JPH0621903A - Fading frequency detection method - Google Patents

Abstract

PURPOSE:To improve the measuring accuracy of the fading frequency by calculating the frequency from the reciprocal of the mean value of the time when the reception level is lower than a set level. CONSTITUTION:The center instantaneous value set at a reception level input terminal 11 is detected by a detecting circuit 12, and the value having the prescribed relation with the center instantaneous value is set by a level setting circuit 13. That is, a level that is relatively constant to the instantaneous value obtained by excluding the fluctuation component of the center value can be supplied to the circuit 13. The circuit 13 compares the instantaneous value of the set level with that of the reception level. If the latter level is lower than the former level, the circuit 13 opens a gate circuit 15 to transmit the sampling clock supplied through a clock input terminal 18 as a detected pulse. A counter 16 counts the detected pulses supplied from the circuit 15 and sends them to an arithmetic processing circuit 17 to calculate the mean value of the time when the instantaneous value of the reception level is lower than that of the set value. Then the counter 16 calculates the fading frequency from the reciprocal of the calculated mean value and outputs the frequency through a fading output terminal 19. Thus the fading frequency is detected and the measuring accuracy of the frequency is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fading frequency detecting method used for measuring a fading frequency in a radio communication such as a mobile communication in which a reception level fluctuates drastically due to fading.

[0002]

2. Description of the Related Art In wireless communication in which the reception level fluctuates significantly due to fading, the transmission quality deteriorates significantly when the reception level decreases. In mobile communication, since the fading frequency is proportional to the moving speed, the fading frequency can be obtained by detecting the speed of the moving body. In that case, a speed detecting function of the moving body is required. However, for example, although a car is naturally equipped with a speed detection function, in order to use the obtained speed information to calculate a fading frequency in a wireless device such as a car telephone, it is necessary to interface between them. Had to be modified.

On the other hand, in order to detect the fading frequency only by the radio system without affecting the moving body, conventionally, there is a method of measuring and detecting the number of level crossings at which the reception level crosses a predetermined level in a unit time. It was This is an amount f (R) in which the number of times Ns of level crossings at a predetermined level Rs is determined by the predetermined level Rs under Rayleigh fading.
s) is a constant and is proportional to the fading frequency fd.
It is noted that the relation is s = f (Rs) × fd.

[0004]

However, when the actual reception level fluctuates, the average value of Rayleigh fading further fluctuates, so that it is difficult to set the predetermined level Rs.
In addition, even if there is noise or slight fluctuation, a predetermined level R
If s is crossed, it is counted as the number of level crossings,
The detection accuracy of the fading frequency largely depends on how to select the setting value.

By the way, the fading frequency is measured by
It is not only useful for estimating the transmission quality, but also an essential element for selecting an effective transmission characteristic improvement method. However, the method of detecting the velocity of the moving body requires a large modification of the moving body, and the method of measuring the number of level crossings has a problem in detection accuracy. It is an object of the present invention to provide a fading frequency detecting method capable of measuring a fading frequency with high accuracy.

[0006]

The present invention compares a predetermined set level, which varies according to the median of the received levels, with the received level, and measures the time when the received level falls below the set level. It is characterized in that the average value is obtained and the fading frequency is calculated from the reciprocal thereof.

[0007]

The present invention, under Rayleigh fading,
Average time length Tm when the reception level is below a predetermined level Rs
Is inversely proportional to the fading frequency fd with the quantity g (Rs) determined by the predetermined level Rs as a constant, and the equation Tm = g (Rs)
Note that they are related by / fd. this is,
In the conventional measurement method based on the number of level crossings, the measured value of the number of level crossings is affected by an instantaneous drop due to noise or a slight fluctuation near a predetermined level Rs, whereas the average time length is measured. In the method, their effect is almost negligible because their time is small compared to the total dip time.

Further, according to the present invention, the reference predetermined level Rs is not fixed, but is changed according to the fluctuation of the median of the reception level in a unit time, whereby the fading frequency is accurately measured from the fluctuation of the reception level. can do. That is, the level Rsm having a predetermined relationship with the median of the reception levels is used as a reference level, the average value of the time when the reception level falls below the predetermined level Rsm is obtained, and the fading frequency can be obtained from the reciprocal thereof.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the structure of an embodiment when the method of the present invention is implemented by a digital circuit. In the figure, the reception level input from the reception level input terminal 11 is input to the median level detection circuit 12 and the level comparison circuit 13. The median level detected by the median level detection circuit 12 is input to the level setting circuit 14, and the output thereof is input to the level comparison circuit 13. The output of the level comparison circuit 13 controls the opening / closing of the gate circuit 15. The output of the gate circuit 15 is input to the counter 16, and the output thereof is further input to the arithmetic processing circuit 17. The clock input from the clock input terminal 18 is supplied to the gate circuit 15, the counter 16, and the arithmetic processing circuit 17. The output of the arithmetic processing circuit 17 is taken out to the fading frequency output terminal 19.

The operation of this embodiment will be described below with reference to FIG. The reception level in mobile communication fluctuates drastically due to fading as indicated by the instantaneous value input A in FIG. 2, and the median level B also fluctuates gently. Therefore, under Rayleigh fading, in order to measure the average time length for which the reception level falls below a predetermined value, first, the median level B is subtracted from the instantaneous value input A to remove the median variation, and then the comparison value is compared. It is necessary to compare it with the standard setting level.

In this embodiment, the reception level input terminal 1
The median value of the instantaneous value input to 1 is detected by the median level detection circuit 12, and the level setting circuit 13 sets a value having a predetermined relationship with the median value (for example, a value which is always 10 dB lower). That is, by generating the set level according to the variation of the median value, it is possible to supply the level comparing circuit 13 with a relatively constant level with respect to the instantaneous value from which the variation of the median value is removed. The level comparison circuit 13 compares the set level with the instantaneous value of the reception level. If the reception level is lower than the set level, the gate circuit 15 is opened to detect the sampling clock C supplied from the clock input terminal 18 as a detection pulse. Pass as. Here, D shows the comparison between the set level and the instantaneous value of the reception level, and E shows the state of the detection pulse output from the gate circuit 15.

The counter 16 counts the detection pulse E output from the gate circuit 15 and sends it to the arithmetic processing circuit 17. This count value corresponds to the time when the instantaneous value of the reception level falls below the set level, the arithmetic processing circuit 17 obtains the average time, calculates the fading frequency from the reciprocal thereof, and outputs it to the fading frequency output terminal 19. That is, in the configuration of the present embodiment, the set level that has a predetermined relationship with the median of the reception level and the reception level are compared, and the time when the reception level is lowered by the set level that changes in accordance with the change of the median. Can be measured, and the fading frequency can be obtained from the reciprocal of the average value.

As described above, since the fading frequency detecting method of the present invention can realize all the functions by the digital circuit, it can be integrated into an LSI. Further, the operation of each digital circuit can be easily replaced by the program of the microcomputer, and in that case, the LIS can be extremely easily configured.

[0014]

As described above, the present invention can detect the fading frequency with high accuracy by avoiding the influence of noise or the like even when the reception level fluctuates greatly like in mobile communication, and the transmission quality can be improved. Can be effectively applied to the estimation and improvement of transmission quality.

Furthermore, since the method of the present invention can be realized by a digital circuit and can be implemented as software by a microcomputer or the like, highly reliable hardware can be provided at a low cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment when the method of the present invention is implemented by a digital circuit.

FIG. 2 is a diagram for explaining the operation of this embodiment.

[Explanation of symbols]

 11 reception level input terminal 12 median level detection circuit 13 level comparison circuit 14 level determination circuit 15 gate circuit 16 counter 17 arithmetic processing circuit 18 clock input terminal 19 fading frequency output terminal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Sakamoto 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation

Claims (1)

[Claims] 1. A predetermined set level, which fluctuates according to the median of the received levels, is compared with the received level, the time when the received level falls below the set level is measured, and an average value thereof is calculated. A fading frequency detecting method, characterized in that a fading frequency is calculated from an inverse number.