Sungoh Kwon

Analysis of shortest path routing for large multi-hop wireless networks

In this paper, we analyze the impact of straight line routing in large homogeneous multi-hop wireless networks. We estimate the nodal load, which is defined as the number of packets served at a node, induced by straight line routing. For a given total offered load on the network, our analysis shows that the nodal load at each node is a function of the nodes Voronoi cell, the nodes location in the network, and the traffic pattern specified by the source and destination randomness and straight line routing. In the asymptotic regime, we show that each nodes probability that the node serves a packet arriving to the network approaches the products of half the length of the Voronoi cell perimeter and the load density function that a packet goes through the nodes location. The density function depends on the traffic pattern generation by straight line routing, and determines where the hot spot is created in the network. Hence, contrary to conventional wisdom, straight line routing can balance the load over the network, depending on the traffic patterns.

Energy-Efficient Interference-Based Routing for Multi-Hop Wireless Networks

In this paper, we develop an energy efficient routing scheme that takes into account the interference created by existing flows in the network. Unlike previous works, we explicitly study the impact of routing a new flow on the energy consumption of the network. Under certain assumptions on how links are scheduled, we can show that our proposed algorithm is asymptotically (in time) optimal in terms of minimizing the average energy consumption. We also develop a distributed version of the algorithm. Our algorithm automatically detours around a congested area in the network, which helps mitigate network congestion and improve overall network performance. Using simulations, we show that the routes chosen by our algorithm (centralized and distributed) are more energy efficient than the state of the art.

Paradox of Shortest Path Routing for Large Multi-Hop Wireless Networks

In this paper, we analyze the impact of straight line routing in large homogeneous multi-hop wireless networks. We estimate the nodal load, which is defined as the number of packets served at a node, induced by straight line routing. For a given total offered load on the network, our analysis shows that the nodal load at each node is a function of the nodes Voronoi cell, the nodes location in the network, and the traffic pattern specified by the source and destination randomness and straight line routing. The traffic pattern determines where the hot spot is created in the network, and straight line routing itself can balance the relay load in certain cases. In the asymptotic regime, each nodes probability that the node serves a packet arriving to the network can be approximated as the multiplication of a half length of its Voronoi cell perimeter and the probability density function that a packet goes through the nodes location. Both simulations and analysis confirm that this approximation converges to the exact value. The scaling order of network performance in our analysis is independent of traffic patterns generated by source-destination pair randomness, but for a given node the performance of each node is strongly related to the source-destination pair randomness.

Mobility-Assisted on-Demand Routing Algorithm for MANETs in the Presence of Location Errors

We propose a mobility-assisted on-demand routing algorithm for mobile ad hoc networks in the presence of location errors. Location awareness enables mobile nodes to predict their mobility and enhances routing performance by estimating link duration and selecting reliable routes. However, measured locations intrinsically include errors in measurement. Such errors degrade mobility prediction and have been ignored in previous work. To mitigate the impact of location errors on routing, we propose an on-demand routing algorithm taking into account location errors. To that end, we adopt the Kalman filter to estimate accurate locations and consider route confidence in discovering routes. Via simulations, we compare our algorithm and previous algorithms in various environments. Our proposed mobility prediction is robust to the location errors.

Energy-Efficient Unified Routing Algorithm for Multi-Hop Wireless Networks

In this paper, we develop an energy-efficient routing scheme that takes into account four key wireless system elements: transmission power; interference; residual energy; and energy replenishment. Since energy is a scarce resource, many energy-aware routing algorithms have been proposed to improve network performance. However, previous algorithms have been designed for a subset of these four main elements, which could limit their applicability. Thus, our contribution is here to develop a unified routing algorithm called the Energy-efficient Unified Routing (EURo) algorithm that accommodates any combination of these above key elements and adapts to varying wireless environments. We study the impact of key wireless elements on routing, and show via simulations that EURo outperforms the state-of-the-art.

Virtual extension of cell IDs in a femtocell environment

In this paper, we solve a cell identification problem in a femtocell environment. In the densely deployed area, the number of Physical Cell Identifiers (PCIs) for femtocells may not be sufficient. The scarcity of PCIs results in identification ambiguity due to duplicated PCIs in a certain area, which may result in handover failure. Using time synchronization between femtocells and macro cells, we propose a scheme to efficiently identify cells in a femtocell environment. Our scheme can increase the number of cell identifiers up to 1024 times using even coarse local time synchronization, without changing the existing physical layer specification. Since time synchronization occurs locally, we can apply the proposed scheme to asynchronous as well as synchronous wireless systems. We verify the proposed scheme via simulations.

Uplink QoS Scheduling for LTE System

In this paper, we propose a QoS uplink scheduling algorithm for LTE collaborating with delay estimation. Unlike downlink scheduling, uplink scheduling cannot incorporate packet delay information due to specification constraints of LTE. The limited information results in difficulty ensuring a QoS when conventional scheduling algorithms are employed. Using a delay estimation tailored to LTE, we have shown that the uplink performance of the proposed QoS scheduling scheme can be improved more than 11% even with a simple estimation via simulations.

Geographic routing in the presence of location errors

In this paper, we propose a new geographic routing algorithm that alleviates the effect of location errors on routing in wireless ad hoc networks. In most previous work, geographic routing has been studied assuming perfect location information. However, in practice there could be significant errors in obtaining location estimates, even when nodes use GPS. Hence, existing geographic routing schemes will need to be appropriately modified. We investigate how such location errors affect the performance of geographic routing strategies. We incorporate location errors into our objective function by considering both transmission failures and backward progress. Each node then forwards packets to the node that maximizes this objective function. We call this strategy maximum expectation within transmission range (MER). Simulation results with MER show that accounting for location errors significantly improves the performance of geographic routing. We also show that MER is robust to the location error model and model parameters. Further, via simulations, we show that in a mobile environment MER performs better than existing approaches.

Unified Energy-Efficient Routing for Multi-Hop Wireless Networks

In this paper, we develop an energy-efficient routing scheme that takes into account three key wireless system elements: transmission power; interference; and residual energy. Since energy is a scarce resource, many energy-aware routing algorithms have been proposed to improve network performance. However, previous algorithms have been designed for a subset of these three main elements, which could limit their applicability. Thus, our contribution is here to develop a unified routing algorithm called the Energy-efficient Unified Routing (EURo) algorithm that accommodates any combination of these above key elements. We show via simulations that EURo outperforms the state-of-the-art.

Cooperative Interference Mitigation Algorithm in Heterogeneous Networks

Heterogeneous hetworks (HetNets) have been introduced as an emerging technology in order to meet the increasing demand for mobile data. HetNets are a combination of multi-layer networks such as macrocells and small cells. In such networks, users may suffer significant cross-layer interference. To manage this interference, the 3rd Generation Partnership Project (3GPP) has introduced enhanced Inter-Cell Interference Coordination (eICIC) techniques. Almost Blank SubFrame (ABSF) is one of the time-domain techniques used in eICIC solutions. We propose a dynamically optimal Signal-to-Interference-and-Noise Ratio (SINR)-based ABSF framework to ensure macro user performance while maintaining small user performance. We also study cooperative mechanisms to help small cells collaborate efficiently in order to reduce mutual interference. Simulations show that our proposed scheme achieves good performance and outperforms the existing ABSF frameworks.