下個世代的無線通訊系統的主要目標是在於兼顧高資料傳輸速率與高傳輸可靠度。
然而,在實用的無線通訊系統中, 訊號傳輸遭遇到有著快速通道係數變化速率的衰退通道環境, 且通道變化的情況通常難以被精確的追蹤與估計。通道估測的準確度對資料傳輸的可靠度有著很大的影響。因此, 一個對傳送端與接收端來說都不需要事先知道通道係數資訊的非同調系統是相當具吸引力且需要被妥善設計的。

在第二章中, 我們聚焦於單輸入單輸出(SISO)非同調通訊系統。在一個未編碼的系統下, 對一群具有非均等功率值的訊號向量來說, 其在非同調區塊衰退通道下的成對錯誤機率(pair-wise error probability)以及它高訊雜比下的近似, 在此章節中被研究且推導出來。而對於一個有著外部編碼的系統, 一個可接近非同調區塊衰退通道(noncoherent block fading channel)的通道容量極限, 且使用碼字交錯(codeword-interleaving)的方法被提出來。針對位元標籤(bit labelling)與碼字交錯的規則, 我們也提出有效的設計方法。在一種特殊設計的遞迴接收演算法的幫助之下, 整個編碼系統可達到一個接近通道容量極限的效果,
且距離最小所需的訊雜比值大約有1.6dB的距離。

另一方面, 在第三章與第四章中, 我們聚焦於針對多輸入多輸出(MIMO)通道的非同調通訊系統所使用的調變與解調技術。在第三章中, 一個適用於正交設計的么正空時調變(orthogonally-designed unitary space-time modulation), 具有非常低的複雜度的非同調最大事後機率(maximum {\it a
posteriori})解調器被提出來。此外, 在使用格雷標籤法則(Gray labelling)QPSK訊號的情況下, 解調所得的軟式值被證明與通道解碼器所回傳的外值資訊(extrinsic information)無關, 因此, 解調器與解碼器之間的遞迴可在沒有任何錯誤效能的損失的情形下被避免。比起使用基於徹底搜尋的傳統非同調最大事後機率解調器的系統, 所提出的系統可達到相同錯誤效能且非常低的複雜度。

在第四章中, 一種針對非同調衰退通道, 嶄新的渦輪編碼空時調變系統被提出。碼字位元被區非為兩部份, 且分別使用么正空時調變與空間多工的方法來傳輸。由於此一方法有效的增加了傳輸空時訊號矩陣的可能性, 我們可不需藉由增加訊號的調變階數(modulation order)來得到一個大的速率增益。在接收端, 一種操作在渦輪解碼器、用於空間多工的同調解碼器、以及用於么正空時調變的非同調解碼器之間的遞迴解調-解碼演算法被提出。與文獻中的結果相比, 我們所提出的系統不論在錯誤效能以及複雜度上都有著顯著的改善。整個編碼系統可達到一個接近通道容量極限的效果, 且距離最小所需的訊雜比值大約有0.7dB的距離。

The main task of the next generation of wireless communication systems is aimed at providing high data rates and high transmission reliability. However, in practical wireless communication systems, the signal transmission experiences channel links with rapid fading coefficients, and it is usually difficult to precisely track the channel variations. The accuracy of the channel estimation may
strongly influence the transmission reliability of the entire communication system. Consequently, the designs for noncoherent coded systems, where neither the transmitter nor the receiver requires the information of the channel coefficients in advance, are desirable. In this thesis, three topics are addressed, which are respectively presented from Chapter 2 to Chapter 4.

In Chapter 2, the focus is on a single-input single-output (SISO) noncoherent communication system. For uncoded schemes, the pair-wise error probability (PEP) and its high-SNR approximation for the signal vectors with non-uniform power values under noncoherent block fading channels are derived. For coded schemes, a method that approaches the capacity limit for the noncoherent block fading channel using a codeword-interleaving strategy is proposed. The labelling/interleaving rules are also investigated. It is shown that with the assistance of a specially-designed iterative receiving algorithm, the overall coded scheme achieves a near-capacity performance, which is about 1.6 dB away from the capacity limit with constrained input signals.

In contrast, in Chapter 3 and Chapter 4, the focus is on modulation and detection strategies for a multiple-input multiple-output (MIMO) noncoherent communication system. In Chapter 3, a noncoherent MAP (maximum {\it a posteriori}) demodulator with very low complexity is proposed for orthogonally designed USTM (unitary space-time modulation) schemes. In addition, it is shown that the detected soft values are independent of the extrinsic information fed back from the channel decoder, when Gray-mapped QPSK signal is adopted. As a result, iterative detection and decoding between the noncoherent demodulator and the channel decoder can be avoided without any degradation in performance. Compared to schemes that use a exhaustive-search-based noncoherent MAP demodulator, the proposed scheme achieves the same error performance, and has a much lower detection complexity.

In Chapter 4, a novel turbo coded space-time modulation scheme for noncoherent block fading channels is presented. The coded bits are divided into two parts, which are then respectively transmitted using USTM and spatial multiplexing (SM). Since this approach effectively increases the cardinality of the set of possible transmit (space-time) signal matrices, a large rate gain can be obtained without increasing the modulation order. At the receiver, an iterative detection-decoding algorithm is performed cooperatively among the turbo decoder, the coherent demodulator for the SM, and the noncoherent demodulator for the USTM. Compared to the previous work in the literature, the proposed scheme can provide significant advantages in both error performance and complexity. The overall designed coded scheme achieves a near-capacity performance, which is
0.7 dB away from the constrained input capacity limit.

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