WCDMA Radio Channel Classification

Abstract:


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 K-factors aligns much better to the expected K-factors. Although they are not exactly the same, they are so close that with further studies, classification of radio channels with the use of cell phone channel estimates should be possible.

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