Research Areas

■ IEEE 802.11 Medium Access Control (MAC)

[Wireless LAN]

 Medium access control protocols define the rules that allow devices to share the medium in an efficient and orderly manner. In contrast to the wired LAN MAC protocols, wireless LAN MAC protocols should cope with the unique properties of wireless medium: half duplex mode, time varying and bursty channel, location dependent carrier sensing, hidden and exposed terminal problems, etc. These properties of the wireless medium make the design of MAC protocols particularly difficult and challenging. Wireless MAC issues in which we are currently interested are as follows:

◆ Distributed and Centralized MAC Protocols
◆ IEEE 802.11 MAC Protocol Family (802.11a/b/g/n/ac/ax)
◆ Providing QoS Guarantees in Wireless MAC Protocols


■ Visible Light Communication (VLC)


 Visible light communication (VLC) is a data communications medium which uses visible light between 400-800 THz instead of radio frequency. The VLC turns a plain lighting into a communication device and enables it to transmit data as the existing RF communications. Since an LED lighting has advantages of energy efficiency, ubiquity and zero-interference with the RF communications, the VLC is considered as a complement or a replacement of the existing RF communications. And it is expected to become a part of the next generation, the fifth-generation (5G) communication system. Despite of its great potentiality, there are several challenges, and issues in which we are currently interested are:

◆ De facto Standardization of the VLC
◆ Coexistence with the existing RF communications
◆ Short communication range and low data rate
◆ Low cost commercial off-the-shelf production
◆ Indoor positioning with the VLC


■ Indoor Positioning

[Indoor Positining]

 Indoor positioning allows people to identify their location inside buildings including school, work and shopping mall, even if outdoor positioning solutions like GNSS or GPS are not available. Nowadays, indoor positioning is not only convenient; it is becoming the essential service. With provided location information, there are many applications available as below: indoor navigation for store finder. asset management and tracking for manufacturer, emergency rescue of urgent patients without explicit report.

◆ Sensor-fusion positioning (Communication + IMU sensors)
◆ Positioning with advanced technologies (e.g. VLC and UWB)
◆ Ultra high accuracy positioning (e.g. FTM (fine timing measurement) and UWB)
◆ Radiomap-free positioning (e.g. ToF (time-of-flight))


■ Next Generation Enterprise Wireless LAN (NEWLAN)


 Next-generation Enterprise Wireless Local Area Network (NEWLAN) is a promising solution for the future WLANs. In NEWLAN, all APs are controlled and managed by special entity called central controller that collects and maintains various status information the APs. In particular, NEWLAN adopts Software Defined Network (SDN) concept for controlling the wireless network entity as well as the wired network entity. There are several research issues for efficient NEWLAN as follows:

◆ Design and implementation of SDN-based NEWLAN architecture
◆ SDN-based wired/wireless network convergence
◆ SDN-based wireless network virtualization
◆ High efficient medium access control mechanism
◆ QoS control and traffic monitoring



■ Internet of Things (IoT)


 Internet of Things (IoT), which describes networking between devices or machines contrast to the existing Internet that is considered as only communication tool between users, has been spotlighted as one of promising network technologies. Major components, which are described as things, of IoT includes existing end-devices of wired/wireless network as well as human, vehicles, various electrical devices and natural environments. In the IoT environments, things establish intelligent relationships such as sensing, networking, and data processing with each other for three type of distributed environments (human, device, and service) without explicit intervention of human.

 Technical perspectives of IoT is divided into three layer - sensing layer, communication layer, and management layer. In each layer, however, technical key enablers are already existing, for instance, device-to-device (D2D) communication and sensor networking are important key enablers for communication layer. For this reason, the key features of IoT are similar to that of fundamental technologies such as mesh sensor networks, machine-to-machine (M2M) communication and services. Nevertheless, need for enhanced performance of communication and network is emerging as brand new services/applications, which are specialized in IoT environment, are released. The key challenges of IoT, in terms of communication and network, are as follows:

◆ Seamless connectivity
◆ Energy efficient networking
◆ Intelligent authentication/association
◆ Resource utilization


■ Cloud Radio Access Networks (C-RAN)


 Cloud Radio Access Network or Centralized Radio Access Network (C-RAN) is a bright and promising technology for 5G cellular network. In contrast to previous cellular network (e.g., 3G or 4G LTE network), a stand-alone Base Station (BS) is splited into Base-Band Unit (BBU) which has upper layer and Remote Radio Head (RRH) which has RF layer or lower layer. In particular, BBU device is installed in single physical BBU pool server (cloud-based server) as multiple virtual instance. Since the single BBU pool server has multiple virtual BBU devices, this concept makes lower capital expenditure (CAPEX) and operation expenditure (OPEX), easier management of multiple BS in cellular network for network operator, efficient inter-BS transmission to user devices (e.g., CoMP), and so on. In order to implement C-RAN, there are several research issues for C-RAN as follows:

◆ Multimode User Terminals1. Design and implementation of C-RAN architecture
◆ SDN-based fronthaul network management system
◆ NVF-based Virtual BBU management system
◆ Implementation of C-RAN monitoring system
◆ Co-operative and inter-BS transmission functions


■ 4G Mobile Systems

[4G Networks]

 Fourth-generation (4G) mobile systems dictate entirely new approaches and novel infrastructure solutions to seamlessly integrate the existing wireless technologies including wireless broadband (WiBro), 802.16e, CDMA, wireless LAN, Bluetooth, and etc.

 The key features of 4G mobile systems can be summarized as follows. First, 4G mobile systems are all-IP based heterogeneous networks that allow users to use any system at any time and anywhere. Second, 4G mobile systems provide end-users with high-speed, large volume, good quality, global coverage, and flexibility to roam between different types of technologies. Finally, 4G mobile systems provide high-data-rate services to accommodate numerous multimedia applications such as video conferencing, on-line gaming, etc. Owing to such characteristics, we have to face a number of challenges to migrate current systems to 4G. The key challenges are summarized:

◆ Multimode User Terminals
◆ Wireless System Discovery/Selection
◆ Seamless Mobility
◆ Vertical Handoff
◆ QoS Support


■ Ad-hoc Networks

[Ad-hoc Networks]

 A mobile ad-hoc network is a collection of autonomous mobile nodes that communicate with each other over wireless links without any central administration. In ad-hoc networks, each host has to act as a router for itself to communicate with hosts outside its transmission range due to the limited range of each host's wireless transmission.

 An ad-hoc routing protocol runs on every host and is subject to the limit of the resources at each mobile host. Therefore, a traditional routing protocol, which is used in IP network, is not suitable to the ad-hoc network. Also, it is not appropriate to use conventional protocols, which are proposed or used in IP networks, such as MAC, QoS, Multicast, and TCP. There are many research issues to design protocols in ad-hoc networks:

◆ Bandwidth Optimization
◆ Power Control
◆ Transmission-quality Enhancement
◆ Network Configuration
◆ Topology Maintenance
◆ Efficient/Reliable Routing
◆ TCP Issues



■ Sensor Networks

[Sensor Networks]

 Sensor networks are composed of a large number of small nodes with sensing, computation, and wireless communication capabilities. In sensor networks, sensor nodes are usually scattered and the position of sensor nodes needs not be predetermined. It means that sensor network protocols and algorithms must provide self-organizing capabilities. Another feature of sensor networks is the coordination of sensor nodes to produce high-quality information about the sensing environment.

 The features of sensor networks provide a wide range of applications such as health, military, and home. The realization of these and other sensor network applications require wireless ad-hoc networking techniques. Although many protocols and algorithms have been proposed for traditional wireless ad-hoc networks, they are not well suited to the unique features and application requirements of sensor networks. Therefore, many routing and data dissemination protocols should be designed for sensor networks where the following issues should be considered:

◆ Energy Awareness
◆ MAC for Wireless Sensor Networks
◆ Time Synchronization
◆ Power-saving Mode of Operation
◆ Routing



■ Wireless Personal Area Networks (WPAN)

[Wireless Personal Area Networks]

 Wireless personal area networks (WPANs) cover smaller areas with low power transmission for network of portable and mobile computing devices such as PCs and personal digital assistants (PDAs). The portable consumer electronics and communications devices are essentially very small computers designed to consume as little power as possible in order to increase the lifetime of their batteries.

 As the above features of WPANs, there are some issues to provide efficient communications in WPANs:

◆ High Precision Ranging/Location Capability
◆ High Aggregate Throughput
◆ Low Power Consumption
◆ Low Cost



■ Home Networking

[Home Networking]

 Home networking is the collection of electronic products and systems, enabling remote access and control of those products and systems, and any available contents such as music, video or data. In home networks, a user wants to accomplish data communication in ways that are affordable, reliable, easy to learn, and easy to use.

 Wireless technology is the most convenient and exciting technology for creating home networking. There are, however, several considerations which are often overlooked and which can impede rapid market growth until they are resolved:

◆ Spectrum or Regulatory Issues
◆ QoS
◆ Throughput
◆ Range
◆ Security