CN113810951B - LoRaWAN anti-collision method based on sector-shaped average division - Google Patents
LoRaWAN anti-collision method based on sector-shaped average division Download PDFInfo
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- CN113810951B CN113810951B CN202111009640.5A CN202111009640A CN113810951B CN 113810951 B CN113810951 B CN 113810951B CN 202111009640 A CN202111009640 A CN 202111009640A CN 113810951 B CN113810951 B CN 113810951B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W28/00—Network traffic management; Network resource management
- H04W28/02—Traffic management, e.g. flow control or congestion control
- H04W28/04—Error control
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- H—ELECTRICITY
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- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W72/00—Local resource management
- H04W72/04—Wireless resource allocation
- H04W72/044—Wireless resource allocation based on the type of the allocated resource
- H04W72/0446—Resources in time domain, e.g. slots or frames
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/16—Gateway arrangements
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
The invention relates to a LoRaWAN anti-collision method based on sector equipartition, which is characterized in that after communication is started, when the time slot number reaches 256, the number of terminal nodes in the communication range with the gateway as the center and the radius not more than 7500 meters is determinednIf (3)nNot more than 354, fan-shaped grouping is not adopted; if it isnIn 354, dividing the communication range into N equal sector areas centered on the gateway, wherein the terminal nodes in each area are a group, and N sector groups are total; then starting the 1 st group of communication, setting the initial data frame length, randomly selecting the time slot in the frame by the terminal node, and sending a signal to the gateway in the communication range; judging the time slot type in each frame and whether the gateway successfully receives the data packet, determining the time slot state, estimating the number of the remaining terminal nodes according to the determined time slot state, and dynamically adjusting the optimal time slot number in the next round of frames; and then carrying out group 2 communication until the N group is completed. The invention improves the communication efficiency of the system and improves the delivery rate and throughput rate of the data packet.
Description
Technical Field
The invention relates to a dynamic frame time slot anti-collision method, in particular to a LoRaWAN anti-collision method based on sector-shaped average division.
Background
The LoRa communication technology is an Internet of things communication technology facing a long-distance wide-coverage application scene, is mainly applied to a physical network, and has the characteristics of low power consumption and long transmission distance. Despite the wide range of applications of LoRa, certain limitations remain. LoRaWAN is used as a MAC layer protocol of LoRa communication technology, and provides a building standard for communication. The channel access of the terminal equipment in the LoRaWAN is realized through a pure Aloha mechanism, so that thousands of equipment can randomly access the channel without detecting the channel state, and the probability of collision of data packets is increased. Therefore, the problem of channel collision of the LoRaWAN is particularly remarkable.
Aiming at the problem of collision of multi-node data packets in LoRa communication, time slot allocation is proposed for the data packets of the nodes, and retransmission time slots can be utilized when data transmission fails, so that the packet loss rate is reduced, and the delivery rate of the data packets is improved. However, the prior art does not solve the problems of time slot waste and deterioration of system stability caused by a great increase in the number of time slots due to the increase of terminal devices.
Disclosure of Invention
The invention aims to provide a LoRaWAN anti-collision method based on sector-shaped average division, which aims to solve the problems of time slot waste and poor system stability caused by great increase of the number of time slots in a communication range.
The invention is realized in the following way: a LoRaWAN anti-collision method based on sector-shaped average division comprises the following steps:
a. when the number of time slots reaches 256 at the beginning of communication, determining the number n of terminal nodes in a communication range with the gateway as the center and the radius not larger than 7500 meters, and if n is smaller than or equal to 354, not adopting sector grouping; if N & gt 354, dividing the communication range into N equal sector areas with the gateway as the center, wherein the terminal nodes in each sector area are a group, and N sector groups are all arranged;
b. communication of the 1 st sector packet, setting initial data frame length, randomly selecting time slots in a frame by a terminal node, and sending signals to gateways in a communication range;
c. judging whether the time slot type and gateway in each frame successfully receive the data packet: if the reception is successful, the time slot is successful; if the reception is not successful, distinguishing a collision time slot from an idle time slot through CAD detection; if the CAD only detects the preamble of the data packet but fails to successfully receive the data packet, determining that the CAD is a collision time slot; if the CAD does not detect the preamble of the data packet, determining to be an idle time slot;
d. estimating the number of the remaining terminal nodes according to the determined state of the time slot, and dynamically adjusting the optimal number of the time slots in the next round of frames; c, converting the successfully transmitted terminal node into a dormant state, retransmitting the data packet with time slot collision in the next frame, and returning to the step c;
e. and (c) repeating the steps b to d after the communication of the 1 st sector group is completed, and carrying out the communication of the 2 nd sector group until the N th sector group is completed, thereby completing the communication of all sector groups in the communication range.
Further, the dynamic adjustment mode of the time slot in the step d is as follows: the number n of predicted terminal nodes is 2.39 times the number of slots in the frame of the previous round.
Aiming at the situation that the LoRa network is easy to collide with data when the number of the terminal devices is large, the invention equally groups the terminal nodes in the gateway communication range according to the number, so that the number of the communication terminal devices in each area is reduced, and an improved Aloha algorithm is respectively used in each group, thereby achieving the effect of reducing the number of the terminal devices, and then the time slot number is optimized after the number of the rest terminal devices which are predicted and regulated is obtained by a time slot regulating method, so that the purpose of high-efficiency communication of the terminal devices is realized.
Because the probability of collision of the data packets in the LoRa communication network is proportional to the number of the terminal nodes, the LoRa network has the characteristics that the smaller the number of the terminal nodes is, the higher the delivery rate of the data packets is, the higher the throughput rate is and the smaller the probability of collision of the data packets is. Therefore, when the terminal nodes reach a certain number, all the terminal nodes in the gateway communication range are equally divided and grouped, so that the number of the terminal nodes in each group is smaller, and the purposes of improving the system communication efficiency and the data packet delivery rate and the throughput rate can be achieved by respectively communicating the terminal nodes in each group.
The calculation basis of the grouping critical of the sector grouping of the terminal node in the invention is as follows:
the ratio of successful time slots in each frame to total time slots, the system throughput rate is denoted by S:
the formula for obtaining the time slot number T and the terminal node number n after deriving the system throughput rate S and obtaining the extremum is as follows:
when the time slot number T of the system is basically equivalent to the terminal node number n and the terminal node number n is far greater than 1, the throughput rate S of the system reaches an extremum, and the calculation formula of the optimal frame value is as follows:
as can be seen from the formula (3), when the number of time slots T is approximately equal to the number of terminal nodes n, and the number of terminal nodes n is much greater than 1, the system throughput rate S reaches an extreme value.
Therefore, the system throughput rate obtained by two adjacent slot numbers T is equal. Substituting two adjacent time slot numbers T into a system swallowing formula (1) to obtain the number n of terminal nodes corresponding to the time slot numbers T, and further obtaining a grouping critical point:
when the number of slots T is 256 (T max =256), the maximum number of terminal nodes n max Taking n=354; when the number n of the terminal nodes is less than or equal to 354, no grouping is adopted; when n & gt 354, then fan-grouping of end nodes within communication range is required. As can be seen from table 1, the relationship between the number of slots T after fan-grouping the terminal nodes and the number of packets N corresponding thereto.
Table 1: number of packets corresponding to number of slots
The calculation basis of the dynamic adjustment of the time slot in the step d is as follows:
with prediction result n of the x-th round (x) Adjustment result n with the x-th round TZ(x) Subtracting the theoretical error value delta i The method comprises the following steps:
Δ＝n (x) -n TZ(x) ＝ξT e(x-1) -2.39T e(x) (6)
wherein T is e(x) For the number of collision time slots of the wheel, T e(x-1) And xi is the estimated weight value for the number of collision time slots of the previous round.
For theoretical error value delta i The square of (a) carries out derivative operation on the estimated weight value xi, and the estimated weight value xi can be obtained by making the minimum value equal to 0 after obtaining the minimum value, namely:
according to the prediction weight value xi, the number n of the terminal nodes predicted in the next round can be obtained (x+1) ：
The invention carries out equal sector grouping on the terminal equipment in the gateway communication range according to the sector area, and carries out dynamic estimation and optimal time slot adjustment on the terminal equipment in each group, thereby solving the problems of low PDR (packet delivery rate) and poor throughput performance of the network caused by the increase of the terminal equipment. According to the invention, simulation experiments are carried out on a single gateway LoRa network of 2000 terminal equipment, and the result shows that when the number of the terminal equipment is 2000, compared with a standard LoRaWAN, the PDR is improved by 51.27%, and the throughput rate is improved by 26.93%. Compared with the DFSA algorithm, the anti-collision method has the advantages that the throughput rate is improved by 20.23%, the total time slots of the anti-collision method are 2947, the total time slots of the DFSA are 20573, and the number of time slots is greatly reduced, so that the expansibility and the reliability of the LoRa network are improved.
Drawings
Fig. 1 is a schematic diagram of sector partition within the communication range of a gateway.
Fig. 2 is a flowchart of the anti-collision method of the present invention.
Fig. 3 is a graph comparing packet delivery rates of the present invention with Aloha algorithm and DFSA algorithm.
Fig. 4 is a graph comparing throughput rates of the present invention with Aloha algorithm and DFSA algorithm.
Fig. 5 is a graph of the number of slots of the present invention compared to Aloha algorithm and DFSA algorithm.
Detailed Description
The invention will be described in detail below with reference to the drawings and the detailed description.
The invention can use Ubuntu18.04 operating system, NS-3 (version 3.29) and C++ language for the simulation assessment of network performance.
As shown in fig. 2, the working flow of the lorewan anti-collision method based on sector division of the invention is as follows:
the first step: when the number of time slots reaches 256 at the beginning of communication, determining the number n of terminal nodes in a communication range with a radius of 7500 meters by taking a gateway as a center, and if n is less than or equal to 354, not adopting sector grouping; if N & gt 354, the communication range is divided into N equal sector areas centered on the gateway, and the terminal nodes in each sector area are grouped together into N sector groups (figure 1).
And a second step of: and 1 st sector grouping communication, setting the initial data frame length, randomly selecting the time slot in the frame by the terminal node, and sending signals to the gateways in the communication range.
And a third step of: judging whether the time slot type and gateway in each frame successfully receive the data packet: if the reception is successful, the time slot is successful; if the reception is not successful, distinguishing a collision time slot from an idle time slot through CAD detection; if the CAD detects the preamble of the data packet but does not successfully receive the data packet, determining the collision time slot; if the CAD does not detect the preamble of the data packet, it is determined to be an idle slot.
Fourth step: estimating the number of the remaining terminal nodes according to the determined state of the time slot, and dynamically adjusting the optimal number of the time slots in the next round of frames; and the terminal node which is successfully transmitted is converted into a dormant state, the data packet which is subjected to time slot collision is retransmitted in the next frame, and then the third step is returned to continue to execute.
Fifth step: and after the communication of the 1 st sector group is completed, repeating the second step to the fourth step, and carrying out the communication of the 2 nd sector group until the N th sector group, so as to complete the communication of all sector groups in the communication range.
The simulation process of the invention realizes the LoRa network establishment of Class A, wherein the gateway takes an SX1301 chip as an example, and the terminal node takes an SX1278 chip as an example. All terminal nodes in the application scene are placed in a round area with a radius of 7.5km by taking a gateway as a circle center according to poisson distribution. The terminal node placement height is 1.2 meters, and the gateway placement height is 15 meters. The transmission time of the periodic data packet is 300 seconds. The parameters of the simulation are shown in table 2.
Table 2: simulation parameter list
The simulation adopts a star topology structure of a single gateway, and all terminal nodes adopt the same parameters. And taking the PDR, the throughput rate and the total time slot number as evaluation indexes of experimental results.
The PDR represents the specific gravity of the gateway received data packets to the total data packets.
Throughput rate represents the ratio of the number of terminal nodes that can successfully communicate in a frame to the total number of time slots.
The total number of time slots represents the number of time slots used in the communication process.
In order to avoid accidental errors of experimental result data caused by a random transmission process, the experimental data are average values of ten times of data in stable transmission.
As can be seen from fig. 3, the increase of the number of terminal nodes leads to a sharp drop in PDR of the LoRa network based on pure Aloha, whereas the drop trend is more gentle based on DFSA and the PDR of the present invention, which are 23.75% and 51.27% higher than the LoRa wan of pure Aloha, respectively, in the scenario where the number of terminal nodes is up to 2000.
As can be seen from the throughput rate extremum of fig. 4, the present invention reaches 42.8% of the maximum value at 500 terminal nodes; when the number of the DFSA is 300, the throughput rate reaches the maximum value of 36.4%; the LoRaWAN reached a maximum throughput of 18.4% at 100 devices. The invention adopts the concept of sector grouping, combines the collision time slot number of the frame and the last frame, dynamically modifies the prediction weight after the time slot number of each round is updated, and changes the time slot number, thereby improving the throughput rate. When the number of the terminal nodes reaches 800, the throughput rate of the invention is still stable at about 32%. When the number of end nodes reaches 2000, the throughput rates of the invention, DFSA and LoRaWAN are 32.56%, 12.33% and 5.63%, respectively.
As can be seen from fig. 5, when the number of terminal nodes is 400, the number of slots consumed by the DFSA increases sharply. When the number of terminal nodes reaches 2000, the total number of slots of the present invention is 2947, and the total number of slots of the DFSA is 20573. As can be seen, the invention performs sector grouping on the total number of the terminal nodes according to the relation between the number of the time slots and the number of the terminal nodes, so that each group of terminal nodes is communicated, thereby effectively inhibiting the increase of collision time slots, saving the number of the time slots and the communication time, and obviously improving the performance over the DFSA.
Claims (2)
1. A LoRaWAN anti-collision method based on sector-shaped average division is characterized by comprising the following steps:
a. when the number of time slots reaches 256 at the beginning of communication, determining the number of terminal nodes in the communication range with the gateway as the center and the radius not more than 7500 metersnIf (3)nNot more than 354, fan-shaped grouping is not adopted; if it isnIn 354, dividing the communication range into N equal sector areas centered on the gateway, wherein the terminal nodes in each sector area are a group, and N sector groups are total;
b. communication of the 1 st sector packet, setting initial data frame length, randomly selecting time slots in a frame by a terminal node, and sending signals to gateways in a communication range;
c. judging whether the time slot type and gateway in each frame successfully receive the data packet: if the reception is successful, the time slot is successful; if the reception is not successful, distinguishing a collision time slot from an idle time slot through CAD detection; if the CAD only detects the preamble of the data packet but fails to successfully receive the data packet, determining that the CAD is a collision time slot; if the CAD does not detect the preamble of the data packet, determining to be an idle time slot;
d. estimating the number of the remaining terminal nodes according to the determined state of the time slot, and dynamically adjusting the optimal number of the time slots in the next round of frames; c, converting the successfully transmitted terminal node into a dormant state, retransmitting the data packet with time slot collision in the next frame, and returning to the step c;
e. and (c) repeating the steps b to d after the communication of the 1 st sector group is completed, and carrying out the communication of the 2 nd sector group until the N th sector group is completed, thereby completing the communication of all sector groups in the communication range.
2. The method for preventing a clash of a LoRaWAN based on sector division according to claim 1, wherein the dynamic adjustment mode of time slots in the step d is as follows: predicted number of terminal nodesnIs 2.39 times the number of slots in the frame of the previous round.
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