Satellite-based automatic dependent surveillance-broadcast (ADS-B) enables global-scale aircraft tracking, but introduces significant challenges in packet detection due to the severe signal attenuation experienced along the propagation path. This paper investigates detection strategies for satellite ADS-B receivers based on the generalized likelihood ratio test (GLRT), providing a statistically sound alternative to existing heuristic solutions. To enhance robustness against residual frequency offsets, we exploit the modulus of the received samples, which is invariant to phase distortions. Additionally, we extend the observation window beyond the packet preamble to improve detection performance. To reduce the computational cost of an exact GLRT implementation, we explore several alternatives, including an asymptotic approximation of the Rician distribution and a Gaussian model for the observation data. Simulation results show that the proposed schemes achieve reliable detection even at low signal-to-noise ratios, and outperform existing methods by leveraging both the preamble and part of the data payload.

The paper analyzes the performance of an advanced random access scheme for the return channel of a satellite communication link. The scheme is an evolution of the E-SSA scheme proposed in [1], [2] that couples an asynchronous Spread Spectrum Aloha access with Successive Interference Cancellation (SIC) at the central Gateway (GW) receiver to increase the channel throughput. Main feature of the proposed scheme is the exploitation of an approximate linear Minimum Mean Square Error (MMSE) detector in place of the conventional Single User Matched Filter (SUMF) detector used in E-SSA. A gain of 50% in terms of spectral efficiency is achieved over E-SSA in most typical scenarios.

We consider realistic satellite communications systems for broadband and broadcasting applications, based on frequency-division-multiplexed linear modulations, where spectral efficiency is one of the main figures of merit. For these systems, we investigate their ultimate performance limits by using a framework to compute the spectral efficiency when suboptimal receivers are adopted and evaluating the performance improvements that can be obtained through the adoption of the time-frequency packing technique. Our analysis reveals that introducing controlled interference can significantly increase the efficiency of these systems. Moreover, if a receiver which is able to account for the interference and the nonlinear impairments is adopted, rather than a classical predistorter at the transmitter coupled with a simpler receiver, the benefits in terms of spectral efficiency can be even larger. Finally, we consider practical coded schemes and show the potential advantages of the optimized signaling formats when combined with iterative detection/decoding.

This papers addresses the design of new energy-efficient Continuous Phase Modulation (CPM) waveforms suitable for being adopted in satellite mesh networks that are characterized by the absence of the Hub, and by small antennas and power amplifiers with moderate to low output saturated power at the user terminal. In particular, a CPM modulation format concatenated with a proper convolutional code for low spectral efficiency values has been selected to implement an efficient waveform for power-limited scenarios. Performance results show the gain obtained with respect to the DVB-RCS2 CPM waveforms at higher spectral efficiency also when transmission techniques, such as Burst Repetition, are considered, and confirm the suitability of the new designed CPM waveforms for satellite hub-less scenarios.

In this paper we investigate capacity optimization mechanisms for multi-beam satellite systems built on a realistic payload model. The first proposed mechanism deals with long term traffic variations, for which capacity optimization algorithms are proposed based on per-beam traffic requests. Due to the high asymmetry of the traffic, our algorithms provide time and spatial flexibility illuminating a specific set of beams within a window of several time-slots. Our algorithms maximize the amount of capacity actually offered while providing reduced power consumption. The second proposed mechanism deals with short-term traffic variations, for which we propose Network Coding (NC) based techniques at the link layer. The aim is to increase the offered capacity taking advantage of overlapping beam coverage, usually considered as a source of interference. This technique is meant to be applied not only in classical multi-beam systems, but also on top of the per-beam capacity optimization as a method to deal with fast traffic unbalances not evaluated in the first mechanism. Analysis and simulations results show that system capacity can be increased up to 13% in the first case and up to 90% in the second case.

This paper addresses detailed waveform trade-offs for mesh satellite networks. The waveform analysis is carried out considering spectral efficiency, resilience against non linear distortion, channel impairments and interference for both linear and continuous phase modulation schemes defined in the DVB-RCS2 standard.

We recently investigated the spectral efficiency, achievable with a symbol-by-symbol receiver, for linear modulations employing time-frequency packing. In this paper, we will investigate the improvements that can be obtained by increasing the receiver complexity. In the numerical results, we will mainly concentrate on time packing (an extension of the so called faster-than-Nyquist signaling technique) and on (i) receivers based on linear processing plus symbol-by-symbol detection or (ii) receivers based on a more sophisticated trellis processing with constrained complexity. Finally, the potential advantage of the proposed signalling scheme when combined with conventional low-density parity-check (LDPC) coding of the DVB-S2 air interface will be presented.

Aiming to exploit the capabilities of next generation terminals to receive and process several, partially overlapping beams of a multibeam satellite, we present a mathematical analysis and propose algorithms to provide enhanced and robust load-balancing to unequal load demands between beams. At the core of our mechanisms is a resource allocation problem that aims to minimize the time to deliver packets taking into account the load (traffic demands) per beam and channel conditions. Network coding is a key enabler of our mechanism, allowing a seamless and efficient exploitation of the multiple, available paths from satellite gateways to end-users and leading to a more efficient allocation of resources in each beam. Advantages over current state-of-the-art for load balancing for multibeam satellites include: i) cooperation amongst neighboring beams to improve system stable throughput, ii) use of random linear network coded packets to enhance reliability and simplify the allocation of packets to the different beams, and iii) adaptation to short-term dynamics of the traffic of each beam, instead of only long term traffic characteristics. We provide numerical results for the case of a multibeam satellite covering Europe with 70 beams showing that our technique can increase the stable throughput by 30% or higher with respect to current techniques.

A non-maximally decimated filterbank structure for pre-equalizing channels with intersymbol interference (ISI) is investigated. The impulse response of the channel is assumed to be known at the transmitter. Compared with the classical Tomlinson-Harashima (1971) precoding technique, the proposed pre-equalizer compensates for the channel without increasing the number of the received signal levels (channel alphabet). The proposed technique does not require the channel to be minimum-phase. The filterbank structure adds redundancy to the input signal to compensate for the channel ISI while keeping the transmitted power bounded. The proposed pre-equalization is particularly useful for data transmission over voice-band PCM channels. The upstream PCM channel is bandlimited, causing severe ISI at the output of the front-end receiver filter. By using the pre-equalizer at the transmitter, channel ISI can be mitigated.

Data transmission over bandlimited channels requires pulse shaping to eliminate or control intersymbol interference (ISI). Nyquist filters provide ISI-free transmission. Here we introduce a phase compensation technique to design Nyquist filters. Phase compensation can be applied to the square-root of any zero-phase bandlimited Nyquist filter with normalized excess bandwidth less than or equal to one. The resulting phase compensated square-root filter is also a Nyquist filter. In the case of a raised-cosine spectrum, the phase compensator has a simple piecewise-linear form. Such a technique is particularly useful to accommodate two different structures for the receiver, one with a filter matched to the transmitting filter and one without a matched filter. We also use the phase compensation technique to characterize a more general family of Nyquist filters which subsumes raised-cosine spectra. These generalized raised-cosine filters offer more flexibility in filter design. For instance, the rate of asymptotic decay of the filter impulse response may be increased, or the residual ISI, introduced by truncation of the impulse response, may be minimized. Design examples are provided to illustrate these choices.