Performance Of HARQ-based MIMO For The LTE System

Mobile communication has gone through major changes since the introduction of firstgeneration mobile phones.High throughput,low processing costs,low latency,and simple architecture are the main features of the Long Term Evolution system(LTEs).LTE system and wireless communications have a fundamental problem which is reliability of data transmission.Fading in wireless channels causes the signal strength variation at the receiver and this variation results a loss of data packets.Hybrid Automatic Repeat Request(HARQ)methods are commonly used in wireless networks to combat the loss of data packets due to channel fading.In HARQ schemes,if the receiver fails in decoding the data correctly,it asks for a retransmission.The Channel Quality Indicator(CQI)is a technique which provides the Evolved Node Base Station(eNodeB)information about the link adaption parameters and the data rate that can be received successfully by the User Equipment(UE).Thus,this research aims to test the effect of HARQ on the relationship between throughput and Signal-to-Noise Ratio(SNR)as well as investigates the role of CQI on the HARQ performance in the LTE system.In addition to explore the differences between multi code word HARQ methods which are independent,blanking,and non-blanking.This research is divided into three parts.First,the parameters of the LTE system in downlink are investigated.These parameters include the effect of the HARQ on the SNR,Block Error Rate(BLER),and throughput by using three cases of CQI: 3,7 and 15.Second,The LTE downlink simulator is built by using an older generation simulator as a reference to explore different HARQ implementation methods,three different simulation cases where the throughputs are calculated for each case and each Signal to Interference-Noise Ratio(SINR).Finally we studying the Hybrid-Automatic Repeat request(HARQ)protocols that are implemented in the Long Term Evolution(LTE)cellular system.Analytical models of these processes are derived and an enhancement is proposed in order to increase the throughput and decrease the delivery delay,exploiting a Bayesian approach.A numerical evaluation of the performances has been carried out.The result of this thesis shows that the effect of HARQ procedure on the performance of the system.It focused on the throughput and BLER.However,it shows HARQ can improve the BLER and throughput when the retransmission between the eNodeB and a UE increased.Further to this,it shows that the performance of the system is improved after deploying HARQ procedure from throughput points of view.It is recommended to deploy one HARQ retransmission for the all cases studied.Regarding the simulation results of the second part of this thesis,HARQ method with two independent HARQ processes is the best method in terms of throughput,nevertheless blanking technique comes very close to it.In addition,the results of the proposed model in the final part obtained via numerical evaluation.The behavior of the Markov chain in the long term has been numerically evaluated using Matlab.The throughput is approximately equal to zero for low average SNR values and increases as the average SNR increase;we note that the throughput tends to saturate for high average SNR values.And the delivery delay is maximum for lower average SNR values and it decreases as the average SNR increase.It tends to saturate for high SNRs too.Enhanced model guarantees a higher throughput while decreasing the delivery delay with respect to the default model.Indeed there is a gap between the standard approach and the intelligent one: the latter provides the same performances of the former for lower average SNR values.However the size of that gap depends on how much correlated the channel is.However,suggestions for the future work would be optimizing the current code before adding more parts into the simulator as well as designing a Graphical User Interface(GUI)into the current simulator.