UBC Theses and Dissertations
Characterization of fading and polarization state dispersion on fixed wireless links in suburban macrocell environments Liou, Anthony En-Lee
Growing use of point-to-multipoint fixed wireless networks to support network access and system automation in suburban macrocell environments has prompted regulators to re-allocate various bands between 200 MHz and 2 GHz to such applications. Links in such networks are usually obstructed by buildings and foliage and are classified as non-line-of-sight. Although it is well-known that such links are susceptible to fading caused by windblown trees and foliage, most past efforts to characterize fading on such links have focused on frequency bands at 1.9 GHz and above. Here, we study how the depth and rate of fading in the 220, 850 and 1900 MHz bands vary with distance and time-averaged wind speed in a representative macrocell environment. We observed that while the signal fading is relatively severe at 1.9GHz, the depth of fading drops rapidly as the carrier frequency decreases. However, the rate of fading is effectively independent of either the average wind speed or the carrier frequency. Further, polarization diversity on narrowband wireless links has traditionally been characterized in terms of the fading statistics and the cross-correlation between the fading signals on each branch. A complementary approach, which is independent of the polarization states of the diversity receiving antennas, is to characterize the manner in which the polarization states observed at the receiver disperse across the Poincaré sphere. First, by simulation, we show that when the fading signals observed on orthogonal diversity branches follow ideal Ricean statistics, the distribution of polarization states on the Poincaré sphere is well-approximated by a Fisher distribution whose concentration parameter is: (1) determined by the corresponding Ricean K-factors and the cross-correlation coefficient between the diversity branches, and (2) a good indicator of the level of cross-polar discrimination (XPD). Finally, from measurements collected in a typical suburban macrocell environment at 1.9GHz, we show that: (1) the means of the polarization state distributions also tends to follow a Fisher distribution and (2) the Fisher concentration parameter is negatively correlated with the average wind speed. Development of a model applicable to a broad range of environments will require additional data from other sites and measurement configurations.
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