Space Communications

This paper, is mainly based on work performed in the framework of the European Union Advanced Communications, Technology and Services (EU‐ACTS) ACCORD project. This project, by collecting the main results carried out from four other different ACTS projects (SECOMS, EXODUS, MEDIAN and SAMBA), aims at the validation, from both a theoretical and an experimental viewpoint, of a truly global Mobile Broadband System (MBS) consisting of multiple (satellite/terrestrial) System components with different complementary characteristics. One of the key aspects is the design of a mobile Multi Mode Terminal (ACCORD MMT), which allows mobile users to access the same ATM‐based Core Network through four different Access Systems, each one designed and optimised to operate in a specific environment (satellite, Digital European Cordless Telecommunications (DECT), indoor Wireless Local Area Network(W‐LAN), urban digital cellular). This paper describes the ACCORD System way of working and the Mobility Management procedures.

The Universal Mobile Telecommunications System (UMTS) under development in the international community has been agreed to include both terrestrial and space segments as integral parts of the system. The purpose of the SINUS project is to demonstrate that UMTS services can be provided seamlessly via satellite, and to make recommendations concerning the interworking between space and terrestrial segments. The SINUS laboratory system demonstrator is being developed to illustrate the role of the Satellite–UMTS, including a real‐time emulator with programmable perturbations in the link to the mobile user, representing all expected satellite constellation and mobile link characteristics. The Mobile Terminal and Fixed Earth Station (FES) consist of CDMA modulator/demodulators for satellite‐specific communication functions, and also include software for more generic UMTS network functions (e.g., call management, mobility, handover). To demonstrate the realistic operation of the system, several examples of multimedia applications will be implemented from end to end.

TOMAS is an R&D‐project within the EU‐funded ACTS Programme. The main objective of the TOMAS project is to realise a Satellite‐UMTS trial platform (testbed) for multimedia services with data rates up to 2 Mbit/s using existing geostationary satellites and to evaluate and enhance this inter‐trial platform in Joint Trials with co‐operating ACTS and non‐ACTS projects. With the TOMAS service and application trials being performed before the introduction of UMTS and before further development of its satellite component, its results, including assessment of user requirements and user acceptance as well as system performance, can be used to improve the design of satellite services and systems complementing UMTS.

This paper presents the TOMAS project, its objectives, the technical approach taken, and the results achieved in Joint Trials with different other R&D projects and user groups. TOMAS’ main objective is to test and evaluate Satellite‐UMTS applications, components and services. The project's focus is on high‐quality services with data rates from 64 kbit/s to 2 Mbit/s, provided globally by existing geostationary satellites. Within the project framework a testbed was set up using Inmarsat satellites and the ESA/EMS space segment onboard Italsat F2. To access the space segments, existing mobile terminals and earth stations were upgraded to TOMAS’ requirements. The performance of the testbed and the services was evaluated in end‐user trials in telemedicine and construction site applications.

The use of non‐linear amplifiers near saturation in satellite channels causes severe distortion of the transmitted signal. These distortions make the matter of power efficiency prevail over spectral efficiency in satellite communication systems. Nowadays, the use of satellite segments for applications requiring ever increasing data rates puts this principle in question. The present article proposes to fight non‐linear distortion caused by satellite amplifiers by resorting to simple neural network equalisation devices in the receiving earth terminals. Several neural network equalisers are introduced, and applied to a satellite Universal Mobile Telecommunication System (S‐UMTS) channel model. They are shown not only to outperform conventional equalisation techniques like the linear transversal equaliser, but also to have better performance than the non‐linear Volterra equaliser. The performance improvement is all the more sensitive as the modulation scheme used is severely distorted. The case of 16‐QAM transmission over a mobile satellite link is studied in details.