JPH08102707A - Mobile communication system - Google Patents

Abstract

PURPOSE: To prevent the interference of frequency and to improve the reception quality in a mobile communication system by securing the service areas of plural base stations by means of the same transmission radio frequency. CONSTITUTION: The different transmission time slots are allocated to the base stations 42 to 44, and these base stations transmit the same information as the transmission signals through each allocated time slot and by means of the same transmission radio frequency. On the other hand, a receiver station 46 uses only the transmission signals that are normally received as the reception signals among those transmission signals that are received from those base stations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more particularly, to a transmission system in which a plurality of base stations are provided to perform transmission at the same radio frequency.

[0002]

2. Description of the Related Art Conventionally, for example, a mobile radio system shown in FIG. 3 is known. In the illustrated mobile radio system (for example, a train radio system), for example, a service zone is divided into an A zone and a B zone, and the A zone and the B zone are each divided into a plurality of small zones.
A base station (transmitting station) is arranged for each small zone. In the illustrated example, the A zone is divided into three small zones, and similarly, the B zone is also divided into a plurality of small zones.

As shown in the figure, base stations 11 to 13 are arranged in zone A, and base station 21 is arranged in zone B (only base station 21 is shown in zone B in FIG. 2). . The base stations 11 to 13 and the base station 21 are arranged at equal intervals.
Is connected to an exchange 31 via a transmission line, and a central office 32 is connected to the exchange 31.

In the mobile radio system shown in the figure, each base station uses the same radio frequency, and the central station 32 controls the exchange 31 when sending information to a mobile body (for example, a train) in the A zone. Then, the information is sent to the base stations 11 to 13 via the exchange 31. The base stations 11 to 13 transmit this information using the same radio frequency.

[0005] In this mobile radio system, since each base station (transmitting station) uses the same radio frequency, interference occurs in a section (hatched section) shown by hatching in FIG. Due to this interference, reception quality is degraded at a receiving station (mobile) existing in the hatched section.

In order to prevent such deterioration of reception quality, generally, each base station uses an expensive oscillator with a temperature-compensated thermostat as an oscillator for generating a transmission frequency, and determines the inter-station frequency difference by a predetermined value. It is necessary to provide a delay compensating circuit that makes the delay time within the transmission signal (modulated signal) equal to the delay time difference between the stations. In addition, it is necessary to provide means for maintaining the inter-station modulation depth difference within a predetermined value.

The above-mentioned mobile radio system is described in, for example, "Railway and Electric Technology", 1992, 1, VO
L. 3, No. 1, page 67 (issued by the Japan Railway Electrical Engineering Association).

[0008]

As described above, in the conventional mobile radio system, not only expensive hardware is required to prevent interference, but also system adjustment costs and maintenance costs are incurred. There is a problem. Further, when the transmission signal speed is high, there is a problem that deterioration of reception quality cannot be prevented.

An object of the present invention is to provide a mobile communication system which is inexpensive and can prevent deterioration of reception quality.

[0010]

According to the present invention, a service area is defined by a plurality of base stations, and communication is performed using at least one of a mobile unit located in the service area and the base station. In the mobile communication system to be performed, different transmission time slots are assigned to the plurality of base stations, and the plurality of base stations each have a transmitting means for transmitting a transmission signal in the assigned transmission time slot using the same radio frequency. A mobile communication system having the above is obtained.

When the mobile unit receives the transmission signal from the plurality of base stations, the mobile unit includes a receiving unit that uses a normal transmission signal among the plurality of transmission signals as a reception signal. Are connected to a central station via a transmission line, the central station transmits transmission signals to the transmission line using time slots allocated to the base stations, and the base station includes: The station has selecting means for selecting the assigned time slot and receiving the transmission signal.

[0012]

EXAMPLES The present invention will be described below with reference to examples.

Referring to FIG. 1, the illustrated mobile radio system comprises a central station 41 and a plurality of base stations 42 to 44, which are arranged at predetermined intervals. ing. Then, the base stations 42 to 44
Is connected to the central office 41 via a transmission line 45. The central office 41 includes a transmission signal sending section 41a and a digital signal and slot distribution section 41b.

Referring also to FIG. 2, when transmitting the information A to C from the central station 41 to the receiving station 46, the transmission signal transmitting section 4
A transmission signal (analog signal) having information A to C is transmitted from 1a (FIG. 2A). The transmission signal is supplied to a digital signal and slot distribution unit 41b. The digital signal and slot distribution unit 41b first converts the transmission signal into a digital signal, and then converts the format of the digital signal into a predetermined format. Convert to For example, the format is converted into a digital signal in which one frame has three time slots. And each time slot of the first frame (ie, the first
To third time slot), and information B in each time slot of the second frame.
However, information C is arranged in each time slot of the third frame. Then, this digital signal is sent to the transmission line 45 as a digital transmission signal.

The base station 42 is assigned a first time slot in each frame, and similarly, the base stations 43 and 44 are assigned second and third time slots in each frame.
Of time slots are assigned. The base station 42 receives the first digital signal of each frame when receiving the digital transmission signal.
Of the first transmission signal is transmitted using a predetermined radio frequency. Therefore, the first transmission signal is transmitted in the first time slot allocated to the base station 42 (FIG. 2B). When the base station 43 receives the digital transmission signal, the base station 43
, And transmits the second transmission signal using the predetermined radio frequency. Therefore, the second
Is transmitted in the second time slot allocated to the base station 43 (FIG. 2 (c)). Similarly, when receiving the digital transmission signal, the base station 44 fetches only the third time slot of each frame and sends out the third transmission signal using the above-mentioned predetermined radio frequency. Therefore, the third transmission signal is transmitted in the third time slot allocated to the base station 44 (FIG. 2 (d)). As can be easily understood from FIGS. 2B to 2D, the first to third transmission signals are substantially time-divisionally transmitted.

The receiving station 46 receives the first to third transmission signals as first to third reception signals, respectively. As a result, as shown in FIG. 2E, the receiving station 46 gives a signal in which three pieces of information A are consecutive, three pieces of information B are consecutive, and then three pieces of information C are consecutive. become.
Then, the receiving station 46 selects the correctly received information for each piece of information and generates the received signal (generation signal) shown in FIG.

[0017]

As described above, according to the present invention, it is possible not only to prevent the reception quality from deteriorating due to mutual interference,
An inexpensive system can be provided. In other words, there is no need to take measures to prevent the reception quality from deteriorating due to the conventional mutual interference, and there is an effect that a mobile communication system that secures a wide service area by allocating only one radio transmission frequency can be constructed. Also, effective use of radio waves can be achieved.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a mobile communication system according to the present invention.

FIGS. 2A and 2B are diagrams showing signal forms in the mobile communication system shown in FIG. 1, wherein FIG. 2A shows a transmission signal, FIG. 2B shows a first transmission signal, and FIG. FIG. 4D is a diagram illustrating a transmission signal, FIG. 4D is a diagram illustrating a third transmission signal, FIG. 4E is a diagram illustrating a signal form provided to the receiving station, and FIG. 4F is a diagram illustrating a signal selectively received by the receiving station. is there.

FIG. 3 is a diagram showing a conventional mobile communication system.

[Explanation of symbols]

 41 Central Station 42-44 Base Station 45 Transmission Line 46 Receiving Station

Claims (3)

[Claims] 1. A mobile communication system in which a service area is defined by a plurality of base stations, and communication is performed with a mobile body located in the service area using at least one of the base stations. Different transmission time slots are allocated to the stations, and the plurality of base stations each have transmission means for transmitting a transmission signal in the allocated transmission time slot using the same radio frequency. 2. The mobile communication system according to claim 1, wherein when the mobile receives the transmission signals from the plurality of base stations, a normal transmission signal among the plurality of transmission signals is regarded as a reception signal. A mobile communication system, comprising: 3. The mobile communication system according to claim 2, wherein the plurality of base stations are connected to a central station via a transmission line, and the central station assigns a time assigned to each of the base stations. A mobile communication system comprising: a transmission means for transmitting a transmission signal to the transmission path using a slot; and a selection means for selecting the assigned time slot to receive the transmission signal.