Space Communications

Satellite systems are expected to assume a very important role in the implementation of the Global Information Infrastructure due to their flexibility and capability for providing global coverage and for enhancing mobile communications. For mobile applications, shadowing represents one of the main problems, especially in regions with multiple tall buildings, mountains or thick vegetation. To evaluate the impact of shadowing on mobile satellite system performance, the characterisation of the propagation channel is a key issue. In particular, the correlation between channel states in consecutive instants in time is an analytical avenue for understanding performance for packet mode transmission (e.g., based on TCP/IP). In this paper results from several measurement campaigns for a limited set of elevation angles have been generalised to any elevation angle. The related shadowing statistics have been utilised to evaluate the time correlation properties of a shadowed environment through simulations.

This paper reports experimental results of the performance of site diversity (SD) systems for sites distance, D, ranging from 500 m (micro scale SD) to 4500 m (small scale SD), at 19.77 GHz, in 31.6° and 30.6° slant paths in Central (Fucino) and Northern Italy (Gera Lario), respectively. The results have been derived by using the synthetic storm technique applied to a large set of rain rate data collected along two linear arrays of 7 rain gauges. Tested against the values of the SD gain predicted by Hodge's empirical formula, our results agree with these predictions down to D≈1.7 km, i.e., in the range of validity of Hodge's formula. For D<1.7 km, our results are still likely to be sound and SD gain for D=500∼750 m is about the same as that found for D≈2 km, namely 15–30% of the single link rain attenuation, the latter expressed in decibels. Micro scale SD can be useful in small cells, or even in large user premises, at carrier frequencies above 10 GHz, in communications systems based on the “sky station” or “sky tower” concept (tropospheric communication systems), or in conventional geostationary satellite systems. The main findings are independent of frequency and elevation angle.

The Data Collection Experiment (DCE) of the scientific mission DAVID (Data and Video Interactive Distribution) of the Italian Space Agency will pioneer the use of the W‐band for telecommunications experiments. In particular, a quasi error‐free collection of high volumes of data will be achieved through the exploitation of a W‐band link between remote or virtually remote sites and the DAVID satellite. To complete the end‐to‐end transfer, data will be transparently forwarded through Ka‐band links provided by the ARTEMIS satellite to ARTEMIS earth stations and then to the Internet. This paper proposes a coding scheme to achieve a quasi error‐free end‐to‐end data transfer and a method to check the presence/absence of errors on all the involved links.

The design of a highly linear microwave driver amplifier is presented. The design uses the latest commercial, off‐the‐shelf components, rather than unique, research devices. Cost‐effective, general‐purpose broadband devices from WJ Communications have been employed. The driver amplifier design is optimized for the satellite communications transmit band, 1626.5–1660.5 MHz. The circuit reported would be of interest to RF designers working on L‐band satellite communications transceivers or designers interested in issues involved in the use of commercial devices designed for terrestrial applications.

Adaptive filters have been used in many diverse applications in the past. An investigation of possible applications in space communications to fixed and mobile platforms is addressed here. Mobile satellite communications has been advanced over the past few years with introduction of several new operational systems (e.g., Thuraya, Globalstar, and Irridium), in addition to the existing INMARSAT and Mobile Satellite Ventures systems. In particular, satellite communications with aircraft are currently receiving considerable development attention. With the potentially large number of users, many issues require attention, particularly interference mitigation for improving signal quality. In this paper, stochastic gradient algorithms, based on the Least Mean Square (LMS) algorithm, and Transform based LMS are used in illustrative applications. The type of algorithm chosen affects both the speed of convergence and the complexity of implementation. Several simulation results are provided using models built to study these applications. Among these applications are channel identification, adaptive channel equalization, interference rejection of narrow band signals within wide band signals, and phased array antenna beam forming.