基於Zadoff-Chu序列的無線動態自組織網路

Abstract

由於不同網路的共存，使得網路變得更加複雜，在未來的網路中，營運商為了實現無線網路的一些自主功能，減少人工操作，以降低營運成本，提出自組織網路(Self-Organizing Network,SON)的概念。 自組織網路是長期演進技術(Long Term Evolution,LTE)或是下一代網路的一項重要功能。此功能支援自動配置和優化新的蜂巢細胞等等重要特性，以減少網路建設人工配置參數的過程、建設的難度和成本，並對網路覆蓋和容量的優化、移動負荷均衡優化、小區內干擾協調，自適應調整參數，優化網路性能。 然而，為了要實現自組織網路的特性，在網路中每個蜂巢細胞內，使用者人數密度，對於基地台的資源利用與分配有著顯著的影響，因此若我們能夠即時且動態的掌握基地台範圍內使用者人數的多寡，將視為一項重要的課題。 在長期演進技術規格中，發現在多處技術上面使用到扎德奧夫-朱(Zadoff-Chu)序列，例如在主同步信號(Primary synchronization signal,PSS)或是參考信號(Reference signal)。 因此先初步了解扎德奧夫-朱序列在長期演進技術中是如何設計與運用後，再針對扎德奧夫-朱序列做分析，並在本篇論文中提出兩個系統架構設計，第一種是不同功率層級所對應不同的扎德奧夫-朱序列，使得扎德奧夫-朱序列能夠動態且即時的做粗略估計去了解每個層級內使用者數。第二種設計是不同調變層級所對應不同的扎德奧夫-朱序列，使得扎德奧夫-朱序列能夠動態且即時的做粗略估計去了解每個層級內使用者數量後可以得知每個層級的流通量(throughput)，因此基地台可以偵測評估目前使用者人數是否已達飽和，若基地台飽和時，在調變層級的系統架構下增加一個機制，來減緩使用者對基地台所造成的負荷，以達到自組織網路的需求與應用。

Since the coexistence of different networks makes the network more complex, in order to reduce manual involvement and operation costs, network operators apply the self-organized network (SON) scheme to implement the next generation network. The SON is an important feature of so-called long-term evolution (Long Term Evolution, LTE) and the new generation network. The SON supports automatic configuration and optimization of the cells, reduces the difficulties and costs of the manually setting process of network parameters, and optimizes network coverage, capacity, and mobile load balance. The SON also adjusts the parameters of the cell according to the interference to improve network performance. The distribution and number of the users in each cell, which have significant impact on the allocation of resources of the base station, are necessary parameters for a SON to function properly. Therefore, to detect how many users associated with the base station dynamically and instantly is important and is also the main topic of the thesis. In the specifications of LTE, we can find that Zadoff-Chu sequence is widely applied in many cases such as the primary synchronization signal and the reference signal. Therefore, this thesis will first briefly introduce how Zadoff-Chu sequence is designed and used in LTE. Then we analyze Zadoff-Chu sequence in detailed. In this thesis, we propose two system structures to estimate user distribution in different levels. The first structure uses the different power levels corresponding to different Zadoff-Chu sequences so that the number of users of each level can dynamically and instantly be estimated. The second structure employs different modulation levels corresponding to different Zadoff-Chu sequences. Again the number of users and throughput in each level can be dynamically and instantly estimated. Thus the base station can detect whether the current number of users has reached saturation. If the base station has reached saturation, a mechanism would be set under the modulation level of the system structure to reduce the loading so that the SON will operate properly.