Research On The HARQ And Related Techniques In LTE System

At the end of 2004, Long Term Evolution (LTE) was introduced under the 3rd Generation Partionship Project (3GPP) for future mobile communication with high transmission rate and reliability, as well as new services. As the last step toward the 4th generation (4G) from the 3rd generation (3G) of mobile communication technologies, LTE is widely recognized as pre-4G technology by the industrial and academic community. The main advantages of LTE are high spectrum efficiency, high peak data rate, low transmission delay and full grouping support, which will most likely lead to large-scale technological upgrades in mobile communication.Hybrid Automatic Repeat Request (HARQ) is well known for its high data rate, high relibility and high QoS (quality of service), which plays a crucial role in building the futhure communication system, also is marked as one of the key technologies in LTE.This thesis which is based on LTE protocol, is concerned with HARQ and two other technologies relevant to the HARQ system:Channel Coding and Rate Control. With the LTE-based simulation platform, the thesis simulate the HARQ system and provide detailed analysis with regard to the simulation results, particuarly on the HARQ system performance and the abovemented two relevant technologies.Firstly, the thesis discusses the HARQ cross-layer design mechnism as presented in LTE protocol. Then with the HARQ system simulation platform, the system performce of HARQ system will be evaluated under various conditions, as different type HARQ systems like theⅡ-type andⅢ-type HARQ system, different combining methods like Chase combining and IR combining, varying code modulations and over Additive White Gaussian Noise (AWGN) channel that are supported by LTE protocol. Then evaluate the system performance in terms of system throughput, system frame error rate and system avarage repeats number.Next, the thesis addresses the channel coding technology that has been officially adopted in the HARQ system. Also, the thesis has a brief discussion about the Turbo coder specified in LTE protocol. Then the thesis has a discussiom about the Maximum a-posteriori (MAP) decoding algorithm, LOG_MAP decoding algorithm and MAX_LOG_MAP decoding algorithm theoreticl. Afterwards the thesis systematically simulate the channel coding/decoding algorithms, and evaluate the system performance of the decoders with a varying number of iterations and data frame length, also contrast the performance of different algorithm decoders.Finally, a discussion on the rate control technolog is presented. In particular, detailed analysis of the implementation of rate control technolog in physical layer, rate matching algorithm, is provided. On the basis of the analysis, the thesis evaluates the system performance of channel coding/decoding algorithms and the HARQ system which has rate control enabled. In this part, the thesis also simulates another HARQ sytem which is based on a simple rate control algorithm and has multi-user multi-rate supported. Brief quantitative analysis of the simulation results will be also provided.