Band-AMC Scheme with Hybrid ARQ in Downlink OFDMA Systems

• Main Authors: Wei-Han Wang, 王維漢
• Other Authors: Hsuan-Jung Su
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/62951176352460984344

碩士 === 國立臺灣大學 === 電信工程學研究所 === 96 === Orthogonal Frequency Division Multiple Access (OFDMA) technique was adopted for the broadband wireless access (BWA) system because of its in- herent immunity to multipath interference and flexible resource allocation in both the time and frequency domains to obtain the multiuser diversity gain. Adaptive modulation and coding (AMC) technique in single-carrier sys- tem has been studied to do the adaptive transmission with the modulation and coding scheme (MCS) adjusted according to the instantaneous chan- nel condition for throughout maximization. Exploiting AMC technique in OFDMA system can be more flexible due to the ability to track the channel variation in both the time and frequency domain. In time-varying channels, the performance degradation of adaptive transmission caused by delayed or inaccurate channel condition feedback can be mitigated with the use of hy- brid automatic repeat request (HARQ). So far, few studies focus on dynamical adjustment of the MCS switching thresholds tracking the time-varying wireless channel in OFDMA system. In this thesis, we will propose a framework of downlink OFDMA system employing band-AMC scheme with HARQ. And the numerical result shows that our work outperforms the traditional method which is adopting fixed- threshold scheme with a target frame error rate (FER).