Hyeonsu Kim

Learn More
Cognitive radio technique has been considered as a strong solution of frequency scarcity due to the limitation of frequency resource. In this paper, we propose an orthogonal beamforming methodology which enables cognitive radio systems to coexist with primary users' systems in the same spectrum and region with no interference to the primary users' systems.(More)
Various channel estimation methods have been proposed for shallow underwater communication channel with sparse channel type. A matching pursuit (MP), which is one of typical sparse channel estimation methods, can detect dominant components of sparse channel sequentially as a portion of matching. Mean squared error of MP, however, converges to fixed value(More)
The purpose of the study is to develop an instructional design model to support learners' continuous reflection during the learning process in cultural diversity education. Current instructional models for cultural diversity education are inappropriately utilized in school settings due to the lack of specific guidelines for instructors’ and learners’(More)
A channel estimation methodology that exploits superimposed pilot sequences for underwater acoustic communication is proposed and evaluated. The proposed scheme first estimates the time-varying channel from the received signal which includes the known superimposed pilot sequence. In a later stage fits the channel response in then fitted to a parametric(More)
This paper proposes a random access method using grouping nodes which are located closely to decrease collisions of nodes by long delay propagation time in underwater acoustic environments. To reduce collision probability, each node selects its group, which is predetermined by a distance from the fusion center based on RSSI level, and aligns its(More)
  • 1