KR101953624B1 - METHOD FOR SENDING DOWNLINK BROADCAST MESSAGE TO A PULRALITY OF END DEVICES IN LoRaWAN AND LoRaWAN SYSTEM - Google Patents

Abstract

A method of transmitting a downlink broadcast message to a plurality of end devices in a long-range wide-area network (LoRaWAN) according to an embodiment of the present invention includes a long-range wide-area (LoRaWAN) A method for transmitting a broadcast message from a network to a plurality of end devices, the method comprising: (a) one of the plurality of end devices becomes a downlink initiator and periodically transmits a downlink request ); And (b) the network server transmitting the broadcast message using a second receive window (RX2 Window) of a class A end device slot timing of a Laura protocol used in the Laura wide area network through the gateway .

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for transmitting a downlink broadcast message to a plurality of end devices in a low-

The present invention relates to a method for transmitting a downlink broadcast message from a long-range wide-area network (LoRaWAN) to a plurality of end devices, and to a large area network system.

Over the past few decades, the rapid development of low-cost, low-power wireless technology has accelerated the development of IoT applications and services. These wireless technologies are typically based on short-range communications such as Bluetooth low energy (BLE), IEEE 802.15.4, and Wi-Fi (IEEE 802.11). However, the range limitation of IoT applications based on this communication technology has made the communication link unreliable, and the reliability of the communication has deteriorated. Thus, the demand for wide communication coverage increases. Finally, due to this strong demand, a low-power long-range wireless communication system called low power, wide area network (LPWAN) emerged.

Various research groups are developing new LPWAN systems based on new standards. These include LoRaWAN [1] by the LoRa Alliance [1], Lombum Evolution (LTE-m) [2] and Narrowband IoT (NB-IoT) [3] for machine- And [4]. Of these new technologies, LoRa is widely accepted as the most promising LPWAN technology in terms of power efficiency, low-cost chipsets and local ISM bands. One of the core technologies of LoRa uses chirp spread spectrum (CSS) for modulation, while legacy low power communication is based on frequency shift keying (FSK) to achieve low power. For decades, CSS modulation has been used in certain areas, such as space communications and the military, because of its long communication capability and robustness to interference. That is, LoRaWAN maintains robustness against interference while maintaining long range characteristics.

Due to its merits, an interesting application [5-7] has already been introduced based on LPWAN; LoRaWAN also attracted many researchers. Adelantado et al. [8] identified the capabilities and limitations of LoRaWAN. In particular, they stressed the need to address the challenges of new multi-access mechanisms and energy-efficient multi-hop solutions. Mikhylov et al. [9] presented LoRaWAN analysis results in terms of uplink throughput and data transmission time. According to the results, the LoRaWAN duty cycle based Medium Access Control (MAC) scheme can increase packet collision probability and delay. They also showed that LoRaWAN has significant downsides in reliability and latency, especially in terms of downlink traffic. Kim et al. [10] pointed out the problem of LoRa gateway capability and proposed a new data transmission network architecture for long-range sensor networks based on hybrid approach combining LoRa infrastructure and sensor network. Taneja et al. [11] proposed a hybrid network architecture for LoRaWAN and 802.11ah, and Schroder et al. [12] also proposed using LoRaWAN for smart grid networks instead of RF mesh networks (Wi-SUN). Toussaint et al. [13] proposed the Markov chain model of OTAA. They analyzed the impact of several parameters on traffic conditions, duty cycle, and channel availability. Petajajarvi et al. [14] studied indoor performance of LoRaWAN based on health and welfare monitoring equipment. The authors also studied the applicability of LoRaWAN [15]. According to the results, the maximum communication range is more than 15 km from the ground and 30 km from the water. Pham et al. [16] designed an inexpensive DIY LoRa gateway with many features.

LoRaWAN has several advantages including low-power and long-range functionality, but there are some limitations and problems as already discussed in several documents [5-7]. In particular, significant problems arise in Class A for low-power operation of end devices.

Therefore, there is a need for a method and system that can solve the limitations and problems of downlink communication in LoRa class A and solve the downlink limitations of class A while maintaining low power characteristics.

[1] LoRa Alliance, Inc. LoRaWAN Specification LoRa Alliance, Inc .: San Ramon, CA, USA, 2015. [2] LTE-M Optimizing LTE for the Internet of Things. White Paper. Available online: https://novotech.com/docs/default-source/default-document-library/lte-m-optimizing-lte-for-the-internetof-things.pdf?sfvrsn=0 (accessed on 3 February 2016 ). [3] Cellular System Support for Ultra-Low Complexity and Low Throughput Internet of Things. Available online: https://portal.3gpp.org/desktopmodules/Specifications/SpecificationDetails.aspx?specificationId=2719 (accessed on 16 August 2016). [4] Sigfox Homepage. Available online: http://www.sigfox.com (accessed on 13 January 2016). [5] Fernandez-Garcia, R .; Gil, I. An alternative wearable tracking system based on a low-power wide-area network. Sensors 2017, 17, 592. [CrossRef] [PubMed] [6] Trasvina-Moreno, C.A.; Blasco, R .; Marco, A .; Casas, R .; Trasvina-Castro, A. Unmanned aerial vehicle based wireless sensor network for marine-coastal environment monitoring. Sensors 2017, 17, 460. [CrossRef] [PubMed] [7] Aquino-Santos, R .; Gonzalez-Potes, A .; Edwards-Block, A .; Virgen-Ortiz, R.A. Developing a new wireless sensor network platform and its application in precision agriculture. Sensors 2011, 11, 1192-1211. [CrossRef] [PubMed] [8] Adelantado, F .; Vilajosana, X .; Tuset-Peiro, P .; Martinez, B .; Melia, J. Understanding the limits of LoRaWAN. Available online: https://arxiv.org/pdf/1607.08011.pdf (accessed on 27 July 2016). [9] Mikhaylov, K .; Petajajarvi, J .; Haenninen, T. Analysis of capacity and scalability of the LoRa low power wide area network technology. In Proceedings of the European Wireless 2016, 22th European Wireless Conference, Oulu, Finland, 18-20 May 2016; pp. 119-125. [10] Kim, D. Y .; Jung, M. Data transmission and network architecture for long range low power sensor networks for iot. Wirel. Pers. Commun. 2017. [CrossRef] [11] Taneja, M. 802.11 ah-LPWA interworking. In Proceedings of the 2016 IEEE NetSoft Conference and Workshops (NetSoft), Seoul, Korea, 610 June 2016. [12] Schroder Filho, H. G .; Pissolato Filho, J .; Moreli., V.L. The adequacy of LoRaWAN on smart grids: A comparison with RF mesh technology. In Proceeding of the 2016 IEEE International Smart Cities Conference (ISC2), Trento, Italy, 1215 September 2016. [13] Toussaint, J .; EI Rachkidy, N .; Guitton, A. Performance analysis of the on-the-air activation in LoRaWAN. In Proceeding of the 2016 IEEE 7th Annual Information Technology, Electronics and Mobile Communication Conference (IEMCON), Vancouver, BC, Canada, 1315 October 2016. [14] Petajajarvi, J .; Mikhaylov, K .; Hamalainen, M .; Iinatti, J. Evaluation of LoRa LPWAN technology for remote health and wellbeing monitoring. In Proceeding of the 10th International Symposium on Medical Information and Communication Technology (ISMICT), Worcester, MA, USA, 2023 March 2016. [15] Petajajarvi, J .; Mikhaylov, K .; Roivainen, A .; Hanninen, T .; Pettissalo, M. On the coverage of LPWANs: Range evaluation and channel attenuation model for LoRa technology. In Proceeding of the 2015 14th International Conference on ITS, Copenhagen, Denmark, 24 December 2015. [16] Pham, C. Building Low-Cost Gateways and Devices for Open Lo-IoT Test-Beds. In Testbeds and Research Infrastructures for the Development of Networks and Communities, Proceeding of the 11th International Conference TRIDENTCOM, Hangzhou, China, 1415 June 2016 Springer: Cham, Switzerland, 2016; pp. 70-80. [17] LoRa Alliance. A Technical Overview of LoRa and LoRaWAN. White Paper. Available online: https://www.lora-alliance.org/portals/0/documents/whitepapers/LoRaWAN101.pdf (accessed on 1 November 2015). [18] Multitech Product. Available online: https://www.multitech.net (accessed on 1 January 2017).

A problem to be solved by the present invention is to solve the limitations and problems of the downlink communication in the LoRa class A, solve the downlink limitation of the class A while maintaining the low power characteristic, And to provide a method for transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network, which can reduce excessive data storage of network servers.

Another problem to be solved by the present invention is to solve the limitations and problems of the downlink communication in the LoRa class A, solve the downlink limitation of the class A while maintaining the low power characteristic, And to reduce the excessive data storage of the network server.

According to another aspect of the present invention, there is provided a method for transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network,

A method of transmitting a broadcast message to a plurality of end devices in a long-range wide-area network (LoRaWAN)

(a) one of the plurality of end devices becomes a downlink initiator and periodically transmits a downlink request to a network server through a gateway; And

(b) the network server transmits the broadcast message using the second reception window (RX2 Window) of the class A end device slot timing of the Laura protocol used in the Laura wide area network through the gateway.

A method for transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an exemplary embodiment of the present invention includes:

Prior to step (a)

(a-1) further comprising the network server determining a fixed channel to be used for the second receiving window,

In step (b), the network server may transmit the broadcast message using the second reception window on the determined fixed channel.

Also, in a Laura wide area network according to an embodiment of the present invention, a method for transmitting a downlink broadcast message to a plurality of end devices,

In the step (b), the network server transmits the broadcast message to the plurality of end devices based on the device address block in which the network address field of the standard device address block (DevAddr) used in the Laura wide area network is divided ,

The divided network address field may include a sensor type and a group address field indicating area information and a reduced network address (Nwk Addr) field.

In the method of transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an exemplary embodiment of the present invention, the sensor type indicates a type of a sensor included in the end device, Information of an area where the end device is installed,

The Group Address field indicating the sensor type and the area information may be represented by a bitmap indicating the type or area of the corresponding sensor when the bit of the predetermined position among the plurality of bits is a specific value.

In a method of transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an embodiment of the present invention, a bit map representation of the type of the sensor and the group address (Group Addr) And may be predetermined and stored in the network server.

In addition, in a Laura wide area network according to an embodiment of the present invention, a method of transmitting a downlink broadcast message to a plurality of end devices may include transmitting, to the network server, ) And an end device that is allowed to join by the network server may be set as the downlink initiator.

In the method of transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an exemplary embodiment of the present invention, the network server calculates a sum of uplink times and downlink times of a current downlink initiator, If it is greater than or equal to the predetermined threshold value, the end device having the minimum sum of the number of uplinks and the number of downlinks can be set as a new downlink initiator.

In the method of transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an embodiment of the present invention, the threshold may be a new threshold value = an existing threshold value x (1 + 1/2 ^R ), And R may represent the number of changes of the downlink initiator.

According to another aspect of the present invention, there is provided a long-range wide-area network (LoRaWAN) system including a plurality of end devices, a plurality of A long-range wide-area network (LoRaWAN) system including a gateway, a network server connected to the plurality of gateways,

Wherein one of the plurality of end devices becomes a downlink initiator and periodically transmits a downlink request to the network server through the gateway,

The network server transmits a broadcast message using the second reception window (RX2 Window) of the class A end device slot timing of the Laura protocol used in the Laura wide area network through the gateway.

In a long-range wide-area network (LoRaWAN) system according to an embodiment of the present invention, the network server determines a fixed channel to be used for the second reception window, And may transmit the broadcast message using the second reception window over a fixed channel.

In addition, in a long-range wide-area network (LoRaWAN) system according to an embodiment of the present invention, the network server includes a network address of a standard device address block (DevAddr) used in the Laura wide- The broadcast message is transmitted to the plurality of end devices based on a device address block in which a field is divided,

The divided network address field may include a sensor type and a group address field indicating area information and a reduced network address (Nwk Addr) field.

In addition, in a long-range wide-area network (LoRaWAN) system according to an embodiment of the present invention, the sensor type indicates a type of a sensor provided in the end device, Indicates the information of the area where the device is installed,

The Group Address field indicating the sensor type and the area information may be represented by a bitmap indicating the type or area of the corresponding sensor when the bit of the predetermined position among the plurality of bits is a specific value.

In addition, in a long-range wide-area network (LoRaWAN) system according to an embodiment of the present invention, the bitmap representation of the type of the sensor and the group address (Group Addr) And may be stored in the network server.

In addition, in a long-range wide-area network (LoRaWAN) system according to an embodiment of the present invention, a connection to the Laura wide area network is firstly transmitted to the network server among the plurality of end devices An end device that is requested to be allowed to connect by the network server may be set as the downlink initiator.

In addition, in a long-range wide-area network (LoRaWAN) system according to an embodiment of the present invention, the network server determines whether the sum of the number of uplinks and the number of downlinks of the current downlink initiator When the number of downlinks is equal to or greater than the threshold value, an end device having a minimum sum of uplink times and downlink times can be set as a new downlink initiator.

Also, in a long-range wide-area network (LoRaWAN) system according to an embodiment of the present invention, the threshold is set to a new threshold value = existing threshold value x (1 + 1/2 ^R ) , And R may represent the number of changes of the downlink initiator.

A method for transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an embodiment of the present invention and a Laura wide area network system solve the limitations and problems of downlink communication in a LoRa class A Class A downlink limitations while maintaining low power characteristics, significantly reducing network traffic, and reducing network server over-data storage.

Figure 1 is a diagram illustrating the use of the LoRa regional spectrum, adapted from the Laura Alliance specification version 1.02 regional parameters in 2016;
Figure 2 shows a LoRaWAN architecture adapted from the Laura Alliance Laura White Paper in 2015;
Figure 3 illustrates a Laura protocol stack adapted from Specification Version 1.02 of the Laura Alliance in 2016;
4 is a diagram illustrating a Class A end device slot timing adapted from Specification Version 1.02 of the 2016 Laura Alliance;
5 shows device time synchronization in the Laura standard.
6 is a diagram showing a device address (DevAddr) block division;
FIG. 7 illustrates a Laura wide area network system according to an embodiment of the present invention; FIG.
8 is a flowchart of a method for transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an embodiment of the present invention.
Figure 9 illustrates cooperative downlink listening (CDL) time synchronization;
10 is a diagram showing a threshold value change;
11 is a diagram for explaining group casting;
12 is a view for explaining geocasting;
13 is a graph showing network traffic observation;
FIG. 14 is a graph showing the power state viewed from the viewpoint of communication. FIG.
15 is a graph showing energy consumption;
16 is a graph showing battery life;

BRIEF DESCRIPTION OF THE DRAWINGS The objectives, specific advantages and novel features of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG.

Prior to that, terms and words used in the present specification and claims should not be construed in a conventional and dictionary sense, and the inventor may properly define the concept of the term in order to best explain its invention Should be construed in accordance with the principles and the meanings and concepts consistent with the technical idea of the present invention.

It should be noted that, in the present specification, the reference numerals are added to the constituent elements of the drawings, and the same constituent elements are assigned the same number as much as possible even if they are displayed on different drawings.

Also, the terms "first", "second", "one side", "other side", etc. are used to distinguish one element from another, It is not.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following description of the present invention, a detailed description of known arts which may unnecessarily obscure the gist of the present invention will be omitted.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Recently, the development of the Internet of Things (IoT) application has been gaining momentum with the emergence of low-power wide-area networks (LPWANs), and low-power wide area networks have advantages of low power and long communication distance. Among the various LPWAN technologies, a long distance wide area network (LoRaWAN or LoRa) is considered the most mature technology. However, since LoRa performs uplink-oriented communication to enhance energy efficiency, there is a limitation in the downlink function from the network server to the end device. In the present invention, cooperative downlink listening is proposed to solve the fundamental problem of LoRa. In particular, the proposed approach can be extended to various communication models, such as group casting and geocasting, in combination with a data-centric model. The main contribution of the present invention is to propose a new algorithm that improves the downlink availability which is considered to be the most serious drawback of LoRa class A. Nevertheless, the new algorithms and protocols are designed to be compatible with the LoRa standard. The present invention also opens up a new area of the data-centric IoT model of LPWAN introduced in wireless sensor networks. Experiments also show that the proposed technique not only can greatly reduce network traffic compared to the LoRa standard, but also ensures the maximum energy efficiency of the LoRa.

LoRaWAN  summary

The LoRaWAN specifies the physical (PHY) and medium access control (MAC) layer protocols for extreme long-haul and low-power networks standardized by the LoRa Alliance. According to the LoRa white paper [17], the whole city or hundreds of kilometers in radius can be covered by a single LoRa base station or LoRa gateway. With CSS, LoRa is able to This characteristic is attractive in many IoT applications and in many regions and countries, it is intended to accommodate LoRa technology in the local ISM band. Figure 1 shows LoRa regional spectrum usage.

One of the outstanding features of the LoRaWAN is based on a star topology that is connected to the network server 204, which serves to relay messages between the end device 200 and the network server 204, as shown in FIG. The gateway 202 has two independent communication links, LoRa communication and an IP backhaul. Supported data rates are 0.3-50 kbps. LoRa also provides an adaptive data rate (ADR) function. Reference numeral 206 denotes an application server.

Figure 3 shows the LoRa protocol stack (PHY and MAC). Based on the local ISM band, the physical layer includes LoRa modulation, and depending on the application characteristics, the MAC has three classes: Class A (baseline), Class B and C (optional). Class A is used for low-energy end devices and allows bidirectional communication between end devices and network servers. However, downlink communication from the network server to each end device is allowed only immediately after the end of the uplink transmission of the end device.

4, immediately after the uplink transmission 400, the end device receives a first reception window (RX1 window 402) and a second reception window (RX2 window 404), which are two windows each for RECEIVE_DELAY1 and 2, . For the RX1 window, the same channel and data rate as used in the uplink transmission is used, but the RX2 window can use a different channel and data rate than the uplink transmission.

LoRaWAN has two types of join methods: over-the-air activation (OTAA) and personalization by activation (ABP). OTAA is an automatic join process performed during node (end device) deployment, and ABP is a manual join process.

The device address (DevAddr) is composed of a 32-bit identifier, 7 bits being used as the network identifier (NwkID) and 25 bits being used as the network address (NwkAddr) assigned to each end device by the network administrator.

CDL : Cooperative Downlink Listening Cooperative Downlink  Listening)

LoRa defines different classes for low-power long-range characteristics and makes it possible to use the appropriate classes according to the requirements of the application. Since most IoT applications are battery powered, LoRa Class A is considered the MAC layer in most applications. Class A allows end devices to send data uplinks to network servers through gateways, but there are some limitations and problems with receiving downlink data from network servers. In order to solve these limitations and problems of LoRa class A, a cooperative downlink reception algorithm is proposed in the present invention.

LoRaWAN Downlink  Limitations and problems of communication

In order to minimize power consumption, the end devices (ED1, ..., EDn) of class A perform uplink-oriented data transmission, as shown in Fig. This approach has the advantage of minimizing power consumption by waking up the device at any event or at a scheduled time, and then entering the sleep mode after transmitting the data. This approach, however, is problematic for downlink communications from the network server to each end device. That is, for a receiving downlink from a network server, each end device must wait until its uplink data transmission to the network server is completed, and the downlink communication is sent to the RX window 1 and / It is available only by Windows2. Also, in this method, downlink broadcasting is not possible.

Generally, the end device periodically sends the detection data to the network server. In this case, time synchronization between the device and the network server is required. This time synchronization task should be executed periodically, not frequently. In the case of the LoRa standard (class A), the only way to ensure that all end devices are synchronized with the network server is to use their own RX window following the individual uplink transmission. However, this greatly increases network traffic as shown in FIG.

This problem can result in increased traffic as well as wasted storage on network servers. Each end device periodically transmits sense data at a scheduled time and the network server stores all uplink data from the managed end device. In effect, after the application, the server is responsible for performing various analyzes based on the stored data. Even if the same detection value is maintained over a long period of time, the network server must store all data from the end device. This unnecessarily increases storage on the network server and makes it difficult for the application server to monitor the sensor field in near real time because the data analysis is based on the storage accumulated on the network server. All of these problems are caused by the limitations of downlink availability.

device  Partition of Address Block

To solve the downlink limitation of the LoRa standard, cooperative downlink listening (CDL) is proposed. First, as shown in Fig. 6, the device address DevAddr used in the standard is modified. While DevEUI is used during the 'join' process, the network server allocates the logical network address (DevAddr) and after the join procedure, all communications are based on the assigned device address (DevAddr).

As shown in FIG. 6, the standard device address (DevAddr) 600 is divided into a network identifier (NwkId) field 602 and a network address (NwkAddr) field 604. The device address (DevAddr) 606 used in the present invention does not change the network identifier (NwkId) field of the standard device address (DevAddr) 600 but changes the network address (NwkAddr) (Addr) field 610 and a network address (NwkAddr) field 612, respectively. Note that, unlike other id fields, the Group Address field 610 is displayed as a bitmap, not a number.

The Group Address field 610 is variable from 8 bits to 13 bits, and the rules are defined by the network server. The Group Address field 610 may be divided into a Type of Sensors (TOS) field 614 and a Region field 616. The TOS is used to define the type of sensor mounted on the end device. For example, temperature, humidity, infrared, and light sensors can be represented as '1000', '0100', '0010', '0001', respectively. Multiple sensor representations are possible. Bitmap '1100' refers to temperature and humidity sensors. LoRa can also have long coverage, so a single LoRa BS or LoRa gateway can cover more than a few kilometers. Therefore, the divided sub-areas can be displayed in the area field 616 of the group address (Group Addr) 610. [ For example, as shown in FIG. 6, the area covered by one gateway is divided into four sub-areas A, B, C, Therefore, the information of the sub-area can be represented by '1000', '0100', '0010' and '0001'. The group address (Group Addr) is determined according to the type of sensor and the area information, and the network address (NwkAddr) is arbitrarily assigned by the network server.

Compared to the standard device address (DevAddr) address scheme, the address space allocated to the CDL is smaller than the standard address space since the network address (NwkAddr) field 612 is reduced by adding a group address (Group Addr) field 610. That is, the address space is calculated as follows.

Where N _n is the size of the network identifier (NwkId) (608), N _t is the sensor type (614) size, and N _r is the local size (616).

Assume that the device sends the detected data to the network server once an hour. Then each end device needs at least 3 seconds of slot duration (including uplink, ACK, and downlink data slots), so it can handle only 3600 seconds / 3 seconds = 1200 end devices with a single gateway in the region. Therefore, the maximum address space of the CDL is 4096 and the space of a single gateway is sufficient.

CDL  Basic algorithm

7 is a diagram illustrating a Laura wide area network system according to an embodiment of the present invention. 7, the Laura wide area network system according to an embodiment of the present invention includes a plurality of end devices ED1, ..., EDn, a plurality of end devices ED1, ..., EDn, A long-range wide-area network (LoRaWAN) system including a gateway 700 for performing communication and a network server 702 connected to the gateway 700. The plurality of end devices ED1,. ..., and EDn is a downlink initiator that periodically sends a downlink request to the network server 702 via the gateway 700 and the network server 702 transmits a downlink request to the network server 702. [ Transmits a broadcast message using the second reception window (RX2 Window) of the class A end device slot timing of the Laura protocol used in the Laura wide area network through the gateway 700. [ Reference numeral 704 denotes an application server 704 connected to a network server, reference numeral 706 denotes a control section, and reference numeral 708 denotes a storage section.

The network server 702 determines a fixed channel to be used for the second receiving window and the network server 702 transmits the broadcasting message using the second receiving window on the determined fixed channel.

The network server 702 is connected to the plurality of end devices (ED1, ..., EDn) based on the divided device address blocks of the network address field of the standard device address block (DevAddr) used in the Laura wide area network And transmits the broadcast message. The divided network address field includes a group address field indicating a sensor type and area information, and a reduced network address (Nwk Addr) field.

Wherein the sensor type indicates a type of a sensor provided in the end device (ED1, ..., EDn), the area information indicates information of an area where the end device (ED1, ..., EDn) The Group Address field indicating the sensor type and the area information is expressed by a bitmap indicating the type or area of the corresponding sensor when the bit at a predetermined position among the plurality of bits is a specific value.

A bit map representation of the type of the sensor and the group address (Group Addr) field indicating the area information is predetermined and stored in the storage unit 708 of the network server 702.

In one embodiment of the present invention, the network server 702 of the plurality of end devices ED1, ..., EDn is first requested to join the Laura wide area network, The end device to which the join is permitted is set as the downlink initiator.

In an embodiment of the present invention, it is assumed that the first end device ED1 is initially set as a downlink initiator.

When the sum of the number of uplinks and the number of downlinks of the current downlink initiator is equal to or greater than a predetermined threshold value, the network server 702 transmits an end device having a minimum sum of uplink times and downlink times to a new downlink initiator Setting.

The threshold value is dynamically changed by the new threshold value = the existing threshold value x (1 + 1/2 ^R ), and R represents the number of changes of the downlink initiator.

8 is a flowchart illustrating a method of transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an exemplary embodiment of the present invention.

Referring to FIG. 8, a method for transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an exemplary embodiment of the present invention includes transmitting a downlink broadcast message to a plurality of end devices in a long-range wide-area network (LoRaWAN) A method of transmitting a broadcast message to end devices (ED1, ..., EDn), comprising the steps of: receiving a second reception window (RX2 Window) of a class A end device slot timing of a Laura protocol used in a Laura wide- (Step S800), one of the plurality of end devices ED1, ..., EDn becomes a downlink initiator and is periodically transmitted to the gateway 700, (Step S802) to the network server 702 via the determined fixed channel, and the network server 702 transmits a downlink request Of the low-protocol used by the end-device A large class slot timing by using the second receiving window (Window RX2) and a step (step S804) to transmit the broadcast message.

Hereinafter, a method for transmitting a downlink broadcast message to a plurality of end devices in a Laura wide area network according to an embodiment of the present invention and a Laura wide area network system will be described in detail.

The LoRa end devices (ED1, ..., EDn) can transmit the data uplink to the gateway using various channels as shown in Table 1. 4, the RX1 window 402 and the RX2 window 404 after uplink data transmission are used for the downlink. In general, RX1 window 402 is used for ACK frames for uplink transmission, and the channel and data rate of RX1 window 402 is the same as that used in uplink transmission. Unlike the RX1 window 402, the RX2 window 404 may use different channels and data rates regardless of the uplink transmission. The core idea of the CDL, which is the basis of the present invention, is to utilize a new device address (DevAddr) system in which the type of sensor and area information are expressed, and enable broadcasting using the RX2 window (404). To this end, the network server 702 determines a fixed channel to be used for the RX2 window 404 among the available channels in the BS2 or the gateway 700, and transmits the broadcast message using the RX2 window (404). An embodiment of the present invention also defines a downlink (DL) initiator, which is responsible for waking up all end devices ED1, ..., EDn in the network and sending a downlink request to network server 702 And is responsible for listening to the broadcast message of the network server 702 through the gateway 700 in the RX2 window 404 by periodically transmitting the broadcast message.

The network manager configures the group address (Group Addr) field as the type of the area information and the sensor. It can be preconfigured at the factory or configured using a specific device such as an installer that can configure each device by connecting to the end devices (ED1, ..., EDn) using UART or wireless in the field. After the installation and distribution, each of the devices ED1,..., EDn starts a joining process by sending a 'join' request message to the neighboring BS (or gateway 700) based on DevEUI, AppEUI and AppKey. The RFU bit of the 'join' request frame is set to '001' to be notified to the CDL device, and its group address (Group Addr) information is included in the MAC payload. The BS (or gateway 700) listening to the device's 'join' request frame delivers it to the network server 702 and the network server 702 sends the devices ED1, ..., EDn to join the network Accept. At this time, if the MType field is '000' (join request) and the RFU field in the received MAC frame header is '001' (CDL device), the network server 702 transmits the group address (Group Addr) information to the frame payload And allocates a device address (DevAddr) rule based on the received group address (Group Addr) information. A 'Join Accept' message is transmitted to the requester, that is, the corresponding end device (D), together with the device address (DevAddr) including the newly allocated network address NwkAddr (12 bits), the network identifier (NwkId) ED1, ..., EDn.

After the join process is completed, the DL initiator periodically sends a downlink request message to the network server 702 regardless of the sensor type or its area. Upon receiving the downlink request message, the network server 702 transmits the broadcast message using the RX2 window (404). The broadcast message of the network server 702 may be a time synchronization from the application server 704 or an instant query. Other devices wake up every period and listen to the broadcast messages of the network server 702, more specifically, switch the BS (gateway 700) to the RX2 channel. Here, the downlink message can be delivered to all the end devices (ED1, ..., EDn) or the selective end device through the group address (Group Addr) information.

Network time synchronization

One of the core functions of LoRaWAN is its low power communication characteristics. In order to extend the life of each battery operated end device (ED1, ..., EDn), LoRa used an uplink-oriented communication method. Therefore, each of the devices ED1, ..., EDn periodically transmits the sensed data uplink to the network server 702 based on the clock. It is well known that a variety of timing errors can occur between the devices ED1, ..., EDn and the network server 702 because the real time clock (RTC) used in the IoT device can drift over time. Therefore, one of the key issues in IoT applications is efficient time synchronization services.

Due to the inherent downlink limitation, time synchronization between the devices ED1, ..., EDn and the network server 702 is not specified by the LoRa specification. Thus, the individual devices ED1, ..., EDn must be synchronized to receive the current time information of the network server 702. [ That is, when the device ED1, ..., EDn transmits the sensed data to the network server 702, it receives the time information from the network server 702 in the next RX slot as shown in FIG. 5 have. However, this increases the amount of additional network traffic and can affect the communication of other devices.

Meanwhile, the CDL, which is the basis of an embodiment of the present invention, enables synchronizing the devices ED1, ..., EDn simultaneously with the network server 702 using the broadcast RX window triggered by the DL initiator. 9, the DL initiator ED1 transmits a DL request message to the network server 702 periodically (generally every hour) (S900), and the network server 702 transmits a DL request message to the network server 702 A broadcast RX window can be used to broadcast time information. Considering the average clock drift, time synchronization can be performed at most once a day. The first RX window for the downlink request following the downlink request message is used to send the ACK frame to the DL initiator (S902), the network server 702 captures the current time at the end of the first RX window, And broadcasts the captured time information at the start of the RX window (S906). All of the end devices ED1, ..., EDn of the network take place at the beginning of the RX2 window 404 and wait for a broadcast message from the network server 702 during the RX2 window 404 period. Upon receiving the time synchronization message, the end devices (ED1, ..., EDn) reconstruct the RTC with the time information received from the network server (702). Unlike the LoRa standard, where individual devices must be synchronized with network sensors, each end device ED1, ..., EDn of the CDL, which is the basis of the present invention, simultaneously receives the time information of the network server 702 and can be synchronized The traffic of the network is greatly reduced, so that the time difference between the devices can be reduced.

Power balance adjustment

One of the outstanding features of the CDL that is the basis of the present invention is that all end devices (ED1, ..., EDn) in the network use a common RX window for the downlink, which is triggered periodically by the DL initiator. However, this feature may result in more power consumption of the DL initiator than other generic listener end devices. Therefore, in order to avoid the intensive power consumption of the specific end device ED1 and to adjust the power of all the end devices ED1, ..., EDn in the network, the DL initiator is dynamically changed. The DL initiator change is based on a Fcnt (frame counter), which is managed by the network server 702 and each end device (ED1, ..., EDn). Fcnt is also separated into FcntUp for the uplink counter and FcntDown for the downlink counter. Thus, whenever the network server 702 receives the DL request message, the network server 702 confirms that:

If (FcntUp + FcntDown ≥ threshold value of current DL initiator)

If the sum of the two counter values is equal to or greater than the threshold value, the network server 702 searches for a new DL initiator candidate as follows to select a new DL initiator.

Where N is the set of end devices in the network.

The problem here is the best threshold. If the value of Fcnt of all the end devices (ED1, ..., EDn) in the network is larger than the threshold value, a new DL initiator can not be selected. On the other hand, when taking a too large threshold value, the energy of the original DL initiator ED1 can be consumed intensively. Therefore, in order to solve this problem, in one embodiment of the present invention, the threshold value is dynamically changed as follows.

This results in a log scale change of the threshold as shown in FIG. That is, the threshold value starts with a small value but remains at a similar value when the maximum value is reached. This makes it possible to continue to find candidate end devices that consume minimal energy and allows end devices to become new DL initiators. The threshold change is also performed with the DL initiator change event. Therefore, in one embodiment of the present invention, since the DL initiator is dynamically selected in consideration of the Fcnt value of all the end devices in the network, the power unbalance problem caused by the periodic DL request message transmission can be solved.

CDL Based IoT Query  spread

The CDL, which is the basis of the present invention, enables data-centric communication that efficiently utilizes the group address field as well as downlink broadcast by cooperatively sharing downlink slots between end devices. Group casting and geocasting are introduced below in relation to CDL.

Downlink (DL) Group casting

Group casting, which is a type of multicasting, is used when data is only requested from certain types of sensors in the network. For example, as shown in FIG. 11, the application server 1104 wants to know a sensor whose temperature is higher than 30 degrees. In this case, the application server 1104 may request a query to the network server 1102 and broadcast a message to the end device 1106, including an Addr field with the temperature sensor bit set and the query shown in FIG. As a result of the query, only sensors satisfying the condition (> 30 [deg.] C) respond to the network server 702. The network server 702 can aggregate data and then send the aggregated results to the application server 704. This group casting capability can reduce the network server 702's excessive data storage as well as the entire network traffic.

CDL Geocasting

The Group Address field already includes the function of configuring the area field as well as the sensor type field. Using the area field, network server 1102 can receive data only from sensors in a particular area without the aid of GPS. In particular, because LoRa can cover more than a few kilometers in radius, it is necessary to divide the area covered by a single gateway into sub-regions. For example, if the sensor field can be divided into four sub-areas (A, B, C and D) as shown in FIG. 12, the CDL can be used to collect sensor data only in sensors in a specific area. In this case, after the user (application server 1104) requests recent data in a particular area, the network server 1102 sets the bitmap in the area field and broadcasts the message to the network, i.e. end device 1106. Only the end devices of the area of interest (e.g., area A) can respond to the network server 1102. [ In addition, since the area field is represented by a bitmap, it is possible to collect data from various areas. For example, if the area field contains " 0101 ", it means both area B and D. You can also use a combination of sensor type field and area field to use more advanced data-centric aggregation. For example, the query may be as follows: Only end devices with temperatures below 0 ° C in zones A and D.

Performance evaluation

Each function of the CDL that is the basis of the present invention is tested and a performance comparison with the LoRa standard is performed. CDL is implemented by adding additional functions at a higher level while using the basic functions of the standard, so data rate and delay analysis are skipped in performance evaluation. As a result of the experiment, these two indices show almost the same performance as the standard, so there is no controversy in the present invention. Instead, overall network traffic is evaluated against the LoRa standard, and the most important feature of LoRa, energy consumption, is analyzed.

Experiment environment

LoRa products [18] were used to implement the LoRa network: Multitech mDot for end devices and Conduit for LoRa gateways. End devices and gateways are configured with the Korean frequency specification specified in LoRa Specification Version 1.02. One gateway and five end devices were used in the experiment. Since mDot and Conduit contain a LoRa standard stack, the LoRa standard performance is tested based on the original system, and the CDR is implemented at the top of the LoRa standard. Experiments were performed on five end devices, but based on actual experimental results, performance was evaluated in a wide range of environments, as shown in Table 2.

traffic  analysis

One of the important features of the present invention is that the network server 702 can process broadcast messages transmitted to each end device ED1, ..., EDn by using a shared downlink slot. In particular, the time synchronization message of this broadcast message should be used periodically to synchronize all end devices (ED1, ..., EDn). Thus, in this experiment, each end device ED1, ..., EDn is synchronized from the network server 702 once a day, and the total amount of packets (i.e., traffic) generated in the network is maintained for 30 days . For the extended experiment, we increased the number of end devices from 1 to 5 and measured the number of packets generated. Based on this data, we calculated the number of packets when the number of end devices increased from 10 to 100. In addition to sending a synchronization message once a day, each end device uses a model that sends sensing data to the network server 702 once an hour and receives ACK.

Figure 13 shows the total number of packets generated for one month in LoRa and CDL. As a result, if the number of end devices is small, the amount of traffic in the LoRa standard and CDL does not have a significant effect on the broadcast, so there is no significant difference in the total amount of traffic, but the amount of traffic becomes remarkable as the number of end devices increases. This is because the broadcasting function of the present invention is effective in reducing traffic. In particular, in LoRa, a large number of end devices are accommodated in a single gateway due to a long communication distance. However, the larger the network, the greater the effect of traffic reduction.

Energy consumption and battery life

One of the most important features of LoRa is low power communication capability. This low power capability is well suited for a variety of IoT applications. This experiment evaluates the LoRa standard and the energy consumption of the present invention. The LoRa gateway is provided with AC power and is not considered. The current consumption in each state is shown in Table 2 (including MCU current consumption). As shown in FIG. 14, the power consumption is divided into three states (TX state, RX state, and SLEEP state) for measuring the power consumption, and the consumption current corresponding to each state is integrated into each state time. Power consumption is calculated by multiplying the power consumption by the power consumed for one hour. FIG. 15 shows the result of increasing the number of data transfers per end device from 1 to 10 for one cycle (1 hour). Indeed, although the present invention is an extended version of the standard LoRa, it accommodates all the low power features of LoRa, so the energy consumption of each end device is not significantly different. This does not take into account the effects of the broadcast, and may consume slightly less energy than standard LoRa when considering time synchronization.

To better understand the more intuitive energy consumption, the battery life of the end devices based on two AA batteries was also calculated. Figure 16 shows the battery life when transferring data from one time to ten times per hour. As shown in the figure, when data is transmitted once or twice within one hour, the present invention tends to have somewhat shorter battery life than standard LoRa due to the additional energy consumption to maintain the shared downlink slots . However, as the number of data increases, it converges to the amount consumed. Also, considering one data transmission per hour, the present invention can guarantee not only LoRa but also a lifetime of more than 10 years, and is suitable for long-life applications such as remote meter reading.

conclusion

In the present invention, LoRaWAN, which is a representative technology of LPWAN, was dealt with. In particular, the present invention solves downlink constraints, a fundamental problem of LoRaWAN, by cooperative downlink listening (CDL) based on shared downlink slots that are periodically triggered by DL initiators. Energy balance has also been achieved through the choice of dynamic DL initiators to avoid intensive energy consumption of DL initiators. It also shows that various data-centric models, group casting and geocasting, are possible in connection with the present invention. The present invention is implemented while minimizing the existing LoRa standard and maintaining compatibility with the LoRa standard. Experiments show that the invention significantly reduces traffic compared to the LoRa standard, especially when the number of end devices in the network is greatly increased. In addition, the present invention showed almost similar energy consumption compared to LoRa, and it was shown that the battery life can be guaranteed for more than 10 years considering 1 hour communication. Based on the experimental results, it is expected that the present invention can be applied to various applications based on LoRaWAN.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It is clear that the present invention can be modified or improved.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

200: end device 202: gateway
204: network server 206: application server
400: uplink transmission 402: first reception window
404: second receiving window 600: standard device address
602: Network Identifier field 604: Network Address field
606: Device address used in the present invention
608: network identifier field 610: group address field
612: network identifier field 614: sensor type field
616: Area field 700, 1100: Gateway
702, 1102: network server 704, 1104: application server
706: Control section 708:
1106, ED1, ..., EDn: end device

Claims (16)

A method of transmitting a broadcast message to a plurality of end devices in a long-range wide-area network (LoRaWAN)
(a) one of the plurality of end devices becomes a downlink initiator and periodically transmits a downlink request to a network server through a gateway; And
(b) the network server transmitting the broadcast message using a second reception window (RX2 Window) of a class A end device slot timing of a Laura protocol used in the Laura wide area network through the gateway,
An end device that is allowed to join by the network server is set as the downlink initiator by requesting the network server to join the Laura wide area network first among the plurality of end devices,
The network server sets an end device having a minimum sum of uplink times and downlink times as a new downlink initiator when the sum of the uplink times and downlink times of the current downlink initiator is equal to or greater than a predetermined threshold value,
The threshold is dynamically changed by the new threshold = the existing threshold x (1 + 1/2 ^R ), and R is the long-range wide- area network to a plurality of end devices. The method according to claim 1,
Prior to step (a)
(a-1) further comprising the network server determining a fixed channel to be used for the second receiving window,
Wherein the network server transmits the broadcast message using the second reception window on the determined fixed channel in step (b), wherein the plurality of end devices in a long-range wide-area network (LoRaWAN) And transmitting the downlink broadcast message. The method according to claim 1,
In the step (b), the network server transmits the broadcast message to the plurality of end devices based on the device address block in which the network address field of the standard device address block (DevAddr) used in the Laura wide area network is divided ,
The segmented network address field may be a long-range wide-area network (LoRaWAN), including a sensor type and a group address field indicating area information and a reduced network address (Nwk Addr) field. A method for transmitting a downlink broadcast message to a plurality of end devices. The method of claim 3,
The sensor type indicates a type of a sensor provided in the end device,
Wherein the area information indicates information of an area where the end device is installed,
The Group Address field indicating the sensor type and the area information includes a LoRaWAN (long-range) field, which is expressed by a bitmap indicating the type or area of the sensor when a bit of a predetermined position among the plurality of bits is a specific value, range wide-area network) to a plurality of end devices. The method of claim 4,
The bit map representation of the type of the sensor and the group address field indicating the area information is predetermined and stored in the network server, in a long-range wide-area network (LoRaWAN) And transmitting the downlink broadcast message. delete delete delete A long-range wide-area network (LoRaWAN) system including a plurality of end devices, a plurality of gateways performing wireless communication with the plurality of end devices, and a network server connected with the plurality of gateways,
Wherein one of the plurality of end devices becomes a downlink initiator and periodically transmits a downlink request to the network server through the gateway,
The network server transmits a broadcast message using a second reception window (RX2 Window) of a class A end device slot timing of a Laura protocol used in the Laura wide area network through the gateway,
Wherein the end device, which is allowed to be connected by the network server, is set as the downlink initiator by first requesting the network server to join the Laura wide area network among the plurality of end devices,
The network server sets an end device having a minimum sum of uplink times and downlink times as a new downlink initiator when the sum of the uplink times and the downlink times of the current downlink initiator is equal to or greater than a predetermined threshold value,
The threshold is dynamically changed by the new threshold = the existing threshold x (1 + 1/2 ^R ), and R is the long-range wide- area network system. The method of claim 9,
The network server determines a fixed channel to be used for the second receiving window,
Wherein the network server transmits the broadcast message using the second receive window over the determined fixed channel. ≪ RTI ID = 0.0 > [0002] < / RTI > The method of claim 9,
Wherein the network server transmits the broadcast message to the plurality of end devices based on a device address block in which a network address field of a standard device address block (DevAddr) used in the Laura wide area network is divided,
The divided network address field includes a long-range wide-area network (LoRaWAN) system (LoRaWAN) system including a sensor type and a group address field indicating area information and a reduced network address (Nwk Addr) . The method of claim 11,
The sensor type indicates a type of a sensor provided in the end device,
Wherein the area information indicates information of an area where the end device is installed,
The Group Address field indicating the sensor type and the area information includes a LoRaWAN (long-range) field, which is expressed by a bitmap indicating the type or area of the sensor when a bit of a predetermined position among the plurality of bits is a specific value, range wide-area network) system. The method of claim 12,
Wherein a bit map representation of a Group Address field representing the sensor type and the area information is predetermined and stored in the network server. delete delete delete

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