| 摘要: | ITU-R將5G系統正式命名為IMT-2020，並設定IMT-2020使用情境主要以滿足三大使用情境為發展重點，分別為增強型行動寬頻服務 (enhanced mobile broadband，eMBB)、巨量多機器型態通訊 (massive machine type communications，mMTC)、超高可靠度和超低延遲通訊 (ultra-reliable and low latency communications，URLLC)。其中 URLLC 著重領域如商業控制應用、感知網路、無人機/機器人等，以改善延遲性、可靠性、持續性為主。由於授權頻譜昂貴，且頻寬需求日益增加，使用非授權頻譜有望成為未來通訊之趨勢。然而，URLLC 嚴格的延遲與可靠標準，實現於非授權頻譜有一定困難性，因此日前僅有少數相關研究。
我們先前的研究分別提出單通道預留機制與多通道預留機制並搭配指向性天線，使 URLLC 得以與非授權頻譜中的異質系統共存。當 URLLC 設備偵測通道為空閒時，則會發送 busy tone 預留該通道，使得下一個時段保證有通道可以做即時傳送。本文針對預約機制做出新改良，由於先前的機制要在同一個時間點找到基地台 (gNB) 與使用者裝置 (user equipment，UE) 皆為空閒時，才可成功預留通道。本文改良為 gNB 先選擇一個可用的通道，並且給定所有的 UE 一段時間加入該通道，避免其他異質系統的干擾，並且只佔用當前正在使用的通道 (R-CH) 與下一段時間要使用的通道 (P-RCH) 最多兩個通道，以維持競爭的公平性。加入網路的時間延長，使預留通道成功率大幅提升，更可以達到 URLLC 嚴苛的標準。
;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. |
