Research Of Scheduling Mechanism And Transmission Performance Of Volte Under Long Term Evolution System Architecture

LTE(Long Term Evolution)is a full IP(Internet Protocol)packet switched network,since the former voice call technologies based on 2G/3G circuit switched network are not suitable for LTE,a new voice call solution fully based on packet switched network is needed.After a series of technologies comparison and standards selection,3GPP decides to utilize Vo LTE(Voice over LTE)which is based on IMS(IP Multimedia Subsystem)as the implementation technology of voice call in LTE network.The paper firstly introduces the existing technologies of LTE and the current research situation of Vo LTE,then it presents the evolution of the voice services of LTE by stages and compares their possible solutions and explains the reasons that Vo LTE is the eventual solution of voice services of LTE.As the other layers of the air interface protocols stack of LTE are more mature,the paper sets its research focus on the MAC layer.Afterwards,the paper introduces the relative channels and their functions of MAC layer,the radio scheduling and its unit,and compares the scheduling algorithms in MAC layer,explains why the most suitable scheduling algorithm for Vo LTE is the semi-persistent scheduling algorithm.But the semi-persistent scheduling algorithm itself doesn't set priority for calls,which is not reasonable from the scheduling point of view,it needs to be further optimized.At the same time,most papers focus on the capacity,coverage area,the establishment and continuity of sessions of Vo LTE,while the radio transmission performance is little studied,this paper has researched it.The main innovation work of this paper is as follows.As to the scheduling mechanism,since the size of voice packet is small and voice packets are scheduled more frequently,the existing scheduling mechanisms such as dynamic scheduling and persistent scheduling are not suitable for Vo LTE.According to the criteria established by 3GPP,it should use semi-persistent scheduling for Vo LTE,but the current semi-persistent scheduling scheme doesn't set priority for voice call,the user with bad channel quality and the user with good channel quality have the same priority when allocating radio resource,while the user with bad channel quality may retransmit many times thus wasting radio resource.Therefore,this scheme can't fully make use of radio resource.For this purpose,this paper presents a modified user-coupled semi-persistent scheduling scheme for Vo LTE based on call priority.The scheme can be divided into two aspects:(1)Modify the calculation method of Vo IP call priority and present that it should be calculated according to queue length,SINR(Signal to Interference plus Noise Ratio),the number of needed physical resource blocks,average channel quality,average transmission rate in order to schedule the calls more accurately and decrease the overhead of control signaling;(2)Improve the whole process of semi-persistent scheduling and propose that dynamically control the duration of Vo IP priority mode to avoid making other services starve.In the Vo IP priority mode,it couples every two users to share the radio resource allocated to them,and decreases the wasted radio resources that made by repeated retransmissions of the users with bad channel quality.Then it applies the algorithm to Vo LTE to further decrease the signaling overhead of radio resource,improve the radio resource utilization rate and scheduling efficiency,increase the satisfaction ratio of users and user capacity of Vo LTE.The paper verifies the modified algorithm for the Vo LTE performance improvement of BER(Bit Error Rate)of voice packets,satisfaction ratio and user capacity by using MATLAB simulation tool.For the transmission performance,this paper sets throughput and BER as the two performance indexes of Vo LTE.It mainly studies the effect of SNR(Signal to Noise Ratio)of receiving antennas on the transmission performance of Vo LTE voice frames and verifies the results by simulation.The simulation results show that by improving the receiving antenna SNR in a certain range,the throughput of Vo LTE can be significantly improved;however,the throughput demonstrates little change beyond the identified range.Additionally,the transmission BER can be reduced by improving the SNR of the receiving antenna.By comparing the simulation results of the two antenna models,it can be concluded that with the increasing of transmitting and receiving antennas,the transmission performance of Vo LTE can be enhanced,at the same time the effect of low SNR can be made up by multiple antennas to a certain degree.