JPS63318825A - Diversity reception system - Google Patents

Abstract

PURPOSE:To reduce the attenuate fading as well as the interferential fading by using an antenna device to produce two beams directed to the direct wave arriving direction and the regular reflected wave arriving direction respectively. CONSTITUTION:A multi-beam antenna 15 has two feeds 13 and 14 in response to the beams 11 and 12 directed to the direct wave arriving direction and the regular reflected wave arriving direction respectively. The outputs of both feeds 13 and 14 are received by a diversity device 16 after synthesization or switching. Thus it is possible to perform the diversity reception between the reception signals of both beams 11 and 12 so that the regular reflected wave is received in case the reception of the direct wave is impossible due to the generation of the attenuant fading. Thus the attenuate fading is improved by the beam 12 directed to the regular reflected wave direction.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a diversity reception system that reduces attenuated fading caused by radio ducts.

``Prior art'' In a propagation path where regular reflected waves from the ground surface are constantly received, fluctuations in the received signal due to interference between direct waves and regular reflected waves, and coherent fading occur frequently, making it difficult to evaluate the line quality. Two major influences. Therefore, in such a propagation path, the third
As shown in the figure 1: A narrow beam reception method that directs the narrow beam to the direct wave, B beam tilt reception method that tilts the beam angle to the direct wave, C main beam direct wave, the direction in which the directivity drops is positive, Interferometric fading is reduced by a reception method that prevents regular reflected waves in the normal reflection direction, a D space diversity reception method, etc.

Here, A is by sharpening the antenna directivity, and B is by tilting the main beam direction of the antenna upward.
D is a reception method that suppresses the strength of the regular reflected wave by creating a point (null point) where the directivity gain becomes small in the arrival direction of the regular reflected wave, and D is a reception method where the interference condition between the direct wave and the regular reflected wave is at the receiving point. This method takes advantage of the difference in the height direction of the antenna and performs divernch reception by installing two antennas separated by a half hit of the interference pattern (hide pattern) in the vertical direction of the reception point.

On the other hand, in the line-of-sight autobiographical channel, direct waves undergo abnormal refraction and propagation when generated in the radio duct, resulting in a phenomenon (attenuated fading) in which the received signal hardly reaches the receiving point and the received signal decreases. In this case, since no direct waves arrive, the above-mentioned coherent fading does not occur. In the above-mentioned receiving method (three types of normal reflected wave suppression reception methods) that suppress the directivity gain in the arrival direction of the normal reflected wave, the direct wave level decreases and the normal reflected wave is suppressed due to the antenna directivity ≦2. The reception level of both radio waves drops significantly, making it impossible to reduce this attenuated fading.

Figure 4 shows an example of fading recorded on a maritime line-of-sight channel where regular reflected waves are regularly received, where A is reception by a normal direct wave direction antenna ζ that does not particularly suppress regular reflected waves, and B is recorded by normal reflected wave suppression reception. A from this figure.

It can be seen that there is a time when the reception level decreases in both cases B, and fading cannot be sufficiently improved by the normal reflected wave suppression reception method alone. That is, the conventional normal reflected wave suppression reception system has the drawback that it cannot improve attenuated fading. Furthermore, the space diverter reception system shown in Figure 3 requires two antennas that are relatively large and capable of a certain distance in the vertical direction, which has the disadvantage of increasing the cost of tower and antenna installation work.

The purpose of this invention is to use one antenna device or two antenna devices installed adjacent to each other to improve not only interference fading but also deterioration in line quality due to attenuated fading, which is a drawback of conventional normal reflected wave suppression reception systems. An object of the present invention is to provide a diversity reception method that can provide a reception method more economically than a space diversity reception method.

[Means for Solving the Problems] According to the present invention, two beams oriented respectively in the direction of arrival of a direct wave and the direction of arrival of a regular reflected wave are generated by one antenna device or two adjacent antenna devices. , the received signals from these two beams are switched or combined to perform diversity reception.

The reduction in the direct wave reception level due to attenuated fading, which was impossible with the conventional normal reflected wave suppression reception method, can be achieved by using a unique technique that occurs when a radio duct occurs, in which the normal reflected wave rarely undergoes attenuated fading at the same time as the direct wave. Using the propagation characteristics, receiving the regular reflected wave with the regular reflected wave directional beam is reduced from ≦2.

FIG. 5 is an example of a radio wave path when a radio duct is generated based on the ray tracing method. The radio duct was assumed to be something like the one shown in section 2 on the left in the same figure. The altitude of the transmitting antenna is 25
0m and shows the paths of radio waves when transmitted at various angles. Without a duct, the transmitted radio waves would travel straight, but with a duct, they would curve. Therefore, as shown by diagonal lines, there is a region where the waves cannot directly reach. Also, the radio waves transmitted from the antenna downwards are reflected by the ground. A line bent at a height of 0 indicates this reflected wave. This reflected wave reaches even in the above-mentioned area where the transmitted wave does not reach. For example, in the diagonally shaded area including the reception point R, direct waves are diverged by the radio duct and attenuated fading occurs, but regular reflected waves from the ground surface have arrived. That is, in this invention, when attenuated fading occurs and the direct wave cannot be received, by performing diversity reception between the received signals of the direct wave directional beam and the normal reflected wave directional beam, so that the normal reflected wave is received. , coherence) aging is improved by a direct wave directed beam receive signal, while attenuated fading is improved by a regular reflected wave directed beam. Figure 4C (
An example of recording the received signal level using a regular reflected wave directional antenna during Nira aging is shown. It can be seen that attenuated fading, which cannot be improved with the normal reflected wave suppression reception method, is improved by normal reflected wave directional antenna reception (;

"Example" An example of the present invention is shown in FIG. A multi-beam antenna 15 is provided which has two feeds 13 and 14 corresponding to a beam 11 directed in the direction of arrival of the direct wave and a beam 12 directed in the direction of arrival of the regular reflected wave, and the two feeds of the multi-beam antenna 15 are The outputs from 13 and 14 are combined or switched and received by diversity device 16.

FIG. 2 shows another embodiment of the present invention, in which 18 antennas with the main beam 17 facing the direction of direct wave arrival, and the main beam 19
An antenna 21 is provided adjacent to the antenna 21, which is directed toward the arrival direction of the regular reflected wave. The outputs of these antennas 18 and 21 are combined or switched and received by the diversity device 16.

"Effects of the Invention" As explained above, this invention, which performs diversity reception between the received signals of the direct wave directional beam and the regular reflected wave directional beam This has the advantage that not only interferential fading but also attenuated fading can be reduced in a line-of-sight autobiographical channel to provide a stable wireless communication line. In addition, compared to the conventional space diverter method, which requires two vertically spaced antennas, this invention makes it possible to confirm the antenna installation position, and to make installation work and tower construction more economical. has great advantages.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing another embodiment of the invention. A diagram showing the relationship between the antenna beam and the arrival angle of radio waves in C regular reflected wave prevention reception method and D space diversity reception method,
Fig. 4 shows an example of fading recording showing the effectiveness of this invention, where A is reception by a normal direct wave direction antenna;
B shows the signal level of regular reflected wave suppression reception, C shows the signal level of regular reflected wave directional antenna reception, and Figure 5 shows the physical basis of this invention, and shows the occurrence of attenuated fading in radio ducts. This is a factor that indicates the arrival status of regular reflected waves.

Claims (1)

[Claims] (1) In a propagation path where there is line-of-sight between the transmitting and receiving points and where not only direct waves but also regular reflected waves from the ground surface are regularly received, a beam directed in the direction in which the direct waves arrive and the regular reflected waves arrive. Diversity reception characterized by using one antenna device having two beams oriented in the same direction or two antenna devices installed adjacently each having one beam of each of the above, and switching or combining received signals from these two beams. method.