Jongkeun Na

GLR: a novel geographic routing scheme for large wireless ad hoc networks

Wireless ad hoc routing has been extensively studied and many clever schemes have been proposed over the last several years. One class of ad hoc routing is geographic routing where each intermediate node independently selects the next hop using the given location information of destination. Geographic routing, which eliminates the overhead of route request packet flooding, is scalable and suitable for large scale ad hoc networks. However, geographic routing may select the long detour paths when there are voids between a source and a destination. In this paper, we propose a novel geographic routing approach called geographic landmark routing (GLR). GLR recursively discovers the intermediate nodes called landmarks and constructs sub-paths that connect the subsequent landmarks. Simulation results on various network topologies show that GLR significantly improves the performance of geographic routing.

Adaptive Optimization of Rate Adaptation Algorithms in Multi-Rate WLANs

Rate adaptation is one of the basic functionalities in todays 802.11 wireless LANs (WLANs). Although it is primarily designed to cope with the variability of wireless channels and achieve higher system spectral efficiency, its design needs careful consideration of cross-layer dependencies, in particular, link-layer collisions. Most practical rate adaptations focus on the time-varying characteristics of wireless channels, ignoring the impact of link-layer collisions. As a result, they may lose their effectiveness due to unnecessary rate downshift wrongly triggered by the collisions. Some recently proposed rate adaptations use RTS/CTS to suppress the collision effect by differentiating collisions from channel errors. The RTS/CTS handshake, however, incurs significant overhead and is rarely activated in infrastructure WLANs. In this paper, we introduce a new approach for optimizing the operation of rate adaptations by adjusting the rate-increasing and decreasing parameters based on link-layer measurement. To construct the algorithm, we study the impact of rate-increasing and decreasing thresholds on performance and show that dynamic adjustment of thresholds is an effective way to mitigate the collision effect in multi-user environments. Our method does not require additional probing overhead incurred by RTS/CTS exchanges and may be practically deployed without change in firmware. We demonstrate the effectiveness of our solution, comparing with existing approaches through extensive simulations.

Greedy Geographic Routing using Dynamic Potential Field for Wireless Ad Hoc Networks

Greedy geographic routing has been considered as an attractive approach due to its simplicity and scalability. However, greedy routing is insufficient in terms of routing convergence because of the local maximum problem. In this letter, we propose a novel greedy routing scheme based on a potential field method that dynamically eliminates the local maximum condition

A dynamic load sharing mechanism in multihomed mobile networks

An entire network can be managed as a single mobility entity when it moves as a unit. To support network mobility (NEMO), a mobile router has been introduced to manage the mobility of whole nodes inside the network. In this mobile network, multiple mobile router (MR)s and home agent (HA)s scenarios are considered to provide reliability and load sharing. In this paper, we present a neighbor MR authentication and registration mechanism in multihomed mobile networks. Also, using registered MRs, we propose a HA-based dynamic load sharing mechanism. Using measured latency from periodic binding update (BU) messages, the HA shares traffic load with an alternative tunnel. Our proposed mechanism requires no additional signaling messages except some options in the BU message.

A Unified Route Optimization Scheme for Network Mobility

Recently Network Mobility(NEMO) is being concerned as new mobility issue. Lots of NEMO issues are already being touched in IETF NEMO WG but the solution is still premature especially to the Route Optimization (RO). NEMO has several problem spaces that need RO such as nested tunnels problem. Unfortunately, there is no solution that can be universally applied as one for all that results in supporting the coherent network mobility. In this paper, we propose a unified route optimization scheme that can solve several types of RO problem by using Path Control Header (PCH). In our scheme, Home Agent (HA) does piggyback the PCH on the packet which is reversely forwarded from Mobile Router (MR). That enables any PCH-aware routing facility on the route to make a RO tunnel with MR using the Care-of address of MR contained in the PCH. By applying to some already known NEMO RO problems, we show that our scheme can incrementally optimize the routes via default HA-MR tunnel through the simple PCH interpretation.

A seamless handover scheme in IPv6-based mobile networks

With the rapid development of wireless technologies, the need to support moving hosts of IPv6-based mobile networks in ubiquitous is growing. Various well-known approaches to optimising the handover latency have been proposed in the literature: MIPv6, FMIPv6, HMIPv6 and F-HMIPv6. However, these approaches are inefficient in packet loss, out-of order problem, dependency of exact predictive information and a sudden disruption of the link. In this paper, we propose a seamless handover scheme with temporal reuse of Care of Addresses (CoAs) and Packet Buffering Point (PBP) in IPv6-Based mobile networks.

Dual wake-up low power listening for duty cycled wireless sensor networks

Energy management is an interesting research area for wireless sensor networks. Relevant dutycycling (or sleep scheduling) algorithm has been actively studied at MAC, routing, and application levels. Low power listening (LPL) MAC is one of effective dutycycling techniques. This paper proposes a novel approach called dual wake-up LPL (DW-LPL). Existing LPL scheme uses a preamble detection method for both broadcast and unicast, thus suffers from severe overhearing problem at unicast transmission. DW-LPL uses a different wake-up method for unicast while using LPL-like method for broadcast; DW-LPL introduces a receiver-initiated method in which a sender waits a signal from receiver to start unicast transmission, which incurs some signaling overhead but supports flexible adaptive listening as well as overhearing removal effect. Through analysis and Mote (Telosb) experiment, we show that DW-LPL provides more energy saving than LPL and our adaptive listening scheme is effective for energy conservation in practical network topologies and traffic patterns.

Analysis of dynamic low power listening schemes in wireless sensor networks

In this letter, we evaluate the performance of dynamic Low Power Listening (LPL) schemes via an analytical model. We also analyze the impact of polling interval parameters on energy consumption.

A Robust Seamless Handover Scheme for the Support of Multimedia Services in Heterogeneous Emerging Wireless Networks

With the rapid development of wireless technologies and numerous types of mobile devices, the need to support seamless multimedia services in Mobile and Ubiquitous Computing (MUC) is growing. To support the seamless handover, several mobility protocols such as Mobile IPv6 (MIPv6) (Johnson et al., Mobility Support in IPv6, IETF, RFC 3775, 2004) and fast handover for the MIPv6 (FMIPv6) (Koodli et al. Past handovers for mobile IPv6 (FMIPv6), IETF, RFC 4068, 2005) were developed. However, MIPv6 depreciates the Quality-of-Service (QoS) especially in multimedia service applications because of the long handover latency and packet loss problem. To solve these problems in the MIPv6, FMIPv6 is proposed in the Internet Engineering Task Force (IETF). However, FMIPv6 is not robust for the multimedia services in heterogeneous emerging wireless networks when the MN may move to another visited network in contrast with its anticipation. In MUC, the possibility of service failure is more increased because mobile users can frequently change the access networks according to their mobility in heterogeneous wireless access networks such as 3Generation (3G), Wireless Fidelity (Wi-Fi), Worldwide Interoperability for Microwave Access (WiMax) and Bluetooth co-existed. In this paper, we propose a robust seamless handover scheme for the multimedia services in heterogeneous emerging wireless networks. The proposed scheme reduces the handover latency and handover initiation time when handover may fail through the management of tentative Care-of Addresses (CoAs) that does not require Duplicate Address Detection (DAD). Through performance evaluation, we show that our scheme provides more robust handover mechanism than other scheme such as FMIPv6 for the multimedia services in heterogeneous emerging wireless networks.

Minimizing recovery overhead in geographic ad hoc routing

Geographic routing has been studied as an attractive approach due to its simplicity and scalability properties in routing for wireless ad hoc networks. Greedy routing is an important component of many geographic routing protocols which use a combined routing approach; a kind of recovery routing is used in case that greedy routing is impossible. In this paper, we propose the stateless extension of greedy routing called GR(k) that implements a k-bound forwarding algorithm where the parameter k controls the routing success rate and the corresponding overhead. We design three k-bound forwarding algorithms and evaluate which one is best via extensive simulation. The proposed approach improves the success rate of greedy routing by 20-40% at low node densities but in low overhead. These improvements mitigate the adverse effect of recovery routing (e.g. face routing) because the use of recovery routing is minimized; In particular, using GR(k) instead of greedy routing can reduce the number of packet transmissions up to 50%. We show that GR(k) is effective in reducing the average hop stretch in geographic routing by at most 30%.