LTE下行鏈路之低複雜度、高效能主同步訊號及其偵測設計

Abstract

本論文討論LTE系統的主同步訊號PSS偵測相關技術，特別是針對運算複雜度高的Zadoff-Chu序列進行改良。我們提出的類QPSK之PN序列，不僅降低比對時的乘法運算量，其效能也和ZC序列十分接近。另外利用分頻方式擺放不同PSS，因此設計出新的分頻PSS碼，其可免於PSS碼間的互相干擾，另一方面，由於不同PSS碼分佔不同子載波，因此只需針對個別PSS碼所對應的子載波做功率估測，即可偵測出正確的PSS碼。此方式亦大大降低運算複雜度，且若將此分頻功率偵測方式與現有PSS碼比對法做適當的權重結合，則新碼及整合方法之效能更是超越了現有LTE標準之ZC主同步訊號的偵測效能。 最後，由於PSS的偵測常伴隨ICFO的估計，我們利用定義的錯位異序列峰均值比來當作判斷一個序列是否擁有良好偵測效能的指標，經由模擬結果顯示這個指標的高低的確可以有效反映出一個PSS碼在偵測時的效能優劣，因此在評定一個碼的好壞時無需跑模擬也能大致推測未知此碼的偵測效能。

This thesis discusses the primary synchronization signal (PSS) detection techniques for LTE systems. We proposed QPSK-based PN sequences to substitute for ZC sequences which have high computational complexity in doing PSS detection. The proposed QPSK-based PN sequences not only have the lower complexity but also have the detection performance close to ZC sequences. In addition, we proposed two PSS code allocation schemes, called disjoint scattered allocation and disjoint clustered allocation, located on different subcarriers for different PSS code sequences in a clustering or scattering ways, respectively. Utilizing this characteristic, one can simply detect PSS by calculating the received signal’s power of the corresponding PSS subcarriers, which has very low computational complexity. By further applying the existing matching operations to the disjoint-allocation codes, and combining it properly with the power computation operations, better performances than using the original ZC sequences can be obtained. Finally, we proposed a new metric of ratio of peak-to-average mismatched value as an indicator of a code’s performance in PSS detection, in order to do a quick evaluation if an arbitrary code could serve as a good PSS code. The metric is verified to be a good performance measure, by conducting PSS detection together with ICFO estimation,