Random Backoff Assisted Random Access Collision Reduction for Massive Machine-Type Cellular Communications

• Main Authors: Che-Wei, Hsu, 許哲維
• Other Authors: Shiann-Tsong Sheu
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/6wkek5

碩士 === 國立中央大學 === 資訊工程學系 === 106 === With the popularity of smart mobile devices, surfing the Internet anytime, anywhere has become a kind of necessity for modern life. How to combine the mobile communication technologies with other technologies to support more services in mobile networks is one of major issues. In current LTE-A network, the base station (eNB) only schedules the channel resource for the devices (UE) which has established the radio resource control (RRC) connections. For the UE staying in IDLE mode, it has to perform the random access procedure (RAP) in order to establish RRC connection with the eNB. The motivation of this thesis is based on the observations from the behavior and performance of RAP in machine type communications. When the number of UEs performing RAP excesses a certain threshold, collisions may occur and result in remarkable resource wastage and delay. In other words, a UE randomly selects one preamble and transmit it on the specified channel resource. The preamble is a specified sequence of a certain length and the system provides a number of orthogonal preambles for RAP. The eNB searches the preamble(s) and allocate uplink resource to UE(s) for each detected preamble. The corresponding UE then transmits RRC connection setup request message to the eNB on the uplink resource. If more than one UE sends the same preamble to eNB, their following messages will collide with each other and the eNB cannot decode any one of them. Then, the eNB utilizes the Hybrid Automatic Repeat Request (HARQ) feedback to notify UE(s) to retransmit message again. The collisions cannot be resolved and retransmissions will be lasted to the maximal HARQ retries. After then, all involved UEs restart RAP again. Obviously, the collision probability is linearly proportional to the number of UEs and more collisions will prolong the access delay and waste power and bandwidth. Due to 5G network has included the massive MTC (mMTC) usage case, how to efficiently reduce the collision probability in mMTC scenario could be an important and patentable technology. This project aims to deal with the contemporary mobile network system and try to integrate the RAP with the random backoff solution adopted in WiFi networks in order to minimize the interference among UEs. We also emphasize that the proposed scheme will not only reduce collision probability in RAP but also consider the full compatibility with current specifications.