目前的行動通訊發展的越來越快速，頻譜效益的提升是目前備受關注的一項議題，由於當今的頻譜資源非常珍貴，為了更好的使用目前較為充裕的頻譜，使用毫米波段(Millimeter Wave, MMW)為第五代通訊中不可或缺的條件。但毫米波段的無線電訊號因為其物理特性，在空氣中的功率衰減十分迅速，因此會使其傳輸距離受到限制，而第五代行動通訊為了使用毫米波的頻段，會使用相較於第四代行動通訊更多的小型基地台，也就是用更小型、更密集的基地台來彌補毫米波段其傳輸距離較短的特性。而這樣小型的基地台為了同時支持更多用戶傳輸數據，使用非正交多重接取(NOMA)能支援的用戶數量 比傳統的分時多工(TDMA)、分頻多工(FDMA)、正交分頻多工(OFDM)、…等還要更具優勢，因此NOMA被視為第五代行動通訊中一項具有潛力的技術。
在傳統用功率作為區別不同用戶的NOMA系統中，會根據用戶的距離來傳送一組具有距離基地台較近和距離基地台較遠的用戶的訊號，而在這樣的安排中，由於離基地台較遠的用戶其訊號受通道的干擾程度較嚴重，為了減少距離較遠的用戶的訊號干擾，在Power domain NOMA的系統中引入了索引調變(Index modulation , IM)的概念，能夠有效的減少大功率訊號解調的錯誤率，但經過IM之後的NOMA架構，在頻譜效率和小功率訊號的錯誤率會做出一定的犧牲。
本篇論文引入了多模索引調變(Dual-mode index modulation)能有效的解決NOMA在頻譜效率上的不足，並且本篇論文提出circular DMIM的星座圖配置方式，能更有效的利用頻譜資源，並且相較傳統NOMA IM有著更良好的延遲表現及更低的複雜度。

Index modulation and orthogonal frequency division multiplexing (OFDM) has become a promising technique in the future , They can conveying extra information for specific activation of the frequency domain subcarriers, therefore improving the achievable throughput at a given bit error ratio (BER) performance. In this paper, Non-orthogonal-multiple assess (NOMA) combine dual-mode OFDM technique is proposed, which is combined with index modulation and enhances the attainable throughput of conventional index-modulation based OFDM. In particular, the subcarriers are divided into several subblocks, and in each subblock, all the subcarriers are partitioned into two groups, modulated by a pair of distinguishable modem-mode constellations, respectively. However, the information bits are conveyed the classic constellation symbols, and implicitly by the concrete activated subcarrier indices, representing the subcarriers’ constellation mode. At the receiver, a maximum likelihood (ML) detector and a reduced-complexity near optimal log-likelihood ratio-based detector are invoked for demodulation. The minimum distance between the different legitimate realizations of the OFDM subblocks is calculated for characterizing the performance of DM-OFDM. Then, the associated theoretical analysis based on the pairwise error probability is carried out for estimating the BER of DM-OFDM. Furthermore, the simulation results confirm that at a given throughput, DM-OFDM achieves a considerably better BER performance than other OFDM systems using index modulation, while imposing the same or lower computational complexity. The results also demonstrate that the performance of the proposed low-complexity detector is indistinguishable from that of the ML detector, provided that the system’s signal to noise ratio is sufficiently high.

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