16 International Journal of Distributed Systems and Technologies, 4(1), 16-28, January-March 2013 Copyright © 2013, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Copyright © 2013, IGI Global. Copying or distributing in print or electronic forms without written permission of IGI Global is prohibited. Keywords: Adaptive Cycle Prefx Length, Adaptive Guard Insertion, Channel Estimation, Kalman Filter, Mobile Worldwide Interoperability for MicrowaveAccess (WiMAX) INTRODUCTION This paper focuses on channel estimation sys- tem, one of the important blocks in the WiMAX receivers (WiMAX Forum, 2008). WiMAX uses OFDM (Orthogonal Frequency Division Multiplexing) as a technical platform because of high spectral efficiency (F. Wang, &A. Ghosh, 2008). Chanel estimation in OFDM systems is traditional topic and researched in many papers because of its important roles (Song & Lim, 2003) and Tirthankar Paul, &Priyabrata Karma- kar, & Sourav Dhar (2011)). Many algorithms of channel estimation for OFDM were explained and simulated for mobile WiMAX by Muham- mad Saad Akram (2007). Waldo Kleynhans (2008) analyzed algorithms of channel estima- tion with block-type pilot and comb-type pilot A Combined Algorithm of Kalman Estimator and Guard Interval Optimization for Mobile WiMAX Quang Nguyen-Duc, Ho Chi Minh City University of Technology, Ho Chi Minh City, Vietnam Lien Pham-Hong, Ho Chi Minh City University of Technical Education, Ho Chi Minh City, Vietnam Thang Nguyen-Manh, Ho Chi Minh City University of Technology, Ho Chi Minh City, Vietnam Tra Luu-Thanh, Ho Chi Minh City University of Technology, Ho Chi Minh City, Vietnam ABSTRACT Mobile WiMAX (Worldwide Interoperability for Microwave Access) system has been recently applied widely in wireless communication systems. In this paper, the channel estimation algorithms were studied for the mobile WiMAX system. The comb-type pilot was used for channel estimation algorithms. The authors pro- posed an adaptive algorithm of channel estimation based on Kalman flter which had good performance in fading channels. Then, based on the result of channel estimation, we proposed an advanced algorithm of GI (Guard Interval) optimization. The results showed that the Kalman estimator combined with GI optimization algorithm showed the best performance in this paper. This algorithm was verifed by computer simulation. DOI: 10.4018/jdst.2013010102