To provide seamless broadband internet and broadcasting services to passengers of high speed train via satellite link, gap filling is key technology to extend the service coverage in NLOS environment, so to speak, tunnel. The XpeedSAT system is a Ka/Ku band broadband mobile multimedia access system based on DVB-S2/DVB-RCS+M standard for satellite TV, video multicasting, Internet through wireless LAN.In this paper we introduce the various gap filling technologies and compare pros and cons. Finally we propose the gap filling method for NLOS environment in XpeedSAT system.
To determine a suitable waveform for Internet of Things (IoT) transmission over low‐Earth orbit (LEO) satellites, this paper reports the results of a performance comparison between chirp spread spectrum (CSS)‐based LoRa and direct sequence spread spectrum (DSSS)‐based Ingenu. The performance of both waveforms was measured in terms of the packet error rate, throughput, and packet loss rate, considering the Doppler effect caused by the high speed of LEO satellites and the interference among multiple terminals. Simulation results indicate that the DSSS scheme is more suitable than the CSS scheme for high‐traffic IoT services because of its robustness against interference among multiple terminals. However, the CSS scheme is more suitable than the DSSS scheme for high‐mobility IoT services because of its robustness against the Doppler effect. We discuss various solutions, such as the preprocessing of Doppler effect and avoidance of packet collision, to enhance the performance of the DSSS and CSS schemes. The simulation results of the proposed solution show that the enhanced DSSS scheme can be a proper waveform in IoT transmission over LEO satellites for both the high‐traffic and high‐mobility services.
For efficient spectral utilization of satellite channels, a shared band transmission technique is introduced in this paper. A satellite transmits multiple received signals from a gateway and terminal in the common frequency band by superimposing the signals. To improve the power efficiency as well as the spectral efficiency, a travelling wave tube amplifier in the satellite should operate near the saturation level. This causes a nonlinear distortion of the superimposed transmit signal. Without mitigating this nonlinear effect, the selfinterference cannot be properly cancelled and the desired signal cannot be demodulated. Therefore, an adaptive compensation scheme for nonlinearity is herein proposed with the proper operation scenario. It is shown through simulations that the proposed shared band transmission approach with nonlinear compensation and self-interference cancellation can achieve an acceptable system performance in nonlinear satellite channels.
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