Research On Self-Organizing Techniques Of Physical Cell Identification In Cellular Mobile Communication Systems

Self-Organizing Network (SON) is considered to be the most effective way to manage and maintain the future networks, to support the heterogeneous network, to improve the performance of the network and to reduce Operating Expense (OPEX) significantly, thus it has been widely concerned in academia and industry in recent years. Physical Cell Identity (PCI) and Neighbor Cell List (NCL) are important cases in SON, which enables User Equipment (UE) to identify serving cell in access procedure an to identify neighbor cell in handover. Cell identification technique unceasingly develops along with the evolution of cellular mobile communication system:From the frequency reuse technique of the second generation GSM system, to the planning of frequency and scrambling code in the third generation TD-SCDMA system, as well as scrambling code classifying configuration in WCDMA system, and then to use physical cell identity to achieve adjacent cell ID "conflict-free" and "confused-free" in the fourth generation system. Due to different system features, cell identification technique has various characteristics, but the core idea of resource reusing remains unchanged.As SON is the research background, the self-configuration and self-optimization of PCI and NCL are studied in-depth and comprehensive. According to the cell identification strategy of previous generations of the cellular mobile communication system, optimal allocation algorithm of PCI and NCL are proposed. Comparing with the existing techniques, feature of physical resources, resource allocation, networking performance and user experience are comprehensivly studied. The main works and innovations of the paper are:1. Rearch on properties of physical cell identityFirstly, the application of PCI in the cell search and synchronization process has been studied, including the relationship of the physical cell identity and the synchronization sequence, the generation of synchronization sequence and its properties. The paper focused on the correlation properties of Primary Synchronization Sequence (PSS) and the Secondary Synchronization Sequence (SSS), analyses the PSS and SSS properties with time and frequency offset. Research discovered that SSS are impact by the scrambling code in the time domain; therefore, there exist a set of high cross-correlation sequence. The paper analysed distribution characteristic of the high cross-correlation SSS, and a grouping allocation mechanism has been proposed.2. Rearch on self-organizing techniques of PCI in single layer ScenarioThis paper has studied on the self-organizing techniques of PCI in single layer Scenario in LTE-A system. Considering the existing algorithms only meets the basic configuration of "conflict-free"and"confusion-free", but not the pursuit of optimization objective for reuse distance. Therefore, this paper has adopted the minimum spanning tree algorithm to map the PCI allocation problem to graph theory. The greedy algorithm is used to search the maximum interference in the network, and avoided by the orthogonal PCI resources; the greedy algorithm is also used in searching the optimal solution while reusing PCI in order to minimum the multiplexing interference. This paper also presents a PCI reuse frequency based algorithm, the allocation order is determined by calculating the network adjacency matrix, and the PCI with minimum reuse frequency will be allocated to the eNB in order, to even the PCI deployment. This paper analyses the algorithm computational complexity and performance. The simulation results indicate that:the proposed algorithm with the self-configuration algorithm has lower complexity and higher user of Carrier to Interference Rate (CIR) comparing the existing self-configuration algorithm.3. Rearch on self-organizing techniques of PCI in multi-layer heterogeneous network ScenarioAccording to the characteristics of the node deployment in multi-layer heterogeneous network, the paper proposes a PCI Color Switching Algorithm (CSA) and a PCI Cassifying Configuration Algorithm (CCA) in order to adapt to the densely deployed network environment with multiple types of nodes. CSA swapped or changed the cell ID according to the local greedy searching algorithm, and then made the decision according to the cost function; the network interference is reduced gradually. CCA used the mechanism of IP address allocation to group and label the PCI resource. Network nodes can address its ID rapidly according to the adjacency cell ID. The simulation results show that the two proposed algorithms can not only guarantee the "collision-free" and "confusion-free" between the macrocells and heterogeneous nodes, but also reduce the network reuse interference effectively. 4. Rearch on self-organizing techniques of NCLThe self-organization of NCL is studied in this paper. The paper proposes a self-configuration algorithm of NCL based on signal propagation prediction, and a self-optimization algorithm for adding and removing neighbor cell caused by dynamic cell coverage is also provided. The cell measurement report and handover information are submitted by the UEs on the edge of cell. The self-optimazation of NCL is determined by the predefined threshold and the offset Time To Live (TTL), thus to achieve the dynamic changes of NCL. Through the dynamic system simulation platform, the Automatic Neighbor Relation (ANR) algorithms are simulated. The results show that after the self-organization of NCL, the Radio Link Failure (RLF) rate is improved significantly, while the success handover rate performance gain is8%.