Satellite networks are capable of contenting a variety of data transmission needs of users in geographically diverse locations throughout the world. Multi-layered satellite networks (MLSNs) can construct efficient communications networks due to their extensive coverage and high network capacity. However, throughput degradation and severe end-to-end delay could occur in MLSNs because of the traffic congestion. To resolve these problems, the authors first propose a novel MEO/LEO satellite network architecture that construct effective inter-satellite links. Then the authors present a network coding-based multi-path routing algorithm to deliver traffic through the hybrid satellite network. The analysis of characteristics of the proposed scheme are addressed by performance evaluations in simulation.

The global availability, strong resiliency and bandwidth management capability of the satellite technology together with the need of ICT solutions for the provision of reliable e-health services lead to the development of innovative technological mechanisms to be adopted in a comprehensive network resources management system for integrated professional medical services. A new paradigm of satellite telemedicine is proposed by the European Space Agency project, KosmoMed. Its aim is to design, develop, deploy and validate an ICT Professional Medical Platform for the delivery of innovative applications through an integrated satellite terrestrial network. To satisfy the end-user requirements in terms of perceived quality, a distributed booking databases system for the network resource management has been developed. A user-transparent system that automatically adapts the satellite bandwidth resources and activates the proper quality of service (QoS) strategies based on the requested service has been implemented. The overall system has been validated and an experimental campaign has been carried out. The fulfilment of the identified requirements is demonstrated by the QoS and quality of experience (QoE) results. This paper describes the solution proposed for the dynamic management of the bandwidth resources and provides an overview of the achieved results and lesson learnt.

The authors consider a low earth orbit (LEO) mobile satellite system (MSS) that accepts new and handover calls of multirate service-classes. New calls arrive in the system as batches, following the batched Poisson process. A batch has a generally distributed number of calls. Each call is treated separately from the others and its acceptance is decided according to the availability of the requested number of channels. Handover calls follow also a batched Poisson process. All calls compete for the available channels under the complete sharing policy. By considering the LEO-MSS as a multirate loss system with ‘satellite-fixed’ cells, it can be analysed via a multi-dimensional Markov chain, which yields to a product form solution (PFS) for the steady-state distribution. Based on the PFS, they propose a recursive and yet efficient formula for the determination of the channel occupancy distribution, and consequently, for the calculation of various performance measures including call blocking and handover failure probabilities. The latter are much higher compared to the corresponding probabilities in the case of the classical (and less bursty) Poisson process. Simulation results verify the accuracy of the proposed formulas. Furthermore, they discuss the applicability of the proposed model in software-defined LEO-MSS.

This study investigates the secrecy performance of a hybrid satellite-terrestrial relay network (HSTRN) in the presence of multiple eavesdroppers, where the satellite link undergoes Shadowed-Rician fading, while the terrestrial link follows Rayleigh fading. The authors suppose the direct link between the satellite and the intended user is unavailable due to heavy shadowing and adopt a multi-antenna relay using either a decode-and-forward (DF) or an amplify-and-forward (AF) protocol to assist the transmission. By employing perfect channel state information of each link at the relay, the authors first apply receive maximal ratio combining beamforming (BF) and transmit zero-forcing BF schemes to obtain the output signal-to-noise ratios (SNRs) of the intended user and eavesdroppers. Then, based on the Meijer-G function and the moment generating function, the authors derive the analytical expressions of the ergodic secrecy rate for the considered HSTRN for both DF and AF protocols. Finally, Monte-Carlo simulations are conducted to validate the theoretical performance analysis and reveal the effects of certain representative parameters on the system secrecy performance.

High-efficiency satellite-ground downlink data transmission system is being demanded to support increasing volume of data with limited spectrum resource. Considering the dynamic link conditions due to the orbital motion of low Earth orbit (LEO) satellite, variable coding modulated orthogonal frequency division multiplexing (VCM-OFDM) is proposed as an effective way to better exploit link resource. In this study, regarding the relative motion between the satellite on-board transmitter and the ground station receiver, filtered-OFDM signal is designed with adjustable coding modulation sets to achieve higher spectral efficiency and get along with the high-Doppler environment at the same time. Physical layer frame structure is proposed taking the Doppler frequency shift compensation into account with minimum overhead. System performance evaluations prove that transmission throughput in the dynamic communication link can be enhanced significantly by the proposed scheme, which indicates the potential for supporting future gigabit X-band reliable satellite-ground downlink transmissions.

Efficient estimation and synchronisation of transmission parameters is key for any satellite receiver, which is especially true for the recovery of carrier frequency and symbol timing. In this respect, a joint feedback solution has been analysed and tested in some recent work conducted by the authors. However, it turned out that the capture range of the carrier frequency is limited by the selected roll-off factor (excess bandwidth), which means that the synchroniser would not work properly for extremely bandwidth-efficient transmission schemes. This motivated them to modify the feedback structure by introducing a different filter operated in parallel to the receiver matched filter. In the sequel, it could be verified by analytical and simulation results that the initial frequency offset synchronised successfully can reach up to ±50% of the symbol rate irrespective of the selected modulation scheme, the roll-off factor, the signal-to-noise ratio value and the timing offset the satellite link is operated with. On top of that, a non-linear modification of the timing error detector has been investigated in detail, since the output of the conventional solution is nullified in case of extremely small excess bandwidths.

Two-way (on-frequency) relaying using simple amplify-and-forward processing at the satellite is an emerging technology that allows doubling of system spectral efficiency for certain networking applications. However, the satellite channel is non-linear and compensation for the self-interfering signal is more difficult than on linear channels, especially when memory effects are recognised. In this paper, we model two-user, asynchronous, bidirectional relaying for uncoded transmission, and proposed a bidirectional satellite communication algorithm under same frequency transmission. First, we employ a table addressed by side-information and the symbol to be detected to model the action of the channel. Then, we employ a linear adaptive canceler followed by a smaller table lookup process to cancel the self-interference and to make decisions. In the simulation part, we focus in the results section is upon 16-amplitude phase shift keying (APSK), widely employed in the DVB-S2 standard for bandwidth-efficient operation. Compared with the existing bidirectional satellite communication algorithm, our proposed algorithm have the far less complexity and training time at the similar performance.

For high data rates satellite systems, where multiple carriers are frequency division multiplexed with a slight overlap, the overall spectral efficiency is limited. This work applies highly overlapped carriers for satellite broadcast and broadband scenarios to achieve higher spectral efficiency. Spectrally efficient frequency division multiplexing (SEFDM) compresses subcarrier spacing to increase the spectral efficiency at the expense of orthogonality violation. SEFDM systems performance degrades compared to orthogonal signals, unless efficient interference cancellation is used. Turbo equalisation with interference cancellation is implemented to improve receiver performance for variable coding, compression and modulation/constellation proposals that may be applied in satellite communications settings. Such parameters may be set to satisfy pre-defined spectral efficiency values for a given quality index or associated application. Assuming low-density parity check coded data, the work proposes two approaches to receiver design: a simple matched filter approach and an approach utilising an iterative interference cancellation structure specially designed for SEFDM. Mathematical models and simulations studies are presented indicating promising gains to be achieved for SEFDM transmission with advanced transceiver architectures at the cost of increased complexity at the receiver.

This study proposes a graphene conductive ink printed textile-based microstrip antenna capable of switching between S-band (3.03 GHz, mode) and C-band (5.17 GHz, mode and 6.13 GHz, mode). The graphene conductive ink printed textile shows surface resistance of , conductivity of and excellent microstructural characteristics, which makes it suitable to be used as a metal sheet to fabricate the antenna structure. To overcome the low-conductivity issue of graphene conductive ink, a multilayered substrate approach is utilised to improve radiation performances of the antenna. A peak realised gain of 2.09 dBi and radiation efficiency of 74% is achieved at the dominant mode (3.03 GHz). The frequency reconfigurability is introduced by exciting the higher order modes, and through two different feeding locations. The excitation of ports is controlled through a radio frequency (RF) pin diode switch integrated microstrip transmission line. Subsequently, the proposed structure is further designed using copper foil of thickness () and a comparative analysis of graphene-based and copper-based antennas is presented. The proposed antenna performs substantially well in terms of peak realised gain and radiation efficiency compared with that of the existing graphene-based antenna and the performance deviation with respect to the copper based antenna is lowered significantly.

A new method based on the matrices reconstruction is proposed to deal with coherent signals in the presence of the unknown mutual coupling. By using a novel expression of the spatial covariance matrix in the presence of mutual coupling, the interference-plus-noise covariance matrix and the desired signal covariance matrix can be reconstructed via estimating the autocorrelation matrix of the signal envelope with unknown mutual coupling in an iteration process. Based on the criterion of the maximum output signal-to-interference-plus-noise ratio, a subspace orthogonal to the interference subspace can be then found out by using these reconstructed matrices. Therefore, the desired signal and the noise can be let out by mapping this estimated subspace to the observed data. Finally, an optimal weight vector can be obtained by maximising the output power of the desired signal. The performance of the proposed method is quite close to the optimal beamforming. The simulations demonstrate the effectiveness of the proposed beamformer.

In this study, a novel multi-beam pattern synthesis algorithm is proposed. The algorithm is divided into three steps. First, the pattern synthesis is performed for each beam without element excitation amplitude constraints, and form a element excitations amplitude matrix (EEAM). Second, the kernel principal component analysis (KPCA) technique is used to acquire a group of common element excitation amplitudes (CEEA). Finally, the semi-definite relaxation technique is employed to obtain the element excitation phase of each beam. The KPCA is a kind of principal component extraction method. Compared with the traditional method, the kernel function and the kernel parameter selection criterion used in the proposed study are designed to ensure that the extracted principal component can hold more than 80% of the information of the EEAM, which means that the acquired CEEA can bestly characterise the EEAM, hence resulting in a better synthesised pattern. In addition, the use of KPCA is a quasi-analytical process, which also speeds up the overall algorithm. Compared to the iterative multi-beam pattern synthesis algorithm, nearly half of the synthesis time is reduced. Through several sets of synthesised examples, and compared with some classical algorithms, this algorithm proves its superiority in the comprehensive effect and calculation time.

In this study, it is aimed to investigate the required signal-to-noise ratio (SNR) that provides a sufficient bit error rate (BER) according to the zenith angle between the ground station and satellite when pulse position modulation is utilised. Many parameters such as scintillation index, link distance, wavelength, Rytov variance, Fried's parameter, aperture diameter of the receiver and zenith angle have been considered to achieve realistic results. Due to the restrictions on the system, some parameters are specified as deterministic; the obtained results suggest that the required SNR value changes in a wide range from small to large values of the zenith angle to achieve sufficient BER. Therefore, either SNR adjustment as a function of the zenith angle is provided or the interval of the zenith angles to establish the link is determined previously in order to avoid the high link margin. It is shown that, instead of the second choice, aperture diversity is utilised at the receiver to establish communication even for large zenith angles with a reasonable value of the SNR. Besides aperture diversity, channel coding with error correction codes further improves the performance.

Underlay cognitive networks allow unlicenced/secondary users (SUs) to opportunistically access licenced frequency bands, and hence information transmission is undoubtedly wire-tapped by eavesdroppers. This study analyses security performance of a relay selection scheme, which selects a secondary relay to minimise information wire-tapping of eavesdroppers, in underlay cognitive networks. Toward this end, the authors propose approximate and asymptotic intercept outage probability expressions which account for interference power constraint for licenced/primary users, maximum transmit power constraint for SUs, independent non-identical fading channels, and direct channel between secondary source and eavesdropper. Moreover, they determine diversity order and coding gain of this relay selection based on the proposed asymptotic expression. Monte Carlo simulations validate these expressions and numerous results demonstrate that the investigated relay selection prevents the eavesdropper from obtaining full diversity order offered by all relays and source, induces the intercept outage probability saturated at either large maximum transmit power or large maximum interference power, and improves information security performance with respect to the increase in the number of relays.

A hybrid porous-core microstructure optical fibre (MOF) is proposed and its guiding properties are characterised for efficient terahertz wave guiding. A numerical investigation using the finite element method showed that a hybrid-core MOF consisted of a diamond-shaped cell and the circular arrangement of air holes exhibited an extremely low-bending loss of 5.24 × 10⁻¹³ cm⁻¹ for a bending radius of 1 cm and an operating frequency of 1.0 THz. The proposed fibre also showed a low effective material loss of 0.08 cm⁻¹ at an optimised core porosity of 52%. Moreover, single mode propagation, dispersion and fabrication feasibility of the proposed MOF are discussed. Due to the excellent guiding properties, this MOF can be potentially used in THz imaging, sensing and flexible communication applications.