Wireless communication system

Abstract

To suppress interference between communication timings of data frames to be transmitted and received at respective nodes by taking into consideration the time arrangement or the like of the communication timings of the data frames to be transmitted and received.SOLUTION: In a wireless communication system in a network structure in which data frames are transmitted and received between two or more arranged nodes 3, at least some of the nodes 3 are assigned active periods during which they wait for the data frames transmitted and received in successive intermittent standby cycles, and are further assigned frame periods, which are periods during which the data frames are allowed to be transmitted and received, from the start time point of the active periods to after the end time point of the data frames, and the frame periods assigned to the respective nodes 3 are adjusted to shorten the intervals between them without overlapping with each other in time series.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a wireless communication system in a network that performs transmission and reception of data frames between nodes arranged over two or more with a collection control station as the root.

Background Art

[0002] In recent years, in a wireless network, a communication device compliant with the IEEE802.15.4g standard that can perform small, inexpensive, and power-saving wireless communication has been used (see, for example, Non-Patent Document 1). In a network compliant with this IEEE802.15.4g standard, various topologies composed of a CS (Collection station) as a collection control station and one or more nodes are adopted.

[0003] Among them, in this IEEE802.15.4 standard, a power-saving superframe structure as shown in FIG. 8 has been proposed. In this superframe structure, under time-division multiple access (TDMA) control, the superframe is defined by a periodic beacon signal. During the interval (intermittent waiting period) of this beacon signal, it can be divided into an active period (AP) for waiting for the signal of the data frame to be transmitted and received, and a sleep period (SP) in which the power is turned off and no transmission, reception, or waiting operations are performed. In the active period AP, each node can be operated as a substantial communication period. On the other hand, in the sleep period SP, each node can shift to a sleep state (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Documents

[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] [Problems to be Solved by the Invention]

[0006] However, in the prior art documents in the IEEE802.15.4 standard described above, there is no particular mention of adjusting the temporal arrangement of the communication timings of the data frames to be transmitted and received with respect to each other. As a result, interference occurs between the communication timings of the data frames to be transmitted and received at each node, and there has been a problem that the communication performance of the entire system deteriorates.

[0007] Therefore, the present invention has been devised in view of the above-described problems, and an object thereof is to suppress interference between the communication timings of the data frames to be transmitted and received at each node by considering the temporal arrangement of the communication timings of the data frames to be transmitted and received, and to provide a wireless communication system capable of improving the coexistence characteristics and communication performance of the nodes of the entire system. [Means for Solving the Problems]

[0008] The wireless communication system according to the first invention is a wireless communication system in a network structure that transmits and receives data frames between nodes arranged over two or more. At least a part of the nodes is assigned an active period in which it waits for the data frame to be transmitted and received in consecutive intermittent waiting periods. Further, a frame period, which is a period allowing the transmission and reception of the data frame, is assigned from the start point of the active period to after the end point of the data frame. The intervals of the frame periods respectively assigned to the nodes are adjusted so as to shorten the intervals without overlapping them with each other in time series.

[0009] The wireless communication system according to the second invention is characterized in that, in the first invention, the frame periods respectively assigned to the nodes are adjusted to be continuous or substantially continuous.

[0010] The wireless communication system according to the third invention is characterized in that, in the second invention, when a higher-level node sets the frame period of a lower-level node, it is adjusted without overlapping with the frame periods of other identified nodes in time series.

Advantages of the Invention

[0011] According to the present invention having the above-described configuration, by considering the temporal arrangement of the communication timing of the data frames to be transmitted and received, interference is suppressed between the communication timings of the data frames transmitted and received at each node, and it becomes possible to improve the coexistence characteristics and communication performance of the nodes in the entire system. In particular, the present invention exhibits a great effect when applied to a wireless communication system that performs power-saving sensor data relay collection by a plurality of wireless communication networks, transmission of control signals to machine tools, and the like.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

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Figure 6

[0013] Hereinafter, a wireless communication system to which the present invention is applied will be described in detail with reference to the drawings.

[0014] As shown in FIG. 1, a wireless communication system 1 to which the present invention is applied includes, as wireless nodes, nodes 3-1, 3-2, 3-3, 3-4, 3-5 having a collection station (hereinafter referred to as CS) 2 as a root, and a so-called tree-type topology in which each node 3 is arranged in a tree type is adopted. In this wireless communication system 1, a lower node 3 performs upstream data communication toward a higher node 3 or CS2. Also, in the wireless communication system 1, a higher node 3 or CS2 performs downstream data communication toward a lower node 3.

[0015] CS2 is the highest master device and collects data frames transmitted by upstream data communication from each of the nodes 3-1 to 3-5. Further, CS2 also serves as a central control unit for controlling the entire wireless communication system 1, and performs downstream data communication of a control system data frame to a specific node 3.

[0016] Node 3 is a general term for devices capable of transmitting and receiving data, including data transmission and relay. For example, it is a communication device compliant with the IEEE802.15.4 standard. Node 3 can be embodied as a sensor that senses predetermined data and transmits it wirelessly. Additionally, it may be embodied as a terminal device capable of wireless communication, such as a mobile phone, smartphone, tablet terminal, wearable terminal, or notebook personal computer (PC). Further, this Node 3 may include a control system such as an actuator. In such a case, it is embodied as a device capable of performing, for example, control to stop a valve, control a robot, or control to stop gas. If Node 3 is embodied as an actuator or the like including a control system, various control operations will be executed based on the control data communicated downstream from CS2 via other Node 3s.

[0017] FIG. 2 shows an example in which a star topology is adopted in the wireless communication system 1 to which the present invention is applied. In the star topology, it includes one CS2 and a plurality of Node 3s that directly transmit and receive data frames with this CS2. A master device - slave device relationship is established between CS2 and Node 3.

[0018] In the wireless communication system 1 to which the present invention is applied, either a tree topology or a star topology may be adopted.

[0019] In the wireless communication system 1 to which the present invention is applied, the superframe structure set for each node 3 when transmitting and receiving data frames is shown in FIG. 3. In this superframe structure, under time-division multiple access (TDMA) control, the superframe is defined by a periodic beacon signal. The interval of this beacon signal is called the intermittent reception waiting period. The superframe is roughly classified into a frame period (FP), a sleep period (SP), and an active period (AP) for waiting for data frames to be transmitted and received. The data frame is set so that the end point thereof is before the start point of the active period in the subsequent intermittent reception waiting period. The length of this data frame may be temporarily defined, but is not limited thereto and can be defined as a permanent one.

[0020] Incidentally, the intermittent reception waiting period of the superframe is not necessarily limited to the case defined by the beacon signal. That is, it is not essential for the beacon signal to be transmitted and received at the start point and the end point of the intermittent reception waiting period in the superframe. There may be a case where a plurality of superframes are included within the interval of the beacon signal. Also, the intermittent reception waiting period of each superframe may be set, for example, to be the minimum interval between beacon signals. In such a case, the superframes with the intermittent reception waiting period set to be the minimum interval between the beacon signals will continue without depending on the interval of the beacon signals to be transmitted and received thereafter.

[0021] The length of the intermittent reception waiting period of the superframe, the start point (start time), and the end point (end time) of the superframe are changeable. Such adjustment of the intermittent reception waiting period of the superframe may be performed by adjusting the interval of the beacon signal.

[0022] The active period AP starts from the start of a superframe and waits for data frames to be transmitted and received during a discontinuous waiting period for a predetermined time. In this active period AP, it is a discontinuous waiting period for at least reading the information described in the header of the data frame. From the information in the header of the data frame read by the active period AP, it is possible to determine whether it is necessary to receive the entire data frame. Note that the active period AP does not have to be set in all superframes, and a part of them may be sufficient.

[0023] As shown in FIG. 4, the active period AP may be shorter than the data frame to be transmitted and received, and the end point of the data frame is not limited to being within the active period, and may be at a point beyond the active period AP. Since the active period AP only needs to read the information described in the header of the data frame, it may be shortened to such an extent that the information in the header can be read regardless of the data frame length. And this active period AP only needs to include the start point of the data frame to be transmitted and received. However, since it is necessary to steadily receive at least the header of the data frame to be transmitted, it is required to always be in a waiting state without shifting to a sleep state.

[0024] The frame period FP is set as a time zone that allows the transmission and reception of data frames, and the end point is set so as to include the time zone of the transmission and reception of data frames from the start of the superframe. In other words, the frame period FP is allocated from the start point of the active period AP to after the end point of the data frame.

[0025] That is, if communication interference occurs during the frame period FP, which is the period actually allowing the transmission and reception of data frames, the communication efficiency of that data frame will decrease. Therefore, it is necessary to avoid communication interference during the frame period FP in which the data frame is being transmitted and received as much as possible.

[0026] This frame period FP is configured to be variable and can be shortened to the shortest time zone that is the same as the active period AP. On the other hand, it can be extended up to the end point of the superframe while including the time zone of data frame transmission and reception from the start point of the active period AP at the longest. Note that the end point of the frame period FP may be the same time point as the completion of data frame transmission.

[0027] Incidentally, the sleep period SP is from the end point of the active period AP to the end point of the superframe.

[0028] By setting such frame periods FP between CS2 and node 3 so as not to overlap with each other in time series, it is possible to prevent interference between data frames included in each frame period FP. For example, as shown in FIG. 5, by setting the frame periods FP set for node 3-1 and node 3-3 to shift so as not to overlap with each other in time series when performing data frame transmission and reception respectively, it is possible to prevent interference between data frames included therein.

[0029] In the wireless communication system 1 to which the present invention is applied, at least one of the intermittent waiting period of the superframe and the length of the frame period FP described above is configured to be variable. In addition to this, the temporal relationship of the frame period FP can be adjusted freely. That is, the start point and the end point of the frame period can be freely determined.

[0030] Adjustment or modification of the temporal context of the frame period FP may be performed on the CS2 side or on the node 3 side. However, as the priority for modifying the temporal context of this frame period FP, in other words, the start and end points of the frame period FP, it may be set in the order of CS2, the higher-level node 3. That is, as shown in FIG. 5, normally CS2 can modify the temporal context of the frame period FP for each lower-level node 3. And between node 3s, a higher-level node 3 can modify the temporal context of the frame period FP including the data frames transmitted and received between it and a lower-level node 3.

[0031] When performing this modification of the temporal context of the frame period FP, as shown in FIG. 5(a), in addition to simply setting to avoid temporally overlapping the frame periods FP assigned to each node 3 with each other, it may be adjusted so that the frame periods FP of each other are substantially continuous or continuous as shown in FIG. 5(b). Here, the fact that the frame periods FP assigned to each node 3 are continuous means that they are temporally continuous without an interval between each frame period FP. However, the interval between these frame periods FP is not limited to a completely temporally continuous one with no interval at all, and may be a so-called substantially continuous one with a somewhat interval between the frame periods FP. That is, the temporal adjustment of the frame period FP in FIG. 5(b) may have an interval as long as the adjustment is made in the direction of shortening the interval between the frame periods FP compared to the case of FIG. 5(a).

[0032] The adjustment of the temporal context of the frame period FP referred to here, as shown in FIG. 5(b), also involves the temporal adjustment of the intermittent waiting period itself in each node 3.

[0033] By adjusting in the direction of shortening the intervals between the frame periods FP respectively assigned to each node 3 in this way, the frame periods FP can be distributed unevenly in time series as shown in FIG. 6, and it is possible to ensure a long continuous idle time during which no frame period FP of any node 3 is set. By being able to ensure a long continuous idle time, when newly performing wireless communication with another node 3, it is possible to ensure a long idle time during which wireless communication can be performed while preventing communication interference with the other node 3. As a result, the possibility of preventing communication interference with other nodes 3 can be increased. Here, the other nodes 3 referred to here include nodes 3 in other wireless communication networks in addition to the relationship between any one and the other of nodes 3-1 to 3-5 in the same wireless communication network.

[0034] In such a case, the other node 3 performs an interference check before starting wireless communication. In this interference check, the temporal precedence relationship of the frame period FP described above is identified. If the temporal precedence relationship of the frame period FP can be identified, the idle time can also be grasped in time series. The other node 3 sets a coexistence period CP including an active period AP and a frame period FP for its own communication in accordance with this idle time, and performs transmission and reception of frame data based on it. Since the coexistence period CP including the frame period FP including the frame data transmitted and received by the other node 3 is set in the idle time, it is possible to perform wireless communication while avoiding communication interference with each node 3.

[0035] Thus, according to the present invention, interference can be prevented by adjusting without overlapping in time series with the frame periods of other identified nodes.

[0036] Also, as shown in FIG. 6, if the coexistence period CP in another node 3 is identified first, it is also possible to adjust the frame periods FP of each node 3 so as to be substantially continuous or continuous without overlapping in time series in the time zone other than the coexistence period CP.

Explanation of Signs

[0037] 1 Wireless communication system 2 Collection control station (CS) 3 Node

Claims

1. In a wireless communication system in a network structure that performs transmission and reception of data frames between nodes arranged over two or more, at least a part of the nodes are assigned an active period for waiting for the data frames to be transmitted and received in consecutive intermittent waiting periods, and further a frame period, which is a period allowing transmission and reception of the data frames, is assigned from the start point of the active period to after the end point of the data frames, adjusting so as to shorten the intervals between the frame periods respectively assigned to the nodes without overlapping them with each other in time series A wireless communication system characterized by the above.

2. Adjusting so that the frame periods respectively assigned to the nodes are consecutive or substantially consecutive A wireless communication system according to Claim 1, characterized by the above.

3. When a higher-level node sets the frame period of a lower-level node, adjusting without overlapping it with the frame periods of other identified nodes in time series A wireless communication system according to Claim 2, characterized by the above.

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