JP7261188B2 - Wireless communication system and base station - Google Patents

Description

The present invention relates to a wireless communication system with multiple base stations using the same frequency.

Conventionally, wireless communication is performed between a terminal station mounted on a moving body that moves along a predetermined route (hereinafter referred to as a mobile station), such as a railway vehicle, and a base station arranged along the route. system is in operation. In such a radio communication system, a functional channel called a control channel for control transmission is used in order for one central unit and a plurality of mobile stations to contend for limited radio resources. However, in cases where radio resources are limited on a linear route, for example, in a train radio system, a plurality of base stations share one pair of frequencies (uplink and downlink) to form one zone. , co-wave interference occurred due to the difference in frequency accuracy between base stations.

In order to solve such problems, co-wave interference elimination techniques such as D-STBC (Differential Space-Time Block Coding) are used (see, for example, Patent Document 1). D-STBC generates signals of two mutually orthogonal sequences (referred to as “A sequence” and “B sequence” for convenience) from a common transmission signal sequence, and uses them as phase differences from each immediately preceding transmission signal. , the transmission is distributed in the time direction. The signals transmitted in this way follow a plurality of propagation paths according to the characteristics of radio waves, are synthesized and input to the antenna of the mobile station. The mobile station can extract the original signal (transmission signal) by extracting the signal with the highest likelihood from the combined signal of the A series and the B series.

JP 2012-134729 A

In actual operation, there are cases where detailed information such as which base station is receiving radio waves is required in addition to handling in one zone. Such a case may be resolved by using a separate system or the like mounted on a mobile object, but basically, it is ideal to be able to operate closed within the wireless communication system. For this reason, in practice, one frame of a superframe composed of a plurality of frames may be used as a frame for transmitting information unique to the base station. However, since this frame transmits different data for each base station, there is a possibility of non-reception or erroneous reception in the interference area of the radio area between the base stations.

The above problem will be described with reference to FIGS. 4 and 5. FIG.
The conventional wireless communication system illustrated in FIG. 4 includes a central device 110, a base station device 120, and a mobile station device . A plurality of base station apparatuses 120 are installed at certain intervals so as to cover a linear wireless area along a predetermined route (for example, railroad track) along which mobile station apparatus 130 moves. In FIG. 4, four base station devices 120-1 to 120-4 are installed.

The central device 110 broadcasts transmission data addressed to the mobile station to a plurality of base station devices 120 . That is, the same transmission data is transmitted from the central apparatus 110 to the plurality of base station apparatuses 120 at the same timing.

Base station apparatus 120 includes control section 121 , first transmitter 122 , second transmitter 123 , first antenna 124 and second antenna 125 . The control unit 121 converts transmission data addressed to the mobile station into orthogonal space-time coded signals of A sequence and B sequence, outputs the A sequence signal to the first transmitter 122, and outputs the B sequence signal to the second transmitter. Output to transmitter 123 . The first transmitter 122 amplifies the A-sequence signal to a predetermined power level, and transmits the amplified signal to space at a predetermined frequency from the first antenna 124 . The second transmitter 123 amplifies the B-sequence signal to the same power level as the A-sequence signal, and transmits it to space from the second antenna 125 at the same frequency as the A-sequence signal. That is, base station apparatus 120 performs signal conversion for interference cancellation such as D-STBC on transmission data addressed to a mobile station, and transmits the data to space.

Radio areas A11 to A14 shown in FIG. 4 indicate ranges within which transmission data from base station apparatuses 120-1 to 120-4 reach, respectively. Radio waves may collide in areas where the wireless areas of adjacent base stations overlap.

The mobile station apparatus 130 is a terminal station that receives signals transmitted from the base station apparatus 120 and performs necessary processing. In FIG. 4, reference numerals 130-1, 130-2, and 130-3 indicate how the mobile station apparatus 130 moves from the left side to the right side of the drawing as time elapses. Mobile station apparatus 130-1 exists in an area where radio waves from both base station apparatuses 120-1 and 120-2 interfere (that is, an area where radio areas A11 and A12 overlap). Mobile station 130-2 is moving to an area where radio waves from base station apparatus 120-2 can be stably received (that is, wireless area A12). Mobile station apparatus 130-3 is moving to an area where radio waves from both base station apparatuses 120-2 and 120-3 interfere with each other (that is, an area where radio areas A12 and A13 overlap).

FIG. 5 shows an example of time-division data transmission by a conventional system. As described above, in principle, the central apparatus 110 gives the same transmission data to each base station apparatus 120 at the same timing. The base station device 120 divides the transmission data into frames with a time length of a predetermined unit (for example, 40 ms unit), and repeatedly transmits a series of data blocks called superframes composed of a plurality of consecutive frames. Realizes time-division data transmission. These data can be correctly received by mobile station apparatus 130 even in an interference area between base stations due to transmission diversity on the premise that each of base station apparatuses 120-1 to 120-4 transmits the same data. .

On the other hand, the “base station 1 information” to “base station 4 information” frames in the superframe are used to transmit unique information (eg, base station number) to each of the base station apparatuses 120 . Since this frame transmits different information for each base station, depending on the position of the mobile station apparatus 130, there is a possibility of non-reception or erroneous reception due to radio wave interference. In other words, there is a possibility that mobile station apparatuses 130-1 and 130-3 in the interference area will not receive or receive erroneously.

The present invention has been made in view of the conventional circumstances as described above. An object of the present invention is to provide a wireless communication system capable of suppressing the occurrence of non-reception and erroneous reception.

In order to achieve the above objects, the present invention configures a wireless communication system as follows.
That is, in a wireless communication system having a plurality of base stations using the same frequency, there are a first period during which each base station transmits the same data and a second period during which each base station can transmit different data. and at least one of the two base stations having partially overlapping radio areas varies the level of its transmission power during the second period differently than the other base station.

According to such a configuration, in an area where the radio areas of two base stations overlap, the reception level of data transmitted from each base station during the second period varies. As a result, it becomes easier to receive transmission data with a higher transmission output level, and it is possible to suppress the occurrence of non-reception or erroneous reception.

Here, as one configuration example, each base station has a mode in which the level of the transmission power is not changed and a mode in which the level of the transmission power is changed. The mode may be switched alternately so that the mode is different between and different from the previous mode. As a result, in an area where the radio areas of two base stations overlap, a state in which it is easy to receive data transmitted from one base station and a state in which it is easy to receive data transmitted from the other base station alternately. Therefore, both data can be received correctly.

A plurality of base stations may be arranged at intervals along a predetermined route. This makes it possible to obtain the above effects even in a wireless communication system having a linear wireless area along a predetermined route.

According to the present invention, when a plurality of base stations transmit different data on the same frequency, it is possible to suppress the occurrence of non-reception or erroneous reception of transmitted data in the interference area of the radio area between the base stations. A wireless communication system can be provided.

1 is a diagram showing a configuration example of a radio communication system according to an embodiment of the present invention; FIG. 2 is a diagram showing an example of time-division data transmission by the wireless communication system of FIG. 1; FIG. 2 is a diagram illustrating another example of time-division data transmission by the wireless communication system of FIG. 1; FIG. 1 is a diagram showing a configuration example of a conventional wireless communication system; FIG. FIG. 3 is a diagram showing an example of time-division data transmission by a conventional system;

A radio communication system according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration example of a wireless communication system according to one embodiment of the present invention. The radio communication system illustrated in FIG. 1 includes a central device 10, a base station device 20, and a mobile station device 30. FIG. A plurality of base station devices 20 are installed at certain intervals so as to cover a linear radio area along a predetermined route (for example, railroad track) along which the mobile station device 30 moves. In FIG. 1, four base station devices 20-1 to 20-4 are installed.

The central device 10 broadcasts transmission data addressed to the mobile station to a plurality of base station devices 20 . That is, the same transmission data is transmitted from the central apparatus 10 to the plurality of base station apparatuses 20 at the same timing.

The base station device 20 includes a controller 21 , a first transmitter 22 , a second transmitter 23 , a first antenna 24 and a second antenna 25 . The control unit 21 converts transmission data addressed to the mobile station into orthogonal space-time coded signals of A sequence and B sequence, outputs the A sequence signal to the first transmitter 22, and outputs the B sequence signal to the second transmitter. Output to transmitter 23 . The first transmitter 22 amplifies the A-sequence signal to a predetermined power level, and transmits the amplified signal to space at a predetermined frequency from the first antenna 24 . The second transmitter 23 amplifies the B-sequence signal to the same power level as the A-sequence signal, and transmits it to the space from the second antenna 25 at the same frequency as the A-sequence signal. That is, the base station apparatus 20 performs signal conversion for interference elimination such as D-STBC on transmission data addressed to the mobile station, and transmits the data to space.

Radio areas A1 to A4 shown in FIG. 1 indicate ranges within which transmission data from base station apparatuses 20-1 to 20-4 reach, respectively. Radio waves may collide in areas where the wireless areas of adjacent base stations overlap.

The mobile station apparatus 30 is a terminal station that receives signals transmitted from the base station apparatus 20 and performs necessary processing. In FIG. 1, reference numerals 30-1, 30-2, and 30-3 indicate how the mobile station apparatus 30 moves from the left side to the right side of the drawing as time elapses. Mobile station apparatus 30-1 exists in an area where radio waves from both base station apparatuses 20-1 and 20-2 interfere (that is, an area where radio areas A1 and A2 overlap). The mobile station 30-2 has moved to an area where it is easier to receive the base station device 20-2 than the base station device 20-1 (that is, an area slightly closer to the radio area A2 than the radio area A1). The mobile station 30-3 has moved to an area where radio waves from the base station device 20-2 can be stably received (that is, radio area A2).

FIG. 2 shows an example of time-division data transmission by the wireless communication system of this example. As described above, in principle, the central apparatus 10 gives the same transmission data to each base station apparatus 20 at the same timing. The base station device 20 divides the transmission data into frames with a time length of a predetermined unit (for example, 40 ms unit), and repeatedly transmits a series of data blocks called superframes composed of a plurality of consecutive frames. Realizes time-division data transmission. These data can be correctly received by mobile station apparatus 30 even in an interference area between base stations due to transmission diversity on the premise that each of base station apparatuses 20-1 to 20-4 transmits the same data. .

On the other hand, the frames of "base station 1 information" to "base station 4 information" (hereinafter referred to as "base station n information") in the superframe contain information specific to each base station device 20 (eg, base station number). Used for transmission. Each base station transmits different information in this frame, but the power level of the transmit power from each base station is controlled to be different from other base stations in its vicinity. For example, when the base station devices 20-1 to 20-4 are divided into a base station group with odd-numbered base station numbers and a base station group with even-numbered base station numbers, the even-numbered base station group (that is, the base station device 20 -2, 20-4) reduce (attenuate) the power level of the transmission output in odd-numbered superframes with an attenuator or the like. Similarly, the odd-numbered base station groups (that is, base station apparatuses 20-1 and 20-3) reduce the power level of the transmission output in even-numbered superframes. Here, it is assumed that each base station apparatus 20 controls the power level without distinguishing between the A-sequence and B-sequence signals.

In FIG. 1, broken lines B2 and B4 indicate the state of the wireless area in odd-numbered superframes. Thus, in odd-numbered superframes, the radio areas B2 and B4 of the even-numbered base station groups are reduced so as not to interfere with the radio areas A1 and A3 of the odd-numbered base station groups. The state of the wireless area in even-numbered superframes is omitted from the drawing.

When such control is performed, the mobile station apparatus 30-1 existing in the interference area where the radio areas A1 and A2 overlap can receive the specific information of the base station apparatus 20-1 during the transmission period of the odd-numbered superframe. However, the unique information of the base station device 20-2 cannot be received because the radio waves are weakened. On the other hand, during the transmission period of even-numbered superframes, the unique information of base station apparatus 20-2 can be received, but the unique information of base station apparatus 20-1 cannot be received because the radio waves are weakened. In other words, the mobile station device 30-1 can alternately receive the unique information of the base station device 20-1 and the unique information of the base station device 20-2. Note that the mobile station apparatus 30 does not update its location information until it can receive the same base station number consecutively in a predetermined number of superframes, so it can rationally hold the most recent location information.

After that, the mobile station device 30-2, which has moved from the wireless area A1 to an area slightly closer to the wireless area A2, becomes less likely to receive the unique information of the base station device 20-1 during the transmission period of the odd-numbered superframe. The unique information of the base station device 20-2 can be received. In addition, during the transmission period of the even-numbered superframes, it becomes easier to receive the unique information of the base station apparatus 20-2, but the unique information of the base station apparatus 20-1 cannot be received. In this way, the mobile station device 30-2 can continuously receive the specific information of the base station device 20-2 for a predetermined number of times, so that it is possible to appropriately update its own location information.

After that, the mobile station device 30-3, which has moved from the wireless area A1 to the wireless area A2, cannot receive any unique information of the base station device 20-1 regardless of whether the superframe is odd-numbered or even-numbered. The unique information of device 20-2 can be successfully received. Therefore, the mobile station device 30-3 can stably maintain its own location information in the radio area A2 of the base station device 20-2.

As described above, the radio communication system of this example includes a plurality of base station apparatuses 20 that use the same frequency, and each base station apparatus 20 transmits the same data during the first period (base station A transmission frame other than n information) and a second period (transmission frame of base station n information) in which each base station apparatus 20 can transmit different data are provided. Then, one of the two base station apparatuses 20 (for example, base station apparatus 20-2) having wireless areas that partially overlap each other sets the power level of the transmission output in the second period to that of the other base station (for example, It is configured to be lowered differently from the base station apparatus 20-1).

By performing such transmission power control, in an area where the radio areas of two base station apparatuses 20 overlap, the reception level of data transmitted from each base station during the second period varies. As a result, the mobile station apparatus 30 existing in the relevant area can easily receive the transmission data with the higher power level of the transmission output, and the occurrence of non-reception or erroneous reception is suppressed.

In the wireless communication system of this example, each base station apparatus 20 has a mode in which the power level of transmission output is not lowered and a mode in which the power level of transmission output is lowered. Then, each time the second period arrives, the mode is alternately switched between the two base station apparatuses 20 so that the mode is different from the previous one. As a result, the mobile station apparatus 30 existing in the area where the radio areas of the two base station apparatuses 20 overlap can easily receive the transmission data of one of the two base station apparatuses 20 and can easily receive the transmission data of the other. and are switched alternately, both transmission data can be correctly received.

If the radio communication system is the D-STBC system as in this example, the power levels of the transmission outputs of the A-sequence and B-sequence signals may be alternately lowered. An example of time-division data transmission in this case is shown in FIG. In the figure, for the A-sequence signal, the even-numbered base station group (for example, the base station apparatus 20-1) lowers the power level of the transmission output in the odd-numbered superframe, and the odd-numbered base station group ( For example, the base station apparatus 20-2) lowers the power level of the transmission output in even-numbered superframes. On the other hand, for B-sequence signals, the even-numbered base station groups reduce the power level of the transmission output in even-numbered superframes, and the odd-numbered base station groups reduce the power level of the transmission output in odd-numbered superframes. Lower. In this way, by controlling the power level of transmission output in consideration of transmission diversity, it is possible to further suppress the occurrence of non-receipt and erroneous reception of transmission data in the interference area of the wireless area between base stations. Become.

Here, in the above description, one of the two adjacent base station apparatuses 20 lowers the power level of the transmission output, thereby controlling the power level of the transmission output to be different from that of the other. , the control mode of the power level of the transmission output is not limited to this. For example, control may be performed so that one of the two base station apparatuses 20 decreases the power level of transmission output and the other increases the power level of transmission output. If the power level of the transmit power is increased, the radio waves may be too strong and the data may be corrupted, but can be received correctly in the next superframe. Note that it is not essential to control the power level of the transmission output in all superframes, and there may be superframes in which the power level of the transmission output is not controlled.

Although the present invention has been described above based on one embodiment, it goes without saying that the present invention is not limited to the wireless communication system described here, and can be widely applied to other wireless communication systems. For example, even if the STBC method is used instead of the D-STBC method, the same effect can be obtained. Moreover, the present invention does not require the transmission diversity function as described above, and can of course be applied to a radio communication system that does not have a transmission diversity function.

The radio communication system according to the present invention is effective when applied to a train radio system as in this example. is also effective for wireless communication systems. In addition, the present invention is not limited to a wireless communication system that secures a linear wireless area along a route along which a mobile station is expected to move, but can be used as a co-wave interference countermeasure technology between two base stations. It is possible.

The present invention can also be provided as, for example, a method or system for executing processing according to the present invention, a program for realizing such a method or system, or a storage medium for storing the program.

INDUSTRIAL APPLICABILITY The present invention can be used in wireless communication systems with multiple base stations using the same frequency.

10, 110: Central device 20, 120: Base station device 30, 130: Mobile station device 21, 121: Control unit 22, 122: A-sequence transmitter 23, 123: B-sequence transmission 24, 124: Antenna on the A series side 25, 125: Antenna on the B series side

Claims (3)

In a wireless communication system with multiple base stations using the same frequency,
a first period during which each base station transmits the same data and a second period during which each base station transmits different data;
Each base station has a mode in which the level of transmission power is not varied and a mode in which the level of transmission power is varied, and each time the second period arrives two base stations having partially overlapping radio areas. A wireless communication system characterized by alternately switching modes such that the modes are different between stations and different from the previous mode . In the wireless communication system according to claim 1 ,
A wireless communication system, wherein the plurality of base stations are arranged at intervals along a predetermined route. A base station that uses the same frequency as a neighboring base station whose radio area partially overlaps,
a first period during which the same data as the neighboring base station is transmitted and a second period during which data different from the neighboring base station can be transmitted;
The base station has a mode in which the level of transmission power is not changed and a mode in which the level of transmission power is changed. A base station characterized by alternately switching modes so that the mode is different from the previous mode .

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