Research On HARQ Technology Based On Retransmission Times Optimization

With the growing demand for various new data business(e.g mobile games, video services, video conferences),new generation mobile communication system has higher demands to the reliability and validity of transmission. The shortage problems of communication resources have become increasingly prominent. How to improve the utilization rate of spectrum in the limited frequency, time and space resources within a larger data rate and high reliability is becoming one of the main emphases of research in recent years.Due to time-varying and multipath fading wireless channel to the effects of signal transmission, some unpredictable interference which will lead to the failure of the signal transmission, mobile communication often uses Hybrid Automatic Repeat request for error control to ensure the quality of service. Hybrid Automatic retransmission request is the combination of Feed-forward Error Correction coding technology and Automatic Repeat request. The FEC in the HARQ is used to reduce the number of retransmission, reduce the error rate; we can use the ARQ retransmission and CRC checking to ensure low error rate. HARQ mechanism can automatically correct errors within the scope of the error correction capability automatic error correction. If it is beyond the scope of error correction, it requests retransmission, which increases the reliability of the system and improve the transmission efficiency of the system. In this paper, taking HARQ as the research object, we analyze and discuss from the following three aspects:(1) For three different types of HARQ, we have respectively made detailed instructions for the principle and characteristics and have carried on the analysis comparison. Results show that although Type-I HARQ signaling has simple structure, and implement more easily, it is not difficult to adapt to the changes in the environment; as for Type-II and Type-III HARQ.it is relatively complex to implement it, so it needs more storage space, but it is more intelligent than Type-I and has a higher throughput.(2) In view of the current channel coding error correcting code in the diversity of types, from the error correcting code of two types: block code and convolution code, and we make comparisons on the properties of several kinds of common error correcting code. The result shows that Turbo code has the best performance but its decoding complexity is the highest, and is suitable for the bad channel conditions; While BCH code has the worst performance, decoding complexity is lowest, so it is suitable for the low efficiency of transmission;The performance of RS code and convolution code and decoding complexity is moderate, and convolution code applies to the mid-transmission, RS code not only applies to the efficient transmission but also can correct burst error.(3) As to the shortcomings of ignoring the feedback information lost in HARQ system shortcomings, an improved HARQ retransmission mechanism technology is put forward, and its performance was simulated under the RS code. Results show that compared with the traditional HARQ, the improved HARQ decreases the number of retransmission and the error rate, and improve the throughput, thus improving the service quality from different performances.