CN107018567B - Method for node concurrent data transmission in wireless sensor network - Google Patents
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- H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
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Abstract
The invention discloses a method for concurrently transmitting data by nodes in a wireless sensor network, which comprises the following steps: (1) the sending node loads the packet to be transmitted to 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; (3) judging whether the channel has only one sending node according to the result of monitoring the channel 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) and the packet transmitted at the synchronous node calls a transmission gating command at the SFD falling edge interruption generated at the node to start transmitting the packet. The invention uses hardware to interrupt the time of the synchronous node sending packet, not only does not bring extra synchronous expense to the network, but also improves the channel utilization rate and further improves the network throughput.
Description
Technical Field
The invention relates to the technical field of communication, in particular to a method for transmitting data by nodes in a wireless sensor network concurrently.
Background
The wireless sensor network consists of wireless sensor nodes distributed in a certain area for monitoring and collecting valuable information. In general, data is finally transmitted to the sink node through a wireless network formed by 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, i.e. the MAC protocol. The current MAC protocols mainly have two types: carrier sense multiple access control protocol CSMA and time division multiple access protocol TDMA. CSMA is a protocol based on competition, a node firstly monitors a channel before sending, and sends the channel if the channel is idle; and if the channel is busy, randomly carrying out backoff for a period of time and then monitoring the channel. 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 allocating time slots for each node to use. The TDMA protocol has the advantage that a higher throughput can be obtained. TDMA, however, requires full network synchronization and may therefore incur a significant scheduling overhead.
In order to increase the throughput of the network and reduce the network transmission delay, most of the currently designed concurrent transmission mechanisms usually enable a plurality of sending nodes to access a channel simultaneously, that is, a plurality of sending nodes concurrently transmit data. However, when determining whether a node accesses a channel, the existing concurrent transmission protocol only considers the influence of transmission power, that is, the signal to interference plus noise ratio SINR of a packet sent by the node at a receiving node is required to meet a certain requirement. In fact, a chip commonly used by a sensor node, such as CC2420, will go through a synchronization process first when receiving a packet, and once a packet is successfully synchronized, other packets will not be synchronized, even though the signal strength of the packet is particularly large. Therefore, when designing a concurrent transmission method, how to control the time when the node transmits the packet needs to be considered.
Disclosure of Invention
In view of the defects of the prior art, the technical problem to be solved by the present invention is to provide a method for nodes to concurrently transmit data in a wireless sensor network, which can improve the throughput of the network under the condition that the network nodes concurrently transmit, in combination with hardware interruption, on the basis of considering packet transmission time.
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 to be transmitted into a sending cache, closes the address recognition function and turns to the step (2);
(2) the transmitting node listens to the channel for a period of time and analyzes the results of the listening to the channel. If the sensed result shows that the channel is idle, continuously sending packets to the receiving node of the channel; if the channel is busy and the packet is not received, randomly carrying out backoff 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) the packet transmitted at the synchronizing node invokes a gating command to start transmitting the packet at the SFD falling edge interrupt generated at the node.
The method for concurrently transmitting data by nodes in a wireless sensor network is characterized in that the step (2) specifically comprises:
(21) the node periodically detects a CCA pin and judges whether a channel is idle;
(22) the node records the packets sent by other nodes in the channel monitoring time, and extracts the source node number of the packet; wherein steps (21) (22) are performed simultaneously; turning to the step (23) after the channel monitoring is finished;
(23) if the CCA pin is detected, the channel is busy at least once and no packet is received, the result is the channel is busy, and the channel is monitored again after random backoff for a period of time; otherwise, turning to the step (3).
The method for concurrently transmitting data by nodes in a wireless sensor network is characterized in that the step (4) specifically comprises:
(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 receiving cache hardware generated by the packet;
(42) and (4) judging whether the source address information in the step (41) is equal to the number of the synchronous node recorded in the step (3), if so, calling a gating command at the SFD falling edge interruption position generated at the node of the packet to start transmitting the packet, and then continuously transmitting the packet to the receiving node of the packet at the fastest speed.
The 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 invention has the beneficial effects that:
1. the invention can still transmit the packet when the channel is busy, thereby improving the channel utilization rate and the network throughput. On one hand, the method ensures that the existing transmission link is not influenced, and on the other hand, the method ensures that a new receiving node can correctly receive the packet sent by the sending node.
2. The present invention utilizes hardware interrupts to synchronize the time at which a node sends a packet. The synchronization mode not only can not bring extra synchronization overhead to the network, but also improves the utilization rate of the channel and the throughput of the network.
The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.
Drawings
FIG. 1 is a flow chart of an implementation of the present invention.
Fig. 2 is a diagram illustrating a standard frame format of IEEE802.14.5.
Fig. 3 is a schematic diagram illustrating the level change of the SFD pin when the node receives and transmits packets.
FIG. 4 is a flow chart of a node sending a packet
Fig. 5 is a schematic diagram of a typical two mutually interfering concurrent transmission link network with 4 nodes.
Fig. 6 is a graph of experimental results in an example scenario.
Detailed Description
The invention is described in detail below with reference to the figures and examples.
As shown in fig. 1, a method for nodes to concurrently transmit data in a wireless sensor network includes the following steps:
(1) the sending node loads the packet to be transmitted into a sending cache, closes the address recognition function and turns to the step (2);
(2) the transmitting node listens to the channel for a period of time and analyzes the results of the listening to the channel. If the sensed result shows that the channel is idle, continuously sending packets to the receiving node of the channel; if the channel is busy and the packet is not received, randomly carrying out backoff 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) the transmission packet at the synchronization node invokes a gating command to start transmitting the packet at the SFD falling edge interrupt generated at the node.
In this embodiment, the step (2) specifically includes:
(21) the node periodically detects a CCA pin and judges whether a channel is idle;
(22) the node records the packets sent by other nodes received in the period of the interception channel and extracts the source node number of the packet; wherein steps (21) (22) are performed simultaneously; turning to the step (23) after the channel monitoring is finished;
(23) if the CCA pin is detected at least once, the channel is busy, and no packet is received, the channel is busy, and the channel is monitored again after a period of random backoff; otherwise, turning to the step (3).
In this embodiment, the step (4) specifically includes:
(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 field) of a receiving cache generated by the packet;
(42) and (4) judging whether the source address information in the step (41) is equal to the number of the synchronous node recorded in the step (3), if so, calling a gating command at the SFD falling edge interruption position generated at the node of the packet to start transmitting the packet, and then continuously transmitting the packet to the receiving node of the packet 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 provided to illustrate the present invention, but are not intended to limit the scope of the invention.
The invention is suitable for the wireless sensor network. The sensor nodes mostly adopt a unicast mode when transmitting data, namely, each sending node corresponds to one receiving node. The sensor node has two address identification functions, namely software address identification and hardware address identification. And will be correctly received by the destination node if and only if both packet hardware and software address identifications pass. Packets sent by the nodes all conform to the standard frame format of IEEE802.15.4. The standard frame lattice schematic diagram refers to fig. 2, which includes five parts, namely a synchronization header SFD, a physical layer protocol header, an MAC protocol payload and an MAC protocol trailer, wherein the synchronization header includes a preamble sequence and a real sequence of a frame; the physical layer protocol header contains the frame length; the MAC protocol head comprises a frame control field, a data sequence number and address information; the MAC protocol load comprises a frame load; the MAC protocol tail contains the content of a frame detection sequence. When receiving the packet, the sensor node firstly goes through the packet synchronization process, and once a certain packet is successfully synchronized, no other packet is synchronized until the synchronization is finished.
SFD (Start of Frame Delimiter) is the IEEE802.15.4 Frame start delimiter. As shown in fig. 3, when the SFD domain of the sensor node to transmit and receive the packet has transmitted and received, the SFD signal changes from low to high and continues until the packet is completely transmitted and received. SFD hardware capture is the capture of an SFD signal by hardware. When the level of the SFD changes, an interrupt function in an upper layer program is triggered, and a timestamp of the SFD level change moment can be obtained in the upper layer function. SFD hardware capture eliminates transmission delays and processing delays of the communication process because hardware capture of the time stamp of the interrupt record does not involve software capture of the time of the record time stamp. If the propagation delay is negligible, the time stamps of the SFD pin level changes of the transceiving nodes can be considered to be at the same time. That is, in fig. 3, the SFD pin levels of the transmitting node and the receiving node are transitioned at the same time.
Each sensor node in the network is provided with two cache regions for sending and receiving data, namely a sending cache and a receiving cache. As shown in fig. 4, when a sensor node needs to send a packet, the packet needs to be loaded into a sending buffer first, and then a sending gating command is called to send the packet out. Through experimental measurement, the following results are found: the time required to load a packet into the transmit buffer is greater than the time required for the packet to be transmitted from the transmit buffer to the channel. Therefore, the time actually required for a sensor node to transmit a packet is often more than twice the packet transmission delay.
Example (b):
fig. 5 is a network of concurrent transmissions of an exemplary interfering link. As shown in FIG. 5, two mutually interfering links l1＝S1,R1、l2＝S2,R2. Wherein the node S1S2Need to be directed to the nodes R respectively1 R 250 packets are sent consecutively. Node S1First a packet needs to be sent, 100 ms later, the node S2A packet needs to be sent.
The specific steps of the present invention will be described with reference to FIG. 1.
Node S1The node address identification function is first turned off, and the CCA is periodically detected 50 milliseconds after the channel is monitored. After the channel is intercepted, because no node transmits the packet, the result that the channel is idle is obtained, and the node S1Immediately starts to move to the node R at the fastest speed1The packets are transmitted continuously. After 50 milliseconds, the same node S1Node S2The node address identification function is first turned off and listening to the channel is started 50 ms later. At node S2During the listening channel time, it receives the node S1A transmitted packet. Node S2After the channel interception is finished, at least half of the detection channel results are obtained and displayed as the idle channel, and the node S2Only receive node S1A transmitted packet. Thus the current channel, only node S1A packet is being sent. Node S2Set the FIFOP threshold required for reception to 5 while letting node S1Set as the synchronization node. After that, the node S2A packet is received and the source node number of the packet is read from the receiving buffer at the fifo break caused by the packet, knowing that the source node number is S1. The transmit strobe command is invoked at the SFD falling edge interrupt generated by the packet to transmit the packet.
Fig. 6 is an experimental result in the scenario of fig. 5, where the abscissa represents the length of a packet transmitted by the transmitting node and the ordinate is the throughput of the system. As can be seen from fig. 6, the system throughput of the two links in the case of concurrent transmission obtained by using the present invention is twice as high as the system throughput of a single link in the case of no interference.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined 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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| US7065376B2 (en) * | 2003-03-20 | 2006-06-20 | Microsoft Corporation | Multi-radio unification protocol |
| CN102387602A (en) * | 2011-11-23 | 2012-03-21 | 南京航空航天大学 | Efficient wireless ad hoc network concurrent transmission method for avoiding conflict |
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