CN1219375C - A Method of Controlling Forward Transmitting Power in CDMA System - Google Patents

Abstract

The invention discloses a method for controlling forward transmission power in a CDMA system. The method proposed by the present invention simultaneously uses the current frame information sent back by the mobile station and the average frame quality information within a period of time to obtain the transmission rate of a certain link by monitoring the average frame error rate within a period of time and combining the value of the deletion indication bit. power. The method proposed by the invention can overcome the drawbacks of frequent power boosts in previous methods, reduce base station transmission power as much as possible on the premise of ensuring link quality, reduce inter-system interference and effectively increase system capacity.

Description

A Method of Controlling Forward Transmitting Power in CDMA System

technical field

The invention relates to a method for controlling forward transmission power in a wireless communication system, in particular to a method for rapidly controlling forward transmission power in a CDMA system.

Background technique

In a CDMA system, the transmission power of the signal transmitted from the base station to the mobile station is restricted by the following factors, including: the distance from the base station to the mobile station, shadowing, fading, and interference from other base stations. It is because of the existence of these factors that the transmit power of the base station changes randomly. Rationally allocating the transmit power of the base station can achieve the purpose of saving transmit power and reducing interference. Since the CDMA system is an interference-limited system, reducing interference will effectively increase the capacity of the system. In addition, reducing the average forward transmit power of each link will also increase the number of users that the system can carry. If the power reaching a certain mobile station from a base station is too large, it will cause interference problems to other mobile stations. But conversely, if the power from the base station to the mobile station is too small, frame errors will occur on the mobile station side, leading to call drop in severe cases. Shading effects caused by buildings and fading caused by movement will affect the received power of the mobile station. Therefore, an effective and fast power control method must be adopted to control the power transmitted by the base station.

In the CDMA system, the main function of the forward power control is to reasonably allocate the forward transmit power of each link. A common method is that the mobile station periodically reports information about the forward frame error, which may be a power measurement report message, and the base station uses this information to calculate the forward frame error rate. The system bases the frame error rate on the basis of a threshold comparison to decide to increase or decrease forward transmit power. This method is described in US Patent No. 5,265,119 "Method and Device for Controlling Transmission Power in a CDMA Mobile Cellular Communication System". Because the control cycle is generally longer based on the power measurement report, it is about 1 second. Such a slow control speed will make it difficult for the system to make a quick response to the forward error frame caused by the low transmit power of the base station. In addition, there is inevitably a certain delay from the time when the base station sends out a frame with a certain power until it receives information about the quality of the frame. This delay will further affect the rapidity of power control. If the mobile phone notifies the base station of the quality of the forward frame it receives by deleting the indicator bit (EIB), then the system can directly decide to increase or decrease the transmission power of the link by judging the quality of the received frame. This control method is mentioned in the US patent US05893035 "Centralized Forward Link Power Control", and the control is coordinated by the BTS and the BSC. The ascending step given in this patent is a fixed step, and for different communication environments, this fixed step will bring different results. In addition, after using the EIB information, the system gives up using the power measurement report information, which is equivalent to only using local information. Another U.S. patent US05461639 "Fast Forward Power Control in CDMA System" adopts a new method. In this method, the mobile station calculates the frame error rate for different rate frames, and at the same time, the mobile station calculates the frame error rate according to the forward frame pair wrong to insert the power control bit. The base station performs frame error rate statistics on frames of different rates, and determines respective power adjustments according to the statistical results. However, this method cannot be supported by IS-95.

Contents of the invention

The purpose of the present invention is to propose a kind of forward power control method that is applicable to frame of different rate for CDMA system, this method can not only guarantee the fast and effective response of system to base station transmit power, can also reduce base station transmit power, increase system capacity.

In order to realize the purpose of the invention, the forward power control method proposed by the present invention mainly includes:

1. The system judges whether the received reverse frame is an error frame;

2. If the received reverse frame is not an error frame, the system monitors the frame error rate of the forward link, and calculates the forward transmission power based on the EIB value of the erasure indication bit;

3. If the received reverse frame is an error frame, count the value of the continuous error frame, and if the value of the continuous error frame is greater than the threshold value, increase the forward transmit power;

4. Determine whether the current sending frame is a signaling frame, and if so, increase the forward transmission power;

5. Control the transmission power value within the specified range through the limiter.

In the forward power control method, between step 4 and step 5 may also include:

For different frame rates, the transmit power value is multiplied by a correction factor.

In the forward power control method, step 2 specifically includes the following steps:

(2.1) Determine whether there is an error frame in the forward direction, if not, perform step (2.5);

(2.2) count the frame error rate within a period of time, if the frame error rate is not greater than the threshold, then perform step (2.7);

(2.3) If the delay counter is in an active state, then the delay count is decremented by 1, the continuous good frame counter is cleared, the transmission power is unchanged, and step (2.7) is performed;

(2.4) If the delay counter is not in the active state, then increase the transmission power, the delay counter is assigned a value of S, the continuous good frame counter is cleared, and the step (2.7) is continued;

(2.5) Adding 1 to the continuous good frame counter, judging whether the value of the continuous good frame counter is greater than the threshold value of the continuous good frame, if greater than then reducing the transmission power;

(2.6) If the value of the continuous good frame counter is less than the threshold value of the continuous good frame, it is judged whether the delay counter is in the active state: if it is in the active state, the power is decreased by the step value of the first step, and the delay counter is decremented 1; otherwise, the transmit power will be reduced by the step value of the second step;

(2.7) Go back to step 3 of the main process.

In the forward power control method, for the increased transmit power in step (2.4), it should satisfy that the increase step corresponding to the small transmit power is greater than or equal to the increase step corresponding to the large transmit power.

Description of drawings

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Figure 1 is a schematic diagram of a simple cellular communication system.

Figure 2 is a complete cellular mobile communication system diagram.

Fig. 3 is a simple block diagram of the system when the mobile station is in the two-party soft handover state, which is used to explain the centralized closed-loop forward power control.

Fig. 4 is a flow chart of the method for controlling the forward transmission power of the system provided by the present invention.

Fig. 5 is a program flow for monitoring and controlling power links in the method of the present invention.

Fig. 6 is an example of increasing step length curves of different power values provided by the present invention.

Fig. 7 is an example of increasing step length curves of different power values given by the present invention.

Detailed ways

As shown in Figure 1, in a cellular mobile communication system, the forward link refers to the propagation link from the base station 2 to the mobile station 8, namely 4A in the figure. Base station 2 transmits signals to mobile station 8 via forward link 4A, and mobile station 8 transmits signals to base station 2 via reverse link 4B.

Fig. 2 has provided the block diagram structure of the applicable cellular communication system of present invention, and mobile station 12A and 12B described in this block diagram are in soft handoff process, and mobile station is in contact with base station 16A and 16B simultaneously, and base station 16A and 16B communicate with the same A base station controller (BSC) 14A communicates. The mobile switching center 10 is in communication with both base station controllers 14A and other base station controllers 14B.

FIG. 3 shows a relatively detailed block diagram of the cellular communication system. The mobile station 20 described in the block diagram is in the process of soft handover, and spread spectrum modulation techniques such as CDMA can be used between the mobile station 20 and the base station 21. In FIG. 2, the mobile station 20 communicates with the base station controller 22 through one or more base stations 21a, 21b. The base station controller 22 includes appropriate hardware and software for controlling the base stations 21a, 21b, etc. Figure 2 corresponds to the case where the mobile station is in two-party soft handover.

Fig. 4 shows the main flow of the forward power control method. According to the method, the power controller first judges whether the received current reverse frame is an error frame, and if the received frame is not an error frame, it will enter into the link of forward frame error rate monitoring and calculation of forward transmission power. If an error frame is received, the value of the error frame counter in the system will be increased by 1. During system initialization, the frame error counter will be assigned a value of 0. When the value of the error frame counter is greater than the threshold value, such as 10, the power controller will increase the transmit power. The power value processed through the above steps is not necessarily the transmission power of the current frame, and it is necessary to judge whether the received signal is a signaling frame. If it is an ordinary speech frame, the system will not adjust the power. If it is a signaling frame, in order to ensure the correct transmission of the signaling frame, the power is increased on the basis of the same power as the transmission of the voice frame, which makes the signaling frame have enough energy to deal with interference and fading during transmission. After that, the obtained power value is limited within the specified range by the limiter. That is, if the calculated power value is greater than the maximum power value preset by the system, the calculated power value will be replaced by the maximum power value. If the calculated power value is less than the minimum power value preset by the system, the calculated power value will be replaced by the minimum power value. In a specific implementation, the power value may be a ratio to pilot power, or a gain ratio. The power value obtained after the above calculation can be transmitted to the base station 21a through forward layer 3 data.

In the state of soft handover, the same power value will be transmitted to all base stations participating in soft handover at the same time, such as 21a and 21b. In the system implementation, the power value transmitted to the base station acts on all information except the power control bit. As for the power control bit, its transmission power can be determined according to the soft handover state of the current mobile station.

In actual forward power control, if the criterion of assigning the same bit energy (Eb) to frames of different rates is followed, the system will inevitably transmit more power. Therefore, before limiting the power value, we can also add a link, that is, to correct the transmit power for different rate frames. In a possible implementation, the correction of the coefficients can be implemented at the base station 21a. For the full rate, the correction factor of the transmit power is K1, for the half rate, the correction factor of the transmit power is K2, and for the 1/4 and 1/8 rates, the correction factors of the transmit power are K3 and K4 respectively. If frames at different rates are required, the frame error rate of the system remains at the same level, and the coefficients K1, K2, K3, and K4 satisfy

K1＞K2＞K3＞K4

A possible good value range of K1, K2, K3, K4 is (1-0.1).

Fig. 5 shows the flowchart of the monitoring link and the power calculation main link in Fig. 4 . First, the system judges whether the forward frame is right or wrong based on the reverse frame information. The quality of the detection link can use the signal-to-interference ratio (SIR), measure the received power, and decode some parameters such as the symbol error rate and "Yamamoto quality indication (Yamamoto)" and so on. In the implementation of this system, the mobile station transmits the relevant forward frame quality information through the duplexer and antenna after coding, modulation, amplification and up-conversion. The receiving system obtains the reverse frame by down-converting, amplifying, demodulating and decoding. The mobile station indicates the quality of the forward link frame by adding the currently received forward frame good or bad indicator bit EIB at a fixed position in the reverse frame or by sending a power measurement report in the reverse frame, that is, through the EIB value Judgment or through the judgment of the power measurement report message to determine whether the forward link has received an error frame. If EIB is 0, it means that the forward frame is a good frame, then reduce the transmit power; if EIB is 1, it means that the forward frame is an error frame, then keep the transmit power or increase the transmit power. The power controller determines the size of the forward transmit gain while detecting the EIB. When the system receives the forward frame quality information, the monitor will count the frame error rate value within a certain period of time, which can be 320 frames. The frame error rate value is compared with a threshold value, and a typical value of the threshold value is 0.5%. If the frame error rate value obtained by the monitor is less than the threshold value, the system will not change its transmission power to wait and see the situation of the next frame. If the next frame is a good frame, it means that the frame error may be caused by a momentary interference or fast fading, and the power control method returns to the original process to continue execution, that is, to reduce the transmit power. In this way, under the action of the monitor, the forward transmission power of the system is reduced. In a specific system, after the forward power controller sends the gain value, it takes at least 5 frames for the good and bad news of the frames sent with the gain value to be captured by the forward power controller. In order to prevent the controller from making unnecessary responses during this process, such as increasing unnecessary transmit power, a delay counter is used in the implementation. In an implementation as shown in Figure 2, the delay counter can be set to 5, which It is equal to the time interval from when a certain frame is sent to when the controller receives relevant information. There is also a good frame counter in the system implementation. The purpose of this counter is to count the length of consecutive correct frames. If the length exceeds a threshold value, such as 100, the controller will reduce the transmission power. If it is found that the value of the continuous good frame counter is not greater than the threshold value, then the system will check the value of the delay counter. If the delay counter is still active, the power is decreased by the step value of the first step length D1, and the value of the delay counter is decremented by 1; otherwise, the power is decreased by the step value of the first step length D2. In an actual system, the value of the first step length D1 should be greater than the value of the first step length D2.

Since the transmission power values of the system at each moment are not necessarily the same, the frame error conditions under different power values should be treated differently. If the transmit power value when a frame error occurs in a certain time is smaller than the transmit power value when a frame error occurs in another time, then for the increased step size, it should satisfy that the increase step size corresponding to the small transmit power is greater than or equal to that corresponding to the large transmit power increase step size. If the increase step is recorded as Delta, the relationship between it and the current transmit power P(n) can be described by the following formula:

Delta=f(P(n))

Figure 6 shows a typical embodiment of the functional relationship. In this example, f(P(n)) is a decreasing step function. As shown in the figure, if the current power is greater than P2, the step size of power increase is Delta3; if the current power is less than P1, the step size of increase is Delta1; otherwise, the step size of increase is Delta2. And there is Delta1>Delta2>Delta3.

FIG. 7 shows another embodiment of the functional relationship, which is a linearly decreasing function and also satisfies the above relationship.

According to the above detailed description, it can be seen that the method proposed by the present invention allocates different bit energies (Eb) to frames of different rates, which can effectively reduce the transmit power of the base station, that is, reduce the interference between systems and effectively increase the number of systems capacity. Meanwhile, adopting the forward power control method of the present invention can effectively overcome the problem caused by link imbalance in the soft handover process. The delay counter adopted in the present invention aims at the control delay problem, overcomes the disadvantage of frequently increasing power in previous methods, and reduces the transmission power as much as possible under the premise of ensuring link quality.

Claims (4)

1, the method for controlling forward transmission power in the CDMA system, is characterized in that, comprises the following steps: (1) The system judges whether the received reverse frame is an error frame; (2) If the received reverse frame is not an error frame, the system monitors the frame error rate of the forward link, and calculates the forward transmission power based on the EIB value of the erasure indication bit; (3) If the received reverse frame is an error frame, then count the value of the continuous error frame, if the value of the continuous error frame is greater than the threshold value, then increase the forward transmit power; (4) judging whether the current sending frame is a signaling frame, if so, increasing the forward transmission power; (5) The transmit power value is controlled within the specified range by the limiter. 2. The method for controlling forward transmit power in a CDMA system as claimed in claim 1, characterized in that, steps (4) and (5) may further include: For different frame rates, the transmit power value can be multiplied by a correction factor. 3. The method for controlling forward transmission power in a CDMA system as claimed in claim 1, wherein step (2) specifically comprises: (2.1) Determine whether there is an error frame in the forward direction, if not, perform step (2.5); (2.2) count the frame error rate within a period of time, if the frame error rate is not greater than the threshold, then perform step (2.7); (2.3) If the delay counter is in an active state, then the delay count is decremented by 1, the continuous good frame counter is cleared, the transmission power is unchanged, and step (2.7) is performed; (2.4) If the delay counter is not in the active state, then increase the transmission power, the delay counter is assigned a value of S, the continuous good frame counter is cleared, and the step (2.7) is continued; (2.5) Adding 1 to the continuous good frame counter, judging whether the value of the continuous good frame counter is greater than the threshold value of the continuous good frame, if greater than then reducing the transmit power; (2.6) If the value of the continuous good frame counter is less than the threshold value of the continuous good frame, it is judged whether the delay counter is in the active state: if it is in the active state, the power is decreased by the step value of the first step, and the delay counter is decremented 1; otherwise, the transmit power will be reduced by the step value of the second step; (2.7) Return to the main process step (3). 4. The method for controlling forward transmission power in a CDMA system as claimed in claim 3, wherein the transmission power increased in said step (2.4) should satisfy that the step size corresponding to the small transmission power increase is greater than or equal to the corresponding Increased step size for large transmit powers.

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