A MAC layer protocol for wireless sensor networks

Abstract

The present invention provides a wireless sensor network MAC layer protocol, and proposes an improved protocol based on the IEEE 802.15.4 standard, which is oriented to the wireless sensor network of the Internet of Things and preferentially processes node information with a relatively high priority. In the present invention, the PAN coordinator regularly broadcasts beacon information, which includes a superframe structure, and synchronizes each sensor node. The present invention double guarantees the information transmission of the node, greatly increases the probability of successful transmission, reduces the transmission delay of high-priority nodes, and is conducive to the system receiving important information in the first time and taking corresponding measures. At the same time, the superframe structure used contains an inactive area, and all nodes can sleep periodically according to the information in the beacon, which can save the energy consumption of all nodes.

Description

Technical Field

[0001] The invention relates to the field of wireless sensor network networking protocols, in particular to a MAC layer protocol, specifically to a high-energy-efficiency wireless sensor network MAC layer protocol based on information priority. Background Art

[0002] The Internet of Things has been widely used in transportation, logistics, security, electricity, home and other fields. Sensor technology is the key technology in the application of the Internet of Things. Sensor nodes collect various required information such as sound, light, heat, electricity, and location, and realize ubiquitous connection between objects and objects and people through various possible network access, so as to realize intelligent perception, identification and management of objects and processes. In sensor networks, power consumption is the main limiting factor of sensor nodes. Therefore, the low-power media access control (MAC) in the IEEE 802.15.4 standard developed by the Institute of Electrical and Electronics Engineers (IEEE) has been used to solve the problem of insufficient power. In the IEEE 802.15.4 standard, a central controller called the personal area network (PAN) coordinator supervises the construction, upgrade and monitoring of the entire network. The PAN coordinator broadcasts beacon information, which includes the structure of the superframe and synchronizes the sensor nodes within the transmission range. The superframe includes active and inactive parts, the former including the contention access period (CAP) and the contention-free period (CFP). During the entire inactive part, the device does not interact with the PAN coordinator and can move to low-power mode to save energy.

[0003] In the active cycle, the contention access period adopts the carrier sense multiple access protocol with collision avoidance function (CAMA / CA) access method, and the non-contention period adopts the guaranteed time slot (GTS) allocation method. All sensor nodes first compete for access to the channel through CSMA / CA. If the node fails to transmit successfully, it can apply for GTS from the PAN coordinator. If the coordinator agrees to the application, the node can ensure that it will successfully obtain GTS in the next superframe CFP.

[0004] In IoT applications, various sensor nodes monitor different information. Some sensors monitor more important information, while others monitor auxiliary information. If the system hopes that important information can be transmitted, the transmission of information needs to consider the priority issue. However, the IEEE 802.15.4 standard does not consider this issue and cannot guarantee the successful transmission of high-priority information. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a wireless sensor network MAC layer protocol. In order to ensure the successful transmission of high-priority information, reduce the energy consumption of sensor nodes, and optimize the life cycle of wireless sensor networks, the present invention proposes an improved protocol based on the IEEE 802.15.4 standard, which is oriented to the Internet of Things wireless sensor network and gives priority to processing node information with relatively high priority. In the present invention, the PAN coordinator regularly broadcasts beacon information, which includes a superframe structure (contention period (CAP), contention-free period (CFP) and inactive period), and synchronizes each sensor node.

[0006] The technical solution adopted by the present invention to solve the technical problem comprises the following steps:

[0007] Step 1: The sensor node listens to the beacon information sent by the PAN coordinator. The beacon information contains the active period and inactive period of the coordinator, which also contains the allocation of GTS. If some sensor nodes have GTS requests in the previous superframe, check whether the PAN coordinator has successfully allocated GTS in the beacon information. The beacon frames received by all sensors have the GTS allocation field. The sensor nodes that requested the non-contention period in the previous frame can compare and check whether the allocation is successful when receiving the beacon frame. If GTS is successfully allocated, it is necessary to maintain communication with the PAN coordinator in the CFP period. If GTS is not successfully allocated, it enters the contention period of the current superframe structure for contention transmission to determine whether to continue GTS application: If the sensor does not successfully allocate GTS in the current beacon frame, it first competes for transmission in the contention period in the superframe. If it successfully competes for the transmission time slot, it successfully transmits the information and does not re-apply for GTS; if it does not successfully get the time slot transmission time slot in the contention period, it continues to apply for GTS and repeats the above process until the information is successfully transmitted;

[0008] Step 2: All sensors within the range of the PAN coordinator enter the contention period within the active period. If there is data transmission, they compete for access through the time slot CSMA / CA. If some node information successfully competes for access to the channel during this period, the information is successfully transmitted. If a sensor fails to compete for the transmission time slot during the contention period, it cannot transmit information during the contention period, that is, the transmission is not successful.

[0009] Step 3: During the CSMA / CA competition process in the time slot, no retransmission is performed. If the channel is not successfully accessed after three consecutive backoffs, GTS is applied to the PAN coordinator. When requesting GTS from the PAN coordinator, as shown in Figure 3(b), different request bytes correspond to different priorities, and the two reserved bits in the request byte are modified. After receiving the GTS request, the PAN coordinator checks the priority of the request information and the current CFP time slot length. If the high priority can be met and there are remaining CFP time slots, GTS is allocated to ensure that the high-priority information is successfully allocated to GTS in the next superframe; the GTS in the current superframe is allocated to the node that successfully requested GTS in the previous superframe;

[0010] Step 4: All nodes enter an inactive period, and the sensor nodes do not exchange information with the PAN coordinator, that is, they can enter a sleep period to save energy consumption of sensor devices.

[0011] The beneficial effects of the present invention are reflected in two aspects. The first aspect is that for sensors with relatively important information, i.e., nodes with relatively high priority, if there is no successful transmission in CAP, GTS can be allocated preferentially in the superframe, and the competition for transmission can continue in the next superframe, and there is already allocated GTS. This doubly guarantees the information transmission of the node, and the probability of successful transmission is greatly increased. The second aspect is that the present invention divides nodes into different priorities, and the information of high-priority nodes is processed preferentially, which reduces the transmission delay of high-priority nodes, and is conducive to the system receiving important information in the first time and taking corresponding measures. The third aspect is that the nodes with relatively high priority in this system adopt a dual mechanism to ensure the timeliness of successful transmission of information. Compared with previous nodes, if there is a situation with relatively high traffic, important information may be constantly trying to be transmitted, which can save energy. At the same time, the superframe structure used contains an inactive area, and all nodes can sleep periodically according to the information in the beacon, which can save energy consumption of all nodes. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of a star network in the wireless communication network of the present invention.

[0013] Figure 2 It is a schematic diagram of the IEEE 802.15.4 superframe structure of the present invention.

[0014] FIG3(a) is a schematic diagram of the format of a GTS request command frame, and FIG3(b) is a schematic diagram of the priority setting in a GTS request command frame.

[0015] Figure 4 Schematic diagram of the allocation of the GTS field in the beacon. DETAILED DESCRIPTION

[0016] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0017] According to the protocol design method of the present invention, the design of node priority is considered on the basis of IEEE802.15.4 standard, and different types of sensor nodes are set to different levels of priority. When a node sends a GTS request to the PAN coordinator, the PAN coordinator preferentially allocates GTS to high-priority nodes.

[0018] Figure 1 This is an application scenario of the present invention, a star network includes a PAN coordinator and N (N≤255) sensor nodes. All sensor nodes can communicate directly with the PAN coordinator. Figure 2 This is a schematic diagram of the superframe format of the IEEE802.15.4 standard, which is divided into two parts: an active period and an inactive period. The active period includes a contention period (CAP) and a non-contention period (CFP), which contains a total of 16 time slots. Figure 3a The frame format of the sensor node applying for GTS request to the PAN coordinator, where bits 0-3 are the requested GTS length (the number of superframe time slots), bit 4 is the GTS direction, bit 5 is the type, bits 6 and 7 are reserved in the original standard, and the present invention uses two bits for priority allocation, such as Figure 3b As shown. 00 has the lowest priority and 11 has the highest priority. Figure 4 It is the information of the GTS field in the beacon information sent by the PAN coordinator to the node, which includes the node address, starting time slot and length of the GTS allocation.

[0019] The present invention provides a method for designing a MAC layer protocol for a wireless sensor network, and the specific implementation methods are as follows:

[0020] The specific steps include:

[0021] Step 1: The definition of contention period and non-contention period in the current superframe information is already specified in the beacon information sent by the PAN coordinator. The basis is that the sensor that had data to send last time did not successfully compete for the time slot in the contention period, so it applies to the PAN coordinator for a non-contention period time slot to obtain a non-contention period time slot in the next frame to transmit information. Of course, a maximum of 7 requests are allowed for the non-contention period time slot. If the number of nodes applying for information transmission is greater than 7, they will be allocated according to the priority of each application information.

[0022] When the sensor node listens to the beacon information sent by the PAN coordinator, it checks the beacon information to confirm whether the GTS is allocated successfully (some nodes apply for GTS requests from the PAN coordinator in the last superframe). Regardless of whether the GTS is allocated successfully, all nodes that have information to interact with the PAN coordinator compete for the channel through the time slot CSMA / CA protocol in the contention period to transmit information. If a node has not successfully transmitted information after backing off three times in the contention period, it can apply to the PAN coordinator for GTS allocation. After receiving the application, the PAN coordinator analyzes it and allocates GTS.

[0023] Step 2: After entering the non-contention period, the nodes successfully allocated to the GTS will perform guaranteed transmission. If some of the nodes successfully compete for the channel during the contention period and have successfully transmitted the information, then this guaranteed transmission will be by-passed.

[0024] Step 3: All nodes enter an inactive period, all nodes do not exchange information with the PAN coordinator, and enter a sleep period.

[0025] Step 4: The node that did not successfully transmit in step 1 can apply for GTS from the PAN coordinator. When requesting GTS from the PAN coordinator, Figure 3b As shown, the sensor nodes are divided into four levels, 11 has the highest priority and 00 has the lowest priority. After receiving this information, the PAN coordinator checks the priority of each requesting node, and the nodes with higher priority are allocated first. The nodes with the same priority are allocated according to the order of request, first come first served. Because the IEEE standard stipulates that GTS can only be allocated to 7 nodes at most, and there is a time slot limit, all nodes that are not allocated GTS can continue to apply in the next superframe if there is still demand.

[0026] Step 5: Repeat step 1.

[0027] In a star network, if the average probability of a node successfully transmitting information during a contention period is set to P CAP The average probability of successfully obtaining GTS allocation in the non-contention period is P CFP , if the node information is successfully transmitted in one superframe on average, then the probability P of successful transmission of the node information is

[0028] P=P CAP +(1-P CAP ) CFP

[0029] Through the probability calculation, it is shown that if a sensor node with a high priority has information transmission, the success probability is greater than that of a sensor node with a low priority, which reflects the advantages of the present invention.

[0030] The present invention takes into account the priority of nodes, so nodes with higher priority are assigned to GTS first, that is, nodes with higher priority P CFP The probability is higher than that of ordinary nodes. CAP In the case of consistency, the above formula shows that the probability of successful information transmission of nodes with higher priority is higher, the average successful transmission time is short, the delay is small, and a lot of time is not spent on competitive transmission. Therefore, the less energy is consumed during the transmission process, the lower the energy consumption.

Claims

1. A method for implementing a MAC layer protocol of a wireless sensor network, characterized in that The steps include: Step 1: The sensor node listens to the beacon information sent by the PAN coordinator. The beacon information contains the active period and inactive period of the coordinator, which also contains the allocation of GTS. If some sensor nodes have GTS requests in the previous superframe, check whether the PAN coordinator has successfully allocated GTS in the beacon information. The beacon frames received by all sensors have the GTS allocation field. The sensor nodes that requested the non-contention period in the previous frame will compare and check whether the allocation is successful when receiving the beacon frame. If GTS is successfully allocated, it is necessary to maintain communication with the PAN coordinator in the CFP period. If GTS is not successfully allocated, it will enter the contention period of the current superframe structure for contention transmission and determine whether to continue to apply for GTS: If the sensor does not successfully allocate GTS in the current beacon frame, it will first compete for transmission in the contention period in the superframe. If it successfully competes for the transmission time slot, it will successfully transmit the information and will not re-apply for GTS; if it does not successfully get the time slot transmission time slot in the contention period, it will continue to apply for GTS and repeat the above process until the information is successfully transmitted; Step 2: All sensors within the range of the PAN coordinator enter the contention period within the active period. If there is data transmission, they compete for access through the time slot CSMA / CA. If some node information successfully competes for access to the channel during this period, the information is successfully transmitted. If a sensor fails to compete for the transmission time slot during the contention period, it cannot transmit information during the contention period, that is, the transmission is not successful. Step 3: During the CSMA / CA competition process in the time slot, no retransmission is performed. If the channel is not successfully accessed after three consecutive backoffs, GTS is applied to the PAN coordinator. When requesting GTS from the PAN coordinator, different request bytes correspond to different priorities, and two reserved bits in the request byte are modified. After receiving the GTS request, the PAN coordinator checks the current CFP time slot length based on the priority of the request information. If the high priority can be met and there are remaining CFP time slots, GTS is allocated to ensure that the high-priority information is successfully allocated to GTS in the next superframe; the GTS in the current superframe is allocated to the node that successfully requested GTS in the previous superframe; Step 4: All nodes enter an inactive period, and the sensor nodes do not exchange information with the PAN coordinator, that is, they enter a sleep period to save energy consumption of sensor devices.

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