International Journal of Informatics Society, VOL.12, NO.1 (2020) 29-39

29Industrial Paper

Proposal of IoT Communication Method for the Rice Field
Mikiko Sode Tanaka**

Global Information and Management, International College of Technology, Japansode@neptune.kanazawa-it.ac.jp

Abstract -Social application of the internet of things (IoT)
and commercialization of the low-power wide-area network(LPWA) by telecommunications carriers are progressing, andefforts to put IoT into practical use using LPWA are ongoing.
LPWA is expected to be applied for automatic meter readingof water, gas, etc., and large-scale demonstration experiments
have been conducted in Japan. Furthermore, application to
fields requiring real-time performance is also being considered. The telecommunications carrier adopts a direct method,
but the direct method is not suitable for a usage method inwhich data are transmitted from IoT nodes at the same time.
To solve this problem, a method that gathers data in the shortest time is proposed to attain the capacity of the network fully
and provide data at the time desired by the users. In this paper,
we provide an example of the field server for rice fields andpropose a method for gathering data in a short time. The
method is effective with low power consumption. Comparison results with a conventional method using a simulation
demonstrate that the proposed method can collect all data inthe shortest amount of time. Moreover, the power consumption is lower than that of the conventional method. It was also
confirmed that the rate of increase in the time necessary forthe parent node to collect data due to an increase in the number of sensor nodes is lower than that of other methods.
Therefore, this proposal makes it possible to transmit the situation of a rice field in a timely manner and can be considered
to be a useful method for reducing the burden of agriculturalwork. In addition, it is effective for other applications that require real-time performance.

Keywords: LoRa, Rice field, Data gathering, Multihop rout-

Figure 1: LPWA network for IoT

Figure 2: Wired LAN + Wi-Fi network for a building

ing

1

INTRODUCTION

Social application of the internet of things (IoT) is progressing. Especially, in factory management, IoT has become
an indispensable basic tool [1]. In addition, the commercialization of the low-power wide-area network (LPWA) by telecommunications carriers is progressing, and efforts to put IoT
into practical use using LPWA are ongoing [2],[3]. Figure 1
shows an illustration of the network provided by telecommunications carriers. With LPWA, it is possible to cover a wide
range of areas and also to collect data in both homes and buildings and units of towns and cities.
LPWA is excellent for low-power and long-distance transmission and is expected to be applied for automatic meterreading of water, gas, etc., and large-scale demonstration experiments have been conducted in Japan [2],[3].

Automatic meter readings such as those for water and gas are
suitable for LPWA because the timing for acquiring and transmitting data is not strictly regulated, and data for a certain period can be sent within an arbitrary period. Furthermore, application to fields that require real-time performance is also
being considered [4].
A field server for rice cultivation management system forrice fields is an application that requires real-time performance. The main function of the rice field server is waterlevel management. The water level must be managed in unitsof several cm in the months immediately after rice planting,and real-time performance is required. However, the telecommunications carrier adopts the direct method. As a result, a
conflict may occur and farmers may not be able to see the datain the time they want. Therefore, direct method is not suitable
for a usage method in which data are transmitted from IoT
nodes at the same time.

ISSN1883-4566 © 2020 - Informatics Society and the authors. All rights reserved.

30

M. S. Tanaka / Proposal of IoT Communication Method for the Rice Field

When there are many applications that acquire and transmit
data at intervals of several minutes, data transmission concentrates at the same time and a conflict occurs. For this reason,
to prevent data transmission from occurring at the same time,telecommunications carriers apply an operation method that
reduces the probability of competition by providing a difference in usage fees. However, the conflict problem has notbeen solved.
There are many cases in which companies construct networks with a wired large area network plus wireless fidelity(LAN + Wi-Fi). Figure 2 shows an illustration of the LAN +Wi-Fi network in a building. This method is effective in termsof security and cost. Cost and security are also important
items for rice cultivation management system. Thus, when
considering a communication system for rice cultivation,
there is a high demand for building a wireless network withthe same structure as a wired LAN + Wi-Fi network in a company. The most important reason is cost. In addition, to prevent the water level management technique from being stolen,
it is desired to manage the water level data locally. However,there is currently no local area wireless network system forrice fields that can realize this objective.
In this paper, we assume an application that acquires andtransmits data at an interval of tens of minutes, particularly
the system for rice cultivation. In addition, a wireless networkthat connects all rice fields locally is assumed. The wirelessnetwork is of the same type as a wired LAN + Wi-Fi network
in a company. We propose a communication protocol to realize real-time performance with this wireless network.
Comparison results with a conventional method obtainedusing a simulation demonstrated that the proposed method
can collect all of the data in the shortest amount of time.
Moreover, it was confirmed that the power consumption is
also lower than that of the conventional method. Furthermore,
it was confirmed that the rate of increase in the time necessary
for the parent node to collect data, due to the increase in thenumber of sensor nodes, is lower than that of other methods.

standard yield per tan is 9 pyo, and this amount of rice can besold in the market for about 13,000 yen. If the cost is deducted,
a profit of about 50,000 yen can be obtained per pyo [5]. In
other words, in Japan, farmers can only make a profit of
50,000 yen per year from 1 tan (Table 1). On the other hand,field servers rent for 8,280 yen per month [6]. Thus, the rentfor 6 months costs 50,000 yen. This calculation indicates very
little profit. Therefore, the introduction of field servers has
not progressed among rice farmers. From these facts, in order
to introduce the field server practically, the selling price mustbe less than 10,000 yen. The manufacturing price can be assumed to be around 3,000 yen. Therefore, we assume a field
server that can realize this price.
Field servers should not interfere with the farmer's work.
Because large agricultural machines are used in the rice field,
the field server needs to be easy to move. Therefore, its heightmust be less than 1 m, and it should be as small as a lunch
box and compact. Additionally, because rice fields do nothave a power source, it is necessary to operate the servers
with batteries from rice planting to rice harvesting. Therefore,
intermittent operation is necessary.
To realize an affordable field server, we decided to use along-range (LoRa) network that does not require a communication line usage fee and can transmit a great distance. LoRa
can send more data than Sigfox [7] and is considered more
effective in an agricultural field having a relatively large
amount of sensor data. In addition, the protocol and frame
format can be created freely, so it is suitable for special applications that require performance and price. LoRa can buildand operate all architectures including base stations by itself,
and its specifications are open. For this reason, it is easy tobuild a system for special purposes.
Furthermore, to build a reasonable price field server forrice cultivation, it is necessary to reduce the number of parts
to the minimum limit. For example, crystal elements and GPS,
which are expensive and highly accurate clock sources, cannot be used. In addition, there must be a lightweight communication protocol that operates without expensive components. For this reason, the design must accept time errors,
which is a fatal problem for communication systems. To
solve the problem of time error, it is necessary to take a timeslot longer to be able to tolerate time error. The time slot is atime interval for sending data.

2

REQUIREMENTS FOR FIELD SERVERSSUITABLE FOR JAPANESE RICE FIELD

In Japan, rice produces a lower income than other crops.
Table 1 shows the profit structure of rice production revenue.
The unit of 1 pyo is equal to 60 kg, and 1 tan is 0.1 ha. The

IncomeSpending

Table 1: Profit structure of rice production revenue
Breakdown
1 pyo (60 kg)
13,000 Yen
Rice crop yield (1 tan)
9 pyo
Fertilizer (1 tan):
Herbicide and pesticide (1 tan)
Agricultural machinery fee (1 tan)
Personnel costs (1 tan)

15,000 Yen
10,000 Yen
20,000 Yen
15,000 Yen

Total
117,000 Yen

60,000 Yen

International Journal of Informatics Society, VOL.12, NO.1 (2020) 29-39

Figure 3: Proposed LPWA network for rice fieldA rice cultivation management system using a field server
focused on in this paper was developed to manage the fieldsmoothly and flexibly. The configuration is shown in Fig. 3.
The system consists of field servers, a parent node, and a
cloud service. From the perspectives of cost and security,
farmers desire a local wireless network like the wired LAN +Wi-Fi network in a building. Farmers want to check the waterlevel in every hour within 5 minutes after sensor data are acquired.
The field server is installed in the rice field. After acquiring
the sensor data, it transmits the data to the parent node via the
LoRa wireless network. The parent node aggregates the sensor data from the field servers installed in each rice field andtransfers these data to the cloud via a 3G line or Wi-Fi. Cloud
services are provided by applications such as smartphones
and tablets and web pages. The system provides functions
such as water level warnings, work plan proposals, preservation of work records, etc., for the farmers.
The average amount of rice field held by a farmer in Japan
in 2010 was 105.1a [8], and the effective transmission distance of LoRa is about 3 km. Therefore, the wireless communication protocol proposed in this paper assumed a rice fieldarea of 3 km × 3 km and a maximum number of field servers
to be installed of 100. In the farmer office, the parent node
always wake up and have a power supply.

3BASIC WIRELESS COMMUNICATIONPROTOCOL

To operate for 6 months in an environment without a power
supply, it is necessary to turn off the power when sensor dataacquisition and communication are not being performed. To
realize these operations, an intermittent operation communication protocol and time synchronization technology are required. Time synchronization technology has been studied extensively [9]-[12].
For example, a time synchronization method using a radio
clock has been proposed [13]. This method requires about 3
minutes to set the time. For this reason, the operation time
becomes longer and it is difficult to realize low power consumption. In addition, the received signal (time code) needs
to be converted to a format that can be handled in the field
server, but a program that performs this processing cannot be

31

written to a low-cost microcomputer, such as a PIC microcomputer, with little memory. Therefore, it is difficult to use
it for a rice field server.
A time synchronization method using GPS has also been
proposed [10]. To use this method, it is necessary to install a
GPS receiver module in each field server, which leads to anincrease in the initial cost at the time of introduction. For thisreason, it is difficult to use the method for field servers where
there is a desire to lower the cost barrier of introduction.
Reference broadcast synchronization (RBS) has been proposed as a time synchronization method for wireless networks[11]. Time synchronization is performed by exchanging time
information between field servers that receive a certain broadcast packet. However, RBS has the problem of increasing
power consumption because the amount of information exchanged increases in proportion to the increase in the numberof receiving field servers. Therefore, it is difficult to apply it
to field servers for rice field.
The Timing-sync Protocol for Sensor Networks (TPSN) has
been proposed as a method for improving RBS [12]. The
TPSN forms a tree structure with the parent node at the top,
and the parent node performs time synchronization with thefield server. The field server synchronizes time with the field
servers below it. In this way, time is synchronized throughout
the system. However, because this method requires a longtime for time synchronization, it is not suitable for field servers that require low power consumption.
We proposed a wireless communication protocol that
achieves low cost [4]. Figure 4 shows a basic communication
protocol sequence diagram of the proposed protocol. Communication is performed according to scheduling. In Fig. 4,
field server A (FS-A) sends the sensor data to field server B.
Then, field server B sends its own sensor data and the sensor
data of the field server A to field server C. Field server C constructs a frame with the sensor data of field servers A and B
and its own sensor data and sends these data to field server D.
The time is transmitted as a signal indicating that data havebeen received. The time can be synchronized among field
servers transmitting and receiving data, but it cannot be synchronized with other field servers. The field server does notinclude a crystal or other system to measure the exact time, so
there is an error of about a dozen seconds between
the field servers in the proposed wireless communication

Figure 4: Communication protocol sequence diagram32

M. S. Tanaka / Proposal of IoT Communication Method for the Rice Field

Table 2: Frame format (Byte length)
Destination
Sender
Payload1
1variable
Table 3: Payload for sensor data (Byte length)
FS
SenSenSensor
Sensensor
ID
sor
sor
data
sor
data
data
data
3
data
5
1
2
4
2
2
2
2
2
2

Figure 5: Time slot shift due to time error

protocol. Transmission / reception between field servers takes
place within the time slot. The time slot is set to long, when atransmission or a reception fails, a retry is made after a random time.
The operation when a field server is newly introduced follows. The newly added field server first sends a wake-up signal to inform the parent node that it has been added. When theparent node receives the wake-up signal from the field server,
the field server number is added to the library and rescheduling is performed. The scheduling result is sent to the field
server at the same time. The field server synchronizes the time
based on the reception time from the parent node. When afield server is newly introduced, the field server works by direct method at first.
The time at which the field server is installed is arbitrary.
Therefore, when another field server is communicating withthe parent node, the newly added field server may start communication. However, in this case, collisions may occur. In
the event of collision, retransmissions are performed after arandom period within a few seconds. This process is repeateduntil the field server receives the current time informationfrom the parent node.
The proposed method allows time errors. Therefore, as
shown in Fig. 5, the original time is deviated and a time slot
is generated. It may also occur when time slots overlap. We
decided to allow them by setting the time slot to about 7 or 8
times the time for a single transmission. Due to the time error,
the transmission times slot executed in each channel are notunified.

4

SYSTEM CONFIGURATION OF RICECULTIVATION MANAGEMENT SYSTEM

In the LPWA network, the time is often overlapped for thegathering sensor data and for sending them to the parent

node that is the gateway. As a result, the user may not be able
to confirm the data at a desired time. To solve this problem, amethod that the gathering data in the shortest time is needed
to fully extract the capacity of the network and the provide
data at the time desired by the users [14]-[17].
A rice cultivation management system monitors the air andwater temperature of rice fields. This system consists of afield subsystem, a home subsystem, and a management subsystem. The field subsystem is installed in the field, acquires
air and water temperature data and transmits the acquired data
to the home subsystem via a wireless network. The home subsystem is a system that uploads the data sent from the fieldsubsystem to the management subsystem via the Internet. The
management subsystem is a system that analyzes and displays
the collected data and allows farmers to check the data accumulated on the cloud via the Internet.
In the field server subsystem, a plurality of field servers are
held; each field server acquires data once per hour, and transmits the acquired data to the home subsystem which is a parent node. This single process is called round one. Table 2
shows the frame format used for transmission. The frame iscomposed of a transmission destination, a transmission source,
and a payload. Table 3 shows the sensor data transmission
format stored in the payload of Table 2. In addition, the parent
node can communicate with at most one field server at thesame time, and the field server can communicate with at mostone field server or parent node. In a single process, the poweris turned off after system startup and after data acquisition,acquisition of a data transmission, and transmission are completed. The time required for this series of processes is defined as one round of operation time. This operation time isthe time required to gather data to the parent node. In eachfield server, the data merging processing is performed as necessary. By this merging process, it is possible to shorten thetime required for transmission.
Synchronization between the parent node and field servers
is carried out by using the current time transmitted according
to the transmission request sent from the parent node [18].
When the field server receives the current time, the time is
updated to the current time.

International Journal of Informatics Society, VOL.12, NO.1 (2020) 29-39

5

LOW DELAYMETHODDATAGATHERING

Currently commercially available LPWA uses the direct
method. However, since this method has a long data-gathering-time problem. When the number of field servers is n, andthe time step T of direct method which is required can be expressed by the following equation.
T=n

(1)

In the direct method, the time required to transmit the dataof all field servers to the parent node increases in proportion to
the number of field servers. If one time slot is set to 30 seconds
and there are 200 field servers, a time of 30 * 200 = 6000 seconds = 100 minutes is required, and a request of 5 minutes orless cannot be satisfied.
In this paper we propose a method that has a low power
consumption and a short data-gathering time. The procedureof the proposed method is shown below.
①
②

③
④

After the rice planting, the field servers are installed in
the rice field. The field server starts in installation mode.
Farmer sets the initialization mode to the parent node,and then the field server position confirmation procedure
is executed in order to collect position information of the
field server.
A transmission network graph is created on the parent
node based on the field server position information, andthe scheduling result is sent to the field servers.
Data gathering procedure on the local wireless network
is performed based on scheduling result.

The newly added field server first sends a wake-up signal toinform the parent node that it has been added. When the parent
node receives the wake-up signal from the field server, thefield server number is added to the database and the time fortransmitting data to the parent node is sent to the field server.
Operation using direct method is started [19].
In this state, when initialization mode is set in the parent
node, the field server position confirmation phase starts at thetiming when data is sent from the next field server to the parent
node.
The field server sends data to the parent node by direct
method, then enters the reception mode. Next the field server
receives data from other field servers, calculates the radio fieldstrength, and creates a list of field server numbers in order ofstrength. At the next transmission timing, a list of field server
numbers in order of strength is transmitted together with sensor data.
The parent node has a list of field server numbers in orderof strength and a list of field server numbers in order ofstrength sent from each field server. Based on this information,a transmission network graph is created and the scheduling result is transmitted to the field servers by broadcasting. Eachfield server is turned off when it receives the scheduling result.
Thereafter, each field server performs transmission processing
with this scheduling result.

6

TRANSMISSION NETWORK GRAPH

We describe the procedure for creating a transfer network
graph. A transmission network graph is a graph that describes

33

the order, direction, and transmission timing of data transmission between a field server and a field server, or between aparent node and a field server. Data collection is performed
according to this graph. The transfer network is defined by theeffective graph G = (V, E). V is a set of the parent node andthe field servers. E is a set of edge, and edges e = {i, j} indicatethat data is transmitted from node i to node j.
is set ofedges which data is sent in m steps.
Here, in order to simplify the following discussion, thesymbols are defined as follows.
V:
N1:
N2:
:

{N1, N2} node set
set of parent node
set of field servers
parent node

:
l:
m:

field server j where j=1, 2, 3, ...
the number of parent node
the number of field server

e={ , }:transmission from to node
: set of edges in the step mE={}: set of edges
F:
set of transmission completion nodesE:
set of un-transmission completion nodes
Nearest(j, G): The node with the closest distance to node jin node set G for which transmission has not been completed
Farthest(j, G): The node with the farthest distance to node jin node set G for which transmission has not been completedt:step numberk:tradeoff variable of processing completion time andpower consumption
The transfer network graph creation flow is shown below.
Procedure Routing(V， E)
1: F={n_0};
2: G=N2;
3: t=0；4: k=4; /* Processing time and power trade-off factor*/
5: While( There are k or more nodes belonging to G) {6:/* Transmission to the parent node*/7:
t=t+1;
8:i= Nearest(n_0, G);
9:/* Find the nearest field server to the parent. */10:Create branch { , } and put in set E_t representing processing at t time step
11:
Delete node i from un-transmit set G.
12:
Put the node i in the transmission complete set F.
13:/* Data transmission between field servers */
14:
H=G;
15:
While(There is a node that belongs to H) {16:
j=Farthest(n_0，H);
17:
Delate j from H.
18:
i=Nearest(j，T).
19:
Delate i from H.
20:
Generate edges {i, j} and put them in the set
E_t representing the processing at t time steps

34

M. S. Tanaka / Proposal of IoT Communication Method for the Rice Field

21:
Delete node j from un-transmit set G.
22：
Put the node j in the transmission complete
set F．
23:}
24:}
25: While(There is a node that belongs to G) {26:/* Transmission to the parent node */27:
t=t+1;
28:
i= Nearest(n_0, G);
29: /* Find the closest field server to the parent node. */30:
Generate edges { , j} and put them in the set E_t
representing the processing at t time steps.
31:
Delete node j from un-transmit set G.
32:
Put the node j in the transmission complete set F．
33:}

The movement of the flow is explained using the example
of one parent node and 11 field servers shown in Fig. 6. In thefirst step, the field servers 5 nearest to the parent node is selected, and an edge representing transmission to the parent
node is made. Next, the field server 11 which is farthest fromthe parent node is selected, and an edge from the field server
11 to the field server 7 is made. Similarly, an edge from field
server 3 to field server 2, an edge from field server 10 to field
server 9, an edge from field server 8 to field server 6, an edge
from field server 1 to field server 4 are created, and the firststep is complete.
In the second step, as in the first step, an edge from the parent node to the nearest field server 9 to the parent node is created, an edge from the field server 7 to the field server 6, anedge from the field server 2 to the field server 4 is created. In
the third step, an edge from the field server 4 to the parent
node, and in the fourth step, an edge from the field server 6 tothe parent node are created.

7

DATA GATHERING PROCEDURE

The data gathering procedure will be described. Data isgathered to the parent node according to the tree structure of
the graph created in the transfer network graph creation flow.
Here, the operation is explained using the example in Fig. 6.
In the first step, transmission corresponding to the edges
belonging to the branch set
representing the processing in
the first step is performed. That is, transmissions from thefield server 5 to the parent node, from the field server 11 to
the field server 7, from the field server 3 to the field server 2,
from the field server 10 to the field server 9, from the field
server 8 to the field server 6, and from the field server 1 to thefield server 4 are performed. The field server receiving thetransmission merges the data held by itself and the transmitted
data, creates a frame, and prepares for the next transmission.
In the second step, transmission corresponding to the edge belonging to the edge set representing the processing in thesecond step is performed. That is, transmissions from the field
server 9 to the parent node, from the field server 7 to the field
server 6, and from the field server 2 to the field server 4 areperformed. The field server receiving the transmission merges
the data held by itself and the transmitted data, and creates aframe. In the third step, transmission corresponding to theedge belonging to the branch set that is transmission fromthe field server 4 to the parent node is performed. In the fourth
step, transmission corresponding to the edge belonging to thebranch setthat is transmission from the field server 6 tothe parent node is performed.
Figure 7 shows a sequence diagram of data exchange between the parent node and field servers. The data of each field
servers is merged step by step, and all data is sent to the parent
node in the fourth step.
The number of field servers in operation at step T is defined as N (T). The number of steps required to gather data
can be expressed by the following equation.
N(T+1)=⌈(N(T)-1)/ 2⌉
Namely, T where N (T + 1) = 0 is a necessary step totransmit all data to the parent node. For example, in the example of Fig. 6,
N(0)=11
N(1)=⌈(11-1)/2⌉=5
N(2)=⌈(5-1)/2⌉=2
N(3)=⌈(2-1)/2⌉=1
N(4)=⌈(1-1)/2⌉=0
In this example, since the number of field servers is 11, N(0) = 11.Then, all data can be transmit to the parent node in 4
steps.
From the above consideration, the number of steps T required for data gathering can be expressed by the following
equation.
(2)
If one time slot is set to 30 seconds and there are 200 field
servers, a time of 30 *= 228 seconds = 3.8
minutes is required, and a request of 5 minutes or less can besatisfied.

Figure 6: Operation example of one roundInternational Journal of Informatics Society, VOL.12, NO.1 (2020) 29-39

35

Table 5: Details of simulation data
#Parent#FS
Radius(m)
DATA1
1
99
500
DATA2
1
200
500
DATA3
1
300
3000

Figure 7: Sequence diagram of operation example

8

PERFORMANCE EVALUATION BY SIMULATION

A comparison was made by simulation to check the data
gathering time. Here, we focus on the prompt confirmation of
the condition of the rice field required for rice cultivation.
Therefore, we verify the data gathering time and the power
consumption required to collect all the field server data. Being
able to verify the data within an allowable time is an important
item even if the number of field servers is increased. The simulator was written in C language. First, the method of calculating the power consumption will be described. Owing to thefact that the parent node is always supplied with power, its
power consumption is excluded from the scope of consideration and only field servers are calculated. Each field server has
a battery and has a capacity of 75,000 mWh. The field server
has six modes (Table 4) according to the operating condition.
The current consumption was set from the actual power consumption measurement report [18] using LoRa. The transmission power depends on the distance. Operation voltage is set
at 2.5 V. The time of data merge is not considered because it
is 1/100 or less of the time required for transmission and reception. Also, since the data transfer network is created only
once at first, the influence on the power consumption is notconsidered because it is small.
Table 4: Six mode of field server
State

1
2
3
4
5
6

State namePower OFF
Data transmission
mode
Data
reception
mode
Systemstartupmode
Sensor data acquisition modeStandby mode

Power consumption(mA/s)

Processing
time
(s)

0
53 ， 62 ，
69，78
13.5

3.4

Parent 78
FS 13.5
60.0

3.4

2.7

3.4

3.4

60.0

The sensor data to be acquired is the data on temperatureand humidity. In each round, when each field server reaches
the activation time, the system is started and the data is acquired from the sensor. Next, the parent node transmits a datatransmission request to all of the field servers. Upon receiving
the data transmission request, the field server measures thedata from the sensor, and transmits the data to the parent node.
Each field server turns off the power source. In this simulation,
it is assumed that the time synchronization is perfectly performed. It was assumed that there was no failure of data transmission / reception. In fact, the merging time of the data by
the field server was ignored in this simulation. Given that the
payload can be transmitted at a data rate of up to 60 bytes, thetransmission time can be shortened by the data merging process.
Table 5 shows the three instances of test data created. The
field servers have been randomly assigned within the circle ofa specified radius, centered on the parent machine.
Comparisons were made between the following methods:
direct [20], pegasis [21], epegasis [22], chiron [23] and the
proposed method. In addition, the following three items arecompared to enable the farmer to confirm the data of the rice
field in real time, while reducing the data gathering time andoperating with batteries from the time of rice planting to harvesting.
Power Efficient Gathering in Sensor Information Systems(pegasis method) is a chain-based protocol [21]. The field
servers are connected only to the closest field server and arechained. Data is sent along the chain to the chain head (thelast filed server of the chain) and from the chain head to theparent node. The chain head is randomly selected and has aduty to transmit data to the parent node. The time required togather data for pegasis method is long.
Epegasis method [22] has been proposed as a method tosolve the pegasis method problem. The field servers are broken down into clusters at a distance from the parent node, anda chain is created in each cluster in the same way as pegasis
method. Each cluster sends data to the chain head along thechain. When data gathers in the chain head in each cluster, thechain head transfers data to the parent node. Therefore, thetime required for data collection can be reduced compared topegasis method.
Chiron method [23] has been proposed as a method forachieving further improvement. It is characterized by using
Beam Star technology [24] to divide into smaller cluster areas
than epegasis method. In each cluster, build a chain. Initially,
the data for each cluster is collected by the chain head in thesame way as pegasis method. Next, a chain between chain
heads is created in order from the chain head farthest from theparent node, along which data is sent to the parent node. Chiron method can shorten the time required for data collectionin each chain by shortening the chain length, but has the problem that the time required for gathering data in each area tothe parent node increases.

36

i.
ii.
iii.

M. S. Tanaka / Proposal of IoT Communication Method for the Rice Field

Time required for data gathering in one round.
Total power consumption of all field servers in one
round.
Maximum working days (the number of days during
which all the field servers are in operation).

The simulation results of DATA 1 are shown in Table 6.
Table 6 shows the operation time, which is the time required
for the parent node to gather data, the total value of the power
consumed by the field server, and the number of operable
days. Figure 8 shows the size of data received by the parent
node in the one round. The vertical axis in Fig. 8 represents
the data size (byte) received by the parent node, and the horizontal axis represents operating time (seconds). Figure 9shows the number of field server whose transmission processing has been completed and the power has been turned off
within one round. The horizontal axis shows the operatingtime (seconds), and the vertical axis shows the number offield servers whose power has been turned off. It can be confirmed that the slope of pegasis method is the slowest.
Table 6: Simulation results of data1
Data col- Total power Number
lectionconsumptionof worktimeof field servers ing days
/ Round/Round
(Day)
(s)
(mAS)
Direct400.074508.5
372
PEGASIS1902.9299237.6
58
EPEGASIS
226.6
55253.0384
CHIRON
158.6
40131.1
448
Proposed
114.4
34177.0
566

Figure 9: Number of power off field servers of DATA1.
Compared to other methods, the proposed method showsthat the time to gather data to the parent node is the shortest.
Moreover, the total power consumption is the smallest, basedon the simulation, it can be concluded that it can operate for aperiod that extends from rice planting to harvesting.
The simulation results for DATA 2 are shown in Table 7.
Compared to other methods, the proposed method shows thatthe time for the parent node to collect data is the shortest. In
addition, it is understood that the total power consumption is
the smallest, and the lifetime is the longest. In the simulation,
we can see that it can operate for a period that extends fromrice planting to harvesting. In addition, although the proposed
method doubles the number of field servers as compared with
DATA 1, it can be seen that the increase in time required fordata gathering is as short as about 7 s.
The simulation results for DATA 3 are shown in Table 8.
Compared to other methods, the proposed method shows thatthe time to for the parent node to collect data is the shortest.
In addition, it is understood that the total power consumption
is the smallest, and the lifetime is the longest. Moreover, interms of the theoretical value, it can be understood that it canoperate for a period extending from rice planting to harvesting.
In addition, compared to DATA 1, the number of field servers
is tripled, but the increase of time increase necessary for collection is short as about 10 s.

Table 7: Simulation results of data2

Figure 8: Number of data received by parent node of
DATA1.

DirectPEGASISEPEGASISCHIRON
Proposed

Data collection
time/ Round(s)

Total power consumption of field
servers/Round(mAS)

Numberof working days
(Day)

743.4
7135.4
721.0
248.7
121.2

243604.6
1763010.2
201747.2
90308.870925.4

210
18
195
209
231

International Journal of Informatics Society, VOL.12, NO.1 (2020) 29-39

Table 8: Simulation results of data3

DirectPEGASISEPEGASISCHIRON
Proposed

Data collection time
/ Round(s)

Total power
consumption offield servers/Round(mAS)

Numberof working
days
(Day)

1083.415771.0695.8519160.05672543.4
487720.8

67
8
97

322.1
124.6

168756.0
117871.6

151
185

Figure 10: Comparison of time required to gather data in
one round.

Figure 11: Excerpt from the Fig. 10
Figure 10 displays the time to gather data to the parent node
in one round. Figure 11 is excerpt from the Fig. 10. The vertical axis represents the operation time (seconds). For the direct and pegasis methods, as the amount data increases, thetime required to gather data to the parent node rapidly increases. For the proposed method, the rate of increase of thetime required for data gathering according to an increase in
the amount of data is the lowest, and data can be collected in37

a short time even if the number of field servers increases. In
addition, the elongation rate is about a 5% growth with respect to an increase in the number of field servers. This result
confirms the validity of Equation (2) and also indicates thatthe proposed method is superior to other methods in terms ofthe data gathering time.
The proposed method gather all field server data in a shorttime. Since all data can be gathered in a short time, the operation time is short and the power consumption can be reduced.
In order to gather the data in a short time, three measures weretaken to reduce the number of the data transmission to theparent node. The first is compression by the data merging to
reduce the number of the transmissions. In order to reduce thenumber of the transmissions, the upper field server merges thedata from multiple lower field servers. The power consumed
in the merge process is negligible compared to the transmission. The second is the scheduling method in which the parent node keeps receiving data without idle time. The third is
the transfer network graph configuration that minimizes thenumber of multihops. This has reduced the total amount ofdata that must be sent.
The proposed method is for IoT, and it is the method for asmall data size such as the environmental data of temperatureand humidity, or the consumption data of electricity and gas.
It is also assumed that the size of the data to be handled isalmost the same. Therefore, when the data size is large, thecompression effect is reduced and the efficiency may be reduced. And when the data size is significantly different, latency may occur and efficiency may be reduced.

9

CONCLUSION

The telecommunications carrier adopts a direct method,
but the direct method is not suitable for a usage method inwhich data are transmitted from IoT nodes at the same time.
To solve this problem, a method that gathers data in the shortest time is proposed to attain the capacity of the network fully
and provide data at the time desired by the users.
In this paper, we assume an application that acquires andtransmits data at an interval of tens of minutes, particularly asystem for rice cultivation. In addition, a wireless network thatconnects all rice fields locally is assumed. The wireless network is of the same type as a wired LAN + Wi-Fi network in
a company. This method is effective in terms of security andcost. We proposed a communication protocol to realize realtime performance with this wireless network.
It is difficult to supply power to rice fields unlike otherfields, so low power consumption is an important factor. In
addition, the line usage fee required for communication must
be reduced as much as possible from the standpoint of the entire cost required for agriculture. Therefore, we investigatedinterfiled communication using LoRa which is an IoT communication standard, low power consumption using the ISM band
and a long transmission distance.
As a result of the comparison with other methods using
the simulation, we confirmed that the time required to gather
field server data to the parent node is the shortest. Moreover,it was confirmed that the power consumption is smaller thanthat of conventional systems. Furthermore, we confirmed thatthe elongation rate of time necessary for gathering data to theparent node due to an increase in the number of field servers

38

M. S. Tanaka / Proposal of IoT Communication Method for the Rice Field

is lower than that of the other methods. This result supports thetheoretical formula.
Therefore, this proposal makes it possible to transmit thesituation of a rice field in a timely manner and can be considered to be a useful method for reducing the burden of agricultural work. In addition, it is effective for other applications that
require real-time performance.

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Mikiko Sode Tanaka received Dr.
Eng. degrees from Waseda University
in Fundamental Science and Engineering. She joined NEC Corporation, NEC Electronics Corporation,
and Renesas Electronics Corporation.
She is Associate Professor of International College of Technology, Kana-International Journal of Informatics Society, VOL.12, NO.1 (2020) 29-39

zawa. Her research interests include wireless communications, AI chip, and personal authentication. She is a member of IPSJ (Information Processing Society of Japan), IEICE (Institute of Electronics, Information and Communication Engineers) and IEEE (Institute of Electrical andElectronics Engineers).

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