KR20120130110A - Channel selection and communication method for considering interference of wifi in multi cannel wireless sensor network - Google Patents

Abstract

PURPOSE: A channel selection method and communication method are provided to convert a communication channel by sensing wireless interference from a Zigbee sensor network. CONSTITUTION: An interference sensing process is repeated(205). When interference is sensed, a channel hopping method is executed by considering a Wi-Fi channel in a current channel. It is determined whether a channel is available(211). When the available channel is not searched, a hopping sequence interval is controlled(215). It is searched whether the channel is available. When the available channel is searched, the available channel is used for communication. [Reference numerals] (205) Interference sensed?; (AA,CC,EE,KK,HH,II,OO,PP) No; (BB,DD,FF,GG,LL,JJ,MM,NN) Yes

Description

CHANNEL SELECTION AND COMMUNICATION METHOD FOR CONSIDERING INTERFERENCE OF WIFI IN MULTI CANNEL WIRELESS SENSOR NETWORK}

Embodiments of the present invention are an interference avoidance method through channel switching after detecting interference in a ZigBee sensor network communication, more specifically, using the same band using 16 multiple channels in a 2.4 GHz band. Wi-Fi interference in a multi-channel wireless sensor network that detects interference when homogeneous or heterogeneous radio interference occurs and enables reliable communication without degrading ZigBee sensor network communication through channel switching in multiple channels It relates to a channel selection and communication method in consideration of.

ZigBee Sensor Networks are designed to distribute hundreds or thousands of sensor nodes over a wide area to detect surrounding information, generate data about the detected surrounding information, and send it to remote information collection devices, primarily for military and natural environments. Used for measurement and emergency monitoring. The sensor nodes not only generate data about the detected surrounding information but also serve as a router that delivers data received from other sensor nodes to the next sensor node. However, sensor nodes have a problem in that communication is impossible when interference occurs with a radio signal due to internal and external factors.

The transmission range of Wi-Fi is about 100m, the transmission range of Zigbee is about 10m, and the transmission power of Wi-Fi is larger than that of Zigbee. Therefore, Zigbee-based sensor network systems are vulnerable to interference from Wi-Fi. In addition, the Wi-Fi system is used in many portable devices such as portable information terminals (PDAs) and portable computers, and may exist anywhere at any time, and because of its mobility, Zigbee and Wi-Fi are also likely to operate in the same area. In addition, due to the explosive popularity of smartphones, the environment in which many Wi-Fi access points (WAP access points) are unplanned around the world is also having an important influence on the coexistence problem caused by the interference of Zigbee and Wi-Fi. .

Due to the characteristics and recent trends of these wireless systems, it can be seen that the interference between Zigbee and Wi-Fi is more serious than the interference between homogeneous Zigbee. Therefore, the problem of Zigbee and Wi-Fi interference should be considered first. The problem of homogeneous ZigBee needs to be presented as a side solution in the channel switching process to avoid the interference with Wi-Fi.

To date, interference avoidance technologies have been developed in various short-range wireless communications. Among them, a method using a carrier sense multiple access-request to send-data (CSMA-RTS-DATA) protocol, a method using a channel switching table, and a CCBM (Interference avoidance method through channel switching of a random method such as a method using a pseudo random sequence generator through a Channel Change Broadcast Message).

Among the channel switching methods based on the CSMA-RTS-DATA protocol, real-time deterioration due to delay caused by CCA process, random back-off process, and the need to continuously change the channel until the receiving node receives the correct RTS. Problems such as unnecessary overhead and reduced efficiency of multi-channel use occur. In addition, ZigBee does not support RTS / CTS, so it is difficult to implement.

In the case of using the channel switching table, since the channel is switched after the interference is detected based on the list of available channel information stored in the channel switching table, the state of the channel cannot be recognized until the interference is detected. If the state of the channel to be switched cannot be guaranteed, and the channel switching table is periodically updated to guarantee the state of the channel, a trade off problem may occur according to the selection of the corresponding period.

In addition, the channel switching algorithm of the random method such as the virtual random sequence generator is caused by a random channel selection method to prevent interference between ZigBee internal channels, and thus cannot guarantee the state of the next channel at all. It is not a way of selecting channels that are likely to be in good condition. In this process, when the new channel selection is the worst, there is a possibility that the result is worse than searching and switching all channels from the beginning.

Therefore, there is a need for a communication method that can provide a channel selection and switching process in a ZigBee sensor network that can provide a fast and no overhead overhead to a guaranteed channel after interference of various factors is detected.

An embodiment of the present invention provides a channel selection and communication method in consideration of the interference of the Wi-Fi in a multi-channel wireless sensor network to switch to a channel with a guaranteed communication state after wireless interference is detected in the Zigbee sensor network.

In addition, an embodiment of the present invention provides a fast channel selection and switching communication method in the interference of the Wi-Fi, which can cause a serious problem of the Zigbee sensor network communication among various interference factors, the Wi-Fi is unplanned worldwide The present invention provides a channel selection and communication method considering the interference of Wi-Fi in a multi-channel wireless sensor network that enables reliable communication of a Zigbee sensor network in an environment.

In addition, an embodiment of the present invention provides a fast and robust communication processing of Wi-Fi in a multi-channel wireless sensor network by enabling channel switching without additional overhead in the channel switching process between nodes requiring communication after interference is detected. A channel selection and communication method considering interference is provided.

As a technical method for achieving the above embodiment, the channel selection and communication method in consideration of the interference of the Wi-Fi in a multi-channel wireless sensor network, comprising the steps of: setting an initial channel value and repeating the interference detection process; Determining whether the channel is available by performing hopping of the selected channel in consideration of the Wi-Fi channel in the current channel when the interference is detected; If no available channel is found as a result of the determination, searching for channel availability by adjusting a hopping sequence interval; And communicating through a usable channel when a usable channel is found as a result of the determination or the search.

According to an embodiment of the present invention, when the initial network is operated in the Zigbee sensor network, the network system detects the interference by selecting an appropriate mode among the channel adaptation method and the channel hopping method in consideration of the interference occurrence factor and the internal and external environment. The network can be operated by selecting and switching a channel having good communication after the interference.

In addition, according to an embodiment of the present invention, not only can effectively avoid the interference of the Wi-Fi, but also through the fast channel selection process for communication interference other than homogeneous and Wi-Fi to reduce the overhead by switching channels in the Zigbee sensor network Benefit from the use of effective multichannels.

In addition, according to an embodiment of the present invention, the ZigBee sensor is used to determine whether to use the contention access period (CAP) reduction mode according to the request of the Guaranteed Time Slot (GTS) slot of the node, and effectively use 16 multiple channels in an interference environment. By operating the network, it is effective for reliable Zigbee sensor network communication.

1 is a view showing a channel in the 2.4GHz band of Wi-Fi and Zigbee for explaining the present invention.
2 is a diagram illustrating interference detection, channel selection and channel switching procedures after interference detection according to an embodiment of the present invention.
3 is a diagram illustrating an embodiment of two MAC (Media Access Control) techniques to be applied by applying an embodiment of the present invention.

Hereinafter, embodiments according to the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to or limited by the embodiments. Like reference symbols in the drawings denote like elements.

In case of interference from Wi-Fi in a Zigbee sensor network, a channel switching technique in multiple channels to avoid the interference is described.

In case of wireless interference of Wi-Fi or Zigbee-like interference in Zigbee sensor network using 2.4GHz band, 16 multi-channels are used to provide a method of switching to another channel capable of operating a normal network without being affected by interference.

In addition, a channel searching function capable of guaranteeing the channel status quickly and at the time of channel switching and a channel switching method which is faster and more reliable by preventing unnecessary additional processing in channel switching after searching are provided.

In addition, the channel search and channel switching method uses a channel adaptation method for transmitting and receiving a frame by changing to a new channel when the channel state becomes worse than a predetermined reception condition for channel diversity when interference occurs, and using a reserved frequency channel sequence for communication. And the receiving node uses the channel hopping method that sends and receives frames by moving the channel.

1 shows channel information of Wi-Fi and Zigbee using 2.4GHz band for explaining the present invention, respectively. The channel information is shown by comparing the number of each channel, the bandwidth of the channel, the interval between the channels and the transmission power.

As can be seen from the information shown in FIG. 1 and the above-mentioned studies, more than 92% of Zigbee frames are lost due to the interference of Wi-Fi, and thus, the interference of Wi-Fi in the unlicensed Industrial Scientific Medical band (ISM) band. It can be seen that the problem solving of coexistence caused by this is the most urgent and important.

2 is a detailed diagram illustrating a procedure for channel selection and channel switching after sensing interference according to an embodiment of the present invention.

Referring to FIG. 2, first of all, two communication nodes have information about a current channel to start communication in step 201. Initially, the default channel is set for each coordinator by the ID of the Zigbee coordinator so that each cluster does not overlap channels as much as possible.

In step 205, the two communication nodes determine whether there is interference by using a threshold value of a received signal strength indicator (RSSI) in the interference detection scheme to determine whether the state for the current channel is available. Each coordinator transmits a beacon using the selected channel, and determines whether the channel is available using the threshold value of the RSSI value that can be confirmed by the request message or test frame of the node receiving the beacon, and then starts slow hopping.

If the channel selected by the ID of the initial coordinator is unavailable, an attempt is made to change to a channel not used by neighboring clusters. If the request message is not transmitted because no node wants to allocate the GTS slot after receiving the beacon, the coordinator may determine that the channel is not available due to interference. Send a test frame to determine the RSSI value.

If the coordinator cannot determine the RSSI value because the request message or the test frame is not received, the coordinator determines that the node is included in the region of interference, and the node determines whether or not the response message does not come accordingly and switches the promised channel. The algorithm switches channels.

By the above method, the initial channel value is set and the interference detection process is repeated. In step 203, the initial hopping sequence value is set to 4. The reason is that when interference occurs in one of 16 channels of ZigBee 11 to 26, as shown in FIG. 1, hopping of the current channel of ZigBee by ± 4 channels to move out of the Wi-Fi interference range. This is because it becomes possible.

In step 207, after the +4 channel hopping on the current channel, the count (cnt) value is increased by 1 in step 209, and the coordinator for the new channel in step 211 to determine the strength of the surrounding signals at the receiver. The availability of the channel is determined by comparing with the threshold value of Energy Detection (ED). If the coordinator checks the ED value, it determines that the channel is unavailable if it is larger than the threshold of ED, and proceeds with the channel selection and switching process. To monitor the detection of interference.

Since the interference of several channels of the Wi-Fi may be performed at the same time, interference may not be avoided even with one hopping of +4 channels. In this case, channel hopping by +4 is performed several more times. The number of channel hopping times for the +4 interval is limited by the n value set in step 213. If no available channel is found in the repetition to the first interference channel during the channel hopping process for the +4 interval, the repetition is limited. .

This is because the proposed channel switching method considers the interference of Wi-Fi first, but also solves the problem of radio interference by Zigbee homogeneous communication or non-Wi-Fi communication. The frequency of non-Wi-Fi or ZigBee homogeneous interferences will be relatively low compared to Wi-Fi interference, but if they do occur, iterations will be repeated until 16 channels are found that have available a +4 interval. Proceeding, the search is performed only for the same four channels among the 16 channels, which causes inefficient use of multiple channels, thereby limiting the number of hopping by n. If n is 4 times, one rotation is made considering the total number of channels of ZigBee 16.

If the available channel is not found until the +4 interval hopping process is limited by the n value in step 213, the hopping sequence interval is adjusted to 2, which is 1/2 of 4, in step 215. In addition, the count (cnt) value that controls the number of repetitions is set to reset to the initial state of zero. In the case of hopping at intervals of +4, the maximum value of the count (cnt) was 4 set to n in step 203. However, when the hopping sequence interval is adjusted to 1/2 at +2, n in step 217 is performed. The value of is changed to 8, which is twice, and 2, the current hopping sequence value, is stored in the value of m. The number of channel hopping will increase as the hopping interval decreases, while the number of hoppings measured by the count (cnt) doubles, but the actual number of hoppings is only four, as in the case of a +4 hopping sequence. . The reason for this is that in the case of hopping at intervals of +2, the channel determined to be unavailable in the process of hopping at intervals of +4 overlaps once every two times. Since it is unnecessary to determine the overlapping channel, in step 225, m is the interval of the hopping sequence stored in step 217 without going through step 211 of determining whether the channel is available using the count (cnt) value. In step 219, the value is simply increased in the current channel and the value of the count (cnt) is increased.

The channel selection and switching process will be described using an example of an actual channel. In case of using 2.4GHz in Zigbee, 16 multi-channels from 11 to 26 are used, assuming that the initial channel is set to 11 by the coordinator ID. If an interference is detected, it is determined that the interference of Wi-Fi is preferred, and the count (cnt) is increased within a limited number of times until it finds a channel that can use hopping by +4 interval. Assuming that no available channel is found after four hopping steps limited by the n value, it returns to the first channel 11 again. In case of No. 15, No. 19, and No. 23, which are already +4 intervals including No. 11 channel, it was determined by the proposed algorithm.

Therefore, it is determined whether or not the availability of the channel with an interval of 11 to +2 or repeatedly skips the process. The channels at intervals 11 through 2 are as follows. Nos. 13, 15, 17, 19, 21, 23, and 25 correspond to the channels at intervals of 2, and 11, 15, and 19 have already been determined in the hopping process by +4. The use of channels 13, 17, 21, and 25 except for 23 is determined. Even though the process of determining whether the channel can be used or ignored for two channels is repeated until the first channel is returned to the first channel 11, the worst case may not be found. According to the example, if you check the status of the channel, it is determined that the channels that can be checked so far are not available as (X) in the status line of Table 1, and the status line for the channel that has not been checked yet is (? It is marked with).

In step 215, the new hopping sequence value and the initialized count value (cnt) are performed again from the 11th channel, which is the current channel. In step 217, the maximum value of (cnt) becomes 16, n is twice the number of 8, thereby controlling the count value (cnt), and a new hopping sequence value of 1 is stored in m. Although the value of the count (cnt) that counts the number of hoppings is increased to 16 in the same manner as the method of the hopping sequence value of 2, the actual number of hoppings is only 8 times. As shown in Table 1, when hopping by 1 interval, the process of determining whether the channel is used is duplicated twice. The channel that has been determined in the hopping process of the previous +4 interval or the +2 interval is ignored in step 225, and the channel is determined only for the remaining channels. That is, since it was determined that the initial channel 11 and the channel that had been determined to be available in the previous hopping process were not available in the previous process, the ED (Energy Detection) process of the coordinator was similarly performed. Instead of going through it repeatedly, it ignores and finds another channel to match the current hopping sequence.

In case of channel selection and channel switching with this proposed method, even if it is not the interference of Wi-Fi, channel switching by interference factor can be successfully performed during hopping repetition process by +4 interval or hopping repetition process by +2 interval. will be. If no new channel is found during the chance of channel selection in the hopping iteration by +4 interval and the hopping iteration by +2 interval, the remaining ones that have not been finally determined by using the +1 hopping sequence All channels will be judged.

It is possible to use an algorithm that repeats as much as +4 intervals after the first detection of interference, if it fails to switch channels, it repeats as much as +2 intervals and +1 intervals for all remaining channels after that. Another strong advantage of the case is that even if a special interference occurs where all 16 channels of ZigBee cannot be used, if a part of the interference is out of range, the channel can be quickly selected and switched to enable normal communication of the ZigBee sensor network. Can be.

Recently, ZigBee's MAC sublayer standard, the IEEE 802.15.4 standard, is modifying the MAC sublayer through task group E. In the IEEE 802.15.4 standard, the MAC sublayer uses a channel adaptation method for transmitting and receiving a frame by changing to a new channel when the channel condition becomes worse than a predetermined reception condition for using multiple channels, and using a reserved frequency channel sequence for communication. The receiving node proposes a channel hopping method for exchanging frames by moving a channel. Alternatively, the receiving node can operate a network.

The present invention assumes a ZigBee capable of using multiple channels, and the network manager can apply the proposed channel selection and channel switching method according to the internal and external interference environment when the network is operated for the first time. In addition, the channel selection and channel switching methods proposed in the two MAC technologies, which are channel adaptation methods that can be used while changing channels according to the state of the channel being used, and channel hopping methods that are repeatedly used in a predetermined pattern for the available channels. It can be used to operate Zigbee sensor network more effectively by applying

3A and 3B illustrate an embodiment of two MAC technologies to be used by applying the proposed algorithm. 3A is an example of a channel adaptation method used by changing a channel appropriately according to a channel state among two MAC technologies. When interference occurs in the process of using channel 1, the channel is changed to channel 5 by the proposed algorithm. In addition, when interference to channel 5 is additionally shown, an embodiment of changing to channel 9 is shown.

FIG. 3B is an example of a channel hopping method that repeatedly uses a predetermined pattern for an available channel. FIG. 3B illustrates an example of a channel hopping method in which a usable channel from channel 1 to channel 6 is repeatedly used. When the use of channel 6 becomes impossible, an embodiment in which channels 5 and 6 are changed to channels 9 and 10 and used repeatedly with a new pattern is shown.

Further, embodiments of the present invention include a computer readable medium having program instructions for performing various computer implemented operations. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks, such as floppy disks. Magneto-optical media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like.

In the present invention as described above has been described by the specific embodiments, such as specific components and limited embodiments and drawings, but this is provided to help a more general understanding of the present invention, the present invention is not limited to the above embodiments. For those skilled in the art, various modifications and variations are possible from these descriptions. It is therefore to be understood that within the scope of the appended claims, the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. .

Claims (1)

Setting an initial channel value and repeating the interference detection process;
Determining whether the channel is available by performing hopping of the selected channel in consideration of the Wi-Fi channel in the current channel when the interference is detected;
If no available channel is found as a result of the determination, searching for channel availability by adjusting a hopping sequence interval; And
Communicating through a usable channel if a usable channel is found as a result of the determination or the search;
Channel selection and communication method considering the interference of the Wi-Fi in a multi-channel wireless sensor network comprising a.

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