The Research Of Hybrid ARQ Protocol In The Fourth Generation Mobilt Commnuications Systems

For the increasing demands of high-speed data users and multimedia services, the fourth generation mobile communications systems should provide higher data transmission rate and reliability. But, with the limitations of the reliable wireless frequency resource and the time-varying nature of wireless channel, communication systems always have low spectrum utilization and high code error ratio. So, how to provide both higher data transmission rate and reliability will be the main challenges for the future wireless communications.Substantial improvement of channel capacity can be achieved by Multi-Input Multi-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques, while Hybrid Automatic Repeat reQuest (HARQ) technique which combined automatic repeat request and forward error correction can guarantee data reliability. The systems which combine the MIMO technique or OFDM technique and HARQ protocol effectively can trade off validity and reliability. Under this background, this thesis proposes several new HARQ schemes in MIMO and OFDM systems.The main innovations and contributions in this thesis can be summarized as follows:1. Investigated a novel post-combining HARQ scheme based linear pre-coder in MIMO communications systems. We get the pre-coder matrix and de-coder matrix under the minimum mean squared error (MMSE) criteria to allocate power and use antenna permutation to balance the reliabilities of sub-streams to acquire more spatial diversity gains. In addition, MAP combining is adopted at the receiver to further improve system performance.2. Proposed two kinds of adaptive power allocation schemes in MIMO systems when channel state information of the transmitter is available. The first class: The receiver adopts zero-forcing successive interference cancellation (ZF-SIC) or minimum mean squared error criterion with successive interference cancellation (MMSE-SIC) detection method to detect and gets the power allocation by minimize the total BER. The second class: Get multiple dependent parallel sub-channels by using Singular Value Decomposition (SVD) and obtain the power allocation by minimizing the total Bit Error Ratio (BER). These two kinds of schemes make use of the retransmission state channel information to allocation power in order to improve the system throughput.3. An adaptive HARQ scheme with data streams permutation in OFDM sustems is proposed. It makes fully use of equivalent channel gain obtained by previously false transmission of the same data frame and the current channel gain to decide how to rearrange sub-streams to the sub-carriers. The simulation results show that our proposed scheme improves the system throughput greatly.