CN107018567B - Method for node concurrent data transmission in wireless sensor network - Google Patents

Abstract

The invention discloses a method for concurrently transmitting data by nodes in a wireless sensor network, comprising: (1), a sending node loads a packet to be transmitted into a sending buffer, and closes the node address identification function, and turns to step (2); ( 2), the sending node continues to listen to the channel for a period of time, and analyzes the result of listening to the channel; (3), according to the result of step (2) listening to the channel, determine whether there is only one sending node in the channel, if there is more than one sending node node, then randomly back off for a period of time and turn to step (2); otherwise, record the sending node as a synchronization node, and turn to step (4); (4), the falling edge of the SFD generated at this node by the packet sent by the synchronization node is interrupted The transmit strobe command is invoked at the location to start transmitting packets. The present invention utilizes the hardware to interrupt the time when the synchronization node sends packets, not only does not bring additional synchronization overhead to the network, but also improves the channel utilization rate, thereby improving the network throughput.

Description

A method for nodes to transmit data concurrently in wireless sensor network

technical field

The present invention relates to the field of communication technologies, in particular to a method for concurrently transmitting data by nodes in a wireless sensor network.

Background technique

Wireless sensor network consists of wireless sensor nodes distributed in a certain area for monitoring and collecting valuable information. Usually, data is finally transmitted to the sink node through the wireless network formed by the cooperation between nodes. Since wireless transmission is based on a shared channel, when a node sends a packet depends on the medium access control protocol used, namely the MAC protocol. There are two main types of MAC protocols: carrier sense multiple access control protocol CSMA and time division multiple access protocol TDMA. CSMA is a contention-based protocol. A node first listens to the channel before sending, and sends if the channel is idle; if the channel is busy, it listens to the channel after random backoff for a period of time. The advantage of the CSMA protocol is that the protocol is simple, but the throughput is low. The TDMA protocol divides time into time slots, and avoids collisions by assigning the time slots used by each node. The advantage of the TDMA protocol is that higher throughput can be obtained. However, TDMA requires synchronization of the entire network, so it may generate a large scheduling overhead.

In order to increase network throughput and reduce network transmission delay, most concurrent transmission mechanisms currently designed tend to allow multiple sending nodes to access the channel at the same time, that is, multiple sending nodes transmit data concurrently. However, the existing concurrent transmission protocol only considers the influence of transmission power when judging whether a node accesses the channel, that is, the SINR of the packet sent by the node at the receiving node is required to meet certain requirements. In fact, the chip commonly used by sensor nodes, such as CC2420, will first go through the synchronization process when receiving a packet. Once a certain packet is successfully synchronized, other packets will not be synchronized, even if the signal strength of the latter packet is particularly large. Therefore, when designing a concurrent transmission method, it is also necessary to consider how to control the time when nodes send packets.

SUMMARY OF THE INVENTION

In view of the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for concurrently transmitting data between nodes in a wireless sensor network by taking into account the packet transmission time and combining hardware interruptions. improve the throughput of the network under the conditions.

In order to achieve the above object, the present invention provides a method for concurrently transmitting data by nodes in a wireless sensor network, which is characterized by comprising the following steps:

(1) The sending node loads the packet that needs to be transmitted into the sending buffer, and closes the address identification function, and turns to step (2);

(2) The sending node continues to listen to the channel for a period of time, and analyzes the result of listening to the channel. If the detected result shows that the channel is idle, it starts to continuously send packets to its receiving node; if the channel is busy and no packets are received, the channel is randomly backed off for a period of time and then listens to the channel again; otherwise, turn to step (3);

(3) Judging whether there is only one sending node in the channel according to the result of listening to the channel in step (2), if there is more than one sending node, then randomly back off for a period of time and turn to step (2); otherwise, record the sending node as a synchronization node , turn to step (4);

(4) The strobe command is invoked at the SFD falling edge interrupt generated by the packet sent by the synchronization node to start sending the packet.

The above-mentioned method for concurrently transmitting data by nodes in a wireless sensor network is characterized in that the step (2) is specifically:

(21) The node periodically detects the CCA pin to determine whether the channel is idle;

(22) The node records the packets sent by other nodes within the listening channel, and extracts the source node number of the packet; wherein steps (21) and (22) are performed simultaneously; after the listening channel ends, turn to step (23) );

(23) If the channel is busy at least once during the detection of the CCA pin, and no packet is received, the result is that the channel is busy, and the channel is re-listened after a random backoff for a period of time; otherwise, turn to step (3).

The above-mentioned method for concurrently transmitting data by nodes in a wireless sensor network is characterized in that the step (4) is specifically:

(41) setting the receiving buffer threshold value to be 5, the node continues to receive a packet, and reads out the source address information of the receiving packet at the receiving buffer hardware generated by this packet;

(42) Judging whether the source address information in (41) is equal to the synchronization node number recorded in step (3), if it is equal, call the strobe command to start sending the packet at the SFD falling edge interrupt generated by the packet at this node, Then continue to send packets to its receiving node at the fastest speed.

The above-mentioned method for concurrently transmitting data by nodes in a wireless sensor network is characterized in that: the sending node and the receiving node are but not limited to CC2420 chips.

The beneficial effects of the present invention are:

1. The present invention still transmits packets when the channel is busy, which improves the channel utilization rate and the throughput of the network. On the one hand, it ensures that the existing transmission link will not be affected, and on the other hand, it ensures that the new receiving node can correctly receive the packets sent by its sending node.

2. The present invention utilizes hardware interrupts to synchronize the time when nodes send packets. This synchronization method not only does not bring additional synchronization overhead to the network, but also improves the utilization rate of the channel and the throughput of the network.

The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings, so as to fully understand the purpose, characteristics and effects of the present invention.

Description of drawings

FIG. 1 is a flow chart of the implementation of the present invention.

FIG. 2 is a schematic diagram of a standard frame format of IEEE802.14.5.

Figure 3 is a schematic diagram of the level change of the SFD pin when the node sends and receives packets.

Figure 4 is a flow chart of the node sending packets

FIG. 5 is a schematic diagram of a typical network of two mutually interfering concurrent transmission links with four nodes.

FIG. 6 is a graph of experimental results in an example scenario.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

As shown in Figure 1, a method for concurrently transmitting data by nodes in a wireless sensor network is characterized in that it includes the following steps:

(1) The sending node loads the packet that needs to be transmitted into the sending buffer, and closes the address identification function, and turns to step (2);

(2) The sending node continues to listen to the channel for a period of time, and analyzes the result of listening to the channel. If the detected result shows that the channel is idle, it starts to continuously send packets to its receiving node; if the channel is busy and no packets are received, the channel is randomly backed off for a period of time and then listens to the channel again; otherwise, turn to step (3);

(3) Judging whether there is only one sending node in the channel according to the result of listening to the channel in step (2), if there is more than one sending node, then randomly back off for a period of time and turn to step (2); otherwise, record the sending node as a synchronization node , turn to step (4);

(4) The strobe command is called to start sending packets at the SFD falling edge interrupt generated by the sending packet of the synchronization node at the local node.

In this embodiment, the step (2) is specifically:

(21) The node periodically detects the CCA pin to determine whether the channel is idle;

(22) The node records the packets sent by other nodes that are received during the listening channel, and extracts the source node number of the packet; wherein steps (21) and (22) are performed simultaneously; after the listening channel ends, turn to step (23);

(23) If during the detection of the CCA pin, there is at least one detection result showing that the channel is busy and no packet is received, then the result is that the channel is busy, and the channel is re-listened after a random backoff for a period of time; otherwise, turn to step (3).

In this embodiment, the step (4) is specifically:

(41) setting the receiving buffer threshold to be 5, the node continues to receive a packet, and reads out the source address information that is receiving the packet at the receiving buffer hardware interrupt FIFOP generated by this packet;

(42) Judging whether the source address information in (41) is equal to the synchronization node number recorded in step (3), if it is equal, call the strobe command to start sending the packet at the SFD falling edge interrupt generated by the packet at this node, Then continue to send packets to its receiving node at the fastest speed.

In this embodiment, the sending node and the receiving node are but not limited to CC2420 chips.

The following examples are used to illustrate the present invention, but are not intended to limit the scope of application of the present invention.

The present invention is suitable for wireless sensor networks. Sensor nodes mostly use unicast form when transmitting data, that is, each sending node corresponds to one receiving node. The sensor node has two functions of address identification, namely software address identification and hardware address identification. If and only if the hardware and software address identification of the packet is passed, it will be correctly received by the destination node. The packets sent by the node comply with the standard frame format of IEEE802.15.4. The schematic diagram of the standard frame grid refers to FIG. 2, which includes five parts: synchronization header SFD, physical layer protocol header, MAC protocol header, MAC protocol load, and MAC protocol tail, wherein the synchronization header also includes a preamble sequence and a frame sequence. The protocol header contains the frame length; the MAC protocol header contains the frame control field, data sequence number and address information; the MAC protocol payload contains the frame payload; the MAC protocol tail contains the frame detection sequence. When a sensor node receives a packet, it will first go through the process of packet synchronization. Once a packet is successfully synchronized, it will not synchronize any other packets until the synchronization ends.

SFD (Start of Frame Delimiter) is the IEEE802.15.4 frame start delimiter. As shown in FIG. 3 , when the SFD field of the packet to be sent and received by the sensor node has been sent and received, the SFD signal changes from low to high, and continues until the packet is sent and received. SFD hardware capture is the capture of SFD signals by hardware. When the level of the SFD changes, the interrupt function in the upper-level program will be triggered, and at this time, the time stamp of the instant of the level change of the SFD can be obtained in the upper-level function. Because the time stamp of the hardware capture interrupt record does not relate to the time the software capture records the time stamp, the SFD hardware capture excludes the transmission delay and processing delay of the communication process. If the propagation delay is negligible, it can be considered that the time stamps of the level changes of the SFD pins of the transceiver nodes are at the same time. That is, in Figure 3, the SFD pin levels of the sending node and the receiving node jump at the same time.

Each sensor node in the network has two buffer areas for sending and receiving data, namely sending buffer and receiving buffer. As shown in Figure 4, when a sensor node needs to send a packet, it first needs to load the packet into the sending buffer, and then call the send gating command to send it out. Through experimental measurement, it is found that the time required to load the packet into the sending buffer is greater than the time required to send the packet from the sending buffer to the channel. Therefore, the actual time required by the sensor node to send a packet is often greater than twice the transmission delay of the packet.

Example:

Figure 5 is a network of typical interfering links transmitting concurrently. As shown in FIG. 5 , two mutually interfering links l ₁ =S ₁ , R ₁ , l ₂ =S ₂ , R ₂ . Wherein, the nodes S ₁ S ₂ need to send 50 consecutive packets to the nodes R ₁ R ₂ respectively. Node S1 _first needs to send a packet, and after 100 milliseconds, node _S2 needs to send a packet.

The specific steps of the present invention will be described below according to FIG. 1 .

Node S1 _first turns off the node address identification function, starts to listen to the channel 50 milliseconds later, and periodically detects CCA. After listening to the channel, since no node is transmitting packets, the result of the channel being idle is obtained, and node S ₁ immediately starts to continuously send packets to node R ₁ at the fastest speed. After 50 milliseconds, the same node S ₁ , node S ₂ first turns off the node address identification function, and starts to listen to the channel 50 milliseconds later. During the time that the node S2 _listens to the channel, it receives the packet sent by the node _S1 . After the node S2 listens to the channel, at least _{half of} the detected channel results show that the channel is idle, and the node _S2 only receives the packets sent by the node S1. Therefore, _on the current channel, only node S1 is sending packets. Node S2 sets the threshold for receiving the required FIFOP to ₅ , while making node S1 _a sync node. Afterwards, the node _S2 will receive a packet, and read the source node number of the packet from the receiving buffer at the FIFOP interrupt caused by the packet. It can be known that the source node number is _S1 . Therefore, the send strobe command is called to send the packet at the SFD falling edge interrupt generated by the packet.

Figure 6 is the experimental result in the scenario of Figure 5, where the abscissa represents the length of the packet sent by the sending node, and the ordinate is the throughput of the system. It can be seen from FIG. 6 that the system throughput obtained by using the present invention in the case of concurrent transmission of two links is twice the system throughput of a single link in the case of no interference.

The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and changes according to the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art through logical analysis, reasoning or limited experiments on the basis of the prior art according to the concept of the present invention shall fall within the protection scope determined by the claims.

Claims (2)

1. A method for nodes to transmit data concurrently in a wireless sensor network is characterized by comprising the following steps:

(1) the sending node loads the packet to be transmitted into a sending cache, closes the node address identification function and turns to the step (2);

(2) the sending node continuously monitors the channel for a period of time and analyzes the result of the channel monitoring; if the result of monitoring the channel shows that the channel is idle, starting to send the packet; if the channel is busy and no packet is received, randomly back off for a period of time and then monitoring the channel again; otherwise, turning to the step (3);

(3) judging whether the channel has only one sending node according to the result of the channel interception in the step (2), and if more than one sending node exists, randomly retreating for a period of time and turning to the step (2); otherwise, marking the sending node as a synchronous node, and turning to the step (4);

(4) calling a transmission gating command at the SFD falling edge interruption generated at the node by the synchronous node transmission packet to start transmitting the packet;

the step (2) is specifically as follows:

(21) the node periodically detects a CCA pin and judges whether a channel is in an idle state;

(22) the node records a packet sent by other nodes in the channel monitoring time, and extracts a source node number of the packet; wherein the step (21) and the step (22) are carried out simultaneously; turning to the step (23) after the channel monitoring is finished;

(23) if the CCA pin is detected at least once, the detection result is that the channel is busy and the packet is not received, the result is that the channel is busy, and the channel is monitored again after the CCA pin is randomly retreated for a period of time; otherwise, turning to the step (3);

the step (4) is specifically as follows:

(41) setting a receiving cache threshold value to be 5, continuously receiving a packet by a node, and reading source address information of the packet being received at a FIFOP (hardware interrupt for receiving cache) caused by the packet;

(42) and (4) judging whether the obtained source address information is equal to the number of the synchronous node recorded in the step (3), if so, calling a transmission gating command at the SFD (Small form-factor pluggable) falling edge interruption position caused by the packet at the node to start transmitting the packet, and then continuously transmitting the packet to the receiving node at the fastest speed.

2. The method of claim 1, wherein the node concurrently transmits data in the wireless sensor network, and the method further comprises: the sending node and the receiving node are, but not limited to, CC2420 chips.

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