extfieldsofstudy:
Computer Science
Physics

text:
BBM92 quantum key distribution over a free space dusty channel of 200 meters

Free space quantum communication assumes importance as it is a precursor for satellite-based quantum communication needed for secure key distribution over longer distances. Prepare and measure protocols like BB84 consider the satellite as a trusted device, which is fraught with security threat looking at the current trend for satellite-based optical communication. Therefore, entanglement-based protocols must be preferred, so that one can consider the satellite as an untrusted device too. The current work reports the implementation of BBM92 protocol, an entanglement-based QKD protocol over 200 m distance using an indigenous facility developed at Physical Research Laboratory (PRL), Ahmedabad, India. Our results show the effect of atmospheric aerosols on sift key rate, and eventually, secure key rate. Such experiments are important to validate the models to account for the atmospheric effects on the key rates achieved through satellite-based QKD.

I. INTRODUCTION
In classical communication, the security of encryption keys for parties communicating with each other is an ongoing challenge. Even after 50 years of digital communication, the security depends upon the hardness of breaking the encryption, which may compromise the security of encrypted messages sent through a public channel once a quantum computer intercepts them. With the development of quantum computers having sufficient numbers of good quality qubits becoming a practical reality, the demand for secure communication has increased. It has already been realized that by using Shor's algorithm [1][2][3], one can break the encryption used in key distribution between communicating parties [4]. Quantum Key Distribution (QKD), on the other hand, relies on the principles of quantum mechanics, like uncertainty principle, no-cloning theorem and monogamy of entanglement to securely distribute keys between the communicating parties [5,6]. These principles make QKD safe even against a quantum computer while making no assumptions on Eve's technological capability.
Every protocol has distance limitations as the loss and disturbance in the channel increases with the transmission distance. Entanglement based QKD (EBQKD) are ideal for long-distance quantum communication like satellite-to-ground, as it can make two far apart ground stations communicate securely. Also, the security is not compromised irrespective of the satellite distributing entangled photon pairs is trusted or not. It must be noted that the satellite-to-ground EBQKD has already been performed [7,8]. The current limitation of using EBQKD is the low key rate, as mostly the entangled photon pairs produced are from spontaneous para- * rpsingh@prl.res.in metric down-conversion (SPDC) [9,10] process that is not very efficient. The two factors contributing to low key rates are low-efficiency of the photon-pair generation, and loss of photons in the communication channel. Low efficiency can be compensated with the high-brightness high-fidelity photon-pair sources. However, one of the ways to mitigate the effect of channel is by studying its effect on parameters controlling the QKD. In the past, the controlled and quantitative studies to observe the influence of atmospheric conditions such as the presence of particulate matter (PM) or aerosols have never been considered. In this study, we account the presence of aerosols and show its effect on the secure key rate.
Atmospheric aerosols, solid or liquid particles suspended in air, are produced by natural sources and anthropogenic emissions. Mineral dust and sea salt are produced from natural sources while sulfate, nitrate, black carbon and organic carbon are emitted primarily and/or converted into particles through a gas-to-particle conversion mechanism. Atmospheric aerosols/PM can scatter and absorb the incident radiation. The dry and long summer of Ahmedabad, a metropolitan city and urban environment, contains a relatively higher amount of aerosols [11]. For carrying out satellite-to-ground based communication, entanglement based QKD (EBQKD), such as BBM92 protocol is the most suitable as it does not require a trusted node [12,13]. In this article, we report the demonstration of BBM92 protocol at the indigenously developed communication channel facility at PRL, and the effect of dust/atmospheric channel on the secure key rate. This is the first attempt, in India, to demonstrate such studies, and eventually will form a strong base for the future long-distance quantum communication.
The article is structured as follows. The section II contains the background information about the BBM92 protocol, the entangled photon-pair source, and the indigenous facility built to study the atmospheric channel. The section III contains the results obtained and the re-arXiv:2112.11961v2 [quant-ph] 9 Jan 2022 lated discussion. And finally, we conclude in section IV.

II. BACKGROUND
BBM92 is a QKD protocol which involves pairs of entangled photons and can be regarded as an entanglementbased version of the BB84 protocol. BB84 is a prepare and measure based QKD protocol where Alice randomly generates polarization states using RNGs whereas in BBM92 the randomness is inherent in the measurement of the entangled photon pairs. The basic block diagram of the BBM92 protocol is shown in  In this protocol, a common sender Charlie generates a pair of entangled photons and sends them to Alice and Bob through a quantum channel. Quantum channels can be free space, water or optical fibre. Alice and Bob independently perform their measurements in a random basis. Once the measurement is done, both declare their basis choices through the public channel. Only those measurements contribute to key for which Alice and Bob have chosen the same basis, and the rest of the measurements are discarded. The key formed after this process is called sifted key. In addition, error correction (EC) and privacy amplification (PA) is performed on sifted key to get a secure key. In our experiment, the quantum channel between Charlie and Alice is not exposed to atmospheric aerosols as both are co-located in the same room. However, the quantum channel between Charlie and Bob experiences the free-space dusty atmospheric channel of 35 m and 200 m.

A. Entangled photon-pair source
The high-efficient, high-brightness, in-house developed polarization-entangled photon-pair source was set up using ppKTP crystal placed in a Sagnac interferometer. The schematic of the experimental setup is shown in Fig. 2 [14]. A continuous-wave laser at the wavelength of 405 nm and output power of ∼5 mW is used to pump a 30 mm long type-0 ppKTP crystal of period Λ = 3.425 µm. A lens L 1 of focal length 400 mm is used to focus the pump beam on the crystal to generate entangled photons using a novel experimental scheme based on polarization Sagnac interferometer consisting of a dualwavelength polarizing beam splitter cube (D-PBS), two half-wave plates (HWP) HWP 3 , HWP 4 , and two high reflecting (R>99%) mirrors M 1 , M 2 at 810 nm. The working principle of this setup is well explained in the article [14]. Since both the clockwise and counter-clockwise pump beams follow the same path in opposite directions inside Sagnac interferometer and the ppKTP crystal is placed symmetric to the D-PBS, the implemented scheme is robust against any optical path changes to produce SPDC photons in orthogonal polarizations with ultrastable phase. The analyzer comprises a PBS and a HWP plate, and is used to measure the polarization entanglement of the generated photon pairs. The polarization entangled state generated from this method is

B. Communication channel and their arrangement
Our communication channel consists of arrangements on two buildings, located nearby, in the Thaltej campus of PRL. The sending and receiving ends are located on the same terrace in two separate rooms. There are two reflectors -one for a path length of 35 m and another for 200 m on the other building to reflect back the photons. The reflector consists of a 1-inch diameter mirror placed on a structure dedicated to this purpose. The channels run through a free-space open atmosphere to study the effect of aerosols/dust on the protocols. The schematic of the building structure and the placement of the equipment is shown in Fig. 3. Charlie who prepares entangled photon-pairs and Alice are co-located in our arrangement, while Bob is placed in the nearby room. Out of each pair generated, one stays at the receiving end with Alice and the second photon travels through the quantum channel consisting of going to the reflector and getting reflected to reach the receiving end to Bob, as shown in the protocol diagram (Fig. 1). The complete optical setup is shown in Fig. 4. The experiment was performed at night (11 PM to 5 AM Indian Standard Time), in order to ensure that there is no interference due to the direct sunlight.

III. RESULTS AND DISCUSSION
To study the effect of aerosols/dust present in the atmospheric channel on the secure key rate, we performed the experiment for 35 m channel on 8 May 2021 and 200 m channel on 10 May 2021. The atmospheric conditions for these two days are summarized in Table I. The extinction coefficient (Ext.) in the table represents the loss of photons due to absorption and scattering, which depends on the concentration of atmospheric aerosols, their size distribution, and refractive index. Aerosol characteristics reported here are measured in Aerosol Monitoring Laboratory, PRL. The extinction coefficient is measured using CAPS PM monitor (Aerodyne Research Inc., USA) and aerosol size distribution and PM less than 2.5 micrometer diameter are measured using an aerosol spectrometer (GRIMM Aerosol Technik, Germany). From the table, the extinction coefficient on 10 May 2021 is lower by ∼37%, leading to clear atmosphere and more transmissivity through channel. Also, the value of particulate matter (PM2.5) has lower concentration. Thus, choosing these two different days have provided the variability in the atmospheric conditions, most suitable for this study. In Ahmedabad, the higher values occur due to lower wind speed and shallow atmospheric boundary layer [11]. ) and particulate matter (PM2.5) concentrations are averages of hourly data from 12 midnight to 5 AM obtained from the Aerosol Monitoring Laboratory, PRL. The extinction coefficients data correspond to 525 nm. The data is fitted with the Angstrom power law for urban aerosols (model) corresponding to 70% relative humidity (appropriate for April-May) and found that wavelength exponent for extinction coefficients between 525 and 800 nm is about 1.5.
The channel transmissivity was measured by sending the output from a beacon laser of 810 nm through the channel and was measured to be 94% for 35 m and 70% for 200 m. The power of laser was measured before the launching optics and after the collecting optics to estimate the channel transmissivity on both days. The use of a beacon laser was crucial for precise alignment and also for further corrections required due to the breeze in the weather on both days.
From Fig. 4, one can observe that eight detectors are used in the experiment, four each for Alice and Bob. Analogous to any classical communication protocol, BBM92 also requires timing synchronization between communicating parties to distribute keys correctly. We connected the SPCM4 and SPCM8 to time-tagger ID900, and found the time-difference between Alice and Bob is 120 ns for 35 m and 666 ns for 200 m channels based on the histogram obtained between the two channels. The coincidences were measured with the time-window of 1 ns.
We started with the channel effect on the entanglement distribution between Alice and Bob, and measured the H/V/D/A polarisation visibilities. The graphs corresponding to these measurements are shown in Figs Table II. The S value greater than 2 ensures that secure key distribution can be done over the given channel. It shows that the atmosphere plays a role as visibilities are higher for 200 m, because of the lower extinction coefficients on May 10, even if the channel length is longer. The total count rate is a combined effect of channel losses and the length of the channel.
The quantum bit-error-rate (Q) and sifted key rate (SKR) can be calculated as [15,16] The value of Q for 35 m is 5.58% and for 200 m it is 4.50%. The expression for sifted key rate can be calculated from the coincidence counts rates (cc) as The factor 4 accounts for the total of all four coincidences (HH, V V , DD and AA), as the correct number of coincidences will contribute to total sifted key rate. The secret key rate after the error correction is given by where n is the number of bits left after error correction, and s is the security parameter [17]. The lower value of R sec is a direct effect of worse atmospheric conditions, which is also consistent with the visibilities. The different key rates obtained for both the distances are summarized in Table II. The measured channel transmission is 0.94 for 35 m and 0.70 for 200 m on the two dates of the experiment. As the atmospheric condition follows Beer-Lambert law [18], the transmission T of the channel can be written in terms of the number of photons sent (N In ) and the  number of photons received (N Out ) on the other end of the free space atmospheric channel as where Sc is the scaling parameter, γ is the extinction coefficient of the atmosphere, and L is the propagation length.
From our channel and experiments, the similar ratios are observed for the coincidence rates (cc), sifted key rate The similar values show that the Beer-Lambert law is suitable for considering the atmospheric aerosols and is consistent with the quantum parameters observed from the channel. One of the reasons is the linear dependence of sifted key rate on the coincidences observed per second. Most of the parameters like visibility, QBER and CHSH Bell parameter do not depend on the atmospheric channel, as the channel does not introduce polarization changes to the photons. To obtain the key rates for any other day, the new factor f need to be calculated from Eq. 6 and similarly the other parameters can be obtained using Eqs 7.
To determine the secure key, the time tags for all the eight channels have been recorded using the eightchannel digital oscilloscope (Tektronix MSO68B 6-BW-2500). The oscilloscope has a bandwidth of 2.5 GHz, and it was used to record the TTL pulses coming from single-photon detectors with a sampling rate of 1.25 GS/s with an integration time of 40 ms to measure the key rate. The recorded data contains the voltage sample, and from that, the rising edge of TTL pulses provides the arrival time. The post-processing includes basis reconciliation, error estimation, error correction, and privacy amplification, which are implemented in MATLAB. We have implemented a low-density parity-check (LDPC) error correction code [19] with a code rate of 0.5 for error correction. Choice of LDPC matrices closely depends on QBER and directly affects the secure key rate. Higher QBER means it takes more parity bits to correct those errors and thus, reduces the key rate.
Once error-corrected keys are generated, privacy amplification [20] is done via 2-universal Toeplitz hash function. During privacy amplification, the length of the hashed output is chosen pertaining to the parity bits used in error correction, QBER, and security parameter which decides the final length of the secure key. The data analysis/post-processing of entanglement-based protocol is time-consuming than prepare-and-measure based QKD protocol as there is no fixed interval of time in which photon can arrive, unlike BB84 protocol.

IV. CONCLUSION
In conclusion, we have demonstrated an entanglement based QKD that is BBM92 protocol over 35 m and 200 m free-space atmospheric channel, and simultaneously studied the effect of aerosols on the secure key rate. This is the first study of its kind where the extinction coefficient of atmospheric aerosols is used to study the variation of entanglement, QBER and key rate. We also found that the key rate follows the same Beer-Lambert's law and the extinction coefficient of the atmospheric aerosols on that particular day. As the key rate depends on the channel length, the larger the channel, the smaller will be the key rate. Further experiments are planned to study the effect for longer duration and to check the validity of models for estimating the key rate due to atmospheric conditions for the satellite based quantum communications [21]. The presented results may find application in setting up large scale quantum communication network using satellites and the placement of entanglement photo-pair sources.


Case Study on the User Interface of GPS Plotters to Enhance Their Usability

: In 2019, the International Maritime Organization (IMO) prescribed guidelines to standardize the user interface (UI) of navigation equipment such as radio detection and ranging (RADAR) and the electronic chart display and information system (ECDIS), which mandate the uniﬁcation of various terminologies and icons to improve usability. However, comprehensive studies on the operability and standardization of global positioning system (GPS) plotters, which are auxiliary equipment installed across various domestic and commercial vessels for navigational purposes, have not been conducted. Therefore, we performed a case study to identify the user requirements for standardizing the UI of GPS plotters in South Korea. Additionally, we conducted a survey to ascertain the frequency of use of the navigational functions in a GPS plotter, in which, several deck ofﬁcers and captains participated. The frequently used navigational functions that were subsequently identiﬁed conﬁrmed the need for standardization of the UI. Furthermore, the users requested the standardization of the menus of these functions using Korean terminologies. Hence, we attempted to derive standardized items that can be applied to both the functions of the GPS plotters and the navigation information obtained, which can contribute to the improvement of the UI across the different types of plotters.

Introduction
The International Maritime Organization (IMO) introduced e-Navigation in 2006 to increase the efficiency of maritime trade and transport along with the infrastructure and digital information necessary for its implementation. Accordingly, the guidelines for the standardization of the user interface (UI) design in navigation equipment ("guidelines") were developed for the integrated navigation system (INS), electronic chart display and information system (ECDIS), and radio detection and ranging (RADAR) system. These guidelines were approved by the IMO in June 2019 at the 101st session of the Maritime Safety Committee (MSC) and are effective from January 2024 [1]. Additionally, the performance standards for the presentation of navigation-related information on shipborne navigational displays (MSC.191(79)) were amended, and the terminologies of the function menu and display information groups included in appendices 2 and 3 of the guidelines were mandated. The upgraded navigational displays would be installed on bridges from July 2025 [2]; therefore, the bridge system would also be required to incorporate the improvements prescribed by the newly introduced guidelines [3,4].
The guidelines aim to improve the usability of navigational equipment and systemssuch as ECDIS and RADAR-by standardizing the interface, facilitating easy access to information and enhancing situational awareness. They achieve this by including standard terminologies and icons in the UI to aid the development of a user-friendly design [5].
Currently, several shipboard users, such as the captains and deck officers of domestic and commercial vessels, primarily utilize electronic chart systems (ECS), such as global 2 of 22 positioning system (GPS) plotters, for navigation [6]. GPS plotters are widely installed in such vessels with varying functionalities such as fishing [4], and are developed by multiple manufacturers. However, they are excluded from the scope of standardization because they are not considered as the mandatory equipement under international convention for the Safety Of Life At Sea(SOLAS), which specifies minimum standards for ships' the construction, equipment and operation regarding to their safety. Therefore, systematic awareness and training programs to improve the quality of the UI are not mandatory. In addition, the dissimilarities among the various interfaces provided by the different manufacturers can cause further challenges in operating the equipment. To address these issues, the requirements of shipboard users, who constitute the majority of GPS-plotter users, must be investigated. Moreover, considering that the guidelines would be applied to all navigation equipment from July 2025, collating user opinions on the standardization of the UI is essential to enhance the operability of GPS plotters and could encourage further research on obtaining the necessary information and developing the relevant functions and menus to improve the overall quality of these systems.
Although several studies related to the improvement of GPS-plotter UI exist, extensive research on user requirements has not been conducted. Hence, the purpose of this study was to collate and evaluate these requirements to improve the quality of GPS-plotter UI in terms of standardization. Accordingly, a survey was conducted, wherein deck officers and captains tested both frequently and sparsely used navigational functions in GPS plotters. Subsequently, we conducted interviews to identify the standardization requirements for UI enhancement. Based on the participants' inputs, the operability of the frequently used navigational functions of existing GPS plotters was evaluated. These results can contribute to the standardization of user interfaces in different GPS plotters.

Literature Review
To identify the user requirements for the effective operation of navigational equipment, a questionnaire was developed using the IMO ECDIS performance standard [7]. Additionally, upon conducting an investigation on the user requirements for advancing existing guidelines, we concluded that the guidelines are crucial to develop standardized displays and user-friendly menu systems [8]. After the introduction of the ECDIS, a study [9] was conducted with 402 mariners during the period of 2012-2018 to gain user insight on the operability of the system compared with nautical paper charts, which confirmed the potential problems associated with the transition to electronic charts. In addition, the opinions of officers on the watch regarding the experience of using the ECDIS were presented [10]. To evaluate the usability of the various navigational functions, the quantitative technique of a questionnaire was conducted to analyze the effectiveness of introducing the ECDIS [11]. Alternatively, an eye-tracking device was employed to perform the usability test on the ECDIS [12][13][14].
Human factors that contribute to the level of operability of marine equipment were also studied in certain usability testing methods, where navigational tasks were monitored through simulations to capture human errors [15]. Similarly, a standard set of navigational tasks were derived and evaluated to improve the UI of navigation equipment [16]. To identify the basic functions of ECDIS and RADAR that require standardization, 22 navigational tasks for voyage planning, route monitoring, and collision prevention were selected based on the performance standards and 26 navigators contributed to the experiment using ship-control simulators by three manufacturers. An analysis of the main task execution time and differences in the operability of the equipment for each task presented a significant time difference in the performance of each simulator for eight tasks, including the line of position function, route correction, and safety contour change. This study highlighted the necessity of enhancing these functions by adopting standardized terminologies and icons.
An area-of-interest analysis was conducted based on the data collected from the navigational systems, wherein deck officers utilized eye-tracking devices on a passenger ship operating from Busan, Korea, to Osaka, Japan [17]. Consequently, the ratio of external visual observation was calculated at 49.2%, and the rate of using ECDIS and RADAR reached 44.6% during the experiment. In addition, it was confirmed that the navigator primarily used own-ship data (heading direction, ship speed, great guideway, ground speed, etc.), other-ship data (target number, ground speed, ground course, nearest point, closest time, etc.), automatic identification system (AIS) information (e.g., ship name), and the indication of the electronic azimuth line. The aforementioned studies contribute to the development of international standardization guidelines of the IMO, chiefly targeting ECDIS and RADAR used in ocean-going vessels.
Compared with previous research cases related to ECDIS and RADAR, there was no study conducted to improve GPS-plotter UI. However, a study was conducted on the usability evaluation of ECS in yachts and boats, and relevant guidelines were presented for stakeholders such as manufacturers and boat owners [18]. Another study identified that GPS plotters installed and used in domestic ships in Korea lack navigational information, and suggested the need for functions, such as alarms, particularly when the voyage speed exceeded the limit [19]. Several studies concluded that although GPS plotters are widely used in small-and medium-sized ships, they cause marine accidents owing to failures in implementing the latest updates [20,21]. Moreover, a geographic information system plotter based on common Linux was developed for small fishing vessels, similar to the GPS plotter [22].
The Korean government ruled that ECS for the intelligent maritime traffic information service would be installed as mandatory equipment on national ships from 2021 [23]. According to the Promotion of the Provision and Use of Intelligent Marine Traffic Information Services Act, the equipment is expected to improve navigation safety and provide optimal route information services based on electronic charts transmitted in real-time through long term evolution networks. This is considered to be an alternative to GPS plotters. The ECS shall be installed with type approval in accordance with the law. The recently revised type-approval standard includes the interface of the terminal and the test criteria for the requirements to implement e-Navigation service functions. It calls for compliance with the international standard for navigation information and terminologies established by the IMO [24]. However, there are no requirements for the guidelines to introduce standardized menu names or icons to implement navigational functions. In other words, performance test requirements for navigational functions exist; however, specific UI requirements, such as menu names or icons, that contribute to the usability of the functions, are not present.
To summarize, numerous studies related to the usability of ECDIS, along with surveys and experiments on the functions of ECDIS and RADAR have been conducted to develop international standardization guidelines. Conversely, there exist limited studies on the current status, problems, and solutions for the use of GPS plotters; compared to ECDIS, opinion surveys, and user evaluation experiments conducted for GPS-plotter users are relatively few. Therefore, this study seeks to highlight the importance of understanding the requirements for improving UI standardization by focusing on user feedback and evaluations on utilizing a type of ECS-GPS plotters.

Status of Type Approval Specifications and Equipment Related to GPS Plotters
A review of the government type-approval standard in Korea determined that the installation of ECS can be type-approved in accordance with the standards for type-approval tests and inspections for marine products ("type-approval standard") mandated by Article 18 of the Ship Safety Act. This standard requires 34 items to be checked before the test, divided as 5 items including appearance and components; 15 items such as salt spray test and vibration test for environmental tests; and 14 items including standard symbol and safety depth indication for performance tests. The navigational function of the GPS plotter must test the performance of eight items: standard symbol, safe depth, and over-scale indications; planning, correction, and monitoring of routes; and the track record and electronic chart update function [25].
To analyze the actual interface, equipment that passed government type approval was investigated. When the status of the GPS plotter type approval by the Ministry of Oceans and Fisheries was inquired through the shipping and port logistics information system, only models B and C produced by company A were type-approved. The product has an electronic chart that uses the existing paper chart symbols and certain symbols established by company A. Figure 1 presents a default screen, wherein the menu structure of model B has a fixed window for displaying the position, speed, and course over the ground, whereas the symbol and vector of the own ship are displayed in the center of the screen. Detailed functions such as route setting can be operated using the menu tree obtained from the menu button, and the shape and definition of private symbols established by the company can be viewed by executing the command "View submarine symbols" [26].
before the test, divided as 5 items including appearance and components; 15 items such as salt spray test and vibration test for environmental tests; and 14 items including standard symbol and safety depth indication for performance tests. The navigational function of the GPS plotter must test the performance of eight items: standard symbol, safe depth, and over-scale indications; planning, correction, and monitoring of routes; and the track record and electronic chart update function [25].
To analyze the actual interface, equipment that passed government type approval was investigated. When the status of the GPS plotter type approval by the Ministry of Oceans and Fisheries was inquired through the shipping and port logistics information system, only models B and C produced by company A were type-approved. The product has an electronic chart that uses the existing paper chart symbols and certain symbols established by company A. Figure 1 presents a default screen, wherein the menu structure of model B has a fixed window for displaying the position, speed, and course over the ground, whereas the symbol and vector of the own ship are displayed in the center of the screen. Detailed functions such as route setting can be operated using the menu tree obtained from the menu button, and the shape and definition of private symbols established by the company can be viewed by executing the command "View submarine symbols" [26]. The review of the type-approval standard resulted in only a few basic navigational function performance tests that require 18 standard symbols to be displayed on the GPS plotter chart. However, requirements for menu names and information items were not displayed on the screen. In addition, no equipment received the type approval except for the models included in this study, as the type approval for GPS plotters in not mandatory. Nevertheless, GPS plotters are widely used in domestic ships; therefore, a thorough investigation of the users' opinions is essential to validate the actual scenario and propose a method for improving the usability of the equipment.

Comparison Between GPS-Plotter UI and the Guidelines
It is essential to check the current status of the GPS plotter by comparing the differences with the guidelines to be applied to the future navigation equipment and analyzing them. Therefore, one GPS-plotter model was selected as a case, and the detailed requirements of the guidelines and its interface were compared and analyzed. The equipment to be compared was a GPS plotter type approved by the Korean government, which is also the equipment to be tested in this paper. The scope of analysis of the The review of the type-approval standard resulted in only a few basic navigational function performance tests that require 18 standard symbols to be displayed on the GPS plotter chart. However, requirements for menu names and information items were not displayed on the screen. In addition, no equipment received the type approval except for the models included in this study, as the type approval for GPS plotters in not mandatory. Nevertheless, GPS plotters are widely used in domestic ships; therefore, a thorough investigation of the users' opinions is essential to validate the actual scenario and propose a method for improving the usability of the equipment.

Comparison between GPS-Plotter UI and the Guidelines
It is essential to check the current status of the GPS plotter by comparing the differences with the guidelines to be applied to the future navigation equipment and analyzing them. Therefore, one GPS-plotter model was selected as a case, and the detailed requirements of the guidelines and its interface were compared and analyzed. The equipment to be compared was a GPS plotter type approved by the Korean government, which is also the equipment to be tested in this paper. The scope of analysis of the guidelines was limited to its Appendix 2, which contains navigation-related terminology and icons of functions. The Hot Keys and Shortcuts included in the Appendix 2 were compared with the GPS-plotter UI and the matched items are shown in Table 1. Here, the hot key allows a specific function to be executed immediately, and the shortcut can be used to access the group of related functions ( Figure 2). As a result of the analysis, only 23.6% matched the items required in the guidelines and the function term on the GPS plotter interface, indicating that improvement for standardization is needed. guidelines was limited to its Appendix 2, which contains navigation-related terminology and icons of functions. The Hot Keys and Shortcuts included in the Appendix 2 were compared with the GPS-plotter UI and the matched items are shown in Table 1. Here, the hot key allows a specific function to be executed immediately, and the shortcut can be used to access the group of related functions ( Figure 2). As a result of the analysis, only 23.6% matched the items required in the guidelines and the function term on the GPS plotter interface, indicating that improvement for standardization is needed.

Concept of the Research Methodology
A quantitative survey was conducted to identify the need of standardization for the various terminologies, symbols, and interfaces designed by various GPS-plotter manufacturers and to identify the standardization requirements by conducting surveys on users such as captains and deck officers. To develop a questionnaire and experimental design for the research, we focused on appendices 2 and 3 of the guidelines, as they were referred by the IMO Resolution MSC.466(101) [2]. According to the IMO performance standard, these appendices will be mandatorily implemented from 2024. Appendix 2 of the guidelines provides standard terminologies and icons for commonly used functions in the navigation equipment, while Appendix 3 presents a logical grouping of information on navigational display. Therefore, we investigated user requirements for the standardization of GPS plotter functions and information display items.

Concept of the Research Methodology
A quantitative survey was conducted to identify the need of standardization for the various terminologies, symbols, and interfaces designed by various GPS-plotter manufacturers and to identify the standardization requirements by conducting surveys on users such as captains and deck officers. To develop a questionnaire and experimental design for the research, we focused on appendices 2 and 3 of the guidelines, as they were referred by the IMO Resolution MSC.466(101) [2]. According to the IMO performance standard, these appendices will be mandatorily implemented from 2024. Appendix 2 of the guidelines provides standard terminologies and icons for commonly used functions in the navigation equipment, while Appendix 3 presents a logical grouping of information on navigational display. Therefore, we investigated user requirements for the standardization of GPS plotter functions and information display items.
Based on user opinions, the frequently used navigational functions were identified, and a usability evaluation was performed. Using actual GPS plotter equipment, the usability of frequently used navigation functions was checked, and user requirements were identified in terms of standardization of GPS plotters through interviews with tested participants. Figure 3 presents the research methodology used to investigate the user requirements for standardization of the plotter UI based on the user-demand survey and usability evaluation.

Designing the Survey Questionnaire
To identify the user requirements for the standardization of GPS plotters and improve usability, we investigated the frequently used navigational information and functions. Therefore, seven items of navigational function terms and abbreviations in the GPS plotter interface approved by the government national standards were considered to render the screen layout and arrangement. A questionnaire was prepared based on 25 functions of the GPS plotter; the functions to be standardized and the user's understanding of each major function and standardization requirements were identified based on the frequently used navigational functions. The main questionnaire items test the understanding of the menu name for the navigational functions of the GPS plotter, inquiring the need to standardize terms and apply the standard icons while determining the frequency of use of the navigational functions, as shown in (Table 2). Additional usage of functions except the aforementioned list

Designing the User Test
To evaluate the user familiarity of the GPS plotter and collect user needs for standardization, simulation experiments and user interviews were conducted using actual equipment. According to the method of performing usability evaluation from the user experience perspective established by the Information Communication Standardization Committee [27], it is recommended that at least five participants take part in the usability evaluation. In addition, the selected task for an experiment must be representative with the functional, error, and temporal aspects considered based on the frequency of use, existence of a problem, and time measurement [28]. Based on these criteria, 10 frequently used navigational tasks were selected based on the results of the initial survey of 132 users (Table 3) to identify the representative navigational functions.

Designing the Survey Questionnaire
To identify the user requirements for the standardization of GPS plotters and improve usability, we investigated the frequently used navigational information and functions. Therefore, seven items of navigational function terms and abbreviations in the GPS plotter interface approved by the government national standards were considered to render the screen layout and arrangement. A questionnaire was prepared based on 25 functions of the GPS plotter; the functions to be standardized and the user's understanding of each major function and standardization requirements were identified based on the frequently used navigational functions. The main questionnaire items test the understanding of the menu name for the navigational functions of the GPS plotter, inquiring the need to standardize terms and apply the standard icons while determining the frequency of use of the navigational functions, as shown in (Table 2). Table 2. Items of user survey on GPS plotter.

1
The need to apply standardized icons; if not, why? 2 Understanding of navigation-related terms and abbreviations (7 items) 3 Users' preference for applying icons to navigational functions 4 Preference for GPS plotter display size 5 Frequency of use of navigational functions (25 items) 6 Additional usage of functions except the aforementioned list

Designing the User Test
To evaluate the user familiarity of the GPS plotter and collect user needs for standardization, simulation experiments and user interviews were conducted using actual equipment. According to the method of performing usability evaluation from the user experience perspective established by the Information Communication Standardization Committee [27], it is recommended that at least five participants take part in the usability evaluation. In addition, the selected task for an experiment must be representative with the functional, error, and temporal aspects considered based on the frequency of use, existence of a problem, and time measurement [28]. Based on these criteria, 10 frequently used navigational tasks were selected based on the results of the initial survey of 132 users (Table 3) to identify the representative navigational functions. In total, five shipboard users including deck officers and captains of incumbent fishing and domestic vessels participated in the experiment. Each participant performed 10 typical sailing tasks using a GPS plotter and confirmed the usability by measuring the time required to perform each task. In addition, based on the experience of performing the task, user opinions on the improvement requirements of terms and symbols, understanding of terms and abbreviations, and functions requiring improved usability were collected. Moreover, group interviews and discussions were conducted on the convenience of performing navigational functions, preferences for displaying information on the navigation screen, and the need for standard terms.

Results of the Questionnaire Survey
A survey of 182 users, primarily mariners experienced in using GPS plotters, was conducted in Korea Institute Maritime and Fisheries Technology (KIMFT) from June to August 2019, and 132 effective questionnaires were retrieved. The personnel composition of the respondents ( Figure 4) included captains (47.7%), navigators (35.6%), land officials (9.9%), and others (6.8%). In addition, the survey showed that they were engaged in coastal fishing boats (26.5%), cargo ships (37.1%), ocean fishing boats (7.6%), passenger ships (6.8%), and others (22.0%). The experience of respondents onboard averaged 16.4 years, wherein and they have sufficiently used GPS plotters ( Figure 4). The survey of 132 questionnaires determined that 77% (43 of the 56 that responded) participants used the GPS plotters manufactured by company A. In addition, other manufacturers were identified; five, four, and four respondents used products from companies B, C, and others, respectively (Table 4).  In terms of the need for the application of standard icons, 73 respondents (55.3%) reported a "high need" and 50 people (37.9%) answered a "moderate need" (Table 5). A subjective opinion was established that the unification of the operation method through the introduction of standard icons was necessary when using different models of GPS plotters. In addition, we analyzed the degree of understanding of the seven terms and abbreviations used in the GPS plotter, and the survey was rated from 1 to 5 in the order of "worst" to "best" ( Table 5). The average result of all functions confirmed that the terms were generally understood at 3.6 points, and the terms that were well and least understood were "MENU" and "EVENT", respectively.
Further, Table 5 presents the use of GPS plotter function keys; 57 (43.2%), 31 (23.5%), and 38 (28.8%) respondents preferred the application of the menu name, icon, and the combination of "icon" and "menu name" in a neutral manner, respectively. In addition, 80 (60.6%) and 28 (21.2%) people answered that the screen size of the GPS plotter was normal and good, respectively. Owing to inadequacy, 90.9% of negative respondents stated that the screen was small. Additionally, the respondents with the opinion of "good" screen size could have considered the limited installation space available on small-and medium-sized vessels.  In terms of the need for the application of standard icons, 73 respondents (55.3%) reported a "high need" and 50 people (37.9%) answered a "moderate need" (Table 5). A subjective opinion was established that the unification of the operation method through the introduction of standard icons was necessary when using different models of GPS plotters. In addition, we analyzed the degree of understanding of the seven terms and abbreviations used in the GPS plotter, and the survey was rated from 1 to 5 in the order of "worst" to "best" ( Table 5). The average result of all functions confirmed that the terms were generally understood at 3.6 points, and the terms that were well and least understood were "MENU" and "EVENT", respectively.
Further, Table 5 presents the use of GPS plotter function keys; 57 (43.2%), 31 (23.5%), and 38 (28.8%) respondents preferred the application of the menu name, icon, and the combination of "icon" and "menu name" in a neutral manner, respectively. In addition, 80 (60.6%) and 28 (21.2%) people answered that the screen size of the GPS plotter was normal and good, respectively. Owing to inadequacy, 90.9% of negative respondents stated that the screen was small. Additionally, the respondents with the opinion of "good" screen size could have considered the limited installation space available on small-and medium-sized vessels.  In addition to the above analysis, we explored the possibility of a difference in the users' need for standardization and their understanding of navigational terms based on their experience using GPS plotters. As shown in Table 6, the respondents were divided into three groups (viz., ≤7 years, 8-14 years, and ≥15 years) based on their level of experience (p < 0.05).
Regarding the preference of applying standardized icons ( Figure 5), there was a significant difference between the group with 7 years (or less) experience and 15 years (or more) experience. Users who were highly familiar with the operation of GPS plotters were more likely to apply standardized icons than those who were not.  In addition to the above analysis, we explored the possibility of a difference in the users' need for standardization and their understanding of navigational terms based on their experience using GPS plotters. As shown in Table 6, the respondents were divided into three groups (viz., ≤7 years, 8-14 years, and ≥15 years) based on their level of experience (p < 0.05).
Regarding the preference of applying standardized icons ( Figure 5), there was a significant difference between the group with 7 years (or less) experience and 15 years (or more) experience. Users who were highly familiar with the operation of GPS plotters were more likely to apply standardized icons than those who were not.  In addition to the above analysis, we explored the possibility of a difference in the users' need for standardization and their understanding of navigational terms based on their experience using GPS plotters. As shown in Table 6, the respondents were divided into three groups (viz., ≤7 years, 8-14 years, and ≥15 years) based on their level of experience (p < 0.05). Regarding the preference of applying standardized icons ( Figure 5), there was a significant difference between the group with 7 years (or less) experience and 15 years (or more) experience. Users who were highly familiar with the operation of GPS plotters were more likely to apply standardized icons than those who were not. As a result of analyzing the degree of understanding of terms (Table 6), the menus showing significant differences (p < 0.05) in their perception by group were EVENT, CENTER, WPT, TRACK, MARK, and ENT, among the seven items surveyed. For the five identified items, we discovered that the degree of understanding of terms differed according to the experience of using the equipment between the groups, and further concluded that the users who operated the equipment for long periods had a better understanding than those who operated them for short periods. Further details are provided in the Appendix A. The frequency of use of the 25 items that form the representative functions of GPS plotters, was evaluated on a five-point scale with one and five points attributed to least and most frequent use, respectively. Consequently, 18 items were detected to be used at frequencies above normal (3 points), including selection of day or night mode, route edit, and track on or off (Table 3). Therefore, these features must be designed in a user-friendly manner. Moreover, the participants suggested functions and position accuracy identical to ECDIS as requirements for improving the GPS plotter user interface. Furthermore, distance measurement and the need for additional estimated time of arrival (ETA) display functions were suggested.

Results of User Testing
A total of five incumbent captains and navigators (the testees) with sufficient experience of using GPS plotters measured the frequency of use for 10 tasks and the time re- As a result of analyzing the degree of understanding of terms (Table 6), the menus showing significant differences (p < 0.05) in their perception by group were EVENT, CEN-TER, WPT, TRACK, MARK, and ENT, among the seven items surveyed. For the five identified items, we discovered that the degree of understanding of terms differed according to the experience of using the equipment between the groups, and further concluded that the users who operated the equipment for long periods had a better understanding than those who operated them for short periods. Further details are provided in the Appendix A.
The frequency of use of the 25 items that form the representative functions of GPS plotters, was evaluated on a five-point scale with one and five points attributed to least and most frequent use, respectively. Consequently, 18 items were detected to be used at frequencies above normal (3 points), including selection of day or night mode, route edit, and track on or off (Table 3). Therefore, these features must be designed in a user-friendly manner. Moreover, the participants suggested functions and position accuracy identical to ECDIS as requirements for improving the GPS plotter user interface. Furthermore, distance measurement and the need for additional estimated time of arrival (ETA) display functions were suggested.

Results of User Testing
A total of five incumbent captains and navigators (the testees) with sufficient experience of using GPS plotters measured the frequency of use for 10 tasks and the time required to perform the tasks. To increase familiarity with the experimental equipment, pre-familiarization training on GPS plotters was conducted for the testees. Table 7 presents the experimental results obtained using the ship handling simulator and GPS plotter installed at the KIMFT. The time required to complete the task was considered as a measure to evaluate the usability of the task. In the first task, the average task completion time for the five testees was 5.8 s, with the longest time being 87.4 s for the task of entering the destination. A follow-up survey was conducted after the completion of all tasks. The five testees determined "entering destination," "distance measurement to target," and "input a symbol" as the frequently used navigation tasks. In terms of convenience of using the functions for task performance, all tasks were scored below average. Further, we conducted a group interview with the testees, wherein they confirmed the need for applying standard Korean terms to be used intuitively, owing to the difficulty in understanding the menu names of the current interface. Moreover, the introduction of standard icons for frequently used functions can significantly improve usability. Table 8 presents the navigational information to be displayed on the GPS plotter screen, as requested by the testees. Additionally, the standard information group suggested in the guidelines was used during the interview. Therefore, the testees requested the same to be displayed on the screen of the GPS plotter as the guideline. To improve the usability of the user interface, the participants requested diversification of input devices by introducing a mouse, trackball, and touch screen to facilitate cursor movement rather than using wired and wireless remote controls to operate the GPS plotters.

Discussions of User Survey and Testing Results
The survey facilitated the understanding of menu terms present in the current user interface, awareness of the need to apply icons, and frequency of use of navigational functions of the GPS plotter. The results of user testing can be summarized as follows.
We determined that despite users typically understanding the main menus of GPS plotters, the need for applying standard icons to the menus was high. Although GPS plotter users generally favor the application of standard icons, contradicting results were derived owing to the convenience of using terminologies in the menu, which is the current method, rather than the icon application method to operate the function keys. This is possibly the effect of intuitively recalling the names of the menu used in the GPS plotter.
Through the analysis of the respondents' experience of using the GPS plotter, we inferred that users who used the equipment for a long time preferred the introduction of icons. Based on the shipboard user experience with GPS plotters, it can be understood that the respondents prefer the introduction of standardized icons to improve usability. In terms of understanding navigation-related terms, comparing the level of understanding by the respondents' experience using the equipment enabled us to identify differences in the understanding level of the specific menu terms (CRT, WPT, MENU, TRACK, MARK, ENG). For users exhibiting a low understanding of items but demonstrating no significant difference in the user experience, the necessity of improving the usability of the menu EVENT is considered to be highly significant. Apart from the results of the analysis performed based on the level of expertise using the equipment, we demonstrated that if the overall average comprehension is 3.6 out of 5, the overall understanding of the term is considered normal; therefore, it can be said that there is a great need to improve understanding in the users. Further, we learned that "EVENT", an item on which users displayed low understanding without significant differences in usage experience, is crucial to improving usability.
Through the above studies, the frequently used navigational functions in the GPS plotter and their usability were identified. In total, 10 frequently used navigational functions were prioritized and the test was done by measuring the time to achieve each task.
Frequently used functions identified by these experiments can be used in two aspects. One is to prioritize functions in GPS plotters needed to improve usability. For example, navigation features can be improved than other features to apply standard terms and icons in practice. The other aspect is these frequently used functions can be a crucial part to set up test cases for testing equipment [29,30].
Target tasks to test were discussed for this research and were advised by the navigation experts and users selected in this study. The results of questionnaire survey over navigation experts and the Bridge procedures guide [31] were contemplated and related tasks of GPS plotters are found out. The 10 tasks were decided after reducing duplication, integrating similar ones.
Times for task completion was specified for individual task and measured as a means of checking usability performance. This is to know that if it takes longer than the given time to complete any task, that means the functions involved in that task need to be improved.
Finally, the interviews of the five participants confirmed the need for intuitive Korean terms to be introduced in the menu names of the GPS-plotter UI and the standardized information (Table 8) items to be displayed on the screen were identified. The GPS plotter manufacturers can utilize the data to display necessary information on the user interface.

Conclusions
As the international standardization guidelines for navigation equipment will be applied from 2024, the standardized terms, icons, and navigational information groups will be introduced in the ECDIS, RADAR, and INS UIs to improve their usability. However, implementing these guidelines of IMO for the standardization of ECS such as GPS plotters is not yet considered. Although the installation of GPS plotters is not legally mandated, almost every domestic vessel utilizes this equipment. However, no application has yet been prepared to designate standard menu names or icons for major navigational services and functions for intelligent marine traffic devices, which are to be introduced in Korea in 2021. Therefore, it is essential to consider the standardization of menu names and icons focusing on user opinions to improve user familiarity and enhance safety.
In this regard, we conducted a case study targeting GPS plotters as the equipment requiring usability improvement in terms of standardization. Studies on GPS plotters used by several Korean shipboard users as auxiliary navigation equipment [32] recognized the need for improvement in terms of standardization. Therefore, the user needs for the introduction of standardization were investigated to improve the primary navigational information and function status along with their usability. To this end, a questionnaire survey was conducted for 182 coastal ship users, and a usability evaluation based on actual equipment was performed with the aid of five incumbent captains and sailors.
In this study, we determined the frequently used navigational functions in the GPS plotter and the level of users' convenience and familiarity with them. Based on the user tests of 10 major navigation tasks in GPS plotters, the convenience for performing tasks was evaluated below normal, indicating that usability improvement is necessary. Particularly, entering destinations, editing route plans such as changing waypoints, and editing coastline drawing functions were found to have poor usability, highlighting the need for improvement. The interview that followed the user testing validated the need for standardization of the Korean terminology in the navigational functions; this is consistent with the survey results. Therefore, to improve usability, it is necessary to enhance the user interface of the current GPS plotter by applying standard Korean terminology to the menu names or introducing icons.
We believe that this study is the first to conduct a user requirement survey and a simulation test on a GPS plotter interface for incumbent ship navigators. Subsequently, comparative experiments must be conducted by introducing different types of plotters from multiple manufacturers. The survey target was selected for masters and officers who are the practical users of GPS plotters on domestic and commercial vessels to aid them in navigating within domestic waters or on a fishing vessel. To better understand/identify the types of vessels that include GPS plotters, the gross tonnage along with ships types were surveyed.
Onboard experience and past experience on using GPS plotters were further surveyed to identify the level of GPS-plotter operational proficiency and previous usage experience. During this process, in addition, the various GPS plotter manufacturers were identified. Appendix A. 1

.2. Identifying the Standardization Requirements
Questionnaires were structured to allow for the identification of the navigation functions frequently used in GPS plotters and included questions on the level of understanding of terms/acronym used in the system and the preferred size of the navigation screen. Based on this, the responses were structured as shown in Table 1. After analyzing the 132 valid responses to our questionnaires, we found that the response rate on the need for introducing standardized icons were significantly higher than that of menu names in navigational functions on the GPS plotter UI (Figure A1), and that the level of comprehension on terms/abbreviations displayed on the GPS plotter was fairly good except for the specific event.
Appendix A.1.2. Identifying the Standardization Requirements Questionnaires were structured to allow for the identification of the navigation functions frequently used in GPS plotters and included questions on the level of understanding of terms/acronym used in the system and the preferred size of the navigation screen. Based on this, the responses were structured as shown in Table 1. After analyzing the 132 valid responses to our questionnaires, we found that the response rate on the need for introducing standardized icons were significantly higher than that of menu names in navigational functions on the GPS plotter UI (Figure A1), and that the level of comprehension on terms/abbreviations displayed on the GPS plotter was fairly good except for the specific event.

Results of Survey Analysis Depending on Respondents' GPS Equipment Usage Experience
The survey analysis was also focused on identifying significant differences (or correlations) between user requirements on standardization and the level of comprehension of menu terminology depending on the level of experience using GPS plotters. Excluding 24 non-respondents who did not include their experience level, the analysis was conducted for the remaining respondents on the preference of the standardized icons, understanding of menu terminologies by categorizing their usage experience (Table A1). Is it necessary to apply standardized icons to functions frequently used for GPS plotters?
After analyzing the preference of applying standardized icons depending on users' usage experience ( Figure A2), a difference was observed between the groups with less than 7 years and the group with more than 15 years of experience using GPS plotters (p < 0.05).
It was found that people who used the GPS plotter for a longer period of time are more inclined to make positive judgments about the application of standardized icon than those who used the GPS plotter for a shorter period of time.
Is it necessary to apply standardized icons to functions frequently used for GPS plotters?
After analyzing the preference of applying standardized icons depending on users' usage experience ( Figure A2), a difference was observed between the groups with less than 7 years and the group with more than 15 years of experience using GPS plotters (p < 0.05). Figure A2. User preference for applying standards icons on frequently used functions by experience of using GPS plotters. Average (1: Worst to 5: Best).
It was found that people who used the GPS plotter for a longer period of time are more inclined to make positive judgments about the application of standardized icon than those who used the GPS plotter for a shorter period of time.
The Level of Comprehension and the Usability of GPS Plotter for Navigation Functional Terms As a result of the analysis on understanding of terminologies in the GPS plotter's EVENT functions based on users' GPS usage experience ( Figure A3), no significant difference was found between groups (p > 0.05). (ii) CNT-CENTER As a result of the analysis on understanding of terminologies in the GPS plotter's CENTER function based on users' GPS usage experience, differences were found between the group with 8 to 14 years of experience and the group with over 15 years of experience (p < 0.5). Those with more experience show a higher level of comprehension on terminologies related to CNT ( Figure A4). (iii) WPT-WAY POINT As a result of the analysis on understanding of terminologies in the GPS plotter's WAY POINT function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05).
As for the GPS plotter WAY POINT function that is currently being used, those with more than 15 years of experience in using the GPS plotter tend to indicate that it is easy to understand; however, those with less than 7 years of experience in using the GPS plotter (ii) CNT-CENTER As a result of the analysis on understanding of terminologies in the GPS plotter's CENTER function based on users' GPS usage experience, differences were found between the group with 8 to 14 years of experience and the group with over 15 years of experience (p < 0.5). Those with more experience show a higher level of comprehension on terminologies related to CNT ( Figure A4). (ii) CNT-CENTER As a result of the analysis on understanding of terminologies in the GPS plotter's CENTER function based on users' GPS usage experience, differences were found between the group with 8 to 14 years of experience and the group with over 15 years of experience (p < 0.5). Those with more experience show a higher level of comprehension on terminologies related to CNT ( Figure A4). (iii) WPT-WAY POINT As a result of the analysis on understanding of terminologies in the GPS plotter's WAY POINT function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05).
As for the GPS plotter WAY POINT function that is currently being used, those with more than 15 years of experience in using the GPS plotter tend to indicate that it is easy to understand; however, those with less than 7 years of experience in using the GPS plotter (iii) WPT-WAY POINT As a result of the analysis on understanding of terminologies in the GPS plotter's WAY POINT function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05).
As for the GPS plotter WAY POINT function that is currently being used, those with more than 15 years of experience in using the GPS plotter tend to indicate that it is easy to understand; however, those with less than 7 years of experience in using the GPS plotter tend to indicate that it is difficult to understand. Their responding tendency of difficulty was relatively higher than the group with more experience ( Figure A5). Figure A4. Users' understanding on the term 'CNT' by experience of GPS plotter usage. Average (1: Worst to 5: Best).
(iii) WPT-WAY POINT As a result of the analysis on understanding of terminologies in the GPS plotter's WAY POINT function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05).
As for the GPS plotter WAY POINT function that is currently being used, those with more than 15 years of experience in using the GPS plotter tend to indicate that it is easy to understand; however, those with less than 7 years of experience in using the GPS plotter tend to indicate that it is difficult to understand. Their responding tendency of difficulty was relatively higher than the group with more experience ( Figure A5).   (v) TRACK As a result of the analysis on understanding of terminologies in the GPS plotter's TRACK function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05).
As for the GPS plotter TRACK function that is currently being used, those with more than 15 years of experience in using the GPS plotter tend to indicate that it is easy to understand; however, those with less than 7 years of experience in using the GPS plotter tend to indicate that it is difficult to understand ( Figure A7). (v) TRACK As a result of the analysis on understanding of terminologies in the GPS plotter's TRACK function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05).
As for the GPS plotter TRACK function that is currently being used, those with more than 15 years of experience in using the GPS plotter tend to indicate that it is easy to understand; however, those with less than 7 years of experience in using the GPS plotter tend to indicate that it is difficult to understand ( Figure A7).
the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05).
As for the GPS plotter TRACK function that is currently being used, those with more than 15 years of experience in using the GPS plotter tend to indicate that it is easy to understand; however, those with less than 7 years of experience in using the GPS plotter tend to indicate that it is difficult to understand ( Figure A7).

(vi) MARK
As a result of the analysis on the understanding of terminologies in the GPS plotter's MARK function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience, the group with 8 to 14 years of experience, and the group with more than 15 years of experience (p > 0.05).
As for the MARK functions, those with more than 15 years of experience in using the GPS plotter were of the opinion that it is easy to understand it in general; however, for those with 8 to 14 years of experience and those with less than 7 years of experience, a higher rate of respondents indicated that it is difficult to understand ( Figure A8).

(vi) MARK
As a result of the analysis on the understanding of terminologies in the GPS plotter's MARK function based on users' GPS usage experience, differences were found between the group with less than 7 years of experience, the group with 8 to 14 years of experience, and the group with more than 15 years of experience (p > 0.05).
As for the MARK functions, those with more than 15 years of experience in using the GPS plotter were of the opinion that it is easy to understand it in general; however, for those with 8 to 14 years of experience and those with less than 7 years of experience, a higher rate of respondents indicated that it is difficult to understand ( Figure A8). (vii) ENT-ENTER As a result of the analysis on understanding the terminologies in the GPS plotter's ENTER function, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05). As for the ENTER functions, those with more than 15 years of experience in using the GPS plotter expressed that it is easy to understand in general; however, for those with less than 7 years of experience, a higher rate of respondents expressed that it is difficult to understand ( Figure A9). (vii) ENT-ENTER As a result of the analysis on understanding the terminologies in the GPS plotter's ENTER function, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05). As for the ENTER functions, those with more than 15 years of experience in using the GPS plotter expressed that it is easy to understand in general; however, for those with less than 7 years of experience, a higher rate of respondents expressed that it is difficult to understand ( Figure A9).
As a result of the analysis on understanding the terminologies in the GPS plotter's ENTER function, differences were found between the group with less than 7 years of experience and the group with more than 15 years of experience (p < 0.05). As for the ENTER functions, those with more than 15 years of experience in using the GPS plotter expressed that it is easy to understand in general; however, for those with less than 7 years of experience, a higher rate of respondents expressed that it is difficult to understand ( Figure A9).

Frequently Used Functions
Users were asked five-point scale questions regarding the functions frequently used when using GPS plotters. They were asked to assign 5 points for a function that was frequently used and 1 point for a function that was rarely used ( Figure A10). The results indicated that the day/night mode changes and the route indication settings were the most frequently used functions.

Frequently Used Functions
Users were asked five-point scale questions regarding the functions frequently used when using GPS plotters. They were asked to assign 5 points for a function that was frequently used and 1 point for a function that was rarely used ( Figure A10). The results indicated that the day/night mode changes and the route indication settings were the most frequently used functions. User Requirements for Improving the GPS Plotter Interface More than 82% of respondents answered that the screen size is either normal or better than normal, which indicates that the screen size is appropriate ( Figure A11). User Requirements for Improving the GPS Plotter Interface More than 82% of respondents answered that the screen size is either normal or better than normal, which indicates that the screen size is appropriate ( Figure A11). User Requirements for Improving the GPS Plotter Interface More than 82% of respondents answered that the screen size is either normal or better than normal, which indicates that the screen size is appropriate ( Figure A11). Figure A11. User preference for GPS plotter display size.
In addition, with regard to subjective responses to various functions of the GPS plotter, it was found that some users were not fully aware of all the functions provided. Some respondents requested that specific functions should be added such as anchor watch functions when the vessel is at anchor, a distance measuring function that can measure the distance from their vessel to the object, and a navigational function that displays the estimated time of arrival. (1) Test participants: three captains and two first officers, a total of five individuals, all with more than 10 years of experience in using a GPS plotter participated in the experiment.
(2) Test scenario: vessel's navigation from Busan Port to Ulsan Port. In addition, with regard to subjective responses to various functions of the GPS plotter, it was found that some users were not fully aware of all the functions provided. Some respondents requested that specific functions should be added such as anchor watch functions when the vessel is at anchor, a distance measuring function that can measure the distance from their vessel to the object, and a navigational function that displays the estimated time of arrival. (1) Test participants: three captains and two first officers, a total of five individuals, all with more than 10 years of experience in using a GPS plotter participated in the experiment. (2) Test scenario: vessel's navigation from Busan Port to Ulsan Port.
(3) Tested Equipment: The GPS plotter installed in the ship-handling simulator was used ( Figure A12). This GPS plotter type was a model approved by the Ministry of Oceans and Fisheries and was the same model that the previous user survey was based on. The equipment was operated by remote control. (4) A preliminary simulation was conducted to familiarize users to the equipment. (5) Navigational tasks for the test: 10 frequently used navigational functions. (6) A fill-out questionnaire was provided, and an interview session was conducted for all participants ( Figure A13).

Appendix B.1.2. Experimental Method
(1) To measure the usability of a function, the time spent on performing a task by a user was measured ( Figure A14). (2) The number of key strokes/clicks was measured to evaluate task performance.
(3) An interview was conducted with regard to standardization requirements of the terms of the information displayed on the GPS plotter screen and the navigational functions. (1) To measure the usability of a function, the time spent on performing a task by a user was measured ( Figure A14).
(2) The number of key strokes/clicks was measured to evaluate task performance.
(3) An interview was conducted with regard to standardization requirements of the terms of the information displayed on the GPS plotter screen and the navigational functions.  (1) To measure the usability of a function, the time spent on performing a task by a user was measured ( Figure A14).
(2) The number of key strokes/clicks was measured to evaluate task performance.
(3) An interview was conducted with regard to standardization requirements of the terms of the information displayed on the GPS plotter screen and the navigational functions.

Appendix B.2. Key Outcomes
Through a simulation test with five participants, the time required to perform 10 tasks and the number of function key strokes/clicks were measured and recorded ( Figure A14).
After the scenario was complete, interviews were conducted with the participants. Participants said that they felt difficulties when modifying the route, drawing user shore lines that involved the handling of a variety of functional keys, or finding the menu for specific tasks, which takes a certain time. In addition, items that must be displayed on the GPS plotter screen were identified, as shown in Table 5.
The participants discussed the menu name of the GPS plotter interface and gave particular attention to frequently used functions, which they hoped they could apply


Stability Data Xbee S2b Zigbee Communication on Arduino Based Sumo Robot

Wireless technology is a solution to reach hardto-reach places using cable technology. The use of wireless technology can reach these areas without using copper or cables in the data transmission process. Communication technology using wireless is one solution to connect the control system to support the creation and achievement of the goals of the 4.0 revolution so that control and monitoring become easier. With the convenience provided by wireless technology such as connecting various types of system devices between other systems. One type of wireless technology is WPAN, especially on the ZigBee system from Digi International with the IEEE 802.15.4 protocol standard with low power consumption and working at a frequency of 2.4 GHz. Utilization of the communication system from the ZigBee protocol can control according to the range capabilities of the ZigBee system. ZigBee's ability and use of communication can perform communication control robot sumobot (slave robot) and remote control (robot leader) as an introduction to command data to carry out movements on the slave robot in accordance with the orders from the robot leader After trying XBEE to send data at a certain distance without experiencing data loss, the best distance is obtained, namely 1 100 meters with the firmware coordinator and router settings. Data delays can be minimized with a transfer rate of 3 kbps in the data transfer rate. Keywords— ZigBee, XBEE Communication, Sumobot, Robot Sumo, WPAN

I. INTRODUCTION
In the era of the industrial revolution 4.0, it refers to very rapid technological advances. Wireless technology or what is often called a wireless sensor network is a technology that is used for monitoring or monitoring. This development in the European region which has used various types of technological innovations has greatly helped humans in various fields, be it defense, health, agriculture, fisheries, clothing, food and others [1] [2][3] [4].
As we know, Indonesia is entering the era of the industrial revolution 4.0. The nation's children have started to carry out various types of innovations to help human work itself [5] [6]. In the current technological era, the use of cables as a conductor for current signals is very widely used. If all are connected using a cable, this will inhibit various activities and large costs [7][8] [9]. To overcome this, you can use wireless technology / wireless [10] [11].
Wireless technology is able to connect the device with other connected devices [12] [13] [14] [15]. At this time, wireless communication is very much in demand, such as the WPAN type or for medium or medium networks. The ability of this wireless is reliable in the efficiency of time and installation costs. One of the most widely used WPAN technologies for communication between devices today is the ZigBee model from Digi International [16] [17][18] [19]. This ZigBee is standardized with IEEE 802.15.4 with low power consumption for short distances and works-on a frequency of 2.4 GHz [20][21] [22][23] [24].
Research conducted by researchers is supported by the results of research conducted by previous people regarding the concept of testing communication on XBEE (Zigbee). From previous research, the researchers tested the work of XBEE and its abilities and tested it by experimenting with several important measured values [25] [26]. Analysis of previous research performance can be continued and developed by communicating in a remote-controlled sumo robot system [27][28] [29]. The concept that is built is remote, which will send a signal in the form of a command that is forwarded to the sumo robot. This information signal can be synchronized with execution with the command given [21].
The STMIK STIKOM Indonesia agency in the Control System Laboratory section has a sumobot robot but still uses the bluetooth communication type. Researchers conducted a research experiment by trying to design a remote control to become a robot leader as a transmitter and a sumobot or slave robot as a data receiver [15] [30] [31]. The experiment that was carried out was trying to implement the peer to peer communication module XBEE / wireless on each device.

A.
Comparison with other studies Researchers conducted this research because the results of previous studies could only reach a distance of 24 meters and experienced interference [32]. This study did not explain the number of repetitions performed. This initial limitation of the Robo Sumo was then fixed by using good quality and transfer distance to get a quick response to the controller for data execution. This data delay can be minimized by using XBEE S2B which has a possible maximum transfer distance of 500 meters [23]. The results of this study, the researchers developed by testing the XBEE S2B to transmit data without losing data with good speed quality and minimizing packet loss.
Researchers conducted this research because the results of previous studies could only reach a distance of 24 meters and experienced interference [32]. This study did not explain the number of repetitions performed. This initial limitation of the Robo Sumo was then fixed by using good quality and transfer distance to get a fast response to the controller for data execution. This data delay can be minimized by using XBEE S2B which has a possible maximum transfer distance of 500 meters [23]. The results of this study, the researchers developed by testing the XBEE S2B to transmit data without losing data with good speed quality and minimizing data packet loss.
B. An explanation of the initial sumo robot STMIK STIKOM Indonesia has a sumo robot using Bluetooth communication with connectivity to a smartphonebased on an app controller to run the system on the robot. However, the robot experienced many problems such as frequent data delays or data loss using the HC-6 Bluetooth module. from that, the researcher tried an experiment to develop it so that data sent from the remote get a fast response When getting commands via the remote controller with the ability of the XBEE S2B itself, it is able to support it without burdening the IC controller because XBEE has its own delivery system or firmware so that the respond coordinator and the router can be more efficient so that data loss such as Bluetooth HC-6 can be minimized.

II.
DESIGN METHODS Researchers will explain the system to be built on the sumo robot with several important values to test the functioning of the robot properly.
In this case, the researcher replaced the existing system in the initial sumo robot with XBEE due to several factors as follows: 1. There is often a delay in receiving data 2. Researchers want to develop a better XBEE response on Robo Sumo 3. The use of XBEE in wireless technology in the industrial era 4.0. This development is for further research.

The advantages of XBEE in digital communication,
where it is possible to focus data on a channel so that at a minimum distance the communication can exchange without obstacles within a certain distance, as well as the stability of XBEE.
A comparison of the use of XBEE with Bluetooth in the initial system does not work optimally, such as delays that affect the response of Robo Sumo when compared to XBEE which has good enough firmware to support communication over medium distances. XBEE itself has an antenna extender to amplify the signal.

Remote Controller (Leader)
The remote controller will be in charge of sending data in the form of information with the aim of being an order to synchronize command data and execution according to the slave robot (robot sumo). The components in Table I will be a remote control system to control all activities that will be carried out by the sumo robot. These components will be built in the form of a remote control system. The schematic form and block diagram of the system being built can be seen in Figures 1 and 2.

Sumo Robot (Slave)
The Sumo robot is a robot that receives signals from the robot leader and executes the data. Sumo robot transfer according to the command sent from the remote controller or leader. Table II below is the components of the sumo robot. The components above will be designed as a system that can be controlled by a remote controller. From these components, you will get a system that becomes one unit. The schematic form and block diagram of the sumo robot system can be seen in Figures 3 and 4.

XBEE Configuration
To be able to communicate between the robot leader and the slave robot, it is necessary to exchange information or it can be called communication. The purpose of this communication, namely the remote control as a robot leader will send commands then forward it to XBEE (transceiver) to be sent to XBEE (receiver) and then forwarded back to the slave robot microcontroller to execute data converted into movement and displacement of the robot in accordance with a signal received. The configuration on each module is in accordance with the scheme in Figure 5. From the picture above, it can be seen that the XBEE coordinator is the transceiver or the one in charge of sending data and the XBEE router is the receiver or the receiver of the data signal. This arrangement aims to exchange data so that data transmission or communication can occur between the XBEE coordinator and the router. From this communication, it will be used to send data from the remote microcontroller to the robot microcontroller so that the robot can be controlled according to the execution signal sent.

System Communication Flowchart
The system communication flowchart is a part that explains the communication system from the remote control with the sumo robot how data processing occurs in the system From the flowchart flow, we can find out how the incoming data is executed when a signal is sent from the remote controller to the Sumo robot. Communication with the data flow concept is described in the form of symbols as a representation of how the data is processed by the system. Figure 6 below is the form of a system flowchart that is built.

System Testing Methods
In testing the design that has been built, a capability test will be carried out which aims to test the limitations of the system that has been designed. Inline, it can be drawn from this test that the function from the transceiver to the receiver is in accordance with the desired execution. Here are the important points tested: • Testing XBEE communication in communications rarely 100 meters range. • Testing the sumobot robot to make a full round of hands • Testing the sumobot robot to do a full left turn • Testing the sumobot robot for forwarding movement • Sumobot robot testing to perform the reverse movement • Testing the sumobot robot to make a right turn forward in a circle • Testing the sumobot robot to turn left forward in a circle • Testing the sumobot robot to turn right backward in a circle • Testing the sumobot robot to turn left backward in a circle From these tests, the researcher obtained the results of controlling the robot with a remote control in accordance with the signal sent and received by the slave robot. The robot can move according to the instructions received from the robot leader or remote control.

III. IMPLEMENTATION OF RESULTS
Testing the best ability of XBEE at a distance of 100 meters. This is better than the research conducted by Hartawan where the XBEE ability in open space is estimated to reach 600 meters.
Researchers try to find the best scale to test the system so that the data received is not too late for robot communication. After being analyzed with the sumo robot signal communication it was decided to test up to 100 meters at the line of sight or without obstruction. The main objective is to get the best communication distance for the coordinator and router to be able to communicate with the maximum capability of the module.
The XBEE ability test was conducted at Jln. Tukad Citarum, Puri Klod Lake, South Denpasar, Bali. The test was carried out 2 times, namely testing using XTCU software on XBEE and testing with a microcontroller. Figure 7 is the XBEE test location.

Testing Using XTCU
In testing the xtcu software was used. The test was carried out using 2 methods, namely the range test and throughput testing. Tables 3 and 4 are the results of the XBEE range test data and the results of the XBEE coordinator and router test data.

Fig. 8. XBEE Range Test Data Graph
When sending data with signal quality as in Table III below, the results are that the packet is sent properly on the line of sight when transferring data with a distance of 100 meters. The transmitter failed to send 1 packet and the receiver failed to receive 1 packet with each packet load of 84 bytes.  The above test is performed to transfer 1000 bytes of data with a transfer time of 5 seconds. The results of the throughput test above can prove that the distance is getting wider the speed or the speed of data transfer decreases, but at a distance of 100 meters with a line of sight, it is still good to use it for data transfer.

XBEE testing using Arduino Uno
Testing using the Arduino Uno R3 aims to test data packet transfers. Testing is done by sending a data packet, "hello world" and checking for missing part of the character with a test distance of 100 meters. Each data packet delivery has a  Arduino test results as a coordinator and router within 100 meters are still good at transferring data. No packet length is lost. It can be said that in a distance of 20 meters to 100 meters implemented on the Arduino it can be said to be good because the data packet "hello world" sent has no missing characters.

Remote Controller Configuration Data
Researchers designed a simple remote control using an analog joystick input with an Arduino nano microcontroller and a transmitter in the form of an XBEE coordinator module. The remote serves as the robot leader (instruction center) for the slave robot (instruction execution).
To control the movement, it is necessary to determine the range division for the joystick direction instruction as the command center for the sumo robot. The division of the direction is divided into the ADC value of the joystick module according to the consumption of the direction taken. Figure 10 is a form of joystick direction configuration designed by researchers. Determining the mapping direction will make it easier for the instructions to be sent by the XBEE coordinator to the XBEE receiver as control instructions for the sumobot robot. ADC division is very important so there is no collision of the same value or value. ADC x-axis 0 -255 and y-axis from 0 -255. Each symbol is based on the x and y-axis values which are divided into 8 parts as a measure of the value sent. This description can be seen in Figure 11. This data is useful for explaining the communication data received by Robo Sumo sent by the controller.

Remote and Robot System Assembly
Assembling remote systems and robots aims to tidy up the various placement of components so as not to interfere with the execution process when the robot is alive, in other words when there is communication between the remote and the robot. Many things must be taken into account in placing the position of the system. Good placement of several components can provide good performance and reduce short or short.

Robot Communication Testing
Researchers conducted robot testing aimed at whether the robot was able to run properly and in accordance with commands from the remote control. From this test, the researchers obtained the data in Table VI.  Figure 13 shows the experiments conducted by researchers in system testers. The following is a description of the symbols in the image above: From the experimental results above, it shows that the slave robot and leader robot are in sync. The command sent by the robot leader is in accordance with the value execution carried out by the slave robot and a good signal range for the XBEE module as a communication medium for robots such as the sumobot robot. This is because this XBEE module has low power consumption or low voltage so it can save power consumption for the system.

IV. CONCLUSION
From the results of research and experiments conducted by researchers to obtain stability data from XBEE, it can be seen that the Sumobot robot receives fast data with good stability. After trying XBEE to send data at a certain distance without experiencing data loss, the best distance is obtained, namely 1 -100 meters with the firmware coordinator and router settings. Implementation of the system can work well in covering communications that occur in remote systems and sumo robots. Data delays can be minimized with a transfer rate of 3 kbps in the data transfer rate. Matching communication criteria with what the system needs must be adjusted so that it can meet the objectives of the system being built.
In this study, the researcher only wanted to achieve the goal of communicating the robot leader and slave to become one system. If the next researcher wants to develop, the researcher gives a little advice in its development. Such as the addition of supporting features to help and monitor the transmission system as well as a more elegant indicator in its development and development of a system on a single board that supports the shape and pattern of the robot itself. And one more thing, the development with XBEE communication can be developed again in various controlled devices to fulfill the integrity of control systems such as RC boats, cars, networks, control, and so on.