JP3148071B2 - Power control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base station required power of a reverse link and a pilot signal power of a forward link in a base station in a mobile communication system based on a code division multiple access (CDMA) communication system. The present invention relates to a power control device.

[0002]

2. Description of the Related Art In the CDMA communication system, all mobile stations communicate using the same frequency band. Therefore, in the base station that receives signals from these mobile stations, signals from each mobile station interfere with each other. In the reverse link (connection from the mobile station to the base station), the base station controls the transmission power of each mobile station so that the received signal powers from the mobile station are all equal (reverse link power control). That is, the required value of the received signal power (base station required power) is set in the base station, and control information is transmitted to each mobile station so that the received power from each mobile station becomes the required value.
Each mobile station controls transmission power based on the control information. By the power control of the reverse link, the quality of each mobile station signal, that is, the signal-to-interference ratio (SIR) is all equal in the base station (see the following document). The quality at this time is defined as the quality of the base station. Reference Eisuke KUDOH and
Tadashi MATSUMOTO: "Effect of Power Control Error o
n the System User Capacity of DS / CDMA Cellular Mob
ile Radios ", IEICETrans.Commun., Vol.E75-B, No.6, June
1992 In general, the received signal power required by a base station for each mobile station is the same for each base station and is unchanged. Also,
The power of the pilot signal transmitted from the base station depends on the size of the cell area, but is constant in one base station. This example is shown in FIGS. In this example, the base station
BS0 to BS2 are arranged in one dimension. The mobile station receives the pilot signal from each base station, compares the received signal strength,
Connect to a base station that has a strong pilot signal. As the distance from the base station increases, the pilot signal strength decreases, and conversely, the adjacent base station pilot signal strength increases and becomes equal at a certain position. This position is used as the cell boundary, and CL in the figure
0-1 and CL1-2 (FIG. 6). When the pilot signal power at each base station is equal, the cell boundary is halfway between the base stations.
Considering this two-dimensionally, when base stations are arranged uniformly, the cell region areas surrounded by cell boundaries are all equal. Assuming that the received signal power required by each base station is PBD0 to PBD2, the following is obtained. PBD0 = PBD1 = PBD2 In general, since a signal attenuates in proportion to the power of the propagation distance, the mobile station transmission power PT to satisfy the base station required power
Is as follows, where r is the propagation distance. PT = PBD × (power of r) In other words, the farther the mobile station is from the base station, the higher the transmission power must be. When the cell boundary is at the center between the base stations, the trajectories of the mobile station transmission power PT satisfying the power requirements of both base stations intersect at the cell boundary (FIG. 7). That is, CL1-
If 2 is between base stations BS1 and BS2, the intersection of PT1 and PT2 is CL1-2
Will be on top. In this case, the interference from the mobile station connected to the adjacent base station is the maximum PBD. When the mobile station connected to the adjacent base station BS2 is on CL1-2, the interference power to the base station BS1 is PBD1. When the mobile station is closer to the base station BS2 than CL1-2, the interference power to the base station BS1 becomes weaker.

[0003]

The quality of a base station on the reverse link of a CDMA system is largely determined by the number of mobile stations connected to the base station and the strength of interference signals from other cells. That is, the number of connected mobile stations is
N, if the total amount of interference from other cells is Z, the base station SIR is:
It looks like this: SIR = PBD / ((N-1) × PBD + Z) However, since the traffic distribution of the mobile station fluctuates depending on the location, time, etc., the traffic concentrates on a certain base station (N increase in the above equation), and the SIR , And conversely, traffic is reduced and the quality becomes excessive. However, since the pilot signal power is constant, the cell area does not change, and it is impossible to cope with the traffic distribution. Also, in a base station with increased traffic, if the pilot signal power is reduced and the cell area is reduced in order to reduce the number of connected mobile stations, interference from neighboring cells increases (Z increase in the above equation). That is, in FIG. 6, assuming that traffic is concentrated on the base station BS1 and the base station SIR of the base station BS1 has deteriorated, the pilot signal power of the base station BS1 is reduced to reduce the number of connected mobile stations, and the cell boundary CL0 If -1 is CL '0-1, the transmission power PT0 of the mobile station connected to BS0 increases,
The reception power PR ′ of the interference wave at the base station BS1 becomes higher than that of PBD1, and the amount of interference increases. In the present invention, when the traffic is concentrated on a certain base station and the quality of the base station deteriorates,
By improving it to the reference value and conversely, when traffic decreases and the quality becomes excessive, by returning the quality to the reference value,
It is an object of the present invention to propose a method of making the quality of each base station uniform and enabling power control of a signal according to a traffic distribution.

[0004]

SUMMARY OF THE INVENTION The present invention relates to control of a required power of a reverse link base station and a power of a pilot signal of a forward link in a base station in a mobile communication system based on a code division multiple access communication system. . The present invention provides a means for receiving a signal, a means for measuring a signal-to-interference ratio at a base station from a received signal, and transmitting control information relating to a required transmission power to each mobile station according to the base station required power. Reverse link power control means to control transmission power according to pilot signal power
Forward link power control means for transmitting the pilot signal to each mobile station, and signal power control means. This signal power control means is used for measuring the measured base station.
In a base station whose SIR is worse than the reference SIR, the pilot signal power is reduced, thereby reducing the cell area covered by the base station and functioning to reduce the number of connected mobile stations, and at the same time, The base station increases the required power, thereby suppressing interference from neighboring cells and improving the base station SIR to the reference SIR, wherein the measured base station SIR is better than the reference SIR. Is to increase the pilot signal power, thereby allowing the base station to function to expand the cell area under its jurisdiction, and at the same time to reduce the base station required power, thereby giving to neighboring cells It functions to suppress interference and suppress excessive quality to the reference SIR.

[0005]

According to the present invention, when traffic concentrates on a certain base station and quality deterioration in the base station occurs, it is improved,
Conversely, if the traffic decreases and the quality becomes excessive, the quality is returned to the reference level to make the quality at each base station uniform. The concept of the present invention is shown in FIGS. Base station BS1
If the traffic is concentrated on the base station and the base station SIR at the base station BS1 deteriorates, the pilot signal power PP1 at the base station BS1 is reduced (FIG. 4). The cell boundary is the intersection of the received power PR of the pilot signal and is indicated by CL0-1 and CL1-2. By lowering pilot signal power PP1, the cell boundary approaches base station BS1, the cell area is reduced, and the number of connected mobile stations at base station BS1 is reduced. In the base station BS1, the required power of the base station is set so that the amount of interference from the cells of the base stations BS0 and BS2 does not increase.
Raise PBD1 (Fig. 5). At this time, the mobile station transmission power PT is made equal at the cell boundary. Base stations BS0 to C
Assuming that the distance from L0-1 is r0, the distance from CL0-1 to BS1 is r1, and the distance attenuation constant is w, PP0 / r0w = PP1 / r1w PBD0 × r0w = PBD1 × r1w. A relationship is obtained. PP0 × PBD0 = PP1 × PBD1 That is, when one side is a constant, the pilot signal power PP is
When multiplied by X, the base station required power PBD becomes 1 / X. As a result, the mobile station transmission power PT becomes equal at the cell boundary,
The power of the interference wave from the adjacent cell mobile station is equal to or less than the required power of the base station. That is, the most effective control can be performed by setting PP × PBD = constant. This reduces the cell area at the base station BS1, reduces the intra-cell interference by allocating a part of the traffic to adjacent cells, suppresses the adjacent cell interference by increasing the base station required power, and reduces the base station SIR Make improvements. 4 and FIG.
This is also explained below. If the traffic decreases at the base stations BS0 and BS2 and the base station SIR becomes excessive, the pilot signal powers PP0 and PP2 are increased, and the base station required powers PBD0 and PBD2 are reduced to improve the quality of the base stations BS0 and BS2. Suppress to the reference value.

[0006]

1 is a block diagram of a power control apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram of a signal power control unit in FIG.
FIG. 3 shows a flowchart for explaining the operation of FIG. These are all on the base station side. Shown in the figure
SIR and signal power are all displayed in decibels. First, a signal is received by the signal receiving unit 1 in FIG. 1 (ST in FIG. 3).
1). Next, the SIR measurement section 2 in FIG. 1 measures the SIR at the base station from the received signal (ST2). CDM
The quality of the base station on the reverse link of system A is
It is largely determined by the number of mobile stations connected to the base station and the strength of interference signals from other cells. That is, assuming that the number of connected mobile stations is N and the total amount of interference from other cells is Z,
The base station SIR is as follows. SIR = PBD / ((N-1) × PBD + Z)

[0007] The measured result varies with time and is represented by SIR (t). The measured SIR value is sent to the signal power control unit 3. The signal power control unit uses the subtractor 8 in FIG. 2 to calculate the deviation between the SIR measurement value SIR (t) and the SIR reference value SIRo.
D_SIR (t) is taken (ST3). That is, it becomes as follows. D_SIR (t) = SIRo-SIR (t) The SIR reference value is a control target value of the SIR measurement value, and the entire system is controlled so that the measurement value always becomes this value. The SIR reference value is set slightly higher than the quality guarantee value (the quality cannot be guaranteed if the SIR falls below that value).

The SIR deviation D_SIR (t) is calculated by the signal converter 9 shown in FIG.
Is converted to a base station required power update value U_PR (t) (ST
Four). Assuming that the conversion function is a proportional function and its coefficient is α, the conversion function is as follows. U_PR (t) = α × D_SIR (t) The base station requested power is updated using this updated value (ST
Five). The update is obtained by adding an update value to the required power before update (ST7) delayed by the delay unit 12 in FIG. That is, the base station required power PR (t) is as follows. PR (t) = PR (t−1) + U_PR (t) = PR (t−1) + α × D_SIR (t) Here, PR (t−1) indicates the required power value before update. For example, S
If the IR measurement is worse than the reference value, the deviation D_SIR
(t) is positive (the SIR value is indicated by a negative decibel value), the required power update value is also positive, and the required power increases. Since the SIR and the power value are shown in decibels, the real number is multiplied by the updated value. The limiter 11 of FIG. 2 limits the range so that the obtained result falls within the dynamic range of the required power (ST
6). This prevents control runaway.

[0009] The base station required power PR (t) is sent to the reverse link power control unit 4 of FIG. 1 (ST8).
The reverse link power control unit 4 compares the calculated base station required power with the received signal power from each mobile station, and transmits control information related to power control to the mobile station. Each mobile station controls transmission power based on the control information. The pilot signal power is calculated using the base station required power. The sum of the base station required power value and the pilot signal power value is defined as a base station reference power value. The base station reference power value is set to be always constant. That is,
In FIG. 2, the base station required power is subtracted from the set base station reference power value 13 using the subtractor 14 to obtain the pilot signal power PP (t) shown below (ST9). PP (t) = PBSo-PR (t) Since these powers are in decibels, the following relationship is obtained in real numbers. PP '= PBSo' / PR '

[0010] The pilot signal power PP (t) is sent to the forward link power control unit 5 of FIG.
0) The pilot signal is transmitted with the pilot signal power. Among the base station reference power values, the initial value of the required power of the base station is constant irrespective of the base station, and the initial value of the pilot signal power can be approximately determined by the cell size at the stage of designing. That is, the base station reference power value is
It is determined and set according to the initial cell size.

In this embodiment, the deviation of the SIR is converted into an updated value of the required power of the base station and the pilot signal power is updated according to the updated value, so that the required power of the base station and the pilot signal power are converted to the SIR. , The SIR deviation is converted into an updated value of pilot signal power and the base station required power is updated according to the updated value. Although the SIR and the signal power are all expressed in decibels, they can be real values. In this case, the decibel addition part is multiplication of real numbers. Although the function in the signal conversion unit is a proportional function, a step function or a multi-order function is also possible. Further, the SIR reference value is fixed, but can be changed while observing the quality in the adjacent base station.

[0012]

As described above, by controlling the required power of the base station and the pilot signal power according to the traffic in each cell, the quality at each base station is kept constant, and the control according to the traffic distribution is performed. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a power control device showing one embodiment of the present invention.

FIG. 2 is a configuration diagram of a signal power control unit in FIG. 1;

FIG. 3 is a flowchart for explaining the operation of the power control device in FIG. 1;

FIG. 4 is an explanatory view of the concept of the present invention.

FIG. 5 is an explanatory view of the concept of the present invention.

FIG. 6 is an explanatory diagram of the concept of the prior art.

FIG. 7 is an explanatory diagram of the concept of the prior art.

[Explanation of symbols]

 Reference Signs List 1 signal receiving unit 2 SIR measurement unit 3 signal power control unit 4 reverse link power control unit 5 forward link power control unit BS0 to BS2 base station PBD0 to PBD2 base station required power PP0 to PP2 pilot signal power CL0-1, 1-2 Cell boundary SIR (t) Measured SIR value SIRo SIR reference value PBSo Base station reference power

────────────────────────────────────────────────── ─── Continuation of the front page (56) References Table 4 Hei 4-502841 (JP, A) International Publication 93/7702 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 7/24-7/26 H04Q 7/00-7/38

Claims (1)

(57) [Claims] 1. A means for receiving a signal, a means for measuring a signal-to-interference ratio at a base station from a received signal, and control information on transmission power required for each mobile station according to a base station required power. A reverse link power control means for transmitting, and a pilot for which transmission power is controlled according to pilot signal power.
Forward link power control means for transmitting a lot signal to each mobile station; and, if the measured signal-to-interference ratio is worse than a reference signal-to-interference ratio, the measured signal-to-interference ratio and the reference signal-to-signal ratio In accordance with the deviation from the interference ratio, the pilot signal power is reduced and the base station required power is increased, and if the measured signal-to-interference ratio is better than a reference signal-to-interference ratio, the measured Signal power control means for increasing the pilot signal power and decreasing the base station required power according to the deviation between the signal to interference ratio and the reference signal to interference ratio. A power control device in a base station of a mobile communication system based on a code division multiple access communication system.