KR101520696B1 - Method of controlling power using dynamic step size - Google Patents

Abstract

The present invention relates to a method of controlling power in a wireless communication system. More particularly, the present invention relates to a method of controlling an outer loop power of a wireless communication system, the method comprising: determining whether an error has occurred in a received block; Down step, wherein the up step size is dynamically changed according to the number of previous consecutive errors.

Code division multiple access, power control, outer loop, step size

Description

[0001] METHOD OF CONTROLLING POWER USING DYNAMIC STEP SIZE [0002]

The present invention relates to a power control method of a wireless communication system. More particularly, the present invention relates to a method of controlling an outer loop power of a wireless communication system.

Code Division Multiple Access (CDMA) uses the same frequency channel simultaneously by multiple receivers and multiple transmitters. Therefore, since the interference occurs between the concurrent talker and the base station, proper control is required to operate the system smoothly.

For this control, various power control schemes are mixed and used in CDMA. The power control is transmitted between the transmitting end and the receiving end with minimum power while satisfying the appropriate quality of the transmitted signal. Therefore, when the power control is appropriately performed, the interference due to the transmission power of each terminal and the base station can be reduced and the system capacity can be maximized. Also, responding to various fast channel changes is an important issue related to power control of communication systems.

The uplink power control should perform power control by overcoming the power problem of the distant power between the terminal far from the cell and the terminal near the base station. That is, the strength of all signals of each terminal received at the base station should have a constant average power. Power control in the downlink should reduce the interference that affects other cells to the maximum, and power control should be applied to the terminals in the own cell to compensate for the influence from other cells. That is, the strength of the signal sufficient to compensate for the interference from the adjacent cell while reducing the influence on the adjacent cell must reach each terminal.

Generally, in a wireless communication system using Code Division Multiple Access (CDMA), power control is classified into an open loop power control and a closed loop power control . The closed loop power control can be divided into an inner loop power control and an outer loop power control.

Open loop power control is the operation of determining the initial transmit power at the beginning of a call connection. The basic principle is that a terminal close to a base station transmits a small output and a terminal located far away transmits a large output. In open loop power control, the terminal only determines the output according to the signal strength from the base station. That is, when the received power from the base station is high, the terminal output is small, and when the received power is low, the terminal output is made large, so that the terminal output reaching the base station can be minimized.

The inner loop power control method during the closed loop power control compares the measured signal quality with the target signal quality determined by the outer loop power control and transmits a Transmit Power Control command (TPC command) to the transmitter according to the comparison result do. The outer loop power control method, as mentioned above, determines the target signal quality used in the inner loop power control. Ultimately, it is desirable to have a fast and efficient outer loop power control scheme because outer loop power control can directly affect overall system capability, performance, and coverage.

The conventional outer loop power control method largely carries out operations for each state in three states of an initial state, an acquisition state, and a tracking state. 1 shows a flow chart of state transition of outer loop power control in a code division multiple access scheme.

The initial state of the outer loop power control is a step for maintaining the initial value of the target reception quality for a certain period of time after the start of the power control to ensure initial setup time of the transmitter and receiver. The signal quality may be related to the signal to interference ratio. For example, the signal quality may be Signal to Interference Ratio (SIR). For convenience, the target signal quality is indicated as target SIR or SIR _target . In acquisition state the block error occurs, or the operation to lower the predetermined value (Down_Step _START) as the SIR _target until it reaches the minimum _target SIR (SIR _{MIN_START_TARGET)} the SIR _target set by the state acquisition is performed. When a satisfying condition of the two conditions occurs, the state transitions to the tracking state. Acquisition status rapidly lowers the SIR _target to the level deemed appropriate in the current channel situation. Therefore, in the acquisition state, the step size lowering the SIR _target is set larger than the tracking state in the next step. Whether or not the block is erroneous is judged by a cyclic redundancy check (CRC) on the received block, and a good CRC OK and a bad CRC not OK Classify.

The tracking state requires a more detailed power control process than the acquisition state. FIG. 2 shows a flow chart schematically showing the operation in the tracking state. In the tracking state, the presence of a CRC is first determined. If CRC exists, CRC check process is performed, and if CRC does not exist, existing SIR _target is maintained. In the CRC error checking process, the CRC determines whether the current block is good or not. If the CRC is bad, the SIR _target is increased by a predetermined size (STEP _up ). If the CRC is good, the SIR _target is decreased by the size (STEP _down ) calculated by the STEP _up and the target block error rate (BLER _TARGET , parameter signaled from the upper layer). If the channel condition is ideal, STEP _down satisfying BLER _TARGET can be determined by Equation (1) below.

Here, STEP _down is a down step size, STEP _up is an up step size, and BLER _TARGET is a target block error rate.

For example, if BLER _TARGET is 1%, STEP _up = 99 × STEP _down . Therefore, when the step-down process is 99 times and the step-up process is performed once, the SIR _target becomes equal to the initial value.

Figure 3 shows the change in SIR _target over time in an ideal situation.

If an error is found in the CRC error checking process, the process of detecting the windup is performed. Windup defines a kind of extreme situation. For example, it occurs when the error is continuously detected in the outer loop power control process and the SIR _target continuously increases. Also, it happens when the UP TPC is continuously sent to increase the power to the transmitting end in the inner loop power control stage, but the actual receiving SIR does not increase accordingly. Generally, if the number of slots with a TPC of UP exceeds a predetermined value, when the slot is a compression mode (measure interval for handover), or if an average SIR is smaller than a predetermined value for detecting a windup, the current interval is determined as a windup interval do. If it is judged to be windup, the SIR _target is maintained. If it is not windup, the SIR _target is increased by STEP _up . Here, STEP _up is a predetermined value based on experimental data.

Conventionally, when a block error occurs consecutively due to deterioration of a temporary channel condition, the SIR _target is constantly increased by using a fixed interval (i.e., an up-step size) until a wind-up is determined to be an extreme situation. Therefore, there is a disadvantage in that excessive power is required to the transmitting end, and the power of the signal transmitted from the transmitting end to the corresponding terminal acts as interference to other users. Also, when the channel condition improves and the increased SIR _target is lowered, it is reduced to a fixed interval (that is, a down step size) that is just a ratio of BLER _TARGET of the up step size regardless of the previous up step number. Therefore, it takes a long time to return to a proper SIR _target , which causes power consumption and interference.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for efficiently performing power control in a wireless communication system.

It is another object of the present invention to provide a method for effectively performing power control in consideration of the number of previous consecutive errors / non-errors in outer loop power control.

It is still another object of the present invention to provide a method for efficiently performing power control in consideration of the number of consecutive up / down steps in outer loop power control.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, unless further departing from the spirit and scope of the invention as defined by the appended claims. It will be possible.

In accordance with one aspect of the present invention, there is provided an outer loop power control method for a wireless communication system, the method comprising: determining whether an error has occurred in a received block; Wherein the up-step size is dynamically changed according to the number of previous consecutive errors.

According to another aspect of the present invention, there is provided an outer loop power control method of a wireless communication system, comprising: determining whether an error has occurred in a received block; Wherein the down-step size is dynamically changed according to a previous continuous error or a number of non-errors.

Here, the block may be a transport block or a code block. Preferably, the block is a transport block.

According to the embodiments of the present invention, the following effects are obtained.

First, power control can be efficiently performed in a wireless communication system.

Second, in the outer loop power control, the target reception quality can be returned and maintained at an appropriate level by considering the number of previous consecutive error / non-errors.

Thirdly, in the outer loop power control, the target reception quality can be restored and maintained to an appropriate level by considering the number of consecutive up / down steps.

The effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description will be.

Hereinafter, the structure, operation and other features of the present invention will be readily understood by the embodiments of the present invention described with reference to the accompanying drawings. The embodiments described below are examples in which the technical features of the present invention are applied to a code division multiple access system.

4 is a flowchart illustrating an operation of performing outer loop power control according to an embodiment of the present invention. Figure 4 relates to the tracking state during outer loop power control.

Referring to FIG. 4, the receiving end starts a tracking state operation (S410) and determines whether a CRC (cyclic redundancy check) exists in the received block (S420). If CRC is not present, the target reception quality (SIR _TARGET ) is maintained as before. If CRC is present, it is determined whether there is an error in the block (S430). The block may be a transport block. If a CRC error is detected in the block, a process for up-stepping SIR _TARGET is performed (S440 to S470). On the other hand, if no CRC error is detected in the block, a process for down-stepping the SIR _TARGET is performed (S480 to S490).

The basic up-step and down-step procedures are similar to those illustrated in Fig. However, in one embodiment of the present invention, in order to prevent excessive transmission power and to return / maintain the SIR _TARGET to an appropriate level, the up-step size STEP _up and down step size (STEP _down ) can be dynamically changed. To this end, an embodiment of the present invention further includes a step S440 of updating the up-step size and a step S480 of updating the down-step size. Preferably, the previous outer loop power control result is the result of the previous continuous outer loop power control. The previous successive outer loop power control results may be the number of previous successive error occurrences. That is, it may be the number of previous consecutive errors or the number of previous consecutive non-errors. In addition, the previous successive outer loop power control result may be the previous consecutive up-step number or down-step number.

Updating the up step size or the down step size using the previous successive outer loop power control results may be performed as follows.

(Up step size update)

1. First up-step size: Always keep the up-step size for the first new error occurring, even if the previous result is non-error or down-step.

2. Up step size after the second:

   - Decrease the size according to the number of previous consecutive error occurrences (upstep).

- To prevent the up step size from approaching 0 and to prevent the SIR _TARGET from stagnating, set the threshold value to prevent the up step size from decreasing below a certain value.

(Down step size update)

1. First down-step size: Increases the down-step size for the first non-error that occurs newly according to the previous number of consecutive error occurrences (upstep).

2. Second down step size:

   - Decrease the size according to the previous consecutive non-error (downstep) counts.

- To prevent the down step size from approaching 0 and to prevent the SIR _TARGET from stagnating, set the threshold value to prevent the down step size from falling below a certain value.

Hereinafter, updating of the up step size and the down step size will be described in more detail with reference to FIGS. 5 to 7. FIG. For the sake of convenience, the figure continuously shows the change in the SIR _TARGET , the up step size and the down step size. However, the actual values will be displayed discretely on the graph of the figure.

5A shows a change in the SIR _TARGET according to the number of consecutive errors (the number of times of the step-up). Referring to FIG. 5 (a), the SIR _TARGET is divided into two stages and increases as the error continues to occur. At the first stage, the SIR _TARGET increases to a convex shape as the up step size continues to decrease (510). The second stage starts with the upsize size decreasing below the threshold. In the second stage, the up-step size is kept constant and the SIR _TARGET is increased in a straight line (520).

5 (b) to 5 (d) show changes in the up-step size in accordance with the number of consecutive errors (the number of step-ups). Referring to Figures 5 (b) - (d), the first up step size is always the same as the basic up step size (UP _default ) regardless of the previous non-error times.

Then, the up-step size can be linearly reduced with respect to the number of consecutive errors (Fig. 5 (b)). For example, the current up step size STEP _up may be smaller than the _default UP step size by a predetermined amount, and the predetermined size may be constantly increased according to the number of consecutive errors. In addition, the present upsize size STEP _up may be smaller than the previous upsize size STEP _up-1 by a predetermined size, and the predetermined size may be constant for each power control step.

In addition, the up-step size can be reduced non-linearly with respect to the number of consecutive errors (Fig. 5 (c) (d)). In Fig. 5 (c), the up-step size is large at the beginning of the error, and decreases as the error continues. For example, it may be the case that the current upsize size exponentially decreases from the basic upsize size according to the number of consecutive errors. Since the SIR _TARGET may already be set high enough at the first _upstep , it may be helpful to maintain a proper SIR _TARGET by rapidly reducing the subsequent upsize size. On the other hand, in Fig. 5 (d), the up-step size has a small decrease width at the beginning of the error and a larger decrease width as the error continues. For example, it may be the case that the difference between the current up step size (STEP _up ) and the previous up step size (STEP _up-1 ) increases in proportion to the number of consecutive errors. If the up step size is kept large in the early stage, the SIR _TARGET rapidly increases, so that the continuous occurrence of errors can be blocked early. Therefore, it is possible to prevent overhead and power waste due to unnecessary up steps.

5 (b) to 5 (d), the up-step size does not continuously decrease, but is maintained at a constant value when the value falls below the threshold value UP _min . The constant value may be a threshold value or a previous up step size.

6 (a) to (c) show the change of the first down step size according to the previous number of consecutive errors (the number of step up times). Referring to Figures 6 (a) - (c), the first down step size DOWN _first may increase linearly with respect to the previous number of consecutive errors (Figure 6 (a)). For example, the first down-step size may be determined by multiplying the basic down-step size (DOWN _default ) by the number of previous consecutive errors. In addition, the down step size may increase non-linearly with respect to the number of consecutive non-errors (Fig. 6 (b) (c)). In Fig. 6 (b), the down step size increases as the number of previous consecutive errors increases. For example, the first down-step size may exponentially increase from the basic down-step size according to the number of consecutive errors. Also, the first down-step size may be a higher-order (> 1 < rd >) function relationship with the previous consecutive number of errors. Basically, the up-step size is considerably larger than the down-step size. Thus, if the upstep has been performed multiple times due to previous successive errors, it may be helpful to keep the SIR _TARGET at a reasonable level by increasing the increment of the downsize size to the number of previous consecutive errors.

On the other hand, in FIG. 6 (c), the first down-step size increases as the number of previous consecutive errors increases. For example, the increase width of the first downsize size may be exponentially decreasing according to the number of consecutive errors. It may also be the case that the first down step size is a lower order (< first order) functional relationship with the previous consecutive number of errors. If, in the previous up-step process, the up-step size is reduced as the error continues, the increase width of the first down-step size according to the previous number of consecutive errors is made smaller as the number of previous consecutive errors increases Can help keep the SIR _TARGET at a reasonable level.

FIG. 7A shows a change in the SIR _TARGET according to the number of consecutive non-errors (the number of stepdown times). Referring to FIG. 7 (a), the SIR _TARGET is divided into two stages as the non-error continues to occur and decreases. At the first stage, the SIR _TARGET increases in a downward concave shape as the down step size continues to decrease (710). The second stage starts with the down step size decreasing below the threshold. In the second stage, the down step size is held constant and the SIR _TARGET is reduced to a straight line (720).

Figs. 7 (b) to 7 (d) show the change of the down step size according to the number of consecutive non-errors (the number of step down times). Referring to FIGS. 7 (b) to (d), SIR _TARGET starts from the first down step size DOWN _first as a non-error occurs.

The down step size can then be linearly reduced with respect to the number of consecutive non-errors (Fig. 7 (b)). For example, the current down step size (STEP _down ) may be smaller than the basic down step size (DOWN _default ) by a predetermined amount, and the predetermined size may be constantly increased according to the number of consecutive non-errors. Also, the current down step size (STEP _down ) may be smaller than the previous down step size STEP _down-1 by a predetermined size, and the predetermined size may be constant for each power control step.

In addition, the down step size may decrease non-linearly with respect to the number of consecutive non-errors (Fig. 7 (c) (d)). In Fig. 7 (c), the down step size is large at the beginning of the non-error, and decreases as the non-error continues. For example, it may be the case that the current downsize size exponentially decreases from the basic downsize size according to the number of consecutive non-errors. Since the SIR _TARGET may already be sufficiently low at the first down step, a rapid reduction of the down step size thereafter may help to maintain the proper SIR _TARGET .

On the other hand, in Fig. 7 (d), the down step size is small at the beginning of the non-error and becomes larger as the non-error continues. For example, it may be the case that the difference between the current down step size and the previous up step size increases in proportion to the number of consecutive non-errors. If the number of consecutive errors occurs before the downstep starts, or if the windup occurs, it can be helpful to keep the downstep size large early in order to quickly reduce the SIR _TARGET to an appropriate level. Thereafter, the decrease width of the down step size according to the number of consecutive non-errors is increased, and the SIR _TARGET can be maintained at an appropriate level.

7 (b) to (d), the down step size does not continuously decrease, and is maintained at a constant value when the value falls below the threshold value DOWN _min . The constant value may be a threshold value or a previous up step size.

8 is a flow diagram illustrating an operation for updating an up-step size and a down-step size in accordance with an embodiment of the present invention. The shown step size update process is a process of determining a down-step size or an up-step size according to a CRC result and a previous outer loop power control result. Table 1 shows the code for the flowchart.

if CRC == OK
CNT _down = CNT _down-1 + 1
if CNT _down == 1
STEP _down (= DOWN _first ) = CNT _up · DOWN _default
else
if DOWN _first - (BLER _TARGET ) ² · (CNT _down ) ≥ DOWN _threshold · DOWN _default
STEP _down = DOWN _first - (BLER _TARGET ) ² - (CNT _down -1)
else
STEP _down = DOWN _threshold · DOWN _default
end
end
CNT _up = 0
else
CNT _up = CNT _up-1 + 1
if UP _default - (BLER _TARGET · CNT _up ) ≥ UP _threshold · UP _default
STEP _up = UP _default - BLER _TARGET - (CNT _up - 1)
else
STEP _up = UP _threshold · UP _default
CNT _down = 0
end

Here, CNT _down is the number of down steps including the current operation, CNT _down-1 is the number of down steps performed consecutively, STEP _down is the down step size to be applied at the current step, STEP _down-1 is the down step size applied in the previous step, DOWN _default is the basic down-step size, DOWN _threshold is the real number less than 1 but less than 1 for the threshold value, and BLER _TARGET is the target block error rate. In addition, CNT _up is the number of up steps including the current operation, CNT _up-1 is the number of up steps performed consecutively, STEP _up is the up step size to be applied at the current step, UP _default is the basic up step size , The UP _threshold is a real number greater than 0 and less than 1 for the threshold value. For example, BLER _TARGET may be 1%, UP _default 0.5 dB, DOWN _default 0.005 dB, UP _threshold 0.5, and DOWN _threshold 0.2.

Referring to the code of FIG. 8 and Table 1, when the CRC is OK, that is, when a block error does not occur, the down step size is updated (S480). If CRC not OK, that is, if a block error has occurred, the up-step size is updated (S440).

The process of updating the down step size is as follows. If the CRC is OK, the down step counter (CNT _down ) is used to adjust how many times the down step is applied before adjusting the down step size (S881). In the following process, the down-step counter acts as a weight when determining the down-step size. Then, it is determined whether the value of the down step counter is 1 (S882). In step S882, CNT _down is an integer equal to or greater than 1, which means the number of consecutive down steps including the present step. Therefore, when the value of the down step counter is 1, it means that the result of the previous outer loop power control is the up step. The fact that the value of the down step counter is not 1 means that the result of the previous outer loop power control is a down step.

If the value of the down step counter is 1, the first down step size DOWN _first is determined by multiplying CNT _down by the basic down step size (DOWN _default ) (S883). The up-step counter means the number of up-steps performed consecutively. That is, the first down-step size dynamically increases according to the number of up-steps performed consecutively in the past. Therefore, the larger the number of up-steps, the larger the first down-step size is, leading to a rapid decrease of the excessively large transmit power.

If the value of the down step counter is not 1, it is determined whether the down step size to be applied before updating the down step size is greater than or equal to a threshold value (S884). The threshold value is for preventing the down step size from continuously converging to zero. For example, the threshold value may be determined using a basic downsize size and a predetermined ratio (DOWN _threshold : e.g., 0.5 (50%) to 0.1 (10%)).

If the down step size to be currently applied is greater than or equal to the threshold value, the down step size is decreased by using the CNT _down to maintain the SIR _target stably (S885). Generally, the down step has a smaller operation range than the up step, so the current down step size can be reduced by BLER _TARGET ² compared with the previous down step size.

On the other hand, if the down step size to be currently applied is less than the threshold value, the down step size is set to the threshold value (S886). Also, the down step size to be currently applied may be maintained at the previous down step size. At the end of the down step size update process, CNT _up is initialized to zero. Accordingly, when an error occurs, the CNT _up is increased from the initial value in the up step size updating process which is newly started (S887).

The process of updating the up step size is performed when an error is detected through the CRC. The basic process is similar to the down step size update process. However, since the basic step size is large in the up step size update process, unlike the down step, the first up step size is not increased in consideration of the previous external power control result. Therefore, the first up-step size is fixed to the basic up-step size (UP _default ) regardless of the previous external power control result. That is, the up step size update process only performs the operation of decreasing the basic up step size (UP _default ) according to the previous outer loop control result. Specifically, if a CRC error is detected, the up-step counter (CNT _up ) is used to store how many times the up-step is successively applied to the memory before adjusting the up-step size (S841). In the following process, the up-step counter acts as a weight when determining the down step size. Then, before updating the up step size, it is determined whether the current up step size to be applied is greater than or equal to a predetermined threshold (S842). The threshold value is for preventing the up step size from continuously converging to 0 by continuously decreasing. For example, the threshold may be determined using a basic up-step size and a predetermined ratio (UP _threshold : e.g., 0.5 (50%) to 0.1 (10%)).

If the up-step size to be currently applied is greater than or equal to the threshold value, the up-step size is decreased by using the CNT _up to maintain the SIR _target stably (S843). In general, since the up-step has a large operation range, the current up-step size can be reduced from the basic up-step size by the number of previous consecutive errors and BLER _TARGET times the product.

On the other hand, if the up-step size to be currently applied is less than the threshold value, the up-step size is set to the threshold value (S844). Also, the up-step size to be currently applied may be maintained at the previous up-step size. In the last step of the up step size update process, CNT _down is initialized to 0 (S845). Therefore, when a non-error occurs, the CNT _down increases from the initial value in the down step size update process that is newly started.

FIG. 9 shows a change in the SIR _target over time when the outer loop power control is performed according to the flowchart shown in FIG. The related parameters are assumed to be UP _default = 0.5 dB, UP _threshold = 0.5, DOWN _threshold = 0.2, BLER _target = 1%, DOWN _defalut = _{0.005 dB} .

Fig. 9 (a) shows a case where a block error occurs consecutively in the received block. Although not explicitly shown in the figure, the first up-step size is fixed at UP _default = 0.5 dB irrespective of the number of previous non-error occurrences. When a block error occurs, the SIR _target is increased by the up-step. SIR _target to continue despite the increase by increasing the SIR _target by an up step each time an error occurs when the block error. In this case, the step size applied at every step decreases as the number of previous consecutive step-ups increases. In addition, the step size may decrease linearly or non-linearly with respect to the block error rate. For example, the current step size is determined by the following equation.

STEP _up = UP _default - BLER _TARGET - (CNT _up - 1)

According to the above equation, the current ups step size is smaller by the target block error rate (BLER _TARGET = 1%, 0.01 dB) than the previous up step size each time an error occurs. In FIG. 9A, it can be seen that the up step size is reduced to 0.5 dB => 0.49 dB => 0.48 dB (910). As the error occurs continuously, the up-step size continues to decrease. However, if the up-step size to be currently applied becomes smaller than the threshold value (UP _default × UP _threshold = 0.25 dB), the current up-step size is fixed to the above threshold value. Therefore, after a certain number of errors occur consecutively, the up-step size is fixed at 0.25 dB even if the error continues to occur, so that the SIR _target increases small but constantly (920).

Fig. 9 (b) shows a case where block errors are mixed in the received block. As in FIG. 9 (a), the size of the up step applied first when a block error occurs is fixed at 0.5 dB. As the error occurs consecutively, the up-step size decreases by 0.01 dB. Thereafter, when the SIR _target becomes sufficiently large, a block error does not occur and the down-step process is started. The first down step size increases in proportion to the number of previous consecutive up steps. As an example, the first down step size is determined by the following equation.

STEP _down (= DOWN _first ) = CNT _up · DOWN _default

Therefore, if the number of up steps performed successively before the down step starts is three, then the first down step size is 0.015 dB (930a). Also, if the number of upsteps performed previously in succession is once, then the first downstep size is 0.005 dB (930b). Thereafter, the step size applied at each down step is reduced as the number of previous consecutive step downs increases. In addition, the step size may decrease linearly or non-linearly with respect to the block error rate. For example, the current down step size is determined by the following equation.

STEP _down = DOWN _first - (BLER _TARGET ) ² - (CNT _down -1)

According to the above equation, the current down step size is calculated by dividing the number of consecutive non-errors from the first down step size and the second power of the target block error rate (BLER _TARGET ² = 0.01%, 0.0001 dB). In FIG. 9 (b), it can be seen that the down step size is reduced to 0.015 dB => 0.0149 dB => 0.0148 dB or 0.005 dB => 0.0049 dB (940).

FIG. 9 (c) shows a case where a non-error (CRC OK) continuously occurs in the received block. Referring to FIG. 9 (c), the first down-step size may be increased in proportion to the number of consecutive errors. In Fig. 9 (c), since the number of errors that have occurred previously is 1, the first down step size starts from 0.005 dB which is the basic down step size (DOWN _default ). As the non-error occurs continuously, the down step size continues to decrease (0.005 dB => 0.0049 dB => 0.0048 dB; 940). However, if the down step size to be applied currently becomes smaller than the threshold value (DOWN _default DOWN _threshold = 0.001 dB), the current down step size is fixed to the threshold value. Therefore, after a certain number of non-errors occur consecutively, the down step size is fixed at 0.001 dB even if a non-error occurs continuously, so that the SIR _target is reduced to a small but constant value (950).

In summary, each step size can be dynamically adjusted using the number of previous consecutive up steps and / or down steps in outer loop power control in accordance with an embodiment of the present invention. In the case of the up step, if the up step operation occurs continuously, it is possible to facilitate the return of the SIR _target to an appropriate level at the channel improvement by reducing the step size. In the case of a down step, unnecessarily high SIR _target can be rapidly reduced by setting the first down step size to be high in proportion to the increase of the SIR _target due to the continuous up step operation. Also, as the down step operation continues, the SIR _target can be maintained at a stable level by reducing the step size.

The embodiments illustrated herein are based on block and target block error rates. However, power control using an outer loop in a WCDMA system may be performed based on a frame. In this respect, blocks and frames can be mixed. Therefore, in the above-described embodiment, "block" may be replaced with "frame &quot;,and" target block error rate BLER _TARGET "may be replaced with" target frame error rate FER _TARGET &quot;.

The embodiments described above are those in which the elements and features of the present invention are combined in a predetermined form. Each component or feature shall be considered optional unless otherwise expressly stated. Each component or feature may be implemented in a form that is not combined with other components or features. It is also possible to construct embodiments of the present invention by combining some of the elements and / or features. The order of the operations described in the embodiments of the present invention may be changed. Some configurations or features of certain embodiments may be included in other embodiments, or may be replaced with corresponding configurations or features of other embodiments. It is clear that the claims that are not expressly cited in the claims may be combined to form an embodiment or be included in a new claim by an amendment after the application.

In this document, the embodiments of the present invention have been mainly described with reference to the data transmission / reception relationship between the terminal and the base station. The specific operation described herein as being performed by the base station may be performed by its upper node, in some cases. That is, it is apparent that various operations performed for communication with a terminal in a network including a plurality of network nodes including a base station can be performed by a network node other than the base station or the base station. A 'base station' may be replaced by terms such as a fixed station, a Node B, an eNode B (eNB), an access point, and the like. The term 'terminal' may be replaced with terms such as User Equipment (UE), Mobile Station (MS), and Mobile Subscriber Station (MSS).

Embodiments in accordance with the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of hardware implementation, an embodiment of the present invention may include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs) field programmable gate arrays, processors, controllers, microcontrollers, microprocessors, and the like.

In the case of an implementation by firmware or software, an embodiment of the present invention may be implemented in the form of a module, a procedure, a function, or the like which performs the functions or operations described above. The software code can be stored in a memory unit and driven by the processor. The memory unit may be located inside or outside the processor, and may exchange data with the processor by various well-known means.

It will be apparent to those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit of the invention. Accordingly, the above description should not be construed in a limiting sense in all respects and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

The present invention can be applied to power control of a wireless communication system. More specifically, the present invention can be applied to outer loop power control of a wireless communication system.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

1 shows a flow chart of state transition of outer loop power control in a code division multiple access scheme.

Figure 2 shows a schematic flow chart of the tracking state in outer loop power control.

FIG. 3 shows a change in target reception quality over time when power control is performed according to the flowchart shown in FIG.

4 is a flowchart illustrating an operation of performing outer loop power control according to an embodiment of the present invention.

5 (a) - (d) show the change of the target reception quality and the up step size according to the number of consecutive errors in the embodiment of the present invention.

FIGS. 6 (a) - (c) illustrate the change of the first down step size according to the number of consecutive errors in an embodiment of the present invention.

FIGS. 7 (a) - (d) show changes in the target reception quality and the down step size according to the number of consecutive non-errors in the embodiment of the present invention.

8 is a flow diagram illustrating an operation for updating an up-step size and a down-step size in accordance with an embodiment of the present invention.

FIGS. 9 (a) to 9 (c) show changes in the target reception quality over time in the case of performing outer loop power control according to the flowchart shown in FIG.

Claims (18)

A method of controlling an outer loop power of a wireless communication system, Determining whether an error has occurred in the received block; And Up or down-stepping a target reception quality value according to whether an error has occurred in the block, When an error occurs in the block, an up-step size dynamically changed according to the number of previous consecutive errors is determined by Equation (1) below, Wherein if the block error does not occur, a down step size that is dynamically changed according to a previous number of consecutive non-errors is determined by Equation (2) below: [Equation 1] STEP _up = UP _default - BLER _TARGET × (CNT _up - 1) Here, STEP _up is an up-step size, UP _default is a basic up-step size, BLER _TARGET is a target block error rate, CNT _up is an integer equal to or larger than 1, &Quot; (2) &quot; STEP _down = DOWN _first - (BLER _TARGET ) ² x (CNT _down - 1) Here, STEP _down is a down step size, DOWN _first is a first down step size, BLER _TARGET is a target block error rate, and CNT _down is an integer of 1 or more as the previous consecutive down step times. The method according to claim 1, Characterized in that the number of previous consecutive errors is determined according to the number of previous consecutive upsteps. The method according to claim 1, Wherein the first up step size is fixed to a basic up step size. The method according to claim 1, And when an error occurs in the block, the up-step size is compared with a basic up-step size to make it smaller by a predetermined size proportional to the number of previous consecutive errors. 5. The method of claim 4, Wherein said predetermined magnitude is linear or nonlinearly proportional to said number of previous consecutive errors. 6. The method of claim 5, Wherein the predetermined size is proportional to a target block error rate (BLER _TARGET ). delete The method according to claim 1, And when the up-step size becomes smaller than the threshold value, the up-step size is maintained at the previous up-step size or is set to the threshold value. delete The method according to claim 1, Wherein the previous successive error or non-error times are determined according to a previous successive upstep or downstep times. The method according to claim 1, Wherein the first down step size is linear or non-linearly proportional to the number of previous consecutive errors. 12. The method of claim 11, Wherein the first down step size is proportional to the basic down step size. 13. The method of claim 12, Wherein the first down step size is determined by the following equation: DOWN _first = CNT _up × DOWN _default Where DOWN _first is the first down step size, CNT _up is the number of previous consecutive up steps, and DOWN _default is the default down step size. The method according to claim 1, Wherein if no error occurs in the block, the down-step size is compared with a first down-step size to make it smaller by a predetermined magnitude proportional to the previous number of consecutive non-errors. 15. The method of claim 14, Wherein said predetermined magnitude is linear or non-linearly proportional to said previous successive non-error times. 16. The method of claim 15, Wherein the predetermined size is proportional to a target block error rate (BLER _TARGET ). delete The method according to claim 1, Wherein the down-step size is maintained at a previous down-step size or is set to the threshold value when the down-step size becomes smaller than a threshold value.

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