CP-OTFS系統之正交多重存取技術之探討

Abstract

正交時頻間距(orthogonal time frequency space; OTFS)調變系統是一個多載波調變技術。適用於具稀疏延遲(delay)和都卜勒(Doppler)擴散性質的高速移動雙重選擇性通道(doubly selective channel)之訊號傳輸。相較於正交分頻多工(orthogonal frequency-division multiplexing; OFDM)等傳統多載波調變技術，訊號對於雙重選擇性通道會有更穩定及強健的表現。然而，在無線通訊領域中多重存取(multiple access; MA)技術是一個能夠實現多用戶之間共享有限頻譜資源的重要方式，因此在接收端對於訊號通過雙重選擇性通道是否存在多重用戶干擾(multi-user interfer¬ence; MUI)是一個很重要的課題。在本篇論文中，共提出4種基於正交多重存取(orthogonal multiple access; OMA)技術設計的方案，並且透過將循環前綴(cyclic-prefix; CP)技術引入OTFS系統中來解決接收端會造成MUI的狀況。而關於正交多重存取式OTFS的可實現的數據速率(achievable data rate; ADR)和符元決策等特性亦於本篇做了研究與探討。

Orthogonal time frequency space (OTFS) modulation system is a multicarrier modulation technique suitable for signal transmission over high-speed mobile doubly selective channels with sparse delay and Doppler spread characteristics. Compared to traditional multicarrier modulation techniques like orthogonal frequency-division multiplexing (OFDM), OTFS provides more stable and robust performance for doubly selective channels. However, in the field of wireless communication, multiple access (MA) tech¬niques are essential for achieving shared spectrum resources among multiple users. Therefore, it is crucial to address the issue of multi-user interference (MUI) when signals pass through doubly selective channels at the receiver end. In this paper, four strategies based on orthogonal multiple access (OMA) techniques are proposed. The cyclic pre¬fix (CP) technique is introduced into the OTFS system to mitigate the MUI caused at the receiver. Additionally, the achievable data rate (ADR) and symbol deci¬sion characteristics of the orthogonal multiple access-based OTFS are studied and dis¬cussed in this paper.