Polarization Diversity System for Mobile Radio

TLDR

Conventional space diversity at base stations requires antenna separations of at least 30 wavelengths for broadside incidence, making implementation difficult. The paper proposes a polarization diversity system for mobile radio. The system employs a two‑branch receiver with arbitrarily close base‑station antennas, and an experimental study at 836 MHz measured vertical and horizontal polarization statistics in a suburban environment. Experiments show both polarizations exhibit Rayleigh‑plus‑lognormal fading, one branch uncorrelated and the other correlated regardless of spacing, with local means correlated within ±3 dB 90 % of the time and little sensitivity to transmitter height, confirming the feasibility of UHF polarization diversity.

Abstract

Conventional space diversity reception at typical elevated base locations requites separation of 30λ for broadside incidence and even more for in-line incidence and is therefore difficult to implement. A polarization diversity system for mobile radio is proposed. This is a two-branch receiver diversity system with the advantage that the base station antennas can be spaced as closely as desired. An experimental program has been carried out to obtain the statistical properties of vertically and horizontally polarized electromagnetic waves in a suburban environment at 836 MHz. It was observed that signals of both polarizations were Rayleigh plus log normal, where one is uncorrelated and other is correlated irrespective of base or mobile antenna spacings. The local means of the two signals were highly correlated and were with ± 3 dB for almost 90 percent of the time. Variation of base transmitter heights appeared to have little effect on the ratio of the local means of the two signals. The analysis and experiment demonstrated the feasibility of providing two diversity branches at UHF by polarization diversity.