| Orthogonal frequency-division multiplexing (OFDM) is the modulation technique for European standards such as the Digital Audio Broadcasting (DAB) and the Digital Video Broadcasting (DVB) systems. As such it has received much attention and has been proposed for many other applications, including local area networks and personal communication systems. OFDM is a type of multichannel modulation that divides a given channel into many parallel subchannels or subcarriers, so that multiple symbols are sent in parallel. Earlier overviews of OFDM can be found.In wireless broadband mobile radio communications like OFDM, to ensure successful communications in such wireless transmission channels, some powerful multi-access schemes and error-control techniques are necessary. One of them is Hybrid Automatic Repeat reQuest with Turbo Code. In this thesis HARQ type-Ⅰ, HARQ type-Ⅱand the four strategies designed for implementing HARQ type-Ⅱare analyzed. Two kinds of methods, one without ARQ and the other one with HARQ were simulated under AWGN and multi-path fading channel. We also proposed and analyzed a hybrid type-ⅡAutomatic Repeat request (ARQ) scheme joint with an Adaptive Modulation System (AMS) that is suitable for Internet Protocols (IP) which consists of and a time-slot scheduler supplied by the channel predictions.The simulation results show that the system without ARQ, and the one with HARQ type-Ⅰhave no significant gain. On the other hand the one with HARQ type-Ⅱsatisfies the Quality of Service (QoS) requirements and improves the utilization of wireless channel. |
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