Using Variable Coding and Modulation to Increase Remote Sensing Downlink Capacity

Abstract

Remote sensing satellites are typically low earth orbit, and often transmit the data gathered with the remote sensors to ground stations at locations on earth. These transmissions are band limited, and must operate within a 375 MHz bandwidth in the X-Band spectrum. This can present a limitation to the amount of data that can be transmitted during the short duration of a pass (typically less than 15 minutes). It is then highly desirable to increase the bandwidth efficiency of a system for data transmission in a remote sensing downlink. This paper describes a method of achieving higher efficiency by pre-programming the satellite to adjust the modulation and coding based in at least part on the slant range to the receiving ground station. The system uses variable coding and modulation to adjust to the slant range to the ground station to achieve a throughput increase of more than 50% of the data transferred during a pass using the currently accepted technology.