1. Department of Information Engineering and Computer Science, Feng Chia University, 100 Wenhwa Rd., Seatwen, Taichung, Taiwan 40724, R.O.C. (Corresponding author), e-mail: leejs@fcu.edu.tw
2. Department of Information Engineering and Computer Science, Feng Chia University, 100 Wenhwa Rd., Seatwen, Taichung, Taiwan 40724, R.O.C.