Enhancing reliability in high-throughput satellites (HTS) operating in geostationary orbit (GEO) is critical, particularly under adverse channel conditions. This study investigates the potential of multi-connectivity (MC) enabled by carrier aggregation (CA) to improve the data rate, ensuring a high level of reliability of multi-band $\mathrm{K a} / \mathrm{Ku}$ GEO HTS systems. A system and channel model for the multi-band GEO satellite system is developed, and an inter-band CA algorithm is proposed. This algorithm dynamically adjusts the user link transmission scheme based on channel quality and user requirements, ranging from a single Ka-band connectivity to MC, utilizing both bands with CA via packet duplication or packet splitting. The numerical results in various weather scenarios validate the effectiveness of the algorithm, demonstrating significant improvements in system performance, reduced outage probability, and improved overall system reliability. These findings highlight the importance of MC and multi-band technologies in future $\mathrm{6 G}$ networks.

Visible Light Communications (VLC) is a candidate technology that complements the benefits of radio communication networks, particularly in those situations where a low-cost solution using license-free spectrum is required to enable ultra-dense deployments of indoor small cells. However, the main drawback that VLC has when compared to wireless communications on RF bands is that, in presence of obstacles between the transmitter and the receiver, full-blockage events are likely to happen as the power received on reflections is much weaker than the power of the blocked line-of-sight link. In this paper, we take advantage of this phenomenon and study the effect that different activities performed by people in the service area to-be-monitored have on the Automatic Repeat reQuest (ARQ) signaling of the VLC link. Based on the presented experimental studies, it is possible to conclude that different relevant events are able to be detected correctly according to the statistics of the ARQ signaling that is collected from the ongoing VLC transmission.

Next generation satellite payload technology is expected to provide digital processing capabilities. This will pave the way to regard satellites as flying base stations. However, the initial access procedure must be improved. In this work we focus on non-geostationary earth orbit (NGEO) satellite networks. In this scenario, the random access preamble signal and the detection must be robust to large carrier frequency offsets (CFOs). Towards this end, we investigate the adoption of the pruned discrete Fourier transform spread filter bank multicarrier waveform. The proposed design is suitable for the access scheme of forthcoming 5G-based NGEO satellite communications. The reason is twofold. First, it improves the spectral confinement with respect to the standard single-carrier frequency-division multiplexing (SC-FDM) waveform. Second, it achieves a high level of commonality with 5G new radio, by keeping unchanged the subcarrier spacing, the slot duration and the preamble sequence. Remarkably, the new design allows the straightforward application of non-coherent post detection integration (NCPDI) techniques, which divide the correlation in blocks. Numerical results show that the proposed solution reduces out-of-band emissions and the missed detection probability in presence of CFO, with respect to the conventional approach based on SC-FDM and preamble detection with full-length correlation.

Emerging Machine-to-Machine (M2M) applications demand small data packet sizes, very low latencies, and ultrahigh energy efficiencies. For all these reasons, Binary Bose-Chaudhuri-Hocquenhem (BCH) codes, which are very simple to implement, could constitute a good option to guarantee the required reliability of M2M transmissions. Nevertheless, existing delay and energy analyses of BCH decoders in the literature neither consider the channel statistics nor the first and second moments of the decoding delay. Therefore, they provide conservative codeword designs that lead to high delays and waste of energy. In this paper, we analyze the first and second moments of the delay and energy performance of Binary Bose-Chaudhuri-Hocquenhem (BCH) codes in realistic channel statistics to show that, if optimized, they can perform very efficiently for M2M transmissions. The results presented in this paper allow for the codeword length optimization for BCH codes given specific delay and energy constraints.

The spread spectrum modulation presents a more robust interference rejection capability than non-code–based modulations. However, the increase of the communication services has augmented the power of the interference signals. One example is unlicensed bands such as the 2.4–2.5 GHz one, where the DS-CDMA communications of the IEEE 802.11b standard are interfered with by other Industrial Scientific and Medical (ISM) services. One way of improving the interference robustness of the DS-CDMA receivers is introducing an interference canceler (IC) before the despreading stage. The optimum criterion to estimate or detect the interference is the maximum-a-posteriori (MAP) one. However, it requires a high computational burden and a complete knowledge of the statistical model, which reduce its feasibility. To overcome these drawbacks this article proposes an interference canceler based on Fuzzy Logic that allows (1) suppressing both analog and digital interferences, and (2) easily controlling the complexity versus performance trade-off. In other words, the design of the fuzzy canceler follows a down/top strategy; that is, a first low complex design is possible just departing from linguistic information and, in a second stage, we refine it, incorporating the available statistical information into its structure. Finally, to assess the proposed fuzzy canceler we have derived asymptotic performance bounds. © 2005 Wiley Periodicals, Inc. Int J Int Syst 20: 253–274, 2005.

The spread spectrum modulation presents a more robust interference rejection capability than the non code-based modulations. DS-SS communications are unlicensed and quite often used to support missions on mobile platforms. In particular, the unlicensed bands such as the Industrial Scientific and Medical (ISM) can seriously saturate the interference rejection of the spread spectrum systems. To overcome this drawback it is possible to use an interference canceller (IC) before the despreading stage. In order to design an optimum IC to suppress analog and digital interferences, we have to implement the Conditional Mean (CM) and the Maximum-A-Posteriori criteria. However, both filters present a high computational burden which reduces their real feasibility. In addition, the communication scenario could be corrupted by Gaussian or/and Non-Gaussian noise, which makes more complex the structure of the optimum detector. This paper proposes an interference canceller based on Fuzzy Logic that allows to suppress either analog or digital interferences and decreases the computational burden of the CM estimator and MAP detector.

The Bayesian or maximum a posteriori (MAP) symbol-by-symbol detector allows minimum BER single user detection in CDMA systems with less memory requirements than the multiuser maximum likelihood sequence estimator. This work proposes a further complexity reduction by developing a fuzzy recursive implementation of the Bayesian detector. Simulation studies demonstrate the almost optimal performance of the developed fuzzy detector. The resulting system offers a performance v.s. complexity trade-off very appealing for detection in a 3/sup rd/ generation mobile handset.

This work studies the usefulness of fuzzy rank ordering for multiuser code division multiple access (CDMA) detection. The robust performance of the proposed receiver is compared with that of two existing detectors.

The maximum likelihood sequence estimator (MLSE) and the Bayesian detector provide the best performance (at BER sense) under a data sequence or a symbol-by-symbol detection philosophy, respectively. However, these detectors present a high computational burden and are quite unaffordable for a mobile terminal that exploits also the spatial diversity. To overcome this problem fuzzy logic has been applied to design a new recursive space-time detector. Simulation results show that the proposed techniques reduce the computational burden and offer similar performance to that of the optimal one.

This work addresses the problem of spatial reference estimation in mobile scenarios. Novel techniques based on fuzzy logic are introduced to enhance the performance of a tracking system. Specifically, the model-free function approximation capability of fuzzy logic is used to obtain high resolution angle estimates from the spatial spectral density. These estimates are used to improve the resolution of the tracker. To the authors knowledge it is the first time that fuzzy logic is introduced in array spectral estimation. This work also develops a fuzzy controller for acting as an interpolative supervisor of different trackers that apply in different operating conditions of the dynamic nonlinear system. The result is a localization and tracking system that attains a resolution comparable to that of high resolution techniques as the minimum variance or Capon estimator. One of the main features of the proposed technique is its low computational burden. In summary, the presented system supports the expectation of adaptive arrays for obtaining a communication front-end of affordable complexity, developing cost and good performance.