Younggoo Kwon

H-SPREAD: a hybrid multipath scheme for secure and reliable data collection in wireless sensor networks

Communication security and reliability are two important issues in any network. A typical communication task in a wireless sensor network is for every sensor node to sense its local environment, and upon request, send data of interest back to a base station (BS). In this paper, a hybrid multipath scheme (H-SPREAD) to improve both the security and reliability of this task in a potentially hostile and unreliable wireless sensor network is proposed. The new scheme is based on a distributed N-to-1 multipath discovery protocol, which is able to find multiple node-disjoint paths from every sensor node to the BS simultaneously in one route discovery process. Then, a hybrid multipath data collection scheme is proposed. On the one hand, end-to-end multipath data dispersion, combined with secret sharing, enhances the security of the end-to-end data delivery in the sense that the compromise of a small number of paths will not result in the compromise of a data message in the face of adversarial nodes. On the other hand, in the face of unreliable wireless links and/or sensor nodes, alternate path routing available at each sensor node improves the reliability of each packet transmission significantly. The extensive simulation results show that the hybrid multipath scheme is very efficient in improving both the security and reliability of the data collection service seamlessly

ODTPC: On-demand Transmission Power Control for Wireless Sensor Networks

Development of efficient transmission power control algorithms providing both high energy efficiency and good link quality is the current major focus in wireless sensor networks research. In the paper, we propose an efficient transmission power control algorithm for wireless sensor networks, namely, the on-demand transmission power control (ODTPC) algorithm. This new algorithm attempts to reduce the initialization overhead in determining the optimal transmission power level while providing good link qualities. Our testbed experiment results show that ODTPC consumes much less energy than previous transmission power control algorithms (PCBL ( D. Son,et al.) and ATPC (S. Lin, et al.)) and is easily implemented with routing protocols like AODV (C. Perkin, and E. Royer) and Directed Diffusion (C. Intanagonwiwat, et al.).

Robust localization over obstructed interferences for inbuilding wireless applications

Location-awareness can be applied to the various consumer applications. A received signal strength (RSS) based localization system is relatively inexpensive and simple to be implemented without additional hardware supports. However, the radio signals are strongly affected by the obstructed interferences. This is a difficult problem for the RSS based localization systems to be implemented in real world. To solve this problem, we propose a practical and robust localization algorithm in the obstructed environments. The proposed algorithm uses the Maximum Likelihood Estimation (MLE) based on the position probability grid. In addition, the proposed algorithm detects and compensates the large measurement error using the Min-Max algorithm. We evaluated the performance of the proposed algorithm in the obstructed environments. Performance results show that the proposed algorithm outperforms other algorithms on the obstructed environments.

Traffic adaptive IEEE 802.15.4 MAC for wireless sensor networks

IEEE 802.15.4 is a new standard uniquely designed for low rate wireless sensor networks(WSNs). It targets low data rate, low power consumption and low cost wireless networking, and offers device level wireless connectivity. In this paper, the general coordinated sleeping algorithm and the traffic-adaptive algorithm are combined in IEEE 802.15.4 MAC protocol to achieve high energy efficiency and high performance at the same time. By observing that the sporadic traffic characteristic of WSNs, we propose the traffic-adaptive IEEE 802.15.4 MAC with coordinated sleeping algorithm. Through the various performance studies, the proposed algorithm shows significant performance improvements in wireless sensor networks

Interference-aware topology control for low rate wireless personal area networks

The topology control technique can prolong the network lifetime, but it can suffer the significant performance degradation due to the interferences of WLAN or Bluetooth devices. This paper proposes a novel topology control algorithm to reduce the interference effects. The basic idea of the proposed algorithm is to estimate the interference effects exactly and re-construct the robust network topology to the interference variations. From the experimental results, we can see that the proposed algorithm shows the good performance results in terms of the delivery ratio and the energy consumptions.

Interference-Aware Transmission Power Control for Wireless Sensor Networks

Maintaining the lowest possible transmission power in the wireless sensor networks (WSNs) is vulnerable to the interference fluctuations because of the bad signal-to-interference-plus-noise-ratio (SINR). The previous transmission power control (TPC) algorithms do not consider much for the interferences from other 2.4GHz devices, which can cause significant performance degradations in real world deployments. This paper proposes the interference-aware transmission power control (I-TPC) algorithm for WSNs. In the proposed algorithm, each node dynamically adjusts the transmission power and the received signal strength (RSS) target, hence the appropriate SINR is provided even when the wireless LAN (WLAN) interferences become strong. The experimental results show that the proposed algorithm outperforms the previous algorithms in terms of the energy and the packet reception ratio (PRR) performance in WLAN interference environments.

Localization and dynamic link detection for geographic routing in non-line-of-sight (NLOS) environments

IEEE 802.15.4a networks can provide the geographic routing solution with high location accuracy for the indoor environments. However, in the non-line-of-sight (NLOS) environments, the IEEE 802.15.4a networks may have a large scale location error and an unstable communication link. In this article, we propose a location estimation and dynamic link detection scheme for the geographic routing in the NLOS environments. The proposed approach corrects the large scale location error and detects the NLOS link in the geographic routing procedure. Simulation and experimental results show that the proposed approach can enhance the performance of the geographic routing.

3-dimensional topology control for wireless sensor networks in presence of interference

This paper proposes a novel 3-dimensional (3D) topology control algorithm to reduce the interference effects by removing the links affected by the interferences. The proposed algorithm uses the regular polyhedron to construct the 3D topology. Experimental results show the significant performance improvements for both the delivery ratio and the energy consumption.

Practical robust localization over obstructed interferences in wireless sensor networks

In this paper, we propose a practical and robust localization algorithm over the obstructed interferences in the wireless sensor networks (WSNs). The proposed algorithm uses the Maximum Likelihood Estimation (MLE) method on the position probability grid. In addition, the proposed algorithm detects and compensates the large RSS measurement errors by using the Min-Max algorithm in obstructed environments. Simulation results show that the proposed algorithm takes the advantages of the range-based and the range-free algorithms simultaneously to handle the obstructed interferences in the wireless sensor networks.

Implementation of DCT based OFDM system

The conventional OFDM system employs the IFFT-FFT structure to impart the orthogonolity feature. However, due to complex nature of FFT, implementation size is large enough. The orthogonolity can also be provided if IDCT-DCT structure is used in place of FFT. This will reduce the implementation area and will also increase the computation speed as only real calculations are required. In this paper we present the implementation of DCT based OFDM system. The DCT structure prevalent in H.264 standard is taken into reference as it has faster operation as compared to conventional DCT structure. The implementation of DCT-IDCT structure was done on ALTERA CYCLONE -II FPGA. The results show that the speed of calculation of orthogonal components is increased three folds while the implementation size reduces to half as compared to FFT based design.