Satellite Uplink Research Articles

Focal-Plane Multibeam Dual-Band Dielectric Lens for Ka-Band

A shaped double-shell dielectric lens is evaluated as a primary feed for a multibeam single-reflector system operating in the satellite uplink and downlink Ka-bands, complying with gain and edge-of-coverage (EoC) directivity requirements. An assembly of dual-band printed feeds is integrated at the base of a single lens, each feed producing a virtual focus far behind the lens base and coincident with the reflector focal arch. The used double-shell lens approach, instead of a single-material lens, allows an extra degree of freedom to accommodate an aberration mitigation condition. This primary feed system is proposed as a low-complexity solution to enable fitting more beams per solid angle than conventional single-feed-per-beam systems based on a cluster of focal-plane horns. A proof-of-concept lens prototype with 87 mm diameter and 62 mm height, fed by a linear arrangement of five dual-band printed feeds, was fabricated and tested at the Ka-band. The lens measured radiation patterns were post-processed to evaluate the combined performance of the lens with an offset F/D ≈ 1 reflector system designed for 45-dBi EoC directivity. It is shown that it duplicates the reflector aperture efficiency compared to horn-fed systems with same feed separation.

Making the Most of Digital Collections through Training and Outreach: The Innovative Librarian’s Guide. By Nicholas Tanzi. Santa Barbara, CA: Libraries Unlimited, 2016. Pp. x+140. $50.00 (paper). ISBN 978-1-4408-4072-2.

<i>Making the Most of Digital Collections through Training and Outreach: The Innovative Librarian’s Guide</i>. By Nicholas Tanzi. Santa Barbara, CA: Libraries Unlimited, 2016. Pp. x+140. $50.00 (paper). ISBN 978-1-4408-4072-2.

OFDM-Like Signaling for Broadband Satellite Applications: Analysis and Advanced Compensation

Orthogonal frequency-division multiplexing (OFDM), special form of multicarrier modulation, is the cornerstone of broad range of current standards. In addition, fifth-generation (5G) terrestrial wireless networks, advancing at accelerated speed, continue to use OFDM air interface. The first part of this paper endeavors to apply OFDM-like signaling for broadband satellite transmission in the forward direction, from gateway to terminals. Two layers of multicarrier operation are invoked. One allows multiple signals to share single on-board high-power amplifier. The other layer permits transmitted symbols from individual signals to modulate multiple narrowband OFDM subcarriers, followed by interpolating filters to suppress interference into adjacent signals and limit out-of-band emission to be compatible with satellite uplink. The second part of this paper proposes novel nonlinear compensation techniques, applied at the transmitter or receiver, and combination of both. Two performance assessments are provided: one exploiting information-theoretic framework using ideal channel coding; another based on total degradation using practical forward-error correction codes. We show that performance loss from nonlinear distortion can be significantly reduced when adopting the proposed correction methods. Furthermore, it is possible to use OFDM-like signaling over satellite, while being competitive, and in some cases surpassing, traditional systems with single-carrier modulation employing state-of-the-art enhanced receiver architecture.

Investigation on adaptive optics performance from propagation channel characterization with the small optical transponder

In order to address the high throughput requested for both downlink and uplink satellite to ground laser links, adaptive optics (AO) has become a key technology. While maturing, application of this technology for satellite to ground telecommunication, however, faces difficulties, such as higher bandwidth and optimal operation for a wide variety of atmospheric conditions (daytime and nighttime) with potentially low elevations that might severely affect wavefront sensing because of scintillation. To address these specificities, an accurate understanding of the origin of the perturbations is required, as well as operational validation of AO on real laser links. We report here on a low Earth orbiting (LEO) microsatellite to ground downlink with AO correction. We discuss propagation channel characterization based on Shack–Hartmann wavefront sensor (WFS) measurements. Fine modeling of the propagation channel is proposed based on multi-Gaussian model of turbulence profile. This model is then used to estimate the AO performance and validate the experimental results. While AO performance is limited by the experimental set-up, it proves to comply with expected performance and further interesting information on propagation channel is extracted. These results shall help dimensioning and operating AO systems for LEO to ground downlinks.

Performance enhancement of free space optical satellite uplink with transmitter spatial diversity technique

In this paper, the performance analysis of a Free Space Optical (FSO) satellite link from Earth to Geostationary Earth Orbit (GEO) satellite is carried out by considering atmospheric turbulence effects. It is observed that spatial diversity is a feasible option at the transmitter side and not at the receiver side. Further, increasing aperture diameter improves the performance due to higher received power (and not because of aperture averaging) and the improvement with increase in aperture diameter is higher at lower ground turbulence levels. For transmitter spatial diversity, the arrangement of transmitters in order to minimize correlation between the received beams is discussed. Initially, we see that there is considerable improvement in link performance by increasing the number of transmitters and the law of diminishing returns sets in with further increase in the number of transmitters. The expression of capacity with outage is derived. It is observed from the results that the maximum achievable capacity increases and the corresponding outage probability reduces with an increase in the number of transmitters for the same average received signal to noise ratio.

A low-cost fiberglass polymer resin dielectric material-based microstrip patch antenna for multiband applications

AbstractThe design analysis and prototype of a compact 8×10-mm2 planar microstrip line-fed patch antenna on a readily available, low-cost, reinforced-fiberglass polymer resin composite material substrate is presented in this article. The proposed compact-size antenna has been configured and numerically analyzed using the finite element method-based three-dimensional full-wave electromagnetic field simulator. The optimized design of the antenna has been fabricated on a printed circuit board (PCB), and experimental results have been collected for further analysis. The measurement results affirm the fractional impedance bandwidths of (return loss of less than -10 dB) of 38.78% (2.03–2.98 GHZ) and 16.3% (5.38–6.35 GHz), with average gains of 2.52 and 3.94 dBi at both lower and upper bands, respectively. The proposed dual resonant antenna shows the radiation efficiencies of 91.3% at 2.45 GHz and 87.7% at 5.95 GHz. The stable and almost symmetric radiation patterns and performance criteria of the antenna can successfully cover IEEE 802.11b/g/n, Bluetooth, WLAN, and C-band telecommunication satellite uplinks.

Lab Measures of Other-Regarding Preferences Can Predict Some Related On-the-Job Behavior: Evidence from a Large Scale Field Experiment

We measure a specific form of other-regarding behavior, costly cooperation with an anonymous other, among 645 subjects at a trucker training program in the Midwestern US. Using subjects’ second-mover strategy in a sequential form of the Prisoners’ Dilemma, we categorize subjects as: Free Rider, Conditional Cooperator, and Unconditional Cooperator. We observe the subjects on the job for up to two years afterwards in two naturally-occurring choices – whether to send two types of satellite uplink messages from their trucks. The first identifies trailers requiring repair, which benefits fellow drivers, while the second benefits the experimenters by giving them some follow-up data. Because of the specific nature of the technology and job conditions (which we carefully review) each of these otherwise situationally similar field decisions represents an act of costly cooperation towards an anonymous other in a setting that does not admit of repeated-game or reputation-effect explanations. We find that individual differences in costly cooperation observed in the lab do predict individual differences in the field in the first choice but not the second. We suggest that this difference is linked to the difference in the social identities of the beneficiaries (fellow drivers versus experimenters), and we conjecture that whether or not individual variations in pro-sociality generalize across settings (whether in the lab or field) may depend in part on this specific contextual factor: whether the social identities, and the relevant prescriptions (or norms) linked to them that are salient for subjects (as in Akerlof and Kranton (2000); (2010)), are appropriately parallel.

Experimental quantum key distribution with simulated ground-to-satellite photon losses and processing limitations

Quantum key distribution (QKD) has the potential to improve communications security by offering cryptographic keys whose security relies on the fundamental properties of quantum physics. The use of a trusted quantum receiver on an orbiting satellite is the most practical near-term solution to the challenge of achieving long-distance (global-scale) QKD, currently limited to a few hundred kilometers on the ground. This scenario presents unique challenges, such as high photon losses and restricted classical data transmission and processing power due to the limitations of a typical satellite platform. Here we demonstrate the feasibility of such a system by implementing a QKD protocol, with optical transmission and full post-processing, in the high-loss regime using minimized computing hardware at the receiver. Employing weak coherent pulses with decoy states, we demonstrate the production of secure key bits at up to 56.5 dB of photon loss. We further illustrate the feasibility of a satellite uplink by generating secure key while experimentally emulating the varying channel losses predicted for realistic low-Earth-orbit satellite passes at 600 km altitude. With a 76 MHz source and including finite-size analysis, we extract 3374 bits of secure key from the best pass. We also illustrate the potential benefit of combining multiple passes together: while one suboptimal "upper-quartile" pass produces no finite-sized key with our source, the combination of three such passes allows us to extract 165 bits of secure key. Alternatively, we find that by increasing the signal rate to 300 MHz it would be possible to extract 21570 bits of secure finite-sized key in just a single upper-quartile pass.

Resource Allocation for Cognitive Satellite Communications With Incumbent Terrestrial Networks

The lack of available unlicensed spectrum together with the increasing spectrum demand by multimedia applications has resulted in a spectrum scarcity problem, which affects satellite communications (SatCom) as well as terrestrial systems. The goal of this paper is to propose resource allocation (RA) techniques, i.e., carrier, power, and bandwidth allocation, for a cognitive spectrum utilization scenario where the satellite system aims at exploiting the spectrum allocated to terrestrial networks as the incumbent users without imposing harmful interference to them. In particular, we focus on the microwave frequency bands 17.7–19.7 GHz for the cognitive satellite downlink and 27.5–29.5 GHz for the cognitive satellite uplink, although the proposed techniques can be easily extended to other bands. In the first case, assuming that the satellite terminals are equipped with multiple low block noise converters (LNB), we propose a joint beamforming and carrier allocation scheme to enable cognitive space-to-Earth communications in the shared spectrum where fixed service (FS) microwave links have priority of operation. In the second case, however, the cognitive satellite uplink should not cause harmful interference to the incumbent FS system. For the latter, we propose a joint power and carrier allocation (JPCA) strategy followed by a bandwidth allocation scheme, which guarantees protection of the terrestrial FS system while maximizing the satellite total throughput. The proposed cognitive satellite exploitation techniques are validated with numerical simulations considering realistic system parameters. It is shown that the proposed cognitive exploitation framework represents a promising approach for enhancing the throughput of conventional satellite systems.

A drifter for measuring water turbidity in rivers and coastal oceans

A disposable instrument for measuring water turbidity in rivers and coastal oceans is described. It transmits turbidity measurements and position data via a satellite uplink to a processing server. The primary purpose of the instrument is to help document changes in sediment runoff from river catchments in North Queensland, Australia. The ‘river drifter’ is released into a flooded river and drifts downstream to the ocean, measuring turbidity at regular intervals. Deployment in the Herbert River showed a downstream increase in turbidity, and thus suspended sediment concentration, while for the Johnstone River there was a rapid reduction in turbidity where the river entered the sea. Potential stranding along river banks is a limitation of the instrument. However, it has proved possible for drifters to routinely collect data along 80km of the Herbert River. One drifter deployed in the Fly River, Papua New Guinea, travelled almost 200km before stranding.

Fiber coupling efficiency in non-Kolmogorov satellite links

Behavior of the fiber coupling efficiency in non-Kolmogorov satellite links is investigated. Examining the fiber coupling efficiency of downlink versus the non-Kolmogorov power law exponent for different rms wind speeds, zenith angles, receiver lens diameters, structure constants and the wavelengths, the fiber coupling efficiency is found to decrease when the non-Kolmogorov power law exponent increases. At a fixed non-Kolmogorov power law exponent, the fiber coupling efficiency of downlink is found to decrease as the rms wind speed, the zenith angle, the receiver lens diameter or the structure constant increases and the wavelength decreases. For any non-Kolmogorov satellite downlink, the reduction of coherence length will make the optimum design parameter larger. And when the fiber coupling efficiency is considered in the satellite uplinks, the effect of non-Kolmogorov turbulence can be neglected.

Strategy for Interference Mitigation from Terrestrial Radio Terminals in Satellite Uplinks

Strategy for Interference Mitigation from Terrestrial Radio Terminals in Satellite Uplinks

An omnidirectional PIFA for downlink and uplink satellite applications in C‐band

ABSTRACTIn this article, we present a dual band planar inverted‐F antenna (PIFA) for downlink and uplink satellite systems in C‐band frequency range. The proposed antenna is fabricated on an FR4 substrate with dielectric constant of 4.4. By cutting a pair of T‐shaped slits in the ground plane, and also by embedding a meander‐line slit in the ground plane a good dual‐band operation antenna can be achieved. The measured impedance bandwidth for 10 dB return loss is from 3.625–4.200 GHz (14%) and 5.850–6.425 GHz (9%), covering the down/up links of satellite communications. Simulated and experimental results obtained for this antenna show that the proposed PIFA has good antenna gain and radiation behavior in the operation bands. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2684–2686, 2014

Just Communicating

Just Communicating

Orthogonal multicarrier modulations in satellite uplinks

SUMMARYIn this paper, we analyze Orthogonal Frequency‐Division Multiple Access and Single‐Carrier Frequency Division Multiple Access as alternative physical layer schemes for the up‐link of a satellite network. Both orthogonal frequency‐division multiple access and single‐carrier frequency division multiple access are orthogonal multicarrier modulations (MCMs). They provide a higher spectral efficiency than the single‐carrier modulations employed today in satellite networks. Unfortunately, MCMs are also more vulnerable to nonlinear distortion, phase noise, and synchronization errors. This has prevented, so far, the use of MCMs in satellite uplinks, where these impairments are very critical. In our analysis, we show that a well‐design MCM system can effectively provide reliable communications in satellite uplinks, even in the presence of nonlinear distortion, phase noise, and synchronization errors. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Multiple fractal-shaped slots-based UWB antenna with triple-band notch functionality

A planar elliptical shape band-notched UWB antenna with multiple fractal-shaped slots and a Sierpinski fractal curve-shaped ring resonator at the back of the substrate is introduced in this paper. The proposed antenna exhibits a triple-band notch characteristic. Koch fractal slot etched from the radiator is responsible for creating notched band centred at 5.5 GHz for wireless local area network rejection. The Minkowski fractal slots in the ground planes create rejection characteristics at 8.1 GHz to avoid interference with X-band uplink satellite communication systems. The RFID rejection band centred at 6.8 GHz is achieved by using a Sierpinski fractal curve-shaped ring resonator at the back of the substrate. Sierpinski fractal slot of third iteration on the radiator contributes to an impedance bandwidth of 2.8–12 GHz with VSWR < 2 by improving matching at lower frequencies except at three notched bands. The antenna gain varies from 1.5 to 4 dBi over the band. Stable radiation patterns are obtained throughout its operating frequency. The antenna has a compact size of 41 mm × 45 mm.

Compact thin ground plane UWB antenna with dual band stop characteristics

AbstractA compact coplanar waveguide (CPW)‐fed convex hexagonal‐shaped ultrawide band (UWB) antenna, with L‐shaped thin ground plane for lower frequency band stop function and tapered rectangular vertical slot in radiating patch for upper frequency band stop is presented. The proposed antenna of dimension 40 × 22 × 1.6 mm3 provides good impedance matching over dual operational UWB resonating at 5.4 and 9.6 GHz with fractional bandwidth 69.54 and 33.83%, respectively. The lower frequency stop band in the vicinity of 2.4 GHz and higher frequency stop band in the vicinity of 7 GHz has bandwidth of 3.17 and 1.8 GHz, respectively, to avoid the interference of PCS, GSM 800/1900, ISM, WLAN, and X‐band satellite uplink (7.25–7.75 GHz) and downlink (7.9–8.4 GHz) communication system. The E‐plane radiation pattern observed is bidirectional in nature due to CPW feed and that of the H‐plane pattern is omnidirectional. The resonating lower and higher UWB achieves the peak gain 2.16 and 6.5 dBi, respectively. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1045–1049, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27470

Design and Performance of a 600-W $C$-Band Amplifier Using Spatially Combined GaAs FETs for Satellite Communications

This paper describes the design and performance of a C-band amplifier with over 600 W of saturated output power. This amplifier is intended for use in commercial broadcast satellite uplink base stations. The amplifier uses spatial power combining to combine the output powers of sixteen internally matched 45-W GaAs FETs. The amplifier also comprises pre-amplification and driver amplification stages, a level control variable attenuator, and a predistortion linearizer. The unit also includes a power supply as well as a user monitor and control interface. We will present various measures of this amplifier's linearity performance, demonstrating its suitability for use in broadcast applications. Finally, we will present results from power combining two of these amplifiers, resulting in a solid-state amplifier with 1.4 kW of saturated C-band output power.

A Comparative Study Between SC-FDMA and OFDMA Schemes for Satellite Uplinks

This paper presents a detailed comparative study of two single-carrier frequency-division multiple access (SC-FDMA) schemes, namely localized FDMA scheme (LFDMA) and interleaved FDMA scheme (IFDMA), versus orthogonal FDMA scheme (OFDMA), for a satellite uplink. The air-interface of the latter is based on the digital video broadcasting (DVB) family of standards. Considering two state-of-the-art high power amplifiers (HPAs), operating in the K- and S-bands, the performance of synchronous and asynchronous LFDMA, IFDMA and OFDMA is evaluated in a multi-user environment. Systematic comparison results show that although for synchronous reception IFDMA outperforms the other two schemes, for asynchronous reception it is the most sensitive to degradation caused by inter-block interference (IBI). Furthermore, due to its relatively large envelope fluctuations, OFDMA is the most sensitive scheme to non-linear distortion. Although for synchronous reception LFDMA shows only slightly inferior performance as compared to IFDMA, it outperforms the other two schemes for the asynchronous reception considered, especially for increased IBI distortion.

Borehole temperatures reveal details of 20th century warming at Bruce Plateau, Antarctic Peninsula

Abstract. Two ice core boreholes of 143.18 m and 447.73 m (bedrock) were drilled during the 2009–2010 austral summer on the Bruce Plateau at a location named LARISSA Site Beta (66°02' S, 64°04' W, 1975.5 m a.s.l.). Both boreholes were logged with thermistors shortly after drilling. The shallow borehole was instrumented for 4 months with a series of resistance thermometers with satellite uplink. Surface temperature proxy data derived from an inversion of the borehole temperature profiles are compared to available multi-decadal records from weather stations and ice cores located along a latitudinal transect of the Antarctic Peninsula to West Antarctica. The LARISSA Site Beta profiles show temperatures decreasing from the surface downward through the upper third of the ice, and warming thereafter to the bed. The average temperature for the most recent year is −14.78°C (measured at 15 m depth, abbreviated T15). A minimum temperature of −15.8°C is measured at 173 m depth, and basal temperature is estimated to be −10.2°C. Current mean annual temperature and the gradient in the lower part of the measured temperature profile have a best fit with an accumulation rate of 1.9×103 kg m−2 a−1 and basal heat flux (q) of 88 mW m−2, if steady-state conditions are assumed. However, the mid-level temperature variations show that recent temperature has varied significantly. Reconstructed surface temperatures (Ts=T15) over the last 200 yr are derived by an inversion technique (Tikhonov and Samarskii, 1990). From this, we find that cold temperatures (minimum Ts=−16.2°C) prevailed from ~1920 to ~1940, followed by a gradual rise of temperature to −14.2°C around 1995, then cooling over the following decade and warming in the last few years. The coldest period was preceded by a relatively warm 19th century at T15≥−15°C. To facilitate regional comparisons of the surface temperature history, we use our T15 data and nearby weather station records to refine estimates of lapse rates (altitudinal, adjusted for latitude: Γa(l)). Good temporal and spatial consistency of Γa(l) over the last 35 yr are observed, implying that the climate trends observed here are regional and consistent over a broad altitude range.