Research Of MAC’s Scheduling And HARQ In LTE System

In order to improve the mobile communication business’s quality, adapt to the demand of the user data quantity’s rapid growth and deal with the challenges from the wireless broadband access technology, such as WiMax, Wi-Fi etc,3GPP started on the standardization of the LTE technology to meet the smooth transition from3G to4G in the end of2004. In wireless communication system spectrum bandwidth is the most valuable resource. A highly efficient wireless scheduling algorithm should be devoted to minimize invalid transmissions on the error link, avoid the waste of bandwidth resources and maximize the throughput of the system ultimately. LTE improves the service quality and the peak speed of the business, which adopts HARQ that is a kind of the key technology to effectively ensure high quality of service and high transmission rate.Firstly, the paper outlines the development process of the mobile communication system and3GPP LTE related network architecture, performance indicators, key technologies. The research status of scheduling algorithms and HARQ are briefly introduced, as well as the main research contents and structures of this paper. Meanwhile, the module functions of LTE MAC subsystem are introduced, especially scheduling and HARQ described in detail.Secondly, this paper introduces the classical scheduling algorithms of real-time and non real-time data business in detail. Based on the proportional fair scheduling algorithm, an integrated scheduling algorithm is proposed for the real-time and non real-time mixed business, which joins delay factor into the expression of user’s priority. It not only maximizes the system throughput, but also guarantees the diversity of service business. Through system simulation, compared with proportional fair scheduling algorithm in the system throughput, packet loss rate, fairness of data rate and packet delay beyond threshold, the integrated scheduling algorithm has been verified of its validity and practicability.Finally, the paper describes the TDD system’s HARQ ACK feedback scheme and CQI related knowledge, then puts forward a kind of HARQ ACK/NACK multiplexing feedback judgment algorithm based on the air quality. The algorithm is used for the case that the UE adopts HARQ ACK/NACK multiplexing model to feedback, four downlink subframes corresponds to one uplink subframe and the results of the feedback are ambiguous. Based on the air quality to judge, the algorithm improves the reliability of judgment, reduces the number of misjudgments and improves the utilization of system resources.The algorithm thoughts and steps are given in this paper. Compared with the current feedback scheme, the results of simulation verify the effectiveness of the proposed judgment algorithm.