JP6566785B2 - Group channel access method - Google Patents

Description

  The present invention relates to a group channel access method.

  Multiple access in a wireless environment enables a limited wireless channel to be shared by a plurality of terminals (see Non-Patent Document 1).

  For example, in a Wi-Fi system or the like, a carrier sense multiple access / collision detection method (CSMA / CD) or a carrier sense multiple access / collision avoidance method (CSMA / CD) is used as a communication method that allows a plurality of terminals to share a channel. CA) is used.

  CSMA / CD confirms that each terminal is not transmitting data on the transmission path, and starts transmission if other terminals are not transmitting. When multiple terminals start transmission at the same time, it avoids collision avoidance. Therefore, both are communication systems in which transmission is stopped and retransmission is attempted after waiting for a predetermined time.

  CSMA / CA is a communication method in which each terminal transmits data after confirming that data transmission is not continuously performed for a certain time or more on a communication path. Whether or not the data is actually transmitted is determined by whether or not an ACK (Acknowledge) signal from the receiving side arrives. If there is no ACK signal, it is considered that there is a communication failure and data is retransmitted.

LAN MAN Standards Committee of the IEEE Computer Society, Wireless LAN medium access control (MAC) and physical layer (PHY) specification, IEEE, New York, NY, USA, IEEE Std 802.11-2012 edition, 2012.

However, in the communication method based on CSMA, when communication is performed between terminals, a communication collision cannot be avoided, and the communication collision adversely affects system performance. Further, the adverse effect on the system performance becomes greater as the number of communication terminals increases.
Such a communication collision is a serious problem in a communication system in which a terminal senses the occurrence of an emergency in a specific area and notifies a base station such as a seismometer, an eruption meter, and a fire sensor.

  FIG. 1 is a schematic diagram showing a state of conventional channel access by CSMA. In FIG. 1, a plurality of terminals 2 are connected to a base station (BS) 1 that is a master device. Such a base station 1 and a plurality of terminals 2 are arranged in the observation target area A.

  When a specific event that is the object of observation, such as an earthquake or eruption, occurs in area A, it is installed in an area (event area) P that can be affected by the event and sensed by the terminal 2, and the event Information indicating that an event has been detected is transmitted from the plurality of terminals 2 that have detected the occurrence of the event to the base station 1.

  Here, when the event to be observed is an event that affects a wide area such as an earthquake or an eruption, the observation target area A is also wide, and the terminal installed to cover this wide observation target area A The number of 2 also increases.

  When an event occurs, the number of terminals 2 included in the event area P increases, and information is simultaneously transmitted from a large number of terminals 2 to the BS 1. This increases the possibility of communication collision.

  In addition, if the event to be observed is an earthquake or eruption, etc., and a communication collision occurs and communication cannot be performed normally, the residents may be evacuated and the rescue operation may be delayed, causing serious damage. There is.

  Accordingly, the present invention has been made in view of the above-described problems, and an object thereof is to provide a group channel access method capable of minimizing communication collisions.

A group channel access method according to a first invention is a group channel access method in a communication network composed of a base station and a plurality of terminals, wherein the base station divides the plurality of terminals into a plurality of groups. A creation step, an early reporter selection step in which the base station selects one or more terminals as the early reporter from the terminals constituting the group, and when an event occurs , among the plurality of early reporters, The event reporter included in the event area affected by the event transmits an event occurrence information indicating the occurrence of the event to the base station, and the base station receiving the event occurrence information The early reporter that sent the event occurrence information belongs For each group, a group access frame configuration step for configuring a group access frame including a group access period for designating a time zone in which the terminal included in the group and the base station can communicate, and the base station includes a configuration A group access frame transmitting step for broadcasting information including the group access frame, and the terminal receiving the information including the group access frame receives a CSMA (carrier sense multiple access) from the base station in a group access period to which the terminal belongs. And a communication step of performing communication using the method.

Group channel access method according to the second invention, in the first invention, wherein the group access frame contains extra group access period in addition to the group access period, it belongs to the group to which the group access period has not been allocated The terminal that has detected the event communicates with the base station in the extra group access period.

  A group channel access method according to a third aspect of the present invention is the group channel access method according to the first or second aspect, wherein when the communication environment changes after the communication step, the base station reconfigures the group and the group access frame. The method further includes a configuration step.

  In the group channel access method according to a fourth invention, in the first invention to the third invention, the early reporter is selected from those having the best communication status with the base station among the terminals constituting the group. It is characterized by that.

  According to the present invention having the above-described configuration, by grouping a plurality of terminals in the network and performing time division multiple channel access, the number of terminals 2 communicating with the BS 1 at a time can be dramatically reduced. A communication collision can be effectively prevented.

It is a schematic diagram which shows the mode of the channel access by the conventional CSMA. It is a schematic diagram which shows the mode of the channel access by CSMA which concerns on embodiment of this invention. 5 is a flowchart illustrating a group channel access method according to an embodiment of the present invention. It is a schematic diagram which shows the example which produces a group using geographic information in the group channel access method which concerns on embodiment of this invention. It is a schematic diagram which shows the group access frame produced by the base station in the group channel access method which concerns on embodiment of this invention.

  Hereinafter, a group channel access method according to an embodiment of the present invention will be described.

  FIG. 2 is a schematic diagram showing a state of channel access by CSMA according to the embodiment of the present invention.

  In the channel access method according to the present embodiment, one base station (BS) 1 and a plurality of terminals 2 are installed in the observation target area A.

  The base station 1 is a master device, and is a device for collecting information from the terminal 2 that is a slave device and transmitting the collected information to the outside. The base station 1 controls communication between the base station 1 and the terminal 2.

  Specifically, the base station 1 divides the terminal 2 into a plurality of groups according to the location information of the terminal 2, and sets a predetermined terminal 2 in the group as an early reporter ER, or the base station 1 and the terminal 2 has a function of setting an access frame used for communication with the communication terminal 2. Details of grouping of the terminals 2 and details of access frame setting will be described later.

  The terminal 2 is a sensor having a function of communicating with the base station 1 provided in the observation target area A in order to detect the occurrence of a specific event that is the observation target in the observation target area A, such as an earthquake or an eruption. It is. The terminal 2 communicates with the base station 1 under the control of the base station 1.

  The terminal 2 registers its own location information in the base station 1 when joining the base station 1 network. This position information is obtained by using position information obtained by a GPS (Global Positioning System) built in the terminal 2.

  In the present embodiment, the position information is obtained by GPS. However, the present invention is not limited to this, and any means that can acquire position information can be used suitably.

  Moreover, in this embodiment, although the terminal 2 does not have a function which communicates between terminals 2, in this invention, it is good not only as this but the aspect which can communicate also between terminals 2, for example. Even in this case, the base station 1 controls communication with all terminals 2 communicating with the own station.

  These terminals 2 are divided into a plurality of groups by the base station 1. In the present embodiment, as shown in FIG. 2, the plurality of terminals 2 are divided into four groups B to E that are surrounded by broken lines.

  In the channel access method according to the present embodiment, there are two types of terminals, the normal terminal S and the early reporter ER, as the terminals 2 belonging to the groups B to D. One or more early reporters ER are set for each of the groups B to E.

  The normal terminal S and the early reporter ER are both terminals having the same configuration, but are controlled by the base station 1 so as to exhibit different functions.

  That is, when an event occurs in the observation target area A and the normal terminal S and the early reporter R exist in the range P where the influence of the event is present, any terminal 2 senses the event. However, the terminal 2 that can communicate with the base station 1 for the first time after detection of the event is set to only the early reporter ER that has detected the event.

  That is, the early reporter ER is a terminal 2 that first communicates with the base station 1 on behalf of all the terminals 2 that are included in the group to which the reporter ER is detected and that has detected the event.

  Next, each step of the channel access method according to the present embodiment will be described in detail. FIG. 3 is a flowchart illustrating a group channel access method according to an embodiment of the present invention.

  First, the base station 1 receives the location information of each terminal 2 for a plurality of terminals 2 subscribing to a network centered on the base station 1, and based on the location information, the plurality of terminals 2 are grouped into a plurality of groups. Divide (step S1). In the present invention, instead of the base station 1 receiving the position information from each terminal 2, it is possible to place the terminal at a position preset by the base station 1. Moreover, the subscription of each terminal 2 to the network with respect to the base station 1 can be performed arbitrarily using various existing technologies.

  Next, for each group, the base station 1 selects one or more terminals 2 from among the terminals 2 constituting the group as an early reporter ER based on a predetermined criterion (step S2).

  As a criterion for selecting the early reporter ER, for example, the communication status with the base station 1 among the terminals 2 in the group is used as a criterion. In this case, the terminal 2 having the best communication status is selected as the early reporter ER.

  However, the present invention is not limited to this, and an embodiment in which the early reporter ER is selected based on other criteria such as selecting the terminal 2 having the shortest distance from the base station 1 as the early reporter ER may be used.

  Thus, at the stage where no event has occurred, each terminal 2 is divided into groups, and one or more terminals 2 are selected as the early reporter ER for each group.

  Such grouping and selection of the early reporter ER are performed as shown in FIG. 4, for example. FIG. 4 is a schematic diagram showing an example of creating a group using geographic information in the group channel access method according to the embodiment of the present invention.

  In the example shown in FIG. 4, nine groups G1 to G9 are created for an area (monitoring area) that is an observation target of the occurrence of an event, and each group includes a plurality of normal terminals S and one early reporter. It is configured with an ER.

  Next, the base station 1 broadcasts to each terminal 2 information indicating which terminal 2 belongs to which group and which terminal 2 is designated as the early reporter ER.

  Each terminal 2 that has received the broadcasted group information and information designating the early reporter ER stores the group to which the own device belongs and the designated information when the own device is designated as the early reporter ER. The terminal 2 designated as the early reporter ER functions as the early reporter ER thereafter.

  When an event occurs, all the normal terminals S and the early reporter ER included in the event area X affected by the event detect the occurrence of the event.

  In the example shown in FIG. 4, the normal terminal S and the early reporter ER included in the groups G5, G6, G8, and G9 detect the occurrence of the event. However, the ER of the group G8 and one normal terminal S of the group G9 are not detecting the event.

  When the early reporter ER of each group detects the occurrence of an event, the early reporter ER transmits event occurrence information indicating the occurrence of the event to the base station 1.

  The base station 1 that has received the event occurrence information, for each group to which the early reporter ER that has transmitted the event occurrence information belongs, sets a group access period that specifies a time zone in which the terminal 2 included in the group and the base station 1 can communicate. A group access frame is configured (step S3).

  FIG. 5 is a schematic diagram showing a group access frame created by the base station 1 in the group channel access method according to the embodiment of the present invention.

  Initial random multiple access is used before the generation of the group access frame. The initial random multiple access is a period in which the base station 1 and each terminal 2 communicate with each other by normal CSMA. The early reporters ER of the groups G5, G6, and G9 described above transmit event occurrence information to the base station 1 using CSMA during the initial random multiple access period.

  The group access frame includes a beacon (B) and a group access frame (GAF).

  The beacon is a signal transmitted to broadcast information indicating a group access frame to each terminal 2 in addition to a signal for synchronization between the base station 1 and the terminal 2.

  The group access frame is configured to include a plurality of group access periods (GAP) including busy, backoff, transmission, SIFS, and ACK. The group access frame includes a plurality of group access periods (GAP). Each group access period is a time interval in which each terminal communicates with the base station, and performs communication using CSMA.

  The group access period is configured and allocated for each group in which event occurrence information is transmitted from the early reporter ER, and indicates a time zone provided for the normal terminal S and the early reporter ER included in the group to perform communication. ing.

  In the present embodiment, three groups G5, G6, and G9 that have transmitted event occurrence information from the early reporter ER are configured and assigned to each group.

  In addition, the normal terminal S that is included in the group that has not been transmitted from the early reporter ER, that is, the event that has not been detected by the early reporter ER and that has detected the event is also transmitted to the base station 1. It is preferable to be able to notify the occurrence in order to improve the observation accuracy.

  Therefore, in the present embodiment, as a group access period, a group access period (hereinafter referred to as “extra group”) about a group other than the group to which event occurrence information is transmitted from the early reporter ER (hereinafter referred to as “other group”). Access period ").

  In this embodiment, an extra group access period is provided. However, in the present invention, this may not be provided.

  Information indicating the group access frame thus configured is broadcast as a part of the beacon signal.

  Information indicating the broadcast group access frame is received by each terminal 2.

  Then, each terminal 2 that has detected the event and in which the group to which the own device belongs is designated in the group access period, communicates with the base station 1 during the group access period (step S4). Such communication in the group access period by each group is called multiple access between groups. Inter-group multiple access is performed using normal CSMA.

  Further, the terminal 2 that has detected the event, and to which the group to which the own device belongs is not allocated in the group access period, communicates with the base station 1 by normal CSMA in the extra group access period.

  Next, the base station 1 performs group reconfiguration and group access frame reconfiguration in the network in order to provide a more appropriate communication environment (step S5).

  Group reconfiguration and group access frame reconfiguration are performed by repeating steps S1 to S3 described above.

  The group reconfiguration and the group access frame reconfiguration are performed at a predetermined timing, for example, every time the group access period ends.

  Note that this group reconfiguration and group access frame reconfiguration are not essential in the present invention, and the same group and early reporter ER may continue to be used.

  According to the group channel access method according to the embodiment described above, when the early reporter ER detects an event, only the early reporter ER first communicates with the base station 1 for the group to which the early reporter ER belongs. Therefore, the number of terminals that communicate with the base station 1 in the initial stage after event detection can be greatly reduced, and occurrence of communication collisions can be effectively prevented.

  Further, by using the group access frame, only the terminals 2 belonging to a predetermined group perform communication for each group access period, so that it is possible to effectively prevent the occurrence of communication collision.

1 Base station 2 Terminal A Observation area P Event area S Normal terminal ER Early Reporter

Claims (4)

A group channel access method in a communication network composed of a base station and a plurality of terminals,
A group creating step in which the base station divides the plurality of terminals into a plurality of groups;
An early reporter selection step in which the base station selects one or more terminals as an early reporter from the terminals constituting the group;
When an event occurs , among the plurality of early reporters, the early reporter included in an event area affected by the event transmits event occurrence information indicating the occurrence of the event to the base station. Process,
The base station that has received the event occurrence information specifies, for each group to which the early reporter that has transmitted the event occurrence information belongs, a time zone in which the terminal included in the group and the base station can communicate with each other. A group access frame configuration step of configuring a group access frame including a group access period;
A group access frame transmission step in which the base station broadcasts information including the configured group access frame; and
The terminal that has received the information including the group access frame communicates with the base station using CSMA (carrier sense multiple access) in a group access period to which the terminal belongs;
A group channel access method comprising: The group access frame includes an extra group access period in addition to the group access period.
Belong to the group to which the group access period has not been allocated, the terminal performing the detection of the event the group of claim 1, wherein the communicating with the base station in the extra group access period Channel access method.   The group channel access according to claim 1 or 2, further comprising a reconfiguration step in which the base station reconfigures the group and the group access frame when a change in communication environment occurs after the communication step. Method.   The group channel access according to any one of claims 1 to 3, wherein the early reporter is selected from the terminals that constitute the group and have the best communication status with the base station. Method.

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