The Research Of The Procedure Of The UE's Random Access Based On LTE System

In order to maintain competitive of theThird-generation(3G) in ten years, the Third Generation Partnership Project(3GPP)organization aprroved the 3G long term evolution(LTE)scheme in the end of 2004.The LTE aims at improving the data rates, reducing latency, increasing system capacity and coverage as well as reducing operating costs.Random Access is a key technique in telecommunication system. Its performance directly influences the performance of system. LTE has specific requests in the respects of the capacity and delay, accordingly, Random Access has become one of the the most important contents among the researches of the LTE system.This dissertation mainly focuses on the theory and design of Random Access Channel (RACH) in 3G LTE. The RACH is mainly used in time offset synchronization of the uplink, power adjustment and resources requestment. Based on analyzing the 3 GPP LTE protocol standards in detail, this paper introduces the random access process and its physical channel,beginning with analysis of the random access process, then illustrates the state transition process. Eventually, it focuses on the UE-side process of random access, involved data processing, process controling, exception handling, etc., it takes the interface between physical layer and the upper protocol stack into consideration, and defines the process of random access interface in UE-side correspondingly.The Random Access Channel (RACH) is a competition-based uplink channel. Thus, collision is the key feature. Multiple UE can attend to access a base station simultaneously, and during the process, collisions may be caused. In the research of random access backoff algorithm, this paper analyzes several common backoff algorithm, including UB (the Uniform Back off the binary), BEB (Exponential Back off), MILD (Multiplicative Increase and Linear Decrease). Based on the application mode of the LTE backoff algorithm, the paper inclines towards the optimal control algorithm and introduces it detailedly, which is a control algorithm based on ideal conditions. It can achieve the maximum system throughput and minimum delay which is the the upper limitation of all the algorithms' performances. Following with the judgement of the channel state, the paper proposes a backoff algorithm fiting for LTE system, namely, pseudo-Bayesian algorithm.Then it analyzes the performance by simulation in terms of latency and throughput. Finally, a method of channel division is proposed, which can approximately meet the conditions of optimal control algorithms in use, and through comparison, the result of simulation shows that the improvement in the average delay and throughput can be achieved by this method. Therefore, it can apply in the system with high standard in access delay.