第五代行動通訊 (5G) 有三種主要服務類型，包括增強型行動寬頻通訊 (enhanced mobile broadband，eMBB)、大規模機器型通訊 (massive machine type communications，mMTC) 以及超可靠度和低延遲通訊 (ultra-reliable and low latency communications，URLLC)。 URLLC 的特點是對低延遲和高可靠性的嚴格要求，即在毫秒內以 10^(-5) 塊錯誤率 (block error rate) 傳輸大小為 32 位元組的封包。網路流量的增加明顯降低授權頻譜的傳輸品質，使得 URLLC 的嚴格要求難以達成。因此，將流量從授權頻譜轉移到非授權頻譜傳送是一種很有希望的解決方案。 我們先前的研究提出單通道預留機制 (single-channel reservation mechanism，SCRM) 與多通道預留機制 (multi-channel reservation mechanism，MCRM)，使 URLLC 得以與非授權頻譜中的異質系統共存。每當 URLLC 設備偵測某個通道為空閒時，它們會發送 busy tone 來保留該通道。SCRM 及 MCRM 使用具有自干擾消除功能的全雙工無線電 (full-duplex radio，FDR) 和 ZC 序列 (Zadoff-Chu sequence，ZC sequence) 來實現 URLLC 設備同時傳輸和接收訊號。然而，當通道忙碌機率高且 UE 數量大時，這些機制的性能無法滿足 URLLC 的需求。因此，本文基於之前的機制，引進波束成形技術來提高通道預留的成功率，且對異質系統更加友好。我們也探討了伴隨波束成形技術產生的隱藏節點問題 (hidden node problem，HNP) 對系統表現的影響。;In fifth-generation (5G), there are three major service types, including enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra-reliable and low latency communications (URLLC). URLLC is characterized by its strict requirements of low latency and high reliability that a 32-byte packet transmitted in sub-milliseconds with a 〖10〗^(-5) block error rate. The increase of network traffic significantly degrades the transmission quality of the licensed spectrum and makes the strict requirements of URLLC hard to be satisfied. Thus, offloading traffic from the licensed spectrum to the unlicensed spectrum is a promising solution to be introduced. Our previous work proposed the single-channel reservation mechanism (SCRM) and multi-channel reservation mechanism (MCRM) to coordinate with heterogeneous systems in unlicensed spectrum. Whenever URLLC devices sense a channel as idle, they send the busy tone to reserve that channel. Both SCRM and MCRM use the full-duplex radio (FDR) with self-interference cancellation and Zadoff-Chu sequence (ZC sequence) technology to allow URLLC devices transmit and receive signals simultaneously. However, when the channel busy probability is high and the number of UEs is large, the performance of SCRM and MCRM mechanisms dissatisfies the URLLC services. This thesis brings beamforming technology to our previous work to enhance the success probability of channel reservation and furthermore be friendlier to heterogeneous systems. We also investigate the influence of the concomitant hidden node problem on system performance.
