預籌未來應用之寬頻異質無線傳輸介面研究-子計畫三：合作式通訊網路之協同綠能編碼技術研究與設計(I)

Abstract

本報告針對三主要成果作說明。首先說明第一個成果：在此報告裡，我們對絕對值放大前送(Absolute-based amplify-and-forward)中繼點傳輸策略[1]進行相關研究。在一個兩路中繼點通道中，實體層網路編碼(Physical network coding)[2]所提供的吞吐率能夠比網路編碼(Network coding)[3]以及傳統的中繼點傳輸策略高。實體層網路編碼的特性是允許兩個終端點經由中繼點同時交換資料，而至今對於實體層網路編碼在兩路中繼點通道也有許多研究被發表。在[1]中，絕對值放大前送中繼點傳輸策略被提出用來壓縮在中繼點的星座圖，這樣做可以減少傳輸所需功率並維持和傳統放大前送(Amplify-and-forward)中繼點傳輸策略一樣的符碼錯誤率(Symbol error rate)。然而，最佳判別邊界(Decision boundary)在[1]中並沒有完整的被討論，因此我們在此報告中討論在絕對值放大前送中繼點傳輸策略裡的最佳判別邊界，讓整個絕對值放大前送中繼點傳輸策略的架構更完整。 第二個成果為關於通道編碼技術方面。本計畫試著找出一個低硬體複雜度且效能逼近或者高於低密度奇偶校驗碼(Low density parity-check code, LDPC)[4]與渦輪碼(Turbo code)[5]的新的編解碼技術。雖然LDPC與Turbo code之效能雖然已經被證明非常逼近向農極限(Shannon limit)，但其所需之運算複雜度過於龐大以至於在應用上必須有所折衷而無法達到預期的效能表現。有鑑於此，本實驗室近幾年來提出一個新的編解碼技術，稱為渦輪-低密度奇偶校驗碼(Turbo-LDPC code)[6]，同時採用了LDPC與Turbo code的核心概念，使其能在較低的運算複雜度下有著比LDPC與Turbo code更好的效能。而在本計畫中，我們將原先Turbo-LDPC code中二維編解碼結構進一步延伸推廣到三維結構。根據初步的模擬結果，我們發現此種新的編解碼技術，稱為Triple-LDPC code，相比於原先的Turbo-LDPC code可以在相同的運算複雜度下有著更高的解碼效能。 此外，根據我們的分析，我們也發現所提出的Turbo-LDPC與Triple-LDPC codes非常適合應用在分散式中繼網路(Relay network)架構中的coded cooperation[7]技術，可以大幅降低中繼站(Relay station)的硬體複雜度並且有較佳的錯誤更正能力。接著第三個研究成果討論LTE系統的主同步訊號PSS偵測相關技術，本研究延伸了先前本實驗室所提出之應用於正交分頻多工系統(OFDM)的細胞搜尋(cellsearch)方法，並且應用到3GPP長期演進技術(3GPP LTE)系統中。具體來說，我們應用了先前所提出的三種對於通道效應具有高彈性之細胞搜尋方法(Channel-effectresilient cell ID detection, CERCD)[8]到3GPP長期演進技術的同步訊號。由於，在3GPP長期演進技術系統所採用的同步訊號是具有完美正交性的Zadoff-Chu序列。但是，由於此序列是複數訊號，因此在進行同步時需要大量的複數乘法量。因此，運用了所提出的CERCD之模擬結果顯示，此方法不但可以保有運算低複雜度的優點，而且也同時有如同在IEEE 802.16.e系統中那樣的高效能細胞搜尋的表現。更值得注意的是，在跟許多運用到3GPP LTE系統的傳統方法比較中，所提出之CERCD的方法，可以大幅地改善運算複雜度同時，也可以有更好的效能。

In this report, among many of our research results, we present three main contributions of our project as follows. The first is regarding the network coding technique. The absolute-based amplify-and-forward (AAF) relay strategy [1] is investigated. The AAF relay strategy can effectively compress the constellation at the relay such that the transmitting power at the relay can be reduced, while maintain the same symbol error rate (SER) as the traditional amplify-and-forward (AF) relay strategy. However, its optimal decision boundary is not derived in [1]. To make the framework more complete, this works specifically investigates the optimal decision boundary for AAF relay strategy.Regarding the techniques of channel coding, although low density parity-check (LDPC) [4] and Turbo [5] codes have been proven to achieve performances close to Shannon limits, their high computational complexities hinder them from widespread applications. In this report, we extend our previous high-performance 2-D turbo-LDPC coding scheme [6] to three dimension. According to preliminary simulation results, it is found that the proposed new coding scheme, named Triple-LDPC code, has better decoding performance than Turbo-LDPC code with comparable computational complexity. Besides, from analysis, both coding schemes are essentially suited for applications to coded cooperation [7] in relay networks, which can significantly reduce the hardware complexity in relay station, and achieve better error-correction capabilities. Finally, this report extends our previous work on cell ID detection for OFDM systems to LTE systems. Specifically, we apply our previously proposed three channel-effect resilient cell ID detection (CERCD) methods [8] to the detection of primary synchronization signals (PSS) in 3GPP LTE systems. Simulation results show that CERCD methods still maintains merits of low complexity and high performance for LTE systems, as in IEEE 802.16e systems. Specifically, the proposed schemes have much lower complexities and significantly higher performances than the popular differential autocorrelation schemes. This is particularly beneficial for LTE system, because PSS are complex signal with high computational complexity.