The Hybrid-ARQ Technology In LTE

At present, the 3GPP LTE is the prime research project, as the evolution of 3G technology. Its advantages are high spectral efficiency, small network delay and large capacity of system and so on. Hybrid automatic repeat request technology is an effective error control technology. When the data rate is high, HARQ reduces effect of multipath interference on the system performance, and enhances the accuracy of the transmission data. In this paper, HARQ and relevant technology are studied in LTE downlink link.The paper studies two error control technologies in LTE:automatic repeat request technology and forward error correction coding technology. Stop and wait protocol, go back n protocol and selective retransmission protocol are analyzed. Forward error correction coding technology applies turbo code. Turbo encoding and decoding technologies are studied. Quadratic permutation polynomial interleaver in LTE is discussed.This paper researches three major types of HARQ technologies and different code combination technologies at the receiver. The data correctness is judged by cyclic redundancy check and decides whether retransmission is needed. Under the gauss channel, types of HARQ technologies with different modulation schemes are analyzed. The performance differences in the traditional HARQ, chase combination, partial incremental redundancy and full incremental redundancy technologies are researched.This paper analyzes the reliability of each bit when 16QAM modulation is applied. When constellation rearrangement technology is used, in every retransmission, different constellation mapping rules are applied so as to average bit reliability and enhance decoding accuracy. The improved full IR scheme is studied by changing the mapping rules of information bits so as to enhance reliability of information bits and reduce block error rate. The adaptive modulation coding schemes are discussed. According to different channel states, choose the optimal modulation and coding rate which maximize the throughput. And AMC with HARQ enhances spectral efficiency.