Following the introduction of contention resolution diversity slotted ALOHA (CRDSA), a number of variants of the scheme have been proposed in literature. A major drawback of these slotted random access (RA) schemes is related to the need to keep slot synchronization among all transmitters. The volume of signaling generated to maintain transmitters' slot synchronization is impractical for large networks. In this paper, we describe in detail asynchronous contention resolution diversity ALOHA (ACRDA), which represents the evolution of the CRDSA RA scheme. ACRDA provides better throughput performance with reduced demodulator complexity and lower transmission latency than its predecessor while allowing truly asynchronous access to the shared medium. The performance of the ACRDA protocol is evaluated via mathematical analysis and computer simulations and is compared with that of CRDSA.

This manuscript provides a general analytical framework to accurately predict the performance of several slotted Random Access (RA) schemes such as Slotted Aloha and Diversity Slotted Aloha. Compared to past literature the proposed analytical framework allows to perform accurate performance estimation of these RA schemes exploiting state-of-the-art forward error correction schemes in the presence of packet power unbalance as it is the case in many practical systems. Furthermore, the analytical framework is also capable to accurately approximate the performance of more recent RA schemes particularly suitable for satellite communications such as Contention Resolution Diversity Slotted Aloha exploiting iterative interference cancellation techniques on top of packet repetition within the frame to further improve the RA scheme performance. The analytical results have been successfully verified against a comprehensive set of simulations covering cases of practical interest.

This paper presents a radio interface recently standardised by ETSI under the name of S-MIM (S-band Mobile Interactive Multimedia) and especially designed to provide messaging services over GEO satellites using low-power terminals.

We propose two new protocols based on physical layer network coding for collision resolution in multiple access networks. When a collision occurs the receiver decodes the sum of the collided packets and after a number of transmissions, equal to or slightly higher than the number of original packets, it can recover all of them. One of the proposed protocols based on fountain codes can resolve collisions by sending out just one acknowledgement (ACK), thus being particularly suited to networks with large round trip delays such as satellite networks. We carry out a comparison of the average delay achieved by the proposed schemes with other access techniques, and show how the performance can be improved with little coordination at the receiver.

Two new schemes are proposed for collision resolution in slotted ALOHA networks based on multi-user physical-layer network coding (MU PHY NC). In the proposed random access schemes, a collision of a generic number of packets can be recovered decoding the XOR of the original messages, such that the signal resulting from the collision is exploited rather than being discarded. Two different schemes that differ in terms of the amount of control information that needs to be transmitted from the access point, are studied.

Emergency Management is an important topic for research community worldwide, especially after recent major disasters. The problem of supporting mobility at the disaster site to rescue teams equipped with different heterogeneous access technologies and providing interoperability between different agencies and jurisdictions is still under investigation. In this work we propose to merge the advantages of IPv6 micro-mobility management of Proxy Mobile IPv6 (PMIPv6) with macro-mobility management, security, inter-technology handover and multi-homing features of Host Identity Protocol (HIP). This new approach applied to our proposed ad-hoc satellite and wireless mesh system architecture for emergency mobile communications can improve mobility, security, reliability and interoperability in Emergency Management domain.

In this paper a new multiple access scheme dubbed contention resolution diversity slotted ALOHA (CRDSA) is introduced and its performance and implementation are thoroughly analyzed. The scheme combines diversity transmission of data bursts with efficient interference cancellation techniques. It is shown that CRDSA largely outperforms the classical lotted ALOHA (SA) technique in terms of throughput under equal packet loss ratio conditions (e.g. 17-fold improvement at packet loss ratio = 2 middot 10-2). CRDSA allows to boost the performance of random access (RA) channels in the return link of interactive satellite networks, making RA very efficient and providing low latency for the transmission of small size sparse packets. Implementation-wise it is shown that the CRDSA technique can be easily integrated in systems equipped with digital burst demodulators.

This paper will examine the potential performances of spread-spectrum-based access techniques via the interaction channel of an Internet protocol (IP)-based multimedia satellite system. In particular, a theoretical analysis of the spread-Aloha technique will be given for the case of forward error correction coded systems. Then, the performance of spread-Aloha access will be confirmed by simulation and compared with that of a conventional time-division multiple-access (TDMA)-based combined free/demand assignment multiple-access system. It appears that spread-Aloha-based techniques, although achieving a lower maximum throughput than the TDMA-based access scheme, may provide a better experience to the user due to the lower transmission latency. Finally, the prospect of a spread-spectrum-based access scheme combining Aloha and reservation mechanisms will be briefly overviewed.

This paper describes the architectural study of an innovative ultra-fast packet-switched transparent processor dealing efficiently with unicast and multicast applications. The proposed architecture aims at outperforming current packet processor architectures in terms of total throughput and efficiency. In order to cope with the limitations of today's on board processors, three new concepts are introduced: transparent burst switching, channel multiplexing, and bandwidth asymmetry . Some of these concepts are already well known in the field of optical terrestrial networks but need further improvements and adaptations to cope with the requirements of satellite processors and systems. Transparent burst switching is used to enhance the transparency of the processor: the packet payload is processed transparently and only the header is demodulated onboard. The channel multiplexing and bandwidth asymmetry techniques are used to consolidate bufferless switch architectures, which appear to be very attractive for increasing the overall throughput of switches. Finally, the paper introduces an innovative efficient and scalable hybrid optical/digital implementation of this processor. The focus here is on a satellite-switched code/time-division multiple-access type of system but the results and concepts provided in this paper can apply to other satellite-switched systems.