| In a wireless system, a hard handover occurs when, during an active call, User Equipment (UE) switches from using one set of radio resources to another set of radio resources. Typically, the handover occurs because the UE has detected degraded signal quality. Often the degradation is due to user movement: the cell-carrier on which the call was originally established no longer offers the best radio path to the user. The UE and Radio Access Network (RAN) signal back and forth to determine a different cell-carrier offering better signal quality. Once the RAN and UE successfully determine to which cell-carrier the call will move, the switch occurs. In a typical terrestrial system, small cell sizes result in handover being a rather common occurrence, and almost a certainty for users participating in calls while traveling in automobiles.
In MUOS, extremely large beams (cells), relatively small number of users traveling at high velocities, and relatively short call hold times indicate that handovers (all of which are hard handovers) will occur far less frequently than in typical commercial systems. In this paper, we estimate the frequency of handovers in MUOS using different levels of handover suppression. Handover suppression refers to the practice of delaying the time at which a handover would normally take place In this work, we develop mathematical expressions representing the probability of handover for MUOS users engaged in point-to-point calls and use Mathematica to evaluate said expressions to extract probability values. We first compute results based upon user movement only and then factor in the effects of satellite motion.
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| Dr. Orcutt is a Member of Technical Staff at General Dynamics C4S in Scottsdale, Arizona. He began work in 1993 with the Government division of Motorola, acquired in 2001 by General Dynamics. During this period, he has assisted in the design and/or analysis of satellite systems such as Iridium, Teledesic, SIBRS Low, and most recently, MUOS. Dr. Orcutt has authored papers in the areas of optical pattern recognition, run-length limited coding for magnetic recording channels, and bandwidth efficient modulation techniques and holds two U.S. patents. |