Ronny Yongho Kim

Snoop based group communication scheme in cellular Machine-to-Machine communications

Machine-to-Machine (M2M)communication is expected to be one of major communication methods in the future. In M2M communications, there are important requirements: extremely low power consumption of devices and mass device transmission. In order to meet the requirements, a novel snoop based relaying method in cellular M2M communications is proposed in this paper. The proposed scheme consists of two steps: 1. snooping group formation including group head selection and group members assignment based on link quality or location, 2 snooping and relaying packets to/from group members. By employing the proposed scheme, efficient M2M communication can be achieved without changing physical layer of wireless communication standards while meeting the requirements of extremely low power consumption and mass device transmission.

Technical challenges of railroad communications using long term evolution

As a next generation railroad communication technology, 3GPP has been considered to provide railroad communication using LTE, known as LTE-R, including railroad control, passenger services, wireless surveillance video, etc. International Union of Railways (UIC) has commenced to generate LTE-R requirements. There are some technical challenges for LTE to be used for todays railroad communications because of the mobility of train up to 430km/h. Since railroad communication is related to public safety, very tight reliability requirement also needs to be met. In this paper, some technical considerations of LTE-R in terms of the possible frequency bands are provided. Upper limit of frequency band for high-speed train up to 500km/h is suggested by investigating the Doppler spread of wireless channel and physical channel structure of LTE.

HiNet: Radio Frequency Communication Based Train Control (RF-CBTC) System Jointly Using Hierarchical Modulation and Network Coding

As Information and Communication Technology (ICT) evolves, unmanned train operation has become norm by using wireless communication technology such as IEEE 802.11. Such a train control system based on wireless technology is called Radio Frequency Communication Based Train Control (RF-CBTC) system. IEEE 802.11 is widely used for RF-CBTC system since IEEE 802.11 is able to operate in license exempt Industrial Scientific and Medical (ISM) band. With the emergence of smartphone, devices using IEEE 802.11 have increased dramatically leading to severe interference to IEEE 802.11 based RF-CBTC system. Since safty of train depends on the reliability of RF-CBTC system, RF-CBTC system must provide reliable communication schemes. This paper proposes HiNet, which is a novel solution to providing a reliablity and efficiency in RF-CBTC system. HiNet takes advantage of network coding and hierarchical modulation in IEEE 802.11 architecture. By jointly using network coding and hierarchical modulation, we show that HiNet is able to provide both reliability through the rateless property of network coding and efficienty through the flexibility of hierarchical modulation. Our simulation results using MATLAB corroborate our intuition that joint use of network coding and hierarchical modulation is able to provide communication reliability and efficiency in RF-CBTC system.

A novel low power WLAN operation scheme for multiple wake-up receivers

In this paper, a novel low power Wireless Local Area Network (WLAN) operation scheme for multiple low power receivers is proposed. Recently, substantial amount of Internet of Things (IoT) devices are used for various applications, and their delay and energy consumption requirements vary depending on their applications. Therefore, the tradeoff between power saving and delay should be carefully considered when power saving scheme is designed for different traffic patterns. In this paper, an efficient low power operation scheme of many low power devices with options to meet the requirements of power consumption and delay.

An Energy Efficient Multiuser Uplink Transmission Scheme in the Next Generation WLAN for Internet of Things

This paper proposes a novel and energy efficient Internet of Things (IoT) communication scheme for next generation Wireless Local Area Network (WLAN). There are a couple of crucial requirements among unique IoT requirements: a large number of communication devices must be supported, and they must have low power consumption. Since sensor-type IoT devices, which are expected to be one of the major types of IoT devices, normally generate uplink traffic rather than downlink traffic, an energy efficient multiuser uplink transmission scheme is a crucial feature of IoT communication. In the next generation WLAN, IEEE 802.11ax, Orthogonal Frequency Division Multiple Access (OFDMA) is adopted to support a greater number of devices. However, uplink OFDMA procedures that consider the unique IoT requirements have not been fully considered in the next generation WLANs. A random access-based WLAN uplink OFDMA transmission scheme is proposed in this paper, and analytical modeling of the proposed scheme is provided. The proposed random access-based WLAN uplink OFDMA transmission scheme is able to dynamically adjust the number of contending users by uniquely applying congestion status in a very simple and distributed manner. Our numerical analysis and extensive simulation corroborate the fact that the proposed scheme is able to support a greater number of IoT devices with less power consumption.

Handover Performance Evaluation of 4G Mobile Networks

Since the core functionality of cellular network mobility management is handover and handover latency directly impacts service continuity and the end-user experience, handover has the most stringent latency requirement on service interruption time compared to other mobility related operations such as reentry from Idle mode. This paper presents the state-of-the-art handover schemes designed for IEEE 802.16m based 4G mobile networks (next generation WiMAX), approved by ITU as an IMT-Advanced technology and handover performance of 4G mobile networks is evaluated in terms of latency. A system-architectural view on handover is provided to analyze the causes of handover latency and methods to optimize them for latency reduction. Through handover latency analysis an insight on how well 4G handover scheme is designed can be provided.

Delay oriented VR mode WLAN for efficient Wireless multi-user Virtual Reality device

In order to enhance user experience of Virtual Reality (VR) devices, multi user VR environments and wireless connection need to be considered for next generation VR devices. Wireless local area network (WLAN) is a popular wireless consumer device which can provide high throughput and can be installed with low cost using unlicensed band. However, WLAN may cause delay in packet transmission due to its distributed nature in channel access. In this paper, feasibility of wireless VR over WLAN is carefully examined and an efficient multi user VR communication scheme using the next generation WLAN is proposed for multi-user VR services.

Hierarchical modulation symbol sharing scheme for multiuser cellular networks

In this paper, a novel hierarchical modulation symbol sharing scheme for multiuser cellular networks is proposed. In order to achieve the maximum channel capacity, various modulation and coding schemes have been developed on Wireless Communication Systems. With good modulation and coding schemes, very high channel capacity could be achieved for 1-to-1 communication systems. Due to different channel conditions of multiple users, high channel capacity of multiple user network systems cannot be achieved with modulation and coding schemes used for 1-to1 communication technology. By exploiting the characteristics of multiple users in cell based multiuser networks, a novel hierarchical modulation symbol sharing scheme for cell based multiuser network systems is proposed. The proposed scheme not only achieves high network capacity but also substantially reduces channel access overhead for cell based multiuser systems. In the proposed symbol sharing scheme, multiple users are able to share one symbol by allocating bits in proper bit positions for each user. Since the proposed scheme allows to provide extra bits to its cell users, multiuser channel access delay could be substantially reduced. The simulation results corroborate the benefits of the proposed scheme. By exploiting the proposed scheme, very high network capacity of the next generation cell based multiuser networks can be achieved.

The Reactive Power Compensation for a Feeder by Control of the Power Factor of PWM Converter Trains

PWM converter trains exhibit excellent load characteristics in comparison with conventional phase-controlled trains with low power factors, as they can be operated at power factors which are close to unity by means of a voltage vector control method. However, in the case of a high track density or extended feeding, significant line losses and voltage drops can occur. Instead of operating these trains at a fixed unity power factor, this paper suggests a continuous optimal power factor control scheme for each train in an effort to minimize line losses and improve voltage drops according to varying load conditions. The proposed method utilizes the steepest descent algorithm targeting each car in the same feeding section to establish the optimized reactive power compensation levels that can minimize the reactive power loss of the feeder. The results from a simulation of a sample system show that voltage drops can be improved and line losses decreased.

Handover Latency Reduction Scheme for Railroad Communications in 4G Mobile Networks

In the design of 4G cellular mobile networks, also known as, IMT-Advanced systems, new air interface enhancements such as multi-carrier support and interference mitigation further require handover protocol to be scalable and flexible to support various 4G deployments. This paper presents the state-of-the-art handover schemes designed for IEEE 802.16m based 4G mobile networks (next generation WiMAX), approved by ITU as an IMT-Advanced technology and provides discussion on technical challenges of railroad communications for high speed trains. Based on the discussion, handover latency reduction scheme for railroad communications is proposed. Various advanced handover procedures accepted in IEEE 802.16m specification are explained in details in order to derive technical challenges and handover reduction scheme of railroad communications.