Handover Optimization In LTE-A System

In order to meet the demand of higher speed transmission, capacity and more applications in mobile communication market in next few years, surpass the IMT-Advanced demand whilst keep fully backward compatibility with LTE,3GPP proposed Advanced Long Term Evolution of universal mobile communication system. LTE-Advanced adopted many key technologies, such as Carrier Aggregation, Coordinated Multi-point Tx&Rx, Relay, etc.. The key techniques can greatly improve the data rate, frequency spectrum efficiency, district average spectral efficiency and performance of edge users in wireless communication system, and at the same time LTE-Advanced also can improve the efficiency and performance of the organization of entire Network, which makes the LTE and LTE-A system become the mainstream in the development of wireless communication in the next few years.Currently, one of the most challenging issues in mobile communications is the smooth integration of small-sized cells in to the predominant macro-cellular network layout. Small cells are short-range, low-power and low-cost cellular access points that support fewer users compared to macrocells, embody the functionality of a regular base station. Two-tier macrocell-smallcell network is considered as a promising solution for improving cellular coverage, enhancing system capacity and supporting the plethora of emerging home/enterprise applications. In mobile communication system, when UE moves across coverage of different cells, handover procedure will be executed to ensure the continuity of network communication. Handover is a key part in radio resource management, it plays an important role in estimating the performance of the communication network. In the future, the support of mobility in the wireless network will be increasingly demanding and stricter, users need seamless connections when making a call. So a quicker, more intelligent and reliable handover algorithms are in desperate need, in order to reduce call drop rate, carry calls crisply and reliably. The impact of the HO decision phase is even more prominent in the presence of small cells, owing to the short-range nature of communications, the denser network layout and the fast varying radio environment.The thesis first introduces the network structure and key technologies of LTE-Advanced system. It surveys and classifies current HO decision algorithms for the two-tier macrocell-smallcell network in LTE-A system. Then it discusses some basic concepts of handover, such as the handover classification, and algorithm stipulated in LTE protocol. Generally, the traditional handover algorithm only takes the singular factor, as the requirement of networks and subscribes gets higher, there’re many existing optimized handover algorithms according to the specific HO decision criterion used. However, not much work has be done about prediction-based handover decision. In LTE-A standard, fixed reporting time period is considered inflexible, hance, prediction-based handover scheme is proposed to allow eNBs to make potential handover decisions within the UE’s reporting period. Focus on the HO decision phase in LTE-A macrocell-smallcell network, three novel handover algorithms are designed based on different emphases. The decision criteria are1) multi-factor and load-balance based;2)performance indicator optimization based;3) network parameter prediction based. Numerical results show that the proposed prediction-based handover schemes outperform conventional handover scheme from the perspectives of success-rate, delay, elimination of unnecessary handovers and system energy consumption, respectively.