KR100873483B1 - Multichannel Operation in Wireless Sensor Networks - Google Patents

Abstract

The present invention relates to a multi-channel operating method in a wireless sensor network, and more particularly, in the case of having a radio interface in a wireless sensor network such as Zigbee, etc., the channel is changed so that mutual interference does not occur. The present invention relates to a multi-channel operating method in a wireless sensor network for transmitting data through multiple channels. In the multi-channel operating method in a wireless sensor network, each PAN (Personal Area Network) using the same gateway by calculating parallelism Setting up a coordinator; A channel information management step of managing channel information of each PAN; Generating a beacon frame including superframe schedule information of a main channel and another channel and transmitting the beacon frame to each node of the corresponding PAN; And a data receiving step of receiving data using superframe schedule information of the other channel in an inactive period of the main channel.

Wireless sensor network, multichannel operation, PAN, parallelism, superframe schedule information

Description

Method for operating multi channel in wireless sensor network

The present invention relates to a multi-channel operating method in a wireless sensor network, and more particularly, in the case of having a radio interface in a wireless sensor network such as Zigbee, etc., the channel is changed so that mutual interference does not occur. A multichannel operating method in a wireless sensor network for transmitting data through multiple channels.

The present invention is derived from the research conducted as part of the IT new growth engine core technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. Networking technology].

Wireless sensor networks (WSNs) are being actively applied in various fields such as environmental monitoring, medical systems, and robot exploration. Such a wireless sensor network is mainly composed of distributed nodes forming a network in a multi-hop form by themselves. Each node has several sensors, an embedded processor, and a low-power radio, which is primarily battery powered. In addition, these nodes are typically in a cooperative relationship that performs common tasks.

As with all shared media networks, Media Access Control (MAC) is a critical technology element for successful network operation.

The most fundamental function of a MAC is to prevent two or more nodes from starting data transmission at the same time to avoid collisions. Many MAC protocols have been developed for wireless voice or wireless data networks. Typical examples include circuit contention based protocols such as Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and IEEE 802.11.

In order to design a good MAC protocol for a wireless sensor network, the first important consideration is energy efficiency. As mentioned earlier, the sensor node is battery powered, so it is difficult to replace or recharge the battery. Therefore, sensor nodes will one day be manufactured at a very low price and discarded at the end of their life rather than being recharged. In the end, extending the lifetime of a network of such nodes has become a very important concern.

Another important issue is scalability as the network size, node density, and topology change. Over time, many factors change the topology of the network, and a good MAC must be able to accommodate this change in the network.

In consideration of these requirements, the ZigBee standard and 'SMAC' have been studied and utilized, and various modified methods have been proposed.

However, although much research has been conducted on low power consumption and scalability of wireless sensor networks, studies on throughput and reliability have not been conducted at all.

1 is an exemplary view of a general wireless sensor network.

As shown in FIG. 1, the sensor node 11 of the wireless sensor network interworks with a server 13 connected to a wired Internet backbone network via a gateway (GW) 12.

At this time, the type of traffic delivered to the wireless sensor network is downstream from the gateway 12 to all the sensor nodes 11 and upstream from all the sensor nodes 11 to the gateway 12. Divided into

In the downstream case, even if traffic is congested, if the gateway 12 has a buffer of sufficient capacity, data loss may be prevented. Typically, a gateway is a device that connects to a wired Internet backbone network that is located in a well-powered location and has a buffer of sufficient capacity.

However, since sensor nodes are basically battery-based, low power consumption nodes, the buffer nodes have a small capacity and are implemented to minimize the operation of the radio interface. Therefore, in case of upstream, if data is transmitted quickly and data is not transmitted, data loss may occur due to overflow of a small buffer in the node of intermediate router during traffic congestion.

On the other hand, the following four methods have been proposed as a study on the multi-channel utilization method.

Dedicated Control Channel (2 Radios)

Common hopping sequence

Split Phase

Parallel Rendezvous

These methods have been proposed to obtain high speed broadband in an IEEE 802.11 wireless LAN based environment and cannot be applied to a wireless sensor network due to the following differences.

In a wireless sensor network, it is mainstream to have one radio interface for low power consumption, and the traffic generated is very low and operates at a low duty cycle. In other words, RF (OFF) is turned off for most of the time and inactive sleep, and then communicates with each other during the active time by waking up at an appointed time. It operates as a beacon-type power consumption reduction type.

In addition, the wireless sensor network may cause a congestion point because traffic is aggregated toward the gateway due to traffic characteristics, and a traffic processing method requiring emergency transmission is required when passing through multiple hops.

In view of this, there is a demand for a method that can satisfy the requirements of a wireless sensor network operating at low power while operating in a multi-channel to improve network transmission performance and prevent data loss.

The present invention has been proposed to meet the above demands, and when a wireless sensor network such as Zigbee is provided with one radio interface, changing the channel so that mutual interference does not occur and transmitting data through multiple channels To provide a multi-channel operation method in a wireless sensor network.

Other objects and advantages of the present invention can be understood by the following description, and will be more clearly understood by the embodiments of the present invention. It will also be readily appreciated that the objects and advantages of the present invention can be realized by the means and combinations thereof indicated in the claims.

According to an aspect of the present invention, there is provided a method of operating a multi-channel in a wireless sensor network, the method comprising: setting a coordinator for each PAN (Personal Area Network) using the same gateway by calculating parallelism; A channel information management step of managing channel information of each PAN; Generating a beacon frame including superframe schedule information of a main channel and another channel and transmitting the beacon frame to each node of the corresponding PAN; And a data receiving step of receiving data using superframe schedule information of the other channel in an inactive period of the main channel.

The foregoing problems, features, and advantages will become more apparent from the following detailed description of the invention in connection with the accompanying drawings, and as a result, those skilled in the art to which the present invention pertains the technical idea of the present invention. It will be easy to do. In addition, in describing the present invention, when it is determined that the detailed description of the known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

According to the present invention, when one radio interface is provided in a wireless sensor network such as Zigbee, the channel is changed so that mutual interference does not occur, and data is transmitted through multiple channels. It is effective to operate.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is an exemplary diagram of a P2P cluster tree structure used in the present invention.

In general, Zigbee is standardized to support 16 channels in the 2.45 GHz band and 10 channels in the 915 MHz band. In the construction of a personal area network (PAN), when a coordinator selects one channel and periodically sends out a beacon through the channel, devices in the coverage area that detects the transmitted beacon are joined. Join to configure the PAN.

Such a PAN may be extended to a peer-to-peer cluster tree structure as shown in FIG. 2. That is, there may be a plurality of PANs having different channels in overlapping propagation regions.

Here, all nodes have a single radio interface, PNC (FFD) 210 is the coordinator of the highest PAN, C (FFD) is the coordinator of the lower PAN, D (FFD or RFD) means a device. .

In addition, the connection line in each PAN (22, 23, 24) means different channels, and constitutes a cluster tree for each channel.

In addition, the PNC 210 operates while changing from the '22' channel to the '23' channel and the '24' channel according to the time zone for the multi-channel operation. A detailed operation and operation method will be described later with reference to FIG. 4.

3 is a structural diagram of an embodiment of a super frame and a beacon frame according to the present invention.

As shown in FIG. 3, the super frame according to the present invention, sleeps or prepares in a state in which a beacon period and an active period in which nodes can transmit and receive and an active period are minimized. (Standby) includes an inactive period (Inactive Period).

In this case, the activation section includes a contention free period (CFP) section used for transporting real time traffic (RTT) requiring guaranteed services and a non-real time traffic (NTT) generally requiring best services. It is divided into CAP (Contention Access Period) sections used to transport non-real time traffic.

In addition, the beacon frame is generated and transmitted by the PNC 210 or the coordinator, and in the payload field that can be defined and used by the user, the superframe schedule information 303 of the current channel, Contains superframe schedule information 304.

Therefore, when traffic is congested on the current channel, data may be transmitted using superframe schedule information of another channel.

Here, the superframe schedule information 303 of the current channel includes channel information (CH {mod-N (k)}), a beacon interval (BI), and a stop time. The superframe schedule information 304 includes channel information CH {mod-N (k + 1)}, a beacon interval (BI), a start time, and a stop time. .

At this time, the number of superframe schedule information of another channel corresponds to the number of beacon frames recognized through the scan.

In addition, the beacon frame includes a depth field 301 indicating how many hops from the root the coordinator is sending the beacon and a number of associated numbers indicating how many devices are currently participating. Device) field 302.

Accordingly, the devices FFD and RFD may easily select a parent node to connect to after recognizing the coordinator transmitting the beacon frame through a scan.

4 is a diagram illustrating an embodiment of a multi-channel operating method using a super frame according to the present invention.

As shown in FIG. 4, the multichannel superframe according to the present invention includes a depth field, a NOAD, superframe schedule information of a main channel, superframe schedule information of another channel, and superframe schedule information of another channel (401). Beacon frame, data field (D: Data), and response field (A: ACK).

Here, 'SD' means a super frame period.

First, the PNC 210 performs channel-by-channel configuration in a beacon frame, that is, channel 1-> channel 2-> channel 3-> channel 1. Repeat in order. At this time, each channel constitutes a different PAN.

Subsequently, the PNC 210 receives a superframe during an activation period through the main channel CH1, and when an emergency data transmission occurs in an inactive period of the main channel, the superframe period of the main channel through another channel CH2. The emergency data may be received using the superframe 401 of another channel after the time of adding the channel switch switching time to the SD.

In this case, the superframe schedule information of each channel is managed through a channel descriptor (CH descriptor) during the scan procedure. That is, it manages channel information of PANs using the same gateway (the same first PAN coordinator ID). This manages the start time and end time of other channels with relative time information based on the schedule of the home channel.

For example, assume that three cluster trees (first tree, second tree, and third tree) using different channels are configured around the PNC 210. The superframe schedule information of each cluster tree will be different. At this time, each tree is adjacent.

It is the current deactivation interval after transmitting data according to the superframe scheduler based on the second tree. When urgent data needs to be transmitted, the superframe information of other channels received together, that is, the first tree or the first channel, is not waited until the next activation interval. 2 Using the superframe schedule information used in the tree, the emergency data is transmitted in accordance with the activation interval.

In this way, data can be transmitted quickly and efficiently without waiting for the next activation section. At this time, since the node transmitting data through the other channel is not a component of the tree using the other channel as the main channel, mutual interference does not occur.

Hereinafter, various multi-channel operation schemes will be described in more detail with reference to FIGS. 1 and 2 and 5 to 8.

The gateway 12 and all the devices are equipped with one radio. When the number of channels to be operated is N, k = {k | 1, 2, ..., N}. In this case, N = 3 when three channels (first channel, second channel, and third channel) are operated.

First, the gateway 12 transmits a beacon to the first channel and serves the activation period 500 for the nodes 11C and 11D participating in the PAN on the first channel in its area.

Thereafter, the first (1st) cluster nodes 11C and 11D of the first channel go to sleep, and the gateway 12 switches RF to the second channel (CH switchover time) and then goes to the second channel. The controller transmits the control and serves the activation period 501 for the nodes 21C and 21D participating in the PAN in its own channel.

At this time, the second cluster nodes 12C and 12D of the first channel are simultaneously activated in the activation section 501 of the second channel according to their schedule through the beacon of the cluster header.

Thereafter, while the first cluster nodes 21C and 21D of the second channel and the second cluster nodes 12C and 12D of the first channel are in the sleep state, the gateway 12 switches the RF to the third channel. After the CH switchover time, the beacon is transmitted to the third channel and served during the activation period 502 for the nodes 31C and 31D participating in the PAN on the third channel in their own area.

At this time, the second cluster nodes 22C and 22D of the second channel are simultaneously activated in the activation section 502 of the third channel according to their schedule through the beacon of the cluster header.

Thereafter, the first cluster nodes 31C, 31D of the third channel and the second cluster nodes 22C, 22D of the second channel go to sleep and are inactive during the beacon interval 503 of the first channel. .

Thereafter, when the first cluster nodes 11C and 11D of the first channel are activated, the second cluster nodes 32C and 32D of the third channel and the third cluster node 23D of the second channel are simultaneously activated.

Thereafter, when the first cluster nodes 21C and 21D of the second channel are activated, the second cluster nodes 12C and 12D of the first channel and the third cluster node 33D of the third channel are simultaneously activated.

Thereafter, when the first cluster nodes 31C and 31D of the third channel are activated, the second nodes 22C and 22D of the second channel and the third node 13D of the first channel are simultaneously activated.

As a result, the gateway 12 sequentially services the first channel, the second channel, and the third channel, and then repeatedly provides the first channel and the second channel. Here, starting from the second cluster, the scheduling relationship between the input beacon and the output beacon is preferably in accordance with the IEEE 802.15.4-2006 version.

This multi-channel operation is a case where the beacon (grand parent beacon) can be received from the PNC 210 from the second node (12C, 22C, 32C) of each channel, for example, the second of the first channel The node 12C should schedule an outgoing beacon taking into account the incoming beacon schedule from the first node 11C of the first channel, the beacon from the PNC 210 (grand parent beacon). ) If there is a reception possible position, there is a disadvantage that the activation interval should be determined in consideration of the schedules in the two incoming beacons. In addition, the time required is also assigned to the disadvantages.

Therefore, when designating a coordinator, it is preferable to designate a device (FFD) at a position where it is impossible to receive a grand parent beacon from the PNC 210 to the coordinator to increase the concurrency.

Hereinafter, the parallelism which means the number of channels that can be activated in the same time interval on the PAN will be described in more detail.

First, when operating three channels, it is usually assumed to be 'beacon interval> superframe period'.

4 × (Superframe Period + Channel Change Duration)> Beacon Interval> 3 × Start Time> 3 × (Superframe Period + Channel Change Time)

When the coordinator is located in an area where two beacon reception is possible under the condition of [Equation 1], in order to operate in parallel 3, as shown in FIG. 5 during scheduling, the parent node “11C” and the grandparent node are shown. It should be activated by avoiding the activation interval of the PNC 210.

However, in a case where the beacon reception from the PNC 210 is impossible, scheduling as shown in FIG. 6 is also possible.

That is, the gateway 12 transmits a beacon to the first channel and serves the activation period 600 for the nodes 11C and 11D participating in the PAN on the first channel in its area.

Thereafter, the first (1st) cluster nodes 11C and 11D of the first channel go to sleep, and the gateway 12 switches RF to the second channel (CH switchover time) and then goes to the second channel. The controller transmits the control and serves the activation period 601 for the nodes 21C and 21D participating in the PAN in the second channel in its area.

At this time, the second cluster nodes 12C and 12D of the first channel are simultaneously activated in the activation section 601 of the second channel according to their schedule through the beacon of the cluster header.

Thereafter, while the first cluster nodes 21C and 21D of the second channel and the second cluster nodes 12C and 12D of the first channel are in the sleep state, the gateway 12 switches the RF to the third channel. After the CH switchover time, the beacon is transmitted to the third channel and served during the activation period 602 for the nodes 31C and 31D participating in the PAN on the third channel in their own area.

At this time, the second cluster nodes 22C and 22D of the second channel are simultaneously activated in the activation section 602 of the third channel according to their schedule through the beacon of the cluster header.

Thereafter, the first cluster nodes 31C, 31D of the third channel and the second cluster nodes 22C, 22D of the second channel go to sleep and are inactive during the beacon interval 503 of the first channel. .

Thereafter, when the first cluster nodes 11C and 11D of the first channel are activated, the second cluster nodes 32C and 32D of the third channel and the third cluster node 13D of the first channel are simultaneously activated.

Thereafter, when the first cluster nodes 21C and 21D of the second channel are activated, the second cluster nodes 12C and 12D of the first channel and the third cluster node 23D of the second channel are simultaneously activated.

Thereafter, when the first cluster nodes 31C and 31D of the third channel are activated, the second nodes 22C and 22D of the second channel and the third node 33D of the third channel are simultaneously activated.

On the other hand, if the coordinator is located in a region capable of receiving two beacons under the condition as shown in [Equation 2] below, a channel for the third cluster nodes cannot be allocated. That is, as shown in FIG.

3 × start time> 3 × (superframe period + channel change time)> beacon interval> 2 × start time> 2 × (superframe period + channel change time)

On the other hand, in the region that can be received two beacons under the conditions as shown in [Equation 3] as shown in FIG.

That is, there is concurrency within the processing time range of all observed incoming and outgoing beacons.

At this time, the section marked with "*" should not be allocated to the area where beacon reception of the highest PAN is possible.

Beacon Interval> 4 × Start Time> 4 × (Superframe Period + Channel Change Duration)

As a result, under the [Equation 1] or [Equation 3], the multi-channel operation can be performed under the parallelity of 3 or less, while under the [Equation 2] condition, the multi-channel operation is possible with the parallelism of 2.

9 is an exemplary view illustrating a multi-channel operating method in a wireless sensor network according to the present invention.

As shown in FIG. 9, each cluster transmits data in a 'CSMA / CA' manner during its home channel activation period. However, if the data cannot be transmitted during the activation period or urgently needed, it wakes up from the activation period of another channel and transmits the data, thereby reducing the delay time and preventing data loss.

Let's look at this in more detail.

First, referring to the multi-hop transmission delay time 900 during normal transmission, the third cluster node '23D' of the second channel transmits data to the coordinator '22C' in its activation period (901).

Thereafter, '22C' as the second node of the second channel transmits data to the coordinator '21C' in its activation period (902).

Then, '21C' as the first node of the second channel transmits data to the PNC through the gateway in its activation period (903).

Next, referring to the multi-hop transmission delay time 910 during the data congestion, the third cluster node '23D' of the second channel transmits data to the coordinator '22C' in its activation period (901).

Then, when the second node of the second channel '22C' does not transmit the data in its first activation interval, and transmits the data to the coordinator '21' in the next activation interval (912).

Thereafter, '21C' as the first node of the second channel transmits data to the PNC through the gateway in its activation period (913).

Next, looking at the multi-hop transmission delay time 920 when using another channel in the multi-channel method according to the present invention, the third cluster node '23D' of the second channel is the coordinator '22C' in its activation period In step 901, data is transmitted.

Subsequently, when '22C' as the second node of the second channel fails to transmit data in its first activation interval, the third channel is used as another channel and the data is transferred to '31C' as the first node of the third channel. Transmit (922).

Thereafter, 31C, the first node of the third channel, transmits data to the PNC in its activation period (923).

Through this, it can be seen that the multi-hop transmission delay time 920 is shorter when using other channels in the multi-channel method than the multi-hop transmission delay time 910 when data is congested.

As described above, the method of the present invention may be implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Since this process can be easily carried out by those skilled in the art will not be described in detail any more.

The present invention described above is capable of various substitutions, modifications, and changes without departing from the technical spirit of the present invention for those skilled in the art to which the present invention pertains. It is not limited by the drawings.

1 is an exemplary view of a typical wireless sensor network,

2 is an exemplary diagram of a P2P cluster tree structure used in the present invention;

3 is a structural diagram of an embodiment of a super frame and a beacon frame according to the present invention;

4 is a diagram illustrating an embodiment of a multi-channel operating method using a superframe according to the present invention;

5 is a diagram illustrating an embodiment of a multichannel operating process using a superframe according to the present invention;

6 is a diagram illustrating another embodiment of a multi-channel operating process using a superframe according to the present invention;

7 is a view illustrating another embodiment of a multi-channel operating process using a superframe according to the present invention;

8 is a view illustrating another embodiment of a multichannel operating process using a superframe according to the present invention;

9 is an exemplary view illustrating a multi-channel operating method in a wireless sensor network according to the present invention.

* Explanation of symbols for the main parts of the drawings

12: gateway 13: server

22: first channel 23: second channel

24: third channel

Claims (9)

In the multi-channel operating method in the wireless sensor network, Calculating a parallelism and setting a coordinator for each personal area network (PAN) using the same gateway; A channel information management step of managing channel information of each PAN; Generating a beacon frame including superframe schedule information of a main channel and another channel and transmitting the beacon frame to each node of the corresponding PAN; And Data receiving step of receiving data by using the superframe schedule information of the other channel in the inactive period of the main channel Multi-channel operating method in a wireless sensor network comprising a. The method of claim 1, The channel information management step, A method of operating a multi-channel in a wireless sensor network, wherein the start time and end time of another channel are managed as relative time information based on a schedule of a main channel. The method according to claim 1 or 2, The data receiving step, If superframe is received during the active period through the main channel and emergency data transmission occurs in the inactive period of the main channel, the superframe of the other channel is added after the time of adding the channel switch switching time to the superframe period of the main channel through the other channel. Multi-channel operating method in a wireless sensor network, characterized in that for receiving emergency data using a frame. The method of claim 3, wherein The beacon frame, Depth field indicating how many hops the coordinator is sending the beacon from the root, Number of Associated Device (NOAD) field indicating how many devices are currently participating, and main channel (currently And superframe schedule information of another channel, and superframe schedule information of another channel. The method of claim 4, wherein Superframe schedule information of the main channel, A method for operating a multi-channel in a wireless sensor network, comprising channel information, beacon interval (BI), and stop time. The method of claim 4, wherein Superframe schedule information of the other channel, A method of operating a multi-channel in a wireless sensor network, comprising: channel information, beacon interval (BI), start time, stop time. The method of claim 3, wherein The parallelism is The method of operating a multi-channel in a wireless sensor network, characterized in that for operating if 3 satisfies [Equation A] below. Equation A 4 × (Superframe Period + Channel Change Duration)> Beacon Interval> 3 × Start Time> 3 × (Superframe Period + Channel Change Time) The method of claim 3, wherein The parallelism is The method of operating a multi-channel in a wireless sensor network, characterized in that for operating if 2 satisfies [Equation B] below. Equation B 3 × start time> 3 × (superframe period + channel change time)> beacon interval> 2 × start time> 2 × (superframe period + channel change time) The method of claim 3, wherein The parallelism is The method of operating a multi-channel in a wireless sensor network, characterized in that for operating if 3 satisfies [Equation C] below. Equation C Beacon Interval> 4 × Start Time> 4 × (Superframe Period + Channel Change Duration)

Images