E-SSA Satellite Messaging Return Channel: Performance Analysis and Field Trials Results T. Heyn * , P. Nagel * , B. Niemann * , A. Recchia # , F. Collard # , R. Hermenier ∞ , M.A. Marchitti ∞ , M. Andrenacci + , G. Mendola + * Fraunhofer Institute for Integrated Circuits - IIS, Erlangen, Germany, {thomas.heyn, peter.nagel, bernhard.niemann}@iis.fraunhofer.de # Eutelsat, Paris, France, {arecchia, fcollard}@eutelsat.fr ∞ DLR, Oberpfaffenhofen, Germany, {romain.hermenier, maria-antonietta.marchitti}@dlr.de + MBI, Pisa, Italy, {mandrenacci, gmendola}@mbigroup.it Abstract— An open ITS platform combining interactive satellite services with other communication channels is being developed and evaluated in field trials within the SafeTRIP project [1]. Prototyping and in-field validation of a novel waveform for messaging return channel over satellite for land mobile is an important objective of the project. The overall system architecture has recently been standardized by ETSI under the name of S-MIM (S-band Mobile Interactive Multimedia). The messaging protocol, described in the Part 3 of the standard, is based on the Enhanced Spread Spectrum Aloha (E-SSA). Its main asset resides in the low power required at the transmitter, which will allow the reuse of off-the-shelf power amplifiers and low-cost omnidirectional antennas. This paper will present a comprehensive summary of previous E-SSA performance analysis from simulations and the first field trials results using the E-SSA waveform. The presented results have been derived from static and mobile field trials carried out in Germany with fully functional E-SSA modulator and demodulator prototypes and the EUTELSAT10A satellite. Results for the static and mobile performance of the E-SSA demonstrator with an omni-directional antenna under Line-of- sight (LOS) conditions are presented. The measured Packet Error Rates of transmissions via satellite at different terminal power levels confirm the theoretical link budget calculations for single and multiple simultaneously transmitting terminals. The degradation due to fading effects of the transmission channel under mobile conditions has been measured during the trials to approx. 3 dB. The resulting overall required transmitter power in the multi-user scenario of the trials setup has been only -3 dBW to reach a high QoS under mobile conditions. This value confirms the suitability of the E-SSA waveform for interactive mobile services for the mass market. I. INTRODUCTION. SATELLITE RETURN CHANNEL SYSTEMS The availability of the S-band frequencies for the development of Mobile Satellite Services (MSS) over the whole of Europe has opened the way to a truly innovative satellite communication system. Thanks to the S-band, the power consumption of the terminal is limited and the size of the antennas comparable to the commonly installed rooftop shark antennas. These features, in addition to the intrinsic “across-boundaries” nature of the satellite, make the S-band best suited to the new generation of “communicating cars”. The main advantage of the system resides in the deployment of an ad-hoc messaging channel, allowing the interaction between the connected terminals and the satellite at affordable prices, thanks to the effectiveness of the ad-hoc return link employed protocol. The overall architecture has recently been standardized by ETSI under the name of S-MIM (S-band Mobile Interactive Multimedia) [2]. The focus of this paper will be the Part 3 of the standard, which is based on the Enhanced Spread Spectrum Aloha (E-SSA) waveform, an asynchronous access protocol especially conceived to provide messaging services over the satellite return link. The absence of synchronization mechanisms simplifies deployment and activation of the terminals. A wide range of applications based on burst transmissions not significantly capacity-demanding have been envisaged, such as telemetry, environment and traffic monitoring, emergency alerts, fleet management, highway tolling, forecast predictions, pay-per-view. Road-safety and emergency applications have been tested and validated in a real scenario through the SafeTRIP demonstration platform. The validation of the applications is out of the scope of this paper. In the following chapters we will demonstrate the viability of the S-MIM transmission protocol for the return link messaging and we will show the on-field validation of the first standard-compliant prototype. II. E-SSA SYSTEM ARCHITECTURE In this section, a high level description of the lower layers of the E-SSA system architecture is given. The protocol stack of the S-MIM return link asynchronous access is composed of three different planes: the User Plane, the Control Plane which supports and controls the User Plane functions, and the Management Plane. The link layer of the User Plane is divided into four sub- layers: • Header Compression, which provides non-compressed as well as unidirectional stateless compressed channels to the higher layers; it is managed by the Header Compression Control. • Transmission Mode, managed by the ARQ Management and Load Control function, providing three access services (a transparent mode and two acknowledged modes).