  This paper presents a statistical modeling approach of the real-life
user-induced randomness due to mobile phone orientations for different phone
usage types. As well-known, the radiated performance of a wireless device
depends on its orientation and position relative to the user. Therefore,
realistic handset usage models will lead to more accurate Over-The-Air
characterization measurements for antennas and wireless devices in general. We
introduce a phone usage classification based on the network access modes, e.g.,
voice (circuit switched) or nonvoice (packet switched) services, and the use of
accessories such as wired or Bluetooth handsets, or a speaker-phone during the
network access session. The random phone orientation is then modelled by the
spherical von Mises-Fisher distribution for each of the identified phone usage
types. A finite mixture model based on the individual probability distribution
functions and heuristic weights is also presented. The models are based on data
collected from built-in accelerometer measurements. Our approach offers a
straightforward modeling of the user-induced random orientation for different
phone usage types. The models can be used in the design of better handsets and
antenna systems as well as for the design and optimization of wireless
networks.
