JP4988474B2 - Wireless communication method, wireless communication system, and wireless communication apparatus - Google Patents

Description

  The present invention defines an arbitrary period within a superframe period of a certain period as an active period and the rest as a sleep period, and divides the active period into a plurality of time slots. The present invention relates to a wireless communication method, a wireless communication system, and a wireless communication apparatus that perform two-way communication using time division.

  In ZigBee (registered trademark) as shown in the following non-patent document 1 as a short-range wireless communication standard, a predetermined period within a certain period is set as an active period (superframe period) with a beacon signal as a synchronization signal, and the rest is set as a sleep period. The active period is defined and divided into a plurality of time slots, and each of the plurality of wireless communication apparatuses performs bidirectional communication in a time division manner using each time slot. In addition, as another conventional example, Patent Document 1 below describes each wireless communication as an ad hoc communication system in which a large number of wireless communication nodes perform direct asynchronous wireless communication without passing through other nodes such as a base station and a control station. There has been proposed a method in which a reception section is provided immediately after a beacon signal transmitted by a node and the remaining period is an unused period. Patent Document 2 below proposes a method of determining a time slot for transmitting a beacon signal when a superframe period of a certain period is set using a beacon signal transmitted by each wireless communication node as a synchronization signal. Yes.

In addition, as a method of assigning each time slot to a node, Patent Document 2 discloses a method of autonomously advertising its own slot use to an empty slot. According to this method, each node scans the specified time slot time to determine the used time slot and the empty time slot, and configures the table. It is possible to use. For example, if there is a node that no longer uses a time slot, the time slot is scanned as an empty time slot and is used by another node.
IEEE 802.15.4 JP 2004-228926 A (FIG. 2) JP 2006-121332 A (Abstract)

  However, in time-division multiplex two-way communication using time-slot-multiplexed TDMA (Time Division Multiple Access), a superframe is configured with a specified time slot, and a sleep period is provided in the superframe period by synchronizing in units of superframes. Thus, when using a method that achieves power savings for nodes with built-in batteries, if there are few nodes in the communication range with respect to the number of time slots in the specified superframe, it is possible to sleep. It is necessary to keep the wireless reception state even for an unoccupied time slot, and there is a problem in power saving.

  Further, even when a method for performing autonomous free slot management as described in Patent Document 2 is used, a case where a communication node is moved and a time slot to be used is frequently changed is specified. Therefore, it is necessary to scan the time slots frequently, and it is difficult to save power.

  In the present invention, in wireless communication in which information is advertised to an unspecified number of wireless communication devices accompanying such movement, the operation can be performed with an appropriate number of time slots, thereby realizing power saving. It is an object of the present invention to provide a wireless communication method, a wireless communication system, and a wireless communication device that can be used.

In order to achieve the above object, the present invention defines an arbitrary period within a superframe period of a fixed period as an active period and the rest as a sleep period, and divides the active period into a plurality of time slots, thereby realizing a plurality of radio communication In a wireless communication method in which each of the devices performs bidirectional communication in a time-sharing manner using each time slot,
Each of the plurality of wireless communication devices transmitting a frame including a reception response information field of a frame received from another wireless communication device in each of the plurality of time slots in each time slot period; and
Each of the plurality of wireless communication devices that have received the frame, based on the reception response information in the reception response information field in the previous superframe period, determines the time slot used by the device in the next superframe period. Step to increase or decrease the number,
It is characterized by having.
With this configuration, an operation with an appropriate number of time slots can be performed, and power saving can be realized.

Each of the plurality of wireless communication devices further transmits a flag indicating that if the device itself cannot transmit a frame in a frame to be transmitted next,
Each of the plurality of wireless communication apparatuses that have received the frame increases the number of use time slots of the own apparatus by the number of the flags in the frame.
Further, when there is error information in the reception response information, the number of used time slots is increased by the number of error information.
With this configuration, an insufficient number of time slots can be increased at a stretch.

In order to achieve the above object, the present invention defines an arbitrary period within a superframe period of a certain period as an active period and the rest as a sleep period, and divides the active period into a plurality of time slots. In a wireless communication system in which each communication device performs bidirectional communication in a time-sharing manner using each time slot,
Means for transmitting a frame including a reception response information field of a frame received from each of the plurality of time slots in each of the plurality of time slots, in each of the plurality of wireless communication apparatuses;
Each of the plurality of wireless communication devices that have received the frame, based on the reception response information in the reception response information field in the previous superframe period, determines the time slot used by the device in the next superframe period. Means to increase or decrease the number,
It is characterized by having.
With this configuration, an operation with an appropriate number of time slots can be performed, and power saving can be realized.

Each of the plurality of wireless communication devices further transmits a flag indicating that if the device itself cannot transmit a frame in a frame to be transmitted next,
Each of the plurality of wireless communication apparatuses that have received the frame increases the number of use time slots of the own apparatus by the number of the flags in the frame.
With this configuration, an insufficient number of time slots can be increased at a stretch.

In order to achieve the above object, the present invention defines an arbitrary period within a superframe period of a certain period as an active period and the rest as a sleep period, and divides the active period into a plurality of time slots. Each of the communication devices is the wireless communication device in a wireless communication system that performs bidirectional communication in a time division manner using each time slot,
Means for transmitting a frame including a reception response information field of a frame received from another wireless communication device in each of the plurality of time slots in each time slot period;
Means for increasing / decreasing the number of use time slots of its own device in the next superframe period based on each reception response information in the field of the reception response information in the previous superframe period when the frame is received; ,
It was set as the structure which has.
With this configuration, an operation with an appropriate number of time slots can be performed, and power saving can be realized.

In addition, when the own device has not been able to transmit a frame, a flag indicating that is transmitted in a frame to be transmitted next,
Means for increasing the number of use time slots of the own device by the number of the flags in the frame when the frame is received;
Furthermore, it was set as the structure provided.
With this configuration, an insufficient number of time slots can be increased at a stretch.

  According to the present invention, in wireless communication that advertises its information to an unspecified number of wireless communication devices (nodes), it exists around itself using efficient reception response information from a plurality of nodes. By estimating the number of nodes and limiting the necessary time slots to operate, it is possible to reduce power consumption without using unnecessary time slots when communication is performed between a small number of nodes. In addition, by providing a flag bit in the reception response field indicating that it was not able to transmit itself, it is possible to know how many time slots are insufficient when the number of communication partners increases, so the time slots can be efficiently The number can be increased.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a wireless node type and a system configuration in the present embodiment. This system includes a gateway (GW) 2 connected to an external network 1 (for example, the Internet) regardless of whether it is wired or wireless, can communicate with the external network 1 and can be supplied with commercial power, and the wireless communication node 3. It is composed of small wireless tags 3a and 3b driven by a battery. The wireless tags 3a and 3b can transmit and receive data and can exchange data in both directions, and are hereinafter also referred to as P2P (Point to Point) tags. The P2P tags 3a and 3b include a P2P-S tag 3a that is a P2P tag that is not supposed to move after installation (Stationary) and a P2P-M tag 3b that is a P2P tag that is moved by a person (Mobile), for example. There are two types.

  As shown in FIG. 1, each P2P tag 3a, 3b exchanges its own ID with the P2P tag 3a, 3b in its communicable range ad hoc. As described above, the P2P tags 3a and 3b exchange and accumulate IDs with each other by the moving P2P-M tag 3b, thereby maintaining the mutual contact history. Thereby, a person's action history can be accumulated in the P2P-M tag 3b, and a person's passage history at a certain point can be accumulated in the P2P-S tag 3a. For example, as an example of a specific application, it is conceivable to acquire human behavior and contact history in a city. In this case, the behavior and contact history of a person having the P2P-M tag 3b can be acquired by arranging the GW2 in a place where a commercial power source can be secured and arranging a large number of P2P-S tags 3a in other places. It becomes possible.

  Further, in such an application in which the wireless node 3 simply exchanges its own ID and leaves a contact history, the information transmitting side does not need to specify the receiving side, and each tag 3a, 3b It is only necessary to broadcast its own ID and store the received tags 3a and 3b.

  Next, FIG. 2 shows a configuration of the superframe period T_p in this embodiment. In the present invention, as shown in FIG. 2A, the super frame period T_p includes the active period Tact in which the tags 3a and 3b, which are the wireless communication nodes 3, transmit and receive frames, and the wireless units of the tags 3a and 3b (FIG. 4). And a sleep period (= T_p−Tact) during which the operation is stopped. The active period Tact is constituted by a variable number of time slots TS (in the figure, the number of time slots = 16) as shown in FIG. 2B, and each tag 3b that moves is periodically connected to each time slot TS in the active period Tact. Are randomly selected, and their information is transmitted in a frame in the selected time slot TS.

  Each node 3 performs the first power saving by having an active period Tact in which frames are transmitted and received and a sleep period (= T_p-Tact) in which the operation of the radio unit is stopped. The active period Tact is configured by a variable number of time slots, and each moving node 3 periodically performs its own time slot in the active period Tact in order from the first time slot by carrier sense multiple access (CSMA). Attempt to send information. For this reason, time slots are used in order from the beginning.

  FIG. 3 shows a response confirmation (ACK) sequence according to the present invention. FIG. 3 shows a state where three nodes A, B, and C broadcast their own frames F [A], F [B], and F [C]. In the present invention, the nodes A to C exchange and accumulate information when passing each other, and the accumulated information is transmitted only to a specific node (GW 2 in FIG. 1). For this reason, a frame received from a certain node is not transferred to another node. Therefore, the broadcast frames F [A], F [B], and F [C] are transmitted / received only between the nodes A to C that are in the communication range.

  In FIG. 3, each node A to C transmits its own information in frames F [A], F [B], and F [C] to a time slot TS randomly selected by each node A to C in a certain superframe period N-1. Indicates the state. However, node A and node C are examples in a place where direct communication is not possible. At this time, the frame F [A] transmitted from the node A is transmitted to the node B, the frame F [B] transmitted from the node B is transmitted to the nodes A and C, and the frame F [C] transmitted from the node C is transmitted to the node B. Assume that all are received normally.

  When the nodes A, B, and C transmit their own frames F [A: b], F [B: a, c], and F [C: b] in the next superframe period N, the respective frames F [A: b], F [B: a, c], F [C: b] The node information received in the previous superframe period N-1 (a, b, c in []) Add and send. As a result, each of the nodes A, B, and C uses their own frames F [A] and F [B] transmitted in the previous superframe period N-1 based on the ACK information added together in the frames of the other nodes. , F [C] can be recognized. At the same time, with respect to node B, by receiving ACK information from node A and node C, reception at a plurality of nodes A and C can be confirmed.

  By using such ACK information, it is possible to confirm that the own frame has actually been received and indirectly know how many nodes other nodes are communicating with. As a result, the moving node can know how many communicable nodes exist in the vicinity of the partner node with which it currently communicates. In the present invention, by using such ACK information, the number of time slots actually received in the superframe period and the number of used time slots in the next superframe period are set based on the number of nodes assumed from the received frame. Do.

  Next, the configuration of the node 3 of the present invention will be described with reference to FIG. The node 3 of the present invention includes a radio unit 11 having a transmission unit 11a and a reception unit 11b, a control unit 12, an ID storage unit 13, a clock 14, and a power supply unit 15. The transmission unit 11a has a function of transmitting a frame F including its own ID to the outside via radio. In the node 3 of the present invention, frame transmission in the transmission unit 11a is performed by periodically broadcasting its own ID. The receiving unit 11b has a function of receiving a frame including an ID transmitted from the other node 3 in the same manner.

  The control unit 12 has a function of controlling the operation of the node 3. The function of the control unit 12 will be described in detail with reference to FIG. The ID accumulation unit 13 has a function of accumulating IDs of other nodes 3 received by the reception unit 11b. In addition, when ID is accumulate | stored in ID storage part 13, the time information at that time may be recorded with ID. Also, its own ID information is recorded in the same manner. The clock 14 has a function of outputting a clock signal for grasping the timing of frame transmission in the transmission unit 11a and frame reception in the reception unit 11b. The power feeding unit 15 is a power source built in the node 3 so that communication is possible even when the node 3 moves to an arbitrary place, and is a battery mounted in the casing of the node 3, for example.

  Next, the function of the control unit 12 in the embodiment of the present invention will be described with reference to FIG. Specifically, the control unit 12 includes a time slot adjustment unit 21, a frame analysis unit 22, a frame generation unit 23, an ACK generation unit 24, and a slot number control unit 25. The time slot adjustment unit 21 has a function of performing synchronization adjustment of a time slot including synchronization of a super frame period, and receiving a frame F and transmitting a frame F generated for a possible time slot TS by CSMA. ing. The frame analysis unit 22 analyzes the reception state in each time slot TS, acquires the ID information from the received frame F and notifies the ID storage unit 13 of the ID information from the ACK generation unit 24 and the congestion control unit 25 It has a function.

  Based on the information from the frame analysis unit 22, the ACK generation unit 24 generates an ACK field to be added to the frame F to be transmitted next time. The slot number control unit 25 determines the number of time slots to be set in its own node in the next superframe period based on information from the frame analysis unit 22. Specifically, the processing described in the flowchart described later is performed. The frame generation unit 23 generates a frame F from its own ID, time slot information to be transmitted, and ACK field information notified from the ACK generation unit 24.

  Next, the structure of the frame F exchanged by each tag (node 3) is shown in FIG. Each node 3 generates a fixed-length frame F that can be transmitted in one time slot TS. Specifically, it responds to the reception of the frame F from each field of the number (Slot Number) of the time slot TS transmitted by itself, the type (Type) of Node 3 and its own ID number (ID), and other nodes. The ACK field notifies the transmission side node of the reception state. The present invention is characterized in that the frame F that transmits its own information includes reception response information of a frame received from another node 3 in another time slot TS. Specifically, the ACK field includes fields indicating the time slots TS1 to TS16 of the superframe SF defined by the system, and the reception status in each time slot TS1 to TS16 is stored as ACK information.

In the present invention, unlike a method such as an individual response using the ID of the receiving side node or a passive ACK for notifying reception by transmitting a frame of the receiving side node, an ACK field of a fixed length for a specified time slot Thus, its own reception information is provided to all other transmission source nodes received in the previous superframe period N-1. Therefore, 16 × 16 reception situations are provided in one superframe period T_p. Each piece of information in the ACK field for each time slot is composed of 2 bits, and the state is shown as follows.
00: No reception
10: Received in error state
11: Received in normal state,

  “10: Received in error” includes a case where the received frame F is discarded due to a bit error or a frame error, or a case where the frame F cannot be correctly received due to a collision. By notifying ACK for individual nodes in this way, but notifying the reception status for fixed time slots, compared with the case of confirming responses to multiple nodes using IDs of individual nodes, etc., The frame length can be kept fixed with respect to the amount of ACK, and at the same time, notification can be made with a very small amount of information.

  Further, a special 1-bit flag field (SP field) is added to the ACK field in addition to the TS fields TS1 to TS16 corresponding to each time slot. As will be described in detail later, this is a field that is set to ON (bit = 1) when the frame cannot be transmitted within the set number of time slots.

  Next, a method for generating an ACK field in the ACK generation unit 24 will be described with reference to FIG. Based on the information from the frame analysis unit 22, the ACK generation unit 24 sets the above-described 2-bit TS fields TS1 to TS16 for each time slot TS received in the superframe period ( Step S1). As a result, all the time slots TS that have been transmitted and received are described in the corresponding TS fields TS1 to TS16, including errors due to collisions.

  In addition, if the result of the CSMA within the time slot during the set superframe period is that there is no transmission opportunity of its own and transmission could not be performed (No in step S2), the SP field is turned on to indicate this. (Step S3). This is because when there is a change in the environment to communicate with more nodes 3 due to movement, the number of nodes is larger than the number of time slots N set in the superframe period, and there is no longer an opportunity for transmission. This is the case. In such a case, in the ACK field inserted in its own frame F, not only the TS field indicating that it transmitted / received itself. This indicates to other nodes that there are insufficient time slots. For example, when there are many frames F whose SP field is ON at the time of frame reception, it indicates that the number of nodes 3 does not have a communication opportunity and cannot be transmitted.

  Next, the operation in the slot number control unit 25 will be described. From the viewpoint of power saving, reducing the number N of reception time slots during the superframe period when the environment changes from the environment in which communication with a large number of nodes 3 to an environment in which there are not so many nodes 3 around to the environment. is important. On the other hand, when the environment changes from an environment during communication with a small number of nodes 3 to an environment where a large number of nodes 3 exist, increasing the number of time slots to an appropriate number of time slots N is more This is important in the sense of exchanging data with many nodes 3. The function of the slot number control unit 25 is to autonomously set the number N of time slots within such a superframe period.

  FIG. 8 is a flowchart showing processing in the slot number control unit 25. Based on the information from the ACK generation unit 24, the reception information of the node 3 in the super frame period is grasped, and the use time slot situation in the super frame period is confirmed. From this information, candidates for the number of time slots N in the next superframe period are obtained. This is the result of adding the transmission and normal received (= 11) frames as 1, and adding the error reception (= 10) status due to collision as 2. The error reception (= 10) state is set to 2 in consideration of the presence of multiple nodes due to collision. However, when there is no received frame, that is, when the ACK generator 24 has only the frame information transmitted by itself, the number of time slots N in the next superframe period is different from the time slot transmitted by itself. Considering reception from the node, 2 slots are set.

  When there is a frame reception, the number of time slots is similarly added from the ACK field in the frame F that has been normally received (= 11) by the information from the frame analysis unit 22, and the number of time slots N in the next superframe period Seek candidates. Of the time slot number candidates thus derived, the maximum value is set as the basic time slot number N in the next superframe period (step S11).

  Next, the number A of frames in which the SP field is set in the ACK field of the normal reception frame is added to the basic time slot number N (step S12). Thus, the number N of time slots in the next superframe period is N + A. In this way, by adding the number A of frames in which the SP field is set to the basic time slot number N to obtain the number of time slots N = N + A in the next superframe period, only the number A of nodes 3 that could not be transmitted. The number N of used time slots is increased. This includes the state of the SP field of the ACK field generated by the own node 3 (steps S13 → S14). In this way, with respect to the node 3 that has changed to an environment in which there are a large number of nodes 3, the possibility of reception is increased by increasing the number of time slots N to other nodes 3 by the number of nodes 3 that could not be transmitted. Increasing.

  In this way, power saving can be realized while efficiently using time slots by increasing / decreasing the number N of time slots based on ACK information from other nodes as well as the state of receiving itself. Further, by providing the SP field in the ACK field, it is possible to grasp the number of time slots that are insufficient by grasping the number of nodes that could not be transmitted in the previous superframe period, and to increase them collectively.

  Note that each functional block used in the description of the above embodiment is typically realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration. Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. An FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used. Further, if integrated circuit technology comes out to replace LSI's as a result of the advancement of semiconductor technology or a derivative other technology, it is naturally also possible to carry out function block integration using this technology. For example, biotechnology can be applied.

  The present invention can perform an operation with an appropriate number of time slots in wireless communication in which its own information is advertised to an unspecified number of wireless communication devices accompanying movement, thereby realizing power saving. In addition to the small battery-powered node of the wireless communication network, particularly the electronic tag system with small exchange data, it can be applied to other network devices.

The figure explaining the wireless node classification and system configuration in the embodiment of the present invention Explanatory drawing which shows the structure of the super-frame period and time slot in embodiment of this invention Explanatory drawing which shows the operation | movement sequence of the response confirmation in embodiment of this invention The block diagram which shows the structure of the radio | wireless communication node in embodiment of this invention The block diagram which shows the structure of the control part of FIG. 4 in detail Explanatory drawing which shows the structure of the frame in embodiment of this invention The flowchart explaining operation | movement of the ACK production | generation part in embodiment of this invention FIG. 5 is a flowchart for explaining the operation of the slot number control unit in FIG.

Explanation of symbols

3 node 21 time slot adjustment unit 22 frame analysis unit 23 frame generation unit 24 ACK generation unit 25 slot number control unit

Claims (7)

An arbitrary period within a superframe period of a certain period is defined as an active period and the rest is defined as a sleep period, and the active period is divided into a plurality of time slots, and each of a plurality of wireless communication devices uses each time slot. In a wireless communication method that performs bidirectional communication in a time-sharing manner,
Each of the plurality of wireless communication devices transmitting a frame including a reception response information field of a frame received from another wireless communication device in each of the plurality of time slots in each time slot period; and
Each of the plurality of wireless communication devices that have received the frame, based on the reception response information in the reception response information field in the previous superframe period, determines the time slot used by the device in the next superframe period. Step to increase or decrease the number,
A wireless communication method comprising: Each of the plurality of wireless communication devices further transmits a flag indicating that when the own device cannot transmit a frame in a frame to be transmitted next,
2. The wireless communication method according to claim 1, wherein each of the plurality of wireless communication apparatuses that have received the frame increases the number of use time slots of the own apparatus by the number of the flags in the frame. . An arbitrary period within a superframe period of a certain period is defined as an active period and the rest is defined as a sleep period, and the active period is divided into a plurality of time slots, and each of a plurality of wireless communication devices uses each time slot. In a wireless communication system that performs bidirectional communication in a time-sharing manner,
Means for transmitting a frame including a reception response information field of a frame received from each of the plurality of time slots in each of the plurality of time slots, in each of the plurality of wireless communication apparatuses;
Each of the plurality of wireless communication devices that have received the frame, based on the reception response information in the reception response information field in the previous superframe period, determines the time slot used by the device in the next superframe period. Means to increase or decrease the number,
A wireless communication system comprising: Each of the plurality of wireless communication devices further transmits a flag indicating that when the own device cannot transmit a frame in a frame to be transmitted next,
The wireless communication system according to claim 3, wherein each of the plurality of wireless communication devices that have received the frame increases the number of use time slots of the own device by the number of the flags in the frame. . An arbitrary period within a superframe period of a certain period is defined as an active period and the rest is defined as a sleep period, and the active period is divided into a plurality of time slots, and each of a plurality of wireless communication devices uses each time slot. The wireless communication device in a wireless communication system that performs bidirectional communication in a time-sharing manner,
Means for transmitting a frame including a reception response information field of a frame received from another wireless communication device in each of the plurality of time slots in each time slot period;
Means for increasing / decreasing the number of use time slots of its own device in the next superframe period based on each reception response information in the field of the reception response information in the previous superframe period when the frame is received; ,
A wireless communication device. Means for transmitting a flag indicating that in the case of a frame to be transmitted next when the own apparatus cannot transmit a frame;
Means for increasing the number of use time slots of the own device by the number of the flags in the frame when the frame is received;
The wireless communication apparatus according to claim 5, further comprising:   2. The wireless communication method according to claim 1, wherein when there is error information in the reception response information, the number of use time slots is increased by the number of error information.