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.     

Simulation analyses of weighted fair bandwidth‐on‐demand (WFBoD) process for broadband multimedia geostationary satellite systems

Advanced resource management schemes are required for broadband multimedia satellite networks to provide efficient and fair resource allocation while delivering guaranteed quality of service (QoS) to a potentially very large number of users. Such resource management schemes must provide well‐defined service segregation to the different traffic flows of the satellite network, and they must be integrated with some connection admission control (CAC) process at least for the flows requiring QoS guarantees. Weighted fair bandwidth‐on‐demand (WFBoD) is a resource management process for broadband multimedia geostationary (GEO) satellite systems that provides fair and efficient resource allocation coupled with a well‐defined MAC‐level QoS framework (compatible with ATM and IP QoS frameworks) and a multi‐level service segregation to a large number of users with diverse characteristics. WFBoD is also integrated with the CAC process. In this paper, we analyse via extensive simulations the WFBoD process in a bent‐pipe satellite network. Our results show that WFBoD can be used to provide guaranteed QoS for both non‐real‐time and real‐time variable bit rate (VBR) flows. Our results also show how to choose the main parameters of the WFBoD process depending on the system parameters and on the traffic characteristics of the flows. Copyright © 2005 John Wiley & Sons, Ltd.     

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.     

TCRA: a time‐based channel reservation scheme for handover requests in LEO satellite systems

In this paper, we propose a time‐based channel reservation algorithm (TCRA) suitable for handover and call admission control procedures in future mobile satellite systems. These systems are characterized by a high rate of handover attempts which can degrade significantly their performance. Therefore, we propose TCRA, a scheme which guarantees a null handover failure probability by using a channel reservation strategy in the cells to be crossed by the user. The performance of TCRA has been compared to the guaranteed handover (GH) scheme. The TCRA reservation method has the advantage of a better channel utilization by locking the resources only for their expected time of use. A mathematical model has been developed for both schemes, and its results have been validated through simulations. Copyright © 2003 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.     

Capturing the spectral response of solar cells with a quasi‐steady‐state,large‐signal technique

A new approach to measure the spectral response of the short‐circuit current of solar cells is presented in this investigation. The main innovative feature is the light source, which produces a broad range of intensities, up to 10 suns in a quasi‐steady‐state mode, thus making the use of a bias light redundant. This results in large, integral signals that can be recorded directly without resorting to lock‐in amplification. Measurements of different solar cell structures with a conventional and the new measurement set‐up resulted in good agreement. Copyright © 2005 John Wiley & Sons, Ltd.     

On the power flux‐density limits to protect the fixed service from HEO FSS satellites emissions in the 18 GHz band

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 different power flux‐density (pfd) masks. These masks establish the maximum allowable pfd produced by each HEO satellite at the Earth's surface. The protections offered by four different pfd masks are analysed in two interfering environments, each containing three HEO systems. Two types of HEO system, with different orbital characteristics, are considered: one having satellites that operate only in the northern hemisphere and another having satellites that operate in both hemispheres. 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 large amount of results and curves is usually generated by the studies, making it difficult to draw general conclusions on the protection offered by the pfd masks under analysis. In looking for alternative ways of presenting the obtained results, a new variable was defined: the interference in excess. This new variable was defined in a way so that its probability distribution function reflects the protection given to an FS receiver located at a given latitude with a given receiving antenna elevation angle. It indicates the protection of an FS receiver for which the location longitude and the azimuth of the pointing direction of its receiving antenna are randomly chosen. This allows the large amount of results to be compacted into a small number of more representative curves from which general conclusions on the protection offered by the different pfd masks are easily drawn. Copyright © 2006 John Wiley & Sons, Ltd.     

On the mechanical strength of monocrystalline,multicrystalline and quasi‐monocrystalline silicon wafers: a four‐line bending test study

Quasi‐monocrystalline silicon wafers have appeared as a critical innovation in the PV industry, joining the most favorable characteristics of the conventional substrates: the higher solar cell efficiencies of monocrystalline Czochralski‐Si (Cz‐Si) wafers and the lower cost and the full square‐shape of the multicrystalline ones. However, the quasi‐monocrystalline ingot growth can lead to a different defect structure than the typical Cz‐Si process. Thus, the properties of the brand new quasi‐monocrystalline wafers, based on low and high crystal defect densities, have been for the first time studied from a mechanical point of view, comparing their strength with that of both Cz‐Si monocrystalline and typical multicrystalline materials. The study has been carried out employing the four line bending test and simulating them by means of FE models. For the analysis, failure stresses were fitted to a three‐parameter Weibull distribution. High mechanical strength was found in all the cases. However, the quasi‐monocrystalline wafers characterized by large density of bulk defects, due to the noticeable density of extended defects, showed lower fracture tensions. Copyright © 2013 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.     

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.     

Reliable space‐to‐Earth communication as a secondary service in the 460–470 MHz band

By regulatory fiat, secondary communication services cannot cause harmful interference to primary communication services, and they cannot claim protection from harmful interference from the primary service. This paper is about establishing reliable high data rate space‐to‐Earth communication in the asymmetric setting of a secondary service in the 460–470 MHz frequency band. In this band, the primary services consist of signals that are narrowband relative to the bandwidth of the signal of interest. A frequency domain approach is adopted to detect and cancel narrowband interference. After this processing, the signal of interest can be demodulated by standard techniques. This approach is shown to be effective on real data collected for the Dynamic Ionosphere CubeSat Experiment mission. The telemetry concept for Dynamic Ionosphere CubeSat Experiment was developed with a view toward demonstrating a high‐speed data downlink capability that may be adopted as a standard for future CubeSat missions. Copyright © 2014 John Wiley & Sons, Ltd.     

On the protection of fixed service receivers from the interference generated by non‐GSO satellite systems operating in the 3.7‐4.2 GHz band

In this work, the current power‐flux density limits in Article 21 of the ITU‐R Radio Regulations for non‐geostationary satellite orbit (GSO) systems operating in the 3.7‐4.2 GHz band are analyzed. These limits aim the protection of fixed service receivers, operating in the same frequency band, from the interference produced by non‐GSO satellite systems. The analysis was motivated by Resolution 157 of the World Radiocommunication Conference 2015, that recognized the need for a revision of Article 21 with a view to enabling non‐GSO systems to operate in these fixed‐satellite service frequency bands while ensuring that existing primary services are protected. In the analysis, 5 different circular Walker Delta type satellite constellation structures, adequately chosen, are considered, and the results show that the current power‐flux density (pfd) limits may impose undue constraints to non‐GSO systems operating in this band. Therefore, a methodology to investigate a more adequate pfd limiting mask is presented and used to generate an alternative mask. An evaluation of the proposed pfd mask shows that it does not impose unnecessary constraints to the non‐GSO satellite systems. This, along with other facts, indicates that the proposed pfd limits are, indeed, much more adequate than the current ones.     

Towards understanding consumption in multi‐user solar energy systems: the cases of villages in Argentina and Cuba

Research on the electrification of remote villages by means of decentralized renewable energy systems increasingly requires consideration of the characteristics of the user communities. Particularly for communities with multi‐user systems (MUS), in order to achieve optimal design and sizing of the system and efficient energy distribution among users, it is important to consider the social characteristics of the community in addition to technical and economic aspects. The solar energy supply is always limited, and distribution of the energy among the users is mainly a matter of coordinating who can use how much at what time, which is influenced by various factors. What we need first of all is knowledge of the actual power needs of each household over a period of time. With the aim of determining typical patterns of energy consumption in households with similar characteristics, the present preliminary research study uncovers the factors that determine energy consumption in five solar power villages in Cuba and Argentina. Correlation and regression analysis of data from surveys and energy consumption measurements showed that type and number of electrical appliances are the most important, but not sufficient, factors for explaining differences in household energy consumption. Demographic factors, occupations, daily routine and other social factors also have an impact on the development of a household's energy consumption. Copyright © 2004 John Wiley & Sons, Ltd.     

Information‐processing capabilities of chemical reaction–diffusion systems. 2: Finding paths in a labyrinth based on reaction–diffusion media

A technique for finding the optimal path in a labyrinth based on wave processes in reaction–diffusion media is elaborated. Three principle points were assumed as a basis for this technique: (i) a hybrid architecture that combines an information‐processing reaction–diffusion medium which performs operations of high computational complexity with a digital computer carrying out supplementary image‐processing operations; (ii) light‐sensitive information‐processing media of Belousov–Zhabotinsky type that enable one to simulate the labyrinth and spreading wave evolution by their images stored in the medium and to reduce the problem to image‐processing operations; (iii) fast light‐induced phase wave processes that spread through the labyrinth in several seconds instead of hours typical for trigger waves. Modern materials for the implementation of reaction–diffusion processes and a contemporary computer‐controlled optical system were used to obtain experimental data good enough for further processing by digital means. These techniques together with the additional procedure for testing for labyrinth fragment connectedness gave the opportunity to elaborate an effective ‘hardware’ system capable of finding paths in a labyrinth. A ‘hardware’ system that would be capable of solving the problem was designed. Copyright © 1999 John Wiley & Sons, Ltd.     

Characterisation of charge voltage of lead‐acid batteries: application to the charge control strategy in photovoltaic systems

In stand‐alone photovoltaic (PV) systems, charge controllers prevent excessive battery overcharge by interrupting or limiting the current flow from the PV array to the battery when the battery becomes fully charged. Charge regulation is most often accomplished by limiting the battery voltage to a predetermined value or cut‐off voltage, higher than the gassing voltage. These regulation voltages are dependent on the temperature and battery charge current. An adequate selection of overcharge cut‐off voltage for each battery type and operating conditions would maintain the highest battery state of charge without causing significant overcharge thus improving battery performance and reliability. To perform this work, a sample of nine different lead‐acid batteries, typically used in stand‐alone PV systems including vented and sealed batteries with 2 V cells and monoblock configurations have been selected. This paper presents simple mathematical expressions fitting two charge characteristic voltages: the gassing voltage (V_g) and the end‐of charge voltage (V_fc) as function of charge current and temperature for the tested batteries. With these expressions, we have calculated V_g and V_fc at different current rates. An analysis of the different values obtained is presented here focusing in the implication in control strategies of batteries in stand‐alone PV systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Insights into Nanoscale Electrochemical Reduction in a Memristive Oxide: the Role of Three‐Phase Boundaries

The nanoscale electro‐reduction in a memristive oxide is a highly relevant field for future non‐volatile memory materials. Photoemission electron microscopy is used to identify the conducting filaments and correlate them to structural features of the top electrode that indicate a critical role of the three phase boundary (electrode‐oxide‐ambient) for the electro‐chemical reduction. Based on simulated temperature profiles, the essential role of Joule heating through localized currents for electro‐reduction and morphology changes is demonstrated.     

Pushing the limits of concentrated photovoltaic solar cell tunnel junctions in novel high‐efficiency GaAs phototransducers based on a vertical epitaxial heterostructure architecture

A monolithic compound semiconductor phototransducer optimized for narrow‐band light sources was designed for achieving conversion efficiencies exceeding 50%. The III‐V heterostructure was grown by metal‐organic chemical vapor deposition, based on the vertical stacking of 5 partially absorbing GaAs n/p junctions connected in series with tunnel junctions. The thicknesses of the p‐type base layers of the diodes were engineered for optimal absorption and current matching for an optical input with wavelengths centered near 830 nm. Devices with active areas of ~3.4 mm² were fabricated and tested with different emitter gridline spacings. The open circuit voltage (Voc) of the electrical output is five times or more than that of a single GaAs n/p junction under similar illumination. The device architecture allows for improved Voc generation in the individual base segments because of efficient carrier extraction while simultaneously maintaining a complete absorption of the input photons with no needs for complicated fabrication processes or reflecting layers. With illumination powers in the range of a few 100 mW, the measured fill factor (FF) varied between 88 and 89%, and the Voc reached over 5.75 V. The data also demonstrated that a proper combination of highly doped emitter and window layers without gridlines is adequate for sustaining such FF values for optical input powers of several hundred milliwatts. As the optical input power is further increased and approaches 2 W (intensities ~58 W/cm²), the multiple tunnel junctions sequentially exceed their peak current densities in the case for which typical (n++)GaInP/ (p++)AlGaAs concentrated photovoltaic tunnel junctions are used. Lower bandgap tunnel junctions designed with improved peak current densities result in phototransducer devices having high FF and conversion efficiencies for up to 5 W optical input powers (intensities ~144 W/cm²). Measurements at different temperatures revealed a Voc reduction of −6 mV/°C at ~59 W/cm². Copyright © 2015 John Wiley & Sons, Ltd.