JP2007036442A - Wireless communication system, base station, wireless communication control method and program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless communication system that efficiently reduces congestion to accept an access from a communication terminal without the need for adding a function to the communication terminal even when a network load is extremely high. <P>SOLUTION: In the wireless communication system comprising a base station 1, and a plurality of communication terminals 2 belonging to a communication area 3 of the base station 1, each communication terminal 2 wirelessly transmits a random access frame to the base station 1. The base station 1 uses its antenna to receive the random access frame transmitted from each communication terminal 2 to detect a congestion state from the received random access frame. When detecting occurrence of congestion, the base station 1 places a limit on an area in the communication area 3 receptible of the random access frame depending on the congestion state and varies the limited area depending on time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio communication system, a base station, a radio communication control method, a radio communication control program, and a recording medium.

Conventionally, in a radio access system, there is a technique for controlling the amount of communication traffic by changing the retransmission waiting time and the number of allocated slots in random access according to the network load, that is, the congestion state (see, for example, Patent Document 1). ).
JP 2001-244939 A

  In the above-described prior art, it is necessary to notify the subscriber station (communication terminal) of control information for instructing a change in the retransmission standby time and the number of assigned slots. However, this has a problem in that a limited number of slots cannot be used effectively because a slot for wireless communication must be used. In addition, when the network load is extremely high such that a large number of subscriber stations try to access, the network load may be increased by the notification of the control information, and the congestion may not be improved. Furthermore, it has been necessary to add a function for performing random access to all the subscriber stations in accordance with changes in the retransmission standby time and the number of assigned slots instructed from the base station.

  The present invention has been made in view of such circumstances, and its purpose is to add a function to a communication terminal in a wireless communication system, and even when the network load is extremely high, An object of the present invention is to provide a wireless communication system, a base station, a wireless communication control method, a wireless communication control program, and a recording medium that can efficiently improve congestion and accept an access from a communication terminal.

  In order to solve the above-described problem, the invention according to claim 1 is a wireless communication system including a base station and a plurality of communication terminals belonging to a communication area of the base station, wherein the communication terminal wirelessly transmits to the base station. The base station detects a congestion state from an antenna that receives a wireless communication frame transmitted from the communication terminal and a random access frame received by the antenna. A congestion detection processing unit, and a reception area control processing unit that limits a communication area in which a random access frame can be received according to a congestion state detected by the congestion detection processing unit, and changes the limited communication area with time. A wireless communication system characterized by comprising:

  The invention according to claim 2 is the wireless communication system according to claim 1, wherein the congestion detection processing unit detects a received power that is equal to or higher than a communicable power level in the antenna and receives the received frame. Can be demodulated, or when the received power that is higher than the communicable power level is detected at the antenna and the bit error as a result of demodulating the received frame is greater than or equal to a certain value, it is regarded as a collision of transmission frames, The congestion state is detected based on the ratio of the number of transmission frame collisions to the maximum number of receivable frames in the unit time.

  The invention according to claim 3 is the base station of a radio communication system comprising a base station and a plurality of communication terminals belonging to a communication area of the base station, wherein the radio communication is transmitted from the communication terminal. Receiving a frame, a congestion detection processing unit for detecting a congestion state from a random access frame received by the antenna, and receiving a random access frame according to the congestion state detected by the congestion detection processing unit And a reception area control processing unit that limits a limited communication area and changes the limited communication area depending on time.

  The invention according to claim 4 is the base station according to claim 3, wherein the congestion detection processing unit detects received power that is equal to or higher than a communicable power level at the antenna, and receives the received frame. When it is impossible to demodulate, or when the received power exceeding the communicable power level is detected at the antenna and the bit error as a result of demodulating the received frame is more than a certain value, it is regarded as a transmission frame collision, and transmission in unit time The congestion state is detected based on the ratio of the number of frame collisions to the maximum number of receivable frames in the unit time.

  The invention according to claim 5 is a radio communication control method used in a radio communication system including a base station and a plurality of communication terminals belonging to a communication area of the base station, wherein the communication terminal A frame is randomly transmitted by radio to a base station, the base station receives a random access frame transmitted from the communication terminal via an antenna, detects a congestion state from the received random access frame, and is detected. A wireless communication control method characterized by limiting a communication area in which a random access frame can be received according to a congestion state, and changing the limited communication area with time.

  The invention according to claim 6 is the wireless communication control method according to claim 5, wherein the antenna detects received power that is equal to or higher than a communicable power level, and the received frame cannot be demodulated, or , A case where the antenna detects a received power that is equal to or higher than a communicable power level and a bit error as a result of demodulating the received frame is a certain value or more is regarded as a transmission frame collision. The congestion state is detected based on a ratio to the maximum number of receivable frames in the unit time.

  The invention according to claim 7 is a wireless communication control program executed on the base station of a wireless communication system comprising a base station and a plurality of communication terminals belonging to the communication area of the base station, A step of detecting a congestion state from a random access frame received by an antenna, a step of limiting a communication area in which a random access frame can be received according to the detected congestion state, and a step of changing the limited communication area with time And a wireless communication control program that causes a computer to execute the processes.

  The invention according to claim 8 describes a radio communication control program executed on the base station of a radio communication system including a base station and a plurality of communication terminals belonging to a communication area of the base station. A computer-readable recording medium, wherein a congestion state is detected from a random access frame received by an antenna, and a communication area in which a random access frame can be received is limited according to the detected congestion state. The recording medium is characterized by recording a wireless communication control program that causes a computer to execute each of the steps of changing a limited communication area depending on time.

  According to the present invention, in a wireless communication system including a base station and a plurality of communication terminals belonging to the communication area of the base station, when the communication terminal performs communication using random access to the base station, The congestion state is detected based on the access status from the communication terminal, the communication area capable of receiving the random access frame is limited to a range corresponding to the congestion state, and the limited communication area is changed with time. Thus, since the number of communication terminals that accept random access in the base station is reduced, there is no need to instruct control from the base station to the communication terminals. As a result, it is possible to effectively use frames without causing bandwidth compression due to transmission of control signals, so that even when the network load is extremely high, the collision probability of frames transmitted from the communication terminal to the base station is reduced. Thus, it is possible to efficiently improve congestion and accept access from a communication terminal. Further, it is not necessary to add a function for congestion control to the communication terminal.

Hereinafter, an embodiment of a wireless communication system of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating the overall configuration of a wireless communication system.
The wireless communication system includes a base station 1 and a plurality of communication terminals 2 existing in a communication area 3. The communication area 3 is an area where the base station 1 and the communication terminal 2 can communicate wirelessly. In the present embodiment, TDMA (Time Division Multiple Access) / TDD (Time Division Duplex) method is used for wireless communication between the base station 1 and the communication terminal 2. Used. Thereby, the base station 1 divides electromagnetic waves of the same frequency according to time and communicates with a plurality of communication terminals 2.

  The communication terminal 2 is, for example, a notebook personal computer, a PDA (Personal Digital Assistants), a mobile phone terminal, a wireless tag, or the like, and performs communication using a random access method. For example, it is assumed that the base station 1 receives a communication request from the communication terminal 2, allocates time-divided frames (slots) in the TDMA / TDD scheme, and performs communication. In this case, the communication terminal 2 sends a signal indicating a communication request to the base station 1 using a frame for random access among the time-divided frames. Since this signal is transmitted at random, a plurality of communication terminals 2 may transmit a signal to the base station 1 using frames with the same timing, and the signals collide. In the random access method, the collided frame is invalidated, and each communication terminal 2 retransmits the frame after a random delay time. Thus, the communication terminal 2 has a function of transmitting frames to the base station 1 at random.

FIG. 2 is a block diagram showing the internal configuration of the base station 1.
The base station 1 includes an antenna 11 and a control processing unit 12. The antenna 11 transmits and receives a frame for wireless communication with the communication terminal 2. The control processing unit 12 includes a congestion detection processing unit 13 and a reception area control processing unit 14. The congestion detection processing unit 13 detects a congestion state from a random access frame received by the antenna 11. When the congestion detection processing unit 13 detects a congestion state, the reception area control processing unit 14 changes the directivity by changing the tilt angle or the half-value width of the antenna 11 from the communication terminal 2 in the communication area 3. An area where a transmitted random access frame can be received is limited according to a congestion state, and the limited area is changed with time.

Next, receivable area control of the wireless communication system will be described with reference to FIGS.
FIG. 3 is a diagram for explaining a “pattern A” for controlling a random access receivable area in the communication area 3 in units of fan-shaped areas.
An electromagnetic wave used for wireless communication between the base station 1 and the communication terminal 2 is time-divided into a period called a super frame. The superframe is further time-divided into a cycle called a control cycle, and the control cycle is further time-divided into a cycle called a frame.
When a period from a certain time T _j to a time T _{j + 1 is} defined as a superframe #j, a previous period of the superframe #j is a superframe # j-1, and a next period of the superframe #j is a superframe # j + 1. To do. In the figure, each super frame is composed of k control periods # 1 to #k, and each control period # 1 to #k is composed of three frames. Each frame includes an area (frame) for communicating with the communication terminal 2 using a slot assigned by the base station 1 in response to a request from the communication terminal 2 and an area (frame) used for random access (RA). Have. Note that there may be a case where the entire frame consists of a random access area, such as a wireless LAN (Local Area Network).

The congestion detection processing unit 13 of the base station 1 detects a congestion state from a random access frame received by the antenna 11 from the communication terminal 2. This congestion state detection uses the ratio of the number of random access frame collisions in a unit time to the maximum number of receivable frames in random access in this unit time. Here, a ratio between the maximum number of receivable frames for random access per unit time and the number of differences obtained by subtracting the number of random access frame collisions per unit time from the maximum number of receivable frames is used. That is, when p is the maximum number of receivable frames for random access per unit time and q is the number of collisions of random access frames per unit time, the congestion level (CL: Congestion Level) is calculated by (p−q) / p. To do. Alternatively, the ratio between the maximum number of receivable frames for random access and the number of collisions of random access frames within the same unit time, that is, q / p may be used. Then, when the congestion level exceeds a predetermined threshold, it is determined that congestion has occurred. Here, “congestion level 0” indicating no congestion, “congestion level 1” indicating that congestion has occurred, and “congestion level 2” indicating that severe congestion has occurred, depending on the value of the congestion level. It shall be divided into three stages.
It should be noted that the congestion detection processing unit 13 determines that a transmission frame collision has occurred when the antenna 11 detects received power that is equal to or higher than the communicable power level and cannot demodulate the received frame. Alternatively, it is also possible to determine that a transmission frame collision has occurred when the antenna 11 detects reception power that is equal to or higher than the communicable power level and the bit error as a result of demodulating the received frame is above a certain level. In addition, here, the unit time is defined as one superframe period.

Congestion level _{CL j-1} in the super frame # j-1 is a value in a range of the congestion level 0. A random access receivable area in communication area 3 in superframe # j-1 is shown in pattern A _j-1 . A shaded range indicates a receivable area in the communication area 3, that is, in the superframe # j-1, the entire communication area 3 is a random access receivable area.

The congestion detection processing unit 13 of the base station 1 calculates the congestion level CL _j at the time T _j when the super frame #j starts. For the calculation of the congestion level CL _j , the maximum number of receivable frames and the number of collisions in random access in the super frame # j−1 are used. If the congestion level CL _j calculated by the congestion detection processing unit 13 is a value in the range of “congestion level 2”, the reception area control processing unit 14 divides the communication area 3 into four sectors in the superframe #j. The random access receivable areas are moved in control cycle units in the order of the areas 3a, 3b, 3c, and 3d. As a result, in the superframe #j, the random access receivable area m-rounds the entire communication area 3 (m is an integer of 1 or more).

Receivable areas for random access in the communication area 3 in the control periods # 1 to k of the superframe #j are shown in patterns A _j −1 to A _j -k. In the pattern A _j −1 in the control cycle # 1 of the superframe #j, the area 3a is a random access receivable area. That is, the reception area control processing unit 14 receives only frames transmitted from the communication terminal 2 existing in the area 3a in the random access areas in the frames # 1 to # 3 in the control cycle # 1 of the superframe #j. Thus, the directivity of the antenna 11 is controlled.

In the pattern A _j -2 in the control cycle # 2, the area 3b is a random access receivable area. The reception area control processing unit 14 directs the antenna 11 to receive only frames transmitted from the communication terminal 2 existing in the area 3b in the random access area in each frame in the control cycle # 2 of the superframe #j. Control gender. In the pattern A _j -k in the control cycle #k, the area 3d is a random access receivable area.

The congestion detection processing unit 13 of the base station 1 calculates the congestion level CL _{j + 1} at the time T _{j + 1} when the superframe # j + 1 starts. For the calculation of the congestion level CL _{j + 1} , the maximum number of receivable frames and the number of collisions in random access in the super frame #j are used. If the congestion level CL _{j + 1} calculated by the congestion detection processing unit 13 is a value in the range of “congestion level 1”, the reception area control processing unit 14 divides the communication area 3 into two sectors in the superframe # j + 1. The receivable areas for random access are moved in units of control periods in the order of the areas 3e and 3f. The area 3e corresponds to an area combining the areas 3a and 3b, and the area 3f corresponds to an area combining the areas 3c and 3d. Thus, the reception area control processing unit 14 limits the receivable area for random access according to the congestion level, and changes the limited receivable area depending on time.
In each control cycle of superframes # j-1, j, j + 1, the range of the receivable area for random access is different, but the maximum receivable frame number for random access is the same.

FIG. 4 is a diagram for explaining a “pattern B” for controlling a receivable area for random access in the communication area 3 in a concentric area unit.
A random access receivable area in communication area 3 in superframe # j-1 is shown in pattern B _j-1 . Congestion level CL _j-1 in the super frame # j-1 is a value in the range of congestion level 0, the entire communication area 3 is receivable area of the random access.

The congestion detection processing unit 13 of the base station 1 calculates a congestion level CL _j at time T _j . Assuming that the calculated value is within the range of “congestion level 2”, the reception area control processing unit 14 in the superframe #j, the areas 3g, 3h, 3i, and 3j obtained by dividing the communication area 3 into four concentric circles. In order, the receivable area for random access is moved in units of control cycles. Thereby, in the super frame #j, the receivable area of random access covers the entire communication area 3.

Random access receivable areas in the communication area 3 in each control cycle # 1 to k of the super frame #j are shown in patterns B _j −1 to B _j −k. In the pattern B _j −1 in the control cycle # 1 of the superframe #j, the area 3g is a random access receivable area. Similarly, in pattern B _j -2 in control cycle # 2, area 3h is a receivable area for random access, and in pattern B _j -3 in control cycle # 3, area 3i is a receivable area for random access, control cycle #. in pattern _B j -k in k, the area 3j is receivable area of the random access.

The congestion detection processing unit 13 of the base station 1 calculates the congestion level CL _{j + 1} at the time T _{j + 1} when the superframe # j + 1 starts. Assuming that the congestion level CL _{j + 1} calculated by the congestion detection processing unit 13 is a value within the range of “congestion level 1”, the reception area control processing unit 14 concentrically communicates the communication area 3 with 2 in the superframe # j + 1. Random access receivable areas are moved in control cycle units in the order of the divided areas 3k and 3l. The area 3k corresponds to the area that combines the areas 3g and 3h, and the area 3l corresponds to the area that combines the areas 3i and 3j.

FIG. 5 illustrates a “pattern C” for controlling the receivable area of random access for each sector into which the communication area 3 is divided in sector-shaped areas.
In pattern C, communication area 3 is divided into four sectors 4-1 to 4-4, and the random access receivable area is changed for each sector as in pattern A.
A random access receivable area in the communication area 3 in the super frame # j-1 is shown in a pattern C _j-1 . Congestion level _{CL j-1} in the super frame # j-1 is a value in the range of congestion level 0, the entire sector 4-1 to 4-4, that is, the entire communication area 3 is a receivable area of the random access .

The congestion detection processing unit 13 of the base station 1 calculates a congestion level CL _j for each of the sectors 4-1 to 4-4. For example, for calculating the congestion level CL _j of the sector 4-1, the maximum number of receivable frames and the number of collisions in random access of the sector 4-1 in the superframe # j-1. The congestion level CL _j of the sector 4-1 is a value in the range of “congestion level 2”, and the congestion level CL _j of the other sectors 4-2 to 4-4 is a value in the range of “congestion level 0”. To do. In the superframe #j, the reception area control processing unit 14 divides the sector 4-1 into four sectors in the order of the areas 4-1a, 4-1b, 4-1c, and 4-1d. Move the receivable area for random access in units of control cycle. Thereby, in the super frame #j, the receivable area of random access covers the entire communication area 3.

Random access receivable areas in the communication area 3 in each control cycle # 1 to k of the superframe #j are shown in patterns C _j −1 to C _j −k. In the pattern C _j −1 in the control cycle # 1 of the superframe #j, the area 4-1a and the sectors 4-2, 4-3, and 4-4 are receivable areas for random access. In the pattern C _j -2 in the control cycle # 2, the area 4-1b and the sectors 4-2, 4-3, and 4-4 are the random access receivable areas, and the pattern C _j- in the control cycle # 3. 3, the area 4-1 c and the sectors 4-2, 4-3, and 4-4 are random access receivable areas. In the pattern C _j -k in the control cycle #k, the areas 4-1 d and Sectors 4-2, 4-3 and 4-4 are receivable areas for random access.

The congestion detection processing unit 13 of the base station 1 calculates the congestion level CL _{j + 1} of each of the sectors 4-1 to 4-4 at the time T _{j + 1} when the superframe # j + 1 starts. A value in the range of congestion level CL _j is "congestion level 1" in the sector 4-1, a congestion level CL _j other sectors 4-2 to 4-4 is a value ranging from "congestion level 0" To do. In the superframe # j + 1, the reception area control processing unit 14 moves the receivable area for random access in units of control periods in the order of the areas 4-1e and 4-1f obtained by dividing the sector 4-1 into two sectors. The area 4-1e corresponds to an area where the areas 4-1a and 4-1b are combined, and the area 4-1f corresponds to an area where the areas 4-1c and 4-1d are combined.

FIG. 6 illustrates a “pattern D” for controlling the receivable area of random access for each sector into which the communication area 3 is divided into concentric area units.
In the pattern D, the communication area 3 is divided into four sectors 4-1 to 4-4, and the receivable area for random access is changed for each sector in the same manner as the pattern B.
It shows a receivable area of the random access in the communication area 3 of the superframe # j-1 to the pattern D _j-1. Congestion level _{CL j-1} in the super frame # j-1 is a value in the range of congestion level 0, the entire sector 4-1 to 4-4, that is, the entire communication area 3 is a receivable area of the random access .

The congestion detection processing unit 13 of the base station 1 calculates a congestion level CL _j for each of the sectors 4-1 to 4-4. The congestion level CL _j of the sector 4-1 is a value in the range of “congestion level 2”, and the congestion level CL _j of the other sectors 4-2 to 4-4 is a value in the range of “congestion level 0”. To do. The reception area control processing unit 14 in the superframe #j, for the sector 4-1, in the order of areas 4-1g, 4-1h, 4-1i, 4-1j obtained by dividing the sector 4-1 into four concentric circles. , The receivable area for random access is moved in control cycle units. Thereby, in the super frame #j, the receivable area of random access covers the entire communication area 3.

Random access receivable areas in the communication area 3 in each control cycle # 1 to k of the super frame #j are assumed to be patterns D _j −1 to D _j −k. In the pattern _D j -1 in the control cycle # 1 superframe #j, area 4-1G, and the sector 4-2,4-3,4-4 are receivable area of the random access. In the pattern D _j -2 in the control cycle # 2, the area 4-1h and the sectors 4-2, 4-3, and 4-4 are the random access receivable areas, and the pattern D _j − in the control cycle # 3. 3, the area 4-1 i and the sectors 4-2, 4-3, and 4-4 are random access receivable areas. In the pattern D _j -k in the control cycle #k, the areas 4-1 _j and Sectors 4-2, 4-3 and 4-4 are receivable areas for random access.

The congestion detection processing unit 13 of the base station 1 calculates the congestion level CL _{j + 1} of each of the sectors 4-1 to 4-4 at the time T _{j + 1} when the superframe # j + 1 starts. The congestion level CL _j of the sector 4-1 is a value in the range of “congestion level 1”, and the congestion level CL _j of the other sectors 4-2 to 4-4 is a value in the range of “congestion level 0”. To do. In superframe # j + 1, reception area control processing unit 14 moves a receivable area for random access in units of control periods in the order of areas 4-1k and 4-1l obtained by dividing sector 4-1 into two concentric circles. . The area 4-1k corresponds to the area where the areas 4-1g and 4-1h are combined, and the area 4-1 corresponds to the area where the areas 4-1i and 4-1j are combined.

  In addition, according to the said embodiment, according to the congestion level, the receivable area of random access is made into the area which divided the communication area 3 or the sector into the fan shape and the concentric circles, and divided into 2 parts, and it changed with every control cycle. However, the period of changing the shape of the division, the number of divisions, and the receivable area is not limited to this. Further, the wireless communication method used between the base station 1 and the communication terminal 2 is not limited to a time division multiplexing method such as TDMA, and may be, for example, an ALOHA method.

  According to the above embodiment, in a communication system including the base station 1 and a plurality of communication terminals 2 belonging to the communication area 3 of the base station 1, the communication terminal 2 communicates with the base station 1 using random access. When performing, the base station 1 detects the congestion state based on the access status from the communication terminal 2 and controls the directivity of the antenna 11 to change the receivable area of random access according to the congestion state. And the receivable area varies with time. In this way, since the number of communication terminals 2 that accept random access in the base station 1 is reduced, it is not necessary for the base station 1 to instruct the communication terminal 2 to perform control. As a result, the frame is not compressed by sending out the control signal, and the frame can be used effectively. Therefore, even when the network load is extremely high, the collision probability of the frame transmitted from the communication terminal 2 to the base station 1 is reduced. It is possible to efficiently reduce congestion by lowering and accept access from the communication terminal 2. Further, it is not necessary to add a function for congestion control to the communication terminal 2.

  The base station 1 and the communication terminal 2 described above have a computer system inside. The operation process of the control processing unit 12 of the base station 1 and the communication terminal 2 described above is stored in a computer-readable recording medium in the form of a program, and this program is read and executed by the computer system. Thus, the above process is performed. The computer system here includes an OS and hardware such as peripheral devices.

  In addition to ROM, “computer-readable recording medium” refers to a portable medium such as a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, or a storage device such as a hard disk built in a computer system. That means. Furthermore, the “computer-readable recording medium” refers to a volatile memory (RAM) inside a computer system that becomes a client or a system when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

Further, the “computer system” includes a homepage providing environment (or display environment) if a WWW system is used.
The “computer-readable recording medium” refers to a storage device such as a flexible medium, a magneto-optical disk, a portable medium such as a ROM and a CD-ROM, and a hard disk incorporated in a computer system. Furthermore, the “computer-readable recording medium” dynamically holds a program for a short time like a communication line when transmitting a program via a network such as the Internet or a communication line such as a telephone line. In this case, a volatile memory in a computer system serving as a server or a client in that case is also used to hold a program for a certain period of time. The program may be a program for realizing a part of the functions described above, and may be a program capable of realizing the functions described above in combination with a program already recorded in a computer system.

It is a figure which shows the structure of the radio | wireless communications system by one embodiment of this invention. It is a block diagram which shows the internal structure of the base station by the embodiment. It is a figure for demonstrating the receivable area control of the radio | wireless communications system by the embodiment. It is a figure for demonstrating the receivable area control of the radio | wireless communications system by the embodiment. It is a figure for demonstrating the receivable area control of the radio | wireless communications system by the embodiment. It is a figure for demonstrating the receivable area control of the radio | wireless communications system by the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base station 11 ... Antenna 12 ... Control processing part 13 ... Congestion detection processing part 14 ... Reception area control processing part 2 ... Communication terminal 3 ... Communication area 4-1, 4-2, 4-3, 4-4 ... Sector

Claims (8)

In a wireless communication system comprising a base station and a plurality of communication terminals belonging to the communication area of the base station,
The communication terminal is
Wireless communication means for randomly transmitting a frame wirelessly to the base station,
The base station
An antenna for receiving a wireless communication frame transmitted from the communication terminal;
A congestion detection processing unit that detects a congestion state from a random access frame received by the antenna;
A communication area that can receive a random access frame according to a congestion state detected by the congestion detection processing unit, and a reception area control processing unit that varies the limited communication area with time.
A wireless communication system. The congestion detection processing unit detects reception power that is higher than a communicable power level at the antenna and cannot demodulate a received frame, or detects reception power that is higher than a communicable power level at the antenna and receives When the bit error resulting from demodulating the received frame is more than a certain value, it is considered as a transmission frame collision, and the congestion state is detected based on the ratio of the number of transmission frame collisions per unit time to the maximum number of receivable frames per unit time. ,
The wireless communication system according to claim 1. The base station of a wireless communication system comprising a base station and a plurality of communication terminals belonging to a communication area of the base station,
An antenna for receiving a wireless communication frame transmitted from the communication terminal;
A congestion detection processing unit that detects a congestion state from a random access frame received by the antenna;
A reception area control processing unit that limits a communication area in which a random access frame can be received according to a congestion state detected by the congestion detection processing unit, and changes the communication area to be limited according to time;
A base station comprising: The congestion detection processing unit detects reception power that is higher than a communicable power level at the antenna and cannot demodulate a received frame, or detects reception power that is higher than a communicable power level at the antenna and receives When the bit error resulting from demodulating the received frame is more than a certain value, it is considered as a transmission frame collision, and the congestion state is detected based on the ratio of the number of transmission frame collisions per unit time to the maximum number of receivable frames per unit time. ,
The base station according to claim 3. A wireless communication control method used in a wireless communication system comprising a base station and a plurality of communication terminals belonging to the communication area of the base station,
The communication terminal is
Randomly transmit a frame by radio to the base station,
The base station is
Receiving a random access frame transmitted from the communication terminal by an antenna;
Detect congestion from received random access frames,
Limit the communication area that can receive a random access frame according to the detected congestion state, and change the limited communication area with time,
A wireless communication control method. The base station detects received power that is higher than a communicable power level at the antenna and cannot demodulate a received frame, or detects received power that is higher than a communicable power level at the antenna and receives the received frame. When the bit error as a result of demodulating is equal to or more than a certain value is considered as a transmission frame collision, the congestion state is detected by the ratio of the number of transmission frame collisions per unit time to the maximum number of receivable frames per unit time.
The wireless communication control method according to claim 5. A wireless communication control program executed on the base station of a wireless communication system comprising a base station and a plurality of communication terminals belonging to the communication area of the base station,
Detecting a congestion state from a random access frame received by an antenna;
Limiting a communication area in which a random access frame can be received according to the detected congestion state, and changing the limited communication area with time;
A wireless communication control program that causes a computer to execute each of the processes. A computer-readable recording medium storing a radio communication control program executed on the base station of a radio communication system including a base station and a plurality of communication terminals belonging to a communication area of the base station,
Detecting a congestion state from a random access frame received by an antenna;
Limiting a communication area in which a random access frame can be received according to the detected congestion state, and changing the limited communication area with time;
A recording medium that records a wireless communication control program that causes a computer to execute the processes described above.

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