CN101557606B - Media access control (MAC) method applicable to wireless sensor network - Google Patents

Abstract

The media access control method for wireless sensor networks adjusts the sending process according to the characteristics of the data flow of the nodes in the specific application of the wireless sensor network that changes with time. Estimate the current data traffic intensity by measuring the interval between data packets arrival and use filters to reduce the interference in the measurement process. And by detecting the current data packet queue length of the node, adaptive control is performed. When the data packet queue length is greater than 1, the data packets in the queue are sent in batches in a burst transmission mode to reduce delay and energy consumption. Otherwise, judge according to the current measured data flow. If the current data flow value is less than a given threshold, the low-flow adaptive mechanism is enabled, and the node can remove unnecessary wake-up cycles through local control packet exchange. This method does not need to adjust the period and duty cycle of the protocol online, avoids the difficult problem of synchronization between nodes, and effectively solves the difficult problem of synchronization and data flow self-adaptation in the current wireless sensor network.

Description

Media Access Control Method for Wireless Sensor Networks

technical field

The invention relates to the field of wireless networks, in particular to the field of wireless sensor network protocol design, and specifically provides a flow adaptive media access control method for wireless sensor networks.

Background technique

In wireless sensor networks, the nodes are generally powered by batteries and their capacity is small. After the nodes are distributed in the actual application environment, the batteries are difficult or costly to replace. Therefore, energy efficiency is the focus of wireless sensor network protocol design considerations. In many application fields such as fire detection, nodes need to send the collected data to the sink node in time and take necessary measures to reduce losses, which requires a high delay time for protocol design.

At present, in the design of wireless sensor network MAC protocol, nodes generally adopt periodic listening and sleep scheduling to reduce energy consumption. The most representative one is the S-MAC protocol proposed by Ye Wei, which was first introduced by the reference "An Energy- Efficient MAC Protocol for Wireless Sensor Networks” (W. Ye, J. Heidemann, and D. Estrin, IEEE INFOCOM, June 2002). The S-MAC protocol operates in a periodic manner. A cycle of the protocol is divided into two parts: the listening period and the sleep period. The listening period is further divided into a synchronization phase and a data phase. The ratio of the listening time to the length of the entire cycle is Duty cycle, the period length and duty cycle are fixed during the operation of the protocol. Nodes wake up for data communication during listening and go to sleep during sleep to reduce power consumption. In order to ensure correct communication between nodes, the protocol design adopts a regular synchronization mechanism. By periodically receiving and forwarding synchronization packets, a consistent listening sleep schedule is formed between nodes, thereby ensuring correct communication between nodes.

However, in practical wireless sensor network applications, the performance of the above-mentioned traditional MAC protocol is greatly limited. The reasons are as follows: ① The data traffic of actual wireless sensor network nodes changes frequently, and in many cases is irregular or irregular. Using the method of fixed period and duty cycle, when the data flow is large, it is easy to cause buffer overflow and packet loss, and when the data flow is small, the unnecessary wake-up process consumes energy, which makes the protocol performance low. ②Maintaining synchronization between sensor network nodes is a complex process, because sensor nodes need to listen for a period of time, set their own schedule after receiving the synchronization packet, and then forward the synchronization packet, and finally make the entire network form a consistent schedule, which is a A process that consumes time and energy.

Contents of the invention

Technical problem: In order to solve the problems in the above-mentioned prior art, the present invention proposes a media access control method for wireless sensor networks, which enables nodes to improve the performance of the protocol under variable data flow conditions, and does not require Period and duty cycle are adjusted online to avoid synchronization difficulties.

Technical solution: The media access control method for wireless sensor networks of the present invention is used to solve the problem of low protocol performance in the environment of node data flow changes. The node performs self-adaptive adjustment by measuring the current data flow and the length of the packet buffer queue. When the data flow is relatively large, the high-flow adaptive mechanism is adopted, and when the data flow is relatively small, the low-flow adaptive mechanism is adopted, thereby effectively improving The performance of the protocol in terms of energy consumption, latency, etc. under traffic changing conditions. The specific method of data flow measurement is: the node continuously records the arrival time of data packets, and takes the reciprocal of the interval between two continuously arriving data packets as the current measured data flow, then the measured data flow can be expressed as: l _k+1 = 1/(t _k+1 -t _k ), where t _k and t _k+1 respectively indicate the time when the previous data packet is received and the time when the current data packet is received, and the measurement results are eliminated by a low-pass filter.

The node performs adaptive adjustment by detecting the current data buffer queue length N _cur . When N _cur > 1, the high flow adaptive mechanism is enabled. When N _cur ≤ 1 and the current measured data flow L _k <β, the low flow is enabled Self-adaptive mechanism, otherwise the communication is carried out by sending a data packet at a time in the traditional MAC protocol. Among them, β is a preset threshold.

In the flow adaptive media access control method in the wireless sensor network of the present invention, the high flow adaptive mechanism uses a burst mode to send data packets, and the node first determines the number N _bst of data packets for this burst transmission, and the method is: preset Determine the maximum allowable burst transmission time T _max and calculate the maximum number of packets M _max allowed for burst transmission. Before sending data, the node first detects the current data buffer queue length N _cur . If N _cur ≥ N _max , then N _bst =N _max , otherwise if N _cur <N _max , then N _bst =N _cur . Then during the data period, the carrier sense method is used to send the request to send packet-RTS packet for channel reservation. Once the reservation is successful, multiple data are sent at a time through the burst mode of RTS/CTS/DATA1/DATA2/.../DATAN _bst /ACK packet, that is, the sending node first sends an RTS packet to the receiving node, and after receiving the permission to send the packet-CTS from the receiving node, the sending node continuously sends N _bst data packets-DATA to the receiving node, and finally receives the confirmation from the receiving node This transmission is completed after the packet-ACK.

If the burst transmission time exceeds the cycle length of the protocol operation, the node will continue to send data until the burst transmission is completed. Each control packet and data packet in the burst transmission series contains the time required until the completion of this transmission. Other non-destination nodes detect any packet in this burst packet sequence, then update their network allocation vector NAV and go to sleep to reduce energy consumption.

In the flow adaptive medium access control method in the wireless sensor network of the present invention, when its high flow adaptive mechanism works under the error channel condition, once a packet in the burst transmission series is detected to be destroyed due to channel error , the node continues to transmit the remaining data packets until the burst data transmission is completed. Corrupted packets will be retransmitted in the next burst series. If the current node has two or more next neighbor nodes, the current node reschedules the data packets accumulated in the data buffer, and schedules the data packets sent to the same destination address into a series, so that when sending data packets , each burst contains only data packets sent to the same destination address.

In the flow adaptive media access control method in the wireless sensor network of the present invention, the low flow adaptive strategy is as follows: the sending node obtains the address of the node of the next entry by detecting the corresponding field of the data packet currently to be sent, and then constructs an invitation to send Packet (ITS) and send this ITS packet to the destination node by means of carrier sense in the synchronization phase, the destination node will reply an agree to send packet (ATS) after receiving the ITS packet to confirm this communication. The sending node and the receiving node use the data packet/acknowledgment packet to communicate directly without carrier sense during the data period, and other neighbor nodes update NAV after receiving ITS or ATS and go to sleep to reduce power consumption.

When the node has no data packets to send and no ITS packets are received, the remaining listening time in this period is removed to reduce power consumption. At the same time, a threshold θ is set. When the node has experienced θ cycles and still does not send or receive data or control packets, the node wakes up to listen for control or data packets that may be sent to itself. If the receiving node detects a collision during the synchronization period, it will keep awake during the DATA period to listen for possible arriving messages. If the sending node detects a collision during the synchronization period, it will use the traditional carrier sense method during the data period of this cycle. data sent. Avoid transmission errors due to node sleep.

Beneficial effects: the flow adaptive medium access control method in the wireless sensor network of the present invention measures the data flow of nodes and the length of the data buffer queue in real time, and performs flow adaptive adjustment based on the measured value. When the data traffic is relatively large, it can greatly reduce the delay time and power consumption of data packet transmission, and can well alleviate the problems of buffer accumulation and packet loss. When the data traffic is relatively small, the energy consumption of nodes is reduced by removing unnecessary listening periods, and the delay performance of the protocol will not be significantly affected. In addition, the method in the invention does not need to adjust the period and duty cycle of the protocol, so that the method is relatively simple to implement and does not cause synchronization difficulties.

Description of drawings

FIG. 1 is an overall schematic diagram of a flow-adaptive media access control method according to the present invention,

Fig. 2 is a schematic diagram of the burst transmission operation of the medium and high flow adaptive mechanism of the present invention,

FIG. 3 is a schematic diagram of the selective wake-up operation of the low traffic adaptive mechanism in the present invention.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and specific implementation examples.

The flow adaptive media access control method in the wireless sensor network of the present invention, its overall operation process is shown in Figure 1, the node carries out self-adaptive adjustment by detecting the current data buffer queue length N _cur , when N _cur > 1, enable High-flow adaptive mechanism, when N _cur ≤ 1 and the current measured data flow L _k <β, the low-flow adaptive mechanism is enabled; otherwise, the traditional MAC protocol sends a data packet at a time for communication. Among them, β is a preset threshold, and its value is determined according to specific network conditions.

The specific method of data flow measurement is: the node continuously records the arrival time of data packets, and takes the reciprocal of the time interval between two consecutive arrival data packets as the current measured data flow, then the measured data flow can be expressed as:

l _k+1 ＝1/(t _k+1 -t _k ) (1)

Among them, t _{k and} t _k+1 represent the time when the previous data packet is received and the time when the current data packet is received respectively. Since there is random interference in the measurement process, a low-pass filter is used to eliminate the measurement interference. The specific method is as follows: Let L _k-1 be the previous data flow value after the filter eliminates interference, and L _cur be the current directly estimated data flow value, then the calculation formula for the data flow value obtained after the filter eliminates interference this time is:

L _k ＝αL _k-1 +(1-α)L _cur (2)

The burst transmission mode of the high flow adaptive mechanism among the present invention is as shown in Figure 2, if a node wishes to send data packet to its next hop destination node, then at first send RTS packet by carrier sense mode during the data period, It includes information such as the number N _bst of data packets of this burst transmission, the time before the end of this burst transmission, and the address of the next node. After receiving the RTS packet, the next-hop destination node replies with a CTS packet for transmission confirmation. If other neighbor nodes hear the RTS packet or CTS packet, they update their NAV and go to sleep to reduce power consumption. At this time, the sending node continuously sends N _bst data packets to the next-hop destination node, and the next-hop destination node replies an ACK packet for confirmation after receiving the data packets. The specific setting method of the packet interval size in the burst transmission sequence is similar to that of 802.11. If the time of the burst parameter exceeds the cycle length of the protocol itself, the transmission process will continue until the current transmission is completed, and will not be interrupted because of exceeding a cycle length.

The calculation method of the number N _bst of data packets contained in a burst transmission is as follows: if the maximum allowable time is T _f and T _s respectively under the condition of fairness and maintaining correct synchronization, then the maximum allowable burst transmission time T _max Can be expressed as:

T _amx = min(T _f , T _s ) (3)

According to the maximum allowable burst transmission time and the characteristics of burst transmission, assuming that the data packets in the burst transmission system have the same length, the maximum number of packets allowed to be sent in burst transmission can be calculated by the following formula N _max

N _max =[k×min(T _f , T _s )-L _RTS -L _CTS -L _ACK - (4)

3k×SIFS+k×PIFS]/(L _DATA +k×PIFS)

Among them, L _RTS , L _CTS , L _DATA , and L _ACK are the lengths of RTS, CTS, DATA, and ACK packets respectively, while SIFS and PIFS are the control packet interval and data packet interval respectively, and k is the data transmission speed. Before sending data, the node first checks the current data buffer queue length N _cur , if N _cur >N _max , then N _bst =N _max , otherwise if N _cur <N _max , then N _bst =N _cur .

When the high-flow adaptive mechanism of the present invention works under the error channel condition, once it detects that a packet in the burst transmission series is destroyed due to channel error, the node continues to transmit the remaining packets until the burst data transmission is completed until. Corrupted packets will be retransmitted in the next burst series. If the current node has two or more next neighbor nodes, the node rearranges the packets in the current data buffer, and schedules the packets sent to the same destination address into a series, so that when sending packets , each burst data packet system contains only data packets sent to the same destination address. For example, the number of packets in the data buffer is 7, assuming that the serial numbers of the data packets are 1, 2, 3, 4, 5, 6, and 7 respectively, and the data packets with the serial numbers 1, 4, and 5 contain the same destination address, and The data packets with sequence numbers 2, 3, 6, and 7 contain another same destination address, then the node rearranges these data packets in the data buffer before the burst transmission, and the order is 1, 4, 5, 2, 3, 6, 7. These packets will be sent in two burst transmissions, one burst transmission containing packets with sequence numbers 1, 4, and 5, and the other burst transmission containing packets with sequence numbers 2, 3, 6, and 7.

In the flow adaptive media access control method in the wireless sensor network of the present invention, its low flow adaptive strategy is shown in FIG. 3 , and the power consumption is reduced by adopting a node selective wake-up method. In Figure 3, node 0 needs to send a data packet to its next-hop node 3, then node 0 first sends an ITS packet to its neighbor node 3 in the synchronization phase, and node 3 checks the relevant fields in the packet after receiving the ITS packet Confirm that it is the destination node, then reply an ATS packet to node 0 for confirmation. Since node 1 and node 2 confirm that they are not the destination node of this communication through the received ITS packet, they update NAV and go to sleep early to reduce power consumption, where the length of NAV update is the time until the end of this data transmission length. At the beginning of the data phase, node 0 directly sends a DATA packet to node 3, and then node 3 replies with an ACK packet for confirmation after receiving the DATA packet, then the transmission between node 0 and node 3 is successfully completed, because Listening performs channel reservation, so carrier sensing is not used in the data communication process. Since nodes 1 and 2 have gone to sleep, these neighbor nodes will not interfere with the communication between nodes 0 and 3.

When the node has no data packets to send and no ITS packets are received, the remaining listening time in this period is removed to reduce power consumption. At the same time, a threshold θ is set. When the node has experienced θ cycles and still does not send or receive data or control packets, the node wakes up to listen for control or data packets that may be sent to itself. Since a node sends an ITS packet for a transmission request at a synchronization node, and the periodic synchronization packet of a node is also sent during the synchronization phase, synchronization packets and synchronization packets, ITS and ITS, and synchronization packets and synchronization packets may occur at both the sending node and the receiving node. Conflict between ITS. If the receiving node detects a collision during the synchronization period, it will keep awake during the DATA period to listen for possible arriving messages, thereby avoiding transmission errors and reducing delays caused by node sleep. For the sending node, if a conflict is detected, the normal communication operation mode is adopted, that is, the node communicates in the RTS/CTS/DATA/ACK mode during the data period, and the sending node sends the RTS packet through the carrier sense mode.

Claims (5)

1. A media access control method for wireless sensor networks, characterized in that the current data flow and data buffer queue length of the real-time measurement node carry out flow adaptive regulation, and when the node buffer queue length is greater than 1, high flow rate is enabled Adaptive mechanism, when the data buffer queue length is less than or equal to 1 and the current data flow is less than the preset threshold, the low-flow adaptive strategy is enabled, otherwise, the communication is carried out by sending a data packet at a time in the traditional MAC protocol. 2. The medium access control method for wireless sensor network according to claim 1, characterized in that the current data flow method of the measuring node is: the node continuously records the arrival time of data packets, and two consecutive data packets The reciprocal of the interval time is used as the current measured data flow, and its calculation method is expressed as data flow l _k+1 =1/(t _k+1 -t _k ), where t _k and t _k+1 respectively represent the previous data packet The time when the data packet is received and the time when the current data packet is received, the measurement result is eliminated by a low-pass filter to measure interference. 3. the media access control method for wireless sensor network according to claim 1, is characterized in that described high flow adaptive mechanism is: ① First determine the number N _bst of data packets contained in the current burst transmission, then the node reserves to send multiple data packets at a time through RTS/CTS/DATA1/DATA2/.../DATAN _bst /ACK, each control Both the packet and the data packet contain the time required for the completion of this sending; other non-destination nodes detect any packet in this burst packet sequence, update their network allocation vector-NAV and go to sleep to reduce power consumption ; ② When the node is working under the error channel condition, once the node detects that a data packet in the burst transmission series is destroyed due to a channel error, it will continue to transmit the remaining data packets until the burst data transmission is completed and is destroyed. The data packets will be retransmitted in the next burst transmission; ③If the current node has two or more next-hop neighbor nodes, the current node reschedules the data packets accumulated in the data buffer, and schedules the data packets sent to the same destination address into a series, so that When sending data packets, each burst transfer series contains only data packets sent to the same destination address. 4. The medium access control method for wireless sensor network according to claim 3, characterized in that the method for determining the number of data packets N _bst contained in the current burst transmission is: presetting the maximum allowable burst The transmission time T _max is used to calculate the maximum number of packets N _max allowed to be sent for each burst transmission. The node first detects the current data buffer queue length N _cur before sending data. If N _cur > N _max , then N _bst = N _max , otherwise if N _cur <N _max , then N _bst =N _cur . 5. The medium access control method for wireless sensor networks according to claim 1, characterized in that the low traffic adaptive strategy is: ①The sending node obtains the address of the next-hop destination node by detecting the corresponding field of the current data packet to be sent, and then constructs an invitation to send packet-ITS and sends the ITS packet to the next-hop destination node through carrier sense in the synchronization phase, After receiving the ITS packet, the destination node replies with an agree-to-send packet-ATS confirms the communication process, the sender and the receiver use data packets/confirmation packets for data communication during the data period, and other non-destination nodes update after receiving ITS or ATS The network allocates vectors and goes to sleep to reduce power consumption; ② When the node has no data packets to send and no ITS packets are received, remove the remaining listening time in this period to reduce power consumption; at the same time set a threshold θ, when the node has experienced θ cycles and still has no packets to send or receive , the node wakes up to listen for packets that may be sent to itself; ③ If the receiving node detects a collision during the synchronization period, it will remain awake during the data period to listen for possible arriving messages. If the sending node detects a collision during the synchronization period, it will use traditional carrier sense during the data period of this cycle Data communication is carried out in a way to avoid transmission errors caused by node sleep.

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