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標題: | 異質行動網路之前瞻型接收機設計 Advanced Receiver Design for Heterogeneous Cellular Networks |
作者: | Yi-Yao Lan 藍義堯 |
指導教授: | 闕志達(Tzi-Dar Chiueh) |
關鍵字: | 異質行動網路,長期演進技術,細胞間干擾,小細胞基地台,多天線輸入輸出正交分頻多工系統,預編碼辨識,疊代接收機,最大事後機率偵測演算法,干擾感知接收機,軟體定義無線電,空氣傳輸驗證, Heterogenous networks (HetNets),LTE-Advanced,inter-cell interference (ICI),small cells,Multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM),active precoder identification (API),maximum a-posteriori (MAP) detection,iterative detector,interference-aware receiver,dual-list,list update,over-the-air,software-defined radio (SDR), |
出版年 : | 2015 |
學位: | 博士 |
摘要: | 近年來異質行動網路因其多層共構(multi-tier deployment)能有效地提升單位區域的頻譜效應而受到許多關注。然而,在此多細胞使用同頻帶共構情境下,細胞間干擾(inter-cell interference, ICI)的問題成為不可避免的問題。現有的解決方案多依賴多基地台間的協同來將資源做區隔分離,雖可有效避開細胞間干擾但卻犧牲了傳輸效率。該缺點可藉由將細胞間干擾的處理機制轉移到接收機上。
為了使接收機可處理細胞間干擾,接收機需要獲取部分或完全得干擾源資訊。在這些干擾資訊中,干擾訊號所使用的預編碼(precoder)與干擾訊號所採用的錯誤更正碼訊息最難被接收端獲取。因此,本論文提出了一種進階型接收機設計,其具備兩個必要的功能區塊: 主動預編碼辨識(active precoder identification, API)與具二維列表雙迴圈更新機制的疊代偵測器(iterative detector with dual-loop dual-list update, IDDDU)。主動預編碼辨識用於辨識干擾訊號所使用的預編碼;而二維列表雙迴圈更新機制的疊代偵測器用於在缺乏干擾訊號所採用的錯誤更正碼訊息下,能有效地偵測資料訊號。 在主動預編碼辨識中,本論文提出辨識準則的理論基礎與分析。並且,提出兩種低複雜度的設計: 遞迴架構與雙模切換技術。遞迴架構藉由Sherman-Morrison公式與矩陣行列式定理來降低計算準則所需的運算複雜度; 雙模切換技術則透過單一與多數模式間切換來調節搜尋空間大小。 在具二維列表雙迴圈更新機制的疊代偵測器中,接收機得以在多天線間與細胞間的二維干擾下偵測資料訊號。雙列表的設計用於將正確的資料訊號與干擾訊號都保留在雙列表中,可達到窮舉搜尋的錯誤率效能但避免其高複雜度。多中心的差量格狀搜尋(multi-center delta lattice search, MC-DLS)用於有效產生雙列表的初始狀態;而該雙列表透過雙迴圈模式,有效運用偵測器(detector)與解碼器(decoder)的軟訊息來來更新列表,其更新過程不須干擾源的錯誤更正碼訊息。此外,提出數個降低複雜度的設計。 在實作方面,本論文透過實際射頻訊號於空氣介質中傳輸來驗證該進階型接收機的功能,其平台涵蓋一個符合4G-LTE的訊號格式的軟體定義無線電進階型接收機。透過實際收錄的訊號,完成上述主動預編碼辨識與二維列表雙迴圈更新機制的疊代偵測器的驗證。 Recently, heterogeneous cellular networks (HCNs) have attractive much attention since its multi-tier deployment increases the spectrum efficiency per area. However, the inter-cell interference problem has become inevitable in many co-channel scenarios in HCNs. Most state-of-the art solutions rely on coordination or resource interleaving among base stations, resulting in low transmission efficiency. Alternatively, these drawbacks can be avoided if the task of ICI reduction is moved to the receive side. To settle the ICI at the receive side, the receiver needs to know part or all of the information about the ICI source. Among the information of ICI source, the precoding codewords of interfering active users and the ECC scheme of the interfering signal are difficult to come by. Therefore, this thesis presents an advanced receiver design with two essential function blocks: active precoder identification (API) and iterative detector with dual-loop dual-list update (IDDDU). The API enables a receiver to identify the precoding codewords of the active interfering users. Equipped with the API technique, the advanced receiver can capture speci_c essential information to achieve ICI mitigation. On the other hand, the IDDDU facilitates the advanced receiver to achieve bit-level data recovery when the ECC scheme of interfering signal is unknown. For the API design, we theoretically derive the design criterion and analyze the performance of the receiver equipped with the proposed API scheme. We also propose two low-complexity techniques: the recursive structure based on the Sherman-Morrison formula/matrix determinant lemma, and the mode-switching technique adapting the search space on-the-y. Numerical simulations demonstrate that such receiver can achieve error rate performance close to a receiver with perfect knowledge of the active precoders. The recursive structure achieves 68% complexity saving, while the mode-switching technique further increases the saving to 83%. For the IDDDU design, we tries to recover signals caused by 2-D interferences: inter-antenna interference (IAI) and inter-cell interference (ICI). In this dual-loop dual-list architecture, a dual-list concept is designed to combat 2-D interferences and achieve near maximum a posteriori (MAP) performance. To initialize the dual-list, we combine a strong ICI detection with a multi-center delta lattice search (MC-DLS) to find out the more-likely candidates. With the dual-list, the log-likelihood ratio (LLR) of each data bit can be efficiently computed. Moreover, to improve the quality of dual-list during iterations, we propose a dual-loop list update mechanism without the need of ECC scheme of ICI source. Furthermore, we further propose three low-complexity designs to avoid most redundant computation. Simulation results show the IDDDU can achieve the ICI-free error rate performance. Concerning feasibility, the IDDDU only requires about twice runtime complexity of the conventional successive interference cancellation (SIC)-based iterative detector, which is quite reasonable overhead to pay. The thesis also validates the effectiveness of proposed advanced receiver in real transmission. We build an over-the-air experiment by using a software-defined radio (SDR) platform and RF front-end devices that transmit real radio frequency (RF) waveform over the air interface. The two proposed essential function blocks API and IDDDU are implemented in this SDR platform and are validated by detecting real captured received signals. Through the over-the-air experiments, we validate the functionalities of both techniques and show the feasibility of such advanced receiver for HCNs. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/52829 |
全文授權: | 有償授權 |
顯示於系所單位: | 電子工程學研究所 |
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