Research On Retransmission Resource Scheduling Algorithm In LTE System

Since resources are very limited in wireless mobile communication system, resource scheduling algorithm greatly affects the system performance, so this aspect has become a research focus. But retransmission resource scheduling problem was rarely mentioned in the study of the LTE system resource scheduling algorithm. This problem means allocating resource to support retransmission through HARQ(Hybrid Automatic Repeat Request). This thesis mainly focuses on retransmission resource scheduling problem and designs an algorithm adapted to wireless channel quality. In the case of real-time traffic, non-real-time traffic and retransmission traffic coexisting, this paper proposes a scheduling strategy for retransmission traffics and designs a scheduling algorithm for hybrid traffics based on the traffic QoS(Quality of Service).Firstly, this paper applies simulated testing to prove that the HARQ technique is useful to improve the quality of data transmission. Therefore it’s necessary to solve the problem that how to allocate resource for retransmission. Then this paper analyzes the requirements to design algorithm of retransmission resource scheduling. According to the features of HARQ, a scheduling scheme is proposed based on adaptive HARQ. Comparing this scheme with another scheduling scheme based on non-adaptive HARQ implemented in NS3 simulator to learn the pros and cons of each scheme.Secondly, combining the two schemes mentioned above, a retransmission resource scheduling algorithm adapted to channel quality is proposed in this paper called ACQ(Adapt-to Channel Quality) algorithm. Simulation results show that this algorithm outperforms any single scheduling scheme by increasing worse channel quality users’ throughput and transmission quality.Thirdly, in case of real system with a variety of traffics, scheduling algorithm as well as retransmission scheduling need take traffic QoS requirements into consideration. This section firstly modifies the CQA(Channel and Qos Aware) algorithm, one of the QoS-based scheduling algorithms, to compensate the non-real-time traffic’s dropped packet rate caused by queue timeout. Modified CQA algorithm is evaluated by simulation to compare with original algorithm. Results show that modified CQA algorithm increases the system throughput and flats the disparity of fairness between real-time and non-real-time traffics transmission. Then this paper proposes a strategy to specify the respective priority of real-time traffics, non-real-time traffics and retransmission traffics. Base on modified CQA algorithm and priority strategy, a scheduling algorithm for hybrid traffics is proposed in this paper, called HTH-MCQA algorithm. By using NS3 simulator, the simulation results show that the hybrid traffics scheduling algorithm can satisfy the service requirement of varied traffics and achieve better system throughput.