JPH03210830A - Directivity diversity receiver - Google Patents

Abstract

PURPOSE:To reduce the switching frequency of an antenna by providing a means identifying an antenna corresponding to the direction of a broadcast station to an on-vehicle directivity diversity receiver and weighting a signal of the identified directivity antenna. CONSTITUTION:Directivity antennas 1 mounted to a vehicle is arranged so as to cover all directions of 360 deg. with a same half-width ([360/n]). The radio wave received by the antennas is branched into two systems and inputted to changeover switches 2, 3 respectively. The changeover Switch 2 applies switching at all times and a detection section 4 detects an reception signal of each antenna and a 1st microcomputer 5 monitors the level of each reception signal. An antenna reception signal whose level is maximum among monitored signals is selected and a control signal corresponding to the antenna reception signal is given from the 1st microcomputer 5 to the changeover switch 3 to control the other changeover switch 3 and an antenna reception signal of a maximum level is inputted to a receiver 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in directional diversity receiving devices.

[Summary of the Invention] In a directional diversity receiving device for a vehicle, a means for identifying an antenna corresponding to the direction of a broadcasting station is provided, and by weighting the identified directional antenna,
This is designed to reduce the frequency of antenna switching.

[Prior Art] In mobile reception, as the reception point moves, severe fading occurs due to interference of multiple waves arriving from various directions.
Significantly deteriorates communication quality. As a measure to reduce such fading, space.

Diversity in frequency, directivity, etc. is well known.

Among these, directional diversity uses a directional antenna to separate and receive multiple waves that arrive in large numbers, so it is possible to significantly reduce interference caused by multiple waves, and is considered to have a large fading reduction effect.

[Problems to be Solved by the Invention] However, in the case of directional diversity reception in urban areas, as shown in FIG. 6, it largely depends on the angle between the direction of incidence of radio waves and the direction of the road (road angle θ).

It is known that the propagation state of radio waves is approximated by the road angle as follows.

(i) When the road angle θ is small (the radio wave incident direction and the road direction are nearly parallel), it is approximated by the geometric optics model shown in FIG. 7(a).

Close to the 2-wave model.

(fi) When the road angle θ is large (the radio wave incident direction and the road direction are close to perpendicular), the random model shown in Figure 7(b) (many waves with equal amplitude and random phase are generated from all directions in the horizontal plane) It is approximated by a statistical model that arrives with different probabilities.

In case (i), reception using a directional antenna enables separate reception of multiple waves, and the effect of reducing fading is greater than reception using an omnidirectional antenna.

When radio waves arrive from the → direction in Figure 8, if the radio waves are received by antennas with directivity A and B at the reception point, interference will occur because antenna B will receive two waves.
Since the A antenna receives only one wave, fading does not occur (the omnidirectional antenna receives three waves at the same time, so the degradation is greater than when receiving with the B antenna).

In the case of (5), since the radio waves arrive uniformly from within the horizontal plane, the combined output of the multiplexed waves received by the directional antenna also has a Rayleigh distribution over a long period where fading can be considered statistically stationary. Put it away.

As shown in Figure 9, if multiplex waves arrive uniformly at each antenna, the same F21 song will occur for each antenna.
It is thought that the correlation between antennas becomes large, and even if switching is performed using directional diversity, it is difficult to obtain the effect.

The effect of directional diversity can be improved by sharpening the directivity of each antenna and increasing the number of branches, but this also increases the frequency of switching, so it is also necessary to consider the effect of distortion caused by switching. be.

[Object of the Invention] An object of the present invention is to obtain a stable reception state in response to the propagation state that changes depending on the road angle in mobile reception.
Another object of the present invention is to provide a directional diversity reception system that minimizes diversity switching frequency.

[Means for Solving the Problems] In order to achieve the above object, the diversity receiving device of the present invention uses a plurality of antennas having directivity in different directions centering on the vehicle, and a desired level of output from the output of the antennas. an antenna selection means for selectively selecting an antenna output and supplying the antenna output to the receiver; a means for identifying an antenna corresponding to the direction of the broadcasting station based on vehicle traveling direction data and received broadcasting station position data; The gist of the present invention is to have a weighting means for weighting the directionality of the identified antenna.

[Effect Once the antenna corresponding to the direction of the broadcast station is identified, weighting is performed for the identified antenna. As a result, directional diversity switching is reduced.

[Examples] The present invention will be described below with reference to examples shown in the drawings. FIG. 1 shows an embodiment of a directional diversity receiver according to the present invention. In the figure, 1 is a plurality of directional antennas provided on the vehicle, 2 and 3 are first and second antenna changeover switches, 4 is a received signal detection section, 5 is a first microcomputer, and 6 is a receiver. , 7 is a second computer, 8 is a navigation system, 9 is a memory such as a CD-ROM, 10 is a weighting circuit, and 11 is an addition circuit.

In FIG. 1, 1 to 6 constitute directional diversity. The directional antennas 1 attached to the vehicle have the same half-width ([360/n]") and are arranged so as to cover all directions of 360°. The radio waves received by these antennas are divided into two systems. The signals are branched and input to changeover switches 2 and 3, respectively.

The changeover switch 2 is always switched, the detection unit 4 detects the reception signal of each antenna, and the first microcomputer 5 monitors the level of each reception signal. An antenna reception signal is selected, and a control signal corresponding to the antenna reception signal is given from the first microcomputer 5 to the changeover switch 3, thereby controlling the other changeover switch 3. The level antenna reception signal is input. By configuring such a system, the reception levels of multiple antennas are constantly monitored and the antenna with the highest level is selected, so only one receiver is required.

10 and 11 are flowcharts of the operation of the first microcomputer 5, respectively. FIG. 10 shows the operation when the changeover switch 2 sequentially compares each antenna reception signal to determine the maximum level R0, and then the switch 3 selects the antenna reception signal at this reception level.

In FIG. 11, the antenna reception signals R1 to Rn of the switch 2 are sequentially stored in the RAM in the microcomputer 5, and then these signals R to Rn are read out and compared, and the antenna with the highest level is selected by the switch 3. The behavior in this case is shown below.

On the other hand, the second microcomputer 7 stores information on the broadcast station selected by the receiver 6, the current position and traveling direction of the vehicle obtained from the navigation system 8, and position information on the broadcast station inputted in advance into the memory 9. is input. The second microcomputer 7 collates these data and detects what direction (angle) the vehicle is currently running with respect to the broadcasting station direction (radio wave emission direction).

Based on this detection result, the weighting circuit 10 weights the directional antennas facing the broadcasting station direction (radio wave emission direction).For example, as shown in FIG. If the direction of the transmitting station is found as shown in FIG. 3(b), weighting W is applied to the antenna having directivity in that direction according to a command from the second microcomputer.

FIG. 12 shows a flowchart of the operation of the second microcomputer 7. As is clear from FIG. 12 and FIG.
The traveling direction θ□ of the vehicle is calculated from wV□′), the direction θ2 is calculated from the position of the broadcasting station (Xat y2), and the road angle θ=02-01 is detected. Whether this θ is positive or negative, the first
As shown in Figure 4, it can be determined whether the broadcasting station is on the right or left side of the vehicle with respect to the direction of travel of the vehicle.

When the road angle θ is small (the direction of radio wave incidence and the direction of the road are nearly parallel), line-of-sight propagation occurs between the transmitting station and the receiving point, and direct waves become dominant.

Therefore, if weighting is applied to antennas having directivity in the direction of the transmitting station (the direction in which direct waves arrive), it is sufficient to receive radio waves from that direction, thereby almost eliminating the need for switching directional diversity.

When the road angle is large (the direction of radio wave incidence and the road direction are close to perpendicular), the frequency of switching due to directional diversity increases because radio waves are incident from various directions as shown in the random model in Figure 8. It's coming. However, even in this case, if weighting is applied to antennas having directivity in the direction of the transmitting station, direct waves will be received preferentially. If a situation arises in which direct waves are completely blocked, another antenna is selected, so the frequency of switching can be reduced and stable reception conditions can be obtained.

As shown in FIG. 3, a specific method of weighting is to turn on any of the weighting selection switches SW1 to SW ports according to a command from the second microcomputer 7 to select the output of the weighting circuit 10. It adds weight to the antenna output.

Other antenna weighting methods include the following.

(i) As a simple method, when the antenna 11 having directivity in the direction of the broadcasting station is selected as shown in FIG.
In response to a command from the microcomputer 7, the corresponding switch SW1 is turned on to drive the antenna telescoping motor M to raise the antenna one step higher than the other antennas.

(it) The directivity of an antenna that has directivity in the direction of the broadcasting station may be sharpened.By sharpening the directivity,
The antenna gain increases and unnecessary radio waves are also prevented from entering.

(iii) As shown in FIG. 5(a), in addition to the original directional diversity antenna 1, a variable directional antenna 1' (the direction of which can be changed) is used.

Radio waves from a broadcasting station are received by the microcomputer 7 using both the directional antenna 1 selected and the variable directional antenna 1' whose directivity is changed in the direction of the broadcasting station, and their reception outputs are combined. Then, as shown in figure (b), the directional characteristic shown in figure (c), which is a combination of the directional characteristics of antenna 1 and antenna 1', is obtained, so the gain can be increased compared to the antenna in the other direction. I can do it. As described above, since the weighting circuit 10 is for increasing the gain of the directional antenna in one direction, the above-mentioned (i) to (
If a weighting method such as ni) is used, there is no need to use a particular weighting circuit.

[Effects of the Invention] As explained above, according to the present invention, by weighting the directional antenna in the direction of the detected road angle, directional diversity can be achieved even in a radio wave environment where many reflected waves arrive. This reduces the frequency of switching, provides a diversity effect, and enables stable mobile reception.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention. FIG. 2 is an explanatory diagram of weighting of directional antennas, FIG. 3 is a diagram showing one specific example of the weighting method, FIGS. 4 and 5 are diagrams each showing other specific examples of the weighting method, Figure 6 is an explanatory diagram of road angles, Figure 7 is a diagram of a radio wave propagation model on an urban road, Figure 8 is an explanatory diagram of multiple wave separation reception of a directional antenna in a geometric optics model, and Figure 9 is a random diagram. Explanatory diagram of multiple wave separation reception of directional antenna in model, 10th
11 and 11 are flowcharts showing the operation of the first microcomputer, FIG. 12 is a flowchart showing the operation of the second microcomputer, and FIGS. 13 and 14 are explanatory diagrams of the road angle calculation method, respectively. It is. 1... Directional antenna, 2, 3...
・・・・・・Antenna selection switch, 4・・・・・・・・・
- Received signal detection section, 50. . ...First microcomputer, 6 old...
...Receiver, 7...Second microcomputer, 8...Navigation system, 1o old...Weighting circuit, SW, ~ SW
n......Switch.

Claims (1)

[Scope of Claims] A plurality of antennas having directivity in different directions centering on the vehicle; and antenna selection means for selectively selecting an antenna output of a desired level from among the outputs of the antennas and supplying the antenna output to a receiver; means for identifying an antenna corresponding to the direction of a broadcasting station based on vehicle traveling direction data and received broadcasting station position data; and weighting means for weighting the antennas identified by the identification means according to their directivity. A directional diversity receiving device comprising: