RAIN COMPENSATION ALGORITHM FOR ACTS MOBILE TERMINAL

Having successfully completed the L-band mobile satellite experiment (MSAT-X), the Jet Propulsion Laboratory is now developing a system to demonstrate Ka-band land-mobile satellite communication technologies in conjunction with NASA's Advanced Communication Technology Satellite (ACTS). The experiment will involve two-way communications between a fixed terminal (FT) in Cleveland and a van-mounted ACTS mobile terminal (AMT) using the satellite in a bent-pipe (30 GHz uplink, 20 GHz downlink) relay mode. Although AMT will initially be located in the greater Los Angeles area, it is designed to operate satisfactorily anywhere within the contiguous United States (CONUS). To a far greater extent than MSAT-X, AMT must cope with the impact of propagation effects on link performance, with particular concern for rain attenuation. This paper describes a novel technique for ameliorating the effects of rain fading on AMT communications by varying the data rate in response to real-time power measurements of the pilot signal received by AMT and the ACTS beacons received by the FT. The AMT rain-compensation algorithm (RCA) employs both fade and fade-rate statistics to determine the appropriate data rate, and uses empirical frequency-scaling formulas, described herein, to accommodate any differences between the measured fading signal and the communications link. A worst-month rain attenuation model is used to argue that the RCA will boost the AMT-ACTS-FT link availability, defined as the percentage of time that the performance margin exceeds 3 dB, from 97.2% to 99.7% when the AMT is in Los Angeles, and from 90.5% to 98.1% in Portland, ME where rain events are more of a factor.