Efficient OFDM Transmission By Using HARQ And Channel Prediction

It is no doubt that the Digital Television (DTV) is the future trend. Now there are a lot of countries announced the DTV broadcasting schedule, and the schedule of import television with DTV receiver device. Now the Europe DVB-T adopted the OFDM as the transmission scheme. In Taiwan, Tatung University have fulfilled some field test to prove that the OFDM technology is better than 8-VSB when applying for mobile devices. Due to OFDM system has the following characteristic, such as anti channel fading and anti multi-path interference, 4G system also want to adopt the OFDM as its transmission specification.Hybrid ARQ (HARQ) is one of the link adaption technologies for reliable high data rate transmission. It has been proposed as one of the key technologies of OFDM system.In this thesis, we will try to show how is the data transmission in OFDM is execute, then we view the transmitter and receiver in OFDM system. We also propose a system suitable for Internet Protocols (IP) which consists of a hybrid type-ⅡAutomatic Repeat request (ARQ) scheme combined with an Adaptive Modulation System (AMS) and a time-slot scheduler supplied by channel predictions, referred to as predictive HARQ-Ⅱ/AMS. The performance of the system in a downlink for fast fading channels is investigated through simulations where in particular, BER, throughput and delay performance are studied. The proposed system is compared to two modified systems where one does not utilize Forward Error Correction/ARQ (FEC/ARQ) at link layer (referred to as predictive AMS) while the other one has no access to the channel prediction (referred to as blind HARQ-Ⅱ/AMS). The results show that with perfect channel prediction both predictive AMS and HARQⅡ/AMS satisfy the Quality of Service (QoS) requirements with some advantages to the former in terms of efficient usage of channel capacity.