| Abstract: | The paper describes a novel development of a previously described technique for the measurement and correction of the Doppler shift (frequency offset) in a received UQPSK signal that has been transmitted over a satellite link. The satellite is here assumed to be in a non-geostationary orbit, so that it introduces a large and time-varying Doppler shift into the transmitted data signal. Correction of the Doppler shift must be achieved as soon as the satellite rises above the horizon and with no prior knowledge at the receiver of the transmitted data. Furthermore, under the given conditions, the signal/noise ratio can be very low and the Doppler shift very high. A non-data-aided technique has therefore been selected, capable of operating under seriously adverse conditions. Results of computer-simulation tests are presented to measure the time taken to correct an initial Doppler shift of 5 kHz in the received UQPSK signal, at low signal/noise ratios. |
