JPS5846892B2 - Mobile radio reception system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a radio reception method for mobile radio communication. In mobile radio communication, deterioration of communication quality due to fading caused by interference of multipath waves has become a major problem.

In order to reduce this fading, various diversity reception methods have been considered that utilize diversity effects due to differences in space, frequency, polarization, directivity, etc.

These methods use multiple diversity models with low correlation.
This attempts to reduce the decrease in received signal strength by switching or combining the received outputs of the channels and extracting the received outputs.

By the way, the frequency of fading due to multipath wave interference is proportional to the moving speed of the moving object and the frequency of the radio wave, so
When both of these are large, extremely fast cycle fading occurs.

For example, if the moving speed of a moving body is 60 km/h and the frequency of radio waves is I GHz, the frequency of fading can reach as high as 100 Hz.

If switching diversity reception is performed in such a state, the frequency of occurrence of noise due to diversity channel switching becomes extremely high, resulting in a significant deterioration of communication quality in terms of S/N.

On the other hand, combined diversity reception generally involves multiple receiving systems (
Because it requires a receiver (receiver) and is expensive, it is not normally used in mobile radio communications where economic efficiency is extremely important.

Furthermore, although it is possible to reduce the decline in received signal strength with these conventional fidelity reception methods as described above, when the facing frequency becomes high and cannot be ignored relative to the modulation signal frequency of the received radio waves, the reception Due to rapid changes in amplitude and phase due to fading of radio waves, analog modulation methods such as FM and PM cause distortion and noise in the information signal, and digital modulation methods such as FSK and PSK cause code errors. cause it to occur.

Among the effects of fading, deterioration in communication quality due to a decrease in S/N can be prevented by increasing transmit power and antenna gain, but deterioration in reception quality due to phase changes in received radio waves cannot be compensated in principle. be.

Furthermore, in mobile communications, many reflected waves arrive from surrounding objects, but these multipath waves are waves that are delayed in time.
In some cases, it may have a delay time of several μs or more.

When such delayed waves interfere, the frequency characteristics of the signal are not uniform within the reception band, resulting in so-called frequency selectivity.

Now when two waves of equal strength are received with delay time τ,
The received signal changes sinusoidally with a period of 1 relative to the frequency.

For example, if τ-1 μS (delay path length is 300 m), this period is IMHz.

At this time, in broadband communication where the frequency band of the signal wave cannot be ignored compared to this period, the signal is distorted and the communication quality is degraded, which limits the signal band.

It is expected that broadband communications such as image communications and high-speed digital communications will be required in mobile communications in the future, but delayed multiplex waves will prevent this from becoming a reality.

In this way, conventional diversity reception methods have problems in their effectiveness against fast-cycle fading, and delayed multipath waves limit the information signal bandwidth or bit rate. The drawback is that it is difficult to cope with the increase in frequencies and wider bands used in mobile radio communications.

This invention has been made in view of the above points, and even when the moving speed of a moving object is fast and the frequency of received radio waves is high, it effectively reduces fading caused by multipath wave interference and its effects. The purpose of the present invention is to provide a mobile radio reception system that can perform high-quality reception even for wideband signals.

The mobile radio reception system according to the present invention prepares three or more directional antennas that have directivity within a limited angular range in a horizontal plane, and forms a directional pattern in each of these antennas in different directions to form a directional pattern as a whole. is characterized in that it is arranged so as to be non-directional and performs switching diversity reception.

Hereinafter, this invention will be explained in detail with reference to Examples.

FIG. 1 is a block diagram of a receiving system showing an embodiment in which the present invention is applied to switching diversity reception with a threshold value.

In this example, 1 to 3 are so-called fan-shaped directional antennas that have directivity within an angular range of 120° in the horizontal plane, and these antennas 1 to 3 are antennas that are oriented in different directions on the same plane as shown in Figure 2. Directional patterns 10 to 30 are formed and arranged so as to have an almost circular non-directional pattern as a whole.

In other words, the directivity center axis of the directivity patterns 10 to 30 is set to A-
C, antennas 1 to 3 are arranged so that the angles formed by A and B, B, C1, and A are 120 degrees.

Each output of the antennas 1 to 3 is selectively taken out by a switching circuit 4 and inputted to a receiver 5, from which a received output is obtained.

A part of this received output is applied to the control signal generation circuit 6.

This circuit 6 determines the received output level (received signal strength) of the receiver 5 using a predetermined threshold, and controls the switching circuit 4 based on this.

For example, when the output of the antenna 1 is currently selected by the switching circuit 4 and is being received by the antenna 1, if the reception output level drops below the threshold value, this is detected by the control signal generation circuit 6 and the switching circuit 4 A predetermined control signal is applied to the switching circuit 4, and the switching circuit 4 is switched to select the output of the antenna 2.

Here, antennas 1 to 3 form directional patterns in different directions as described above, and the correlation between their respective outputs is extremely small due to the directional diversity effect, but even when the output of antenna 2 is selected, it happens that the received output If the level is below the threshold, the switching circuit 4 is further switched to select the output of the antenna 3 by a similar operation.

Since the probability that all received output levels will be below the threshold value when any of the outputs of antennas 1 to 3 is selected is extremely small, fading can be effectively reduced by the above operation.

At first glance, the above configuration seems similar to the conventional directional diversity reception system, but it has characteristics in terms of the directional pattern of antennas 1 to 3 and its arrangement method, and accordingly, it is similar to the conventional directional diversity reception system. It exhibits a significantly different effect from that of conventional methods, and has the great effect of eliminating fast fading, extending the fading period, and widening the transmission band, which was difficult to do in the past.

Note that extending the fading period has the effect of reducing the number of antenna switching times and reducing the amount of noise during switching.

These effects will be explained in detail below.

Now, as shown in FIG. 3, n multipath waves arriving at a moving body P traveling in the direction of arrow X are called El.

E2 j...En, and the respective arrival angles are ψ1, φ2,...ψ with respect to the X direction.

Then, complicated fading occurs due to the interference of these multipath waves.

Any two waves Ei among these n multipath waves,
The fading period Tij caused by Ej (1tJ=1t2t'''n, where i\j) is where λ is the wavelength of the received radio wave.

Tij is Ei. Taking various values depending on the combination of Ej,
The fading that actually occurs is a combination of these various periods.

In equation (1), l cos ψ1-CO3 φi≦2, so T...≧Z.

In other words, any Hue3 2 one Jifugu period is greater than or equal to λ/2, and the two waves EitEj
When arriving from the moving direction X of the moving body P and the opposite direction (when ψ1=00, ψ·=1800), the fading period Tij4 is set to the minimum value λ/2.

In urban areas, where fading is the biggest problem in mobile radio communications, the direction of arrival of the main multipath waves is determined by the geometrical optical mode determined by the placement of buildings, that is, the diffracted and reflected waves of the buildings, and the propagation of various multipath waves It is known that the characteristics can be clearly explained by this propagation model.

Now, consider a road as shown in FIG. 4 (diagonal lines indicate buildings) as an example of a city area, and let θ be the angle of the radio wave arrival direction y with respect to the traveling direction X of the moving body P.

If the main radio waves are the diffracted wave ■ and the diffracted reflected waves ■ and ■, then from equation (1), the fading period of the wave caused by ■ becomes T1□ = (1), and the wave ■.

■Fading does not occur due to waves, fading is caused by waves,
It is created by ■, ■, and ■, and its period is .

In other words, the fading period depends on θ, and when the moving direction of the moving object P matches the arrival direction of the radio wave (θ=0°),
The minimum value is ln when T = λ/2, and Tm (1) when θ = 900.

Figure 5 shows the results of actually measuring the fading period T for various values of θ in an urban area, with θ on the horizontal axis and T/λ on the vertical axis. 2) It agrees well with the theoretical value calculated by formula.

When θ>60°, the measured values vary due to the influence of waves outside the main wave order, and even when θ=90°, they do not become unreliable, but it is clear from the figure that as θ increases, the fading period tends to lengthen. , demonstrating the validity of the predicted propagation model.

Now, if we consider the case where reception is performed using an antenna with a fan-shaped directivity pattern shown by the dotted line in Fig. 4, this antenna receives waves (2) and (2), but depending on the waves (2) and (3), fading may occur as described above. Since the wave (2) that causes fading is not received, the fading caused by the interference of these waves (1) to (2) is removed.

Based on the above, let's consider the effects of this embodiment.

First, when the radio wave arrival direction is O20<600, the fourth
Fading disappears by selecting the output of antenna 3 as described in the example of the figure.

On the other hand, considering the case of 60'≦θ≦90°, the fading period is minimum when θ=600, that is, when the direction of arrival of the radio wave is indicated by ■ in FIG.

At this time, the fading period Tab caused by the radio waves arriving from the ■ direction interfering with the reflected waves of ■ coming from the ■ direction
is Tab, = λ from θ-60°, and Tm1n (
-λ/2).

In other words, if the directivity and arrangement of antennas 1 to 3 are selected as explained in Fig. 2, the fading period will be one wavelength or more of the received radio wave no matter how the arrival direction of the radio wave changes. When the direction of arrival is within the directivity pattern of the antenna 3 located behind the moving direction X of the moving body P, no fading occurs at all.

On the other hand, when reception is performed using an omnidirectional antenna commonly used in mobile radio communication, fading always occurs, and moreover, when θ is less than approximately 30', fading almost always occurs with λ
Very fast fading with a period close to /2 will occur.

That is, according to this embodiment, when it is assumed that the angle between the direction of arrival of the radio wave and the direction of movement of the moving object changes randomly, fading with a fast period is removed with a probability of 1/3, and fading with a fast period is removed with a probability of 1/3, and fading with a fast period is removed with a probability of 1/3. Even if fading is not eliminated by probability, the fading period will be extended to one wavelength or more of the radio wave, and reception with less fading or its influence can be performed.

Moreover, what should be noted here is that these effects can be achieved without performing diversity reception.
The effect of reducing fading due to diversity reception is synergistically exhibited.

By the way, according to the present invention, the combination of three or more directional antennas has the following advantages compared to the combination of two directional antennas.

That is, as shown in FIG.
, 2', when a radio wave arrives in the two directions ■ and ■ of 1800, there is a risk that even if it is received by either antenna 1' or 2', the two types of waves will cancel each other out and reception will not be possible. .

On the other hand, if, for example, three directional antennas 1 to 3 are arranged as in this embodiment, as shown in FIG.

Even if radio waves arrive simultaneously in the direction (2), normal reception can be achieved by selecting and extracting one output from either antenna 1 or 2.

The present invention is also effective as described below even when the multipath waves do not follow the geometrical optical path as shown in FIG. 4, but arrive as scattered waves from telephone poles or irregular structures.

Generally, consider the case where two waves Ei and Ej arrive as shown in FIG.

If the angle formed by the arrival directions of these two waves Ei and Ej is Φ, and the angle formed by the traveling direction X of the moving body P with respect to the direction perpendicular to the bisector thereof is O, the fading The period Tij is given by.

On the other hand, the minimum fading period T... is obtained when Q=O, so it becomes Jmln, and when Φ=O, the period is ■, and when Φ-π/2, it takes the minimum value of λ/2.

Therefore, if a fan-shaped directional antenna with directivity within the angular range Φ is used, the direction of arrival of the multipath wave and the moving object ρ
Regardless of the direction of travel, the minimum period of fading that can occur is given by equation (4).

For example, as in this embodiment, the directivity of antennas 1 to 3 is 12.
If it is within the angle range of 0°, use formula (4) to calculate Φ120°.
Then, T...in=λX/end.

That is, even in the minimum case, the fading period is extended to 2/vf\ compared to an omnidirectional antenna.

Generally, 360'/! is divided into n parts in the horizontal plane. If n directional antennas, each with a directivity within an angle range of 1, are arranged so as to have no directivity as a whole, it is easy to see that as n increases, the effect of extending the minimum period of fading increases. can be understood.

Furthermore, in this case as well, fading disappears depending on the direction of arrival of the multipath wave, as in the case of diffraction and reflection from a building.

Furthermore, by using such a directional antenna, the number of multipath waves to be received can be reduced and the transmission band can be expanded.

That is, since only one wave is received when the fading mentioned above disappears, there is no frequency selectivity and a significantly wide band transmission is possible.

Even when fading does not disappear, waves with a large delay time usually arrive only from a certain direction, so the probability of receiving both a wave with a large delay time and a wave with a small delay time at the same time is low, resulting in frequency selectivity. The probability is significantly reduced, allowing broadband transmission.

The thin and thick lines in Figure 9 show actual measurement examples of fading when mobile radio reception is performed using an omnidirectional antenna and a directional antenna, respectively. Measure the signal strength.

The measurement conditions in this case are that the angle between the direction of arrival of the received radio wave and the moving direction of the moving object is θ-18°, the frequency of the received radio wave is f = 200 MHz, and the directional antenna has a half-value angle of the directional pattern Φ ( directional angle range) =
A 65° angle was used, and the maximum gain direction was placed in the direction opposite to the moving direction of the moving body.

As is clear from this figure, the fast and intense fading with a period of about 1/2 wavelength observed when receiving with an omnidirectional antenna almost disappears when receiving with a directional antenna, and Only long fading is observed.

Although not particularly shown, θ=90° (θ−72
) When we similarly measured the fading in the case of It was observed that an elongation effect approximately twice that of that of the previous one was obtained.

Although this experiment demonstrated the effect of eliminating or reducing fading and the effect of extending the fading period by using a single directional antenna, the effect of directional diversity reception itself using multiple antennas has already been clarified. It is clear that by performing diversity reception using a directional antenna, extremely better reception can be achieved compared to conventional directional diversity reception.

In addition, although three directional antennas were used in the above example,
As shown in FIGS. 10a and 10b, four, five or more directional antennas may be arranged in the same way, and as the number increases, fading disappears, is reduced, and the fading period is extended. Broadband bandwidth will improve.

In addition, in Figures 2 and 10, it was assumed that each directivity had a perfect fan-shaped directivity, but in reality, such directivity is difficult to achieve, and a part of the directivity pattern is shown by the dotted line. will overlap.

However, even in that case, the effects mentioned above will not be lost,
It is clear from the previous experimental examples that even actual directional antennas have sufficient effects.

Furthermore, the directivity of the directional antenna used in this invention can be easily achieved using known antenna structures and electrical directivity synthesis techniques, and especially in high frequency bands where aperture antennas can be used, horn antennas are not suitable. It can also be realized with a simple antenna structure like this.

Further, in the above embodiment, the case of switching diversity reception with a threshold value has been described, but the present invention provides a selective switching diversity reception method ( It can also be applied in the same way to other systems (usually requiring the same number of receiving systems as diversity channels).

As described above, the radio reception system according to the present invention eliminates or reduces fading by using a directional antenna to remove part or all of the interference components of complex multipath waves that occur particularly in mobile radio communications. Even if it cannot be eliminated, it has the effect of lengthening the cycle and widening the transmission band, so combined with the directional diversity effect, it is possible to perform good wideband reception with less fading itself or the influence of fading.

Therefore, the present invention can significantly improve communication quality deterioration and transmission band limitations caused by fading in ordinary land-based mobile radio communications.In particular, the effects of fading elimination, reduction, and period extension can be improved in high-speed mobile radio communications. When performing radio reception at a high frequency, it is effective in preventing deterioration in communication quality such as distortion, noise, and code errors caused by sudden phase changes of received waves that are unavoidable with conventional methods. It is extremely useful for high bit rate communications and future mobile radio reception in the microwave band.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a diagram showing the constituent countries of an embodiment of the present invention, Fig. 2 is a diagram showing the directional pattern of a directional antenna and its arrangement in the same embodiment, and Fig. 3 is a diagram showing a mobile object. Fig. 4 is a diagram showing the main propagation paths of multipath waves in an urban area, Fig. 5 is a diagram showing an actual measurement example of the change in fading period with respect to the direction of arrival of radio waves, FIG. 6 and FIG. 7 are diagrams for explaining the operation of the same embodiment, and FIG. 8 is a diagram showing how multipath waves arrive at a moving body as scattered waves.
FIG. 9 is a diagram showing an actual measurement example of fading when receiving with an omnidirectional antenna and a directional antenna for explaining the present invention in detail, and FIG. FIG. 2 is a diagram showing a directional pattern of a directional antenna and its arrangement. 1-3...Directional antenna, 4...Switching circuit, 5.
...Receiver, 6...Control signal generation circuit.

Claims (1)

[Claims] 1 On the receiving side in mobile radio communication, three or more directional antennas each having directivity within a limited angular range in the horizontal plane are used to form directional patterns in different directions, resulting in an overall non-directional antenna. A mobile radio reception system characterized in that diversity reception is performed by arranging antennas such that