Long term fading in microcellular radio

The authors investigate signal variation in cellular mobile radio systems so that handover and diversity techniques can be evaluated. Fading in mobile radio is often studied by separating the variation into two separate effects termed long and short term fading. The short term fading is measured over distances of the order of a wavelength and is caused by interference between multipath components. Long term fading can be caused by relative variation in the location, size, shape and orientation of obstacles such as buildings and vegetation which may be affecting the signal through the processes of diffraction or reflection. In cellular mobile radio systems the mobile must be capable of selecting a suitable base station, both at the beginning of a call and when a handover is necessary. In current systems these decisions are primarily based on measurements of signal strength as an estimate of channel quality. A series of measurements is averaged so that for the moving mobile the measurement is representative of the local mean signal strength. The main subject of the paper is long term fading