Recently, random access protocols have acquired a new wave of interest, not only from the satellite communication community, but also from researchers active in fields, such as Internet of Things and machine-to-machine. Asynchronous (slot- and frame-wise) ALOHA-like random access protocols, are very attractive for such applications, enabling low complexity transmitters and avoiding time synchronization requirements. Evolutions of ALOHA employ time diversity through proactive replication of packets, but the time diversity is not fully exploited at the receiver. Combining techniques, as selection combining and maximal-ratio combining, are beneficial and are adopted in the enhanced contention resolution ALOHA (ECRA) scheme, presented here. A tight approximation of the packet loss rate for asynchronous random access, including ECRA, well suited for the low channel load region is derived. Finally, ECRA is evaluated in terms of spectral efficiency, throughput and packet loss rate in comparison with recent protocols, showing that it is able to largely outperform both slotted synchronous and asynchronous schemes.

In this paper we investigate several central aspects of using the unslotted Contention Resolution Diversity ALOHA (CRA) scheme with Successive Interference Cancellation (SIC). A model for the co-user-interference under consideration of time-, phase- and frequency-offsets is presented. With this model, the throughput and Packet Loss Ratio (PLR) performance of CRA is investigated when using Low Density Parity Check (LDPC) codes, showing that CRA can achieve remarkable performance also in these conditions. Moreover, the throughput and PLR gain of CRA in presence of power unbalance is studied, showing that significant gains can be expected. Following this, the central question is answered which channel rates optimize the goodput of CRA, showing that for CRA with few replicas a low, robust channel rate achieves optimum while for high numbers of replicas a high channel rate performs optimum. Finally an investigation of the interference distribution of an asynchronous TDMA scheme with replicas and the SIC operations in it are shown.

The most widely used transport protocols (i.e, TCP and UDP) are not suitable for aeronautical services because of the reliability and strict transfer delay requirements that cannot be met by TCP and UDP in such environment. In this respect, the paper proposes a novel message-oriented transport protocol Reliable Aeronautical Services Protocol (RASP) enabling reliable aeronautical services. Simulation campaigns carried out in ns-2 show the superiority of RASP with respect to TCP in terms of end-to-end message transfer delay and number of performed retransmissions.

Random Access MAC protocols are simple and effective when the nature of the traffic is unpredictable and sporadic. In the following paper, investigations on the new Enhanced Contention Resolution ALOHA (ECRA) are presented, where some new aspects of the protocol are investigated. Mathematical derivation and numerical evaluation of the symbol interference probability after SIC are here provided. Results of the optimum header positioning which is found to be in the beginning and in the end of the packets, are exploited for the evaluation of ECRA throughput and Packet Error Rate (PER) under imperfect knowledge of packets positions. Remarkable gains in the maximum throughput are observed for ECRA w.r.t. Contention Resolution ALOHA (CRA) under this assumption.

Recent advances in Random Access (RA), improving throughput and loss rates, make the usage of such technique particularly interesting to complement Demand Assigned Multiple Access (DAMA) channels for the return link of satellite systems. In this paper, a novel approach for the integration of the two access strategies aimed at transmission delay optimization is presented. An algorithm for DAMA and RA delay estimation is presented, and its accuracy shown by simulations. Furthermore, the benefits of the proposed integration concept are demonstrated with significant gains in delay and throughput in moderate to high load operating regions.

Contention Resolution Diversity Slotted ALOHA (CRDSA) and its burst degree optimizations (CRDSA++, IRSA) make use of MAC burst repetitions and Interference Cancellation (IC) making possible to reach throughput values as high as T ≃ 0.8 in practical implementations, whereas for the traditional slotted ALOHA T ≃ 0.37. However, these new techniques introduce a frame-based access to the channel that limits the performance in terms of throughput and packet delivery delay. In this paper, a new technique named Sliding Window CRDSA (SW-CRDSA) and its counterpart for irregular repetitions (SW-IRSA) are introduced in order to exploit the advantages of MAC burst repetition and Interference Cancellation (IC) with an unframed access scheme. Numerical results are also provided in order to validate the statement of better performance.

The stability of Random Access protocols is of high importance to ensure an efficient usage of resources and good service perception by the users. In this paper the stability region for the recently proposed Contention Resolution Diversity Slotted ALOHA random access protocol is discussed for finite user populations. The system dynamics of a CRDSA Random Access channel are described and a mathematical model is formulated, which allows predicting the stability of the system. From the derived model quantitative approximations of the stability regions and parameter selection for stable operation are provided. Numerical results are derived by means of simulations for validating the mathematical model and the quantitative approximations of the stability region.

In this paper, a novel enhancement of the well known ALOHA random access mechanism is presented which largely extends the achievable throughput compared to traditional ALOHA and provides significantly lower packet loss rates. The novel mechanism, called Constant Rate Assignment (CRA), is based on transmitting multiple replicas of a packet in an unslotted ALOHA system and applying interference cancellation techniques. In this paper the methodology for this new random access technique is presented, also w.r.t. existing Interference Cancellation (IC) techniques. Moreover numerical results for performance comparison with state of the art random access mechanisms, such as Contention Resolution Diversity Slotted ALOHA (CRDSA) are provided. Finally the benefit of taking strong forward error correcting codes for the performance of CRA is shown.

The authors examine two different non-geostationary satellite constellation networks with inter-satellite links for global air traffic control and air passenger communication. After developing a traffic model for aeronautical communication services, the authors derive bandwidth requirements for such a global system. The influence of different routing policies is discussed and they show that link loads are comparable for both medium earth orbit and low earth orbit constellations. All considerations are based on real global flight data of all commercial flights during 1 day.