Woongsoo Na

Mitigating wifi interference to improve throughput for in-vehicle infotainment networks

In recent years, in-vehicle infotainment networks (IVINs) have rapidly become one of the most valuable features auto makers have used to promote their flagship models as an advanced competitive marketing weapon. IVINs can provide passengers with multimedia services locally as well as Internet connectivity through a gateway known as a mobile hotspot. The in-vehicle mobile hotspot is embedded in the car and supports cellular connection. Utilizing this system, mobile devices can access the in-vehicle unified infotainment framework to comfortably enjoy streaming services, online games, online commerce, social network services, and so on. However, because of wireless access characteristics, if a significant number of Wi-Fi mobile hotspots are densely located, the throughput of the mobile devices will be tremendously diminished due to the interference among the mobile hotspots of IVINs, as well as with existing fixed office or residential APs along the road. In this article, we discuss the interference problems of Wi-Fi access in IVINs, provide effective solutions to these problems, and present the performance of each proposed approach within typical case studies.

Deafness-aware MAC protocol for directional antennas in wireless ad hoc networks

The use of directional antennas is a promising technique for the provision of high-speed wireless local and personal area networks such as IEEE 802.11ac, IEEE 802.11ad, and IEEE 802.15.3c. In this paper, we propose a new directional MAC protocol for wireless ad hoc networks that is referred to as deafness-aware MAC (DA-MAC). Although a significant number of directional MAC protocols have been proposed, they have not comprehensively resolved the deafness problem. Our proposed DA-MAC protocol can distinguish the deafness problem from collisions by employing logical data and control channels. We provide a discrete-time Markov chain model to analyze the impact of deafness for both an existing technique and DA-MAC. Through extensive simulations, we show that our DA-MAC protocol can significantly outperform the other existing techniques with respect to the throughput, deafness duration, energy consumption, and transmission fairness.

Reliable multicasting service for densely deployed military sensor networks

Wireless sensor networks (WSNs) have drawn attention for military applications where a large number of light-weight sensor nodes can detect enemies and intruders in the battlefield and alert a command post (CP) to our forces. In particular, in the military sensor networks, QoS (quality-of-service) is one of the most important requirements to support their mission-critical applications. However, achieving reliable data transmission is not an easy task because sensor nodes are densely deployed and wireless channel is unpredictable due to high mobility. Also, in the multihop deployed sensor networks, redundant data forwarding occurs frequently and it causes interference among the nodes. In this paper, we propose an efficient reliable multicast scheme using pre-ACK frames to provide fully reliable multicasting and decrease unnecessary data forwarding in the military sensor networks. When a receiver node overhears a multicast frame, the pre-ACK is used to announce its reception of the multicast frame to neighboring nodes which then do not need to duplicate the same multicast frame to it. The performance evaluation shows that the proposed scheme provides full reliability (100%) and outperforms the existing schemes in terms of aggregate throughput (612%) and energy consumption (514%) when the number of nodes is 512 with full buffer.

Using social Internet of Things (SIoT) demand side management on the plant

Demand-side management program is important for future smart grid. Most of the DSM program developed in the past interact customer and utility company. We suggest the Factory Management System using Social Internet of Things. It is not interaction between customer and utility company but interaction between things and things. Therefore we propose a autonomous demand-side management system and a system architecture.

Fully-distributed multicast routing protocol for IEEE 802.15.8 peer-aware communications

IEEE 802.15 task group 8 (IEEE 802.15.8) has been recently chartered to define PHY and MAC mechanism for wireless personal area networks (WPAN) peer aware communications (PAC) optimized for peer to peer and infrastructureless communications with fully distributed coordination. The most promising services created by IEEE 802.15.8 would be multicast communication with simultaneous membership in multiple groups, typically up to 10, in dense network topology. Most existing multicast techniques in mobile ad hoc networks (MANET) have relied upon a central coordinator to manage its multicast group and thus cannot be used for fully-distributed PAC networks. In this paper, we propose a graph-based multicast routing protocol referred to as fully-distributed multicast routing protocol (FDMRP) for IEEE 802.15.8 PAC networks. The FDMRP minimizes routing table entries and thus reduces control message overhead for its multicast group management. To balance the control message, all nodes in the network have a similar number of routing entries to manage nodes in a same multicast group. To measure the effectiveness of the proposed FDMRP against the ODMRP [10], we evaluated performance by OPNET simulator. Performance evaluation shows that the FDMRP shows less control message overhead and multicast group join latency than the ODMRP.

Event detection in composite context aware-service

Recent computing paradigm will advance in a form of more user-centric services spurred by smart phone where smart phone users enjoy a large variety of contextual information. Under the context-aware domain, contexts are forming more complicated and thus the concept of composite context has been proposed. While providing a useable context to users is important, it is also essential to reserve such a composite context even if it is not available. Once the context is available to user, there should be a methodology maintained to alarm the user of its existence. In this paper, we propose new event detection architecture for new composite system. In the later part of the paper, we provide two case studies using the proposed event detection architecture: video streaming service and office automation service.

Complex context information for video streaming service

Advances in computer networking combined with powerful home computers and modern operating systems made streaming media practical and affordable for ordinary consumers. We are enjoying different streaming services such as DMB, PMP, smart phone, etc. that have never experienced before. In the future computing environment such as ubiquitous environment, user can be served video streaming service by complex contexts. In the paper, we suggest and simulate the complex context information for multimedia streaming. In this paper, we applied complex context awareness concept to video streaming service and demonstrate our applications.

Performance analysis of circular directional MAC protocol

There have been great attentions on directional MAC (D-MAC) protocol recently in wireless ad hoc networks. Even if directional MAC has benefits such as spatial reuse and thus increased throughput, it has significant problems that have not been effectively rectified including hidden terminal and deafness problems. To tackle the hidden terminal and deafness problems, we propose a new D-MAC protocol that uses circular RTS (CRTS) and circular CTS (CCTS). We evaluate the performance of our protocol using ns-2 simulator. Performance evaluation shows that our proposed D-MAC protocol can reach up to 800% throughput gain with scenario 2 (24 nodes) against scenario 1 (3 nodes).

Optimization of ISM Band interference coordination between WLAN and IEEE 802.15.4 using NAV on PAN Coordinator

2.4GHz Industrial Scientific Medical(ISM) Band is shared by both WLAN and IEEE 802.15.4. Therefore, WLAN and IEEE 802.15.4 get interfered by each other where WLAN and IEEE 802.15.4 deploy locally. Especially, IEEE 802.15.4 devices are more influenced by the interference from LWAN devices because WLAN devices transmit data with higher power than IEEE 802.15.4 devices. In this paper, we proposed a possible algorithm for interference coordination in the Heterogeneous Network (HetNet) and optimized an important parameter, NAV, of the proposed mechanism. Our goal is to mitigate the interference problem and to make IEEE 802.15.4 work properly while minimizing the loss of WLAN by making PAN Coordinator conduct the role of both WLAN and IEEE 802.15.4 devices.

Fully distributed multicast routing protocol for IEEE 802.15.8 peer-aware communication

The IEEE 802.15.8 provides peer-aware communication (PAC) protocol for peer-to-peer infrastructureless service with fully distributed coordination. One of the most promising services in IEEE 802.15.8 is group multicast communication with simultaneous membership in multiple groups, typically up to 10 groups, in a dense network topology. Most of the existing multicast techniques in mobile ad hoc networks (MANET) have significant overhead for managing the multicast group and thus cannot be used for fully distributed PAC networks. In this paper, we propose a light-weight multicast routing protocol referred to as a fully distributed multicast routing protocol (FDMRP). The FDMRP minimizes routing table entries and thus reduces control message overhead for its multicast group management. To balance the control message, all nodes in the network have a similar number of routing entries to manage nodes in the same multicast group. To measure the effectiveness of the proposed FDMRP against the existing schemes, we evaluated performance by OPNET simulator. Performance evaluation shows that the FDMRP can reduce the number of routing entries and control message overhead by up to 85% and 95%, respectively, when the number of nodes is more than 500.