JP2011044759A - Diversity reception system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a diversity reception system, as a mobile communication system having a plurality of base stations 1, 2 adjacent to a railway, which has high reception quality by reducing the influence of high-speed fading or interference due to beat. <P>SOLUTION: The base stations 1, 2 synchronize frequencies of carriers by a reference frequency signal received from a reference frequency signal-generating means 14 to match the carrier frequencies, and emit a radiowave. Two mobile station antennas 11, 12 for diversity reception in the mobile station 10 are disposed on the mobile station 10 in accordance with disposition conditions in which when the phases of two radiowaves received with one mobile station antenna cancel each other, the phases of two radiowaves received with the other mobile station antenna are added to each other in accordance with relation between the phases of radiowave propagation path length from each of the base stations 1, 2. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a mobile communication system in which a mobile station moving on a line and a plurality of base stations arranged along the line exist, and in particular, diversity for obtaining good reception quality on the mobile station side with a simple device configuration. Regarding the receiving system.

  In a mobile communication system having a plurality of base stations, when transmitting the same information to many mobile stations at the same time, there is a simultaneous transmission system with the same frequency that transmits the same information from each base station at the same carrier frequency. Used. In commercial mobile communication systems such as train radio systems, the same frequency multi-station simultaneous transmission method is effective from the aspect of frequency utilization efficiency.

  However, the carrier in this case is a carrier of “the same frequency as the design value”, and actually, the oscillation source of each base station carrier is independent. Therefore, when radio waves are emitted from a plurality of base stations using carriers with the same design value, if the oscillation source of the carrier for each base station is different, each actual carrier frequency is not strictly the same frequency. Therefore, there is a problem that beat interference occurs due to a difference in carrier frequency.

  In addition, since the mobile station is affected by high-speed fading and the like by moving while receiving radio waves in the environment of a multipath propagation path that performs complicated reflection and diffraction, the quality of the received signal is greatly degraded.

  The above background art will be described in more detail with reference to the example of FIG. FIG. 1 is a diagram showing an outline of an example of a train radio system.

  The train radio system shown in FIG. 1 includes a plurality of base stations 1, 2, 3, a mobile station 10, and a central device 5. The mobile station 10 moves on the line 4. The base stations 1 to 3 are arranged along the line 4, and each base station 1 to 3 receives an information signal from the central apparatus 5 via the transmission path 6.

  The base stations 1 to 3 transmit the information signals received from the central apparatus 5 by using the respective antennas 7 to 9 with the carrier frequency of “the same frequency as the design value”. The mobile station 10 receives the information signal using at least two mobile station antennas 11 and 12.

The radio wave from the base station 1 and the radio wave from the base station 2 are emitted by the same frequency multi-station simultaneous transmission method, but if the carrier oscillation source is different, it causes beat interference. That is, when the mobile station 10 is between the base station 1 and the base station 2, the carrier frequency f ₁ of the base station ₁ and the carrier frequency f ₂ of the base station 2 are designed with “the same frequency as the design value”. However, if the oscillation sources at the respective frequencies are different, the carrier frequencies f ₁ and f ₂ do not completely coincide with each other, and a slight frequency difference Δf is generated. Therefore, beat interference occurs in the mobile station 10 on the receiving side due to this frequency difference Δf. This beat interference fluctuates most when the mobile station 10 is near the center of the base station 1 and the base station 2 and the radio waves arriving from the base stations 1 and 2 are received with the same intensity. .

For example, in a carrier having a frequency of 150 MHz, if a crystal having a stability of 1 × 10 ⁻⁶ is used as an oscillation source in each base station, a beat due to a frequency difference of Δf = f ₁ −f ₂ = 150 Hz is generated.

  In addition, since multipath propagation occurs due to reflection and scattering of radio waves from surrounding buildings, location environments, etc., the mobile station 10 is affected by high-speed fading in such a radio wave propagation environment.

  As a countermeasure against conventional fast fading and beat interference, as shown in Non-Patent Document 1, when transmitting the same information from a plurality of base stations, the transmission timing is delayed on each base station side, or There has been employed a method of performing transmission such as inserting waveform distortion so that the waveform of a signal to be transmitted becomes a different waveform.

Kubo, Okazaki, Tanada, Murakami: “A Study on Beat Interference Suppression Using Transmit Diversity and Adaptive Equalizer”, IEICE Transactions B, Vol. J86-B, no. 3, pp. 468-476, March 2003.

  In order to avoid degradation of reception quality due to high-speed fading and beat interference, the method described in Non-Patent Document 1 described above processes signals such that each base station shifts the transmission timing or controls the waveform. In addition, each mobile station needs to be compensated by an adaptive equalizer and receive complicated processing in order to receive the signal sent from each base station. . As a result, both the base station and the mobile station not only make the circuit configuration complicated, but also increase the number of inspection and maintenance items, and not only the initial cost but also the maintenance cost is an economical burden. was there.

  In a mobile communication system in which a mobile station moving along a track and a plurality of base stations arranged along the track exist like a train radio system, beat interference generated by radio wave interference from a plurality of base stations An object of the present invention is to provide a diversity reception system that reduces the influence of high-speed fading and the like and realizes good reception quality in a mobile station with a simple and inexpensive device configuration.

  In order to solve the above problems, the present invention provides diversity reception by providing two mobile station antennas, a first mobile station antenna and a second mobile station antenna, on the mobile station side. The positional relationship of the antenna is determined as follows.

Among the plurality of base stations, for example, two base stations that are adjacent to a section having the worst radio wave propagation condition are selected to be the Nth base station and the (N + 1) th base station, and the Nth base station to the Nth base station are selected. Transmitting from the (N + 1) th base station using the (N + 1) th base station antenna, and
A radio wave propagation path length until a radio wave transmitted from the Nth base station antenna reaches the first mobile station antenna is represented by X ₁ ,
A radio wave propagation path length until a radio wave transmitted from the (N + 1) th base station antenna reaches the first mobile station antenna is represented by X ₂ ,
The radio wave propagation path length until the radio wave transmitted from the Nth base station antenna reaches the second mobile station antenna is defined as Y ₁ ,
A radio wave propagation path length until a radio wave transmitted from the (N + 1) th base station antenna reaches the second mobile station antenna is represented by Y ₂ ,
If the wavelength of the radio wave is λ,
The two mobile station antennas exist in the vicinity of the center of the Nth base station antenna and the (N + 1) th base station antenna, and one mobile station antenna has X ₁ = X ₂ or Y ₁ = When it exists to be any of Y ₂ ,
[1] As a method to prevent the reception quality from deteriorating,
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) −M × λ | ≧ λ / 10 (1)
Is determined for the value of an arbitrary integer M, so that the arrangement of the two mobile station antennas is determined.
[2] Of the conditions that satisfy the above equation (1), a relatively effective method is as follows:
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) − (kλ + λ / 2) | ≦ λ / 4 (2)
Are arranged such that two mobile station antennas are satisfied for an arbitrary integer k.
[3] Furthermore, among the conditions that satisfy the above equation (2), the most effective method is:
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) − (kλ + λ / 2) | ≦ λ / 10 (3)
Are arranged such that two mobile station antennas are satisfied for an arbitrary integer k.

  For transmission from multiple bases, each base station is provided with a base station antenna, and instead of transmitting from the base station antenna, each base station is provided with an LCX (leakage coaxial cable: the same applies hereinafter) and transmitted from the LCX. This case is also included in the present invention.

  In addition, if all the carrier frequencies of multiple base stations are synchronized and set to exactly the same frequency, amplitude fluctuation due to beat interference does not occur in time, so that the carrier frequency of each base station is significantly higher than when the carrier frequencies are asynchronous. Expected. Therefore, in the present invention, a means for generating a reference frequency signal is provided, and a means for transmitting to each base station by the transmission means and synchronizing the carrier frequency of each base station with the reference frequency signal is provided.

  As described above, by configuring the present invention, it is possible to more effectively reduce the degradation of reception quality with respect to beat interference as compared with the case where the carrier frequencies of the base stations are not synchronized.

  If the mobile station antennas are arranged according to the method of the present invention, not only the reception level of both mobile station antennas does not become low at the same time, but also when the reception level of one mobile station antenna is low, the other mobile station Two mobile station antennas are arranged in such a positional relationship that the reception level of the antenna becomes high.

  Therefore, according to the present invention, it is possible to perform good diversity reception by determining the positions of the two mobile station antennas in an optimal relationship, and it is possible to prevent beat interference without using a complicated and expensive method as in the prior art. And fading countermeasures can be realized.

  In the present invention, when the base station side transmits using LCX instead of the base station antenna, the middle of each base station is located between LCX and LCX. In this case, the radio wave propagation environment is relatively simple between all base stations and tends to be in the same condition, so a higher diversity reception effect can be obtained.

  Furthermore, in the present invention, all carrier frequencies of the base station are frequency-synchronized so as to be exactly the same frequency, so that no beat interference occurs in time in the positional relationship of the mobile station antenna, and further excellent diversity reception is achieved. Can be realized.

It is a figure which shows the outline | summary of an example of a train radio system. It is a figure which shows the 1st example for describing embodiment of this invention. It is a figure which shows the 2nd example for describing embodiment of this invention. It is a figure which shows the 3rd example for describing embodiment of this invention. It is a figure which shows the 1st structural example of a base station. It is a figure which shows the 2nd structural example of a base station. It is a figure which shows the 1st structural example of a diversity receiver. It is a figure which shows the 2nd structural example of a diversity receiver. It is a figure which shows the amplitude of the electromagnetic wave near the center between two base stations, and the magnitude | size of electric power. It is a figure which shows the amplitude of the electromagnetic wave near the center between two base stations in the specific mobile station antenna space | interval, and the magnitude | size of electric power.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[First example]
FIG. 2 is a diagram showing a first example for explaining the embodiment of the present invention. As an example of the configuration of the diversity receiving system, a system including an adjacent base station 1 and base station 2, a line 4, a central device 5, a transmission path 6, and a mobile station 10 is shown. In this first example, in order to make it easier to understand the effects of the present invention, which will be described in detail later, an example will be described in which the carrier frequencies in each base station are not synchronized. Note that the vicinity of the center between the base station 1 and the base station 2 is assumed to have the worst radio wave propagation conditions as compared to the vicinity of the center between the other base stations. For example, when there is no significant difference in the radio wave propagation environment such as the landform along the track 4 or buildings, the distance between the two base stations (between the base stations 1 and 2) is farthest from that between the other base stations. Sometimes, the radio wave propagation condition is considered to be the worst in the vicinity of the center between the two most distant base stations.

  An information signal sent from the central apparatus 5 is transmitted to each of the base stations 1 and 2 via the transmission path 6. The base stations 1 and 2 convert the received information signal into a modulated signal with a carrier frequency designed at the same frequency, and transmit it as a radio signal via the base station antennas 7 and 8.

In the case of the configuration of FIG. 2, the carrier frequencies of the base station 1 and the base station 2 are generally different from each other because the oscillation sources are different, so that they do not completely coincide with each other unless frequency synchronization is performed. If the carrier frequency of the base station 1 is represented by f ₁ (angular frequency is ω ₁ = 2πf ₁ ) and the carrier frequency of the base station 2 is represented by f ₂ (angular frequency is ω ₂ = 2πf ₂ ), the frequency difference between the respective carriers Due to Δf = f ₁ −f ₂ , beat interference occurs on the receiving side of the mobile station 10.

  The mobile station 10 receives radio waves transmitted from the base station 1 and the base station 2 by the mobile station antennas 11 and 12 for diversity reception while moving on the line 4, and sends the received signal to the diversity receiver 13. .

In FIG. 2, the radio wave propagation path lengths until the radio waves transmitted from the base station antenna 7 and the base station antenna 8 reach the mobile station antenna 11 are X ₁ and X ₂ , respectively. The radio wave propagation path lengths until the radio waves transmitted from the station antenna 8 reach the mobile station antenna 12 are Y ₁ and Y ₂ .

The radio wave E ₁ transmitted from the base station antenna 7 of the base station ₁ is
E ₁ = A ₁ cos (ω ₁ t + θ ₁ ) (4)
The radio wave E ₂ transmitted from the base station antenna 8 of the base station ₂ is
E ₂ = A ₂ cos (ω ₂ t + θ ₂ ) (5)
And Here, the amplitude A ₁ and the amplitude A ₂ are the amplitude values in the radio wave E ₁ and the radio wave E ₂ , respectively, and the phase θ ₁ and the phase θ ₂ are the phases of the oscillation sources of the base station 1 and the base station 2, respectively. It is. Therefore, Equation (4) and Equation (5) indicate the radio wave at an arbitrary time t.

The reception input R ₁ of the mobile station antenna 11 is a combination of the radio wave E ₁ and the radio wave E ₂ transmitted from the two base stations, and the reception input (reception radio wave) R ₁ indicates the radio wave propagation speed c. Then, it is expressed as the following formula (6).

R ₁ = (A ₁ / X ₁ ) cos {ω ₁ (t−X ₁ / c) + θ ₁ }
+ (A ₂ / X ₂ ) cos {ω ₂ (t−X ₂ / c) + θ ₂ } (6)
Similarly, the reception input R ₂ of the mobile station antenna 12 is expressed by the following equation (7).

R ₂ = (A ₁ / Y ₁ ) cos {ω ₁ (t−Y ₁ / c) + θ ₁ }
+ (A ₂ / Y ₂ ) cos {ω ₂ (t−Y ₂ / c) + θ ₂ } (7)
Equations (6) and (7) can be modified as follows.

R ₁ = B ₁ cos {ω ₁ (t−X ₁ / c) + θ ₁ + φ ₁ } (8)
R ₂ = B ₂ cos {ω ₁ (t−Y ₁ / c) + θ ₁ + φ ₂ } (9)
Here, the amplitude B ₂ of amplitude B ₁ and the receiver input R ₂ of the receiving input R ₁ is expressed by the following equation.

B ₁ = sqrt [(A ₁ / X ₁ ) ² + (A ₂ / X ₂ ) ² + 2A ₁ A ₂ / (X ₁ X ₂ ) cos {(ω ₂ −ω ₁ ) t + 2π (X ₁ / λ ₁ −X ₂ / λ ₂ ) + θ ₂ −θ ₁ }] (10)
B ₂ = sqrt [(A ₁ / Y ₁ ) ² + (A ₂ / Y ₂ ) ² + 2A ₁ A ₂ / (Y ₁ Y ₂ ) cos {(ω ₂ −ω ₁ ) t + 2π (Y ₁ / λ ₁ −Y ₂ / λ ₂ ) + θ ₂ −θ ₁ }] (11)
Here, sqrt [...] represents the square root of [...]. The wavelengths λ ₁ and λ ₂ are the wavelengths of the radio waves having the carrier frequencies f ₁ and f ₂ , respectively, and are expressed by the following equations.

λ ₁ = c / f ₁ (12)
λ ₂ = c / f ₂ (13)
Further, the phases φ ₁ and φ ₂ are expressed by the following equations.

φ ₁ = tan ⁻¹ [(A ₂ / X ₂ ) sin {(ω ₂ −ω ₁ ) t + 2π (X ₁ / λ ₁ −X ₂ / λ ₂ ) + θ ₂ −θ ₁ } / [(A ₁ / _{X 1) + (A 2 /} X 2) cos {(ω 2 -ω 1) t + 2π (X 1 / λ 1 -X 2 / λ 2) + θ 2 -θ 1}] ] ... (14)
φ ₂ = tan ⁻¹ [(A ₂ / Y ₂ ) sin {(ω ₂ −ω ₁ ) t + 2π (Y ₁ / λ ₁ −Y ₂ / λ ₂ ) + θ ₂ −θ ₁ } / [(A ₁ / Y ₁ ) + (A ₂ / Y ₂ ) cos {(ω ₂ −ω ₁ ) t + 2π (Y ₁ / λ ₁ −Y ₂ / λ ₂ ) + θ ₂ −θ ₁ }]] (15)
In the present invention, even if the amplitude B ₁ or B ₂ of the received radio wave of one of the two mobile station antennas (11 or 12) for diversity reception is the smallest, the other mobile station antenna (12 or 11) The antenna interval between the mobile station antennas 11 and 12 is maintained so that the amplitude B ₂ or B ₁ of the received radio wave falls within a predetermined range. Therefore, a condition for minimizing the amplitude B ₁ is obtained.

cos {(ω ₂ −ω ₁ ) t + 2π (X ₁ / λ ₁ −X ₂ / λ ₂ ) + θ ₂ −θ ₁ } = − 1
… (16)
When this equation (16) is satisfied, the amplitude B _{1 of the} received radio wave may be minimized.
(Ω ₂ −ω ₁ ) t + 2π (X ₁ / λ ₁ −X ₂ / λ ₂ ) + θ ₂ −θ ₁ = ± odd number × π
… (17)
It is. In fact, at this time,
_{B 1 = sqrt {(A 1} / X 1 -A 2 / X 2) 2} ... (18)
For example, if the radio wave propagation path length X ₁ = X ₂ near the middle of the two base stations 1 and 2, the radio wave having the same amplitude (A ₁ = A ₂ ) is received by the mobile station antenna 11. Amplitude B ₁ = 0.

In such a case, when the condition that the amplitude B ₂ of the received radio wave of the other mobile station antenna 12 falls within a predetermined range is obtained from the equation (17) as follows.

(Ω ₂ −ω ₁ ) t + θ ₂ −θ ₁ = ± odd number × π−2π (X ₁ / λ ₁ −X ₂ / λ ₂ )
… (19)
When this equation (19) is substituted into equation (11), the following value is obtained as the value of the amplitude B ₂ when the amplitude B ₁ decreases.

B ₂ = sqrt [(A ₁ / Y ₁ ) ² + (A ₂ / Y ₂ ) ² + 2A ₁ A ₂ / (Y ₁ Y ₂ ) cos [2π {(Y ₁ / λ ₁ −Y ₂ / λ ₂ ) − (X ₁ / λ ₁ −X ₂ / λ ₂ )} ± odd number × π]] (20)
In the case of the same frequency multi-station simultaneous transmission system, the carrier frequency f ₁ ≈f ₂ , so the wavelength λ ₁ ≈λ ₂ . Therefore, when the wavelengths λ ₁ and λ ₂ are expressed as λ, the equation (20) is as follows.

B ₂ = sqrt [(A ₁ / Y ₁ ) ² + (A ₂ / Y ₂ ) ² + 2A ₁ A ₂ / (Y ₁ Y ₂ ) cos [2π {(Y ₁ −Y ₂ ) − (X ₁ −X ₂ )} / λ ± odd × π]] (21)
Let's do numerical calculations for equation (21). In order to simplify the calculation, the depth distance on the drawing of FIG. The calculation is performed under the condition of amplitude A ₁ = A ₂ .

In FIG. 2, the distance between the base station antenna 7 of the base station 1 and the base station antenna 8 of the base station 2 is L, the distance between the extension of the antenna axis of the base station antenna 7 and the mobile station antenna 11 is X, and the mobile station If the antenna interval between the antennas 11 and 12 is D, the distance between the extension lines of the antenna axes of the mobile station antenna 12 and the base station antenna 8 is L−X−D. Further, the radio wave propagation path lengths X ₁ , X ₂ , Y ₁ , Y ₂ shown in FIG. 2 are as follows.

X ₁ = sqrt [X ² + H ² ] (22)
X ₂ = sqrt [(L−) ² + H ² ] (23)
Y ₁ = sqrt [(X + D) ² + H ² ] (24)
Y ₂ = sqrt [(L−X−D) ² + H ² ] (25)
FIG. 9 is a diagram showing the amplitude of received radio waves and the magnitude of power near the center between two base stations. Note that FIG. 9B is an enlarged view of part of FIG. FIG. 9 shows the result of numerical calculation of Equation (21) with {(Y ₁ −Y ₂ ) − (X ₁ −X ₂ )} / λ on the horizontal axis and amplitude and power on the vertical axis. For the amplitude peak, the values of the amplitudes A ₁ and A ₂ are selected so as to be 1 near the center.

“B2 (amplitude)” indicated by a solid line in FIG. 9A and FIG. 9B represents the received radio wave of one mobile station antenna 11 in the vicinity of the center between the two base stations 1 and 2. This is the amplitude B ₂ of the received radio wave of the other mobile station antenna 12 when the amplitude B ₁ is minimized. Further, “B2 (power)” indicated by a broken line is a value proportional to the received power of the mobile station antenna 12 at this time, and is a value obtained by squaring Equation (21).

From the above calculation results, for any integer M value,
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) −M × λ | ≧ λ / 10 (26)
(Corresponding to section A in FIG. 9B), when the amplitude B ₁ of the received radio wave of the mobile station antenna 11 is minimized, the amplitude B ₂ of the received radio wave of the other mobile station antenna 12 is There is no minimum, and when viewed in terms of received power, at least about 10% of the peak can be received.

Next, for any integer k,
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) − (kλ + λ / 2) | ≦ λ / 4 (27)
(Corresponding to the section B in FIG. 9B), the amplitude B ₂ of the received radio wave of the other mobile station antenna 12 when the amplitude B ₁ of the received radio wave of the mobile station antenna 11 is minimum is a peak. In addition, when viewed in terms of received power, at least 50% of the peak can be received.

Furthermore, for any integer k,
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) − (kλ + λ / 2) | ≦ λ / 10 (28)
(Corresponding to the section C in FIG. 9B), the amplitude B ₂ of the received radio wave of the other mobile station antenna 12 when the amplitude B ₁ of the received radio wave of the mobile station antenna 11 is minimized is a peak. When viewed in terms of received power, at least 90% of the peak can be received.

  FIG. 10 shows the amplitudes of the received radio waves of the mobile station antennas 11 and 12 when the two mobile station antennas 11 and 12 are arranged in the traveling direction of the mobile station 10 by a distance of D = λ / 4. It shows the magnitude of power. FIG. 10A shows a case where the radio wave emitting unit of the base station is configured with a base station antenna, and FIG. 10B shows a case where the radio wave emitting unit is configured with LCX. Note that FIG. 10B will be described later.

  In FIG. 10A, “B1 (amplitude)” and “B2 (amplitude)” are values proportional to the amplitudes of the received radio waves of the mobile station antennas 11 and 12, respectively, and “B1 (power)”. , “B2 (power)” is a value proportional to the power of the radio waves received by the mobile station antennas 11 and 12, respectively. The vertical axis shows these amplitudes and power, and the horizontal axis shows the value (XL / 2) / λ obtained by dividing the distance from the center (XL / 2) by the wavelength λ. Yes. In addition, as a specific numerical value, it calculated about the case where distance L = 1km and height H = 10m.

  As is clear from the result shown in FIG. 10A, when the two mobile station antennas 11 and 12 are separated by D = λ / 4, when the power of one received radio wave is the lowest, It can be seen that the power of the other received radio wave has the highest value, and the most excellent reception diversity effect can be obtained.

  According to the first example, two mobile station antennas that satisfy a predetermined arrangement condition are provided on the mobile station side, and diversity reception is performed. According to the present invention, if the mobile station antennas are arranged so as to satisfy a predetermined arrangement condition, not only the reception levels of both mobile station antennas do not become low simultaneously, but also the reception level of one mobile station antenna. When is low, the reception level of the other mobile station antenna can be increased. Therefore, by setting the positions of the two mobile station antennas in an optimum relationship, diversity reception that can obtain good reception quality in the mobile station can be realized. Further, as will be described later, beat interference countermeasures and fading countermeasures can be realized with a simple device without using complicated and expensive circuits and devices.

[Second example]
FIG. 3 is a diagram showing a second example for explaining the embodiment of the present invention.

  In the second example, a reference frequency signal generator 14 is provided in addition to the configuration of the first example described above. A reference frequency signal is sent from the reference frequency signal generator 14 to each of the base stations 1 and 2 via the signal line 15, and the base stations 1 and 2 synchronize the carrier frequency based on the reference frequency signal. The carrier frequencies of the stations 1 and 2 are matched.

As is clear from the above-described equations (10), (11), (14), and (15), when there is a carrier frequency difference Δf between the base station 1 and the base station 2, (ω ₁ −ω ₂ ) = 2π (f ₁ −f ₂ ) ≠ 0, the amplitude and phase fluctuate in time according to the frequency difference Δf = f ₁ −f ₂ . This temporal change in amplitude and phase greatly affects the quality of the received signal of the mobile station 10. For example, when the received signal is an analog signal, the received signal interferes with the beat and a beat sound is generated, which is annoying. When the received signal is a digital signal, the error rate of the received signal is deteriorated.

The smaller the frequency difference Δf, the slower the temporal amplitude fluctuation and phase fluctuation, so that the quality of the received signal is improved. Therefore, in the present invention, the carrier frequencies f ₁ and f ₂ of the base stations 1 and ₂ are matched by frequency synchronization to realize (ω ₁ −ω ₂ ) = 2π (f ₁ −f ₂ ) = 0. Thus, when the carrier frequencies of the respective base stations 1 and 2 are matched, the influence of beat interference is eliminated in terms of time.

The amplitude in this case is expressed by the following equation. If λ ₁ = λ ₂ = λ, then
B ₁ = sqrt [(A ₁ / X ₁ ) ² + (A ₂ / X ₂ ) ² + 2A ₁ A ₂ / (X ₁ X ₂ ) cos {2π (X ₁ −X ₂ ) / λ + θ ₂ −θ ₁ } ] (29)
B ₂ = sqrt [(A ₁ / Y ₁ ) ² + (A ₂ / Y ₂ ) ² + 2A ₁ A ₂ / (Y ₁ Y ₂ ) cos {2π (Y ₁ −Y ₂ ) / λ + θ ₂ −θ ₁ } ] (30)
There is a phenomenon that the amplitude of the received signal disappears when the radio waves from the respective base stations are emitted in a phase relationship that cancels each other's signal. For example, in equation (29)
{2π (X ₁ −X ₂ ) / λ + θ ₂ −θ ₁ } = ± odd number × π (31)
When
_{B 1 = sqrt {(A 1} / X 1 -A 2 / X 2) 2}
_{= | A 1 / X 1 -A} 2 / X 2 | ... (32)
Where
_{A 1 / X 1 = A 2} / X 2 ... (33)
When the above condition is satisfied, the two mobile station antennas cannot cancel each other because they cancel each other. In particular, when the mobile station 10 is stopped under such conditions on the line 4, the mobile station antenna cannot receive radio waves indefinitely.

  On the other hand, in the present invention, the reference frequency signal generator 14 is provided so that the mobile stations 10 and 10 have the same base station 1, 2 carrier frequency, that is, in a state in which beat interference does not occur. Even if is stopped, the other mobile station antenna is devised so that it can receive at a sufficient level, and the best reception quality can be obtained.

  Even in this case, the same numerical calculation as that shown in FIG. As shown in FIG. 10A, when the distance D between the two mobile station antennas is set to D = λ / 4, when the amplitude and power of the received radio wave of the mobile station antenna 11 are the smallest, the other The amplitude and power of the received radio wave at the mobile station antenna 12 have a peak. Therefore, in the case of the present invention, when the mobile station 10 stops on the line 4, even if the power of the radio wave received by one mobile station antenna is minimum, the power of the radio wave received by the other mobile station antenna is sufficient. Therefore, sufficient reception quality can be ensured.

  As described above, according to the second example, all the carrier frequencies of the base station are frequency-synchronized so as to have the same frequency. Diversity reception that can obtain better reception quality can be achieved without generating a typical beat interference.

[Third example]
In the second example, an example in which the radio wave emitting unit of the base station is a base station antenna has been described. However, as in the third example described below, the radio wave emitting unit is a leaky coaxial cable LCX (Leaky CoaXial cable). Even in the case where the middle of adjacent base stations is located between the leaky coaxial cable LCX and the leaky coaxial cable LCX, diversity that can obtain good reception quality in the mobile station 10 by using the present invention is provided. Reception can be realized.

  FIG. 4 is a diagram showing a third example for explaining the embodiment of the present invention. The third example is an example in which the base station antennas 7 and 8 in the second example described above are replaced with LCXs 16 and 17, respectively.

  When transmission from all base stations is performed using LCX designed at the same interval, the radio wave propagation conditions between LCX 16 and LCX 17 are the same regardless of which adjacent base stations 1 and 2 are selected. Conceivable. In such a case, the arrangement of the mobile station antennas 11 and 12 is determined near the center of the LCX 16 of the adjacent base station 1 and the LCX 17 of the base station 2 that are arbitrarily selected. Thus, when the radio wave propagation conditions between the respective base stations are considered to be the same regardless of which adjacent base station is selected, the mobile station antennas 11 and 12 are located near the center of any adjacent base station. The arrangement is determined according to the arrangement conditions of the present invention, and this is also included in the technical scope of the present invention.

The mobile station 10 is a train vehicle, and a diversity receiving mobile station antenna 11 and a mobile station antenna 12 are arranged on the roof of the vehicle, and receive radio waves emitted from the LCX 16 of the base station 1 and the LCX 17 of the base station 2. In this case, as shown in FIG.
The distance from the end of the LCX 16 to the mobile station antenna 11 is X ₁ ,
The distance from the end of the LCX 17 to the mobile station antenna 11 is X ₂ ,
The distance from the end of the LCX 16 to the mobile station antenna 12 is Y ₁ ,
The distance from the end of the LCX 17 to the mobile station antenna 12 is Y ₂ ,
When the calculation is performed in the same manner as in FIG. 10A, the amplitude and power of the received radio wave are as shown in FIG. 10B. FIG. 10B shows that when the mobile station 10 is in the vicinity of the centers of the two base stations 1 and 2, the two mobile station antennas 11 and 12 have an antenna interval D = λ / in the traveling direction of the line 4 of the mobile station 10. 4 shows the amplitudes of received radio waves and the power levels of the mobile station antennas 11 and 12 when they are separated by four. As a condition, calculation is made for an example in the case of distance L = 40 m and height H = 5 m.

  As shown in FIG. 10 (B), for example, even if the distance L between the end of LCX 16 and the end of LCX 17 is about 40 m, one mobile station can be used as long as the antenna distance is D = λ / 4. When the power of the received radio wave of the antenna 11 (or 12) is minimum, the power of the received radio wave of the other mobile station antenna 12 (or 11) has a substantially peak value, and good reception quality can be obtained.

[Explanation by approximate expression]
The height difference H between the base station antennas 7 and 8 and the mobile station antennas 11 and 12 is very small compared to the distance L between the adjacent base station antennas 7 and 8 (or the transmitting ends of the LCXs 16 and 17; the same applies hereinafter). In the case, the amplitude of the radio wave received by the other mobile station antenna when the amplitude of the radio wave received by one mobile station antenna becomes very small will be described using an approximate expression. In the case of FIG. 2, since it is considered that X >> H, L >> H, LX >> H, and LXD >> H in the vicinity of the center between the two base station antennas 7 and 8,
{(Y ₁ −Y ₂ ) − (X ₁ −X ₂ )} / λ≈2D / λ (34)
It becomes. Therefore, equation (21) becomes
B ₂ = sqrt [(A ₁ / Y ₁ ) ² + (A ₂ / Y ₂ ) ² + 2A ₁ A ₂ / (Y ₁ Y ₂ ) cos (4πD / λ ± odd number × π)] (35)
It becomes. From Equation (35), let k be an arbitrary integer.
D = λ / 4 + kλ / 2 (36)
If,
B ₂ = A ₁ / Y ₁ + A ₂ / Y ₂ (37)
Thus, it can be seen that the radio waves transmitted from the two base stations 1 and 2 add to each other in the mobile station 10 and have sufficient amplitude. Although the approximation in the first example has been described above, the same applies to the second and third examples.

[Explanation of effects on fast fading]
As described above in the first to third examples, according to the present invention, a mobile station is installed under a predetermined arrangement condition against beat interference from two base stations placed along a line. In the case of diversity reception with two mobile station antennas, when the received radio wave of one mobile station antenna is very small, the received radio wave of the other mobile station antenna is the highest value, so that Diversity reception is possible.

  In a diversity receiving system such as the present invention, when a base station exists along a line, not only beat interference but also radio waves from the base station are reflected and diffracted and arrive at the mobile station by multipath propagation. Is also effective. The reason for this is that radio waves transmitted from base station antennas and leaky coaxial cables (LCX) placed along the track as in a train radio system are in a location environment with few obstacles in the track direction. This is because multi-path propagation caused by reflection and diffraction is likely to propagate along the line. Actually, even if two waves with similar amplitudes interfere with each other at the same time, it is considered that the probability of interference with three or more waves at the same time is low. Therefore, assuming that two waves propagating in the line direction interfere with each other, as described above, two mobile stations are set such that k is an arbitrary integer and the antenna interval D is D = λ / 4 + kλ / 2 in the line direction. By arranging the antennas apart from each other, it is easily estimated that the reception amplitude of the other mobile station antenna becomes the highest value even when the reception amplitude of one mobile station antenna is the smallest.

[First configuration example of base station]
FIG. 5 is a diagram illustrating a first configuration example of the base stations 1 and 2. This first configuration example is used, for example, in the first example described with reference to FIG.

  In the base stations 1 and 2, the information signals sent from the central device 5 (see FIG. 2) are modulated by the quadrature modulator 18, respectively. In the quadrature modulator 18, the waveform generation circuit 21 generates waveforms of the in-phase component and the quadrature component based on the input information signal. The in-phase component signal generated by the waveform generation circuit 21 is input to the mixer 22, and the quadrature component signal is input to the mixer 23.

  The in-phase component signal output from the waveform generation circuit 21 is multiplied by the output of the carrier oscillator 19 in the mixer 22. The signal of the quadrature component output from the waveform generation circuit 21 is multiplied in the mixer 23 by the carrier whose phase is shifted 90 degrees by the π / 2 phase shifter 20 in the output of the carrier oscillator 19.

  Thus, the two signals resulting from the multiplication by the mixers 22 and 23 are added by the adder 24 to be orthogonally modulated. The signal subjected to quadrature modulation by the quadrature modulator 18 is amplified by the transmission amplifier 25 and transmitted from the base station antennas 7 and 8 to the mobile station 10.

In the configuration shown in FIG. 5, the higher the stability of the carrier oscillator 19, the smaller the carrier frequency difference Δf between the base stations 1 and 2 shown in FIG. That is, at the carrier frequencies f ₁ and f ₂ of the base stations 1 and 2, the beat frequency of the received signal at the mobile station 10 can be kept low by Δf = (f ₁ −f ₂ ) ≈0. Quality is good. For example, if a carrier oscillator 19 is provided with a rubidium oscillator, a TCXO (Temperature Compensated Crystal Oscillator) or the like as an oscillation source, a highly stable carrier frequency can be realized.

  When the first configuration example of the base station is used in the second example and the third example described with reference to FIGS. 3 and 4, a carrier frequency wave is generated as the reference frequency signal generator 14. By replacing the wave with the output of the carrier oscillator 19 of FIG. 5, the information signal can be similarly quadrature modulated.

[Second configuration example of base station]
FIG. 6 is a diagram illustrating a second configuration example of the base stations 1 and 2. This second configuration example is used in, for example, the second or third example described with reference to FIG. 3 or FIG.

  The information signal sent from the central device 5 shown in FIG. 3 (or FIG. 4) is input to the quadrature modulator 18, and the reference frequency shown in FIG. 3 (or FIG. 4) is input to the carrier frequency signal generator 26. A reference frequency signal sent from the signal generator 14 via the transmission line 15 is input.

  Since the quadrature modulator 18, the π / 2 phase shifter 20 and the transmission amplifier 25 shown in FIG. 6 have the same functions as those shown in FIG. 5, the description thereof is omitted here, and other configurations shown in FIG. The function will be described.

  The carrier frequency signal generator 26 receives a reference frequency signal and generates a carrier frequency signal that is frequency-synchronized with the input reference frequency signal. For this purpose, the carrier frequency signal generator 26 includes a phase comparator 27, a filter 28, an oscillator 29, and a frequency divider 30.

  The phase comparison unit 27 performs phase comparison between the reference frequency signal and the signal obtained by dividing the output signal of the oscillator 29 by the frequency divider 30, and outputs an output signal corresponding to the phase comparison to the filter 28. The filter 28 performs a filter process on the output signal corresponding to the phase comparison output from the phase comparison unit 27, and controls so as to stabilize the output of the oscillator 29 according to the result of the filter process. For the oscillator 29, for example, an inexpensive voltage controlled oscillator such as a crystal oscillator having a carrier frequency within a frequency variable range can be used.

  Through the above control, a carrier frequency signal using the reference frequency signal as a reference for frequency synchronization is output from the carrier frequency signal generator 26 to the π / 2 phase shifter 20.

  The π / 2 phase shifter 20 shifts the phase of the carrier frequency signal output from the carrier frequency signal generator 26 by π / 2, and outputs the phase-shifted signal to the mixer 23 of the quadrature modulator 18. As described above with reference to FIG. 5, the quadrature modulator 18 performs quadrature modulation, and the quadrature-modulated signal is output as a transmission signal via the amplifier 25.

  The frequency of the reference frequency signal output from the reference frequency signal generator 14 used in the second and third examples described above is not limited to the carrier frequency, but is a frequency convenient for wired transmission of the transmission line 15 ( A frequency lower than the carrier frequency) can be selected. Therefore, in this case, the carrier frequency can be set to the same frequency in each base station by the carrier frequency signal generation unit 26 of an inexpensive apparatus with a simple configuration.

[First Configuration Example of Diversity Receiver]
FIG. 7 is a diagram illustrating a first configuration example of the diversity receiver 13. FIG. 7 shows a configuration example based on the selection diversity method, and can be used in any of the first to third examples described with reference to FIGS.

  The mobile station 10 includes a diversity receiver 13 for inputting radio waves received by the mobile station antennas 11 and 12 as a received signal and generating a demodulated output from the received signal. The diversity receiver 13 shown in FIG. 7 includes receivers 31 and 32, envelope level detectors 33 and 34, envelope level comparator 35, demodulators 36 and 37, and an electronic switch 38.

  Radio waves received by the mobile station antennas 11 and 12 are input to the receivers 31 and 32 as received signals, respectively. Envelope level detectors 33 and 34 for detecting the envelope level of the received signal are connected to the outputs of the receivers 31 and 32, respectively. The envelope level detection units 33 and 34 detect the envelope level of the received signal from the outputs of the receivers 31 and 32, respectively, and output the detected envelope level of the received signal to the envelope level comparison unit 35.

  In addition, the receivers 31 and 32 output the received signals, which have been subjected to predetermined modulation by the transmission-side base stations 1 and 2, to the demodulators 36 and 37. Demodulators 36 and 37 perform predetermined demodulation processing on the input received signals, respectively, and then output them to the electronic switch 38 as demodulated signals.

  The envelope level comparison unit 35 determines which received radio wave level is higher based on the envelope levels of the receivers 31 and 32, and selects the higher received radio wave level. That is, the envelope level comparison unit 35 selects the side having the higher envelope level from the demodulated signals of the demodulators 36 and 37 based on the envelope level of the received signal detected by the envelope level detection units 33 and 34. The selection of the electronic switch 38 is switched so as to output the selected demodulated signal.

  As a result, in the first configuration example of the diversity receiver 13, a signal obtained by demodulating the higher level of the received radio waves received by the mobile station antennas 11 and 12 is selected and output. Therefore, the demodulated output is an information signal with good signal quality.

[Second Configuration Example of Diversity Receiver]
FIG. 8 is a diagram illustrating a second configuration example of the diversity receiving device 13. FIG. 8 shows a configuration example based on the maximum ratio combining diversity method, and can be used in any of the first to third examples described with reference to FIGS.

  The diversity receiver 13 shown in FIG. 8 includes receivers 31 and 32, envelope level detectors 33 and 34, amplitude control amplifiers 39 and 40, a phase difference detector 41, a variable phase shifter 42, an adder 43, and a demodulator. 44.

  Radio waves received by the mobile station antennas 11 and 12 are input to the receivers 31 and 32 as received signals, respectively. Envelope level detectors 33 and 34 for detecting the envelope level of the received signal are connected to the outputs of the receivers 31 and 32, respectively.

  The envelope level detectors 33 and 34 detect the envelope level of the received signal from the outputs of the receivers 31 and 32, respectively, and output the detected envelope level of the received signal to the amplitude control amplifiers 39 and 40.

  The outputs of the receivers 31 and 32 are input to amplitude control amplifiers 39 and 40, respectively. The amplitude control amplifiers 39 and 40 receive the received signals from the receivers 31 and 32, and change the amplitude of the received signals based on the envelope levels of the received radio waves detected by the envelope level detectors 33 and 34. To do. In this case, the amplitude control amplifiers 39 and 40 have a high amplification factor when the envelope level is high (or the CN ratio is high), and low amplification factor when the envelope level is low (or the CN ratio is low).

  The outputs of the amplitude control amplifiers 39 and 40 are respectively input to the phase difference detection unit 41, and the phase difference detection unit 41 detects the phase difference between the outputs. The phase difference detector 41 outputs an output signal corresponding to the phase difference to the variable phase shifter 42.

  The variable phase shifter 42 calculates the phase of the output of one amplitude control amplifier (the output of the amplitude control amplifier 40 in the example of FIG. 8) based on the detected phase difference (output signal of the phase difference detection unit 41). Variable. In this case, the variable phase shifter 42 varies the phase so that the amplitude of the signal added by the adder 43 is increased. The output of the amplitude control amplifier 40 whose phase is changed by the variable phase shifter 42 is added by the adder 43 with the output of the other amplitude control amplifier 39.

  As a result, the signal added by the adder 43 is enhanced in amplitude based on the higher level of the radio wave received by the mobile station antennas 11 and 12, and a signal added in phase can also be obtained. Therefore, the demodulated output obtained by demodulating the output of the adder 43 by the demodulator 44 is an information signal with good signal quality.

1, 2, 3 Base station 4 Line 5 Central device 6, 15 Transmission path 7, 8, 9 Base station antenna 10 Mobile station 11, 12 Mobile station antenna 13 Diversity receiver 14 Reference frequency signal generator 16, 17 LCX (Leakage) coaxial cable)
18 Quadrature Modulator 19 Carrier Oscillator 20 π / 2 Phase Shifter 21 Waveform Generation Circuit 22, 23 Mixer 24, 43 Adder 25 Amplifier 26 Carrier Frequency Signal Generator 27 Phase Comparator 28 Filter 29 Oscillator 30 Divider 31, 32 Receiver 33, 34 Envelope level detector 35 Envelope level comparator 36, 37, 44 Demodulator
38 Electronic switch 39, 40 Amplitude control amplifier 41 Phase difference detector 42 Variable phase shifter

Claims (5)

A mobile station moving on the line receives radio waves transmitted from radio wave emitting units of a plurality of base stations arranged along the line by a multi-station simultaneous transmission method. The first mobile station antenna and the second mobile station antenna A diversity receiving system for receiving with two mobile station antennas,
Reference frequency signal generating means for generating a reference frequency signal for synchronizing the carrier frequency of the radio wave;
Transmission means for transmitting a reference frequency signal obtained from the reference frequency signal generation means to the plurality of base stations,
The plurality of base stations are provided with frequency synchronization means for making the carrier frequencies of radio waves transmitted by the radio wave emitting sections of the base stations the same based on the reference frequency signal received by the transmission means,
As an arrangement condition of the two mobile station antennas in the mobile station,
Two adjacent base stations selected from the plurality of base stations are defined as a first base station and a second base station,
The radio wave propagation path length to the radio waves transmitted from the radio wave portion of the first base station reaches the first mobile station antenna and X _1,
The radio wave propagation path length to the radio waves transmitted from the radio wave of the second base station reaches the first mobile station antenna and X _2,
The radio wave propagation path length until the radio wave transmitted from the radio wave emitting unit of the first base station reaches the second mobile station antenna is Y ₁ ,
The radio wave propagation path length until the radio wave transmitted from the radio wave emitting unit of the second base station reaches the second mobile station antenna is Y ₂ ,
When the wavelength of the radio wave is λ,
The two mobile station antennas are present in the vicinity of the center of the radio wave emission unit of the first base station and the radio wave emission unit of the second base station, and the first mobile station antenna is X ₁ = X ₂ or when the second mobile station antenna is located at Y ₁ = Y ₂
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) −M × λ | ≧ λ / 10
The diversity receiving system, wherein the two mobile station antennas are arranged at positions on the mobile station that satisfy the following condition (M is an arbitrary integer). The diversity reception system according to claim 1,
As an arrangement condition of the two mobile station antennas in the mobile station,
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) − (kλ + λ / 2) | ≦ λ / 4
The diversity receiving system, wherein the two mobile station antennas are arranged at positions on the mobile station that satisfy the following condition (k is an arbitrary integer). The diversity reception system according to claim 1,
As an arrangement condition of the two mobile station antennas in the mobile station,
| (Y ₁ −Y ₂ ) − (X ₁ −X ₂ ) − (kλ + λ / 2) | ≦ λ / 10
The diversity receiving system, wherein the two mobile station antennas are arranged at positions on the mobile station that satisfy the following condition (k is an arbitrary integer). The diversity reception system according to any one of claims 1 to 3,
The diversity reception system according to claim 1, wherein the two mobile station antennas in the mobile station are arranged apart from each other by an integer (λ / 4 + nλ / 2) in the traveling direction of the line. The diversity receiving system according to any one of claims 1 to 4, wherein:
The diversity receiving system, wherein the radio wave emitting section of the reference station is an antenna or a leaky coaxial cable.

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