本論文主要探討正交時間序列多工（Orthogonal Time Sequency Multiplexing, OTSM）系統於高速時變通道下之低複雜度訊號偵測問題。由於高速移動環境中所產生之多普勒效應，容易造成傳統正交分頻多工（Orthogonal Frequency Division Multiplexing, OFDM）系統子載波正交性破壞，進而導致嚴重干擾與效能劣化。相較之下，OTSM 利用 Walsh--Hadamard Transform（WHT）對訊號進行 sequency spreading，可改變資訊符號與時變通道之耦合方式，使都普勒效應所造成之主要干擾能量傾向集中於局部鄰近區域，形成具局部化（localized）特性之等效符號耦合結構。此外，由於時域通道矩陣本身具有近似帶狀（near-banded）結構，因此有利於低複雜度區塊式迭代偵測器之設計，使 OTSM 成為適用於高速移動通訊環境之潛力調變技術。

為降低 OTSM 偵測器之計算複雜度並提升其於高速時變通道下之偵測效能，本論文提出一種結合 Jacobi initialization、Gauss--Seidel（GS）迭代、residual refinement 與 selective bulk interference cancellation（Bulk-IC）之低複雜度迭代式偵測架構。其中，Jacobi initialization、GS 迭代與 residual refinement 用於近似求解 MMSE 線性系統，而 selective bulk IC 則依據符號可靠度優先鎖定高可靠度符號並進行干擾消除，以進一步改善收斂速度與偵測效能。模擬結果顯示，所提出之方法於不同移動速度與不同調變階數下，皆能有效改善 OTSM 系統之位元錯誤率（Bit Error Rate, BER）表現。在高速移動環境（500 km/h）下，相較於傳統 1-tap equalizer 與 Block-LMMSE 偵測器，本文方法可獲得更佳之干擾抑制能力與 BER 效能。此外，於 4-QAM 情況下，本文方法於不同 SNR 區域皆可獲得優於 Matched Filter Gauss--Seidel（MFGS）偵測器之 BER 表現，顯示所提出之局部化迭代更新與 selective bulk IC 機制，可有效改善高速時變通道下之符號估測品質。

綜合上述結果可知，本文所提出之迭代式近似 MMSE 與 selective bulk IC 架構，可有效提升 OTSM 系統於高速時變通道下之偵測能力，並於合理迭代配置下取得良好之效能與複雜度平衡，顯示其於未來高速移動無線通訊系統中具備潛在應用價值。

Orthogonal Time Sequency Multiplexing (OTSM) has recently attracted considerable attention for high-mobility wireless communications due to its robustness against doubly selective fading channels. Compared with conventional Orthogonal Frequency Division Multiplexing (OFDM), OTSM utilizes Walsh--Hadamard Transform (WHT) based sequency spreading to modify the coupling structure between transmitted symbols and time-varying channels. As a result, the dominant interference caused by Doppler effects tends to concentrate within localized neighboring regions, while the time-domain channel matrix also exhibits a near-banded structure.
To reduce detection complexity while maintaining reliable detection performance, this thesis proposes a low-complexity iterative approximate MMSE detector combining Jacobi initialization, Gauss--Seidel (GS) iteration, residual refinement, and selective bulk interference cancellation (Bulk-IC). The proposed method improves initial symbol estimation quality and suppresses dominant interference generated by highly reliable symbols.
Simulation results demonstrate that the proposed method effectively improves the bit error rate (BER) performance of OTSM systems under different mobility conditions and modulation orders. Under high-mobility EVA channels with a speed of 500 km/h, the proposed detector achieves superior BER performance compared with conventional one-tap equalizers and Block-LMMSE detectors. Furthermore, under 4-QAM modulation, the proposed method achieves better BER performance than the Matched Filter Gauss--Seidel (MFGS) detector over a wide range of SNR conditions.
Overall, the proposed iterative approximate MMSE and selective bulk IC framework provides an effective tradeoff between detection performance and computational complexity for future high-mobility wireless communication systems.

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