When studying channel properties in cellular networks two key parameters are
the delay spread and the type of fading. The delay spread holds information
about the time dispersion the channel induces, whereas the effect the
channel has on the power of propagating waves is reflected in the fading.
Line-of-sight communications results in Rician fading whereas non-line-of-
sight means Rayleigh fading. Measurements and classification of channel
environments have, to the writer's knowledge, so far only been done with the
use of complex sounding devices. In this work, channel classification is
performed using low-level data from a regular cell phone.
Measurements were performed with a real cell phone in a controlled milieu
where different radio environments were emulated. With the use of channel
estimates from the cell phone, probability density function parameter
estimations were performed with both maximum likelihood and method of
moments techniques. The Rician K-factor, which expresses the ratio of line-
of-sight components to scattered waves, was calculated with the results from
the estimation.
The K-factor calculations showed, as expected, obvious differences between
various simulated environments. The K-factor increases with stronger line-of-
sight component, which is in line with theory. For weak direct waves, the
estimate often becomes zero which is due to the difficulty of detecting a
weak direct wave in lots of scattered waves. To achieve better results,
other estimation techniques might therefore be necessary.
For repeated measurements with the same settings the variance of the K-
factor estimates is quite high. Also, the variance increases with stronger
direct wave. This might be due to additive noise during measurement. The
mean of the K-factor estimates seems to be 3dB higher than expected. This
offset is possibly due to the difference in the noise power between complex
and real noise, which is exactly 3dB, or internal differences in the power
level of the channel simulator. The reason for the difference is not clear
but power measurements confirms it.
With compensation for this, the calculated ...
