KR100204032B1 - The critical power decision method adapting to fading - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

A method for determining the base station threshold reception power adaptive to fading environment changes.

2. The technical problem to be solved by the invention

The frame error rate is improved by varying the unit increase / decrease to suit the change characteristic of the partial average value of the Eb / No threshold due to the change in the fading environment.

3. Summary of Solution to Invention

Checking a partial mean value change state of a received power-to-noise ratio (Eb / No) threshold value according to a result of comparing a threshold value of a current error frame with a previous error frame threshold; Increasing the increase of the threshold value if the partial mean value is increased, and maintaining the decrease of the threshold value as it is; Maintaining an increase amount of the threshold value and increasing the decrease amount of the threshold value when the change state of the partial mean value is reduced; Reducing both the increase and decrease of the threshold value if the change in the partial mean value is an increase-decrease state or a decrease-increase state; If there is no change in the partial mean value, the step of setting the increment and decrement of the threshold value to the initial unit increment.

4. Important uses of the invention

Used for base station controller of CDMA mobile communication system.

Description

How to Determine Base Station Threshold Received Power Adaptive to Fading Environment Change

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a base station threshold reception power that is adaptive to changes in fading environments. In particular, a frame data error rate directly related to voice quality in a code division multiple access (CDMA) mobile wireless communication system is disclosed. By adaptively changing the fading environment of the radio channel when determining the base station threshold received signal bit energy to noise spectral-density (Eb / No) needed to keep the rate constant The present invention relates to a method for efficiently adjusting a threshold Eb / No value to improve a frame error rate.

The conventional method varies the Eb / No threshold by a fixed unit increment in accordance with the frame error rate. If the fading environment is constant, a fixed unit increase or decrease suitable for the target frame error rate is sufficient.

In practice, however, the fading environment is constantly changing due to the mobile characteristics of the mobile telephone. In this case, the variable increase / decrease amount adaptive to the fading environment change is more efficiently adjusted than the fixed unit increase / decrease amount, thereby improving frame error rate performance.

Therefore, since the present invention is implemented in software with a small amount of code in the base station controller, the implementation is simple, and by varying the unit increase / decrease amount to suit the change characteristic of the partial average value of the Eb / No threshold due to the change in the fading environment, An object of the present invention is to provide a method for determining a base station threshold reception power that is adaptive to a fading environment change that can improve a frame error rate.

1 is a structural diagram of a base station receiver and a base station controller for explaining a power control procedure in a base station to which the present invention is applied;

2 is an overall flowchart according to the present invention;

3 is a flowchart illustrating a process of determining an increase / decrease amount of a threshold value according to the present invention;

4 is a graph for comparing the frame error rate result against time for the conventional method and the present invention when the mobile station speed is constant;

Fig. 5 is a graph for comparing the frame error rate result against time for the present method and the present invention when the mobile station speed changes over time.

* Description of the symbols for the main parts of the drawings *

11: pseudonoise and Hadamard correlator

12: squared synthesizer

13: hard decision maker

14: Eb / No predictor

15: deinterleaver

16: Viterbi decoder

17: CRC Checker

18: Eb / No threshold determiner

19: comparator

20: closed circuit power control bit generator

In order to achieve the above object, the present invention provides a method for determining a base station threshold reception power applied to a mobile communication system, wherein when an error frame is received, a current threshold of an error frame and a threshold when an error of a past frame occurs A first step of comparing the values; A second step of checking a change in a partial average value of a received power-to-noise ratio (Eb / No) threshold value according to a result of comparing the threshold value of the current error frame with the threshold value of the previous error frame; A third step of increasing the amount of increase of the threshold by maintaining a constant for determining the amount of increase or decrease of the threshold value if the change state of the partial mean value is an arbitrary first value and maintaining the amount of decrease of the threshold value as it is; A fourth step of maintaining the increase amount of the threshold value and increasing the decrease amount of the threshold value by setting a constant for determining the increase / decrease amount of the threshold value if the change state of the partial mean value is a predetermined first value; A fifth step of reducing both an increase amount and a decrease amount of the threshold value by setting a constant for determining an increase or decrease amount of the threshold value when the change state of the partial mean value is an increase-decrease state or a decrease-increase state; A sixth step of setting an increase and decrease of a threshold value as an initial increase or decrease, if there is no change in the partial mean value; And a seventh step of varying the current threshold value according to the increase / decrease amount of the determined threshold value.

A method of determining a base station reception threshold adaptive to a fading environment change of the present invention may be represented by Equation 1 below.

,

here, Is a threshold newly determined by the quality of the i th frame, Is the initial threshold, Is a logarithmic function for converting in decibels (dB), Is the threshold just before raising the threshold by the kth bad frame, and If the decoded frame is good as the quality of the j th frame, it has a constant minus one (-1) value and a bad prus one (+1) value, and receives two consecutive bad frames. When the second bad frame has a value of zero (0). Also Is a constant that determines the criteria for determining that there is no change in the partial mean of the threshold, , Is the threshold unit increment amount at this time. And Is a constant that determines the rate at which the threshold unit increases and decreases.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention;

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a structural diagram of a base station receiver and a base station controller for explaining a power control procedure in a base station, in which 11 is a pseudo noise and Hadamard correlator, 12 is a square synthesizer, 13 is a hard decision, and 14 is a hard decision. An Eb / No predictor, 15 is a deinterleaver, 16 is a Viterbi decoder, 17 is a CRC checker, 18 is a threshold determiner, 19 is a comparator, and 20 is a closed circuit power control bit generator.

The measured Eb / No value obtained while the signal received from the mobile station to the base station passes through the pseudo noise and Hadamard correlator 11, the square synthesizer 12, the hard determiner 13 and the Eb / No predictor 14 is determined by the threshold value. The closed circuit power control bit command is made in the closed circuit power control bit generator 20 as compared in the comparator 19.

At this time, the threshold value is determined by the base station controller, and the base station receiver sends a frame generated through the deinterleaver 15 and the Viterbi decoder 16 from the output of the square synthesizer 12 to the base station controller. The base station controller checks the frame quality by performing a cyclic redundancy check (CRC) through the CRC checker 17.

Then, the threshold determiner 18 determines whether to increase or decrease the current threshold value according to the CRC check.

At this time, the threshold value is determined by Equation 2.

here, Is a threshold newly determined by the quality of the i th frame, Is the initial threshold, Is the logarithm function for converting in decibels (dB), Is the unit increment of the threshold, Is the unit decrease of the threshold, Has a value of minus one (-1) if the decoded frame is good as the quality of the j th frame, and has a value of the frus one (+1) if it is bad, and receives two consecutive bad frames. When the second bad frame has a value of zero (0).

To illustrate the threshold determination procedure, observe a situation where a good frame continues several times from one bad frame to the next bad frame. When a bad frame, a state in which the threshold just before increasing the threshold value is within the same or constant margin for the two bad frames is called 'balanced state'.

Equation 3 can be derived from the following two facts when the system is in an 'balanced state'.

First, the ratio of threshold increments to increments is equal to the length of the good frame.

Second, the inverse of the frame error rate is equal to the length of the good frame plus one (1).

here, Is the frame error rate.

The variables shown in Equation 3 are actually determined by the system operator in consideration of the trade-off between the frame error rate, which is the service voice quality, and the average threshold, and usually sets the frame error rate to 1% or less.

The selected unit increase or decrease varies the Eb / No threshold by a fixed increase or decrease according to the frame error rate.

If the fading environment is constant, a fixed unit increase or decrease suitable for the target frame error rate is sufficient. In practice, however, the fading environment is constantly changing due to the mobile nature of the mobile phone. In this case, the variable increase / decrease adaptive to the fading environment change is more effective in improving the frame error rate and the Eb / No performance than the fixed unit increase or decrease.

The variable increase and decrease is adjusted by the partial mean value of the threshold. The change of the partial mean value of the threshold can be divided into the following four types, and the unit increment of the appropriate threshold for each is as follows.

First, when the partial mean of the threshold increases for two constant time intervals, the increment in threshold unit increments and maintains the decrease intact.

Second, when the partial mean of the threshold falls for two constant time intervals, the threshold unit decreases and increases the threshold.

Third, when the partial mean of the threshold repeats rising and falling over two constant time intervals, both the amount of increase and the amount of decrease decrease.

Fourth, when the partial mean of the threshold values is in the 'balanced state' for two constant time intervals, a proper increase and decrease is maintained.

Equation 1 was considered based on the equation of the Giant used in Adaptive Delta Modulation (ADM) to enable the above operation to change the threshold value.

The above process will be described with reference to FIGS. 2 and 3.

2 is an overall flowchart according to the present invention, in which a CRC is inspected in units of frames (201), and if an error occurs in a received frame (202), a process of re-determining a unit increase / decrease value of a threshold value is performed (203). In case of an error according to the received frame quality, the threshold value is increased by an increase amount, and if the received frame quality is good, the threshold value is decreased by a decrease amount (204).

3 shows a process flow for determining an increase / decrease value of a threshold according to the present invention.

When an error occurs in the received frame, the current threshold value of the frame in which the error occurs once is stored in Pthresh, k (301).

When the difference between the stored current threshold value Pthresh, k and the threshold value Pthresh, k-1 when a past frame error occurs is a positive number, it is determined whether the difference is greater than a certain margin (302).

If the difference between the Pthresh, k value and the Pthresh, k-1 value is greater than a certain margin, it is determined that the partial mean value of the threshold value increases in the corresponding time interval and stores a value of '1' in Ck (303).

If the difference between the Pthresh, k value and the Pthresh, k-1 value is not greater than a certain margin, the Pthresh, k value, which is the threshold at which the error of the current frame occurred, and the Pthresh, k-1, which is the threshold at which the previous frame error occurred When the difference in value is '0' or negative, it is determined whether the absolute value of the difference is greater than a certain margin (304).

If the absolute difference between the Pthresh, k and Pthresh, k-1 values is not greater than a certain margin, a value of '0' is stored in Ck, an indicator variable indicating a change state of the partial mean value of the threshold (305).

If the absolute value of the difference between Pthresh, k and Pthresh, k-1 is greater than a certain margin, it is determined that the partial mean value of the threshold decreases in the relevant time interval. The value of '-1' is stored (306).

The Pthresh, k value, which is the threshold at which the current frame error occurs, is stored in Pthresh, k-1 to be compared with the threshold value when the next frame has an error (307), and the current unit time interval. It is determined whether the value is greater than '0' by multiplying the indicator variable Ck at and the indicator variable Ck-1 in the unit time interval when a past error occurs (308). In other words, it is examined whether there is a change in the tendency of the partial mean value in the current time interval and the tendency of the partial mean value in the past time interval.

If the determination result 308 is greater than '0', the K value for determining the increase or decrease of the threshold increase / decrease amount is stored as an arbitrary value K1 (309), and the increase or decrease of the tendency (Ck) of the partial mean value is increased. It is determined whether the state (310).

If the product of the current indicator variable and the immediately preceding indicator variable is positive, and the current indicator variable is positive, the partial mean value is increased-increased, the threshold increase amount is increased according to Equation 1 (311), and the threshold decrease amount is Maintain it as it is (312).

If the product of the current indicator variable and the immediately previous indicator variable is positive, and the current indicator variable value is negative, the partial mean value is reduced-decreased, and thus the threshold increase amount is maintained (313). Increase accordingly (314).

If the determination result 308 is less than '0', that is, the product of the current indicator variable and the immediately preceding indicator variable is negative, the partial mean value is increased-decreased or decreased-increased to determine the threshold increase or decrease. A value of K is stored as an arbitrary K2 value (315), and the threshold increase / decrease value is all reduced according to Equation 1 using the K2 value (316,317).

As a result of the determination 308, if any one of Ck or Ck-1 is '0', the increment and decrement of the threshold value are set as unit increments, which are initial values (318 and 319).

After the error occurs in the current frame and the threshold increase / decrease amount is newly determined, when the next frame has an error, Ck, which is a conversion indicator of the current partial mean value, is used to determine the threshold increase or decrease again. Is stored at Ck-1 (320).

In order to verify the effect of the present scheme, the transmitter of the reverse link is implemented in C code based on IS-95, and the receiver is configured in the structure as shown in FIG. The code synchronization is assumed to be perfect, the information bit rate is 9.6kbps, and the voice activation detection technique is not used. The wireless air channel also uses 3 (three-path model) for the IS-97 specification, where each delay path undergoes independent Rayleigh fading.

The number of correlators is three because the number of delay paths is three. The interference power is equal to the additive noise characteristic and has a constant power level. Therefore, in this simulation, the signal bit energy-to-noise spectral density (Eb / No) and the bit energy-to-noise power density (Eb / Io; bit-Energy per Interference-power-density was treated the same.

The simulation was carried out under two different fading environments, where the air channel had a constant fading rate and was variable. The constant fading rate was used for verification of the simulation. Was carried out to check the performance.

The mobile station speed was kept constant to have a constant fading rate, and the mobile station speed was varied as follows to have a variable fading rate. In other words, in consideration of the vehicle movement characteristics in the city with many traffic lights, the characteristics of moving from stop or low speed to medium speed and again at low speed are repeated. Therefore, the initial mobile station speed started at 5 Km, and after 60 seconds to 60 Km, and maintained this speed for 30 seconds, and then again to 5Km for 10 seconds (total after 50 seconds), and this was repeated for 5 minutes.

The value applied to each variable value in the simulation 3072, 24, 1.2, 1.03, and and silver And The same values as are applied, but these variables can be set to suit the actual operation.

As a simulation result, FIG. 4 shows the frame error rate versus time when the conventional method and the present invention are applied under the condition that the mobile station speed is constant.

It can be seen from the chart lines (i) and (ii) of FIG. 4 as follows. In other words, under a constant fading rate, the system is mostly in an 'balanced state' on the time axis, so that Equation 1 Since the value becomes zero, Equation 1 is equal to Equation 2.

Therefore, under this environment, the frame error rate result applying the existing method and the frame error rate result applying the present method are approximately equal. In addition, FIG. 2 also shows that the frame error rate result (calculated line (iii)) calculated by Equation 3 almost coincides with the simulation result.

Figure 5 shows the average frame error rate results when applying the conventional method and the method of the present invention in a variable fading environment, (i) is a conventional method, (ii) is a method of the present invention, (iii) Denote each change in mobile station speed.

It can be seen that the method of the present invention improves the frame error rate by up to 0.4% over the conventional method. As a result of simulation for a total of 5 minutes, the average value of the total required Eb / No value is about 6.01 dB in the conventional method, and the result of applying this method is about 6.06 dB. On the other hand, the frame error rate results for each method are 0.75% and 0.53%, respectively. Therefore, under the condition of having approximately the same Eb / No, the improvement of the frame error rate between the existing method and the method of the present invention is improved by up to 0.4%, which shows that there is a 30% frame error rate performance improvement over the existing method.

The present invention described above is capable of various substitutions, modifications, and changes within the scope without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains, and thus is limited to the above-described embodiments and drawings. It is not.

Therefore, the present invention made as described above is simple to implement in addition to the existing software code mounted on the memory device of the selector card in the base station controller, Eb / No threshold due to the change in the fading environment as described above By varying the unit increase / decrease amount to suit the change characteristic of the partial mean value of, it has an excellent effect of improving the frame error rate by efficiently using the required Eb / No.

Claims (6)

In the base station threshold reception power determination method applied to a mobile communication system, A first step of, when an error frame is received, comparing a current threshold value of the frame in which the error occurred with a threshold value when an error in the past frame occurs; A second step of checking a change in a partial average value of a received power-to-noise ratio (Eb / No) threshold value according to a result of comparing the threshold value of the current error frame with the threshold value of the previous error frame; A third step of increasing the amount of increase of the threshold by maintaining a constant for determining the amount of increase or decrease of the threshold value if the change state of the partial mean value is an arbitrary first value and maintaining the amount of decrease of the threshold value as it is; A fourth step of maintaining the increase amount of the threshold value and increasing the decrease amount of the threshold value by setting a constant for determining the increase / decrease amount of the threshold value if the change state of the partial mean value is a predetermined first value; A fifth step of reducing both an increase amount and a decrease amount of the threshold value by setting a constant for determining an increase or decrease amount of the threshold value when the change state of the partial mean value is an increase-decrease state or a decrease-increase state; A sixth step of setting an increase and decrease of a threshold value as an initial increase or decrease, if there is no change in the partial mean value; And And a seventh step of varying a current threshold value according to the determined increase or decrease of the threshold value. The method of claim 1, The first step is, If the error frame is received, storing a current threshold of the frame in which the error occurred; And determining whether a difference between a threshold of a current error frame and a threshold when an error of a previous frame is greater than a certain margin. The method of claim 2, The second step, Storing the partial mean value of the threshold in an indicator variable indicating a change state of the partial mean value of the threshold when the difference between the threshold value of the current error frame and the threshold value of the previous error frame is greater than a certain margin value; If the difference between the threshold of the current error frame and the threshold of the previous error frame is not greater than any margin, it is determined whether the absolute value of the threshold difference of the current error frame and the threshold of the previous error frame is greater than any margin. step; If the absolute value of the difference between the threshold value of the current error frame and the threshold value of the previous error frame is not greater than a certain margin, the indicator variable indicating the change state of the partial mean value of the threshold is stored. step; If the absolute value of the difference between the threshold value of the current error frame and the threshold value of the previous error frame is greater than a certain margin, storing the partial mean value of the threshold in a decreasing state in an indicator variable indicating a change state of the partial mean value of the threshold; After performing the step, resetting the threshold of the current error frame to the threshold of the previous error frame; And After performing the above steps, the state of change of the threshold partial mean value is compared by comparing the value stored in the indicator variable indicating the state of change of the threshold partial mean value of the current error frame with the value stored in the indicator variable indicating the change state of the threshold partial mean value of the immediately preceding error frame. Determining the base station threshold received power, characterized in that it comprises a step of checking. The method of claim 3, wherein The amount of increase of the threshold value when the threshold partial mean value is in the increase-decrease state, the increase-decrease state or the decrease-increase state, (here, Is the increase in the previous threshold, K is a constant that determines the rate of increase and decrease in threshold unit increments, Is the change in the partial mean over the current time interval, Is determined by a change in a partial mean value in a previous time interval. The method of claim 3, wherein The amount of increase of the threshold value when there is no change in the threshold partial mean value is (here, Is the current threshold unit increase, K is a constant that determines the rate at which the threshold unit increases or decreases, Is the change in the partial mean over the current time interval, Is determined by a change in a partial mean value in a previous time interval. The method of claim 5, The current threshold is, (here, Is the initial threshold, Is the logarithm function for converting in decibels (dB), Is the unit increment of the threshold, Is the unit decrease of the threshold, Is determined by the quality of the current frame.