Yeonsoo Kim

An Adaptive Mobility-Supporting MAC Protocol for Mobile Sensor Networks

In this paper, we design an energy efficient MAC protocol for mobile sensor networks. In our MAC protocol, to reduce idle listening, each node has its listen-sleep schedule. A subset of nodes that follow the same schedule forms a virtual cluster. The network consists of multiple virtual clusters and nodes in one virtual cluster may follow a different listen- sleep schedule from that of nodes in another virtual cluster. Hence, to support a mobile sensor node that moves into a new virtual cluster that follows a different listen-sleep schedule, it is necessary to have a fast and energy efficient listen-sleep schedule adaptation protocol. To this end, in our MAC protocol, we utilize schedule information on border nodes between virtual clusters. This allows us to implement fast and energy efficient listen- sleep schedule adaptation, which consists of two main functions: energy efficient secondary listen period and smart scheduling adaptation. Simulation results show that our protocol can provide fast scheduling adaptation while achieving energy efficiency.

A MAC protocol with adaptive preloads considering low duty-cycle in WSNs

Leading MAC protocols developed for duty-cycled WSNs such as BMAC employ a long preamble and channel sampling. The long preamble introduces excess latency at each hop and results in excess energy consumption at non-target receivers in ultra low-duty cycled WSNs. In this paper we propose AS-MAC (Asynchronous Sensor MAC), a low power MAC protocol for wireless sensor networks (WSNs). AS-MAC solves these problems by employing a series of preload approach that retains the advantages of low power listening and independent channel sampling schedule. The preload massage includes a destination address and a remaining time until data transmission. Moreover ASMAC offers an additional advantage such as flexible duty cycle as data rate varies. We demonstrate that AS-MAC is better performance than B-MAC through analysis and evaluation.

Decision-directed channel estimation for M-QAM-modulated OFDM systems

When decision-directed channel estimation is used for QAM-OFDM systems, the optimal shape of the two-dimensional filter depends on the amplitudes of the modulated symbols as well as the channel characteristics such as delay spread. Doppler frequency, and signal-to-noise ratio. While most conventional channel estimation methods did not consider the amplitudes of the modulated symbols because of the large computational complexity, we propose a simple channel estimation method for multi-level-amplitude-modulated systems. The proposed method can effectively reduce the noise variance of the estimates with small-sized filtering and there is a possibility of reducing the implementation cost and producing better results by avoiding unnecessarily large biased term.