Mobile satellite communications are gaining more and more interest in recent years, with SOS-via-satellite, location updating and satellite mobile messaging being important applications for customers. An efficient satellite waveform is the key technology to enable the mobile satellite communication service that will be provided by satellite constellations in the 5G and 6G era. In this paper, we conduct an experimental evaluation of the satellite waveform transmitted by the first satellite-enabled smartphone, the iPhone 14. We forced the device to transmit location data via L-band using the Find My application, while it had no other connectivity than the Globalstar satellites. The results show the temporal and spectral properties of the satellite waveform, and we performed a first estimate of the modulation scheme and data rate.

In satellite communication downlinks, physical layer security is challenging to achieve due to their broadcasting nature and Line-of-Sight channel characteristics. This paper provides a precoding algorithm to secure the downlinks of multiple users against multiple eavesdroppers with optimization of the minimum secrecy capacity. By the use of artificial noise, a positive secrecy capacity is achievable even if the number of eavesdroppers is higher than the number of beams. We demonstrate that a multiple-reflector antenna design provides a significantly higher secrecy and throughput performance when compared to a single-reflector design due to additional degrees of freedom, exhibited by the signal phases. The total vulnerability region is introduced as a new figure of merit with respect to unidentified eavesdroppers.

A particular problem in satellite communications is the estimation of the current operating point of a bent-pipe transponder. Various special effects aggravate this estimation problem, among which the capture effect, gain compression, unknown attenuation in the transmission channel, or noisy received signals are the most prominent. In most practical cases, operators desire a fully blind estimator that is nevertheless able to cope with these unwanted impairments. We provide the theoretical background and further results on a novel estimator based on signal statistics that enables accurate operating point estimation in multicarrier operation as well as in single carrier mode with higher-order modulation. In this paper we focus on three basic use cases for our estimator, and we discuss results on the estimation accuracy.