ADAPTIVE MODULATION TECHNIQUE AND SATELLITE COMMUNICATION NETWORK IMPLEMENTING THE SAME

摘要

A method is presented which compensates for changes in the quality of an RF link by adaptively varying the type of modulation utilized over the RF link in response to changes in link conditions, whereby the gain and information throughput over that RF link are adaptively varied in dependence upon link conditions, while maintaining a constant symbol rate. In a presently contemplated embodiment, this method is implemented in a satellite communications network that includes two or more terminals (22) and a network controller (NCC) (24) by monitoring various modem performance parameters at the terminals (22). The NCC (24) then transmits control data to the terminals (22) to adaptively vary the type of modulation used in allocating bursts between various pairs of terminals (22) in dependence upon the monitored link conditions. In a specifically contemplated embodiment, the modulation type is changed from QPSK to BPSK in response to link degradation (e.g., due to heavy rain), thereby providing 3 dB of gain. The change from QPSK to BPSK modulation necessitates that the information throughput be reduced by a factor of 2, thereby maintaining a constant symbol rate.