Robust Self-Optimization of Handover in Wireless Systems
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This thesis presents a cellular radio network design and operating guideline based on LTE-Advanced (LTE-A) technology to improve the cell edge user performance. Coordinated Multi-Point (CoMP) transmission / reception is being studied in LTE-A to provide seamless mobility. This study derived macro-diversity gain based on a mathematical analysis for multiple deployment scenarios including homogeneous and heterogeneous networks. And we characterized RF propagation parameters to support a seamless handover based on collaborative transmission. Support of soft handover is essential for improving the performance of cell edge users. This study evaluates the soft handover gain in LTE-A downlink. Reference signal received power (RSRP) is used to define the triggers and the measurements for soft handover. Pathloss, intra-cell and inter-cell interference are modeled and are characterized for the calculation of handover gain. Mathematical analysis in terms of SINR gain and HO margin between soft handover and hard handover is performed in a CoMP set. The results show that propagation parameters significantly affect the choice of the handover margin and the SINR performance. Heterogeneous network deployment scenarios are also being studied in the LTE-A. One of objectives is to provide seamless mobility in the mixed case of macro and pico eNBs in co-channel deployment scenario where the RF coverage areas may be overlapped. Support of heterogeneous network will require the modification of radio link connection approach due to coverage imbalance between DL and UL by the different transmit powers of macro and pico eNBs. In a conventional network including LTE, the UE is typically connected to the cell that provides the strongest DL signal power. However, the UE suffers from strong interference due to UL/DL link imbalance in a heterogeneous network. We investigate possible solutions to address this issue based on analytical framework and characterized RF parameters based on collaborative transmission.