Cross-correlation between 900 MHz signals received on vertically separated antennas in small-cell mobile radio systems

Abstract

In order to establish the antenna separation necessary to receive sufficiently decorrelated samples of the signal at both base and mobile stations, extensive field trials have been carried out in which a CW signal was transmitted over a distance of 1.3 km. The receiving station was equipped with two vertical halfwave dipoles which were spaced in a vertical configuration. The received signals were coherently demodulated by a two-branch phase-locked receiver which could measure both the complex and envelope cross-correlation. Results show that a cross-correlation less than 0.7 can be achieved using an antenna separation of 8 lambda to 13 lambda at the base station and approximately=1 lambda at the mobile, for a 1.3 km cell radius. At 900 MHz such an antenna separation is easily obtained and, in both cases, the space required is small. The cross-correlation using vertically spaced antennas at the base station is independent of the incoming arrival angle and hence low correlation can be achieved whilst maintaining omnidirectional coverage. At the mobile the small vertical antenna separation required suggests that an unobtrusive antenna arrangement is feasible. >