JP2993525B2 - Propagation delay measuring device in wireless communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring a propagation delay in wireless communication. In wireless communication, not all transmitted radio waves are directly received by a receiving antenna, but radio waves 51 emitted from an antenna 50 of a base station are transmitted to surrounding buildings 52 and mountains as shown in FIG. Since it is reflected at 53 etc., it becomes a multiplex wave and the receiving point 5
Arriving at 4. The generation of a time-delayed wave due to a multiplex wave is called a propagation delay, and the propagation delay degrades the communication quality of wireless communication. This is the same phenomenon that words spoken quickly at the summit are hard to hear due to mountain biking.

[0002]

2. Description of the Related Art Conventionally, the following method has been used to obtain a delay spread used for evaluating communication quality from correlation coefficients of a plurality of narrowband waves. While traveling through a plurality of different frequency radio waves transmitted from one transmitting antenna, received by one receiving antenna,
The relationship between the frequency difference and the correlation coefficient of the reception level as shown in FIG. 9 is obtained (in FIG. 9, crosses indicate measured values). From these relationships, a frequency difference (frequency correlation bandwidth B) at which the correlation coefficient ρ becomes 0.5 is obtained. In order to determine the delay spread S from the frequency correlation bandwidth B, the delay profile S is determined assuming that the delay profile is an exponential function. Delay spread S in that case
And the frequency correlation bandwidth B are expressed as “delay spread S =
1 / (2πB) ”.

The delay profile in the above description is shown in FIG.
FIG. 4B is a time-dependent distribution chart of a radio wave (delayed wave) arriving late due to a propagation delay as shown in (b), with the horizontal axis representing delay time and the vertical axis representing received power. In the figure, NL indicates a noise level, L _O , L _{I to} L _N indicate reception levels of delayed waves, and T _O , T _{I to} T _N indicate relative delay times of the delayed waves.

The delay spread is a second moment of the propagation delay time defined by the evaluation value (1) for quantitatively expressing the propagation delay amount. As the delay spread increases, communication quality deteriorates. The received power of the delayed wave is L _O , L
_I ... relative delay time T ₁ at L _N for L _O, ... delay electronic table in the case of T _N to become N-wave is calculated by the equation (1) and (2) below.

(Equation 1)

(Equation 2)

[0005] The techniques described above are described in detail in the following documents 1 and 2. Reference 1 [Mitsuishi, Akiyama, Kinoshita, "Frequency correlation characteristics in urban area propagation", IEICE Technical Report, AP79-7, 1979] Reference 2 [AAMSa
leh, and RAValenzuela: “A statistical model for
indoor multipath propagation ”, IEEE J. Select.Areas
Commun., SAC-5, No2 pp.128 (Feb.1987)]

[0006]

In the above document 2,
It is statistically stated that the delay profile can be approximated by an exponential function. there were. The present invention
In view of such conventional problems, it is an object of the present invention to provide a propagation delay measuring device capable of estimating a delay spread with high accuracy even when a delay profile is not an exponential product number.

[0007]

According to the present invention, the above objects are achieved by the means recited in the claims. That is, the present invention is an apparatus for measuring a propagation delay using reception level correlation of a plurality of frequency waves in wireless communication, and stores a type of a frequency correlation function obtained in advance corresponding to a plurality of types of delay profiles. Correlation function storage function, correlation detection function to find the correlation coefficient of the reception level of the received multi-frequency radio waves, and the reception level obtained by measurement by changing the value of the delay spread for each of the above types of frequency correlation functions This is a propagation delay measuring apparatus provided with a delay spread calculating function for calculating a type of a frequency correlation function and a value of a delay spread that best match the relationship between the correlation coefficient and the frequency difference.

[0008]

According to the conventional method for estimating the delay spread from the correlation coefficient of the reception level as described above, the delay spread is estimated on the assumption that the delay profile is an exponential function. If it deviates from the exponential function and becomes another function form, an estimation error occurs.

In the present invention, a plurality of frequency correlation functions corresponding to the assumed delay profile are prepared in advance by assuming some shapes of the delay profile other than the exponential function. By selecting the function that best fits the measured value from the correlation function, the estimation error is prevented from increasing even if the delay profile has a function form different from the exponential function, so that the accuracy of delay spread estimation can be improved. it can. As shown in FIG. 7, the above-mentioned frequency correlation function is a function of the correlation coefficient of the reception level with respect to the frequency difference between different frequencies, and has a Fourier transform relationship with the delay profile.
The frequency difference at which the correlation coefficient is 0.5 is particularly called a frequency correlation bandwidth. The figure shows the relationship among the above-described delay profile, delay spread, frequency correlation function, and frequency correlation bandwidth. The delay spread and the frequency correlation bandwidth are numerical values related to the magnitude of the propagation delay.

[0010]

1 is a diagram showing the configuration of an embodiment of the present invention, wherein 1 is a receiving antenna, 2 is a duplexer, 3 is an electric field strength measuring device, 4 is a vehicle speed measuring device, and 5 is an A / D. A converter, 6 is a shadowing remover, 7 is a correlation coefficient calculator, 8 is a frequency correlation function ROM, 9 is a delay spread calculator, and 10 is a display. Hereinafter, the operation of the propagation delay measuring apparatus of the present embodiment when the apparatus is mounted on an automobile to perform measurement will be described.

While traveling on a plurality of radio waves of different frequencies transmitted from one transmission antenna, the radio waves are received by one reception antenna 1 and the reception level for each frequency is measured by an electric field strength measuring device 3. The frequency to be measured can be set by key input, and the frequency and its reception level are displayed. The A / D converter 5 samples the analog reception level at regular intervals to obtain digital data. In order to perform sampling at regular intervals, a vehicle speed measuring device 4 that generates pulses at regular intervals is used.

From the sampled data, the influence of shadowing (the reception level fluctuates periodically (several hundred m periods) due to the influence of a shadow of a building or the like) is removed. The method uses a shadowing remover 6 to move data over a certain distance (for example, 1
m) and subtract from the original data. Alternatively, a high-pass filter (H
PF) may be added. Among the frequencies measured by the correlation coefficient calculator 7, the cross-correlation coefficient of the reception level is obtained for all combinations of two frequencies.

The frequency correlation function ROM 8 stores frequency correlation functions obtained from a plurality of function profiles of delay profiles assumed in advance. The frequency correlation function uses delay spread as a parameter. The delay spread calculator 9 obtains, for each frequency correlation function, a delay spread that minimizes the standard deviation of the error between the data obtained with the respective frequency correlation functions stored in correspondence with the function types of the respective delay profiles. The delay spread with the smallest error among the delay spreads with the smallest error obtained for each frequency correlation function is defined as the delay spread at that point. The display 10 displays the delay spread.

FIG. 2 is a diagram for explaining an example of measurement by the propagation delay measuring apparatus according to the present invention, in which 11 is a base station station, 12 is a transmitting antenna, 13 is a duplexer, and 14-1 to 14-1.
4-3 transmitter 15 measuring wheel, 16 is propagation delay measurement unit, 17-1 and 17-2 represents the building, _{also, f 1, f 2, f} 3 each represent a transmission frequency ing. Hereinafter, description will be made with reference to FIG.

A plurality of frequencies (f ₁ , f ₂ , f ₃ ) transmitted by the transmitter 14 of the base station are set such that the frequency difference Δf between them becomes approximately 1 / (2πS) (MHz) (S ( μs) is the assumed delay spread.) For example, if the assumed delay spread is 2 μs, the frequency difference is set to about 80 kHz. Transmitter 14-1
14-3 are combined by the duplexer 13 and transmitted by the transmission antenna 12. The transmitted radio waves are reflected on the buildings 17-1 and 17-2 and the like, causing a propagation delay. While traveling on the measuring vehicle 15, the radio wave from the base station is received. FIG. 3 shows the reception level and the trigger pulse. A in FIG. 3 indicates a reception level of each frequency, and P indicates a trigger pulse that is output at every fixed traveling distance in conjunction with a vehicle speed measurement device.

A reception level is sampled by an A / D converter based on a trigger pulse of a vehicle speed measuring device, and shadowing (short section fluctuation) is removed by a shadowing remover. A correlation coefficient calculator calculates a correlation coefficient for each frequency difference. FIG. 4 is a diagram showing the relationship between the frequency difference and the measured correlation coefficient, and the crosses indicate the measured values. The type of the frequency correlation function corresponding to the assumed delay profile is stored in the frequency correlation function ROM. FIG. 5 shows an example of the assumed delay profile. The vertical axis is dB
21 is a square wave, 22 is a triangular wave, 23 is an exponential wave (EXP (t) type), and 24 is an exponential square wave (EXP (t
² ) Type).

The delay spread calculator obtains the type of the frequency correlation function and the value of the delay spread that best match the frequency correlation value obtained from the above based on the type of the frequency correlation function. FIG. 6 shows the correspondence between the type of the frequency correlation function and the measured frequency correlation value. In the figure, 31 is the frequency correlation value obtained by the measurement, 32 'and 32 "are the frequency correlation functions of the exponential wave in the delay profile. When the delay spread is 1 and 2 μs, respectively, 33' and 33" are the same square. In the case of waves, the delay spread is 1,2 μs each
Is the case.

Although the frequency correlation function shown in FIG. 1 is only for the exponential wave and the square wave, other types of the frequency correlation function are similarly considered. As described above, for each type of the frequency correlation function, the value of the delay spread is changed, the measured frequency correlation value is compared, and the frequency correlation function and the delay spread that best match are determined. It is estimated that the value of the delay spread is the delay spread of the measurement system.
In the example shown in the figure, the best match is obtained when the delay spread is 2 μs in the frequency correlation function in the case of the delay profile of a square wave. From this, the delay spread is estimated to be 2 μs.

[0019]

According to the conventional delay spread estimation, the estimation error is minimum when the delay profile is an exponential function, and the estimation error increases when the delay profile deviates from the exponential function. Since it is configured to cope with this by having a function, there is an advantage that the estimation error does not increase even if the delay profile deviates from the exponential function.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of measurement by a propagation delay measuring device according to the present invention.

FIG. 3 is a diagram illustrating a state of a reception level and a trigger pulse.

FIG. 4 is a diagram illustrating a relationship between a frequency difference and a measured correlation coefficient.

FIG. 5 is a diagram illustrating an example of an assumed delay profile.

FIG. 6 is a diagram illustrating a correspondence between a type of a frequency correlation function and a measured frequency correlation value.

FIG. 7 is a diagram illustrating a relationship between a delay profile and a frequency correlation function.

FIG. 8 is a diagram illustrating a propagation delay and a delay profile.

FIG. 9 is a diagram illustrating a frequency correlation function.

[Description of Signs] 1 Receiving antenna 2 Duplexer 3 Electric field strength measuring device 4 Vehicle speed measuring device 5 A / D converter 6 Shadowing remover 7 Correlation coefficient calculator 8 Frequency correlation function ROM 9 Delay spread calculator 10 Display 11 Base station building 12 Transmitting antenna 13 Duplexer 14-1 to 14-3 Transmitter 15 Measurement vehicle 16 Propagation delay measuring device 17-1, 17-2 Building 21 Square wave 22 Triangular wave 23 Exponential wave 24 Exponential square wave 31 Frequency correlation value obtained by measurement 32 ', 32 "Frequency correlation function when delay profile is exponential wave 33', 33" Frequency correlation function when delay profile is square wave

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G01R 29/00 G01R 29/08 H04B 17/00

Claims (1)

(57) [Claims] 1. An apparatus for measuring propagation delay using reception level correlation of a plurality of frequency radio waves in wireless communication, wherein the correlation stores a type of a frequency correlation function obtained in advance corresponding to a plurality of types of delay profiles. A function storage function, a correlation detection function for obtaining a correlation coefficient of a reception level of a received multi-frequency radio wave, and a reception level phase obtained by measurement by changing a delay spread value for each of the types of the frequency correlation function. An apparatus for measuring propagation delay in wireless communication, comprising: a type of a frequency correlation function that best matches a relationship between a relationship number and a frequency difference thereof; and a delay spread calculation function for calculating a delay spread value.