| Summary: | 碩士 === 國立中央大學 === 通訊工程學系 === 107 === 3GPP had released the preparation schedule for the fifth-generation mobile communication standard IMT-2020 in 2017, which includes the Release-15, Release-16 and subsequent 5G standard specifications. The IMT-2020 focuses on three application scenarios, Enhanced Mobile BroadBand (eMBB), Massive Machine Type Communication (mMTC) and Ultra Reliable Low Latency Communication (URLLC). Since the licensed band is expensive and the increasing requirement for bandwidth, the use of unlicensed spectrum is expected to become a trend of future mobile communication industry. In 3GPP LTE-A standard, the Licensed Assisted Access (LAA) is used as a technology for accessing Unlicensed Band (UB). Currently 3GPP also discusses the feasibility of implementing 5G New Radio over unlicensed spectrum. How to utilize UB is a main trend of developing new technologies to support various applications. Considering the low latency and high reliability of URLLC, it is extremely difficult and challenge to realize URLLC service on UB. Therefore, there are only few researches related to the design of supporting URLLC over UB.
As the IEEE 802.11 (WiFi) system is matured and wildly deployed, the LAA shall consider the coexistence with WiFi products. LAA applying the Listen-Before-Talk (LBT) mechanism to coexist with WiFi users, meanwhile promoting the overall system throughput. However, the time required to perform the LBT mechanism may not fulfill the latency requirement of URLLC. Taking the features of URLLC into consideration, all URLLC devices need to have the access right on at least one channel on UB for transmitting URLLC data at any time. This research will propose two channel reservation mechanisms in order to accomplish the goal. To do this, whenever a URLLC device detects an idle channel, it will send a special busy tone on that channel in order to occupy it. To avoid the self-interference, the URLLC device equips with the Interference Cancellation System (ICS) in the Full Duplex Radio (FDR) to allow the concurrently bidirectional communications between devices. Thanks to the ICS technology, the busy tone issued from a device can be well eliminated by itself. Consequently, the signals transmitted from others URLLC devices can be received successfully. Due to the restriction of Maximum Channel Occupancy Time (MCOT), the channel reservation mechanism incorporates the frequency hopping technique.
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