JPH0546128B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-station transmission method for wirelessly transmitting time-series information mainly to mobile bodies.

In wireless communication targeting a mobile object, it is difficult to maintain a stable communication line at all times because the radio wave propagation conditions change as the mobile object moves. Furthermore, when considering not only temporal fluctuations but also spatial service areas, there are areas where it is difficult to construct communication lines, such as behind obstacles to radio wave propagation.

Conventionally, multi-station transmission systems have been used to overcome such obstacles. The multi-station transmission system is intended to reduce shadows on radio wave propagation and construct a stable communication line by transmitting the same information from a plurality of regionally distributed transmitting stations. However, in this system, if the carrier frequencies of each transmitting station are selected to be the same, the radio waves transmitted from each transmitting station will interfere with each other, resulting in areas where the electric field strength is strong and areas where it is weak. In particular, at points where the distance to the two transmitting stations is equal, there are points where the electric field strength is almost zero. As a method to solve such problems, a method of shifting the carrier frequency of each station (frequency offset method) has been proposed.
Shown in 1744. When this method is used, the electric field strength does not steadily decrease at a certain point, and the electric field strength changes at a period corresponding to the frequency difference, so that a sufficient electric field strength can be obtained on average.
However, in order to fully utilize the effects of this method, it is necessary to select a difference in carrier frequency so large that the time-series information generates one or more beats within a symbol period. Therefore, as the number of transmitting stations increases, it is necessary to separate the frequencies between these stations by more than the symbol frequency (reciprocal of the symbol period), resulting in an increase in the overall required band. In addition to being undesirable from the point of view of effective frequency utilization, widening the required band also requires widening the reception band on the receiver side, which has the undesirable effect of increasing noise power.

An object of the present invention is to provide a multi-station transmission method that eliminates such drawbacks.

The multi-station transmission method of the present invention, in a system in which the same time-series information is transmitted by a plurality of regionally distributed transmitters, synchronizes the pointing directions of directional antennas connected to each transmitter, It is characterized by rotation in synchronization with the symbol period of time-series information.

This will be explained in detail below using the drawings. FIG. 1 is a block diagram showing an example of a transmitter used in the method of the present invention, where 1 is a time series signal input terminal, 2 is a symbol timing signal input terminal, 3 is a transmitter including a modulator and a power amplifier, and 4 is a transmitter including a modulator and a power amplifier. , 5, 6 are transmitting antenna elements, 7 is transmitting antenna element 4,
This is a phase shift circuit that changes the phases of the transmission high-frequency signals supplied with signals 5 and 6, and together with the transmission antenna element, constitutes a phased array antenna system in which the beam direction can be controlled. Reference numeral 8 denotes a control circuit that supplies a control signal to the phase circuit 7 in response to the symbol timing signal to rotate the pointing direction of the antenna by 360 degrees in the horizontal plane in one symbol period.

FIG. 2 shows an embodiment of a multi-station transmission communication system realized using the transmitting device shown in FIG. 9,
Reference numerals 10 and 11 are the same transmitting devices as shown in FIG. 1, but are arranged in a regionally distributed manner. Here, the carrier frequencies of each transmitter do not necessarily need to be synchronized, and there is no need to shift the frequencies as in the frequency offset method. The same time series information is supplied to these transmitting devices from the time series information source 12 together with the symbol timing signal. When distributing this information, if the distances from the time-series information source 12 to each transmitter differ greatly and the delay time difference is not sufficiently small to be ignored compared to the symbol period, the time-series information source 12 The timing of information transmission to the transmitting device is
The signals are staggered so that they reach each transmitting device at the same time.

FIG. 3 is a diagram showing the positional relationship between each transmitting device in FIG. 2 and a moving receiving device. In FIG. 3, 13, 14, and 15 indicate the positions of the transmitting devices. The transmitting devices located at positions 13, 14, and 15 will be distinguished by names A, B, and C hereinafter. 13,14,1
The arrow placed at position 5 indicates the orientation direction of the antenna at a certain time (to). It is assumed that this pointing direction rotates clockwise on the paper at a rate of 360° per symbol period. 16, 17, and 18 indicate the receiving positions of the mobile receiving device.

FIG. 4 is a waveform diagram showing received signals at reception positions 16, 17, and 18 in FIG. 3. The diagram shows time on the horizontal axis and the envelope amplitude of the signal on the vertical axis, and A is the received signal waveform at the reception position 16 in FIG. 3. This point is equidistant from transmitters A, B, and C, and receives signals with equal strength. Furthermore, at time to, only the signal from transmitter C is received, and as the antenna orientation direction rotates, signals from transmitters A and B are sequentially received. In this case, the signals from each transmitter are received without interfering with each other. Since the receiving device integrates and detects the received information over the symbol period T using a filter or the like, the signals from each transmitting device are effectively used for signal detection. The waveform in FIG. 4B is the received signal waveform at the receiving position 17 in FIG. At this point, the signal of transmitter B is received most strongly.
Since the signals from transmitters A and C are close to each other, they are received somewhat overlapping and cause interference, but since the signal from transmitter B is dominant,
The effect of interference is minor. The waveform in Figure 4 C is the third waveform.
This is a received signal waveform at the receiving position 18 in the figure.
Also at this point, the signal from transmitter B is received most strongly. However, since the arrival directions of the signals from transmitters B and C completely overlap, interference occurs.

However, in this case as well, since the signal from transmitter B is dominant, the influence of interference is slight. In particular, when a frequency variable method is adopted as a modulation method, the effect of suppressing weak signals is excellent, and therefore it is effective in such a multi-station transmission system.

The reception signals at reception points 16, 17, and 18 have been explained above, but as is clear from these examples, the signals from each transmitter are received independently in time without interference, or Since the signal from one of the transmitting devices is received preferentially even when the transmitting devices overlap, it is possible to prevent the signals from each transmitting device from interfering with each other at the same level and in opposite phases, resulting in an insensitive state.

In the above explanation, only the receiving points 16, 17, and 18 were described, but it is clear that such effects can be widely expected in the area including the transmitting devices A, B, and C. In addition, since the directional direction of the transmitting antenna is rotated, the reception time per station is shortened.
Although the received energy per symbol appears to decrease, this effect is canceled out by the antenna gain based on the directivity of the transmitting antenna, and no effect remains at all.In other words, the output power of the transmitter used in the transmitter is Even if this method is adopted, there is no need to increase the number. Furthermore, it is clear that this method is effective not only when there are three transmitters, but also when a large number of transmitters are generally arranged randomly on a plane.

In the example of the transmitting device shown in Figure 1, a phased array antenna is used as the directional antenna whose pointing direction can be rotated, but it is also possible to switch between multiple unidirectional antennas installed in different directions. Rotational directivity can be obtained by using a unidirectional antenna, or if the symbol period is long enough, a unidirectional antenna can be mechanically rotated.

As explained above, according to the present invention, it is possible to realize a multi-station transmission communication system with less interference between transmitting devices and a large diversity effect, and to perform communication targeting mobile objects over a wide area without any dead areas. It is highly effective when used in applications where it is necessary.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of a transmitting device used in the method of the present invention, FIG. 2 is an embodiment of a multi-station transmission communication system using the method of the present invention, and FIG. 3 is a block diagram showing the multi-station transmission communication of FIG. FIG. 4 is a diagram showing the positional relationship between the transmitting device and the receiving device in the system, and FIG. 4 is a received signal waveform diagram at each receiving position in FIG. 3. In the figure, 1 is a time series information input terminal, 2 is a symbol timing signal input terminal, 3 is a transmitter, 4, 5,
6 is a transmitting antenna element, 7 is a phase shift circuit, 8
is a control circuit for controlling the antenna pointing direction.

Claims (1)

[Claims] 1. In a system that transmits the same time-series information from multiple transmitters that are geographically distributed, the directional direction of the directional antenna connected to each transmitter is
A multi-station transmission method characterized by azimuth synchronization and rotation in synchronization with the symbol period of time-series information.