The Research Of Random Access In LTE-A Digital Relay Node

As the 4th generation mobile communication system, LTE-A proposed relay Node transmission which is a key technology. RN not only optimizes the city hot spots, but also expands cell coverage in blind area, subway and rural areas. RN accessing to eNB and UE accessing to RN need random accessing process, so improving the performance of random accessing can improve the overall performance of the wireless communication system.This paper introduces the background knowledge and basic concept of random accessing process of RN. Then, the processing procedure of random accessing in MAC layer was analyzed in detail. Now, there are a lot of problems in the random accessing process of RN, such as incomplete functional module, large time delay, high rate of collision and so on. So, the functional framework of MAC layer and three Algorithmic Mechanisms of random accessing are designed.1. In order to improve the performance of random accessing, the functional structure and process of RN's accessing in MAC layer is designed on the basis of 3GPP protocol. The function architecture of uplink accessing of RN as user and downlink receiving of RN as eNB are included.2. For the random accessing to eNB of RN, in other words, the existing scheme requires two phases of random accessing. So the direct random accessing process for RN is proposed, which reduces the time delay of random accessing, and improves the accessing probability of RN.3. For the overload system, the preamble allocative scheme based on retransmission was proposed. Preambles will be divided into two groups, one group will be uesd for the new users, the other group will be used for the retranstted users, which will improve the accessing probability of the retransmitted user, and reduce the average time of accessing.4. The existing backoff algorithm GB does not take the fairness problem of users into account. And NGB algorithm is proposed in this paper, which improves the fairness of users, on the basis of the time of user's accessing.In this paper, the functional framework in MAC layer of RN is designed, and three kinds of Algorithmic Mechanisms of random accessing are proposed, then C++ simulation and performance analysis are carried out.