JP2019054333A - Wireless terminal, wireless communication system, wireless communication method and wireless communication program - Google Patents

Abstract

To provide a wireless terminal capable of executing wireless communication even when time of communication slot does not synchronize with high precision, and a wireless communication system, a wireless communication method and a wireless communication program.SOLUTION: A wireless terminal in one embodiment comprises: a group part; a slot selection part; and a transmission delay part. The group part is configured to acquire information representing a group to which its own terminal belongs. The slot selection part is configured to select a slot from multiple slots which have time long more than a second unit on the basis of the group. The transmission delay part is configured to acquire delay time on the basis of a probability density function and to transmit data at a point of time which is delayed by the delay time from a start point of time of the selected slot.SELECTED DRAWING: Figure 3

Description

  Embodiments described herein relate generally to a wireless terminal, a wireless communication system, a wireless communication method, and a wireless communication program.

  Wireless communication lines in the Internet of Things (IoT) are effective in reducing communication line installation costs. A conventional wireless terminal that performs time-division transmission needs to include a real time clock (RTC) in order to synchronize the time of a communication slot between the wireless terminal and the wireless station with high accuracy. In a conventional wireless terminal, there are cases where wireless communication cannot be executed unless the times of the communication slots are synchronized with high accuracy.

Japanese Patent Laid-Open No. 2006-19200

  The problem to be solved by the present invention is to provide a wireless terminal, a wireless communication system, a wireless communication method, and a wireless communication program capable of executing wireless communication even when the times of communication slots are not synchronized with high accuracy. It is.

  The wireless terminal according to the embodiment includes a group unit, a slot selection unit, and a transmission delay unit. The group part acquires information representing the group to which the terminal belongs. The slot selection unit selects a slot based on a group from a plurality of slots having a time length equal to or greater than a second. The transmission delay unit acquires a delay time based on the probability density function, and transmits data at a time delayed by the delay time from the start time of the selected slot.

The figure which shows the example of a structure of the radio | wireless communications system of 1st Embodiment. The figure which shows the example of a structure of the radio station of 1st Embodiment. The figure which shows the example of a structure of the radio | wireless terminal of 1st Embodiment. The figure which shows the 1st example of the probability density function of 1st Embodiment. The figure which shows the 2nd example of the probability density function of 1st Embodiment. The figure which shows the 1st example of the slot arrangement | positioning of 1st Embodiment. The figure which shows the 2nd example of slot arrangement | positioning of 1st Embodiment. The figure which shows the example of the transmission time of 1st Embodiment. The figure which shows the example of the simulation conditions of the transmission failure rate of 1st Embodiment. The figure which shows the example of the simulation result of the transmission failure rate of 1st Embodiment. FIG. 3 is a sequence diagram illustrating an example of a data collection operation of the wireless communication system according to the first embodiment. FIG. 3 is a sequence diagram illustrating an example of data transmission operation of the wireless terminal according to the first embodiment. The figure which shows the example of a structure of the radio | wireless communications system of 4th Embodiment. The figure which shows the example of a structure of the radio station of 4th Embodiment. The figure which shows the example of a structure of the radio | wireless terminal of 4th Embodiment. The sequence diagram which shows the example of the time adjustment operation | movement of the radio | wireless communications system of 4th Embodiment.

  Hereinafter, a wireless terminal, a wireless communication system, a wireless communication method, and a wireless communication program according to embodiments will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram illustrating an example of the configuration of the wireless communication system 1a. The wireless communication system 1a is a system that executes wireless communication. The radio communication system 1a includes a radio station 100a and radio terminals 200a-1 to 200a-N (N is an integer of 2 or more). The radio station 100a and the radio terminal 200a are installed in a building, for example.

The radio station 100a will be described.
The radio station 100a is a host device of the radio terminal 200a. The radio station 100a acquires the radio signal generated by the radio terminal 200a from each radio terminal 200a. The radio station 100a transmits the radio signal generated by the radio station 100a to each radio terminal 200a.

  FIG. 2 is a diagram illustrating an example of a configuration of the radio station 100a. The radio station 100 a includes a radio unit 110, an access control unit 120, and a data storage unit 130. The radio unit 110 transmits and receives radio signals between the radio station 100a and the radio terminal 200a. The access control unit 120 manages one-to-one communication between the radio station 100a and the radio terminal 200a. For example, the access control unit 120 establishes one-to-one communication based on the IEEE 802 standard. The access control method executed by the access control unit 120 is, for example, a CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) method or an ALOHA method.

  The data storage unit 130 stores data included in a radio signal transmitted toward each radio terminal 200a. The data storage unit 130 stores data included in the wireless signal transmitted from each wireless terminal 200a. The data storage unit 130 stores the address and the like of each wireless terminal 200a. The data storage unit 130 may store a program. The data storage unit 130 is, for example, a non-volatile recording medium (non-temporary recording medium) such as a flash memory or an HDD (Hard Disk Drive). The data storage unit 130 may include a volatile recording medium such as a RAM (Random Access Memory) and a register, for example.

Next, the wireless terminal 200a will be described.
The wireless terminal 200a generates data at regular intervals. Data generated at a fixed cycle (fixed cycle data) is, for example, data such as temperature measured by a sensor. The radio terminal 200a generates a radio signal according to the data generated at regular intervals. The radio terminal 200a transmits the radio signal generated by the radio terminal 200a to the radio station 100a.

  FIG. 3 is a diagram illustrating an example of the configuration of the wireless terminal 200a. The wireless terminal 200a includes one or more fixed-cycle data generation unit 210, a transmission time control unit 220, an access control unit 230, and a wireless unit 240. Some or all of the functional units of the wireless terminal 200a are realized by, for example, a processor such as a CPU (Central Processing Unit) executing a program stored in the storage unit. Some or all of the functional units of the wireless terminal 200a may be realized using hardware such as LSI (Large Scale Integration) and ASIC (Application Specific Integrated Circuit).

The periodic data generator 210 is a sensor that measures temperature or the like, for example. The fixed cycle data generation unit 210 generates data such as measured temperature at a fixed cycle.
The transmission time control unit 220 controls the transmission time (transmission timing) of a radio signal including data generated at a regular cycle. The transmission time control unit 220 retransmits data when data transmission fails.

The access control unit 230 manages one-to-one communication between the radio station 100a and the radio terminal 200a. For example, the access control unit 230 establishes one-to-one communication based on the IEEE 802 standard. That is, the access control unit 230 transmits and receives predetermined data between the radio station 100a and the terminal itself via the radio unit 240 based on the address of the radio station 100a.
The radio unit 240 transmits and receives a radio signal including predetermined data between the radio station 100a and the radio terminal 200a.

Next, details of the transmission time control unit 220 of the wireless terminal 200a will be described.
The transmission time control unit 220 includes a group unit 221, a slot selection unit 222, and a transmission delay unit 223. The group unit 221 acquires information representing a group to which the terminal belongs (hereinafter referred to as “group information”). The group to which each wireless terminal 200a belongs is determined in advance by an administrator of the wireless communication system 1a, for example. The group unit 221 stores group information.

  The data transmission cycle is divided into a plurality of slots having a time length of at least a second. Therefore, the data transmission cycle has a time length of at least a second unit longer than the time length of the slot. Based on the group information, the slot selection unit 222 selects a slot assigned to the group to which the own terminal belongs from a plurality of slots having a time length equal to or greater than a second.

  The transmission delay unit 223 stores a probability density function. The transmission delay unit 223 determines the delay time from the start time of the slot assigned to the group to which the terminal belongs, based on the probability density function. For example, the transmission delay unit 223 calculates a delay time according to the probability random number by generating a probability random number based on the probability density function. For example, the transmission delay unit 223 sets the delay time to 0 seconds when the random variable is 0 seconds. For example, the transmission delay unit 223 sets the delay time to 1 second when the random variable is 1 second. The transmission delay unit 223 transmits data to the access control unit 230 at a time delayed by a delay time from the start time of the selected slot.

  FIG. 4 is a diagram illustrating a first example of the probability density function. The horizontal axis shows random variables. The vertical axis represents the probability density. The probability density function is a function representing a probability density distribution that changes nonlinearly according to a positive random variable. For example, the probability density function is a function representing a positive random variable region in a probability density normally distributed with a standard deviation σ = 0.4. In FIG. 4, when the random variable is 0 second, the probability density is the maximum value (2%).

  FIG. 5 is a diagram illustrating a second example of the probability density function. The horizontal axis shows random variables. The vertical axis represents the probability density. The probability density function shown in FIG. 5 is a function representing a probability density distribution that changes linearly according to a positive random variable. For example, the probability density function is a function that changes linearly in the interval [0, 1] of the random variable. In FIG. 5, when the random variable is 0 second, the probability density is the maximum value. When the random variable is 1 second or longer, the probability density is the minimum value (0%).

  The radio terminal 200a transmits a radio signal including data to the radio station 100a using the slot assigned to the group to which the own terminal belongs.

  FIG. 6 is a diagram illustrating a first example of the slot arrangement. In FIG. 6, the transmission cycle is divided into a plurality of slots having the same time length. The group to which the wireless terminal 200a belongs is determined in advance for each wireless terminal 200a so that, for example, all the wireless terminals 200a belong to each group equally. The group to which the wireless terminal 200a belongs may be determined in advance for each wireless terminal 200a so that, for example, a plurality of wireless terminals 200a that transmit periodic data having similar data lengths belong to the same group. The group to which the wireless terminal 200a belongs may be determined in advance for each wireless terminal 200a so that, for example, the total amount of the periodic data transmitted from the wireless terminal 200a is equal in a plurality of groups.

  For example, the slot selection unit 222 selects a slot assigned to a group to which the terminal belongs, from a plurality of slots having the same time length. The transmission delay unit 223 transmits data to the access control unit 230 in the slot selected by the slot selection unit 222.

  FIG. 7 is a diagram illustrating a second example of the slot arrangement. In FIG. 7, the transmission cycle is divided into a plurality of slots having different time lengths for each group. The slot length of the group to which the wireless terminal 200a that transmits the periodic data having a long average data length belongs is longer than the slot length of the group to which the wireless terminal 200a that transmits the periodic data having a short average data length belongs. Determined. The slot length of the group having many radio terminals 200a may be set longer than the slot length of the group having few radio terminals 200a.

  For example, the slot selection unit 222 selects a slot based on a group to which the own terminal belongs from among a plurality of slots having different slot time lengths for each group. The transmission delay unit 223 transmits data to the access control unit 230 in the slot selected by the slot selection unit 222.

  FIG. 8 is a diagram illustrating an example of transmission time. In FIG. 8, radio terminals 200a-1 to 200a-3 that transmit periodic data having similar data lengths belong to group A as an example. Radio terminals 200a-4 to 200a-5 that transmit periodic data having similar data lengths belong to group B as an example. In FIG. 8, the slot length of the group B to which the wireless terminals 200a-4 to 200a-5 that transmit the periodic data having a long average data length belong is the same as that of the wireless terminal 200a- that transmits the periodic data having a short average data length. It is longer than the slot length of group A to which 1 to 200a-3 belongs.

  Time t1 is the start time of the group A slot. Each wireless terminal 200a belonging to group A transmits data at a transmission time that is a time elapsed from time t1 by a delay time determined based on the probability density function. For example, the radio terminal 200a-1 belonging to the group A transmits data at a transmission time that is a time elapsed from the time t1 by a delay time determined based on the probability density function.

  The time t2 is the end time of the group A slot and the start time of the group B slot. Each wireless terminal 200a belonging to group B transmits data at a transmission time that is a time elapsed from time t2 by a delay time determined based on the probability density function. For example, the radio terminal 200a-4 belonging to the group B transmits data at a transmission time that is a time elapsed from the time t2 by a delay time determined based on the probability density function.

  The radio terminal 200a transmits a radio signal including data to the radio station 100a in another slot adjacent to the slot assigned to the group to which the radio terminal 200a belongs because the time synchronization accuracy is in seconds. It may be. For example, the radio terminal 200a-3 may transmit a radio signal including data to the radio station 100a after time t2. For example, the radio terminal 200a-4 may transmit a radio signal including data to the radio station 100a before time t2.

Next, an example of transmission failure rate simulation will be described.
FIG. 9 is a diagram illustrating an example of a transmission failure rate simulation condition. The simulation conditions are no control, only grouping, only delay control, and grouping and delay control. Without the control, neither the control for delaying the data transmission time nor the grouping of the radio terminals 200a is performed. The items of each condition include the number of wireless terminals, data size, period, number of retransmissions of data (number of retransmissions of wireless signals), data retransmission interval (interval of retransmission times of wireless signals), and access control. There are a method, a frequency band, a probability density function, the number of groups, a group to which a wireless terminal belongs, and a time length of a slot.

  FIG. 10 is a diagram illustrating an example of a simulation result of the transmission failure rate. The horizontal axis shows the transmission failure rate simulation conditions. The vertical axis represents the transmission failure rate. In FIG. 10, the radio station 100a collects data from 40 radio terminals 200a at a cycle of 10 seconds.

  In “no control”, the wireless terminals 200a are not grouped. Data transmission time is not delayed. For this reason, all the radio terminals 200a transmit data at approximately the same time. In “no control”, the transmission failure rate is 881,278 ppm, which is the highest among the respective conditions.

  In “grouping only”, the wireless terminals 200a are grouped. Data transmission time is not delayed. For this reason, all the radio terminals 200a transmit data at approximately the same time. In “grouping only”, the transmission failure rate is 608,020 ppm.

  In “delay control only”, the wireless terminals 200a are not grouped. The data transmission time is delayed. For this reason, all the radio | wireless terminals 200a transmit data at the transmission time delayed based on the probability variable of the probability density function shown in FIG. In “delay control only”, the transmission failure rate is 1000 ppm or more and less than 10,000 ppm.

  In the “grouping and delay control”, the wireless terminals 200a are grouped. The data transmission time is delayed. Therefore, each wireless terminal 200a transmits data at a transmission time delayed based on the probability variable of the probability density function shown in FIG. In “grouping and delay control”, the transmission failure rate is 665 ppm, which is the lowest among the conditions. Thus, the wireless communication system 1a can reduce the transmission failure rate as compared with “no control”, “only grouping”, and “only delay control”.

Next, an example of the operation of the wireless communication system 1a will be described.
FIG. 11 is a sequence diagram illustrating an example of a data collection operation of the wireless communication system 1a. The periodic data generation unit 210 of the wireless terminal 200a generates data at a predetermined period. The periodic data generation unit 210 outputs the generated data to the transmission time control unit 220 (step S101). The transmission time control unit 220 holds data until a delay time based on the probability density function elapses (until the transmission time is reached) (step S102).

  When the current time becomes the transmission time, the transmission time control unit 220 outputs data to the access control unit 230 (step S103). The access control unit 230 executes access control between the radio station 100a and the own terminal. The access control unit 230 determines whether data transmission is possible based on the execution result of the access control (step S104). If data transmission is possible, the access control unit 230 outputs the data to the radio unit 240 (step S105). The radio unit 240 generates a radio signal including data. The radio unit 240 transmits the generated radio signal to the radio station 100a (step S106).

  The radio unit 110 of the radio station 110a acquires a radio signal from the radio terminal 200a. The wireless unit 110 converts a wireless signal into data. The wireless unit 110 outputs the data to the access control unit 120 (S107). The access control unit 120 records data in the data storage unit 130 (step S130). The data storage unit 130 stores data (S109).

  FIG. 12 is a sequence diagram illustrating an example of a data transmission operation of the wireless terminal 200a. The periodic data generation unit 210 outputs the generated data to the transmission time control unit 220 (step S101). The slot selection unit 222 of the transmission time control unit 220 requests group information from the group unit 221 (step S102-1). The group unit 221 outputs group information indicating the group to which the terminal belongs to the slot selection unit 222 (step S102-2).

  The slot selection unit 222 selects a communication slot based on the group information (step S102-3). The slot selection unit 222 holds data until the start time of the selected slot is reached (step S102-4). When the current time is the slot start time, the slot selection unit 222 outputs data to the transmission delay unit 223 (step S102-5). The transmission delay unit 223 generates a probability random number based on the probability density function. The transmission delay unit 223 determines a delay time from the start time of the slot based on the probability random number (step S102-6). The transmission delay unit 223 holds the data until the delay time elapses from the slot start time (until the transmission time is reached) (step S102-7). When the delay time has elapsed from the start time of the slot, the transmission delay unit 223 outputs data to the access control unit 230 (step S103).

  As described above, the radio terminal 200a according to the first embodiment includes the group unit 221, the slot selection unit 222, and the transmission delay unit 223. The group unit 221 acquires information representing a group to which the terminal belongs. The slot selection unit 222 selects a slot based on a group from a plurality of slots having a time length equal to or greater than a second. The transmission delay unit 223 acquires a delay time based on the probability density function. The transmission delay unit 223 transmits data at a time delayed by a delay time from the start time of the slot selected by the slot selection unit 222.

  As a result, the wireless terminal 200a of the first embodiment can execute wireless communication even when the times of the communication slots are not synchronized with high accuracy. The grouped wireless terminals 200a control the transmission time according to the slot start time and the delay time determined based on the random number, so that collision between data is avoided and the transmission failure rate is reduced. be able to. The radio terminal 200a of the first embodiment can increase transmission efficiency.

  The wireless terminal 200a of the first embodiment does not need to include a real-time clock for executing highly accurate time synchronization. That is, since the wireless terminal 200a of the first embodiment delays the transmission time of the wireless signal based on the probability random number instead of based on the fixed delay time for each wireless terminal 200a, real-time for performing highly accurate time synchronization There is no need to provide a clock. Thereby, the radio terminal 200a of the first embodiment can suppress an increase in cost of the own terminal.

(Second Embodiment)
The second embodiment is different from the first embodiment in that the probability density function is different for each group. In the second embodiment, only differences from the first embodiment will be described.

  The transmission delay unit 223 stores different probability density functions for each group. The variance of the probability density function of the group to which the wireless terminal 200a that transmits the periodic data having a long average data length belongs is compared with the variance of the probability density function of the group to which the wireless terminal 200a that transmits the periodic data having a short average data length belongs. And set to a large value. Further, the variance of the probability density function of the group having many radio terminals 200a belonging to the group is determined to be larger than the variance of the probability density function of the group having few radio terminals 200a to which the radio terminal 200a belongs.

  As described above, the variance of the probability density function of the second embodiment is determined based on the average data length of the periodic data. The variance of the probability density function of the second embodiment is determined based on the number of radio terminals 200a belonging to the group. As a result, the radio terminal 200a of the second embodiment increases the variance of the probability density function of the group having a relatively large amount of data, so that collision between data of the group having a large amount of data can be avoided. The radio terminal 200a of the second embodiment can reduce the transmission failure rate.

(Third embodiment)
The third embodiment is different from the second embodiment in that the interval between data retransmission times is different for each group. In the third embodiment, only differences from the second embodiment will be described.

  The data retransmission time interval (radio signal retransmission time interval) differs for each group. The interval between retransmission times of fixed-cycle data with a long average data length is set longer than the interval between retransmission times of fixed-cycle data with a short average data length. In addition, the interval between the retransmission times of the periodic data transmitted from the wireless terminals 200a belonging to the group having many wireless terminals 200a belongs to the periodic data transmitted from the wireless terminals 200a belonging to the group including few wireless terminals 200a. It is set longer than the interval between retransmission times.

  As described above, the interval between the retransmission times of the periodic data in the third embodiment is determined based on the average data length. The interval between retransmission times of the periodic data in the third embodiment is determined based on the number of radio terminals 200a belonging to the group. As a result, the wireless terminal 200a of the third embodiment increases the retransmission time interval of data of a group having a relatively large amount of data, and thus collision between data retransmitted from the wireless terminal 200a of a group having a large amount of data is performed. Can be avoided. The radio terminal 200a of the third embodiment can reduce the transmission failure rate.

(Fourth embodiment)
The fourth embodiment is different from the first embodiment in that the wireless terminal adjusts the time based on the broadcast data. In the fourth embodiment, only differences from the first embodiment will be described.

  FIG. 13 is a diagram illustrating an example of the configuration of the wireless communication system 1b. The wireless communication system 1b is a system that executes wireless communication. The wireless communication system 1b includes a wireless station 100b and wireless terminals 200b-1 to 200b-N. The radio station 100b acquires a radio signal generated by the radio terminal 200b from the radio terminal 200b. The radio station 100b transmits the radio signal generated by the radio station 100b to the radio terminal 200a.

  FIG. 14 is a diagram illustrating an example of the configuration of the radio station 100b. The radio station 100b includes a radio unit 110, an access control unit 120, a data storage unit 130, and a broadcast data generation unit 140. The broadcast data generation unit 140 generates broadcast data that can be acquired by each subordinate radio terminal 200b as data for time synchronization. The broadcast data includes information indicating that it is broadcast data. The broadcast data may further include time information. The broadcast data generation unit 140 broadcasts a radio signal including the broadcast data to the radio terminal 200a via the radio unit 110.

  The wireless terminal 200b generates data such as the measured temperature at regular intervals. The radio terminal 200b generates a radio signal including data generated at regular intervals. The radio terminal 200b transmits the radio signal generated by the radio terminal 200b to the radio station 100b.

  FIG. 15 is a diagram illustrating an example of a configuration of the wireless terminal 200b. The wireless terminal 200b includes one or more fixed-cycle data generation unit 210, a transmission time control unit 220, an access control unit 230, a wireless unit 240, and a synchronization unit 250. The synchronization unit 250 adjusts the time of its own terminal based on the broadcast data output from the radio station 100b. That is, the synchronization unit 250 synchronizes the time of its own terminal with the time of the radio station 100b using the broadcast data output from the radio station 100b.

  For example, the synchronization unit 250 synchronizes the time of its own terminal with the time of the wireless station 100b by using the time when the wireless unit 240 acquires the broadcast data as the reference of the time of the own terminal. Further, for example, when the radio station 100b adds time information (time count value) to the broadcast data, the synchronization unit 250 may synchronize the time of the own terminal with the time of the radio station 100b based on the time information.

Next, an example of the operation of the wireless communication system 1b will be described.
FIG. 16 is a sequence diagram illustrating an example of the time adjustment operation of the wireless communication system 1b. The broadcast data generating unit 140 of the radio station 100b generates broadcast data that can be received by each subordinate radio terminal 200b as data for time synchronization. The broadcast data generation unit 140 outputs the broadcast data to the access control unit 120 (step S201).

  The access control unit 120 executes access control between the own radio station and the radio terminal 200b. The access control unit 120 determines whether or not data transmission is possible based on the execution result of the access control (step S202). If data transmission is possible, the access control unit 120 outputs the broadcast data to the wireless unit 110 (step S203). The wireless unit 110 transmits a wireless signal including the broadcast data to the wireless terminal 200b (step S204).

  The radio unit 240 of the radio terminal 200b acquires a radio signal including broadcast data. The wireless unit 240 converts the wireless signal into broadcast data. The radio unit 240 outputs the broadcast data to the access control unit 230 (step S205). The access control unit 230 outputs the broadcast data to the synchronization unit 250 (step S206). The synchronization unit 250 synchronizes the time of the own terminal with the time of the radio station 100b using the broadcast data (step S207).

  As described above, the wireless terminal 200b according to the fourth embodiment includes the synchronization unit 250. The synchronization unit 250 synchronizes the time of its own terminal with the time of the radio station 100b using the broadcast data. As a result, the radio terminal 200b of the fourth embodiment adjusts the time of the radio terminal 200b based on the broadcast data output from the radio station 100b, so that the time synchronization of each radio terminal 200b can be easily executed. it can. The wireless terminal 200b of the fourth embodiment can correct the synchronization shift when the wireless communication system 1b operates for a long period of time.

  Even if the wireless terminal 200b of the fourth embodiment acquires broadcast data (beacon information) from the wireless station 100b, it is not necessary to extract and analyze group information, slot time information, and delay time information from the broadcast data. Absent. Thus, the wireless terminal 200b can execute wireless communication without significantly increasing the processing amount. The radio terminal 200b may synchronize the time of the radio station 100b and the time of the own terminal based on the time when the own terminal acquires the broadcast data from the radio station 100b.

  According to at least one embodiment described above, a slot selection unit that selects a slot based on a group from a plurality of slots having a time length of at least a second unit, and a delay time based on a probability density function is acquired and selected. By having a transmission delay unit that transmits data at a time delayed by a delay time from the start time of the slot, the wireless communication can be executed even if the times of the communication slots are not accurately synchronized.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1a, 1b ... Wireless communication system, 100a, 100b ... Wireless station, 200a, 200b ... Wireless terminal, 110 ... Wireless part, 120 ... Access control part, 130 ... Data storage part, 210 ... Fixed period data generation part, 220 ... Transmission Time control unit, 221 ... group unit, 222 ... slot selection unit, 223 ... transmission delay unit, 230 ... access control unit, 240 ... radio unit

Claims (14)

A group part for obtaining information representing a group to which the terminal belongs;
A slot selection unit for selecting a slot based on the group from a plurality of slots having a time length of at least a second unit;
A wireless terminal comprising: a transmission delay unit that acquires a delay time based on a probability density function and transmits data at a time delayed by the delay time from a start time of a selected slot.   The wireless terminal according to claim 1, wherein the probability density function is a function having a maximum probability density when a random variable is zero.   The variance of the probability density function of the group to which a wireless terminal that transmits data having a long average data length belongs is compared with the variance of the probability density function of the group to which a wireless terminal that transmits data having a short average data length belongs. The wireless terminal according to claim 1, wherein the wireless terminal is set to a large value.   The variance of the probability density function of the group with a large number of wireless terminals belonging to the group is determined to be larger than the variance of the probability density function of the group with a small number of wireless terminals to which the wireless terminal belongs. 2. A wireless terminal according to 2.   The slot length of a group to which a wireless terminal that transmits data having a long average data length belongs is determined to be longer than a slot length of a group to which a wireless terminal that transmits data having a short average data length belongs. The wireless terminal according to claim 4.   The length of the slot of the group having many wireless terminals belonging to the group is determined to be longer than the length of the slot of the group having few wireless terminals to which the wireless terminal belongs. The wireless terminal described.   The group to which a wireless terminal belongs is determined such that a plurality of wireless terminals that transmit data having similar data lengths belong to the same group. Wireless terminal.   The wireless terminal according to any one of claims 1 to 6, wherein the group to which the wireless terminal belongs is determined so that a total amount of data transmitted from the wireless terminal is equal in a plurality of the groups.   The wireless terminal according to any one of claims 1 to 8, wherein an interval between retransmission times of data having a long average data length is set longer than an interval between retransmission times of data having a short average data length.   The interval between retransmission times of data transmitted from the wireless terminals belonging to the group having many wireless terminals belonging to the group is determined to be longer than the interval between retransmission times of data transmitted from wireless terminals belonging to the group including few wireless terminals belonging to the group. The wireless terminal according to any one of claims 1 to 8.   11. The wireless communication apparatus according to claim 1, further comprising a synchronization unit that synchronizes the time of the terminal with the time of the wireless station using broadcast data output from a wireless station that is a higher-level device of the terminal. The wireless terminal described in 1. A group part for obtaining information representing a group to which the terminal belongs;
A slot selection unit for selecting a slot based on the group from a plurality of slots having a time length of at least a second unit;
A radio terminal having a transmission delay unit that acquires a delay time based on a probability density function and transmits data at a time delayed by the delay time from a start time of a selected slot;
A radio communication system comprising: a radio station having a radio unit that acquires data transmitted from the transmission delay unit. A wireless communication method executed by a wireless terminal,
Obtaining information representing a group to which the terminal belongs;
Selecting a slot based on the group from a plurality of slots having a time length of at least a second unit;
Obtaining a delay time based on a probability density function, and transmitting data at a time delayed by the delay time from a start time of a selected slot. On the computer,
A procedure for obtaining information representing a group to which the terminal belongs;
Selecting a slot based on the group from a plurality of slots having a time length of at least a second unit; and
A radio communication program for obtaining a delay time based on a probability density function and transmitting data at a time delayed by the delay time from a start time of a selected slot.

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