CN111586791A - Multi-domain cooperative multiple access method for star wireless sensor network - Google Patents
Multi-domain cooperative multiple access method for star wireless sensor network Download PDFInfo
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Abstract
The invention discloses a multi-domain cooperative multiple access method of a star-type wireless sensor network, which comprises the following steps: placing a sink node at the central position of a sensor node of an area to be monitored; dividing an area to be monitored into m sectors by taking a sink node as a center, and dividing sensor nodes in each sector into a group; dividing a total frequency band used by the star-type wireless sensor network into m sub-channels, wherein each sub-channel occupies a frequency band of 125kHz and is spaced by 25kHz, and each group of sensor nodes located in the same sector is allocated with an independent sub-channel; in each determined group, dividing the sensor nodes into n layers according to the link quality from the sensor nodes to the sink node, and distributing different spreading factors to the sensor nodes in each layer; and adopting carrier sense multiple access in the same group of same-layer sensor nodes with the same physical layer parameters, sensing the channel state through a channel occupancy detection mechanism, uploading data if the channel is idle, otherwise, detecting the channel state after time delay, and completing data uploading until the channel is idle.
Description
Technical Field
The invention relates to the technical application field of Internet of things equipment and wireless sensor networks, in particular to a multi-domain collaborative multiple access method of a star-type wireless sensor network.
Background
The wireless sensor network is a network formed by a large number of randomly distributed low-cost micro sensor nodes in a self-organizing manner through wireless communication, environmental information is sensed in a specific area, data are collected and processed, and finally the environmental information is uploaded to a monitoring center, so that unmanned monitoring of the specific area is achieved. The wireless sensor network is widely applied and relates to the fields of environmental monitoring, intelligent home, medical health, military investigation and the like. But have not been deployed on a large scale in commercial applications due to limitations in wireless communication technology and application costs. The early wireless sensor network adopts short-distance communication technologies such as Bluetooth, WiFi, ZigBee and narrow-band radio, and the network coverage is limited, so that the application requirements cannot be met. Since a wireless sensor network based on 3G, LTE, NB-IoT technology is appeared later, long-distance communication can be achieved, but relay transmission needs to be performed by means of an operator base station, power consumption and deployment cost are greatly increased, and the wireless sensor network cannot be widely used. Therefore, a wireless communication technology with low power consumption, long transmission distance and low cost is needed, and the appearance of the lora (long range) communication technology can solve the above problems to a certain extent, and has a wide application prospect.
The LoRa technology is a typical technology for low-power consumption, long-distance wireless communication. The method adopts a Chirp Spread Spectrum (CSS) modulation technology, and utilizes a sinusoidal pulse signal with the frequency changing linearly in the whole bandwidth range to transmit information. The information "1" is represented by a linear increase (Up-Chirp) of the frequency in the bandwidth range, and the information "0" is represented by a decrease (Down-Chirp) of the frequency in the bandwidth range. Meanwhile, the spread spectrum modulation technology can be configured to use different spread spectrum sequences, and signals modulated based on the different spread spectrum sequences are mutually orthogonal. In addition, the LoRa communication is built in with a forward error correction coding technology, so that the code rate can be set in a user-defined mode, and the sudden interference can be responded.
Due to the above characteristics of the LoRa communication technology, the LoRa has the following advantages over other communication technologies: firstly, the communication sensitivity can reach-148 dBm, the single-hop transmission distance of 10km can be realized, the power consumption is extremely low, and the service life can reach 8 years under the condition of power supply of a lithium battery. Secondly, a special spread spectrum modulation technology is adopted, and the influence caused by crystal oscillator drift and Doppler frequency shift can be effectively resisted. Thirdly, the built-in forward error correction coding technology with the self-defined set code rate can resist the sudden interference to a certain degree and correct the error data packet. In addition, the LoRa operates in an ism (industrial Scientific medical) unlicensed frequency band, and can be applied to various scenarios. Finally, the network adopts a star topology structure, the complexity is lower than that of a mesh topology structure, the deployment is easy, massive nodes can be accessed, and a stable, safe and low-maintenance-cost wireless sensor network can be provided by means of a LoRaWAN protocol established by a LoRa alliance.
The single-hop transmission distance of the LoRa is long, and the coverage range of the wireless sensor network based on the LoRa is wide, so that more sensor node devices need to be deployed in a monitoring area. When more and more sensor nodes are accessed to the network, the channel occupancy rate is greatly improved, and the node collision probability is increased accordingly. When multiple nodes simultaneously occupy channels for data transmission, transmission conflicts can be generated, communication interference among the nodes is caused, link quality is reduced, and link reliability cannot be guaranteed. And the link quality reduction can cause the frequent retransmission of the nodes, which in turn aggravates the channel congestion and the network performance is rapidly deteriorated. Therefore, the research on the wireless sensor network multiple access technology avoids node collision, and has important significance for improving the quality of a communication link of the wireless sensor network and promoting the application of the wireless sensor network in an intensive monitoring scene.
In the process of implementing the invention, the inventor finds that the prior art and the system have the following disadvantages and shortcomings:
(1) the physical layer parameters of each sensor node in the LoRa wireless sensor network are configured consistently, and the physical layer parameters of each node cannot be configured differently according to actual demands, so that the problems of inter-node interference, communication resource waste and the like are caused.
(2) When a large number of sensor nodes exist in the LoRa wireless sensor network, the situation that a plurality of nodes upload data simultaneously occurs, so that collision between the nodes is caused, packet loss rate and packet error rate are increased, and finally, the performance of the wireless sensor network is poor.
Disclosure of Invention
The invention provides a multi-domain collaborative multiple access method for a star wireless sensor network, which improves the number of nodes of an LoRa wireless sensor network and is described in detail in the following description:
a multi-domain cooperative multiple access method of a star-type wireless sensor network comprises the following steps:
1) in the star-type wireless sensor network, a sink node is placed at the central position of a sensor node in an area to be monitored;
2) dividing an area to be monitored into m sectors by taking a sink node as a center, and dividing sensor nodes in each sector into a group;
3) dividing a total frequency band used by the star-type wireless sensor network into m sub-channels, wherein each sub-channel occupies a frequency band of 125kHz, each sub-channel is separated by 25kHz, and each group of sensor nodes located in the same sector is allocated with an independent sub-channel;
4) in each determined sensor node group, dividing the sensor nodes into n layers according to the link quality from the sensor nodes to the sink node, and distributing different spreading factors to the sensor nodes in each layer;
5) adopting carrier sense multiple access in the same group of sensor nodes with the same physical layer parameters, sensing the channel state through a channel occupation detection mechanism, uploading data if the channel is idle, otherwise, detecting the channel state after the channel is occupied and delaying, and finishing data uploading until the channel is idle;
wherein, the step 3) is specifically as follows:
(3.1) setting the bandwidth of each subchannel to be 125kHz, setting the channel interval to be 25kHz, and setting the frequency point interval of each subchannel to be 150 kHz;
(3.2) setting the frequency point of the 1 st sub-channel as (F)base+1 × 0.15) MHz, with the 2 nd subchannel frequency bin set to (Fbase+2 × 0.15) MHz, and so on, the frequency bin for the m-th sub-channel is set to (F)base+m×0.15)MHz，FbaseIs a working frequency point;
(3.3) allocating an independent sub-channel to each of the m groups of sensor nodes to realize frequency division multiple access of each group of sensor nodes;
wherein, the step 4) is specifically as follows:
(4.1) based on the received signal strength value RssiEvaluating link quality from the sensor node to the sink node when RssiWhen the spread spectrum factor of the sensor node is more than or equal to-100 dBm, setting the spread spectrum factor of the sensor node to be 7;
when-103 dBm is less than or equal to RssiWhen the spread spectrum factor of the sensor node is less than-100 dBm, the spread spectrum factor of the sensor node is set to be 8;
when-106 dBm is less than or equal to RssiWhen < -103dBm, the spreading factor is set to 9;
when-109 dBm is less than or equal to Rssi-106dBm, the spreading factor is set to 10;
when-112 dBm is less than or equal to Rssi-109dBm, the spreading factor is set to 11;
when R isssiWhen < -112dBm, the spreading factor of the sensor node is set to be 12;
and (4.2) dividing the nodes with the same spreading factor in each group of sensor nodes into the same layer according to the distributed values of the spreading factors, setting the spreading factor of the sensor node at the 1 st layer to be 7, setting the spreading factor of the sensor node at the 2 nd layer to be 8, and so on, setting the spreading factor of the sensor node at the 6 th layer to be 12, thereby completing the layering of the nodes in the group.
Wherein, the step 5) is specifically as follows:
(5.1) starting channel activity detection in the sensor nodes for the same group of sensor nodes with the same physical layer parameters;
(5.2) the sensor node finishes information acquisition and samples the wireless signal in the current sub-channel when data uploading is needed;
(5.3) processing the wireless signals in the sub-channels, and comparing and matching the wireless signals with the effective preamble signals;
and (5.4) if the matching is unsuccessful, the node uploads the data, otherwise, the node delays and waits until the channel is idle to upload the data.
The technical scheme provided by the invention has the beneficial effects that:
1. the wireless sensor network of the star-shaped topological structure is realized based on the LoRa technology, the transmission distance between the sensor nodes and the sink nodes is effectively increased, the network structure is simple, and compared with the existing mesh and tree-shaped wireless sensor networks, the wireless sensor network of the star-shaped topological structure has the advantages that the network coverage is enlarged, the realization is easier, and the network maintenance cost is low;
2. according to the LoRa-based star wireless sensor network, the sink node comprises a plurality of paths of radio frequency front ends, and the design based on the SX130X radio frequency chip can demodulate signals under a plurality of channels and a plurality of spreading factors at the same time, so that concurrent communication can be realized, and the network throughput is increased;
3. according to the invention, the sensor nodes are divided into a plurality of groups according to the positions of the sensor nodes, each group of sensor nodes is distributed with independent channels, and each channel is distributed at different frequency points, so that the same frequency interference among the sensor nodes of each group is avoided;
4. in each sensor node group, the link quality is evaluated according to the RSSI of a data packet, if the RSSI is larger, the link quality is good, a smaller spread spectrum factor is distributed and selected, the transmission rate is accelerated, and the power consumption is reduced; if the RSSI is smaller, the link quality is not reliable, and the communication performance is improved by allocating a larger spread spectrum factor, so that the network resource allocation is optimized, the interference among the sensor nodes in the group is reduced, the power consumption and the communication performance are balanced, and the service life of the wireless sensor network is prolonged;
5. the invention introduces a channel occupation detection mechanism aiming at the sensor nodes with the same physical layer parameter configuration, can effectively avoid the sensor nodes with the same physical layer parameter from uploading data at the same time, reduces the communication collision probability of the sensor nodes and enhances the reliability of data uploading.
Drawings
FIG. 1 is a block diagram of a multi-domain cooperative multiple access method of a star-type wireless sensor network according to the present invention;
fig. 2 is a schematic diagram of sink node positions of a LoRa wireless sensor network;
FIG. 3 is a flowchart of the operation of the channel occupancy detection mechanism;
FIG. 4 is a schematic diagram of a grouping method of sensor nodes;
FIG. 5 is a schematic diagram of a hierarchical approach to sensor nodes;
fig. 6 is a flow chart of channel sensing based on preamble detection;
FIG. 7 is a schematic diagram of a test scenario according to an embodiment of the present invention;
fig. 8 is a graph comparing packet loss rates of a random multiple access method and a multi-domain cooperative multiple access method;
fig. 9 is a packet error rate comparison graph of the random multiple access method and the multi-domain cooperative multiple access method.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.
In order to overcome the defects and shortcomings of the prior art and the prior system, the invention provides a multi-domain cooperative multiple access method of a star-type wireless sensor network, which is used for solving the problem of node collision of the existing LoRa wireless sensor network. In the method, the positions of sink nodes are determined according to the distribution condition of sensor nodes in an area to be monitored; secondly, combining space division multiple access and frequency division multiple access methods, dividing all the sensor nodes into a plurality of groups according to the relative convergent node directions of the sensor nodes, and allocating an independent sub-channel to each group to avoid co-channel interference among the nodes; thirdly, layering the sensor nodes in the same group according to the link quality from the nodes to the aggregation center, wherein different spreading factors are set in each layer and are used for inhibiting communication interference among the sensor nodes in the same group; and finally, introducing a carrier sense multiple access technology into the same group of same-layer sensor nodes with the same physical layer parameter configuration, and avoiding communication collision between the nodes through a channel occupation detection mechanism based on lead code detection.
The technical idea of the invention is as follows: firstly, determining the positions of the aggregation nodes according to the distribution of the sensor nodes in the area to be monitored. Secondly, combining space division multiple access and frequency division multiple access methods, dividing all the sensor nodes into a plurality of groups according to the relative convergent node directions of the sensor nodes, and allocating an independent channel to each group to avoid co-channel interference between the nodes. And thirdly, layering the sensor nodes in the same group according to the link quality from the nodes to the aggregation center, and setting different spreading factors for each layer to inhibit communication interference among the sensor nodes in the same group. And finally, introducing a carrier sense multiple access technology into the same group of same-layer sensor nodes with the same physical layer parameter configuration, and avoiding communication collision between the nodes through a channel occupation detection mechanism based on lead code detection.
Example 1
The invention provides a multi-domain cooperative multiple access method of a star-type wireless sensor network, which specifically comprises the following steps of:
(1) in the star wireless sensor network, a sink node is placed at the center position of a sensor node in an area to be monitored, so that the distance between the sink node and each sensor node is within the coverage range of a single-hop communication distance; the single-hop communication distance is a term of technical skill in the art, and is not described in detail in the embodiments of the present invention.
(2) Taking a sink node as a center, dividing an area to be monitored into m sectors, dividing sensor nodes in each sector into a group, dividing the sensor nodes into m groups, wherein m is an integer greater than or equal to 1, and m is determined according to the number p of the sensor nodes, a sending time interval T and air transmission time T of a data packet1Determining;
wherein the content of the first and second substances,
(3) dividing a total frequency band used by the star-type wireless sensor network into m sub-channels, wherein each sub-channel occupies a frequency band of 125kHz, each sub-channel is separated by 25kHz, and each group of sensor nodes located in the same sector is allocated with an independent sub-channel;
that is, the number of subchannels is the same as the number of groups of sensor nodes.
(4) In each determined sensor node group, dividing the sensor nodes into n layers according to the link quality from the sensor nodes to the sink nodes, wherein the value of n is an integer value between 1 and 6, distributing different spreading factors to the sensor nodes of each layer, and distributing the spreading factors of 7 to 12 to the sensor nodes of each layer according to the link quality of the nodes from good to bad;
(5) adopting a carrier sense multiple access technology in the same group of sensor nodes with the same physical layer parameters, sensing the channel state through a channel occupation detection mechanism, if the channel is idle, the sensor node immediately uploads data, if the channel is occupied, the sensor node continuously detects the channel state after corresponding time delay, and the data uploading is finished until the channel is idle;
referring to fig. 3, a working flow of a channel occupancy detection mechanism includes steps of firstly, performing data processing after a sensor node acquires information, then opening a channel detection function to monitor a channel before data uploading, if a CadDone flag bit is not set, indicating that the channel is idle at the moment, immediately uploading data, if the CadDone flag bit is set, indicating that the channel is occupied, performing corresponding delay waiting on the sensor node, then performing channel interception again, until the channel is idle, completing data uploading, repeating channel interception detection for a maximum of N times, wherein the value of N is consistent with the number of sensor nodes in the same group and the same layer, preventing the sensor node from falling into channel detection and failing to stop when a transmission fault occurs, and if the channel is detected for N times continuously, indicating that the transmission fault occurs at the moment, terminating the data uploading.
The CadDone zone bit is the name of the register and can be used for judging the channel state, if the channel is in an idle state, the zone bit is '0', and if the channel is in an occupied state, the zone bit is '1'. In a specific implementation, other flag bits may also be used, which is not limited in this embodiment of the present invention.
(6) And (5) completing the establishment of the LoRa wireless sensor network according to the steps (1) to (5), and then enabling each sensor node to work according to the configuration.
The radio frequency front end of the sink node is designed on the basis of an SX1301 radio frequency chip, the sink node comprises 4 paths of radio frequency front ends, the C8051F120 single chip microcomputer completes initialization configuration of physical layer parameters through an SPI (serial peripheral interface), and wireless signals of various spreading factors can be received at the same time. The radio frequency front end of the sensor node is designed on the basis of an SX1278 radio frequency chip, and the C8051F120 single chip microcomputer completes initialization configuration of physical layer parameters through an SPI interface.
Wherein, the step (2) specifically comprises:
(2.1) determining the positions of the sink nodes in the area to be monitored, wherein the sensor nodes are all within the single-hop transmission distance range of the sink nodes;
(2.2) according to the number of the sensor nodes and the information acquisition period of the sensor nodes, dividing the sensor nodes into 4 groups in the reference model description, wherein m is 4, and the angle of each fan-shaped monitoring area is 90 degrees;
(2.3) referring to fig. 4, taking the sink node as a center, dividing the area to be monitored into a sector a, a sector B, a sector C and a sector D according to angles, dividing the nodes in each 90-degree sector monitoring area into the same group, wherein 4 groups are provided in total, and completely covering all sensor nodes around the sink node.
Wherein, the step (3) specifically comprises:
(3.1) determining the working frequency points of the sink node and the sensor node to be F according to the deployment condition of the practical application of the LoRa wireless sensor networkbase；
(3.2) setting the bandwidth of each subchannel to be 125kHz, setting the channel interval to be 25kHz, and setting the frequency point interval of each subchannel to be 150 kHz;
(3.3) setting the frequency point of the 1 st sub-channel as (F)base+1 × 0.15) MHz, with the 2 nd subchannel frequency bin set to (Fbase+2 × 0.15) MHz, and so on, the frequency bin for the m-th sub-channel is set to (F)base+m×0.15)MHz；
And (3.4) allocating an independent sub-channel to each of the m groups of sensor nodes to realize frequency division multiple access of each group of sensor nodes.
Wherein, the step (4) specifically comprises:
(4.1) in the dynamic network parameter configuration stage, each group of sensor nodes need to send detection data packets to the sink node, and the sink node records the received signal strength value R of the received detection data packetsssi；
(4.2) according to RssiEvaluating link quality from the sensor node to the sink node when RssiWhen the spread spectrum factor of the sensor node is more than or equal to-100 dBm, setting the spread spectrum factor of the sensor node to be 7;
when-103 dBm is less than or equal to RssiWhen the spread spectrum factor of the sensor node is less than-100 dBm, the spread spectrum factor of the sensor node is set to be 8;
when-106 dBm is less than or equal to RssiWhen < -103dBm, the spreading factor is set to 9;
when-109 dBm is less than or equal to Rssi-106dBm, the spreading factor is set to 10;
when-112 dBm is less than or equal to Rssi-109dBm, the spreading factor is set to 11;
when R isssiWhen < -112dBm, the spreading factor of the sensor node is set to be 12;
(4.3) referring to fig. 5, according to the allocated spreading factor values, dividing the nodes with the same spreading factor in each group of sensor nodes into the same layer, setting the spreading factor of the sensor node at the 1 st layer to 7, setting the spreading factor of the sensor node at the 2 nd layer to 8, and so on, setting the spreading factor of the sensor node at the 6 th layer to 12, thereby completing the layering of the nodes in the group.
Wherein, the step (5) specifically comprises:
(5.1) starting a channel activity detection function in the sensor nodes for the same group of sensor nodes with the same layer and the same physical layer parameters (frequency point, spreading factor and bandwidth);
(5.2) the sensor node finishes information acquisition and samples the wireless signal in the current sub-channel when data uploading is needed;
(5.3) processing the wireless signals in the sub-channels, and comparing and matching the wireless signals with the effective preamble signals;
(5.4) if the matching process is unsuccessful, the current channel is idle, the node immediately uploads data, if the matching is successful, the current channel is occupied, delay waiting is needed until the data are uploaded when the channel is idle;
referring to fig. 6, in a channel interception implementation process based on preamble detection, first, a frequency is locked to a frequency point of a channel used for communication transmission, an LoRa preamble is ready to be received, then, a receiver acquires an LoRa preamble symbol from the channel, a modem starts to analyze a received wireless signal, then, a sample signal acquired by the modem is compared with an ideal preamble waveform, if waveform association is successful, a CadDone setting signal is generated to represent that an effective preamble signal exists in the channel at this time, and if association is failed, it is indicated that no preamble signal exists in the channel at this time, preamble detection is continued;
and (5.5) the channel detection of the sensor nodes is repeated for N times at most, the numerical value of N is consistent with the quantity of the sensor nodes in the same group and layer, the sensor nodes can be prevented from falling into the channel detection and being incapable of stopping when the transmission fault occurs, if the channel is detected for N times continuously, the transmission fault occurs at the moment, and the data uploading is stopped.
In summary, the invention divides the sensor nodes into multiple groups according to the techniques of space division multiple access and frequency division multiple access, each group allocates sub-channels with independent frequency bands, and avoids the same frequency interference among the nodes of each group; then, the nodes in the group are further layered according to the link quality, and the spreading factors of the nodes in each layer are set differently, so that the node interference is reduced; and finally, introducing a channel occupation detection mechanism into the sensor nodes in the same group and layer, and further avoiding sending collision between the nodes.
Example 2
The invention provides a multi-domain cooperative multiple access method of a star-type wireless sensor network, which mainly takes indoor transmission of an LoRa wireless sensor network as an example and comprises the following steps:
(1) firstly, determining the positions of a sink node and a sensor node according to an indoor transmission scene of a LoRa wireless sensor network;
referring to fig. 7, a test scene is located in an experimental building, 8 sensor nodes S1, S2, S3, S4, S5, S6, S7, and S8 are respectively placed in corridor positions, and a sink node is placed in a laboratory at a middle position, so that each sensor node is ensured to be within a single-hop communication distance range of the sink node;
(2) in the embodiment, due to the limitation of indoor scenes and the number of the sensor nodes, the sensor nodes are divided into two groups, wherein S1-S4 are grouped into one group, S5-S8 are grouped into one group, and the sink node can cover 8 sensor nodes;
(3) the total frequency band of the wireless sensor network is divided into 2 sub-channels, each sub-channel occupies a frequency band of 125kHz, each sub-channel is separated by 25kHz, sensor nodes in each group of monitoring areas are allocated with an independent sub-channel, and the condition that frequency spectrums of each group of sensor nodes are overlapped is guaranteed not to be generated;
(3.1) determining the working frequency point F of the node according to the deployment condition of the actual wireless sensor networkbaseIs 433 MHz;
(3.2) setting the bandwidth of each subchannel to be 125kHz, setting the channel interval to be 25kHz, and setting the frequency point interval of each subchannel to be 150 kHz;
(3.3) the frequency point of the 1 st sub-channel is set to 433MHz, the frequency point of the 2 nd sub-channel is set to 433.15MHz, and the two sub-channels are divided due to the limitation of the number of nodes;
and (3.4) the 1 st group of sensor nodes adopt a 433MHz subchannel, and the 2 nd group of sensor nodes adopt an 433.15MHz subchannel, so that frequency division multiplexing of each group of sensor nodes is realized.
(4) Due to the limitation of experimental scenes and the number of sensor nodes, the sensor nodes are divided into 2 layers in the embodiment, the spreading factors of the sensor nodes S1, S2, S5 and S6 are set to be 7 as the layer 1, and the spreading factors of the sensor nodes S3, S4, S7 and S8 are set to be 8 as the layer 2;
(5) adopting a carrier sense multiple access technology in the same group of sensor nodes with the same physical layer parameters, sensing the channel state through a channel occupation detection mechanism, if the channel is idle, the node immediately uploads data, if the channel is occupied, the node continues to detect the channel state after corresponding time delay until the channel is idle and finishes uploading data;
(5.1) turning on the channel activity detection function of the sensor nodes S1, S2, S3, S4, S5, S6, S7, S8;
(5.2) sampling wireless signals in the current channel by each sensor node before uploading data;
(5.3) judging whether a CadDone register in the radio frequency chip is set or not;
(5.4) if the flag bit of the CadDone register is set, indicating that the channel is occupied at the moment, delaying for 150ms, then detecting the channel occupancy again, and if the flag bit of the CadDone register is not set, indicating that the channel is idle and immediately uploading data;
(5.5) in this embodiment, the number of the sensor nodes is small, so that there are only two sensor nodes in the same group and the same layer, and therefore, the number of times of channel activity detection is 2, and if it is detected that the channel is occupied twice, the data upload is terminated.
(6) And (5) completing the establishment of the LoRa wireless sensor network according to the steps (1) to (5), and then enabling each sensor node to work according to the configuration.
Example 3
In order to verify the performance of the multi-domain cooperative multiple access method of the star wireless sensor network, in the embodiment, the random multiple access technology is compared with, when the random multiple access technology is adopted, frequency points of 8 sensor nodes S1, S2, S3, S4, S5, S6, S7 and S8 are all set to be 433MHz, and a spreading factor is set to be 7, during experimental test, the number of the sensor nodes in the two methods is gradually increased from 1 until the 8 sensor nodes are accessed into the network, the sensor nodes randomly start to send data, the sending time interval is 150ms, a sink node records the data uploading packet loss rate and the packet error rate of the sensor nodes, and the performance of the two access methods is compared;
referring to fig. 8 and 9, when the random multiple access method is adopted, as the number of transmitting nodes increases, the packet loss rate increases from 0.0196 to 0.7562, and the packet error rate increases from 0.0231 to 0.1654; when a multi-domain cooperative multiple access method of the star wireless sensor network is adopted, the packet loss rate is increased from 0.0180 to 0.0322, and the packet error rate is increased from 0.0225 to 0.0341; therefore, with the increase of the number of the sending nodes, the packet loss rate and the packet error rate of the two multiple access methods are increased, and the communication performance is gradually deteriorated; however, the comparison result of the two methods shows that compared with the random multiple access method, the packet loss rate of the multi-domain cooperative multiple access method of the star-type wireless sensor network is reduced by 95.74% to the maximum, the packet error rate is reduced by 79.38% to the maximum, and the communication performance is superior to that of the random multiple access method.
In the embodiment of the present invention, except for the specific description of the model of each device, the model of other devices is not limited, as long as the device can perform the above functions.
Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (2)
1. A multi-domain cooperative multiple access method of a star-type wireless sensor network is characterized by comprising the following steps:
1) in the star-type wireless sensor network, a sink node is placed at the central position of a sensor node in an area to be monitored;
2) dividing an area to be monitored into m sectors by taking a sink node as a center, and dividing sensor nodes in each sector into a group;
3) dividing a total frequency band used by the star-type wireless sensor network into m sub-channels, wherein each sub-channel occupies a frequency band of 125kHz, each sub-channel is separated by 25kHz, and each group of sensor nodes located in the same sector is allocated with an independent sub-channel;
4) in each determined sensor node group, dividing the sensor nodes into n layers according to the link quality from the sensor nodes to the sink node, and distributing different spreading factors to the sensor nodes in each layer;
5) adopting carrier sense multiple access in the same group of sensor nodes with the same physical layer parameters, sensing the channel state through a channel occupation detection mechanism, uploading data if the channel is idle, otherwise, detecting the channel after time delay if the channel is occupied, and finishing data uploading until the channel is idle;
wherein, the step 3) is specifically as follows:
(3.1) setting the bandwidth of each subchannel to be 125kHz, setting the channel interval to be 25kHz, and setting the frequency point interval of each subchannel to be 150 kHz;
(3.2) setting the frequency point of the 1 st sub-channel as (F)base+1 × 0.15) MHz, with the 2 nd subchannel frequency bin set to (Fbase+2 × 0.15) MHz, and so on, the frequency bin for the m-th sub-channel is set to (F)base+m×0.15)MHz，FbaseIs a working frequency point;
(3.3) allocating an independent sub-channel to each of the m groups of sensor nodes to realize frequency division multiple access of each group of sensor nodes;
wherein, the step 4) is specifically as follows:
(4.1) based on the received signal strength value RssiEvaluating link quality from the sensor node to the sink node when RssiWhen the spread spectrum factor of the sensor node is more than or equal to-100 dBm, setting the spread spectrum factor of the sensor node to be 7;
when-103 dBm is less than or equal to RssiWhen the spread spectrum factor of the sensor node is less than-100 dBm, the spread spectrum factor of the sensor node is set to be 8;
when-106 dBm is less than or equal to RssiWhen < -103dBm, the spreading factor is set to 9;
when-109 dBm is less than or equal to Rssi-106dBm, the spreading factor is set to 10;
when-112 dBm is less than or equal to Rssi-109dBm, the spreading factor is set to 11;
when R isssiWhen < -112dBm, the spreading factor of the sensor node is set to be 12;
and (4.2) dividing the nodes with the same spreading factor in each group of sensor nodes into the same layer according to the distributed values of the spreading factors, setting the spreading factor of the sensor node at the 1 st layer to be 7, setting the spreading factor of the sensor node at the 2 nd layer to be 8, and so on, setting the spreading factor of the sensor node at the 6 th layer to be 12, thereby completing the layering of the nodes in the group.
2. The multi-domain cooperative multiple access method of the star-type wireless sensor network according to claim 1, wherein the step 5) specifically comprises:
(5.1) starting channel activity detection in the sensor nodes for the same group of sensor nodes with the same physical layer parameters;
(5.2) the sensor node finishes information acquisition and samples the wireless signal in the current sub-channel when data uploading is needed;
(5.3) processing the wireless signals in the sub-channels, and comparing and matching the wireless signals with the effective preamble signals;
and (5.4) if the matching is unsuccessful, the node uploads the data, otherwise, the node delays and waits until the channel is idle to upload the data.
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