| 摘要 |
A mobile telephone makes successive measurements of the amplitude of a signal that it receives. The magnitude of fluctuations in the amplitude represents the vehicle's speed. A moving window may be used to collect the signals and determine the variations by forming a cumulative sum of the absolute differences of successive amplitudes. Alternatively a distribution of differences can be set up and compared with expected distributions to give the speed, eg by using a least squares method. Alternatively, the measurement may be at the base station on a signal received from the mobile telephone. When handing over between cells/subcells in a cellular system, assessments of the need to hand over are made periodically at a frequency determined by the speed. The speed can alternatively be used to set a signal sample frequency which is used in a signal quality determination system: the average signal quality is then used to control handover. |
