| dc.description.abstract | The ITU-R officially named the 5G system IMT-2020, and set the IMT-2020 use scenario to meet the three major use scenarios as the development focus, which are enhanced mobile broadband (eMBB) and massive multi-machines, massive machine type communications (mMTC), ultra-reliable and low latency communications (URLLC). Among them, URLLC focuses on business control applications, perception networks, drones/robots, etc. It focuses on improving latency, reliability, and continuity. Owing to licensed spectrum is expensive and the demand for bandwidth is increasing, the use of unlicensed spectrum is expected to become the trend of future communications. However, URLLC′s strict delay and reliability standards are difficult to implement in unlicensed spectrum. Therefore, there are only a few related studies recently.
Our previous research separately proposed a single-channel reservation mechanism and a multi-channel reservation mechanism with directional antennas, so that URLLC can coexist with heterogeneous network in unlicensed spectrum. When the URLLC device detects that the channel is idle, it will send a busy tone to reserve the channel so that there is a channel for real-time transmission in the next period. This research improves the previous reservation mechanism, since the previous mechanism needs to find that the base station (gNB) and user equipment (user equipment, UE) are both sense the channel idle at the same time so that the channel can be successfully reserved. The improvement in this research is that gNB first selects an available channel, and given all UEs to join the channel for a period of time, to avoid interference from other heterogeneous systems, and only occupy the reserved channel (R-CH) and pre-reserved channel (P-RCH) up to two channels for the friendliness of channel access. The increase in the time of joining the network greatly increases the success rate of reserved channels, and can even reach the stringent standards of URLLC. | en_US |