Byoung Hoon Jung

Adaptive Interference-Aware Multi-Channel Clustering Algorithm in a ZigBee Network in the Presence of WLAN Interference

In ubiquitous networking environments, we generally need two or more heterogeneous communication systems coexisting in a single place. Especially, wireless local area networks (WLANs) based on IEEE 802.11 specifications and wireless personal area networks (WPANs) based on IEEE 802.15.4b or g specifications need to coexist in the same Industrial, Science and Medial (ISM) band. If the WPAN communication coverage is expanded using a cluster-tree network topology, then the 802.15.4 network is more susceptible to interference from neighboring WLANs. In this paper, we propose an adaptive interference-aware clustering algorithm using multiple channels in a WPAN in the presence of WLAN interference. The algorithm includes interference detection and avoidance schemes to adaptively reconfigure multiple channels in an IEEE 802.15.4 cluster-tree network to avoid interference from WLANs. To evaluate the performance of the proposed algorithm, the frame error rate (FER) is measured in a real network testbed. The measurement result shows that the proposed algorithm is effective in an IEEE 802.15.4 cluster-tree network in the presence of multiple IEEE 802.11 interferers

A Network-Assisted User-Centric WiFi-Offloading Model for Maximizing Per-User Throughput in a Heterogeneous Network

In this paper, we propose a novel network-assisted user-centric WiFi-offloading model for maximizing per-user throughput in a heterogeneous network. In the proposed WiFi-offloading model, the heterogeneous network collects network information, such as the number of users in WiFi networks and their traffic load. Then, the network decides the specific portion of traffic to be transmitted via WiFi networks, i.e., φ*, which maximizes the per-user throughput. After informing the φ* to users, users offload their traffic with the probability of φ* and achieve the maximum per-user throughput while offloading more traffic into WiFi networks. Through the proposed WiFi-offloading model, a user and the heterogeneous network achieve 20% higher throughput than the on-the-spot WiFi-offloading model in a dense traffic environment.

Throughput, energy consumption, and energy efficiency of IEEE 802.15.6 body area network (BAN) MAC protocol

Low-powered and light-weight sensor nodes will be deployed for e-health services in wireless body area networks (WBANs). Recently, the Institute of Electrical and Electronic Engineering (IEEE) introduced a new standard, IEEE 802.15.6 for wireless body area communications. The goal of this standard is to specify several physical layers (PHY) and medium access control (MAC) layer protocols for variety of applications with various QoS requirements. In this paper, we evaluate the performance of the IEEE 802.15.6 WBAN MAC protocol in terms of throughput, power consumption, and energy efficiency under unsaturated conditions. We develop a discrete-time Markov chain based analytical model to evaluate the performance of CSMA/CA based WBAN MAC protocol during contention access phases. To verify the numerical results obtained from analytical model, we performed simulations and compared the results.

Interference mediation for coexistence of WLAN and ZigBee networks

In emerging ubiquitous wireless environments, mobile devices can have multiple communication modules such as WLAN and ZigBee. Since IEEE802.15.4 ZigBee devices and IEEE802.11b WLAN devices share the same 2.4 GHz ISM band, a ZigBee network operating in a low power environment can be severely interfered by overlapped WLAN networks with much larger bandwidth due to higher transmission power. To overcome this inter-system interference problem and guarantee the ZigBee communications, we propose an interference mediation scheme in an overlaid network environment of WLAN and ZigBee devices by using an interference mediator, and evaluate the performance of ZigBee and WLAN networks for three different resource allocation schemes in terms of throughput and channel occupancy time.

Placement of WiFi access points for efficient WiFi offloading in an overlay network

In order to alleviate a mobile data explosion problem, WiFi offloading has been proposed. The key issue is how many access points (APs) are needed to accommodate a proper number of users per WiFi AP without severe performance degradation. Although WiFi networks can provide higher throughput as more and more APs are deployed, it may not be a reasonable solution if we consider an increase in the corresponding capital and operational expenditure (CAPEX/OPEX). Therefore, it is important to investigate the minimum required number of WiFi APs which achieve a certain level of performance improvement. In this paper, we focus on the minimum required number of WiFi APs for efficient WiFi offloading. We first set the target average per-user throughput when a WiFi network can play a role as an offloading network of a given cellular network. Based on this criterion, we find the minimum required number of WiFi APs in an overlay network through mathematical analysis.

Ubiquitous Wearable Computer (UWC)-Aided Coexistence Algorithm in an Overlaid Network Environment of WLAN and ZigBee Networks

Emerging ubiquitous wireless networks are being spread widely. Ubiquitous wearable computers (UWCs) which may contain various communication protocol modules such as WLAN, Bluetooth, ZigBee, Wibro, and CDMA can be a solution in this era to support the ubiquitous wireless network environment. In ubiquitous wireless environments, ubiquitous wearable computers (UWCs) with multiple communication modules can control each communication module as a coordinator and communicate with other devices containing WLAN and ZigBee modules in the surrounding networks. Since IEEE802.15.4 ZigBee and IEEE802.11b WLAN share the same 2.4 GHz ISM band, WLAN causes severe interference to ZigBee devices due to higher transmission power in a large bandwidth of 22 MHz. We propose a UWC-aided coexistence algorithm in an overlaid network environment of WLAN and ZigBee networks to solve this problem, and measure the performance of WLAN and ZigBee communication modules for two scenarios in a real network testbed in terms of frame error rate (FER) and goodput.

An energy-efficient WiFi offloading model in a heterogeneous network

In this paper, we model power consumption of a heterogeneous network consisting of overlapped cellular and WiFi networks. Then, we propose a novel WiFi offloading model for maximizing per-user energy efficiency in terms of bps per Joule. In the proposed WiFi offloading model, the heterogeneous network gathers user information and decides which portion of generated per-user traffic should be transmitted via WiFi networks in order to maximize the per-user energy efficiency; the heterogeneous network informs users of this portion, i.e, WiFi offloading ratio. Finally, each user offloads the traffic from the cellular network by the WiFi offloading ratio. Consequently, a user and the heterogeneous network achieve more than 20% higher energy efficiency than the conventional WiFi offloading model in a dense traffic environment through the proposed WiFi offloading model.

Adaptive transmission power control and rate selection scheme for maximizing energy efficiency of IEEE 802.11 stations

Energy efficiency in wireless communications is one of important research issues. Previous studies on reducing the energy consumption of IEEE 802.11 WLAN systems mainly focused on the energy consumption of a single-link transmission only. However, due to its carrier sensing property, all the WLAN stations in the network receive the transmitted frames. Hence, this single-link transmission not only consumes the energy of the transmitter and receiver of the link, but also consumes the energy of the other stations. Moreover, most of the previous work on energy efficiency optimization problems were considered in MAC perspectives. In this paper, we show that the energy efficiency of all the stations in WLAN network can be optimized by our proposed adaptive transmission power control and rate selection scheme, with more accurate analysis of the energy consumption in IEEE 802.11 MAC and IEEE 802.11n PHY. The proposed adaptive transmission power control and rate selection scheme achieves an increase in an average energy efficiency of 34% at the cost of 5% throughput degradation for 800bits payload size and 20 users, for varying the distance from 0m to 90m.

Modeling and analysis of an energy-efficient sleep-mode operation in IEEE 802.16e system

Power saving mechanisms with sleep-mode operations have been used in IEEE 802.16e in order to extend the battery lifetime of mobile devices. The standard sleep-mode operation needs to meet a given delay constraint. However, it may incur unnecessary energy consumption due to frequent state transitions. In this paper, we propose a new energy-efficient sleep-mode operation while meeting a given delay requirement. We apply an M/G/1 queue model with multiple vacations for downlink traffic in an error-free environment in order to evaluate the energy efficiency performance of the proposed sleep-mode operation in terms of packets/Joule. We compare the proposed sleep-mode operation with the standard sleep-mode operation. The results show that our proposed sleep-mode operation improves the total energy efficiency consumption per unit frame time by 35% and energy efficiency by 21% while meeting a given delay requirement.

Adaptive beamforming antenna scheme to minimize the interference in a unmanned aerial vehicle (UAV) MANET

Unmanned aerial vehicle (UAV) network is a network consisting of ¤ying UAVs with communication capabilities. There are many technical challenges and problems due to a highly dynamic and mobile UAV network environment. In this paper, we focus on an inter-node interference problem. To overcome the interference problem and guarantee the communication quality, we propose an adaptive beamforming antenna scheme to meet a given outage constraint and to mitigate the interference. We analyze the outage probability of the communication link, and £nd the optimal beamwidth of the directional beam. Numerical results show that an adaptive beamforming antenna scheme is the most ef£cient among £xed beamwidth schemes and an omnidirectional antenna scheme in terms of outage and the amount of interference.