is assumed that communication quality has deteriorated in BS1. In BS1, the target reception power TPR1 is increased. That is, S in the equation (1) is increased. Due to the increase in S, the deterioration of SIR based on the adjacent cell interference amount B is suppressed, and the quality can be improved. Cell boundary CL
The amount of interference from the mobile station connected to BS0 on 0-1 to BS1 is represented by I
Assuming that M0, IM0 is equal to or less than TPR1 in BS1. If S is infinite, the quality SIR in equation (1) is approximated by 1 / A, and B can be ignored.

FIG. 10 is a functional block diagram showing a power control function of the base station in the conventional system. Let the measured communication quality at the base station be SIR (t). The quality reference value SIRo is set in the quality reference value holder 1, and control is performed so that the quality converges to the reference value. The difference from the reference value of the quality obtained by the differentiator 2 is defined as DSIR (t).

[0010] DSIR (t) = SIR (t)-SIRo (3)

The converter A3 converts the quality difference value into an updated difference value DTPR (t) of the target reception power TPR (t).

DTPR (t) = f (DSIR (t)) (4)

The conversion function f () may be a proportional function, a step function, or the like. The adder 4 adds the current TPR (t) and DTPR (t) held in the holder A6, and updates TPR (t).
The target reception power TPR (t) is updated at short update time intervals (for example, several hundred milliseconds to several seconds). The signal power limiter A
5 sets the dynamic range (upper limit and lower limit) of the reception target power. In the base station, the obtained reception target power TP
R (t) is compared with the received power from each mobile station, and the transmission power of each mobile station is controlled so that the received power from each mobile station converges on TPR (t).

[0014]

However, when the number A of mobile stations in the own cell in the above equation (1) increases, SIR = 1 / A due to an increase in the target reception power, and the influence of interference from an adjacent cell is reduced. Even if it decreases, if this value is below the guaranteed value of quality, the above-mentioned conventional method cannot cope with it. Also,
Increasing the target reception power increases the transmission power at the mobile station,
This will increase interference with neighboring cells. In FIG. 11, if the amount of interference of the transmission power TM2 connected to BS1 from the mobile station to BS0 near the cell boundary is IM1, the problem is that IM1 is greater than or equal to the signal power TPR0 in BS0, which degrades the quality in BS0. There was a point.

FIG. 12 shows the number of mobile stations and the quality in the above method.
FIG. 4 is an explanatory diagram showing a relationship with SIR. The horizontal axis is time,
The vertical axis is the quality SIR and the number of mobile stations connected in the own cell, and the case where the number of mobile stations increases with time is considered. When the control of the reception target power as described above is performed, assuming that the number of controllable mobile stations in this method is Ac, the control is performed so that the quality is kept constant up to the number of mobile stations Ac. However, there is a problem in that it is impossible to cope with the problem and quality is deteriorated.

An object of the present invention is to solve the above-mentioned problems of the prior art, suppress the influence of traffic non-uniformity in the CDMA system, and reduce handoff due to cell boundary movement due to a change in pilot signal power. It is an object of the present invention to provide a power control device capable of causing the power control to be performed.

[0017]

SUMMARY OF THE INVENTION The present invention relates to a power control apparatus for a radio base station which performs CDMA communication. The power control apparatus is controlled at predetermined intervals so that the number of mobile stations under its control falls within a predetermined range. Downlink power control means for controlling the pilot signal transmission power in the downlink from the station, so that the communication quality in the base station converges to a predetermined reference value,
Uplink power control means for constantly controlling a target reception power, which is a target value of transmission power control in an uplink from a mobile station, is provided.

In the present invention, the number of mobile stations is controlled within an appropriate range by controlling the transmission power of the pilot signal, and the update of the transmission power is executed in a long cycle to prevent frequent handoffs. . Further, by controlling the target power received from the mobile station under its control, the communication quality is controlled so as to converge to the reference value.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 3 is an explanatory diagram showing the principle of power control in the present invention. FIG. 3 (a) shows the relationship between the base station pilot signal power in the downlink and the reception power at the mobile station, and FIG. 3 (b) shows the relationship between the base station reception target power and the mobile station transmission power in the uplink. is there. (a)
Let PPS0-2 be the base station pilot signal transmission power and RP0-2 be the reception power curve at the mobile station.

The mobile station is connected to a base station having the highest pilot signal reception power. Therefore, the cell boundary CL0-
1 and CL1-2 are positions where the pilot signal reception power curves RP according to the distance from each base station intersect. If communication quality deteriorates in BS1, pilot transmission power PPS1 is reduced. Thereby, the cell boundary moves to the BS1 side, and the cell of BS1 is reduced. As a result, of the mobile stations connected to BS1, the mobile station outside the boundary is allocated to the adjacent cell, and the handoff is performed. As a result, the number of mobile stations A in the above equation (1) decreases, and the direct cause of quality degradation is eliminated.

However, as shown in FIG. 3B, when the cell boundary moves, the transmission power TM0,2 at the mobile station near the cell boundary increases, and the interference power to BS1 increases. . To deal with this, the target target power TPR in BS1
By increasing 1, interference from adjacent cells is suppressed. Each cell controls the pilot signal power and the reception target power in accordance with the number of mobile stations and the communication quality, thereby changing the cell area and controlling the communication quality to be constant. As a result, efficient connection control can be performed while maintaining communication quality in response to uneven traffic.

However, when the mobile station moves along the cell boundary by controlling the pilot signal power, the connected base station is changed even when the mobile station is not moving, and handoff occurs. For this reason, frequent updating of pilot signal power is desired to be suppressed in maintaining communication stability. Further, as shown in FIG. 12, the non-uniformity to some extent can be eliminated only by the control of the target power in the related art. Therefore, the pilot signal power control and the target power control are performed independently, and the interval of the pilot signal power control is set to be longer than the target power control interval. Some non-uniformity is addressed by target power control, and any further non-uniformity is addressed by pilot signal power control. This allows
The number of handoffs can be reduced without impairing the effect of suppressing traffic nonuniformity.

FIG. 2 is a block diagram showing a configuration of a base station and a mobile station of a mobile communication system to which the present invention is applied. The base station 20 includes a base station transmitter 21, a base station receiver 22, and a base station controller 23. The base station receiver 22 receives a radio wave from the mobile station 24 and outputs a demodulated digital voice signal to an exchange (not shown). In addition, it measures the signal power of each channel separated by the code and the signal power of the entire band, and outputs the reception quality information SIR (t) of each mobile station, which is the ratio, to the base station controller 23.

The base station controller 23 that performs power control receives the quality information SIR (t) and the number of mobile stations A (t) of the cell, performs processing described later, and performs a pilot signal power value PPS (t). And a target reception power TPR (t). Base station transmitter 21
Modulates the digital voice signal input from the switch,
The signal is subjected to frequency spread processing and transmitted. The transmission power of the transmitter 21 is
Controlled by PPS (t). Further, the reception target power TPR (t) output from the control device 23 is compared with the reception power from each mobile station measured by the receiver 22, and based on the difference, the transmission power control information of the mobile station is calculated. Generated. The control information is transmitted to the mobile station transmitter 2 via the base station transmitter 21, the mobile station receiver 25, and the mobile station controller 26.
7 is controlled. In this way, the transmission power of each mobile station is controlled such that the received power from each mobile station at the base station converges on TPR (t).

FIG. 1 shows a first example of the base station controller 23 of FIG.
FIG. 3 is a functional block diagram illustrating functions of the embodiment. The upper part of FIG. 1 shows the power control means of the uplink from the mobile station, and the configuration and operation of this power control means are the same as those of the conventional example shown in FIG. Uplink power control means is used for speech quality SIR
Control the update of the target reception power TPR (t) at short intervals so that converges to a predetermined quality reference value.

The lower part of FIG. 1 shows control means for downlink power from the mobile station. The current number of connected mobile stations input from the control device for the entire base station (not shown) is represented by A (t). The reference mobile station number holder 11 holds and outputs the reference mobile station number Ao, and the subtractor 12 calculates a difference DA (t) from the reference value of the mobile station number.

DA (t) = A (t) -Ao (7)

The converter B13 converts the mobile station number difference value DA (t) into an updated difference value DPPS (t) of the pilot signal power PPS (t).

DPPS (t) = f (DA (t)) (8)

As f (), a proportional function, a step function and the like can be considered. The adder 14 updates the PPS (t) by adding the current PPS (t) and DPPS (t) held in the holder B16. The update period of the pilot signal power TPR (t) is an update period that is sufficiently long, for example, several seconds to the update period of the reception target power.
Updated every few minutes. Thereby, frequent occurrence of handoff can be prevented. The signal power limiter B15 sets a dynamic range (upper limit and lower limit) of pilot signal power. The base station controls the pilot signal transmission power of the base station based on the obtained pilot signal power PPS (t).

FIG. 4 is an explanatory diagram showing an example of changes in the number of mobile stations and call quality in the first embodiment. This example shows a case where the number of mobile stations monotonously increases in the cell. The pilot signal power is updated negatively every update time, and the cell area is narrowed. As a result, the number of mobile stations decreases to the reference value. During the update time, only the target power control is performed, but since the number of mobile stations does not exceed the number of controllable mobile stations in the target power control (Ac in FIG. 12), the quality SIR
Is kept constant. The update time is set according to the traffic fluctuation situation.

FIG. 5 is a functional block diagram showing the configuration of the second embodiment of the present invention. The target power control unit in the upper part of FIG. 5 is the same as that in FIG. What differs from the first embodiment in the lower downlink power control means is the DPPS generation means. In the second embodiment, the current number of connected mobile stations is A
(t), maximum allowed mobile station number is Amax, minimum allowed mobile station number is Ami
When n is set, the pilot signal power is controlled so that the number of connected mobile stations always falls within the allowable number of mobile stations.

The comparator 40 compares the number of connected mobile stations A (t) with the allowable number of mobile stations Amax and Amin, and sends out a pilot signal update value DPPS when the number of mobile stations exceeds the maximum allowable value Amax. . In this case, DPPS is a negative constant value. vice versa,
If the number of mobile stations falls below the minimum allowable value Amin, a positive update value
Transmit DPPS and increase pilot signal power. In this configuration, the control of the target reception power is performed at short fixed intervals, and the pilot signal power control is performed irregularly.

FIG. 6 is an explanatory diagram showing an example of changes in the number of mobile stations and call quality in the second embodiment. The case where the number of mobile stations fluctuates irregularly is shown. If the pilot signal power is updated at regular intervals, there may be cases where the number of stations cannot be completely followed or where the update is unnecessarily performed. In FIG. 6, when the number of mobile stations reaches the maximum or minimum allowable number of mobile stations (t
Only at (3, t4, t5), the power of the pilot signal is updated irregularly, the number of connected mobile stations is reduced or increased, and control is performed so that the number of mobile stations always falls within the allowable range.

FIG. 7 is a functional block diagram showing the configuration of the third embodiment of the present invention. Let the current communication quality be SIR (t). The maximum allowable communication quality is SIRmax, and the minimum allowable communication quality is SI
Rmin is set, and the pilot signal power is controlled so that the communication quality always falls within the allowable communication quality range. The comparator 50 compares the current communication quality with the allowable communication quality, and when the communication quality exceeds the maximum allowable value, updates the pilot signal update value.
Generates DPPS. In this case, DPPS is a negative constant value.
Conversely, if the communication quality falls below the minimum allowable value, a positive update value DPPS is generated, and the pilot signal power is increased. In this embodiment, usually, by controlling the target reception power,
Since the SIR is kept constant and the PPS is controlled only when the SIR cannot be maintained by the control, the occurrence of handoff can be reduced.

FIG. 8 is a functional block diagram showing the configuration of the fourth embodiment of the present invention. TPR (t)
And The maximum permissible reception target power is TPRmax and the minimum permissible reception target power is TPRmin, and the pilot signal power is controlled so that the reception target power is always within the permissible reception target power range. The comparator 60 compares the target reception power with the allowable target power, and sends out the pilot signal update value DPPS when the target reception power exceeds the maximum allowable value. In this case, DP
PS is a negative constant value. Conversely, when the reception target power falls below the minimum allowable value, a positive update value DPPS is transmitted, and the pilot signal power is increased.

In the above embodiment, since the state of the communication quality in equation (1) changes by updating the pilot signal power, it is necessary to converge the target reception power to the optimum value. In the configurations of the first to fourth embodiments shown in FIGS. 1, 5, 7, and 8, it is assumed that the update time of the reception target power is short.
The target reception power is updated independently of the pilot signal power to converge. However, if the update interval of the target power is set longer, or if the conversion coefficient of the target power converter (the coefficient of f () in equation (4)) is set to a smaller value (actually, system runaway may occur). To prevent
It is conceivable that it takes time to converge to the optimum value.

FIG. 9 is a functional block diagram showing a configuration of a fifth embodiment of the present invention for solving the above problem. As shown in FIG. 9, a configuration is conceivable in which a target power calculator 70 is provided to calculate a reception target power TPR (t) in accordance with the updated pilot signal power value PPS (t) and to set it in the holder A6. Can be When the path loss characteristics in the uplink / downlink are the same, the balance is maintained by setting the pilot signal power PPS and the target reception power TPR as PPS × TPR = constant (9). Therefore, when the pilot signal power is updated, the target power calculator 70 calculates and outputs the target power TPR from equation (9),
It is possible to converge more quickly to the optimum value of the reception target power. FIG. 9 is for the first embodiment of FIG.
The same applies to the second to fourth embodiments of FIGS.

[0039]

As described above, according to the present invention,
In the CDMA mobile radio base station, by adaptively controlling the downlink pilot signal power and the uplink reception target power according to the communication quality and the number of mobile stations, it is possible to deal with traffic unevenness, By making the pilot signal power update interval longer than the reception target power update interval, or by performing control only when it exceeds the allowable range, there is an effect that it is possible to reduce the movement of cell boundaries and reduce the number of handoffs. . Therefore, the efficiency of the entire mobile radio system can be improved while maintaining the communication quality.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of a first embodiment of a base station controller 23.

FIG. 2 is a block diagram showing a configuration of a mobile communication system to which the present invention is applied.

FIG. 3 is an explanatory diagram showing the principle of power control in the present invention.

FIG. 4 is an explanatory diagram showing an example of changes in the number of mobile stations and call quality according to the first embodiment.

FIG. 5 is a functional block diagram illustrating a configuration of a second exemplary embodiment of the present invention.

FIG. 6 is an explanatory diagram showing an example of changes in the number of mobile stations and call quality according to the second embodiment.

FIG. 7 is a functional block diagram showing a configuration of a third embodiment of the present invention.

FIG. 8 is a functional block diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 9 is a functional block diagram showing a configuration of a fifth embodiment of the present invention.

FIG. 10 is a functional block diagram showing a power control function of a base station in a conventional system.

FIG. 11 is an explanatory diagram showing the principle of a conventional power control method.

FIG. 12 is an explanatory diagram showing an example of changes in the number of mobile stations and call quality in a conventional power control method.

[Explanation of symbols]

1: quality reference value holder, 2: subtractor, 3: converter A, 4
... Adder, 5 ... Signal power limiter A, 6 ... Holder A, 11
... Reference mobile station number holder, 12 ... Subtractor, 13 ... Converter B, 14 ... Adder, 15 ... Signal power limiter B, 16 ... Holder B

Claims (5)

[Claims] 1. A power control apparatus in a wireless system for performing CDMA communication, wherein the power control apparatus is controlled at a predetermined interval or at least one of timings when a predetermined condition is satisfied, and the number of mobile stations under control falls within a predetermined range. Downlink power control means for controlling the pilot signal transmission power in the downlink from the radio base station, and in the uplink from the mobile station, so that the communication quality in the base station converges to a predetermined reference value. A power control apparatus comprising: uplink power control means for controlling a target reception power serving as a target value of transmission power control. 2. The downlink power control means sets an allowable range of the number of mobile stations under its control, and performs update control of the pilot signal transmission power only when the number of connected mobile stations exceeds the allowable range. The power control device according to claim 1, wherein: 3. The downlink power control means sets an allowable range of communication quality, and performs update control of the pilot signal transmission power only when the communication quality exceeds the allowable range. 2. The power control device according to 1. 4. The downlink power control means sets an allowable range of a target reception power, and performs update control of the pilot signal transmission power only when the target reception power exceeds the allowable range. The power control device according to claim 1. 5. The uplink power control means sets a target reception power based on the pilot signal power value when the downlink power control means performs update control of the pilot signal transmission power. The power control device according to claim 1, wherein