In cellular systems, due to the mobility, proper handoff or handover management is critical to ensure seamless migration from one cell to another cell. Besides of maintaining the connection quality during a handover process, any advanced handover algorithms which can minimize required resources for the connection are critical. In 2G, 3G, and future wireless systems, to maintain the best connection quality, fast switching and soft handoff are considered for high transmission performance. To achieve fast-switching or soft handoff, multiple sectors/cells are required to be activated prior to the actual connection. As a result, extra resources from cells/sectors are needed to support the connection. Algorithms which can effectively minimize active sector/cell set without affecting connection quality is important to reduce the required hardware and RF resources. In this paper, considering handoff controls for the same cellular system, we will review the development of related critical patents. Even those patents are originally designed for CDMA cellular systems, the control concepts can also apply to recent OFDMA based systems like WiMAX and 4G cellular systems.
Keywords: Handoff, handover, CDMA, WIMAX, OFDMA, pilot, slope, cellular system, mobility