Future satellite communications systems will be characterized by two-way connection between many UT User Terminals and a GEO satellite with On-Board Processing. They will propose different kind of services such as Internet access and interactive multimedia applications. The transmitted data consists of many audio and video contents, so it requires QEF (Quasi-Error-Free) transmission and high bandwidth efficiency. System will operate in Ka-band with MF-TDMA access method on the uplink. Such systems have to overcome specific difficulties that may affect its QoS Quality of Service. First, low cost power amplifier used in the UT induces non-linearity when operating near saturation. Such non-lincarity incrcascs thc intcrfcrcncc lcvcl and a back-off is oftcn considcrcd for limiting non-linearity effects. Secondly, ACI (Adjacent Channel Interference) level is highly affected by the frequency spacing between adjacent carriers. It becomes more harmful when the useful carrier is attenuated relatively to its adjacent ones. Finally, channel attenuation is very high due to precipitation when operating in Ka band. Many FMT (Fade Mitigation Techniques) may be necessary to overcome signal attenuation. With such constraints, the choice of the waveform is of the uppermost important. The adopted waveform must provide good power and spectral efficiency while being insensitive to amplifier non-linearity. It shall also be adaptive to mitigate fading by allowing switching from one mode to another. In this context, this paper is proposing a CPM (Continuous Phase Modulation) based waveform. This class of modulation seems to be a promising solution since it yields a constant envelope signal so that SSPA (Solid Sate Power Amplifier) terminal amplifier can operate near saturation. Some CPM schemes provide also good spectral properties that may mitigate ACI [Z]. Finally, from power efficiency point of vicw, scrially codcd CPM providcs high powcr gain whcn itcrativc dccoding proccss is pcrformcd. Simulation results are presented in the paper to show that such coding and decoding schemes achieve good power performance [ 13. For example gain of more than 5 dB' is obtained when iterative decoding of MSK is performed rather than classic decoding. The paper starts with a brief review of the characteristics and requirements of future satellite communications systems. Then, after a brief ' Code=(7,5), Interleaver Size=1024 0-7803-8482-2104/$20.00 02004 IEEE. 269 summary of the main CPM signal properties and the receiver complexity, serially coded CPM with iterative decoding process is tackled. Simulation results of few binary and quaternary CPM schemes are given. Those results are very helpful for the selection of CPM parameters that cope with system constraints. The subsequent part emphasizes the usefulness of CPM to design an adaptive waveform. In fact, propagation conditions in Ka band are very stringent and the signal to noise ratio (SNR) could be highly reduced. Adaptive waveform could help to overcome channel degradation and increase system av...

This paper presents a solution to enhance the navigation of LEO satellites by mitigating the multipath influence. In several cases, Navigation of LEO satellites needs a very high accuracy in positioning, while GPS receivers suffer from leak of accuracy. As multipath is a major source of inaccuracy, we propose to use a neural networks (NN) technique in the range domain in order to estimate and compensate for Phase and code (delay) tracking errors. In this paper we present a rich discussion of the NN application in the range domain and the major factors influencing its performance.

No abstract

No abstract