在下世代5G 無線通訊系統中，要求更高的頻譜效率、更高的能源效率以及更大量的連結數目。然而，現行的LTE 系統使用的正交頻分多址並不適合使用於下世代5G 無線通訊系統，為了解決這個問題，提出了非正交多重接取技術。然而，大部分現行的碼域非正交多重接取技術都需要指派不同的的編碼簿給不同的使用者，因此傳送的過程會需要和接收端建立連線以及交換控制訊號。因此，這篇論文的動機就是設計出一種可以避免需要碼本指派的碼域非正交多重接取技術。
在這篇論文中，我們提出了索引調變多重接取技術。索引調變多重接取技術是一種使用編碼簿來調變的非正交多重接取技術，而其概念是由索引調變啟發而來。索引調變多重接取技術利用使用的子載波和未使用的子載波來當作索引，這些索引可以夾帶調變位元以外的位元，也就是索引位元。因此，索引調變多重接取技術可以透過調整使用的子載波和未使用的子載波來達到不同的頻譜和能量效率。
為了降低索引調變多重接取技術的位元誤碼率，我們使用了旋轉邊碼技術。模擬果證實了使用旋轉編碼技術對於索引調變多重接取技術的位元誤碼率是有效果的，索引調變多重接取技術的頻譜以及能源效率也的確比正交頻分多址和稀疏碼分多址還好。另外，我們提出不同的接收器像是廣度優先球型解碼器以及深度優先球型解碼器來解決最大似然解碼器的高計算複雜度問題，至於位元誤碼率的上界在本篇論文也有分析。簡言之，這篇論文提出了一個碼域非正交多重接取技術，且和稀疏碼分多址以及正交頻分多址相比有更好的頻譜和能量效率。

In the fifth generation (5G) communication system, massive connectivity of users and devices, higher spectral efficiency (SE), higher energy efficiency (EE), better link reliability
and lower latency are expected. Since the current LTE system that uses the Orthogonal Frequency Division Multiple Access (OFDMA) technique is less efficient to meet these requirements,
one of the most popular solutions for 5G is non-orthogonal multiple access (NOMA) technique. However, most current code-domain NOMA solutions require user-specific codebook assignment, which require grant based transmission. Therefore, the motivation is to design a code-domain NOMA scheme that can facilitate grant free random multiple access.
In this thesis, the “Index Modulation Multiple Access”(IMMA) scheme is proposed. IMMA is a codebook-based NOMA scheme that is inspired from the index modulation (IM) technique. To be specific, IMMA uses the active subcarriers and inactive subcarriers to make
index indices, and the index indices can carry index bits in addition to the modulation signal bits. By adjusting different active subcarrier numbers and modulation types, the IMMA can
reconfig and improve the spectral efficiency (SE) and energy efficiency (EE).
The rotation code is proposed to resolve the inter-user interference (IUI) in contention based multiple access. Furthermore, different decoders such as the breath-first search sphere decoder (BFS-SD) and depth-first search sphere decoder (DFS-SD) are proposed to relieve the high computational complexity of the joint maximum likelihood (JML) decoder, the theoretical average bit error rate (ABER) upper bound is also derived. Our simulation results show that the BER of IMMA is improved with rotation code for better diversity. The SE and EE of IMMA are also better than OFDMA and sparse code multiple access (SCMA). In brief, we design a code-domain NOMA scheme that can facilitate grant free random multiple access, and has better SE, EE than OFDMA and SCMA.

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