Protection of FS receivers from the interference produced by HEO FSS satellites in the 18 GHz band: Effect of the roll‐off characteristics of the HEO system satellite antenna beams

This paper focuses on the protection of fixed service (FS) receivers from the aggregate interference produced by the satellites of multiple highly elliptical orbit satellite systems (HEOs). It analyzes the protection given to FS receivers operating in the 18 GHz frequency band by the power flux‐density (pfd) mask contained in Article 21 of the 2003 edition of the Radio Regulations [International Telecommunication Union, 2003.]. This mask establishes the maximum allowable value for the pfd produced by any of the satellites of a non‐geostationary system at the Earth's surface. The protection offered to FS receivers by this mask is analyzed in four interfering environments, each containing three identical HEO systems. Four types of HEO systems, with different orbital characteristics, are considered: three having satellites that operate only in the northern hemisphere and one having satellites that operate in both hemispheres. All satellite antennas are assumed to radiate 0.3° spot beams. Each HEO satellite is modelled so that the maximum pfd it produces at the Earth's surface just meets the RR Article 21 mask and the analysis takes into account the roll‐off characteristics of the satellite antenna beams. To reflect the multiplicity of possibilities concerning the geographical location and technical characteristics of the victim FS receiver (e.g. latitude, longitude, azimuth and elevation of its receiving antenna, antenna gain, receiver noise temperature, etc.) a number of cases were evaluated. The concept of interference in excess [Int. J. Satellite Commun. Networking 2006; 24 : 73–95] was used to combine the results corresponding to FS receivers located at the same latitude and having the same receiving antenna elevation angle but for which the location longitude and the azimuth of the pointing direction of its receiving antenna are randomly chosen. Results are expressed in terms of the cumulative distribution function of the interference in excess. Copyright © 2008 John Wiley & Sons, Ltd.     

Protection of fixed service receivers from the interference produced by the non‐geostationary satellites in a fixed satellite service network: a statistical interference analysis

Until 1997, the power flux density (pfd) limits applicable to fixed satellite service (FSS) satellite transmitters to protect fixed service (FS) receivers operating in the same frequency band were those in Article 21 of the radio regulations. They were developed assuming that potentially interfering satellites in the FSS would only operate in the GSO. The need to revise these limits to allow for the protection of FS receivers from interference generated by non‐geostationary satellites has led to several studies, most of them based on the non‐realistic assumption that every visible satellite in a NGSO constellation produces the maximum allowed pfd level at the FS receive station location. To provide a quantitative indication of how pessimistic this assumption is, this paper considers a more realistic model in which the pfd entries reaching a given FS receiver location are characterized by statistically independent random variables. The probability density functions of these random variables depend on the operational characteristics of the NGSO network. The obtained results have also shown the need to consider some of the operational characteristics of NGSO satellite networks when evaluating the interference produced by their satellites. If these operational characteristics are not taken into account in the calculations, higher values of interference, that do not reflect the real interference environment, are obtained. Copyright © 2002 John Wiley & Sons, Ltd.     

Impact of avoidance angle mitigation techniques on the interference produced by non‐GSO systems in a multiple non‐GSO interference environment

This paper adresses the impact of avoidance angle mitigation techniques on the interference produced by non‐GSO systems in a multiple non‐GSO interference environment. It considers a situation involving a victim LEO system and two other non‐GSO interfering systems (one MEO and another LEO) that mitigate around (and only around) the victim LEO system. Interference statistics are obtained using the so called Analytical Method for non‐GSO interference computations. The methodology described, including the interference model adopted, and the type of result obtained in Section 3, that shows the variation of the percentage of the total time allowance used by the interference as a function of the Earth station‐based and the satellite‐based avoidance angles, are very helpful in the process of selecting adequate values for these angles. The burden imposed on the mitigating systems by the use of avoidance angle strategies was evaluated through its impact on the coverage capability of the mitigating systems. Copyright © 2003 John Wiley & Sons, Ltd.     

On the interference from space research service uplink transmissions into the inter‐satellite links of a non‐GSO system operating in the 22‐GHz band

This paper presents a compatibility analysis involving space research service lunar mission uplink transmissions and the inter‐satellite links of non‐geostationary orbit systems operating in the 22‐GHz band. Three points differentiate this analysis from the currently available studies: (1) the mathematical model used here allows for the consideration of the time varying nature of the inclination of the Moon orbital plane; (2) besides the usual unconditional interference cumulative distribution functions, this analysis also considers the conditional cumulative distribution functions given that the victim satellite is receiving interference, important to characterize the interference affecting users that, because of their location, are most of the time using satellites, which are under interference; and (3) instead of dynamic time simulation, the analytical method in Recommendation ITU‐R S.1529 is used to determine the various cumulative distribution functions involved. Four scenarios are examined in the paper. Their main differences concern the number and location of the space research service transmitting Earth stations and the strategy under which they are active (transmitting). In all scenarios, cumulative distribution functions of the ratio I/N were determined for both the in‐band and the out‐of‐band interference cases. Copyright © 2012 John Wiley & Sons, Ltd.     

非静止卫星星座地球站的等效全向辐射功率包络计算方法

新兴的非静止轨道(non geo-stationary orbit,NGSO)卫星星座系统可支持分布在地球任何位置的海量地面终端,NGSO星座系统大多使用与GSO卫星星座系统同频的频段,再加上NGSO星座系统在空、时、频、码等域的高动态特性,必然会对GSO星座系统带来时变的频率干扰问题.为解决NGSO星座系统上行链路对...     

Examination of the data rate obtainable with low‐gain non‐tracking antenna applied to user terminal used for mobile communications and broadcasting services provided by quasi‐zenithal satellites

Link budgets between the mobile user terminal and a feeder link station (2‐m‐diameter antenna) through the quasi‐zenithal satellite system (QZSS) (7‐m‐diameter antenna for Tx, 5‐m‐diameter antenna for Rx) under the power flux density (PFD) limit were calculated for the Ka‐ and Ku‐band. The PFD limit for non‐geostationary satellites is applied for frequency sharing between QZSS and geostationary satellites. The maximum data rate in the Ka‐band was 1.7 times higher than in the Ku‐band in the forward link, while the maximum data rate at Ku‐band is nine times higher than that in the Ka‐band in the return link when the transmit power derived from the regulations of the PFD is applied. And it is more than three times higher than that in the Ka‐band when transmit power is fixed to 2W. In the forward link, maximum data rates are 149 kbps in the Ka‐band and 86 kbps in the Ku‐band when the user terminal antenna is non‐tracking (gain at the satellite direction is 7.1 dBi) and the frequency bandwidth per beam is 30 MHz. Required bandwidth per channel for a certain data rate is large, e.g. in Ka‐band, 20.9 MHz for 64 kbps, 125 MHz for 384 kbps, and 326 MHz for 1 Mbps. In the return link, the maximum data rates are 44 kbps in the Ku‐band and 13.6 kbps in the Ka‐band when the user terminal antenna gain in the satellite direction is 7.1 dBi and transmit power is 2 W. Copyright © 2005 John Wiley & Sons, Ltd.     

Implementing polarization shift keying over satellite – system design and measurement results

Polarization shift keying (PolSK) is a digital modulation technique using the state of polarization of an electromagnetic wave as the signalling quantity. PolSK comes from fibre communications, where the channel offers two orthogonal states of polarization. This article develops on the idea to adapt this technology to satellite communications, where similar channel conditions exist. For this purpose, a digital PolSK modem was implemented on a programmable logic board. A proposal for constellation design as well as thoughts on synchronization of PolSK over satellite is presented. The modem was used to demonstrate a 16‐state Polarization Shift Keying link over a commercial satellite in K_u band. Measurements have been conducted in a back‐to‐back setup on intermediate frequency and on a K_u band transponder simulator to assess the impact of path‐length differences, carrier recovery and non‐linearity. Copyright © 2015 John Wiley & Sons, Ltd.     

ATM‐based multimedia communication via NGSO‐satellites

Future broadband satellite networks for multimedia will be seamlessly integrated into terrestrial broadband networks which often use asynchronous transfer mode (ATM) and recently also the less complex multi protocol label switching (MPLS) technique as transmission and switching protocol. In light of this, future broadband satellite networks may adopt the ATM transmission scheme and implement ATM or ATM‐like switches on board the satellites. However, as compared to communication in fixed networks, satellite communication is characterized by special constraints (e.g. signal delay, channel quality, dynamic network topology) that require novel ATM‐based communication technology for satellite systems. This paper presents results from the ATM‐Sat project that aims to complete this technically challenging and important R&D task in the cooperation between DLR, Fraunhofer Gesellschaft and Tesat‐Spacecom. In brief the following aspects have been addressed in the ATM‐Sat project:

• development of the concept and communication technology for a multimedia satellite system with,
  • non‐geostationary orbit (NGSO) satellites;
  • inter satellite links (ISLs);
  • on‐board ATM switching;
  • fixed and mobile terminals;
• verification of the developed communication technology with a demonstrator.

In particular the ATM‐Sat R&D tasks cover the system and protocol architecture, on‐board processing, ISL routing, up/downlink and on board ATM resource management (including medium access control), error control, IP over satellite‐ATM, and active intelligent antennas. Copyright © 2005 John Wiley & Sons, Ltd.     

Semi‐random LDPC codes for CDMA communication over non‐linear band‐limited satellite channels

This paper considers the application of low‐density parity check (LDPC) error correcting codes to code division multiple access (CDMA) systems over satellite links. The adapted LDPC codes are selected from a special class of semi‐random (SR) constructions characterized by low encoder complexity, and their performance is optimized by removing short cycles from the code bipartite graphs. Relative performance comparisons with turbo product codes (TPC) for rate 1/2 and short‐to‐moderate block sizes show some advantage for SR‐LDPC, both in terms of bit error rate and complexity requirements. CDMA systems using these SR‐LDPC codes and operating over non‐linear, band‐limited satellite links are analysed and their performance is investigated for a number of signal models and codes parameters. The numerical results show that SR‐LDPC codes can offer good capacity improvements in terms of supportable number of users at a given bit error performance. Copyright © 2006 John Wiley & Sons, Ltd.     

Deep‐space communications with a 2‐hop downlink with high link‐availability

We recall and discuss the theory of a 2‐hop downlink in deep‐space communications. The first hop (length d₁) links the deep‐space spacecraft to either a geostationary satellite or to a low Earth orbiting satellite. The second hop (length d₂, with d₂ ? d₁) links the satellite to the Earth receiver through a transparent or regenerative transponder, in slant paths affected by troposphere attenuation. If we adopt a BPSK or QPSK modulation scheme and the same carrier frequencies in the two hops with a transparent transponder, a particular value of the carrier frequency makes the noise‐to‐signal ratio minimum. A better choice is to assign a low carrier frequency (X‐band) to the second hop and a high one (W‐band) to the first hop. A 2‐hop downlink is superior to a 1‐hop downlink with a large power gain proportional to (d₁/d₂)² ? 1 at high microwave frequencies and large troposphere attenuation (high link‐availability). Shannon's capacity theorem provides the same large gain independently of the choice of the carrier frequencies in the two hops, if we use a regenerative transponder. The carrier frequencies of a 2‐hop downlink need not be those reserved to deep‐space communication, because the spacecraft could communicate as if it were transmitting ‘from the Earth’ through a conventional satellite connection. We have applied the theory to a first‐order design in the frequency range 10–100 GHz, slant path elevation angles 30°, 45° and 90° at Gera Lario or Fucino (Italy), and downlinks form Mars and Saturn, although the general findings and methodology are of global applicability. Copyright © 2005 John Wiley & Sons, Ltd.     

Theatre in the Sky: a ubiquitous broadband multimedia‐on‐demand service over a novel constellation composed of quasi‐geostationary satellites

To meet an ever‐growing demand for wideband multimedia services and electronic connectivity across the world, development of ubiquitous broadband multimedia systems is gaining a tremendous interest at both commercial and academic levels. Satellite networks will play an indispensable role in the deployment of such systems. A significant number of satellite communication constellations have been thus proposed using Geostationary (GEO), Medium Earth Orbit (MEO), or Low Earth Orbit (LEO) satellites. These constellations, however, either require a potential number of satellites or are unable to provide data transmission with high elevation angles. This paper proposes a new satellite constellation composed of Quasi‐GeoStationary Orbit (Quasi‐GSO) satellites. The main advantage of the constellation is in its ability to provide global coverage with a significantly small number of satellites while, at the same time, maintaining high elevation angles. Based on a combination of this Quasi‐GSO satellites constellation and terrestrial networks, the paper proposes also an architecture for building a global, large‐scale, and efficient Video‐on‐Demand (VoD) system. The entire architecture is referred to as a ‘Theatre in the Sky’. Copyright © 2006 John Wiley & Sons, Ltd.     

Filter bank‐based multiple access in next‐generation satellite uplinks: A DVB‐RCS2‐based experimental study

In the context of the on‐going evolution of satellite communications (SatCom) systems to their next generation, and in the direction of their integration with fifth generation (5G) terrestrial networks, it is of interest to study in depth the applicability in realistic SatCom of waveforms that have shown promise to meet the 5G requirements. This paper presents a comparative study, based on total degradation (TD) over a range of output back‐off (OBO) values, on out‐of‐band emission and spectral efficiency, of frequency division multiple access (FDMA) schemes employing offset quadrature amplitude modulation‐based filter bank multi‐carrier (FBMC /OQAM), classical orthogonal FDMA (OFDMA), and their single‐carrier counterparts to illustrate the potential gains from the integration of the FBMC waveforms in the satellite context and standards. The air interface simulated follows the digital video broadcasting (DVB) family of standards for the satellite uplink, considering both time and frequency synchronization impairments and two typical input constellations. Our results confirm the superiority of the single‐carrier (SC) schemes in such a nonlinear environment. The SC‐FBMC waveform is shown to be the most practical candidate since it is shown to attain a TD performance similar to that of SC‐OFDM at absolutely no cost in spectral efficiency.     

Enhanced Electron Mobility Due to Dopant‐Defect Pairing in Conductive ZnMgO

The increase of the band gap in Zn_1‐xMg_xO alloys with added Mg facilitates tunable control of the conduction band alignment and the Fermi‐level position in oxide‐heterostructures. However, the maximal conductivity achievable by doping decreases considerably at higher Mg compositions, which limits practical application as a wide‐gap transparent conductive oxide. In this work, first‐principles calculations and material synthesis and characterization are combined to show that the leading cause of the conductivity decrease is the increased formation of acceptor‐like compensating intrinsic defects, such as zinc vacancies (V_Zn), which reduce the free electron concentration and decrease the mobility through ionized impurity scattering. Following the expectation that non‐equilibrium deposition techniques should create a more random distribution of oppositely charged dopants and defects compared to the thermodynamic limit, the paring between dopant Ga_Zn and intrinsic defects V_Zn is studied as a means to reduce the ionized impurity scattering. Indeed, the post‐deposition annealing of Ga‐doped Zn_0.7Mg_0.3O films grown by pulsed laser deposition increases the mobility by 50% resulting in a conductivity as high as σ = 475 S cm^‐1.     

Robust Non‐negative Matrix Factorization with β‐Divergence for Speech Separation

This paper addresses the problem of unsupervised speech separation based on robust non‐negative matrix factorization (RNMF) with β‐divergence, when neither speech nor noise training data is available beforehand. We propose a robust version of non‐negative matrix factorization, inspired by the recently developed sparse and low‐rank decomposition, in which the data matrix is decomposed into the sum of a low‐rank matrix and a sparse matrix. Efficient multiplicative update rules to minimize the β‐divergence‐based cost function are derived. A convolutional extension of the proposed algorithm is also proposed, which considers the time dependency of the non‐negative noise bases. Experimental speech separation results show that the proposed convolutional RNMF successfully separates the repeating time‐varying spectral structures from the magnitude spectrum of the mixture, and does so without any prior training.     

Preparation and Memory Performance of a Nanoaggregated Dispersed Red 1‐Functionalized Poly (N‐vinylcarbazole) Film via Solution‐Phase Self‐Assembly

A nanoaggregated dispersed red 1‐grafted poly(N‐vinylcarbazole) (abbreviated PVDR) is self‐assembled via π–π stacking interactions of the carbazole groups in the polymer system after adding a solution of PVDR in N,N‐dimethylformamide to dichloromethane. Upon self‐assembly, the nanoaggregated PVDR film displays helical columnar stacks with large grain sizes, whereas a non‐aggregated PVDR film exhibits an amorphous morphology with smaller grain size. A write‐once read‐many‐times (WORM) memory device is shown whereby a pre‐assembled solution of PVDR is spin‐coated as the active layer and is sandwiched between an aluminum electrode and an indium‐tin‐oxide (ITO) electrode. This device shows very good memory performance, with an ON/OFF current ratio of more than 10⁵ and a low misreading rate through the precise control of the ON and OFF states. The stability of the nanoaggregated PVDR device is much higher than that of the non‐nanoaggregated PVDR device. This difference in device stability under constant voltage stress can be mainly attributed to the difference in the film crystallinity and surface morphology. No degradation in current density was observed for the ON‐ and OFF‐states after more than one hundred million (10⁸) continuous read cycles indicating that both states were insensitive to the read cycles. These results render the nanoaggregated PVDR polymer as promising components for high‐performance polymer memory devices.     

Enhanced Light‐Harvesting Capability of a Panchromatic Ru(II) Sensitizer Based on π‐Extended Terpyridine with a 4‐Methylstylryl Group for Dye‐Sensitized Solar Cells

A novel Ru π‐expanded terpyridyl sensitizer, referred to as HIS‐2, is prepared based on the molecular design strategy of substitution with a moderately electron‐donating 4‐methylstyryl group onto the terpyridyl ligand. The HIS‐2 dye exhibits a slightly increased metal‐to‐ligand charge transfer (MLCT) absorption at around 600 nm and an intense π–π* absorption in the UV region compared with a black dye. Density functional theory calculations reveal that the lowest unoccupied molecular orbital (LUMO) is distributed over the terpyridine and 4‐methylstyryl moieties, which enhances the light‐harvesting capability and is appropriate for smooth electron injection from the dye to the TiO₂ conduction band. The incident photon‐to‐electricity conversion efficiency spectrum of HIS‐2 exhibits better photoresponse compared with black dye over the whole spectral region as a result of the extended π‐conjugation. A DSC device based on black dye gives a short‐circuit current (J_SC) of 21.28 mA cm^?2, open‐circuit voltage (V_OC) of 0.69 V, and fill factor (FF) of 0.72, in an overall conversion efficiency (η) of 10.5%. In contrast, an HIS‐2 based cell gives a higher J_SC value of 23.07 mA cm^?2 with V_OC of 0.68 V, and FF of 0.71, and owing to the higher J_SC value of HIS‐2, an improved η value of 11.1% is achieved.     

Inverse‐Woodpile Photonic Band Gap Crystals with a Cubic Diamond‐like Structure Made from Single‐Crystalline Silicon

Three dimensional photonic band gap crystals with a cubic diamond‐like symmetry are fabricated. These so‐called inverse‐woodpile nanostructures consist of two perpendicular sets of pores in single‐crystal silicon wafers and are made by means of complementary metal oxide–semiconductor (CMOS)‐compatible methods. Both sets of pores have high aspect ratios and are made by deep reactive‐ion etching. The mask for the first set of pores is defined in chromium by means of deep UV scan‐and‐step technology. The mask for the second set of pores is patterned using an ion beam and carefully placed at an angle of 90° with an alignment precision of better than 30 nm. Crystals are made with pore radii between 135–186 nm with lattice parameters a = 686 and c = 488 nm such that a/c = √2; hence the structure is cubic. The crystals are characterized using scanning electron microscopy and X‐ray diffraction. By milling away slices of crystal, the pores are analyzed in detail in both directions regarding depth, radius, tapering, shape, and alignment. Using optical reflectivity it is demonstrated that the crystals have broad reflectivity peaks in the near‐infrared frequency range, which includes the telecommunication range. The strong reflectivity confirms the high quality of the photonic crystals. Furthermore the width of the reflectivity peaks agrees well with gaps in calculated photonic band structures.     

A High‐k Fluorinated P(VDF‐TrFE)‐g‐PMMA Gate Dielectric for High‐Performance Flexible Field‐Effect Transistors

A newly synthesized high‐k polymeric insulator for use as gate dielectric layer for organic field‐effect transistors (OFETs) obtained by grafting poly(methyl methacrylate) (PMMA) in poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) via atom transfer radical polymerization transfer is reported. This material design concept intents to tune the electrical properties of the gate insulating layer (capacitance, leakage current, breakdown voltage, and operational stability) of the high‐k fluorinated polymer dielectric without a large increase in operating voltage by incorporating an amorphous PMMA as an insulator. By controlling the grafted PMMA percentage, an optimized P(VDF‐TrFE)‐g‐PMMA with 7 mol% grafted PMMA showing reasonably high capacitance (23–30 nF cm^?2) with low voltage operation and negligible current hysteresis is achieved. High‐performance low‐voltage‐operated top‐gate/bottom‐contact OFETs with widely used high mobility polymer semiconductors, poly[[2,5‐bis(2‐octyldodecyl)‐2,3,5,6‐tetrahydro‐3,6‐dioxopyrrolo [3,4‐c]pyrrole‐1,4‐diyl]‐alt‐[[2,2′‐(2,5‐thiophene)bis‐thieno(3,2‐b)thiophene]‐5,5′‐diyl]] (DPPT‐TT), and poly([N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)) are demonstrated here. DPPT‐TT OFETs with P(VDF‐TrFE)‐g‐PMMA gate dielectrics exhibit a reasonably high field‐effect mobility of over 1 cm² V^?1 s^?1 with excellent operational stability.     

A novel compressed sensing ultra‐wideband channel estimation method based on non‐convex optimization

Due to the low power spectral density and complicated transfer propagation of ultra‐wideband (UWB) signal, it is important to estimate UWB channel accurately. But it is difficult to sample UWB signals directly due to their wider band width. However, compressed sensing (CS) theory provides a feasible way through lower sampling speed. Common CS‐UWB channel estimation methods adopt convex optimization, non‐sparse or non‐restricted form. In order to strengthen the restriction on sparsity of the reconstructed channel vector, a non‐convex optimization method is proposed in this paper to estimate UWB channel. Proposed method sets the objective function as a non‐convex optimization model using l_p–norm. This model is combined as a convex function to approximate the objective function and reconstruct the UWB channel vector iteratively. Because l_p–norm is closer to l₀–norm than l₁ and l₂–norm, its restriction on sparsity of objective vector is stricter. The simulation results show that this method can enhance reconstruction performance compared with existing CS‐UWB channel estimation methods. Copyright © 2013 John Wiley & Sons, Ltd.