Use of cell-site diversity to mitigate rain attenuation in 10-66 GHz fixed WiMAX
The broadband wireless access system operating with a dominant Line-Of-Sight (LOS) component provides high receiver signal power and channel capacity. The fixed WiMAX LOS link requires inexpensive and less time consuming deployments and is easily scalable in accordance with the demand of the application. The focus of this paper is on the propagation impairments caused due to rain attenuation on the WiMAX technology and means of mitigating it. Rain attenuation is the major contributor of signal loss in a LOS set-up and Cell Site Diversity (CSD) technique is suitable for alleviating the losses incurred as a result of it. An experimental analysis of CSD was performed based on an extensive data set spanning over 4 years of Hydrological Radar Experiment (HYREX) rain gauge network. The study was performed on frequencies extending from 20 GHz to 54 GHz. This led to the observation that confirmed that the optimum angular separation is 180°, the point providing maximum CSD gain. Rain attenuation along diversity paths are strongly correlated at small azimuth angles. The CSD gain increases with increase in link distance and when links have equal link distances. A distance of about 6 km has been suggested as the maximum distance from the subscriber station to the base station.