Payload nonlinearity impact on the Globalstar forward link multiplex. I. Physical layer analysis

Forthcoming satellite personal communication networks (S-PCNs) like Globalstar are going to use bent-pipe transponders and an active phased-array antenna in conjunction with code-division multiple access (CDMA). Efficient payload operations require operating the on-board power amplifiers (PAs) close to their saturated power whereby distortion effects cannot be neglected. This paper analyzes the impact of solid-state amplifiers on the Globalstar forward link multiplex when a single PA per beam is used and for the more practical case of an active phased-array satellite antenna. It is shown that the conventional noise power ratio (NPR) intermodulation figure fails to accurately predict the end-to-end system performance. Multibeam active-phased array is shown to provide superior performance compared to a system employing a single amplifier per antenna beam.