The Study Of Retransmission Mechanism Of Hybrid Automatic Repeat Request (HARQ) In The System Of TD-LTE

The Long Term Evolution (LTE) is the largest new technology research and development project in recent year which 3GPP started. It is regarded as the "quasi-4G" technology which is based on the application of OFDM/FDMA system. The technology of hybrid automatic retransmission (HARQ) in LTE not only able to obtain forward error correction coding (FEC) coding gain brought, but also get soft-combined to bring diversity gain, thereby enhancing the system against the wireless mobile channel time-varying and multi-path fading effects on the signal transmission and reduce the system bit error rate in order to ensure quality of service.In this paper, the retransmission mechanism of the HARQ in TD-LTE is being deeply studied. It first briefly described the traditional HARQ type and implementation mechanism, and introduced the simulation platform of uplink transmitter and receiver in TD-LTE system, built under the 3GPP protocol. Then, the paper analyzed the different contents as well as their decoding performances of each HARQ retransmission versions. After that, two types of HARQ technology:Chase merger and incremental redundancy, both supported in the LTE system, were being analyzed, simulated and compared. At the same time, the paper focused on the study of several times retransmission of HARQ and obtained the optimal retransmission mechanism which brought the best decoding performance through comparative simulation for a particular example. Finally, the paper mapped the data transfer size, specified by the 3GPP protocol, which is indicated by the transmit data block size parameter ITBS, to the format of retransmission data packets. Furthermore, the initial coding rate and the optimal retransmission mechanism are being mapped which leaded to a look-up table for selecting the best retransmission mechanism when doing the HARQ in TD-LTE.After obtained the mapping relations between the initial coding rate and the best retransmission, we can easily select the retransmission sequence for different transmission cases, which leads to maximum system throughput and low block error rate. This is also the purpose of our research.