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One of the significant challenges for satellite communications is to serve the ever-increasing demand for the use of finite resources. One option is to increase channel utilization, i.e., to transmit as much data as possible in a given frequency range. Since the channel is highly variable, primarily due to the ionosphere and troposphere, this goal can only be achieved by adaptively varying modulation and coding schemes. Most procedures and algorithms estimate the channel characteristics and descriptive quantities (e.g., signal-to-noise ratio). Ultimately, these procedures solve a regression problem. The resulting quantity is used as the basis for a decision process. Since valuation can also be subject to error, the decision mechanisms based on it must compensate and mitigate this error. The main element of the current research is to combine these two steps and solve them together using deep neural networks. The theoretical advantages of the method include that a better result can be achieved by having a joint estimation and decision process with a standard algorithm and cost function. The theoretical approach was tested with an actual protocol -- Digital Video Broadcasting - Satellite - Second Generation -- where we observed a significant improvement in channel utilization on previously recorded Alphasat satellite data.

One of the significant challenges for satellite communications is to serve the ever-increasing demand for the use of finite resources. One option is to increase channel utilization, i.e., to transmit as much data as possible in a given frequency range. Since the channel is highly variable, primarily due to the ionosphere and troposphere, this goal can only be achieved by adaptively varying modulation and coding schemes. Most procedures and algorithms estimate the channel characteristics and descriptive quantities (e.g., signal-to-noise ratio). Ultimately, these procedures solve a regression problem. The resulting quantity is used as the basis for a decision process. Since valuation can also be subject to error, the decision mechanisms based on it must compensate and mitigate this error. The main element of the current research is to combine these two steps and solve them together using deep neural networks. The theoretical advantages of the method include that a better result can be achieved by having a joint estimation and decision process with a standard algorithm and cost function. The theoretical approach was tested with an actual protocol – Digital Video Broadcasting - Satellite - Second Generation – where we observed a significant improvement in channel utilization on previously recorded Alphasat satellite data. [ABSTRACT FROM AUTHOR]

In this letter, a joint route selection and time‐slot allocation problem is formulated in a satellite‐terrestrial communication system. An optimization problem that minimizes the total system energy consumption is proposed to solve the formulated problem. Two algorithms, including a multi‐time‐expanding graph‐based maximum transmission rate route (MTEG‐R) selection algorithm and a minimum system energy consumption ‐ Dijkstra (MSEC‐D) algorithm, are proposed to find the optimal route and time‐slot for data transmission, and simulation results demonstrate the effectiveness of the proposed scheme. [ABSTRACT FROM AUTHOR]

Abstract The tracking and data relay satellite (TDRS) in geosynchronous orbit (GEO) can provide ranging and communication services for user spacecraft in low Earth orbit (LEO) through the inter‐satellite link (ISL). The time delay of TDRS ISL transponder in orbit differs from its pre‐launch state and changes due to the complex space environment, adding significant errors to the user spacecraft's orbit determination based on four‐way ranging data. The authors have developed a calibration system and proposed an efficient on‐orbit calibration method for the ISL transponder's time delay in TDRS. Experimental results demonstrate the effectiveness of the authors’ method, and the RMS of calibration residuals is less than 0.5 m.

Abstract In this letter, a novel digital pre‐distortion (DPD) scheme for an end‐to‐end forward link (FL) channel in a satellite internet network (SIN) is first proposed. It aims at the unprecedented challenge of the model of non‐stationary (NS) cascade response consisting of channel fading and non‐linear behaviour of onboard payload. Unlike most existing schemes, the proposed DPD scheme explores a new model to describe the distortion with improved band‐limited memory polynomial (BLMP) by the equivalent response. To decrease the complexity of utilization, the authors design a new strategy to divide the unified non‐stationary situation into several different stationary situations. Meanwhile, a space‐time‐frequency stationary window function (STF‐WF) is proposed to compensate for the signal distortion. The experimental results demonstrate that the proposed schemes realize maximum total degradation (TD) gain by 15%.

The tracking and data relay satellite (TDRS) in geosynchronous orbit (GEO) can provide ranging and communication services for user spacecraft in low Earth orbit (LEO) through the inter‐satellite link (ISL). The time delay of TDRS ISL transponder in orbit differs from its pre‐launch state and changes due to the complex space environment, adding significant errors to the user spacecraft's orbit determination based on four‐way ranging data. The authors have developed a calibration system and proposed an efficient on‐orbit calibration method for the ISL transponder's time delay in TDRS. Experimental results demonstrate the effectiveness of the authors' method, and the RMS of calibration residuals is less than 0.5 m. [ABSTRACT FROM AUTHOR]

In this letter, a novel digital pre‐distortion (DPD) scheme for an end‐to‐end forward link (FL) channel in a satellite internet network (SIN) is first proposed. It aims at the unprecedented challenge of the model of non‐stationary (NS) cascade response consisting of channel fading and non‐linear behaviour of onboard payload. Unlike most existing schemes, the proposed DPD scheme explores a new model to describe the distortion with improved band‐limited memory polynomial (BLMP) by the equivalent response. To decrease the complexity of utilization, the authors design a new strategy to divide the unified non‐stationary situation into several different stationary situations. Meanwhile, a space‐time‐frequency stationary window function (STF‐WF) is proposed to compensate for the signal distortion. The experimental results demonstrate that the proposed schemes realize maximum total degradation (TD) gain by 15%. [ABSTRACT FROM AUTHOR]

Predicting precipitation rate and rainfall attenuation are key aspects in planning and dimensioning of wireless communications systems operating at frequencies above 10 GHz, such as satellite communication systems at Ku and Ka bands. In this paper, contour maps of rainfall rate and rain attenuation are developed for the first time in Venezuela, based on 1-min rain rate statistics obtained from measurements carried out in Venezuela over at least 30 years period with a higher integration time and using Rice-Holmberg model, refined Moupfouma-Martin model and Recommendation ITU-R P.837-7, for rain rate estimation and Recommendation ITU-R P.618-13, Ramachandran-Kumar model, Yeo-Lee-Ong model and Rakshit-Adhikari-Maitra model, for rain attenuation prediction in “Simon Bolivar” satellite links in Venezuela. The overall results of both types of maps represent a useful tool for preliminary planning of those links in the country, specifically, in Ku and Ka bands

First built models of Remotely Piloted Air System (RPAS) communication channels based on Wideband Code Division Multiple Access (WCDMA) 3GPP Standard were designed. Base Station (BS) transmission within the Radio Line of Sight (RLoS) and through the satellite using Beyond Radio Line of Sight (BRLoS) was considered. The dependencies of the Bit Error Rate (BER) on the signal-noise ratio for different RPAS velocities and WCDMA сhannel models were obtained. The dependences of the BER on the signal-noise ratio for different levels of satellite transponder nonlinearity were studied. The dependence of the BER on the BS antenna diameter in case of the transponder nonlinearity was analysed. The dependencies for satellite channel characteristics, first obtained taking into account the motion of the RPAS, make it possible to predict the behavior of the communication system in critical conditions.

Shipboard platforms have numerous antennas crowding topside space. Consolidating these antennas would require having antennas with multi-frequency capabilities. A Gregorian parabolic stacked antenna provides multi-frequency capabilities on a single pedestal which reduces the number of antennas required on a US Navy shipboard platforms. This Letter depicts the simulated design and radiation pattern results of a 1.9 m Gregorian parabolic stacked antenna that is capable of operating at the X-, K-, Ka- and Q-band frequencies at VSWR values <2:1. These frequency band capabilities allow for satellite communication links where two antennas that are currently fielded are operating within. The dual Gregorian parabolic stacked antenna presented is capable of operating at the same frequencies on a single antenna pedestal which would reduce the number of antennas required on shipboard platforms. [ABSTRACT FROM AUTHOR]

Existing high‐precision inter‐satellite radio frequency (RF) measurement systems were mostly based on two‐satellite formations, and there lacks further research on measurement schemes for multi‐satellite formations. The frequency division multiple access (FDMA) and the code division multiple access based schemes are widely used, but not applicable for distributed applications due to their poor scalability. The time division multiple access (TDMA) based scheme can overcome this weakness, and has been applied in the global positioning system (GPS) IIR/IIF inter‐satellite link. However, the atomic clock used in GPS is not suitable for microsatellites. If a miniaturised frequency source instead of the atomic clock is utilised, the two way ranging (TWR) method adopted in this system would encounter a sharp decrease of measurement accuracy. To this end, this Letter aims to propose a novel TDMA based distributed RF measurement scheme for multi‐microsatellite formations. A TDMA based distributed broadcast protocol is employed in the media access control layer, closely integrated with the asymmetric double‐sided two‐way ranging method adopted in the physical layer. Numerical and simulation results demonstrate the superiority of the proposed scheme over the conventional TDMA scheme. The proposed scheme can be recommended for future multi‐microsatellite formation missions. [ABSTRACT FROM AUTHOR]

First built models of Remotely Piloted Air System (RPAS) communication channels based on Wideband Code Division Multiple Access (WCDMA) 3GPP Standard were designed. Base Station (BS) transmission within the Radio Line of Sight (RLoS) and through the satellite using Beyond Radio Line of Sight (BRLoS) was considered. The dependencies of the Bit Error Rate (BER) on the signal-noise ratio for different RPAS velocities and WCDMA hannel models were obtained. The dependences of the BER on the signal-noise ratio for different levels of satellite transponder nonlinearity were studied. The dependence of the BER on the BS antenna diameter in case of the transponder nonlinearity was analysed. The dependencies for satellite channel characteristics, first obtained taking into account the motion of the RPAS, make it possible to predict the behavior of the communication system in critical conditions. [ABSTRACT FROM AUTHOR]

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Long-distance entanglement is a very precious resource, but its distribution is very difficult due to the exponential losses of light in optical fibres. A possible solution consists in the use of quantum repeaters, based on entanglement swapping (ES) or quantum error correction. Alternatively, satellite-based free-space optical links can be exploited, achieving better loss-distance scaling. We propose to combine these two ingredients, quantum repeaters and satellite-based links, into a scheme that allows to achieve entanglement distribution over global distances with a small number of intermediate untrusted nodes. The entanglement sources, placed on satellites, send quantum states encoded in photons towards orbiting quantum repeater stations, where ES is performed. The performance of this repeater chain is assessed in terms of the secret key rate achievable by the BBM92 cryptographic protocol. We perform a comparison with other repeater chain architectures and show that our scheme, even though more technically demanding, is superior in many situations of interest. Finally, we analyse strengths and weaknesses of the proposed scheme and discuss exemplary orbital configurations. The integration of satellite-based links with ground repeater networks can be envisaged to represent the backbone of the future quantum internet.

A phenomenon that also causes impairment in the received signal strength of the RF signal in satellite links operating at frequencies above 10 GHz, especially in those systems that operate at higher frequencies with small fade margins, is the tropospheric scintillation that occurs in the lower layer of the troposphere. In order to estimate the intensity, i.e. the variance between the scintillation amplitude fluctuations, there are several models in the literature, whose accuracy depends on the locality in which the models are implemented. In this Letter, new models are developed for the prediction of tropospheric scintillation that adjusts to localities in Spain, specifically Madrid city, based on measurements of the aforementioned phenomenon reported from Spain and the bios‐inspired technique Cuckoo Search (CS). The results obtained, evaluated in terms of the root mean square error, were totally satisfactory, being the most outstanding cases the improved versions of the Ortgies‐T, Statistical Temperature and Humidity 2 and Statistical Temperature and Refractivity 2 models. [ABSTRACT FROM AUTHOR]

A satellite-based measurement-device-independent quantum key distribution model is proposed and its performance is analyzed through numerical simulations. The simulation result shows that the key rate increases almost linearly as transmittance increases and the higher the key rate is, the lower its probability may be. More significantly, as the transmission distance increases, the optimal intensities of the signal states decrease while those of the decoy states increase. The optimal values in the daytime are slightly larger than those at night. This work may provide some important parameters for the relevant experiment on satellite-based quantum communication network.

The design of spectrally-efficient, high-throughput satellite (HTS) systems with capacity approaching one terabit per second requires operating at Ka-band frequencies and above, where there are several gigahertz of allocated radio spectrum, using multiple spot beams with dual orthogonal polarisation mode. At these high frequencies, rain attenuation poses a major obstacle to the design of high-availability satellite links which are needed for the realisation of ubiquitous broadband multimedia communication services including high-speed Internet access at rural and remote locations. Furthermore, depolarisation-induced interference in such systems could have a performance-limiting impact if a co-channel cross-polar signal combines with system noise to drive the carrier-to-noise-plus-interference ratio (CNIR) below an acceptable threshold. This paper employs real measurement data to investigate the impact of depolarisation-induced interference on dual-polarised HTS systems for temperate and tropical climatic regions. Scenarios that cause significant system performance degradation are analysed, including the effects of signal frequency, antenna size, and regional rainfall rate. The impact of depolarisation on system performance is quantified by the reductions in the CNIR and link availability of a dual-polarised system when compared with those of a similarly-dimensioned single-polarised system.

The establishment of a world-wide quantum communication network relies on the synergistic integration of satellite-based links and fiber-based networks. The first are helpful for long-distance communication, as the photon losses introduced by the optical fibers are too detrimental for lengths greater than about 200 km. This work aims at giving, on the one hand, a comprehensive and fundamental model for the losses suffered by the quantum signals during the propagation along an atmospheric free-space link. On the other hand, a performance analysis of different quantum key distribution (QKD) implementations is performed, including finite-key effects, focusing on different interesting practical scenarios. The specific approach that we chose allows to precisely model the contribution due to different weather conditions, paving the way towards more accurate feasibility studies of satellite-based QKD missions.

The performance of optical inter‐satellite communications using microwave photonics technologies employing intensity modulation with direct detection (IMDD) and phase modulation (PM) with interferometric detection are investigated and demonstrated with a numerical example. The theoretical model considering the saturated gain and amplifier spontaneous emission noise of optical booster amplifier and optical preamplifier is constructed for both architectures. Furthermore, the authors compare the performance of PM with interferometric detection to optimum biased IMDD in terms of radio frequency (RF) gain, RF noise figure and compression dynamic range (CDR). The numerical results show that the PM with interferometric detection can achieve better RF gain, RF noise figure and CDR than the optimum biased IMDD link as the laser output power is lower than 14.34, 12.45 and 4.2 dBm, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Fade duration database was built to enhance the study of propagation characterises in the Equatorial region. The data was measured via a beacon receiver Ku-band whereby the antenna was directed to a SUPERBIRD-C2 satellite at 12.255GHz. The performance of the measured data has been compared with ITU-R model, Kormanyos et al. and Paulson–Gibbins. The results show that the Paulson–Gibbins fits well with measured data with a low RMS error of 0.2dB. The number of statistics available for the equatorial is small and the periods of measurement are short compared to those for temperate regions. [Copyright &y& Elsevier]

An exact analytical expression of signal‐to‐noise ratio (SNR) for inter‐satellite microwave photonics links using a low‐biased Mach‐Zehnder modulator, and with both an optical booster amplifier and a preamplifier, is derived with the method of Bessel expansion and Graf's addition theorem. It is observed that the most limitative noise is changed from the thermal noise to the signal‐amplifier spontaneous emission beating noise that arises from the optical preamplifier, and the signal power is seen to increase more compared with the power of noise because of optical preamplifier. Thus, the SNR of system configurations with both an optical booster amplifier and an optical preamplifier can be improved compared with the SNR of system configurations with only an optical booster amplifier. For the preamplifier gain of 20 dB and noise figure of 3 dB, an increase of about 19.7 dB in optimum SNR is accessible. In addition, the effect of optical booster amplifier and preamplifier parameters on the optimum DC bias phase shift and SNR is also investigated. [ABSTRACT FROM AUTHOR]

In this paper, a semi-empirical method for the prediction of rain attenuation in slant paths and terrestrial links is proposed. The method uses the same simplified model of equivalent rain cell that is the basis for the ITU-R rain attenuation prediction methods but, additionally, the concept of an effective rain rate is introduced. This allows the use of the full rainfall rate distribution for the prediction of the rain attenuation distribution and the unification of the slant path and terrestrial links prediction algorithms. The numerical coefficients in the method's expressions were derived by multiple non-linear regressions using the experimental data currently available in the ITU-R data banks. Test results indicate that the proposed method provides significant improvement over the current ITU-R methods. [ABSTRACT FROM AUTHOR]

A deep space satellite downconverter receiver was proposed by Jet Propulsion Laboratory (JPL) and NASA Lewis Research Center (LeRC) for the Naval Research Laboratory's (NRL) high temperature superconductivity space experiment, phase-II (HTSSE-II) program. Space qualified low-noise cryogenic downconverter receivers utilizing thin-film high temperature superconducting (HTS) passive circuitry and semiconductor active devices were developed and delivered to NRL. The downconverter consists of an HTS preselect filter, a cryogenic low-noise amplifier; a cryogenic mixer, and a cryogenic oscillator with an HTS resonator. HTS components were inserted as the front-end filter and the local oscillator resonator for their superior 77 K performance over the conventional components. The semiconducting low noise amplifier also benefited from cooling to 77 K. The mixer was designed specifically for cryogenic applications and provided low conversion loss and low power consumption. In addition to an engineering model, two space qualified units (qualification, flight) were built and delivered to NRL. Manufacturing ,integration and test of the space qualified downconverters adhered to the requirements of JPL class-D space instruments and partially to MIL-STD-883D specifications. The qualification unit has /spl sim/50 K system noise temperature which is a factor of three better than a conventional downconverter at room temperature. Commercial applications such as intersatellite links and V-SATS are envisioned to benefit by >3 dB link margin, or a factor of 2 in antenna size, from a future hybrid HTS/semiconducting cryogenic receiver employing new InP based HEMT LNA. In a spread spectrum communication network, the number of users per beam would more than double. [ABSTRACT FROM AUTHOR]

Available beyond line‐of‐sight time synchronisation means are mainly through satellite and optical fibres. When considering that satellite links have insurmountable bandwidth and security problems, and cable links are not feasible for mobile stations, a backup two‐way time synchronisation means via troposcatter is proposed. The feasibility of the proposed method based on coherence bandwidth and transmission loss is analysed, and references for the time pulse signal design are provided. Then, two different signal time sequences schemes aiming at co‐channel interference are presented and evaluated, and the clock errors due to the incomplete symmetrical two‐way link are analysed. Finally, it is concluded that the proposed means is a promising candidate for beyond line‐of‐sight time synchronisation in emergency communication. [ABSTRACT FROM AUTHOR]