Hyunsoon Kim

A synthesis procedure for associative memories based on space-varying cellular neural networks

In this paper, we consider the problem of realizing associative memories via space-varying CNNs (cellular neural networks). Based on some known results and a newly derived theorem for the CNN model, we propose a synthesis procedure for obtaining a space-varying CNN that can store given bipolar vectors with certain desirable properties. The major part of our synthesis procedure consists of solving generalized eigenvalue problems and/or linear matrix inequality problems, which can be efficiently solved by recently developed interior point methods. The validity of the proposed approach is illustrated by a design example.

Implementing home energy management system with UPnP and mobile applications

The power grid is undergoing a revolution and modernization through integrating information and communication technologies with the power system and also installing new electricity system technologies. Distributed controls in a certain self-reliant power-service area are critical means to modernize the power system to be the Smart Grid. Since the self-reliant area is assumed to perform physical and/or expert-engineered operations that should be integrated, monitored and controlled by a computational cyber system, the area is one area where the cyber and physical systems interact together, and home in the Smart Grid is one example for the area. In this paper, we propose a home energy management system (HEMS) to realize full automation combining computational and physical systems in a home area, which excludes operator-based control and management. The proposed system is designed to be built on the Universal Plug-and-Play architecture, and it can be accessed remotely over the Internet via mobile applications that work in Apple iPhone. Based on the design, we actually implemented the HEMS and constructed an empirical testbed that consists of networked personal computers, home appliances, and portable wireless devices. With the empirical testbed, we verified the monitoring and controlling functions of the HEMS. Additionally we carried out an extensive simulation study with the measured data of power consumption and the collected data of power price in order to see the effectiveness of the proposed HEMS. We also discuss about some limitations and challenges that we have encountered in designing and implementing the HEMS.

Wi-Fi Seeker: A link and Load Aware AP Selection Algorithm

The demand of mobile traffic increases tremendously as various Internet services are provided to mobile phones and computing devices, making mobile carriers increase the capacity of their cellular network. Since current cell towers and auxiliary devices cannot carry an excessive amount of traffic, several mobile carriers try to install low cost wireless equipment such as a Wi-Fi access point (AP) in order to offload overloaded traffic on cell towers. However, APs are installed randomly unlike cell towers because they can be installed by anyone and anywhere. The randomized allocation of APs incurs interference that causes serious degradation of wireless communication quality. Therefore, it is necessary to design mobile devices to use the environment or channel that contains the least interference for proper Wi-Fi communication. In order to make a mobile device experience the best wireless download quality, this paper proposes a novel AP selection mechanism that selects an AP that contains the least interference level compared to others with different number of communicating devices and amount of traffic load. The proposed selection mechanism does not require any additional feedback from nearby devices or APs. Performance evaluation was done by using real mobile devices with open source platform called Android.

MACoD: Mobile Device-Centric Approach for Identifying Access Point Congestion

These days, since many mobile devices support Wi-Fi, the number of Wi-Fi hotspots are increasing. At the same time, the number of places where users can use wireless LAN are increasing. Unlike the cellular network, the traffic of wireless LAN may not be distributed evenly because there is no supervisor to control the network traffic. In addition, due to the low throughput and the high packet error rate in wireless communication, the network traffic may converge at some Access Points (APs) which take a role of connecting wired and wireless communication interfaces. Therefore, congestion can easily happen at APs in wireless LAN. However, received signal strength indicator (RSSI) frequently used does not mean the network state of AP, and existing sender-based congestion detection and control protocols cannot recognize accurately where the congestion occurs. Therefore, current mobile devices continuously use the connected AP even if it is congested after the association. In this paper, we propose MACoD, the low power AP congestion detection system for mobile devices, in order to resolve aforementioned problems. Furthermore, by conducting diverse simulations, actual experiments, and power consumption analysis, we validate that MACoD can detect congestion effectively and that it is suitable for mobile devices.

Augmenting small cell with personal area cell for performance improvement

Since mobile traffic has been increased tremendously due to popularization of high-end mobile devices, many mobile carriers and smartphone manufacturers have put their best effort on solving the capacity problem. Small cell is introduced as an idea for the solution, and various mobile carriers have installed small cells to provide more bandwidth to areas that have too much traffic to be handled by single cell tower. In this paper, we state a problem that is an extended version of current capacity problem, and argue that the problem cannot be solved by installing small cells only. Therefore, we propose the concept of Personal Area Cell (PAC) that is portable and able to perform multi-hop transmissions. In order to justify the proposed problem and solution, a traffic model is designed and simulated. The simulation results show that small cell based network is inefficient when population and traffic of each cell are changed over time while PAC adopted network is cost-efficient and adaptive to such the change.

Integrated approach of streaming 3d multimedia contents in real-time for mobile devices

It is popular to watch a 3D video through a 3D display nowadays. However, it is still difficult to enjoy the 3D multimedia contents with a mobile device even if a mobile device with a 3D display is currently introduced into the market. The main technological challenges for watching 3D contents via the mobile devices can be identified as the following: generating and streaming 3D contents. Generating 3D contents requires extra computational resources. Moreover, streaming 3D contents demands additional network bandwidth for receiving and transmitting the 3D data. To overcome these technological challenges, we propose ReMA, a novel 3D video streaming system in this paper. We devised a novel architecture for transmitter, receiver, and a distribution system to efficiently disseminate and generate 3D videos for the mobile devices. We implemented ReMA in a real test-bed and conducted a thorough empirical evaluation study to see the feasibility of streaming 3D contents for the mobile devices. Based on our empirical study, the resulting system presents a great promise in streaming 3D video in real-time to the mobile devices.

Designing interference-aware network selection protocol for WLAN mobile devices

Due to increasing demand of wireless services for portable devices, numerous efforts to enhance wireless network performance have been made for decades. Many researchers were focused on the word ‘seamless’ for sustaining connectivity during a handover process, but wireless performance of destined access point (AP) is rarely considered. This paper analyses thoroughly usual network connection behaviour, captures several problems from the procedure, and proposes interference-avoiding selection (IAS) mechanism that associates a wireless AP, which is expected to perform better than other APs nearby. Proposed selection mechanism concentrates on utilization of each channel within one hop range and received signal strength measured by incoming beacons from surrounding APs. Possible interference by adjacent channels is also considered in this paper. Moreover, unlike any other prior selection mechanism, IAS protocol does not require any modification on existing communication protocols, extra delay to evaluate surrounding APs, and support from huge data server that collects information and derives quality of surrounding APs ahead of the selection phase. Various analysis and performance evaluations are progressed using OPNET, ns2, and Android programming, and the evaluation results showed that proposed selection mechanism can increase the throughput of original selection mechanism by more than 55% in average. Copyright

Improving quality of multimedia services through network performance isolation in a mobile device

Due to the advancement of hardware and software, today’s mobile devices, such as smartphones, tablet PCs, and laptops, are capable of providing a wide range of services. Among various services, a lot of users use multimedia services on mobile devices, and the size of mobile multimedia traffic is constantly increasing. Especially, the growth of social networking services and content-sharing sites stimulates creating and sharing of multimedia contents. Such environment made it possible for today’s mobile users to frequently download or upload multimedia data. Nowadays, smartphones allow users to multi-task between different services, so the multimedia service often coexists with background services in a mobile device at the same time. In these cases, the performance degradation of a multimedia service happens due to concurrently running background services in the device. In this paper, we propose MuSNet, a scheme for improving QoS and QoE of multimedia services through network performance isolation in a mobile device, which resolves the aforementioned problem by applying the concept of performance isolation to the multimedia services. MuSNet is the mobile device-based scheme without any modification on servers. Furthermore, unlike most performance isolation implemented by virtual machines, we suggest a scheme that does not require virtualization that might be heavy for mobile devices. The proposed scheme was implemented on a smartphone by modifying the kernel, and various experiments were conducted to evaluate the advanced system behavior of MuSNet.

Drone formation algorithm on 3D space for a drone-based network infrastructure

With the rapid proliferation of drones, there have been numbers of opportunities and challenges in drone application research area. One of the highlighted topics about the drones is constructing an ad-hoc network of drones and utilizing each as an access point (AP) to build an instant network infrastructure. However, there has been no research about drones optimal position improving network service quality of end users. We analyze the drone-based network infrastructure in terms of the network capacity allocation, and propose a drone formation algorithm that determines the 3D geographic location of each drone. Since each drone is hovering in the air while acting as an AP, its altitude must be also considered for the efficiency and performance of wireless communication. We assume the signal propagation model of the drone to be the shape of a sphere and define the relationship between the altitude and the coverage area of the drone. With this property, our algorithm finds the appropriate coordinates of drones one by one. Through the mathematical analysis, we show that the proposed algorithm can make drone-based network infrastructure provide reliable and user-satisfying network service.

Devising geographic diffusion for drone networks

With the rise of drones, providing a strong connectivity to the drones has become an indispensable part. Especially when the multiple drones are deployed, communication among each drone and a ground control station (GCS) is essential for delivering control message. However, traditional routing algorithms take too long time to construct routing table (eg. proactive routing protocol) or require large memory and high computing power (eg. reactive routing protocol). In this paper, we provide concept of an adaptive forwarding area based routing algorithm (AFAR) and exploit it for drone networks after making several modifications for drones. Although AFAR is originally designed for the smart grid, its routing algorithm is based on geographic information and flooding. Since these design fundamentals correspond to characteristics of drones, we adopted AFAR for drones. We increased dimensions of geographic information to 3D from 2D, and we made use of global positioning system (GPS) for new grid system. The real implementation of AFAR-D was evaluated with a traditional routing algorithm.