The Design and Implementation of Enhanced Random Access Mechanism in Nb-Iot System(1/2)

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 versatile services in mobile networks is one of major issues.In NB-IoT 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 research is from observing the behavior and performance of RAP in machine type communications. When the number of UE(s) 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 subcarrier and transmit the preamble on the specified channel. The preamble is a specified sequence of a certain length and the system provides only one preamble for all devices to perform RAP. The eNB searches the preamble from subcarriers and then allocate uplink resource(s) to UE(s) based on the number of detected preambles . The UE then transmits RRC connection setup request message to the eNB on the granted uplink resource. If more than one UE selects the same initial subcarrier to transmit the preamble to eNB, their signals will overleap with each other and the eNB can not tell how many UE(s) transmit the preamble and therefore their following messages will collide together. Then, the eNB utilizes the Hybrid Automatic Repeat Request (HARQ) feedback to notify those UE(s) to retransmit message again. The collisions can not be resolved and retransmissions will continue until reaching the maximal HARQ retries. After then, all involved UE(s) restart RAP again. Obviously, the collision probability is linerly proportional to the number of UE(s) and more collisions will prolong the access delay, 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 focuses on the Narrow Band Internet of Thing (NB-IoT) and try to integrate the RAP with the radndom backoff solution which has been 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.