Myung J. Lee

Will IEEE 802.15.4 make ubiquitous networking a reality?: a discussion on a potential low power, low bit rate standard

The new IEEE standard 802.15.4 shows promise to bring ubiquitous networking into our lives, at least technically. Unlike other standards targeting high- or moderate-data-rate applications, IEEE 802.15.4 is a global standard designed for low-data-rate, low power consumption, and low-cost applications. This so-called enabling standard brings many simple, originally standalone devices into networks, and thus not only open the door to an enormous number of new applications, but also add values to many other existing applications. In this article we first present a few application scenarios to show the potential extent to which the new standard can affect our lives, and then give an overview of the standard, focusing on its feasibility and functions in establishing ubiquitous networks. We also outline some quantitative results from our experiments so as to have a better view of the standard.

A resource-efficient and scalable wireless mesh routing protocol

By binding logic addresses to the network topology, routing can be carried out without going through route discovery. This eliminates the initial route discovery latency, saves storage space otherwise needed for routing table, and reduces the communication overhead and energy consumption. In this paper, an adaptive block addressing (ABA) scheme is first introduced for logic address assignment as well as network auto-configuration purpose. The scheme takes into account the actual network topology and thus is fully topology-adaptive. Then a distributed link state (DLS) scheme is further proposed and put on top of the block addressing scheme to improve the quality of routes, in terms of hop count or other routing cost metrics used, robustness, and load balancing. The network topology reflected in logic addresses is used as a guideline to tell towards which direction (rather than next hop) a packet should be relayed. The next hop is derived from each relaying nodes local link state table. The routing scheme, named as topology-guided DLS (TDLS) as a whole, scales well with regard to various performance metrics. The ability of TDLS to provide multiple paths also precludes the need for explicit route repair, which is the most complicated part in many wireless routing protocols. While this paper targets low rate wireless mesh personal area networks (LR-WMPANs), including wireless mesh sensor networks (WMSNs), the TDLS itself is a general scheme and can be applied to other non-mobile wireless mesh networks.

Statistical synchronization among participants in real-time multimedia conference

In this paper, an algorithm to determine the set of packets generated continuously and periodically from different participants that are arriving at a node either for mixing at the master of a conference, or for simply playing back at a regular participant of a conference, is proposed. The essence of the algorithm is to estimate the average packet arrival time (or reference time) for each participant. With the reference time at hand, the maximum jitter and the optimum waiting time for a mixer to wait packets from all participants can be determined. An enhancement to improve synchronization which deals with the estimation of the time offsets between the individual periods of the sources and the period of the receiver is also presented. The error of the proposed algorithm is enumerated by the Chernoff bound and is shown to be acceptable in practical application.<<ETX>>

Design and analysis of asynchronous wakeup for wireless sensor networks

In wireless sensor networks, scheduling the sleep duration of each node is one of the key elements for controlling critical performance metrics such as energy consumption and latency. Since the wakeup interval is a primary parameter for determining the sleeping schedule, how to tune the wakeup interval is crucial for the overall network performance. In this paper, we present an effective framework for tuning asynchronous wakeup intervals of IEEE 802.15.4 sensor networks from the energy consumption viewpoint. First, we derive an energy consumption model of each node as an explicit function of the wakeup interval, and empirically validate the derived model. Second, based on the proposed model, we formulate the problem of tuning the wakeup interval with the following two objectives: to minimize total energy consumption and to maximize network lifetime. We show that these two problems can be optimally solved by an iterative algorithm with global information by virtue of the convexity of the problem structure. Finally, as practical solutions, we further propose heuristic optimization algorithms that only exploit local information. In order to develop heuristic algorithms, we propose two broadcasting schemes, which are entitled as maximum wakeup interval broadcasting and efficient local maximum broadcasting. These broadcasting algorithms enable nodes in the network to have heterogeneous wakeup intervals.

Dejittering in the transport of MPEG-2 and MPEG-4 video

Abstract. When multimedia information is transported over a packet-switched network, the quality of presentation can be degraded due to network delay variation or jitter. This paper presents a dejittering scheme that can be used in the transport of MPEG-4 and MPEG-2 video to absorb any introduced network jitter, thus preserving the presentation quality of transported media streams. The dejittering scheme is based on the statistical approximation of delay variation in the arrival times of video packets carrying encoded clock reference values and a filtering and re-stamping mechanism. In addition, a brief overview of the MPEG-4 system is presented.

A new efficient medium access control protocol for multi-hop wireless mesh networks

This paper presents a new medium access control (MAC) scheme, which exploits the code division multiple access (CDMA) technology to provision many-to-one simultaneous wireless communication service without utilizing any time division multiple access (TDMA) scheme. This, combined with existing one-to-one (i.e., unicast) and one-to-many (i.e., multicast or broadcast) wireless communication services, brings into life a new communication paradigm, that is, mesh communications. The new scheme also supports accumulative receptions, namely, a receiver can buffer partially damaged (re-)transmitted frames and add those frames efficiently to form an error-free frame. Our simulation results show that the new scheme outperforms IEEE 802.11 in both non-mobile and mobile environments.

Design of an adaptive configuration management architecture for tactical battlefield networks

Management of tactical battlefield networks presents a host of challenges. The challenges arise due to the volatile and sometimes, unpredictable nature of these networks. This is because, in a battlefield environment, the network elements (switches/routers) can appear and disappear sporadically, due to jamming, hostile attacks, etc. This results in sporadic changes in the network connectivity. Furthermore, mission re-assignments can occur and may also result in frequent traffic pattern shift. Thus an auto-configuration management system that can adapt to the dynamic network conditions is extremely important. In this work, we have designed an adaptive configuration management system (ACMS) that is sensitive to the battlefield dynamics. We use the concept of directory service systems to facilitate automated configuration management. We have also developed an initial design framework of a simulation model that can be used to demonstrate our ACMS design.

De-jittering in the transport of MPEG-4 and MPEG-2 video over ATM

In this paper a de-jittering scheme which can be used in the transport of MPEG-4 and MPEG-2 video to absorb any introduced network jitter is proposed. The essence of the de-jittering scheme is based on the statistical approximation of delay variation in the arrival times of video packets carrying encoded clock reference values and a filtering and re-stamping mechanism. In addition, a brief overview of the MPEG-4 system is presented.

Improving military operations using low rate wireless personal area networks

Low rate wireless personal area networks (LR-WPANs) target low data rate, low power consumption and low cost wireless networking, and offer device level wireless connectivity. They are ideal for applications such as public security, battle field monitoring, inventory tracking, as well as home and office automation. IEEE 802.15.4 is the first standard designed for LR-WPANs, We develop an NS2 simulator based on IEEE 802.15.4 and conduct several sets of experiments to study various features of LR-WPANs, including: (1) star topology and peer-to-peer topology; (2) beacon enabled mode and non-beacon enabled mode; (3) association, tree formation and network auto-configuration; (4) orphaning and coordinator relocation; and (5) direct, indirect and guaranteed time slot (GTS) data transmissions.