• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.17 no.1
• /
• pp.185-201
• /
• 2023

Grant-free random access (GFRA) can reduce the access delay and signaling cost, and satisfy the short transmission packet and strict delay constraints requirement in internet of things (IoT). IoT is a major trend in the future, which is characterized by the variety of applications and devices. However, most existing studies on GFRA only consider a single type of device and omit the effect of access delay. In this paper, we study GFRA in multicell massive multipleinput multiple-output (MIMO) systems where different types of devices with various configurations and requirements co-exist. By introducing the backoff mechanism, each device is randomly activated according to the backoff parameter, and active devices randomly select an orthogonal pilot sequence from a predefined pilot pool. An analytical approximation of the average spectral efficiency for each type of device is derived. Based on it, we obtain the optimal backoff parameter for each type of devices under their delay constraints. It is found that the optimal backoff parameters are closely related to the device number and delay constraint. In general, devices that have larger quantity should have more backoff time before they are allowed to access. However, as the delay constraint become stricter, the required backoff time reduces gradually, and the device with larger quantity may have less backoff time than that with smaller quantity when its delay constraint is extremely strict. When the pilot length is short, the effect of delay constraints mentioned above works more obviously.

• International Journal of Internet, Broadcasting and Communication
• /
• v.12 no.2
• /
• pp.37-44
• /
• 2020

The fifth generation (5G) mobile communication has been commercialized and the 5G applications, such as the artificial intelligence (AI) and the internet of things (IoT), are deployed all over the world. The 5G new radio (NR) wireless networks are characterized by 100 times more traffic, 1000 times higher system capacity, and 1 ms latency. One of the promising 5G technologies is non-orthogonal multiple access (NOMA). In order for the NOMA performance to be improved, sometimes the additive signal-dependent Gaussian noise (ASDGN) channel model is required. However, the channel capacity calculation of such channels is so difficult, that only lower and upper bounds on the capacity of ASDGN channels have been presented. Such difficulties are due to the specific constraints on the dependency. Herein, we provide the capacity of ASDGN channels, by removing the constraints except the dependency. Then we obtain the ASDGN channel capacity, not lower and upper bounds, so that the clear impact of ASDGN can be clarified, compared to additive white Gaussian noise (AWGN). It is shown that the ASDGN channel capacity is greater than the AWGN channel capacity, for the high signal-to-noise ratio (SNR). We also apply the analytical results to the NOMA scheme to verify the superiority of ASDGN channels.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.15 no.12
• /
• pp.4364-4384
• /
• 2021

The dynamic network state and the mobility of the terminals make the service function chain (SFC) orchestration mechanisms based on static and deterministic assumptions hard to be applied in SDN/NFV mobile edge computing networks. Designing dynamic and online SFC orchestration mechanism can greatly improve the execution efficiency of compute-intensive and resource-hungry applications in mobile edge computing networks. In order to increase the overall profit of service provider and reduce the resource cost, the system running time is divided into a sequence of time slots and a dynamic orchestration scheme based on an improved column generation algorithm is proposed in each slot. Firstly, the SFC dynamic orchestration problem is formulated as an integer linear programming (ILP) model based on layered graph. Then, in order to reduce the computation costs, a column generation model is used to simplify the ILP model. Finally, a two-stage heuristic algorithm based on greedy strategy is proposed. Four metrics are defined and the performance of the proposed algorithm is evaluated based on simulation. The results show that our proposal significantly provides more than 30% reduction of run time and about 12% improvement in service deployment success ratio compared to the Viterbi algorithm based mechanism.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.14 no.8
• /
• pp.3201-3223
• /
• 2020

Wireless communication has become the promising technology in the recent times because of its applications in Internet of Things( IoT) devices. The IEEE 802.15.4e has become the key technology for IoT devices which utilizes the Time-Slotted Channel Hopping (TSCH) networks for the communication between the devices. In this paper, we develop a Two Level Scheduling Algorithm (TLSA) for scheduling multiple packets with different arrival rate at the source nodes in a TSCH networks based on the link activated by a centralized scheduler. TLSA is developed by considering three types of links in a network such as link i with packets arrival type 1, link j with packets arrival type 2, link k with packets arrival type 3. For the data packets arrival, two stages in a network is considered.At the first stage, the packets are considered to be of higher priority.At the second stage, the packets are considered to be of lower priority.We introduce level 1 schedule for the packets at stage 1 and level 2 schedule for the packets at stage 2 respectively. Finally, the TLSA is validated with the two different energy functions i.e., y = e^ax - 1 and y = 0.5x² using MATLAB 2017a software for the computation of average and worst ratios of the two levels.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.10 no.4
• /
• pp.221-231
• /
• 2015

This paper provides the trend of Internet of Things (IoT) for smart healthcare services and applications. IoT has provided a promising opportunity to build intelligent healthcare system and smart wearable applications by using the growing capability of wireless mobile devices, interactive sensors/actuators, and RFID technologies. For analysis of state-of-art technology of smart healthcare system, this paper includes comparative analysis and investigation of existing standard, network protocol, and devices, etc. In this paper, we examine the market trend of IoT healthcare. In particular, we examine the variety of IoT based healthcare type such as mobile, wearable device. After that, we examine the technologies of IoT healthcare such as standard, sensor, network and security. This survey contributes to better understanding of the challenges in existing IoT healthcare and further new light on future research directions.

• ETRI Journal
• /
• v.38 no.6
• /
• pp.1163-1171
• /
• 2016

Integration technologies involving flexible substrates are receiving significant attention owing the appearance of new products regarding wearable and Internet of Things technologies. There has been a continuous demand from the industry for a reliable bonding method applicable to a low-temperature process and flexible substrates. Up to now, however, an anisotropic conductive film (ACF) has been predominantly used in applications involving flexible substrates; we therefore suggest low-temperature lead-free soldering and bonding processes as a possible alternative for flex-on-flex applications. Test vehicles were designed on polyimide flexible substrates (FPCBs) to measure the contact resistances. Solder bumping was carried out using a solder-on-pad process with Solder Bump Maker based on Sn58Bi for low-temperature applications. In addition, thermocompression bonding of FPCBs was successfully demonstrated within the temperature of $150^{\circ}C$ using a newly developed fluxing underfill material with fluxing and curing capabilities at low temperature. The same FPCBs were bonded using commercially available ACFs in order to compare the joint properties with those of a joint formed using solder and an underfill. Both of the interconnections formed with Sn58Bi and ACF were examined through a contact resistance measurement, an $85^{\circ}C$ and 85% reliability test, and an SEM cross-sectional analysis.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.18 no.6
• /
• pp.63-68
• /
• 2018

Offloading is a method of communicating, processing, and receiving results from some of the applications performed on local computers to overcome the limitations of computing resources and computational speed.Recently, it has been applied in mobile games, multimedia data, 360-degree video processing, and image processing for Internet broadcasting to speed up processing and reduce battery consumption in the mobile computing sector. This paper implements a viewer that enables users to convert various flat-panel images and view contents in a wireless Internet environment and presents actual results of an experiment so that users can easily understand the images. The 360 degree spherical image is successfully converted to a plane image with Double Panorama, Quad, Single Rectangle, 360 Overview + 3 Rectangle depending on the image acquisition position of the 360 degree camera through the interface. During the experiment, more than 100 360 degree spherical images were successfully converted into plane images through the interface below.

• Asia-pacific Journal of Multimedia Services Convergent with Art, Humanities, and Sociology
• /
• v.8 no.6
• /
• pp.909-917
• /
• 2018

Recently, the Internet of Thing (IoT) technology is expanding explosively in the number of devices and applications in many application areas. In IoT systems, sensors and actuators are connected to the Internet and cooperate to do some applications by exchanging information. In this paper an IoT smart home system is developed to monitor and control home devices easily. Our system consists of sensor devices, IoT gateways, and an IoT server. Sensor devices developed using Rfduino sense the physical world and transmit their data using BLE to the IoT server thru the IoT gateway. We implemented the IoT gateway using Raspberry Pi and the IoT server using ARTIK cloud. We installed our system and made a test in our lab, which showed that our system can be installed and managed easily and extended its functionality in an easy way. By taking advantage of the rule mechanism and action messages of ARTIK cloud, we implemented the control of device parameters easily by sending action messages to the ARTIK cloud.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.26 no.2
• /
• pp.230-238
• /
• 2022

Internet of Things(IoT) is a communication technology that collects information of object remotely and controls the function of object by adding a communication function to object that does not have a communication function. For the IoT, various communication technologies such as Wi-Fi, 3GPP, and Bluetooth are available, and Long Range(LoRa) is communication technologies specialized in the IoT concept. LoRa is a communication technology that support long-distance, low-power, and low-speed communication, and is suitable for collecting information generated form object in remote equipment and controlling equipment. Because of these characteristics, it is used in many application field, and various performance improvement studies are in progress. This paper intends to propose an ultra-long-range LoRa communication module that can be used in a wider range of applications. We design and implement hardware, firmware, and application software for testing to develop ultra-long-range LoRa communication modules. The implemented module will be tested in a real environment to verify its performance and to check its utilization.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.54 no.8
• /
• pp.3-11
• /
• 2017

Research and development are being conducted to apply low-power Bluetooth (BLE) technology to IoT (Internet of Things) applications. The characteristic of this application environment is that many piconets can operate in the same space. Therefore, interference between homogeneous networks is likely to occur. In the BLE data channel, adaptive frequency hopping (AFH) scheme is used among the 37 frequency channels, and the master and the slave communicate while changing the carrier frequency. If there are multiple BLE piconets in the same space, there is a risk of frequency collision and packet errors will occur. In this paper, we analyze the packet collision probability due to cochannel interference in multiple asynchronous BLE piconet environments. Specifically, we analyzed packet collision probability according to the number of concurrently operating BLE piconets with the ratio of connection interval to connection event length as the main parameters. The analysis result can be used to set connection event related parameters for a desired packet collision probability according to the number of users having BLE devices in a given space.