The Design and Implementation of Lte/Nb-Iot-Based Random Access Random Backoff (Rarb) Mechanism

Project Details


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 rardio 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 project is from observing the behavior and performance of RAP in machine type communications. When the number of UEs performing RAP excesses a certain threshold, collions will 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. The preamble is a specified sequence of a certain length and the system provides a number of orthogornal preambles for RAP. The eNB searches the preamble(s) and allocate uplink resource to UE(s) if the preamble is detected. The 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 messages will collide with each other and the eNB can not 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 can not resolved and retransmissions will be lasted to the maximal HARQ retries. After then, all involved UEs restart RAP again. Obviously, the collision probability is linerly proportional to the number of UEs and more collisions will prolong the access delay and power and bandwidth wastage. 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 patenable technology.This project aims to deal with the contemporary mobile network system and try to integrate the RAP with the radndom 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 compatability with current specifications. The major advantages of compatability are twofolds: 1) getting rid of standardization process and 2) the interesting of industry.
Effective start/end date1/08/1831/07/19

UN Sustainable Development Goals

In 2015, UN member states agreed to 17 global Sustainable Development Goals (SDGs) to end poverty, protect the planet and ensure prosperity for all. This project contributes towards the following SDG(s):

  • SDG 3 - Good Health and Well-being
  • SDG 17 - Partnerships for the Goals


  • Massive Machine Type Communication (mMTC)
  • Long Term Evolution (LTE)
  • Random Access (RA)
  • Random Backoff (RB)
  • 5G New Radio (5G NR)
  • Narrow Band Internet of Thing (NB-IoT)


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