KR20210070797A - Tdma mac operating method on communication system based low speed variable transmission - Google Patents

Abstract

The present invention relates to a time division multiple access (TDMA) media access control (MAC) operation method in a low-speed variable transmission rate-based communication system, capable of defining a repetition period of a super frame is based on 24 hours since a transmission period of sensing data is long due to characteristics of a low-speed low power wide area (LPWA) network, configuring a super frame in a set of frames in units of one hour and a frame in sub-frames in units of one minute, using a beacon of a sync time slot to maintain synchronization without using a PPS signal of GPS, providing a protocol so that a length of a data time slot to be operated variably according to a G/W and a distance, and performing scheduling of all time slots by the G/W, and broadcasting slot information by the G/W in each sub-frame. Therefore, the present invention has an effect of effectively increasing the battery life of a sensor node in collecting sensing information of the sensor node located at a long distance of 10 Km or more (LOS standard).

Description

TDMA MAC OPERATING METHOD ON COMMUNICATION SYSTEM BASED LOW SPEED VARIABLE TRANSMISSION}

The present invention relates to a TDMA MAC operation method in a low-speed variable transmission rate-based communication system, and more particularly, to effectively improve the battery life of a sensor node in collecting sensing information of a sensor node that exists at a long distance of 10Km or more (LOS basis). Low power/real-time information transfer function can be supported for systems that require accurate data transfer such as factory automation, and the wake-up and sleep times of sensor nodes can be precisely controlled by using the time division communication method in the LPWA network. It relates to a TDMA MAC operation method in a communication system based on a low-speed variable transmission rate that can extend the lifespan of a node.

In general, the awake time of the sensor node in a low-speed LPWA network is closely related to the battery life time.

The LPWA network defines a spreading factor whose distance is determined according to the transmission rate, and the data transmission distance is changed accordingly.

When a variable spreading factor according to the communication distance is applied, the efficiency is very low when the time division communication method having an equal timeslot is used.

In the LPWA network, the MAC method uses the CSMA/CA method.

A phenomenon occurs that the interval of data collected through G/W is variably changed according to the number of peripheral sensor nodes.

By using the CSMA/CA method, the waiting time and transmission error of the sensor node increase due to congestion caused by data transmission attempts between sensor nodes in a specific situation.

The increase in waiting time and transmission error is directly related to the battery life time of the sensor node, and the lifespan of the sensor node is significantly reduced.

Republic of Korea Patent Publication No. 1366362 - Communication method using energy-efficient TMDA protocol for hierarchical cooperative communication

It is an object of the present invention to provide a TDMA MAC operation method in a low-speed variable transmission rate-based communication system that can effectively increase the battery life of a sensor node in collecting sensing information of a sensor node that exists over a long distance (LOS basis) of 10Km or more. have.

It is an object of the present invention to provide a TDMA MAC operation method in a low-speed variable transmission rate-based communication system capable of supporting a low-power/real-time information transfer function in a system requiring accurate data transfer such as factory automation.

It is an object of the present invention to operate TDMA MAC in a communication system based on a low-speed variable transmission rate that can extend the lifespan of a sensor node by precisely controlling the wake-up and sleep times of a sensor node by using a time division communication method in an LPWA network. to provide a method.

An object of the present invention is to change the spreading factor by defining the length of the timeslot to be variably operated when the sensor nodes using TDMA MAC exist at different distances, thereby enabling TDMA communication with sensor nodes at various distances. An object of the present invention is to provide a TDMA MAC operation method in a rate-based communication system.

The TDMA MAC operation method in the low-speed variable transmission rate-based communication system according to the present invention for achieving the above object is to define the repetition period of the super frame based on 24 hours because the transmission period of sensing data is long due to the characteristics of the low-speed LPWA network. It is the basic characteristic of the technical method.

The present invention has the effect of effectively increasing the battery life of the sensor node in collecting sensing information of the sensor node existing at a long distance of 10Km or more (LOS standard).

The present invention has the effect of supporting a low-power/real-time information transfer function in a system requiring accurate data transfer, such as factory automation.

According to the present invention, the wake-up and sleep times of the sensor node can be precisely controlled by using the time division communication method in the LPWA network, thereby extending the lifespan of the sensor node.

When sensor nodes using TDMA MAC exist at different distances, by defining the length of timeslot to be variably operated, there is an effect that TDMA communication with sensor nodes of various distances is possible by changing the spreading factor.

1 is a configuration diagram for explaining a TDMA MAC operation method in a low-speed variable transmission rate-based communication system according to the present invention.
2 is a block diagram illustrating a TDMA MAC operation method in a low-speed variable transmission rate-based communication system according to the present invention or a basic network structure.
3 is a graph showing the superframe structure of the designed TDMA MAC.
Figure 4 is a flow chart showing the SF change according to the distance between the G / W and a sensor node.
5 is a graph showing the structure of a sync timeslot that performs this role.
6 is a graph showing the configuration of a shared timeslot.
7 is a graph showing the configuration of a data timeslot.

A preferred embodiment of a TDMA MAC operation method in a low-speed variable transmission rate-based communication system according to the present invention will be described with reference to the drawings, and a plurality of the embodiments may exist. A better understanding of the purpose, features and advantages will be achieved.

1 Overview

1.1 Detailed overview

The present invention develops a hybrid MAC that can use both CSMA/CA MAC and TDMA MAC as the main development item of the "Marine/Industrial IoT Complex Sensing Chip Development and Commercialization" task, so that the method of use is selected and operated according to the purpose of the sensor node. This helps to increase the efficiency of network operation.

An object of the present invention is to propose a method for TDMA-based media control that guarantees the minimum delay or efficiency.

1.2 Scope

The scope of the present invention is defined as follows.

■ Hybrid MAC - Dual mode (TDMA + CSMA/CA) operation function

- TDMA: Low power/low delay operation function

- CSMA/CA: Resource allocation function to support various requirements

- Own network operation function and commercial network connection function

1.3 References

1.4 Abbreviations and Definitions

Time-Division Multiplexing Access (TDMA)

- A media access control method that divides the time axis into several times and provides a service so that each user can use the time section assigned to him/her without overlapping with the time of other users

LoRa (Long Range)

- It is a low-power wide area network technology based on spread spectrum modulation technology derived from Chirp Spread Spectrum (CSS) technology. It is a low-power long-distance communication network that can communicate with low power and supports communication over 10km with minimal power consumption.

Low Power Wide Area (LPWA)

- A communication technology for the Internet of Things that supports long-distance transmission and stable communication of small amounts of data based on low power and low cost as a wireless communication system that can communicate over long distances (over 10km in total) with minimal power.

SF (Spreading Factor)

- A factor that increases the gain of communication using the signal-to-noise ratio obtained by spreading the original data bit into several bit strings

Superframe

Time division multiple access (TDMA: Time Division Multiple Access) type MAC defines a time arrangement structure that repeats for a specific time

2 System overview

2.1 System Development Goals

The present invention is a hybrid MAC design that can selectively operate two types of LPWA RF transceivers in a single CPU, and aims to manufacture MAC S/W supporting hardware structure miniaturization and light weight.

Through this development, it was attempted to overcome the limitations of self-network construction and secure compatibility and scalability by supporting both commercial and private networks at the same time.

In particular, the operation method of MAC is supported in two types, and the corresponding types are configured so that the functional operation can be determined according to the operation type of the sensor node. In other words, by developing TDMA-based low-speed MAC, TDMA-based MAC was applied to enable TX/RX/Sleep scheduling of IoT sensor nodes to maximize low-power operation and network efficiency, and to increase transmission efficiency by applying CSMA/CA. configured to be able to.

1 is a configuration diagram for explaining a TDMA MAC operation method in a low-speed variable transmission rate-based communication system according to the present invention.

In particular, the present invention aims to define a TDMA-related structure among hybrid MACs through time-division-oriented MAC structure design.

3 TDMA MAC (Time Division Multiple Access MAC)

The present invention includes a design for a time division multiple access method, which is one of the communication systems for enabling efficient transmission/reception using limited wireless media. In particular, it defines a TDAMAC (Media Access Control) scheme used in a low-speed LPWA network, which is the basis of the present invention.

3.1 Network Configuration

The figure below shows the network structure that is the basis of the present invention. The network structure basically has a star structure in which G/W controls the entire network.

2 is a block diagram illustrating a TDMA MAC operation method in a low-speed variable transmission rate-based communication system according to the present invention or a basic network structure.

G/W has decision-making authority for communication of all competent nodes and is responsible for resource allocation. That is, communication between LPWA nodes is not possible in principle, and it defines a structure in which communication is possible only through G/W. Due to the nature of the sensor node, it is based on low power operation, and because it plays the role of transmitting the sensing value of each sensor node to the center, unidirectional data exists, and if necessary, it receives ACK and performs separate processing. may be

In this communication structure, a short-distance LPWA node can communicate even using a low spreading factor, and it is concluded that the transmission time is fast when transmitting the same capacity. Likewise, LPWA nodes far away from G/W must use a high spreading factor to enable communication. That is, the transmission time of the same data becomes relatively long.

3.2 Network operation parameters

In the present invention, LoRa was selected from among various LPWA communication methods to design, and parameters for Chirp spread spectrum (CSS), a modulation method used in LoRa, can be summarized as shown in Table 1 below.

[Table 1] Chip Spread Spectrum (Css) PHY parameter

Based on this, parameters necessary for MAC design can be derived as shown in Equation 1 below.

[Equation 1] LoRa standard time-related parameter definition

Table 2 below shows the transmission rate according to the spreading factor.

[Table 2] Lora transmission/reception speed and reception sensitivity

LPWA network operation should support smooth communication between distant LPWA nodes and G/W, and as shown in the table above, the transmission time of a low spreading factor and a transmission time of a high spreading factor are too short for the same amount of transmitted data. There are many differences.

TDMA configuration of such a network by allocating timeslots of the same length is very wasteful of resources. In order to efficiently use radio resources, a short timeslot is used for communication with a nearby node and a long timeslot is used for communication with a distant node. It should be assigned to perform communication.

3.3 TDAMAC superframe configuration

The TDMA MAC designed in the present invention operates in a low-speed LPWA network. The characteristic of the low-speed network is that the transmission rate can be adjusted by changing the SF (Spreading Factor) according to the distance of the communication target, and the transmission distance can be adjusted through this.

TDMA MAC is configured to support both long and near distances and to increase network efficiency according to distance by applying a variable spreading factor to the TDMA frame to increase efficiency.

Due to the characteristics of the LPWA network operating at low speed, the basic condition is to transmit at least once a day, and the number of transmissions is limited according to the spreading factor.

That is, Spreading Factor 12 defines that the transmission interval can be adjusted according to the number of associated nodes.

3 is a graph showing the superframe structure of the designed TDMA MAC.

Since the transmission period of sensing data is long due to the characteristics of the low-speed LPWA network, the repetition period of the super frame is defined based on 24 hours.

Super frame is a set of frames in units of 1 hour, and frames are composed of sub-frames in units of 1 minute.

Use the sync timeslot beacon to keep the sync without using the GPS's PPS signal.

A protocol is provided so that the length of data timeslot can be operated variably according to G/W and distance.

All timeslot scheduling is performed by G/W, and slot information is broadcast by G/W in each sub-frame.

The LPWA network, which operates at low speed but provides long-distance communication range, is implemented in CSMA/CA Media Access Control (MAC) and operates in a contention manner.

Due to this, if each sensor node competes at a slow speed, the waiting time for sensor node communication inevitably becomes longer.

As a result, battery consumption increases rapidly.

An effective way to overcome this is to divide the time so that all sensor nodes can communicate using the TDMA method that enables communication without overlapping.

By configuring in this way, each sensor node wakes up at its own transmission timing, transmits without contention, and can transition to sleep state again, increasing the efficiency of the battery system.

However, when using the existing timeslot of the same size, radio resources are greatly lost due to the huge difference in data length according to the application of the spreading factor according to the distance.

To overcome this, the utilization of radio resources can be maximized by changing the length of the timeslot for data in proportion to the distance between the G/W and the sensor node.

When an emergency situation occurs in the vehicle in which the OBU is installed, the information is propagated to other vehicles through V2V (vehicle-to-vehicle communication) and V2I (vehicle-to-infrastructure communication), and the situation is notified to the operating system corresponding to the center through V2I. is composed of a list.

The repetition interval of the superframe is based on 1 day (24 hours), and each superframe is composed of a frame with an interval of 1 hour, and each frame consists of a sub-frame with an interval of 1 minute. Superframe has a repeating structure, and although frame and sub-frame are composed of several timeslots in detail, they do not have a repeating structure.

As previously premised, the timeslot used by each communication node for data communication has a dynamic time length, and additional timeslots are allocated and used for network management and timeslot management.

1. Guard time

- space allocated between each timeslot

- It has a fixed length regardless of the spreading factor

- Processing delay + Propagation delay + RX/TX switching time

2. Sync timeslot

- timeslot used for synchronization

- The section in which the gateway transmits the beacon frame

- have a fixed length

- Maximum Spreading Factor

3. Shared timeslot

- A section used by a new communication node to establish or disconnect a connection

- Contention section operated by CSMA/CA method

- have a fixed length

- Maximum Spreading Factor

4. Data timeslot

- Timeslot where Sensing data frame and ACK frame are transmitted

- Variable length of timeslot with variable spreading factor

- Spreading Factor is determined according to the distance between communication node and G/W

- Timeslot length can be defined with or without ACK reception time.

Table 3 below defines the characteristics of superframe, sub-frame, frame, and timeslot occupancy time.

[Table 3] Characteristics of each component of TDMA Superfarame

In addition, the format of the frame delivered by each communication node can be divided into a report frame with a certain period and an event frame with aperiodicity.

In the case of a periodic frame, the size is the same, and it can be concluded that the size of the frame known by the registration procedure is grasped by G/W and is used to determine the length of the frame, so that full allocation is possible without wasting timeslots. .

Conversely, when it is necessary to transmit a frame with a variable length, it can be defined to be arbitrarily transmitted by classifying it as an event frame.

All these series of timeslot lengths and decisions about timeslot configuration within superframes are left to G/W.

3.4 Synchronize timeslots on each node

As mentioned above, one network is operated centered on G/W, and in the TDMA system, maintenance of synchronization information is one of the most important factors. In most precision TDMA systems, time synchronization is performed using PPS information of GPS. However, in the case of the sensor node of the present invention, a low-cost, low-power system should be operated as a basis. When a GPS module is installed, it becomes difficult to achieve both of these.

Therefore, in the present invention, synchronization is performed using a beacon frame to which a spreading factor of the highest level transmitted by G/W is applied. By transmitting a beacon frame containing only the minimum synchronization information and timeslot related information, time information and network information can be delivered to all managed networks.

G/W transmits beacon frames periodically (1 sub-frame interval), and each terminal operates to receive beacon frames by periodically waking up according to the power efficiency setting. Through this, superframe synchronization of the network operated by G/W is acquired. The synchronization information of the superframe refers to the start information of the superframe, the start of the frame, and the start of the sub-frame.

The terminal node performs synchronization through the reception of the beacon frame in the following procedure.

1. Add the time on air of the beacon frame according to the set SF and the processing time after receiving the frame.

2. Add the guard time to the result of 1.

3. Subtract the result of 2 from the total time of the superframe to derive the time remaining until the start of the next superframe.

4. Set the result value of 3 as the timer timeout value.

The time-out point can be viewed as the approximate starting point of the superframe. After that, calibration is performed for more accurate synchronization.

Correction work is performed as follows.

1. Find the time difference between the start point of the superframe and the reception of the beacon frame.

2. Time on Air of Beacon frame according to set SF, processing time and guard time after frame reception are added.

3. Find the difference between the results of 1 and 2 and repeat this process 3 times to derive the average value.

4. Decide the timeout time of the next Superframe by reflecting the average value.

After that, a timeout point can be regarded as the starting point of the synchronized Superframe. Each node transmits a data frame in its own data transmission slot.

3.5 Variable SF for Data Frame

In most LPWA networks, G/W is fixed, and the sensor node is also fixed in many cases. However, there may be a structure in which G/W is also movable and the sensor node is also movable in some cases. In this case, to communicate with each other with a fixed spreading factor, it is necessary to repeat the operation of disconnecting from the network and then connecting again.

In order to determine and determine this case in the G/W stage, a structure applicable to variable SF as shown in FIG. 4 below may be defined.

4 is a flowchart illustrating SF change according to a distance between G/W and a sensor node.

A low-speed sensor node must support a long battery life with low power consumption. Assuming that the sensor node wakes up at least once a day and transmits sensing data, the super frame duration is defined as 24 hours, and the substructure of frame and sub-frame is defined, respectively, and the scheduling information of timeslot is managed by G/W. define what can be done

In most LPWA networks, G/W is fixed, and the sensor node is also fixed in many cases.

However, in some cases, a structure in which G/W can be moved and a sensor node can also be moved.

In this case, to communicate with each other with a fixed spreading factor, it is necessary to repeat the operation of disconnecting from the network and then connecting again.

In such a case, a structure applicable to variable SF as shown in FIG. b can be defined so that the G/W stage can determine it.

The sensor node transmits data to G/W using the spreading factor determined at the time of association. As the time passes, the sensor node or G/W moves and the distance between each other changes, the G/W determines this and the ACK frame can be used to change the spreading factor.

The sensor node transmits data to G/W using the spreading factor determined at the time of association, and if the location of the sensor node or G/W changes over time and the distance between them changes, the G/W judges this. Thus, the spreading factor can be changed using the ACK frame.

3.6 TDMA MAC frame format

As described above, timeslot can be divided into three types. It is divided into sync timeslot transmitted to G/W, shared timeslot used for processing such as breaking in/out at terminal node, and data timeslot transmitted from terminal communication node.

3.6.1 Sync timeslot

The most important role of Sync timeslot is to deliver the synchronization information possessed by G/W. The starting point of the frame is recognized by the terminal as the reception time of the frame, which can be converted into time through the length of the frame based on a determined spreading factor (maximum value 12). That is, the transmission start point of the frame can be inferred from the total reception time of the frame.

The second important task of the sync timeslot is to determine the length of the timeslot composed of the sub-frame. That is, the number of data timeslots constituting the current sub-frame and when each data timeslot starts are divided and delivered for each node ID.

The length of data timeslot is determined by G/W, and as will be explained later, it is determined by SF according to the length and distance of sensing data to be transmitted by each node during association. All of these decisions are made by G/W.

5 is a graph showing the structure of a sync timeslot that performs this role.

The most important role of Sync timeslot is to deliver synchronization information possessed by G/W.

The starting point of the frame is recognized by the terminal as the reception time of the frame, which can be converted into time through the length of the frame based on a determined spreading factor (maximum value 12).

That is, the transmission start point of the frame can be inferred from the total reception time of the frame.

The second important task of the sync timeslot is to determine the length of the timeslot composed of the sub-frame. That is, the number of data timeslots constituting the current sub-frame and when each data timeslot starts are divided and delivered by each node ID.

The length of data timeslot is determined by G/W, and as will be explained later, it is determined by SF according to the length and distance of sensing data to be transmitted by each node during association. All of these decisions are made by G/W.

The fields configured above can be defined as shown in Table 4 below.

[Table 4] Sync timeslot configuration field definition

3.6.2 Shared timeslot

The terminal node can determine the existence of the G/W based on the beacon information transmitted by the G/W and request access to the network managed by the G/W. Also, a node that is already connected to the network and operating must have a way to leave the network in a specific situation.

A timeslot to perform this process is required, and access to the network must be performed in the state that no timeslot is allocated. That is, although the synchronization information is acquired, a separate timeslot is required to perform the procedure for allocating a timeslot. A timeslot that performs a corresponding role is a shared timeslot.

In the shared timeslot, subscription and withdrawal are processed, and has a configuration as shown in FIG. 6 below.

6 is a graph showing the configuration of a shared timeslot.

The terminal node can determine the existence of the G/W based on the beacon information transmitted by the G/W and request access to the network managed by the G/W.

Also, a node that is already connected to the network and operating must have a way to leave the network in a specific situation. A timeslot to perform this process is required, and access to the network must be performed in the state that no timeslot is allocated.

That is, although the synchronization information is acquired, a separate timeslot is required to perform the procedure for allocating a timeslot. A timeslot that performs a corresponding role is a shared timeslot.

In the shared timeslot, subscription and withdrawal are processed and have the same configuration as the drawing.

The frame included in the shared timeslot consists of an association request frame and an association response frame related to subscription, and a dis-association request and dis-association response frame related to leaving the network.

The frame included in the shared timeslot consists of an association request frame and an association response frame related to joining, and a dis-association request and dis-association response frame related to network withdrawal.

Table 5 below defines the composition of fields included in the association request frame.

[Table 5]

Table 6 below defines the composition of fields included in the association response frame.

[Table 6] Association request frame configuration field definition

Table 7 below defines the composition of fields included in the dis-association request frame that performs the disconnection procedure for the network.

[Table 7] Association request frame configuration field definition

3.6.3 Data timeslot

Since the data timeslot is determined according to the configuration of the sensor included in each node, the payload value is determined according to the vendor definition of the sensor node.

7 is a graph showing the configuration of data timeslot.

Since the data timeslot is determined according to the configuration of the sensor included in each node, the payload value is determined according to the vendor definition of the sensor node.

The data timeslot has a variable length according to the spreading factor and the payload length. The data transmitted in the data timeslot determines whether to transmit the ACK frame according to the G/W policy.

As mentioned above, the data timeslot has a variable length according to the spreading factor and the payload length. As for the data transmitted in the data timeslot, as shown in Table 8 below, whether to transmit the ACK frame is determined according to the G/W policy.

[Table 8] Association request frame configuration field definition

Table 9 below shows the structure of the ACK frame. The Change SF field included in the ACK frame defines that the transmission method according to the distance can be changed by changing the spreading factor when the signal strength varies over a certain level while the G/W receives the data frame of each node.

[Table 9]

The present invention can be used in industrial fields that can support a low-power/real-time information transfer function to a system requiring accurate data transfer, such as factory automation.

1 is a configuration diagram for explaining a TDMA MAC operation method in a low-speed variable transmission rate-based communication system according to the present invention.
2 is a block diagram illustrating a TDMA MAC operation method in a low-speed variable transmission rate-based communication system according to the present invention or a basic network structure.
3 is a graph showing the superframe structure of the designed TDMA MAC.
Figure 4 is a flow chart showing the SF change according to the distance between the G / W and a sensor node.
5 is a graph showing the structure of a sync timeslot that performs this role.
6 is a graph showing the configuration of a shared timeslot.
7 is a graph showing the configuration of a data timeslot.

Claims (5)

TDMA MAC operation method in low-speed variable transmission rate based communication system, characterized in that the repetition period of super frame is defined based on 24 hours because the transmission period of sensing data is long due to the characteristics of the low-speed LPWA network. According to claim 1,
A TDMA MAC operation method in a low-speed variable transmission rate-based communication system, characterized in that a super frame is a set of 1-hour frames and a frame is configured as a 1-minute sub-frame. 3. The method of claim 2,
A TDMA MAC operation method in a low-speed variable transmission rate-based communication system, characterized in that a beacon of sync timeslot is used to maintain synchronization without using the PPS signal of GPS. 4. The method of claim 3,
TDMA MAC operation method in a low-speed variable transmission rate-based communication system, characterized in that it provides a protocol so that the length of data timeslot can be variably operated according to G/W and distance. 5. The method of claim 4,
All timeslot scheduling is performed by G/W, and TDMA MAC operation method in a low-speed variable transmission rate-based communication system, characterized in that G/W broadcasts slot information in each sub-frame.

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