JP7748671B2 - wireless communication system - Google Patents

Description

This relates to a wireless communication system in a network that transmits and receives data frames between two or more nodes located around a collection control station based on time division multiple access (TDMA).

In recent years, wireless networks have begun to use communication devices that comply with the IEEE802.15.4g standard, which are small, inexpensive, and capable of low-power wireless communication (see, for example, Non-Patent Document 1). Networks that comply with the IEEE802.15.4g standard employ various topologies consisting of a collection control station (CS) and one or more nodes.

The IEEE802.15.4 standard, among others, proposes a power-saving superframe structure as shown in Figure 7. In this superframe structure, superframes are defined by periodic beacon signals 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 nodes wait for data frame signals to be transmitted or received, and a sleep period (SP) during which the power is turned off 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).

Japanese Patent Application Laid-Open No. 2020-167636

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

Downstream data communication from CS to nodes is often achieved by broadcasting data frames in bulk. Broadcast data frame distribution can be completed in a shorter timeframe than unicast distribution to individual nodes. On the other hand, upstream data communication from nodes to CS rarely involves sending data frames by broadcast; most nodes send data frames independently to CS via unicast. In such cases, if multiple nodes initiate upstream data communication to 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 upstream data communication for all nodes to complete. In particular, as the number of nodes increases, the difference in communication time between upstream data communication and downstream data communication becomes greater.

In contrast, with the conventional energy-saving superframe structure described above, no special 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.

For this reason, it is necessary to extend the active period AP until all standby and data frame transmission and reception is complete, not only for downstream data communications via broadcast, but also for upstream data communications, which are mostly unicast. As a result, the sleep period SP inevitably becomes shorter, making it difficult to reduce power consumption across the entire network.

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.

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

The present invention was devised in light 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 of an IEEE802.15.4 standard wireless network.

The inventors have resolved the above-mentioned issues by using time division multiple access (TDMA) to transmit and receive data frames between two or more nodes located around a collection control station, enabling data frames to be transmitted and received in successive intermittent standby periods, and allocating to each node an active period divided chronologically into an early and late period, and a sleep period in which operation is suspended. Depending on the number of detected nodes, upstream data communication from the node to the collection control station and downstream data communication from the collection control station to the node are allocated to the early and late periods of the active period, respectively.

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 is 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 either uplink data communication from the node to the collection control station or downlink data communication from the collection control station to the node to the early period of the active period according to the number of detected nodes, and The other of the upstream data communication and the downstream data communication is assigned to the latter period between the upstream and downstream data communication, and when the node itself performs downstream data communication to each of the nodes by broadcast, the node itself assigns upstream data communication to the former period and downstream data communication to the latter period, and adjusts the proportion of the earlier period in time series to be greater than when the node itself performs downstream data communication to each of the nodes by unicast, or assigns downstream data communication to the earlier period and upstream data communication to the latter period, and adjusts the proportion of the later period in time series to be greater than when the node itself performs downstream data communication to each of the nodes by unicast .

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 is 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 either uplink data communication from the node to the collection control station or downlink data communication from the collection control station to the node to the early period of the active period according to the number of detected nodes, and and allocates the other of the uplink data communication and the downlink data communication to the latter part of the active period, and when the node itself performs downlink data communication to each of the nodes by broadcasting, allocates the uplink data communication to the former part and the downlink data communication to the latter part, and adjusts so that the end point of the data frame of the downlink data communication is before the start point of the former part of the next intermittent standby cycle, or allocates the downlink data communication to the former part and the uplink data communication to the latter part, and adjusts so that the end point of the data frame of the uplink data communication is before the start point of the former part of the next intermittent standby cycle .

The wireless communication system according to the third aspect of the present invention is the first or second aspect of the present invention, characterized in that the collection control station adjusts the chronological ratio between the early and late periods depending on the number of detected nodes.

The present invention, configured as described above, makes it possible to reduce power consumption and achieve low-latency operation while still satisfying the communication functions expected of wireless networks conforming to the IEEE 802.15.4 standard.

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. 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. FIG. 3 is a diagram showing a superframe structure that is set for each node when transmitting and receiving a data frame. 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. 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. FIG. 6 is a diagram showing an example in which the latter active period is adjusted to be shorter than the data frame length of downstream data communication. FIG. 7 is a diagram for explaining the prior art.

Below, a wireless communication system to which the present invention is applied will be described in detail with reference to the drawings.

In Figure 1, a wireless communication system 1 to which the present invention is applied comprises wireless nodes 3-1, 3-2, 3-3, 3-4, 3-5, 3-6, and 3-7 with a collection control station (CS) 2 as the root, and employs a so-called tree topology in which the nodes 3 are arranged in a tree structure. In this wireless communication system 1, lower-level nodes 3 communicate upstream data toward higher-level nodes 3 and CS2. In addition, higher-level nodes 3 and CS2 communicate downstream data toward lower-level nodes 3.

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

Node 3 is a general term for devices capable of sending and receiving data, including transmitting and relaying data, and is, for example, a communications 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 communications, 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 cases, it may be embodied as a device that can, for example, control the stopping of a valve, control a robot, or control the stopping of gas. If node 3 is embodied as an actuator or the like that includes a control system, it will perform various control operations based on control data transmitted downstream from CS2 via other nodes 3.

Figure 2 shows an example of a wireless communication system 1 to which the present invention is applied, employing a star topology. The star topology includes one CS2 and multiple nodes 3-1 to 3-5 that directly transmit and receive data frames with this CS2. A master device-slave device relationship is established between the CS2 and the nodes 3-1 to 3-5.

A wireless communication system 1 to which the present invention is applied may employ either a tree topology or a star topology.

Figure 3 shows the superframe structure set for each node 3 when transmitting and receiving data frames in a wireless communication system 1 to which the present invention is applied. 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 the intermittent standby period. The superframe includes an active period (AP) during which data frames to be transmitted or received are awaited, and a sleep period (SP).

By the way, 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 between beacon signals. 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 be the minimum interval between beacon signals will continue in succession, regardless of the interval between beacon signals transmitted and received thereafter.

The length of the intermittent standby period of the superframe, as well as the start point (start time) and end point (end time) of the superframe, can be freely changed. Adjustment of the intermittent standby period of such a superframe may be performed by adjusting the interval between beacon signals.

The active period AP begins at the start of the superframe and waits for a predetermined period of time during the 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.

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 limited to being 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 during the active period AP, 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, it is possible to shorten the active period AP and transition to a sleep state, no matter how long the data frame is. Therefore, the IEEE 802.15.4 standard allows the sleep state to be extended longer than normal, 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 at all times without transitioning to a sleep state.

The length of this active period AP can be freely set for each node 3. The active period AP can be as short as 0. In other words, there can be no active period AP at all from the start to the end of a superframe, and it can be entirely made up of sleep periods SP. The active period AP can also be extended to its longest length, from the start to the end of the superframe. In other words, the entirety of a superframe can be made up of active periods AP.

In a superframe, the sleep period SP runs from the end of the active period AP to the end of the superframe. As mentioned above, the length of the active period AP is variable, so 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 during 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 during which node 3 transitions to this sleep state, it is possible to reduce power consumption in node 3. Incidentally, the sleep period SP runs from the end of the active period AP to the end of the superframe.

Furthermore, as shown in Figure 3(b), in a superframe, if the time period for transmitting and receiving a data frame 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 has ended, there is no particular problem if it transitions to the sleep period SP without delay.

In a 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 chronologically into an early period and a late period, as shown in Figure 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.

Each of the early active period AP1 and the late active period AP2 is assigned either uplink data communication or downlink data communication. That is, as shown in FIG. 4(a), if uplink data communication is assigned to the early active period AP1, downlink data communication is assigned to the late active period AP2. As shown in FIG. 4(b), if downlink data communication is assigned to the early active period AP1, uplink data communication is assigned to the late active period AP2. In other words, either uplink data communication or downlink data communication is assigned to the early active period AP1, and the other of uplink data communication or downlink data communication is assigned to the late active period AP2.

In addition, the early active period AP1 and the late active period AP2 are configured so that their chronological proportions can be adjusted relative to each other. In other words, 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 makes up 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.

By the way, the entire active period AP can also be set freely, so first determine the active period AP, and then freely set the chronological proportions of the early active period AP1 and the later active period AP2 that make up that period.

In other words, in a 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 chronological ratio of the assigned early active period AP1 and late active period AP2 can be freely adjusted. This assignment and adjustment of the early active period AP1 and late active period AP2 is performed on the CS2 side.

In this case, the allocation of upstream data communication and downstream data communication for 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.

During this allocation and adjustment process, CS2 detects and counts the number of nodes 3 subordinate to itself. Some nodes 3 move and are no longer within the wireless communication range of CS2, while others may newly enter the wireless communication range of CS2. As such, the number and number of nodes 3 subordinate to CS2 change over time, so each time the above-mentioned allocation and adjustment is performed, all nodes 3 subordinate to itself are detected and counted.

Then, depending on the number of detected nodes, the system allocates upstream data communication and downstream data communication to the early active period AP1 and the later active period AP2, respectively, and adjusts the time-series ratios. This allocation and adjustment of active periods AP1 and AP2 may be performed for each intermittent standby cycle, or may be performed collectively for multiple intermittent standby cycles.

Downstream data communication from CS2 to node 3 in particular 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; most data frames are unicast, with each node individually sending a data frame to CS2.

In such a case, if multiple nodes 3 start upstream data communication to 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 greater.

Therefore, 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 late active period AP2, and the time series proportion of the early active period AP1 may be adjusted to be greater than that of the late active period AP2. Here, "increasing the time series proportion of the early active period AP1 greater than that of the late active period AP2" includes any adjustment that increases the time series proportion of the previous early active period AP1. In such a case, it is not necessary for the absolute length of the early active period AP1 to be longer than that of the late active period AP2. Conversely, even if the time series proportion of the early active period AP1 itself is shorter than that of the late active period AP2, it is sufficient as long as the time series proportion is greater than that of the previous period. Of course, as a result of increasing the time series 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 late active period AP2, which results in the effects described below.

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 from each node 3 to 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, and so this can be covered by further increasing the time-series proportion of the early active period AP1 accordingly.

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 distributed in bulk 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.

In this case, when CS2 performs downstream data communication to each node 3 by broadcast, it may allocate upstream data communication to the early active period AP1 and downstream data communication to the later active period AP2, and adjust the time series proportion of the early period to be higher than when CS2 performs downstream data communication to each node 3 by unicast. In such a case, CS2 itself determines whether to perform downstream data communication to the node 3 by broadcast or unicast. When performing downstream 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 downstream data communication by unicast. Because broadcast downstream data communication can be achieved in an extremely short time compared to unicast, increasing the time series proportion of the early active period AP1 allows the active period AP to be used effectively for upstream data communication. On the other hand, when performing downstream data communication by unicast, the communication time increases accordingly, so this 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.

However, when CS2 itself performs downstream data communication by broadcast to each node 3, this is not limited to allocating upstream data communication to the early active period AP1 and downstream data communication to the late active period AP2, as described above. Conversely, the same effect as described above can be achieved by allocating downstream data communication to the early active period AP1 and upstream 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 downstream data communication by unicast to each node 3.

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

Note that CS2 does not necessarily perform downstream data communication entirely via broadcast; it may also perform downstream data communication via unicast. Therefore, if CS2 itself knows whether it will use broadcast or unicast for downstream data communication, it may allocate and adjust the early active period AP1 and late active period AP2 based on that information. In such a case, when CS2 itself performs downstream data communication via broadcast to each node 3, it may allocate upstream data communication to the early active period AP1 and downstream 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 this significantly reduces communication time when CS2 itself performs downstream data communication via broadcast to each node 3, CS2 allocates downstream data communication to the late active period AP2 and reduces the time series proportion of the late active period AP2. The shortened late active period AP2 can then be used to lengthen the early active period AP1, to which upstream data communication is allocated.

In this case, as shown in Figure 6, the late active period AP2 may be adjusted to be shorter than the data frame length of downstream 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 of downstream data communication. As described above, since only the beginning of the data frame of 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. By adjusting the early active period AP1 to be shorter than the data frame length of downstream data communication, the early active period AP1 can be lengthened accordingly, allowing more time to be allocated to upstream data communication.

In such cases, in other words, it is sufficient to adjust the end point of the data frame for downlink 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 downlink data communication is later than the end point of the late 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. 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 late active period AP2. In such cases, it is also possible to adjust the end point of the late active period AP2 so that it is before the end point of the data frame for uplink data communication.

In such a case, in other words, it is sufficient to adjust the end point of the data frame for upstream 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 upstream data communication is after the end point of the late 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.

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 over time. Since downlink data communication by unicast takes a correspondingly longer communication time than downlink data communication by broadcast, this can be addressed by increasing over time the proportion of the early active period AP1 and the late active period AP2 to which downlink data communication is allocated.

1 Wireless communication system 2 CS
3 nodes

Claims (3)

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 allocated to the earlier period, and upstream data communication is allocated to the later period , and the ratio of the latter period is adjusted to be increased in time series compared to when the node itself performs downstream data communication by unicast to each of the nodes.
A wireless communication system comprising: 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,
assigning upstream data communication to the first period and downstream data communication to the second period , and adjusting the end point of a data frame for the downstream data communication so that the end point is before the start point of the first period in the next intermittent standby cycle;
Alternatively, downstream data communication is allocated to the first period and upstream data communication is allocated to the second period , and the end point of the data frame of the upstream data communication is adjusted so that it comes before the start point of the first period in the next intermittent standby cycle.
A wireless communication system comprising: 3. The wireless communication system according to claim 1, wherein the collection control station adjusts the time-series ratio between the earlier period and the later period in accordance with the number of detected nodes.