CN100375405C - Inverse external external ring power controlling method for CDMA mobile communication system - Google Patents
Inverse external external ring power controlling method for CDMA mobile communication system Download PDFInfo
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Abstract
The present invention relates to a control method for reverse external-loop power in a CDMA mobile communication system. Firstly, statistic is carried out to the total frame error rate of all soft branch circuits; then, the total frame error rate is compared with the preset total frame error rate of a target, and dynamic adjustment is carried out to the threshold of the frame error rate of the soft branch circuits according to a comparison result by the following method to make the total frame error rate tend to be balanced. If a statistic value is higher than the total frame error rate of a target, and the total frame error rate of a plurality of continuous frames is higher than the frame error rate of a target, then, a threshold for reducing the frame error rate of one or a plurality of soft branch circuits is selected; if the statistic value is lower than the total frame error rate of a target, and the total frame error rate of a plurality of continuous frames is lower than the total frame error rate of a target, then, a threshold for improving the frame error rate of one or a plurality of soft branch circuits is selected. The method provides a method for calculating the total frame error rate by comprehensively considering the condition of service frames of each soft branch circuit, and respectively carries out statistic to the threshold of the frame error rate of each soft branch circuit; the present invention compromises the condition of a wireless environment of the current system and has high flexibility.
Description
Technical Field
The invention relates to a reverse outer ring power control method, in particular to a reverse outer ring power control method used in a third generation 3G code division multiple access CDMA mobile communication system, belonging to the technical field of mobile communication.
Background
Code Division Multiple Access (CDMA) is a spread spectrum technology platform that allows multiple users to communicate using the same radio frequency band at the same time. Since all mobile stations transmit signals in the same frequency band, the interference generated within the system plays a key role in determining the capacity and voice quality of the system, and therefore the transmit power from each mobile station must be controlled to maintain high quality communication while avoiding unnecessary interference to other mobile stations.
When the mobile station MS moves, the radio frequency environment is constantly changing, and power control is performed on the radio frequency environment, so that the transmission quality of the link can be ensured under various conditions, and the transmission power of the forward link and the reverse link can be limited. The reverse link interferes much more severely than the forward link due to non-coherent detection by the base station. Therefore, reverse link power control is essential.
Because of the attenuation characteristic of electromagnetic waves, the signal strength of the near user received by the base station is higher than that of the far user, and when all users transmit signals with the same power, the near user must cause serious interference to the far user, which is the "near-far effect" in mobile communication. To overcome the "near-far effect," a CDMA system must perform power control to ensure that all mobile stations achieve the same received power at the base station.
Therefore, it can be said that power control is a key technique in CDMA, which determines the performance of the system to a large extent. Power control of CDMA is divided into forward power control for reducing interference to neighboring cells and reverse power control; reverse power control is not only used to overcome the near-far effect, but also to reduce multiple access interference between users to increase the capacity of the communication system.
Reverse power control is divided into two types, open loop and closed loop. In open loop power control, the mobile station estimates the transmit power of the reverse traffic based on the received power strength of the forward channel. The closed-loop power control is divided into an inner-loop power control part, an outer-loop power control part and an outer-loop power control part, and the working process of the closed-loop power control is shown in a figure 1.
Reverse inner loop power control is performed between the base transceiver station BTS and the mobile station MS. BTS measures E of received reverse channel b /N t (ratio of signal energy per bit to effective noise power spectral density, applicable to IS-2000 systems) or E w /N t (the ratio of energy per Walsh symbol to effective noise power spectral density, applicable to IS-95 systems), and then compares the measured value with an outer loop threshold preset by reverse outer loop power control to determine the power control bit: when the measured value is smaller than the outer loop threshold, the BTS sets the power control bit to be 0 and indicates the mobile station to improve the transmitting power; conversely, when the measurement value is greater than the outer loop threshold, the BTS controls the power to be set to 1, instructing the mobile station to decrease the transmission power.
The reverse outer-loop power control is a process of dynamically adjusting the reverse outer-loop power control threshold of each soft switching branch by selecting a distribution unit SDU according to the frame error rate FER of a reverse service channel. In the process of outer ring power control, SDU receives frame quality report of reverse service channel from BTS, counts error frame rate of soft switching branch, compares the counted value with set error frame rate threshold of soft switching branch, and dynamically adjusts outer ring power control threshold of each soft switching branch according to the compared result.
The reverse outer loop power control is used for dynamically adjusting the frame error rate threshold of each soft switching branch according to the total frame error rate of the current service channel when the mobile station MS is in soft switching, so that the total frame error rate of the service channel can reach the preset requirement. The principle of reverse outer loop power control is substantially the same as that of reverse outer loop power control and may be represented by the same model. Thus, with reference to reverse outer loop power control, outer loop power control in a reverse traffic channel may have two states: the frame error rate switching method comprises the following steps that a state that the total frame error rate is lower and a state that the total frame error rate is higher are converted along with the change of the total frame error rate; as shown in fig. 2.
At present, most of patent applications in the aspect of reverse power control are directed to improving strategies and methods for reverse outer loop power control, however, there are relatively few researches and patent applications for reverse outer loop power control. Therefore, how to improve the power control method of the reverse outer loop becomes a hot point and a new topic studied by those skilled in the art.
Disclosure of Invention
In view of the above, the present invention provides a reverse outer loop power control method for a cdma mobile communication system, which comprehensively considers the service frame condition of each soft handover branch, calculates the total frame error rate, separately counts the frame error rate thresholds of each soft handover branch, and considers the wireless environment of the current system, thereby providing a flexible, convenient, accurate, and comprehensive reverse outer loop power control method.
In order to achieve the above object, the present invention provides a reverse outer loop power control method for use in a CDMA mobile communication system, which is characterized in that when a mobile station MS performs soft handover, a selection distribution unit SDU dynamically adjusts the frame error rate threshold of each soft handover branch according to the total frame error rate of the current traffic channel, so that the total frame error rate of the traffic channel can reach a predetermined target total frame error rate; the method is characterized in that: the method comprises the steps of firstly counting the total frame error rate of all soft switching branches, then comparing the total frame error rate obtained by counting with a preset target total frame error rate, and dynamically adjusting the frame error rate threshold of the soft switching branches according to the comparison result according to the following method to ensure that the total frame error rate tends to be balanced:
if the statistical value is higher than the target total frame error rate, namely the initial state is a state that the total frame error rate is higher than the target frame error rate, and the total frame error rate is continuously multi-frame higher than the target frame error rate, which indicates that the quality of a reverse service channel does not meet the service requirement, the frame error rate threshold of one or more soft switching branches is selected to be reduced, so that the branch obtains a higher outer ring power control threshold in the outer ring power control process, and then an instruction of 'increasing the transmitting power' is sent to the mobile station through the inner ring power control of the branch;
if the statistical value is lower than the target total frame error rate, i.e. the initial state is the lower state of the total frame error rate, and the continuous multiframes of the total frame error rate are lower than the target frame error rate, which indicates that the reverse service channel is more ideal, the frame error rate threshold of one or more soft switching branches is selected to be increased, so that the branch obtains a lower outer loop power control threshold in the outer loop power control process, and then an instruction of reducing the transmission power is sent to the mobile station through the inner loop power control of the branch.
The object for dynamically adjusting the frame error rate threshold of the soft handover branch is all soft handover branches, or one or more soft handover branches with more prominent frame error rates.
When the initial state is "total frame error rate is higher state", the dynamic adjustment of the frame error rate threshold of the soft switching branch comprises the following steps:
(301) The reverse service frames sent by each soft switching branch are optimized, and whether the selected optimal service frame is a 'good frame' is judged;
(302) Calculating the total frame error rate of the reverse channel: calculating the total frame error rate once every frame of data is received, simultaneously comparing the total frame error rate with the target total frame error rate, and if the total frame error rate is higher than the target total frame error rate, sequentially executing subsequent operations; otherwise, jumping to execute step (307);
(303) Calculating the average frame error rate of each soft switching branch; then according to the preferred result of the step (301), if the frame is a 'bad frame', the subsequent operation is executed in sequence; otherwise, the operation is finished, and the system is still in a high total frame error rate state;
(304) Firstly adding 1 to the Count value Count in the frame counter, then judging whether the Count value Count is smaller than a preset natural number M, if so, ending the operation, and still keeping the system in a state that the total frame error rate is higher; otherwise, sequentially executing subsequent operations;
(305) Selecting one or more soft switching branches, and reducing the frame error rate threshold of the selected branches;
(306) Setting the count value in the frame counter to be half of the original count value so as to realize the target requirement faster by the next adjustment when the total frame error rate is adjusted once and still does not reach the preset target frame error rate requirement; after the operation is finished, the system is still in a state that the total frame error rate is higher;
(307) Clearing the frame counter;
(308) Setting an average frame error rate FER (n) of a soft handover branch as a current instantaneous frame error rate FEL _ i of the branch, namely FER (n) = FER _ i at the current time; in the formula, the natural numbers n and i are the serial numbers of the average frame error rate and the instantaneous frame error rate respectively, and the system enters a state that the total frame error rate is lower.
When the initial state is a "total frame error rate is lower state", the dynamic adjustment of the frame error rate threshold of the soft switching branch comprises the following steps:
(401) Selecting the reverse service frame from each soft switch branch and judging whether the selected optimal service frame is 'good frame';
(402) Calculating the total frame error rate of the reverse channel: calculating the total frame error rate once every frame of data is received, simultaneously comparing the total frame error rate with the target total frame error rate, and if the total frame error rate is lower than the target total frame error rate, sequentially executing subsequent operations; otherwise, skipping the execution step (407);
(403) Calculating the average frame error rate of each soft switching branch; then according to the preferred result of the step (401), if the frame is a 'good frame', the subsequent operation is executed in sequence; otherwise, the operation is finished, and the system is still in a low total frame error rate state;
(404) Firstly adding 1 to the Count value Count in the frame counter, then judging whether the Count value Count is smaller than a preset natural number L, if so, ending the operation, and still keeping the system in a state that the total frame error rate is lower; otherwise, sequentially executing subsequent operations;
(405) Selecting one or more soft switching branches, and improving the frame error rate threshold of the selected branches;
(406) Setting the count value in the frame counter to be half of the original count value so that when the total frame error rate is adjusted once and still does not reach the preset target frame error rate requirement, the next adjustment can quickly realize the target requirement; after the operation is finished, the system is still in a low total frame error rate state;
(407) Clearing the frame counter;
(408) Setting an average frame error rate FER (n) of a soft handover branch as a current instantaneous frame error rate FER _ i of the branch, namely FER (n) = FER _ i at the current time; in the formula, the natural numbers n and i are the serial numbers of the average frame error rate and the instantaneous frame error rate respectively, and the system enters a state that the total frame error rate is higher.
The calculation formula of the total frame error rate of the soft handover leg in the steps (302) and (402) is as follows:
the total frame error rate = 'bad frame' number/total frame number received in a period of time;
the judgment basis of the bad frame and the good frame is as follows: only when the service frames obtained from all the soft switching branches are error frames, the SDU considers that a 'bad frame' is received; and as long as the correct frame is obtained from one of the soft handover legs, the SDU determines that the frame is a "good frame".
The step (303) and (403) of calculating the average frame error rate of each soft handover leg includes the following specific steps:
a. determining a statistical period N1 of the instantaneous frame error rate by taking the number of the data frames as a statistical unit, counting the number of error frames N _ error in N1 frame time, and then calculating an instantaneous frame error rate FER _ i: FER _ i = N _ error/N1; in the formula, a natural number i is a serial number of the instantaneous frame error rate;
b. determining a statistical period N2 of the average frame error rate: n2= m × N1, that is, N2 is an integer multiple of N1, the coefficient m is a natural number, and the value of the coefficient m is adjusted according to actual conditions; then, the calculated value FER _ i of the instantaneous frame error rate is put into an array which is m bits long and is updated in real time according to the chronological order, so as to prepare for calculating the average frame error rate;
c. carrying out weighted average on the instantaneous frame error rate in N2 frame time to obtain an average frame error rate FER (N): FER (n) = fac _1 × FER _1+ fac _2 × FER _2+ - + fac _ m × FER _ m, where a natural number n is a sequence number of an average frame error rate; each weight fac _1, fac _2, fac _ m is a positive number and is given by a simulation environment or dynamically adjusted according to an actual environment; wherein the weighting value of the instantaneous frame error rate closer to the current time is larger, i.e. each of the weights fac _1, fac _2,. Ang, fac _ m is in an increasing sequence, so that the adjustment is faster.
The selection principle for selecting one or more soft handover branches whose frame error rate threshold needs to be lowered in the step (305) is: the branch circuits of which the average frame error rate before and after the threshold value is lower than the frame error rate threshold, and/or the branch circuits of which the average frame error rate before and after the threshold value is equal to the frame error rate threshold and the average frame error rate after the threshold value is lower than the frame error rate threshold, and/or the branch circuits of which the average frame error rate before and after the threshold value is higher than the frame error rate threshold and the average frame error rate after the threshold value is lower than the frame error rate threshold; the threshold value is the moment when the total frame error rate is higher or lower than the target frame error rate.
The selection principle of selecting one or more soft handover branches whose frame error rate thresholds need to be increased in the step (405) is as follows: a branch in which the average frame error rate before the threshold is lower than the frame error rate threshold and the average frame error rate after the threshold is higher than the frame error rate threshold, and/or a branch in which the average frame error rate before the threshold is equal to the frame error rate threshold and the average frame error rate after the threshold is higher than the frame error rate threshold, and/or a branch in which the average frame error rate before the threshold and the average frame error rate after the threshold are both higher than the frame error rate threshold; the threshold value is the moment when the total frame error rate is higher or lower than the target frame error rate.
Setting an initial frame error rate threshold (FER) for each soft handover leg in the steps (305) and (405) i The calculation formula of (2) is as follows: (FER) i ＝Target(FER) total X is N; where the natural number i is the number of the soft handover leg, the Target total frame error rate Target (FER) total The target value of the total frame error rate preset by the system, and the natural number N is the number of soft switching branches in the reverse channel.
The invention is a reverse outer loop power control method used in CDMA mobile communication system, which has the following advantages: the method for calculating the total frame error rate is provided by comprehensively considering the service frame condition of each soft switching branch, and the frame error rate threshold of each soft switching branch is separately counted while calculating the total frame error rate, so that the method not only considers the condition of the wireless environment of the current system, but also has high flexibility; the reverse outer-outer loop power control method is flexible, convenient, accurate and comprehensive.
In addition, the calculation formula for setting the initial target frame error rate of each soft switching branch provided by the invention has scientificity and simplicity, so that the initial frame error rate of each soft switching branch is related to the total target frame error rate, and the base station has rationality when comparing the actual total frame error rate with the target frame error rate of each soft switching branch after calculating the actual total frame error rate, and can reasonably adjust the target frame error rate of each soft switching branch according to the current wireless environment.
Drawings
Fig. 1 is a schematic flowchart of the operation of reverse closed loop power control in a CDMA mobile communication system.
Fig. 2 is a diagram illustrating state transition of reverse outer loop power control in a CDMA mobile communication system.
Fig. 3 is a block diagram of the process of performing reverse outer loop power control when the initial state is "total frame error rate is higher".
FIG. 4 is a block diagram illustrating the process of reverse outer loop power control when the initial state is "low total frame error rate".
The diagrams (a) to (I) in fig. 5 are respectively nine exemplary diagrams of soft handover leg frame error rate fluctuation models.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the accompanying drawings.
In CDMA mobile communication system, reverse outer ring power control is that when mobile station MS generates soft switch, the selection distribution unit SDU dynamically adjusts the frame error rate threshold of each soft switch branch according to the total frame error rate of current service channel, to make the total frame error rate of service channel reach the preset target total frame error rate; a large difference from the reverse outer loop power control is the judgment of frame error. The reverse outer-loop power control can obtain service frames from a plurality of soft switching branches, and as long as one correct and error-free frame exists in the service frames, the frame is judged to be a 'good frame' by selecting a distribution unit SDU; only if the service frames obtained from all soft handover legs are erroneous frames, the SDU assumes a "bad frame" has been received. The SDU counts the total frame error rate according to the judgment and calculation of "good frame" and "bad frame", i.e. the total frame error rate = "bad frame" number/total number of frames received in a period of time.
The invention is a reverse outer ring power control method used in CDMA mobile communication system, which firstly counts the total frame error rate of all soft switching branches, then compares the total frame error rate with the preset target total frame error rate, and according to the comparison result, dynamically adjusts the frame error rate threshold of the soft switching branch according to the following method, to make the total frame error rate tend to balance:
if the statistical value is higher than the target total frame error rate, namely the initial state is a state that the total frame error rate is higher than the target frame error rate, and the total frame error rate is continuously multi-frame higher than the target frame error rate, which indicates that the quality of a reverse service channel does not meet the service requirement, the frame error rate threshold of one or more soft switching branches is selected to be reduced, so that the branch obtains a higher outer ring power control threshold in the outer ring power control process, and then an instruction of 'increasing the transmitting power' is sent to the mobile station through the inner ring power control of the branch;
if the statistical value is lower than the target total frame error rate, that is, the initial state is a state where the total frame error rate is lower, and the continuous multiframe total frame error rate is lower than the target frame error rate, indicating that the reverse traffic channel is more ideal, the frame error rate threshold of one or more soft switching branches is selected to be increased, so that the branch obtains a lower outer loop power control threshold in the outer loop power control process, and then an instruction of reducing the transmission power is sent to the mobile station through the inner loop power control of the branch.
The dynamic adjustment object of the soft switching branch frame error rate threshold can be aimed at all soft switching branches, and can also be aimed at only one or more soft switching branches with more prominent frame error rates.
For a reverse channel having a plurality of soft handover legs, each soft handover leg performs independent reverse outer loop and reverse inner loop power control and transmits power control commands to the mobile station, respectively. After receiving the power control commands of a plurality of branches, the mobile station determines the own transmitting power according to the following principles: if all branches require the mobile station to increase the transmitting power, the mobile station will increase its transmitting power; otherwise, the mobile station will reduce its transmit power whenever a leg issues a power reduction command.
When the total frame error rate is higher than the target frame error rate, the mobile station should increase the transmission power so that one or more branches can achieve better reception. According to the above mobile station reception principle, all soft handover legs should issue a command to "increase the transmission power" at this time, otherwise, the mobile station considers itself to decrease the transmission power. This is reflected in that a higher outer loop power control threshold is required for outer loop power control, which means that the frame error rate threshold of this branch should be lowered. Therefore, the outer loop power control needs to lower the frame error rate threshold of one or more soft handover branches when the total frame error rate is higher.
Otherwise, when the total frame error rate is lower than the target frame error rate, the outer-loop power control will increase the frame error rate threshold of one or more soft handover branches, so that the branch obtains a lower outer-loop power control threshold in the outer-loop power control process, and then sends an instruction of "reducing transmission power" to the mobile station through the inner-loop power control of the branch.
Referring to fig. 3, the operation steps of dynamically adjusting the frame error rate threshold of the soft handover branch when the initial state is "total frame error rate is higher" will be described specifically:
(301) The reverse service frames from each soft switching branch are selected to select the optimal service frame, and then the frame is judged to be a good frame or a bad frame.
(302) Calculating the total frame error rate of the reverse channel soft switching branch: the total frame error rate = 'bad frame' number/total frame number received in a period of time; when a frame of data is received, calculating a total frame error rate, comparing the total frame error rate with a target total frame error rate, and if the total frame error rate is higher than the target total frame error rate, sequentially executing subsequent operations; otherwise, the step (307) is executed by jumping.
(303) Firstly, calculating the average frame error rate of each soft switching branch according to the following steps:
a. determining the statistical period N1 of the instantaneous frame error rate by taking the number of the data frames as a statistical unit, counting the number of frame error frames N _ error in the N1 frame time, and then calculating the instantaneous frame error rate FER _ i: FER _ i = N _ error/N1; in the formula, a natural number i is a serial number of the instantaneous frame error rate;
b. determining the statistical period N2 of the average frame error rate: n2= m × N1, that is, N2 is an integer multiple of N1, and the coefficient m is a natural number, and the value of the coefficient m is adjusted according to actual conditions; then, the calculated value FER _ i of the instantaneous frame error rate is put into an array which is m bits long and is updated in real time according to the chronological order, so as to prepare for calculating the average frame error rate;
c. and carrying out weighted average on the instantaneous frame error rate in N2 frame time to obtain an average frame error rate FER (N): FER (n) = fac _1 × FER _1+ fac _2 × FER _2+ - + fac _ m × FER _ m, where a natural number n is a sequence number of an average frame error rate; each weight fac _1, fac _2, fac _ m is a positive number, is given by a simulation environment, or is dynamically adjusted according to an actual environment; and the weighting value of the instantaneous frame error rate closer to the current time is larger, i.e. each of the weights fac _1, fac _2,. And fac _ m is an increasing sequence, so that the adjustment is quicker.
Then according to the preferred result of the step (301), if the frame is a 'bad frame', the subsequent operations are sequentially executed; otherwise, the operation is finished, and the system is still in a state that the total frame error rate is higher.
(304) Firstly adding 1 to the Count value Count in the frame counter, then judging whether the Count value Count is smaller than a preset natural number M, if so, ending the operation, and still keeping the system in a state that the total frame error rate is higher; otherwise, the subsequent operations are sequentially executed.
(305) One or more soft handover legs are selected to lower the frame error rate threshold of the selected leg (a particular selection method is described later).
(306) Setting the count value in the frame counter to be half of the original count value so as to realize the target requirement faster by the next adjustment when the total frame error rate is adjusted once and still does not reach the preset target frame error rate requirement; after the operation is finished, the system is still in a state that the total frame error rate is higher.
(307) The frame counter is cleared.
(308) Setting an average frame error rate FER (n) of a soft handover branch as a current instantaneous frame error rate FER _ i of the branch, namely FER (n) = FER _ i at the current time; in the formula, the natural numbers n and i are the serial numbers of the average frame error rate and the instantaneous frame error rate respectively, and the system enters a state that the total frame error rate is lower.
Referring to fig. 4, the operation steps of dynamically adjusting the frame error rate threshold of the soft handover branch when the initial state is "the total frame error rate is lower" will be described specifically:
(401) And selecting the reverse service frame from each soft switching branch to select the optimal service frame and judge whether the frame is a good frame or a bad frame.
(402) Calculating the total frame error rate of the reverse channel: the total frame error rate = 'bad frame' number/total frame number received in a period of time; when a frame of data is received, calculating a total frame error rate, comparing the total frame error rate with a target total frame error rate, and if the total frame error rate is lower than the target total frame error rate, sequentially executing subsequent operations; otherwise, the step (407) is executed by jumping.
(403) Calculating the average frame error rate of each soft switching branch according to the method in the step (303), and then sequentially executing subsequent operations if the frame is a 'good frame' according to the preferred result in the step (401); otherwise, the operation is finished, and the system is still in the state of low total frame error rate.
(404) Firstly adding 1 to the Count value Count in the frame counter, then judging whether the Count value Count is smaller than a preset natural number L, if so, ending the operation, and still keeping the system in a state that the total frame error rate is lower; otherwise, the subsequent operations are sequentially executed.
(405) One or more soft handover legs are selected to raise the frame error rate threshold of the selected leg (a particular selection method is described later).
(406) Setting the count value in the frame counter to be half of the original count value so as to realize the target requirement faster by the next adjustment when the total frame error rate is adjusted once and still does not reach the preset target frame error rate requirement; and after the operation is finished, the system is still in a low total frame error rate state.
(407) The frame counter is cleared.
(408) Setting an average frame error rate FER (n) of a soft handover branch as a current instantaneous frame error rate FER _ i of the branch, namely FER (n) = FER _ i at the current time; in the formula, the natural numbers n and i are the serial numbers of the average frame error rate and the instantaneous frame error rate respectively, and the system enters a state that the total frame error rate is higher.
In the reverse outer loop power control process, the goal is to make the total Frame Error Rate (FER) of the channel total The predetermined requirements are met. According to different requirements for service quality of a traffic channel, a corresponding target frame error rate can be set. In the case of N soft handover legs in the reverse channel, assume that the frame error rate threshold of a soft handover leg i is (FER) i The frame quality status of each soft handover branch is a random variable, and if the random variables are independent of each other, the following relationship exists:
after the probability is expressed by the frame error rate, the total frame error rate is obtained
If the initial values of the frame error rate thresholds of the soft switching branches are assumed to be equal, the initial values are obtained
In fact, the frame error rate thresholds of the soft handover branches are not independent of each other, becauseThe above values are only an upper limit. As a practical application, the invention simplifies the processing, namely setting the initial frame error rate threshold (FER) of each soft switching branch i The calculation formula of (c) is: (FER) i ＝Target(FER) total X N; in the formula, the natural number i is the serial number of the soft handover branch, the natural number N is the number of the soft handover branches in the backward channel, and the Target total frame error rate Target (FER) total Is the target value of the total frame error rate preset by the system. The calculation formula can meet practical requirements.
The outer ring power control method of the invention does not adjust immediately after detecting that the total frame error rate is higher than (or lower than) the target frame error rate threshold value, but continues to track a plurality of frames, if the total frame error rate is still higher than (or lower than) the target value in the period of time, the soft switching branch frame error rate is considered to be adjusted. The moment when the total frame error rate is detected to be higher (or lower) than the target value is called the threshold value, and the moment when the adjustment of the tributary frame error rate threshold is started is called the action point. In addition, the condition that the average frame error rate of the soft handover branch may be lower than, equal to or higher than the "equal" of the frame error rate thresholds of the branch should be more relaxed, that is, as long as the distance between the average frame error rate of the branch and the frame error rate threshold is controlled within a set range, the average frame error rate may be considered to be "equal to" the frame error rate threshold.
According to the variation trend of the average frame error rate of the soft switching branch before and after the threshold value, the frame error rate states of the branches can be summarized into the following nine models, because the nine models can be used as the basis for adjusting the frame error rate threshold of the soft switching branch, namely, the variation trend of the frame error rate of the soft switching branch is analyzed through the average frame error rate, and the branch needing to adjust the frame error rate threshold of the soft switching branch is selected according to the variation trend.
Referring to fig. 5, nine model diagrams of the average frame error rate fluctuation of the soft handover branch are specifically introduced (in the diagram, the abscissa represents time, a represents a threshold value, the ordinate represents a frame error rate, and E represents a preset frame error rate threshold):
model (a): the average frame error rate before the threshold value is lower than the frame error rate threshold, and the average frame error rate after the threshold value is higher than the frame error rate threshold. This is an indication of deterioration of channel quality or an increase in communication distance.
Model (B): the average frame error rate before the threshold value is equal to the frame error rate threshold, and the average frame error rate after the threshold value is higher than the frame error rate threshold. At this time, the channel quality is changed from an ideal state to a little deteriorated.
Model (C): the average frame error rate before and after the threshold value is higher than the frame error rate threshold, and the channel quality can not meet the requirement all the time. This indicates that it may be that the legs are too far apart or that the channel quality is too poor.
Model (D): the average frame error rate before the threshold is lower than the frame error rate threshold, and the average frame error rate after the threshold is equal to the frame error rate threshold. This is the case when the channel quality is slightly degraded, but the branch frame error rate is brought into the ideal state.
Model (E): the average frame error rate before and after the threshold value is equal to the frame error rate threshold. This is the case when the tributary frame error rate is always kept at the ideal state.
Model (F): the average frame error rate before the threshold value is higher than the frame error rate threshold, and the average frame error rate after the threshold value is equal to the frame error rate threshold. This indicates that the channel quality is improved and the branch frame error rate enters the ideal state.
Model (G): the average frame error rate before and after the threshold value is lower than the frame error rate threshold. At this time, the channel quality is good, but it is likely to cause excessive interference to other users.
Model (H): the average frame error rate before the threshold value is equal to the frame error rate threshold, and the average frame error rate after the threshold value is lower than the frame error rate threshold. At this time, if the mobile station is to increase its own transmit power, care should be taken to minimize interference to other users.
Model (I): the average frame error rate before the threshold value is higher than the frame error rate threshold, and the average frame error rate after the threshold value is lower than the frame error rate threshold. This is the case where the channel quality is significantly improved.
When the total frame error rate is continuously higher than the target frame error rate for a period of time, it may be considered that the quality of the reverse channel is poor, and at this time, the reverse outer loop power control needs to lower the frame error rate threshold of one or more soft handover branches. In the process of researching the strategy for reducing the frame error rate threshold of the soft handover branch, the most important thing is how to select the soft handover branch meeting the condition, that is, the selection principle of selecting one or more soft handover branches and reducing the frame error rate threshold of the selected branch in the aforementioned step (305), so as to achieve the goal of enabling the selected soft handover branch to issue the command of "increasing the transmission power" in the inner loop power control process.
For models (a), (B), (C), the average frame error rate of the branches is higher than the corresponding frame error rate threshold. According to the outer loop power control principle, the branches will raise the outer loop power control threshold, and then instruct the mobile station to raise the transmission power in the inner loop power control. Thus, the expected effects can be achieved without lowering their frame error rate thresholds.
For the models (D), (E), (F), the average frame error rate of the branch fluctuates above and below the corresponding frame error rate threshold. Their frame error rate thresholds may not be adjusted for the moment. Of course, properly lowering the frame error rate thresholds for these branches can also help improve the overall frame error rate.
For the models (G), (H), and (I), the frame error rate threshold of the branch is too high, and the average frame error rate of the branch is significantly lower than the corresponding frame error rate threshold, resulting in the outer loop power control reducing its own outer loop threshold. Therefore, the branch will send a command of "decreasing transmission power" to the mobile station, which will eventually result in that the transmission power of the mobile station will not increase or decrease, and the total frame error rate will not be improved. Therefore, it is a relatively urgent task to reduce the frame error rate thresholds of these branches, which are also the main choice targets for reducing the frame error rate thresholds of soft handover branches.
When the total frame error rate is continuously lower than the target frame error rate for a period of time, the reverse channel quality may be considered to be better, and at this time, the reverse outer-outer loop power control needs to increase the frame error rate threshold of one or more soft handover branches. In the process of researching the strategy for increasing the frame error rate threshold of the soft handover branch, the most important thing is how to select the soft handover branch meeting the condition, that is, the selection principle of selecting one or more soft handover branches and increasing the frame error rate threshold of the selected branch in the aforementioned step (405), so as to achieve the goal of enabling the selected soft handover branch to issue the command of "decreasing the transmission power" in the inner loop power control process. .
For models (a), (B), (C), the average frame error rate of the branches is above the corresponding frame error rate threshold, which are instructing the mobile station to increase the transmit power through the inner loop power control. This is disadvantageous for reverse channels that require a reduction in transmit power, as it may cause the mobile station to erroneously make a "raise transmit power" determination; at this time, the frame error rate threshold should be raised to slightly raise the total frame error rate, so as to reduce the interference to other mobile stations. That is, these soft handover legs are the main choice targets for increasing the frame error rate threshold.
For the models (D), (E), and (F), the average frame error rate of the branches fluctuates above and below the corresponding frame error rate threshold, and at this time, the frame error rate thresholds thereof may not be adjusted temporarily. Of course, it can also play a certain role to properly increase the frame error rate threshold of these branches.
For models (G), (H), and (I), the average frame error rate of the branches is significantly lower than the corresponding frame error rate threshold, and according to the principle of outer loop power control, the branches will lower their own outer loop threshold, and then instruct the mobile station to reduce the transmission power in the inner loop power control. Therefore, it is not effective to increase the frame error rate threshold of these branches.
Claims (9)
1. A reverse outer ring power control method used in CDMA mobile communication system is that when mobile station MS generates soft switch, the frame error rate threshold of each soft switch branch is dynamically adjusted by selecting and distributing unit SDU according to the total frame error rate of current service channel, so that the total frame error rate of service channel can reach the preset target total frame error rate; the method is characterized in that: the method comprises the steps of firstly counting the total frame error rate of all soft switching branches, then comparing the total frame error rate obtained by counting with a preset target total frame error rate, and dynamically adjusting the frame error rate threshold of the soft switching branches according to the comparison result by the following method to ensure that the total frame error rate tends to be balanced:
if the statistical value is higher than the target total frame error rate, namely the initial state is a state that the total frame error rate is higher than the target frame error rate, and the total frame error rate is continuously multi-frame higher than the target frame error rate, which indicates that the quality of a reverse service channel does not meet the service requirement, the frame error rate threshold of one or more soft switching branches is selected to be reduced, so that the branch obtains a higher outer ring power control threshold in the outer ring power control process, and then an instruction of 'increasing the transmitting power' is sent to the mobile station through the inner ring power control of the branch;
if the statistical value is lower than the target total frame error rate, i.e. the initial state is the lower state of the total frame error rate, and the continuous multiframe of the total frame error rate is lower than the target frame error rate, it indicates that the reverse service channel is more ideal, the frame error rate threshold of one or more soft switching branches is selected to be increased, so that the soft switching branches obtain a lower outer loop power control threshold in the outer loop power control process, and then the instruction of reducing the transmission power is sent to the mobile station through the inner loop power control of the soft switching branches.
2. The reverse outer loop power control method of claim 1, wherein: the objects for dynamically adjusting the frame error rate threshold of the soft handover branches are all soft handover branches, or one or more soft handover branches with more outstanding frame error rates.
3. The reverse outer loop power control method of claim 1, wherein: when the initial state is "total frame error rate is higher state", the dynamic adjustment of the frame error rate threshold of the soft handover branch includes the following steps:
step 301, performing optimization on the reverse service frames sent by each soft handover branch, and determining whether the selected optimal service frame is a "good frame";
step 302, calculating the total frame error rate of the reverse channel: calculating the total frame error rate once every frame data is received, simultaneously comparing the total frame error rate with the target total frame error rate, and if the total frame error rate is higher than the target total frame error rate, sequentially executing subsequent operations; otherwise, jumping to execute step 307;
step 303, calculating the average frame error rate of each soft handover branch; then, according to the preferred result of step 301, if the frame is a "bad frame", the subsequent operations are sequentially executed; otherwise, the operation is finished, and the system is still in a high total frame error rate state;
step 304, first adding 1 to the Count value Count in the frame counter, then determining whether the Count value Count is smaller than a preset natural number M, if so, ending the operation, and the system is still in a "total frame error rate higher state"; otherwise, sequentially executing subsequent operations;
305, selecting one or more soft switching branches, and reducing the frame error rate threshold of the selected branches;
step 306, setting the count value in the frame counter to be half of the original count value, so that when the total frame error rate still does not reach the predetermined target frame error rate requirement after one adjustment, the next adjustment can achieve the target requirement faster; after the operation is finished, the system is still in a state that the total frame error rate is higher;
step 307, clearing the frame counter;
step 308, setting the average frame error rate FER (n) of the soft handover branch as the current instantaneous frame error rate FER _ i of the branch, that is, FER (n) = FER _ i at the current time; in the formula, the natural numbers n and i are the serial numbers of the average frame error rate and the instantaneous frame error rate respectively, and the system enters a state that the total frame error rate is lower.
4. The reverse outer loop power control method of claim 1, wherein: when the initial state is "the total frame error rate is lower state", the operation steps of dynamically adjusting the frame error rate threshold of the soft handover branch are as follows:
step 401, performing optimization on the reverse service frames sent by each soft handover branch, and determining whether the selected optimal service frame is a "good frame";
step 402, calculating the total frame error rate of the reverse channel: calculating the total frame error rate once every frame data is received, simultaneously comparing the total frame error rate with the target total frame error rate, and if the total frame error rate is lower than the target total frame error rate, sequentially executing subsequent operations; otherwise, jump to execute step 407;
step 403, calculating an average frame error rate of each soft handover branch; then, according to the preferred result of step 401, if the frame is a "good frame", the subsequent operations are sequentially executed; otherwise, the operation is finished, and the system is still in a low total frame error rate state;
step 404, first adding 1 to the Count value Count in the frame counter, then determining whether the Count value Count is smaller than a preset natural number L, if so, ending the operation, and the system is still in a "total frame error rate is lower state"; otherwise, sequentially executing subsequent operations;
step 405, selecting one or more soft switching branches, and increasing the frame error rate threshold of the selected branches;
step 406, setting the count value in the frame counter to be half of the original count value, so that when the total frame error rate still does not meet the predetermined target frame error rate requirement after one adjustment, the next adjustment can achieve the target requirement faster; after the operation is finished, the system is still in a low total frame error rate state;
step 407, clearing the frame counter;
step 408, setting the average frame error rate FER (n) of the soft handover branch as the current instantaneous frame error rate FER _ i of the branch, that is, FER (n) = FER _ i of the current time; in the formula, natural numbers n and i are the serial numbers of the average frame error rate and the instantaneous frame error rate respectively, and the system enters a state that the total frame error rate is higher.
5. The reverse outer loop power control method according to claim 3 or 4, wherein: the calculation formula of the total frame error rate of the soft handover leg in step 302 and step 402 is:
the total frame error rate = 'bad frame' number/total frame number received in a period of time;
the judgment basis of the bad frame and the good frame is as follows: only if the service frames obtained from all the soft handover branches are error frames, the SDU considers that a 'bad frame' is received; and as long as the correct frame is obtained from one of the soft handover legs, the SDU determines that the frame is a "good frame".
6. The reverse outer loop power control method according to claim 3 or 4, wherein: the calculating the average frame error rate of each soft handover branch in steps 303 and 403 includes the following specific steps:
a. determining the statistical period N1 of the instantaneous frame error rate by taking the number of the data frames as a statistical unit, counting the number of frame error frames N _ error in the N1 frame time, and then calculating the instantaneous frame error rate FER _ i: FER _ i = N _ error/N1; in the formula, a natural number i is a serial number of the instantaneous frame error rate;
b. determining a statistical period N2 of the average frame error rate: n2= m × N1, that is, N2 is an integer multiple of N1, the coefficient m is a natural number, and the value of the coefficient m is adjusted according to actual conditions; then putting the calculated value FER _ i of the instantaneous frame error rate into an array which is m bits long and is updated in real time according to the chronological order, and preparing for calculating the average frame error rate;
c. and carrying out weighted average on the instantaneous frame error rate in N2 frame time to obtain an average frame error rate FER (N): FER (n) = fac _1 × FER _1+ fac _2 × FER _2+ - + fac _ m × FER _ m, where a natural number n is a sequence number of an average frame error rate; each weight fac _1, fac _2, fac _ m is a positive number and is given by a simulation environment or dynamically adjusted according to an actual environment; wherein the weighting value of the instantaneous frame error rate closer to the current time is larger, i.e. each of the weights fac _1, fac _2, ·, fac _ m is an increasing sequence, so that the adjustment is faster.
7. The reverse outer loop power control method of claim 3, wherein: the selection principle of selecting one or more soft handover branches whose frame error rate threshold needs to be reduced in step 305 is as follows: a branch in which the average frame error rate before and after the threshold value is lower than the frame error rate threshold, and/or a branch in which the average frame error rate before and after the threshold value is equal to the frame error rate threshold and the average frame error rate after the threshold value is lower than the frame error rate threshold, and/or a soft switching branch in which the average frame error rate before and after the threshold value is higher than the frame error rate threshold and the average frame error rate after the threshold value is lower than the frame error rate threshold; the threshold value is the moment when the total frame error rate is detected to be higher or lower than the target frame error rate.
8. The reverse outer loop power control method of claim 4, wherein: the selection principle of selecting one or more soft handover branches whose frame error rate thresholds need to be increased in step 405 is as follows: a branch in which the average frame error rate before the threshold is lower than the frame error rate threshold and the average frame error rate after the threshold is higher than the frame error rate threshold, and/or a branch in which the average frame error rate before the threshold is equal to the frame error rate threshold and the average frame error rate after the threshold is higher than the frame error rate threshold, and/or a branch in which the average frame error rates before and after the threshold are higher than the frame error rate threshold; the threshold value is the moment when the total frame error rate is higher or lower than the target frame error rate.
9. The reverse outer loop power control method according to claim 3 or 4, wherein: setting an initial frame error rate threshold (FER) for each soft handover leg in steps 305 and 405 i The calculation formula of (2) is as follows: (FER) i ＝Target(FER) total X N; where the natural number i is the number of the soft handover leg, the Target total frame error rate Target (FER) total The target value of the total frame error rate preset by the system, and the natural number N is the number of soft switching branches in the reverse channel.
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