wireless communication system

Abstract

To reduce power consumption and achieve low-latency operation while satisfying expected communication functions.SOLUTION: In a wireless communication system in a network in which data frames between two or more nodes arranged with a CS 2 as a root are transmitted and received based on time division multiple access (TDMA), each node 3 is assigned, in consecutive intermittent standby cycles, an active period in which the data frames can be transmitted and received and which is divided chronologically into early and late periods and a sleep period in which operation is suspended. The CS 2 allocates uplink data communication from the node 3 to the CS 2 and downlink data communication from the CS 2 to the node 3 to the early period and late period of the active period, respectively, according to the number of detected nodes.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This relates to a wireless communication system in a network in which data frames are transmitted and received between two or more nodes located around a collection control station based on time division multiple access (TDMA). [Background technology]

[0002] In recent years, wireless networks have been using communication devices conforming to the IEEE802.15.4g standard, which are small, inexpensive, and capable of power-saving wireless communication (see, for example, Non-Patent Document 1). Networks conforming to the IEEE802.15.4g standard employ various topologies, each consisting of a collection control station (CS) and one or more nodes.

[0003] Among these, the IEEE802.15.4 standard proposes a power-saving superframe structure as shown in Fig. 7. In this superframe structure, a superframe is defined by a periodic beacon signal under Time Division Multiple Access (TDMA) control. The interval between these beacon signals (intermittent standby period) can be divided into an active period (AP) during which the node waits for a data frame signal to be transmitted or received, and a sleep period (SP) during which the node is powered down and no transmission, reception, or standby operations are performed. During the active period AP, each node can operate as a substantial communication period. Meanwhile, during the sleep period SP, each node can transition to a sleep state (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-167636 [Non-patent literature]

[0005] [Non-Patent Document 1] IEEE802.15.4g, “Part 15.4: Low-Rate Wireless Personal Area Networks (LR-WPANs), Amendment 3: Physical Layer (PHY) Specifications for Low-Data-Rate, Wireless, Smart Metering Utility Networks”, 2012 Summary of the Invention [Problem to be solved by the invention]

[0006] In most cases, downstream data communication from a CS to a node involves broadcasting data frames in bulk. Broadcasting data frames can be completed in a shorter timeframe than unicasting data frames to individual nodes. However, upstream data communication from a node to a CS rarely involves broadcasting data frames; most nodes transmit data frames independently to the CS via unicast. In such cases, if multiple nodes initiate upstream data communication with the CS at the same time, the other nodes must wait until one node's upstream data communication is complete. As a result, it takes a considerable amount of time for all nodes to complete their upstream data communication. As the number of nodes increases, the difference between the communication time for upstream data communication and that for downstream data communication becomes even greater.

[0007] In contrast, according to the conventional energy-saving superframe structure described above, no particular distinction is made between upstream data communication from the node to the CS and downstream data communication from the CS to the node, and data frames are sent and received during the active period AP.

[0008] For this reason, it is necessary to extend the active period AP until all standby and data frame transmissions are completed, not only for downstream data communications by broadcast but also for upstream data communications, which are mostly unicast. As a result, the sleep period SP is inevitably shortened, making it difficult to reduce power consumption across the entire network.

[0009] On the other hand, if the active period AP is made too short and the sleep period SP is made too long, although power consumption can certainly be reduced, it may cause problems in achieving so-called low-latency operation, which reduces communication delays in sending and receiving data frames and in standby mode.

[0010] Therefore, the network as a whole needs to satisfy the expected communication functions while reducing power consumption and achieving low-latency operation, but until now, no technology has been proposed that can satisfy these conditions.

[0011] The present invention has been devised in consideration of the above-mentioned problems, and its purpose is to provide a wireless communication system that can reduce power consumption and achieve low-latency operation while satisfying the communication functions expected in a wireless network of the IEEE802.15.4 standard. [Means for solving the problem]

[0012] The inventors have attempted to solve the above-mentioned problems by transmitting and receiving data frames between two or more nodes arranged around a collection control station based on time division multiple access (TDMA), enabling transmission and reception of data frames in successive intermittent standby periods, and allocating to each node an active period divided chronologically into an early period and a late period, and a sleep period in which operation is suspended, and allocating upstream data communication from the node to the collection control station and downstream data communication from the collection control station to the node to the early period and the late period, respectively, depending on the number of detected nodes.

[0013] A wireless communication system according to a first aspect of the present invention is a wireless communication system in a network in which transmission and reception of data frames between two or more nodes arranged around a collection control station are performed based on time division multiple access (TDMA), wherein each of the nodes is capable of transmitting and receiving the data frames in successive intermittent standby periods, and is assigned an active period divided into an early period and a late period in time series, and a sleep period in which operation is suspended, and the collection control station assigns, according to the number of detected nodes, to the early period of the active period either uplink data communication from the node to the collection control station or downlink data communication from the collection control station to the node, and assigns the other of the uplink data communication and the downlink data communication to the late period of the active period; When the node itself performs downstream data communication by broadcast, the node itself allocates upstream data communication to the earlier period and downstream data communication to the later period, and adjusts the proportion of the earlier period in time series to be larger than when the node itself performs downstream data communication by unicast, or allocates downstream data communication to the earlier period and upstream data communication to the later period, and adjusts the proportion of the later period in time series to be larger than when the node itself performs downstream data communication by unicast. It is characterized by:

[0014] A wireless communication system according to a second aspect of the present invention is a wireless communication system in a network in which transmission and reception of data frames between two or more nodes arranged around a collection control station are performed based on time division multiple access (TDMA), wherein each of the nodes is capable of transmitting and receiving the data frames in successive intermittent standby periods, and is assigned an active period divided into an early period and a late period in time series, and a sleep period in which operation is suspended, and the collection control station assigns, according to the number of detected nodes, to the early period of the active period either uplink data communication from the node to the collection control station or downlink data communication from the collection control station to the node, and assigns the other of the uplink data communication and the downlink data communication to the late period of the active period; When the node itself performs downstream data communication by broadcasting to each of the nodes, the node allocates upstream data communication to the earlier period and downstream data communication to the later period, and adjusts the data frame of the downstream data communication so that the end point of the data frame is before the start point of the earlier period in the next intermittent standby cycle, or allocates downstream data communication to the earlier period and upstream data communication to the later period, and adjusts the data frame of the upstream data communication so that the end point of the data frame is before the start point of the earlier period in the next intermittent standby cycle. It is characterized by:

[0015] The wireless communication system according to the third invention is characterized in that, in the first or second invention, the collection control station adjusts the chronological ratio between the early period and the later period according to the number of detected nodes. [Effects of the Invention]

[0017] According to the present invention having the above-described configuration, it is possible to reduce power consumption and achieve low-latency operation while satisfying the communication functions expected in a wireless network conforming to the IEEE802.15.4 standard. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing an example in which a tree topology is adopted in a wireless communication system to which the present invention is applied. [Figure 2] FIG. 2 is a diagram showing an example in which a star topology is adopted in a wireless communication system to which the present invention is applied. [Figure 3] FIG. 3 is a diagram showing a superframe structure that is set for each node when transmitting and receiving a data frame. [Figure 4] FIG. 4 is a diagram for explaining an example in which an active period is divided into a first period and a second period in time series. [Figure 5] FIG. 5 is a diagram showing an example of adjusting the time-series proportion of the early active period so as to be greater than that of the late active period. [Figure 6] FIG. 6 is a diagram illustrating an example in which the latter active period is adjusted to be shorter than the data frame length of downstream data communication. [Figure 7] FIG. 7 is a diagram for explaining the prior art. DETAILED DESCRIPTION OF THE INVENTION

[0019] A wireless communication system to which the present invention is applied will be described in detail below with reference to the drawings.

[0020] In Fig. 1, a wireless communication system 1 to which the present invention is applied includes wireless nodes 3-1, 3-2, 3-3, 3-4, 3-5, 3-6, and 3-7 with a collection control station (hereinafter referred to as CS) 2 as the root, and employs a so-called tree topology in which the nodes 3 are arranged in a tree shape. In this wireless communication system 1, lower nodes 3 perform upstream data communication with higher nodes 3 and CS2. Also, in the wireless communication system 1, higher nodes 3 and CS2 perform downstream data communication with lower nodes 3.

[0021] The CS2 is the highest-level master device, and collects data frames transmitted by upstream data communication from the nodes 3-1 to 3-7. The CS2 also serves as a central control unit for controlling the entire wireless communication system 1, and transmits control data frames to a specific node 3 via downstream data communication.

[0022] Node 3 is a generic term for devices capable of transmitting and receiving data, including transmitting and relaying data, and is, for example, a communication device conforming to the IEEE802.15.4 standard. Node 3 may be embodied as a sensor that senses and wirelessly transmits predetermined data, or as a terminal device capable of wireless communication, such as a mobile phone, smartphone, tablet device, wearable device, or laptop personal computer (PC). Node 3 may also include a control system for a machine tool, such as an actuator. In such a case, it may be embodied as a device capable of, for example, controlling the stopping of a valve, controlling a robot, or controlling the stopping of gas. If node 3 is embodied as an actuator or the like including a control system, it will perform various control operations based on control data transmitted downstream from CS2 via other nodes 3.

[0023] 2 shows an example of a wireless communication system 1 to which the present invention is applied, which employs a star topology. The star topology includes one CS 2 and multiple nodes 3-1 to 3-5 that directly transmit and receive data frames to and from this CS 2. A master device-slave device relationship is established between the CS 2 and the nodes 3-1 to 3-5.

[0024] The wireless communication system 1 to which the present invention is applied may adopt either a tree topology or a star topology.

[0025] In a wireless communication system 1 to which the present invention is applied, a superframe structure set for each node 3 when transmitting and receiving data frames is shown in Figure 3. In this superframe structure, the superframe is defined by periodic beacon signals under Time Division Multiple Access (TDMA) control. The interval between these beacon signals is called an intermittent standby period. The superframe includes an active period (AP) during which nodes wait for data frames to be transmitted or received, and a sleep period (SP).

[0026] Incidentally, the intermittent standby period of a superframe is not necessarily limited to being determined by a beacon signal. In other words, it is not necessary for a beacon signal to be transmitted or received at the start or end of the intermittent standby period of a superframe. Multiple superframes may be included within the interval of a beacon signal. Furthermore, the intermittent standby period of each superframe may be set to, for example, the minimum interval between beacon signals. In such a case, superframes whose intermittent standby period is set to the minimum interval between beacon signals will be consecutive, regardless of the interval between beacon signals transmitted or received thereafter.

[0027] The length of the intermittent standby period of the superframe, and the start point (start time) and end point (end time) of the superframe can be freely changed. The intermittent standby period of the superframe can be adjusted by adjusting the interval of the beacon signal.

[0028] The active period AP starts at the start of the superframe and waits for a predetermined time in an intermittent standby cycle for data frames to be transmitted and received. During this active period AP, at least the information written in the header of the data frame is read. From the information in the header of the data frame read during the active period AP, it is possible to determine whether or not the entire data frame needs to be received.

[0029] As shown in Figure 3(a), the active period AP may be shorter than the length of the data frame being transmitted or received. The end point of the data frame is not necessarily limited to within the active period, but may extend beyond the active period AP. Because only the information contained in the header of the data frame needs to be read, the active period AP may be shortened to the extent that the header information can be read regardless of the data frame length. In other words, as long as the active period AP can listen for only the header portion of the data frame sent by each node, the active period AP can be shortened and the node can transition to a sleep state, regardless of the length of the data frame. Therefore, the IEEE 802.15.4 standard allows the sleep state to be extended longer than usual, thereby reducing power consumption. However, because the active period AP must reliably receive at least the header of the data frame being transmitted, it is required to remain in a standby state without transitioning to a sleep state.

[0030] The length of this active period AP can be freely set in each node 3. The active period AP may be 0 at its shortest. In other words, there may be no active period AP from the start to the end of one superframe, and it may be entirely composed of a sleep period SP. Furthermore, this active period AP can be extended at its longest from the start to the end of the superframe. In other words, one superframe may entirely be composed of an active period AP.

[0031] In a superframe, the sleep period SP extends from the end of the active period AP to the end of the superframe. As described above, the length of the active period AP is variable, and therefore the sleep period SP can also be varied according to the length of the active period AP. During the sleep period SP, node 3 enters a sleep state, i.e., the power is turned off and node 3 transitions to a period in which it does not transmit or receive data frames or wait for them. In a superframe, by providing not only the active period AP but also the sleep period SP in which node 3 transitions to this sleep state, it is possible to reduce the power consumption of node 3. Incidentally, the sleep period SP extends from the end of the active period AP to the end of the superframe.

[0032] 3(b), if the time period for transmitting and receiving a data frame in a superframe exceeds the active period AP and it is determined that transmitting and receiving a data frame is necessary, the active period AP may be extended until after the end of the data frame in actual communication. In actual communication, by controlling the time for transmitting and receiving a data frame and the active period AP to overlap in time series, the device is always in a standby state, but after transmitting and receiving a data frame is completed, there is no particular problem if the device transitions to the sleep period SP without delay.

[0033] In the wireless communication system 1 to which the present invention is applied, such active periods AP and sleep periods SP are set for each node 3. At this time, the active period AP assigned to each node 3 is divided into an early period and a late period in time series, as shown in Fig. 4. Hereinafter, the early active period AP will be referred to as an early active period AP1, and the late active period will be referred to as a late active period AP2.

[0034] The early active period AP1 and the late active period AP2 are each allocated to either uplink data communication or downlink data communication. That is, as shown in Fig. 4(a), when uplink data communication is allocated to the early active period AP1, downlink data communication is allocated to the late active period AP2. As shown in Fig. 4(b), when downlink data communication is allocated to the early active period AP1, uplink data communication is allocated to the late active period AP2. In other words, either uplink data communication or downlink data communication is allocated to the early active period AP1, and the other of uplink data communication or downlink data communication is allocated to the late active period AP2.

[0035] In addition, the early active period AP1 and the late active period AP2 are configured so that their chronological proportions can be adjusted. That is, assuming that the overall length of the active period AP is constant, by freely determining the proportion of this early active period API, it is possible to freely determine the late active period AP2, which constitutes the remaining active period AP. Note that, in the present invention, adjusting the chronological proportions of the early active period AP1 and the late active period AP2 is not essential, and may, of course, be omitted.

[0036] Incidentally, the entire active period AP can also be set freely, so the active period AP is first determined, and then the chronological proportions of the early active period AP1 and the later active period AP2 within it can be set freely.

[0037] That is, in the wireless communication system 1 to which the present invention is applied, either uplink data communication or downlink data communication can be assigned to the early active period AP1 and the late active period AP2, respectively, and the time-series ratio of the assigned early active period AP1 and late active period AP2 can be freely adjusted. The assignment and adjustment of the early active period AP1 and late active period AP2 are performed on the CS2 side.

[0038] At this time, the allocation of upstream data communication and downstream data communication to the early active period AP1 and the later active period AP2, respectively, and the time-series adjustment of the ratio may be performed according to the number of detected nodes 3.

[0039] In the process of this allocation and adjustment, CS2 detects and counts the number of nodes 3 subordinate to itself. Some nodes 3 move and go out of the wireless communication range of CS2, while others newly enter the wireless communication range of CS2. As such, the number and number of nodes 3 subordinate to CS2 change over time, so every time the above-mentioned allocation and adjustment is performed, all nodes 3 subordinate to itself are detected and counted.

[0040] Then, depending on the number of detected nodes, the upstream data communication and the downstream data communication are allocated to the early active period AP1 and the late active period AP2, respectively, and the time-series proportions are adjusted. Such allocation and adjustment of the active periods AP1 and AP2 may be performed for each intermittent standby cycle, or may be performed collectively for multiple intermittent standby cycles.

[0041] In particular, downstream data communication from CS2 to node 3 often involves broadcasting data frames in bulk. Broadcasting data frames can be done in bulk in a shorter time than unicasting to individual nodes 3. On the other hand, upstream data communication from node 3 to CS2 rarely involves broadcasting data frames, and in most cases, individual nodes send data frames to CS2 individually via unicast.

[0042] In such a case, if multiple nodes 3 start upstream data communication to the CS2 during the same time period, the other nodes 3 must wait until one node 3 finishes its upstream data communication. As a result, it takes a considerable amount of time for all nodes 3 to complete their upstream data communication. In particular, as the number of nodes 3 increases, the difference in communication time between the upstream data communication and the downstream data communication becomes larger.

[0043] For this reason, as shown in FIG. 5 , as the number of nodes 3 subordinate to CS2 increases, upstream data communication may be assigned to the early active period AP1 and downstream data communication may be assigned to the later active period AP2, and the chronological proportion of the early active period AP1 may be adjusted to be greater than that of the later active period AP2. Here, increasing the chronological proportion of the early active period AP1 greater than that of the later active period AP2 includes any adjustment that increases the chronological proportion of the previous early active period AP1. In such a case, it is not necessary to make the absolute length of the early active period AP1 longer than that of the later active period AP2. Conversely, even if the chronological proportion of the early active period AP1 itself is shorter than that of the later active period AP2, it is sufficient as long as the chronological proportion is increased compared to the previous period. Of course, as a result of increasing the chronological proportion of the early active period AP1, it is inevitable that the absolute length of the early active period AP1 will often be longer than that of the later active period AP2, which results in the effects described below.

[0044] By first allocating upstream data communication to the early active period AP1 and increasing the time-series proportion, more active periods AP can be allocated to upstream data communication, which mainly involves unicast data frame transmission and takes a considerable amount of time for each node 3 to complete transmitting data frames. If the time-series proportion of the early active period AP1 is increased, it becomes possible to time-series cover the upstream data communication performed by each node 3 to the CS2 through this early active period AP1. In particular, as the number of nodes 3 increases, the time until upstream data communication by all nodes 3 completes increases, so it becomes possible to cover this by further increasing the time-series proportion of the early active period AP1 accordingly.

[0045] Increasing the chronological proportion of the early active period AP1 in this way results in a decrease in the chronological proportion of the late active period AP2. However, even if the chronological proportion of the late active period AP2 decreases, downstream data communication from CS2 to node 3 can be adequately covered within the late active period AP2 because data frames are often delivered en bloc by broadcast in a short period of time. Moreover, as shown in Figure 3(a), since only the beginning of the data frame for downstream data communication needs to be included in the late active period AP2, communication can be carried out without delay even if the late active period AP2 to which downstream data communication is allocated becomes shorter.

[0046] In this case, when CS2 performs downlink data communication to each node 3 by broadcast, it may allocate uplink data communication to the early active period AP1 and downlink data communication to the later active period AP2, and adjust the time series proportion of the early period to be larger than when CS2 performs downlink data communication to each node 3 by unicast. In such a case, CS2 itself determines whether to perform downlink data communication to the nodes 3 by broadcast or unicast. When performing downlink data communication by broadcast, it increases the time series proportion of the early active period AP1 and decreases the time series proportion of the later active period AP2 compared to when performing downlink data communication by unicast. Because the time required for downlink data communication by broadcast can be significantly shorter than when performing downlink data communication by unicast, increasing the time series proportion of the early active period AP1 allows the active period AP to be effectively used for uplink data communication. On the other hand, when performing downlink data communication by unicast, the communication time increases accordingly, so it is addressed by decreasing the time series proportion of the early active period AP1 and increasing the time series proportion of the later active period AP2.

[0047] However, CS2 is not limited to allocating uplink data communication to the early active period AP1 and downlink data communication to the late active period AP2 as described above when CS2 itself performs downlink data communication by broadcast to each node 3. Conversely, the same effect as described above can be obtained by allocating downlink data communication to the early active period AP1 and uplink data communication to the late active period AP2, and adjusting the time-series proportion of the late active period AP2 to be higher than when CS2 itself performs downlink data communication by unicast to each node 3.

[0048] In the above-described embodiment, it is assumed that as the number of nodes 3 subordinate to CS2 increases, upstream data communication is allocated to the early active period AP1 and downstream data communication is allocated to the later active period AP2. However, regardless of the number of nodes 3, upstream data communication may be uniformly allocated to the early active period AP1 and downstream data communication to the later active period AP2.

[0049] Note that CS2 does not necessarily perform downlink data communication entirely via broadcast, but may also perform downlink data communication via unicast. Therefore, if CS2 itself knows whether it will use broadcast or unicast for downlink data communication, it may adjust and allocate the early active period AP1 and the late active period AP2 based on that information. In such a case, when CS2 itself performs downlink data communication to each node 3 via broadcast, it may allocate uplink data communication to the early active period AP1 and downlink data communication to the late active period AP2, and adjust the time series proportion of the early active period AP1 to be greater than that of the late active period AP2. Since the communication time is significantly reduced when CS2 itself performs downlink data communication to each node 3 via broadcast, CS2 allocates downlink data communication to the late active period AP2 and reduces the time series proportion of the late active period AP2. The shortening of the late active period AP2 allows the early active period AP1, to which uplink data communication is allocated, to be lengthened accordingly.

[0050] In this case, as shown in FIG. 6, the late active period AP2 may be adjusted to be shorter than the length of the data frame for downlink data communication. As a result, the end point of the late active period AP2 can be adjusted to be before the end point of the data frame for downlink data communication. As described above, since only the beginning of the data frame for downlink data communication needs to be included in the late active period AP2, communication can be carried out without delay even if the late active period AP2 to which downlink data communication is allocated becomes shorter. By adjusting the early active period AP1 to be shorter than the data frame length for downlink data communication, the early active period AP1 can be lengthened accordingly, and more time can be allocated to uplink data communication.

[0051] In such a case, in other words, it is sufficient that the end point of the data frame for downlink data communication is adjusted to be before the start point of the early active period AP1 in the next intermittent standby cycle. Even if the end point of the data frame for downlink data communication is after the end point of the later active period AP2, it is sufficient that it is located before the start point of the early active period AP1 in the next intermittent standby cycle. Furthermore, when downlink data communication is performed by broadcast, it is possible to assign downlink data communication to the early active period AP1 and uplink data communication to the later active period AP2. In such a case, it is also possible to adjust the end point of the later active period AP2 to be before the end point of the data frame for uplink data communication.

[0052] In such a case, it is sufficient to adjust the end point of the data frame for uplink data communication so that it is before the start point of the early active period AP1 in the next intermittent standby cycle. Even if the end point of the data frame for uplink data communication is after the end point of the later active period AP2, it is sufficient as long as it is located before the start point of the early active period AP1 in the next intermittent standby cycle.

[0053] Furthermore, when CS2 performs downlink data communication by unicast without broadcasting to each node 3, it may adjust the proportion of the early active period AP1 and the late active period AP2 to which downlink data communication is allocated so as to increase in a time series manner. Downlink data communication by unicast requires a longer communication time than downlink data communication by broadcast, and this can be addressed by increasing in a time series manner the proportion of the early active period AP1 and the late active period AP2 to which the downlink data communication is allocated. [Explanation of symbols]

[0054] 1. Wireless communication systems 2 CS 3 nodes

Claims

1. In a wireless communication system in a network in which data frames are transmitted and received between two or more nodes arranged around a collection control station based on time division multiple access (TDMA), each of the nodes is capable of transmitting and receiving the data frames during successive intermittent standby periods, and is assigned an active period divided into an early period and a late period in time series, and a sleep period in which operation is suspended; The collection control station Depending on the number of detected nodes, one of the upstream data communication from the node to the collection control station and the downstream data communication from the collection control station to the node is allocated to the first half of the active period, and the other of the upstream data communication and the downstream data communication is allocated to the second half of the active period; When the node itself broadcasts downstream data to each of the nodes, Allocating upstream data communication to the first period and downstream data communication to the second period, and adjusting the time series ratio of the first period to be increased compared to when the node itself performs downstream data communication by unicast to each of the nodes; Alternatively, downstream data communication is assigned to the earlier period and upstream data communication is assigned to the later period, and the ratio of downstream data communication to the later period is adjusted to be higher than when the node itself performs downstream data communication by unicast to each of the nodes. A wireless communication system comprising:

2. In a wireless communication system in a network in which data frames are transmitted and received between two or more nodes arranged around a collection control station based on time division multiple access (TDMA), each of the nodes is capable of transmitting and receiving the data frames during successive intermittent standby periods, and is assigned an active period divided into an early period and a late period in time series, and a sleep period in which operation is suspended; The collection control station Depending on the number of detected nodes, one of the upstream data communication from the node to the collection control station and the downstream data communication from the collection control station to the node is allocated to the first half of the active period, and the other of the upstream data communication and the downstream data communication is allocated to the second half of the active period; When the node itself broadcasts downstream data to each of the nodes, allocating upstream data communication to the first period and downstream data communication to the second period, and adjusting the end point of the data frame of the downstream data communication to be before the start point of the first period of the next intermittent standby cycle; Alternatively, downlink data communication is assigned to the first period and uplink data communication is assigned to the second period, and the end point of the data frame of the uplink data communication is adjusted so that it is before the start point of the first period in the next intermittent standby cycle. A wireless communication system comprising:

3. The collection control station adjusts the time-series ratio between the early period and the late period according to the number of detected nodes.

3. The wireless communication system according to claim 1, wherein:

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