基於札克變換的正交時頻空間調變通訊系統上使用多疊加導頻序列進行迭代通道估計及數據檢測

Abstract

正交時頻空間調變是一種用於有效處理高速時變通道的調變方法，已經在很多論文中被廣泛的討論。而基於札克變換的正交時頻空間調變在近幾年被提出，做為正交時頻空間調變的延伸，透過該調變方法能夠直接通過接收端取樣訊號重建訊號輸入輸出關係，而無需完全了解底層通道係數。 在本論文中，根據基於札克變換的正交時頻空間調變的特性，推導了使用扎德奧夫-朱序列做為導頻序列的可行性並提出了一種基於多個扎德奧夫-朱序列的疊加導頻符號輔助迭代通道估計與數據檢測的方法。這種導頻放置的方式使我們能在延遲-都普勒域上設置比原有分散導頻方案更多的導頻符號，並且額外放置的導頻僅增加少量導頻之間的污染，這有助於減輕通道估計時由數據符號引起的干擾，能得到更精準的通道估計結果。 模擬結果顯示，與原有的分散疊加導頻方案相比，所提出的疊加導頻放置方案在保持相同的峰值平均功率比的前提下實現了更低的誤碼率。

The Orthogonal Time Frequency Space (OTFS) modulation is a novel approach designed to effectively handle fast time-varying channels. The Zak transform-based OTFS (Zak-OTFS), as an extension of OTFS, can directly reconstruct the input-output (I/O) relationship through receiver samples without needing to fully understand channel coefficients. In this thesis, the suitability of placing Zadoff-Chu (ZC) sequence as pilot sequence is derived, and a superimposed pilot-aided iterative channel estimation and data detection scheme based on multiple ZC sequences for Zak-OTFS systems is proposed. This form of pilots allows us to set more pilots than the existing scattered pilots scheme on Delay-Doppler (DD) domain and perform channel estimation without or with little pilot pollution, which helps mitigate the interference caused by data symbols. The simulation results demonstrate that the proposed scheme achieves superior BER performance compared to scattered pilot schemes while maintaining the same peak-to-average power ratio (PAPR) performance.