Joongsoo Ma

Link stability and route lifetime in ad-hoc wireless networks

Many routing algorithms, proposed for ad-hoc wireless networks, are based on source routing scheme. When a route is broken in source routing, route recovery and maintenance procedures are executed. However these procedures consume many resources. To minimize route breaking, it important to find a route that endures longer time. Shortest path route has short lifetime especially in highly dense ad-hoc wireless networks, and it due to the edge effect discovered in this paper Some routing protocols such as SSA and ABR are considering the link stability and try finding more stable route. In this paper, we will focus on the link stability and the lifetime of a route, and propose link stability comparison models for previously proposed routing algorithms. We will show properties of these models and compare them with local optimal algorithm that finds longest lifetime route at a given time. Finally, we will propose an enhanced link stability estimation model to find a route with longer lifetime.

Grapes: topology-based hierarchical virtual network for peer-to-peer lookup services

Peer-to-peer systems and applications are distributed systems without any centralized control. The core operation in most peer-to-peer systems is efficient location of data items. The current well-known peer-to-peer systems like Napster and Gnutella have scalability problem in location of data items. To solve the scalability problem, some scalable peer-to-peer lookup services show up, such as CAN, Chord, Pastry and Tapestry. In this paper we propose a self organizing hierarchical virtual network infrastructure, called Grapes, for peer-to-peer lookup services. Hierarchical approach of Grapes brings two benefits. First, a node can find data in its subnetwork with the high probability due to the data replication in its subnetwork. Second, the hierarchical structure makes lookup hops shorter than those of the flat one.

Performance evaluation for delay time estimation in IEEE 802.16m sleep mode

Frequent use of various mobile application services consumes a great amount of battery power in mobile devices. In order to satisfy user convenience and keep the portability of mobile devices, a power saving mechanism is essential for the success of mobile communication technologies. This paper evaluates performances of the power saving mechanism of IEEE 802.16m, one of the solutions for the fourth generation mobile communication technology. When a mobile device does not communicate with a base station, it temporarily shuts down communication-related modules and circuits in order to save the battery power. During that period, the device cannot listen to incoming traffic from the base station, which causes an inevitable delay at the expense of reducing power consumption. Arriving packets are transmitted only after the device enters either the awake mode or the listening window in the sleep mode. Four power saving mechanisms are examined in the simulation:1) fixed maximum operating parameters, 2) fixed minimum operating parameters, 3) moving average policy, and 4) exponential increase policy. To evaluate the performance of the sleep mode operation in IEEE 802.16m, an analytical model is developed for delay time based on M/D/1 queueing system. Performances of the power saving mechanisms are evaluated with Poisson and traffic models for five applications: WEB, FTP, GAME, VIDEO, and VOICE, which reflects real service environment.

Interference estimation for channel selection in wireless mesh networks

Nowadays, a number of wireless devices compete for medium on each channel and many nodes are in the relation of hidden terminal. Therefore, the interference-aware channel allocation becomes important to efficiently manage the networks. We address the problem of estimating the interfering node to select the least interfered channel in a multi-channel, multi-radio wireless mesh network (WMN). Incorrect interfering node estimation easily overestimates or underestimates the interference of each channel and it causes the wrong channel selection. We introduce an interference estimation method adapting to the varying interference area according to the data rate and radio propagation property. We use simulations to validate the accuracy of the proposed method and compare to other schemes in various scenarios.

Novel distance estimation algorithm of two-hop neighbor in wireless sensor networks

In case of wireless networks which does not contain a localization system, Euclidean distance between two nodes those are out of carrier sensing range each other cannot be measured with ranging techniques such as RSSI, ToA, and TDoA since they are not able to communicate directly. To deal with this issue, range-free schemes like a hop-count based approach and a connectivity based approach were used. These methods, however, are decreased in accuracy at low node density networks, so it is hard to apply to other wireless network except the densely deployed sensor networks. In this paper, we present a novel distance estimation method. When two nodes are in 2-hop neighbor relation, our method can estimate a distance using ranging information of their overlapped neighbors and connectivity information. Simulation results show that the proposed method outperforms hop count based and connectivity based distance estimation methods.

Interference estimation of wireless mesh network in a shadow fading environment

As an enormous increase of wireless network usage, WLAN devices interfere with each other in a crowded place, such as downtown. Hence, it is important that choose the least interfered channel around it for better network condition. In this paper, we propose a method which estimates the interfering nodes accurately in a shadow fading environment without localization systems like GPS. This estimation algorithm considers the varying interference area that is caused by the data rate and radio propagation property, especially shadow fading. To evaluate our scheme, we simulate and compare it to other schemes in various scenarios.