Method and apparatus for Doppler compensation in a satellite communications system

摘要

A method and apparatus for Doppler compensation in a satellite communications system such as Inmarsat's SATCOM network are disclosed. An aircraft terminal provides satellite communications services in one of several user-selectable modes including a circuit-mode services only mode and other modes providing some data packet services. The terminal includes multiple channel units coupled to a processing circuit. The channel units communicate radio signals via data or circuit channels between the aircraft and a satellite. Each channel unit can receive a channel input transmitted at a known frequency, and measure its frequency. Each channel unit can also transmit a channel output at an adjustable frequency. Each channel unit is operated as a circuit channel when circuit-mode services only is selected. Doppler shift is measured using the difference between the measured and known transmitted frequencies of at least one channel input. The measured Doppler shift is used to determine a Doppler correction for each transmission, and the correction is applied to adjust the frequency of each transmitted channel output to maintain the transmissions within an error budget.