Donghyuk Han

Multihop Hybrid Virtual MIMO Scheme for Wireless Sensor Networks

Wireless sensor network devices commonly use a single antenna for transmission and reception, as well as for relaying packets over multiple hops to a final destination, which is referred to as single-input-single-output (SISO) multihop transmission. Advancements in multiple antenna systems enable reliable broadband wireless communications using multiple-input-multiple-output (MIMO) transmission technology. In addition, through collaboration of several single-antenna-equipped devices, cooperative MIMO communication is possible in the form of virtual MIMO (V-MIMO), virtual multiple-input-single-output (V-MISO), and virtual single-input-multiple-output (V-SIMO), which are collectively called V-MIMO technology. In this paper, a multihop hybrid V-MIMO (HV-MIMO) networking scheme is proposed to configure a minimum energy consuming route (MECR) that provides high end-to-end connectivity while satisfying end-to-end data rate and bit error rate (BER) requirements by using the best cooperative MIMO configuration for each hop. In the proposed scheme, first, the source-to-destination path is divided into long wireless communication hops, and the minimum energy consuming V-MIMO configuration is applied to each hop. Next, the long communication hops are individually evaluated for replacement with two half-length V-MIMO hops, where changes are applied only when a gain in energy consumption is obtainable. If no gain is obtainable for a certain hop, then the hop configuration is not changed, and that hop is no longer compared for replacement. This procedure of testing for possible replacement with two half-length hops is repeated individually for all hops until no further changes are made in the source-to-destination path, which is when the HV-MIMO MECR is complete. For equivalent end-to-end data rate and BER requirements, the proposed HV-MIMO multihop scheme provides a significant energy saving (e.g., 52.32% energy saving at the node density of 0.003 nodes/m2) compared with the conventional SISO multihop paths MECR. In addition, the HV-MIMO scheme always results in an energy saving gain and a significantly higher end-to-end multihop MECR connection probability compared with using the same type of cooperative MIMO configuration for each hop (i.e., homogeneous V-MIMO configuration).

Measurement and stochastic modeling of handover delay and interruption time of smartphone real-time applications on LTE networks

For continuous services of mobile user equipment (UE), Long Term Evolution (LTE) systems conduct evolved node B (eNB) switching based on hard handover technology, which breaks a connection before the connection to the target eNB (T-eNB) is made. As handover service interruption seriously degrades network performance, precise knowledge of the handover (HO) performance is necessary in finding out defects of the current system and discovering clues for improvements. Although the performance of LTE handover and its anticipated effect on network services are important evaluation indexes, in existing literature only the theoretical performance is analyzed and very few actual measurements on practical LTE networks have been presented. In this article, the HO delay and handover interruption time (HIT) performance of LTE networks are measured for several cases in accordance with the average number of users in a cell. Based on the internal HO procedures that influence HO delay and HIT, the key parameters are analyzed. In addition, based on the estimated number of users in a cell, a reference probability density function (PDF) that can be used for HIT prediction is presented.

TCP and MPTCP Retransmission Timeout Control for Networks Supporting WLANs

This letter investigates the problem associated with retransmission timeout (RTO) that is used in transport layer protocols. The current RTO algorithm is designed for wired networks, and is not properly prepared for IEEE 802.11-based wireless local area networks (WLANs). In this letter, a WLAN RTO (WRTO) algorithm, which can be applied to TCP and MPTCP is proposed. The experiments show that at poor channel conditions the proposed scheme results in a 18%, 29%, and 68% faster recovery time when compared to CMT-PF, cWPTCP, and CMT-QA, respectively, and also results in less spurious retransmission when compared to CMT-PF, which has the shortest recovery time among the existing schemes.

Self-Similar Traffic End-to-End Delay Minimization Multipath Routing Algorithm

In this letter, a multipath routing algorithm to reduce end-to-end delay and loss rate is proposed. The proposed multipath routing algorithm, self-similar delay minimization (SDM), estimates network delay of realistic network traffic by analyzing self-similar parameters based on fractional Brownian motion (fBm) traffic models, computes the optimal number of paths for average delay minimization, and also derives an optimal traffic distribution ratio for multipath routing using a cooperative game algorithm. Simulation results show that the average end-to-end delay and loss rate performance can be significantly improved when using SDM compared to using the average delay minimisation (ADM) or maximum delay minimisation (MDM) multipath routing algorithms.

Energy efficient wireless sensor networks based on 6LoWPAN and virtual MIMO technology

6LoWPAN (IPv6 over Low-power Wireless Personal Area Network) is a standard defined by IETF (Internet Engineering Task Force), which enables IPv6 transmission over IEEE 802.15.4 based WPANs (Wireless Personal Area Networks) to support many types of services, including WSNs (Wireless Sensor Networks). 6LoWPAN technology is rapidly gaining popularity for its extensive applicability, ranging from healthcare to environmental monitoring. In order to provide more reliable and effective IPv6 connectivity on top of LoWPAN, the 6LoWPAN WG (Working Group) has defined some key technologies. This paper introduces the 6LoWPAN technology and its applications, and discusses on possible technology that can enhance the energy efficiency of 6LoWPAN. One possible technology that is considered for combination with 6LoWPAN is the virtual multiple input and multiple output (V-MIMO) technology. The technical details of V-MIMO and its possible combination with 6LoWPAN are described in this paper.

Virtual MIMO based wireless communication for remote medical condition monitoring

Remote medical monitoring services for elderly people is necessary, especially for societies where the population of elderly people are rapidly increasing and healthcare costs are increasing due to lack of human resources. Wearable health-monitoring systems (WHMSs) can provide real-time medical condition monitoring using multiple biosensors attached to the human body. In this paper, virtual multiple input multiple output (MIMO) is proposed as a suitable technique for biosensor networks as it enables higher throughput capacity and less energy consumption than conventional schemes. The performance analysis of the proposed system shows that the lifetime of the virtual MIMO-based system outperforms existing systems.

Improved Association and Disassociation Scheme for Enhanced WLAN Handover and VHO

The number of mobile devices and wireless connections is significantly increasing. Among many wireless protocol types, wireless local area networks (WLANs) are expected to support a significant number of devices. Due to this reason, effective and efficient handover (HO) and vertical handover (VHO) support for WLAN mobile devices is important. A significant improvement in quality of service (QoS) can be obtained by reducing the association and disassociation interruption time for user equipment (UE) servicing real-time applications during WLAN HO and VHO operations. Based on this focus, this paper investigates the problem of using only the received signal strength indicator (RSSI) in HO and VHO decisions, which is what the current IEEE 802.11 based WLAN systems use. Experimental results presented in this paper demonstrate that only using the RSSI results in significant interruption time during HO to another WLAN access point (AP) or to a cellular base station during VHO. Therefore, in this paper, an improved association and disassociation scheme that can reduce the data interruption time (DIT) and improve the throughput performance is proposed.

Analysis of Wi-Fi data interruption and handover decision parameters

In this paper, IEEE 802.11 based Wi-Fi data interruption situations are categorized for effective handover decision into moving out of coverage, initial attachment, congestion, and sudden disconnection. In addition, this paper analyzes representative handover decision parameters based on effect on data interruption time.

Minimum jitter probability routing for DiffServ wireless mesh networks

In this letter, a minimum jitter probability (MJP) route selection algorithm for wireless mesh networks (WMNs) is proposed. To create the MJP algorithm, the inter-arrival packet jitter probability mass function (PMF) for differentiated service (DiffServ) priority classes is derived, which considers the effect of retransmissions due to packet errors in WMNs. Simulation results show the effectiveness of the proposed MJP algorithm compared to the popular minimum hop (MH) and expected transmission count (ETX) WMN routing schemes.