Adjacent Satellite Research Articles

Multi-Satellite MIMO Communications at Ku-Band and Above: Investigations on Spatial Multiplexing for Capacity Improvement and Selection Diversity for Interference Mitigation

This paper investigates the applicability of multiple-input multiple-output (MIMO) technology to satellite communications at the Ku-band and above. After introducing the possible diversity sources to form a MIMO matrix channel in a satellite environment, particular emphasis is put on satellite diversity. Two specific different topics from the field of MIMO technology applications to satellite communications at these frequencies are further analyzed: (i) capacity improvement achieved by MIMO spatial multiplexing systems and (ii) interference mitigation achieved by MIMO diversity systems employing receive antenna selection. In the first case, a single-user capacity analysis of a satellite MIMO spatial multiplexing system is presented and a useful analytical closed form expression is derived for the outage capacity achieved. In the second case, a satellite MIMO diversity system with receive antenna selection is considered, adjacent satellite cochannel interference on its forward link is studied and an analytical model predicting the interference mitigation achieved is presented. In both cases, an appropriate physical MIMO channel model is assumed which takes into account the propagation phenomena related to the frequencies of interest, such as clear line-of-sight operation, high antenna directivity, the effect of rain fading, and the slant path lengths difference. Useful numerical results obtained through the analytical expressions derived are presented to compare the performance of multi-satellite MIMO systems to relevant single-input single-output (SISO) ones.

Adjacent Satellite Interference Effects on the Outage Performance of a Dual Polarized Triple Site Diversity Scheme

The design of reliable, modern satellite communication networks, in which both frequency and orbital congestion are increasing, requires modeling of interference effects. The dominant sources of aggravation of nominal interference due to propagation phenomena are assumed to be differential rain attenuation from an adjacent satellite communication network operating at the same frequency and cross polarization due to rain and ice-crystals. A physical methodology to predict the statistics of the carrier-to-noise-plus-total-interference (CNIDR), which has already been applied to single and double-site systems, is extended to include triple-site diversity reception schemes. This method is based on a model of convective raincells model and the lognormal assumption for both the point rainfall statistics and slant path rain attenuation. The statistical properties of spatial inhomogeneity of rain attenuation over six satellite slant paths is firstly here presented. A set of simple, approximate formulas are presented which follow from a regression analysis on the previous theoretical results. The results serve to examine the influence of various parameters upon the total availability performance.

Study on ISL network structure in LEO satellite communication systems

Many parameters have to be taken into account in designing an LEO satellite constellation including transmission delay, service coverage, minimum elevation angle, and the effects of space radiation. We selected the 2 π constellation for the NeLS ISL study to maintain continuous ISL connections, which is expressed by using a Walker notation of 120/10/1 with 55° of inclination. The satellite orbit parameters were examined under conditions where at least two satellites were always visible from the user terminal to enable satellite diversity. The optimum inclination angle for the 2 π constellation was directly derived from the spherical triangle formed by three adjacent satellites. To evaluate the NeLS's ISL performance, the structure for ISL connections was simplified by using constellation parameters of 121/11/0 instead of 120/10/1. The ISL network had a bi-directional MSN structure with these parameters. The inter-orbital ISL, especially, achieved a ring network shaped like a figure-of-eight using n to n - 1 connections. The bi-directional MSN topology of ISL connections is also discussed. A combination of constellation parameters P , S , and F were found to have simple relations in the n to n - 1 connections of inter-orbital ISLs. Finally, optimum parameters for the NeLS constellation are discussed, and a candidate parameter ( T / P / F = 132 / 11 /- 1 , h = 1100 km , and I = 57 . 92 ∘ ) is proposed.

Satellite DNA junctions identify the potential origin of new repetitive elements in the beetle Tribolium madens

Two related satellite DNA families (satellite I and satellite II) with complex higher-order repeat (HOR) monomers represent major DNA components equilocated in the pericentromeric heterochromatin of all Tribolium madens chromosomes. Fragments obtained upon genomic DNA restriction revealed two subfamilies of satellite II monomers, and also identified regions of transition between satellite I and satellite II sequences. The two subfamilies differ not only in diagnostic nucleotides, but also in flipped orientation of constituent subunits. Hybrid genomic fragments comprise directly linked satellite I and satellite II monomers that cannot be distinguished from randomly cloned monomers of corresponding families. An exception is the most proximal satellite I monomer in the hybrid fragment named TMADhinf, which shows sequence divergence typical for repeats evolving at array ends, in zones of low homogenization efficiency. This pattern points to the extensive rearrangement processes generating abrupt transitions between satellite arrays combined with array maintenance by unequal crossover. Switching points between adjacent satellites as well as the edges of flipped subunits are localized within a short sequence segment, indicating a preferential site of recombination within satellite subunits. Multiple copies of TMADhinf junction fragment support the hypothesis that sites of evolutionary origin of novel satellite repeat (sub)families can be localized at array ends, in regions of enhanced sequence divergence.

Error Performance of Satellite Links Interfered by Two Adjacent Satellites

An analytical model concerning the BEP performance of a satellite link suffering from the combined interference by two adjacent satellites is presented. Satellite communication networks operate at frequencies above 10 GHz, specifically at the Ku, Ka and V bands, where rain attenuation severely affects the availability and performance of satellite links. Therefore, the performance evaluation taking into account rain attenuation is of utmost importance for the reliable design of a satellite communication network. In this letter, the bit error probability of a coherent demodulator subjected to Gaussian noise and interference from two adjacent satellites is determined taking into account rain attenuation. Numerical results for the QoS of satellite links are presented examining the effect of several factors such as the frequency of operation, the interference levels and the climatic conditions. The results obtained demonstrate the significant aggravation of the interference estimates when a second adjacent interfering satellite is taken into account.

An integrated mathematical programming approach for the design and optimisation of offshore fields

The paper presents a systematic methodology for the optimal design and operational management of offshore oil fields. It is comprised of two stages. At the design stage, the optimal production capacity of a main field is determined with an adjacent satellite field and a well drilling schedule. The problem is formulated as a mixed-integer linear programming formulation. Continuous variables represent individual well, jacket and topsides costs. Binary variables are used to select individual wells within a defined field grid. The mathematical formulation is concise and efficient. An MINLP model is proposed for the operational management optimisation of the offshore oilfields. In the latter model, non-linear equations are extensively used to model the pressure drops in pipes and wells for multiphase flow. Non-linear cost equations have been derived for the production costs of each well accounting for the length, the production rate and their maintenance. Operational decisions determine the oil flowrates, the operation/shut-in for each well and the pressures for each point in the piping network.

An Early Miocene Dome-Skulled Chalicothere from the “Arikaree” Conglomerates of Darton: Calibrating the Ages of High Plains Paleovalleys Against Rocky Mountain Tectonism

Fragmentary skeletal remains discovered in 1979 in southeastern Wyoming, associated with a mammalian fauna of early Hemingfordian age (∼18.2 to 18.8 Ma), represent the oldest known occurrence of dome-skulled chalicotheres in North America. The chalicothere and accompanying fauna were found in silica-cemented fluvial sandstones and conglomerate capping a series of west-to-east trending buttes in Goshen County, Wyoming, extending eastward into Sioux County, Nebraska. These butte caprocks, herein named the Carpenter Ranch Formation, are the reversed topographic remnants of a major paleovalley incised in the early Miocene and filled with coarse granitic/mafic gravels and sands derived from Precambrian-cored upifts to the west. The Carpenter Ranch Formation is identified as a coarser-grained, westward extension of the early Hemingfordian Runningwater paleovalley of Skinner, Skinner, and Gooris (1977) situated in northwest Nebraska. The age-diagnostic mammal faunas and coarse crystalline gravels of the Carpenter Ranch Formation of Wyoming and the coeval Martin Canyon beds of northern Colorado document the timing of tectonic rejuvenation of Rocky Mountain uplifts to the west in the early Hemingfordian.A second line of buttes situated 3 miles (∼ 4.8 km) north of the Carpenter Ranch paleovalley includes the regional landmark recorded as “Spoon Butte” in 19th century military and topographic surveys of the region. Spoon Butte, its caprock in northwest-southeast alignment with adjacent satellite buttes, represents a second and younger mid-Miocene paleovalley trend, characterized by silica-cemented sandstones and basal granitic/chert gravel with Barstovian mammals.N.H. Darton and G.I. Adams of the U.S. Geological Survey first described these caprocks as Arikaree conglomerates and mistakenly assumed they were of the same age as the caprock at Spoon Butte and its accompanying buttes to the north. However, this investigation shows that (a) mammal faunas from the two caprock trends are of markedly different ages; (b) the clast composition of the gravels is distinct; and (c) the paleovalleys align along two entirely different geographic trends.Furthermore, a loose gravel found on top of Spoon Butte, previously believed to date the caprock, is identified as a lag deposit sharing the same distinctive clast composition as high Quaternary terrace gravels in the vicinity. These terrace gravels include acid volcanics (not present in the Carpenter Ranch and Spoon Butte basal gravels) and a composite assemblage of water-worn mammal bones of Barstovian, Clarendonian, and Pleistocene ages. Thus they demonstrate that late Cenozoic deposits once occupied the extensive tableland east of the Hartville Uplift, but were later removed by erosion and reworked into Pleistocene and Holocene drainages.

Aggravation of radio interference effects on a dual polarized Earth‐space link by two adjacent interfering satellites under rain fades

Interference phenomena affecting the performance and availability of an Earth‐space system are of utmost importance for the reliable design of a satellite communication network. Commercial satellite networks operate or will operate at Ku, Ka, and V frequency bands, in which rain is the dominant fading mechanism. Nominal interference induced on an Earth‐space link by an adjacent satellite network operating at the same frequency is further aggravated because of the potential existing differential rain attenuation, as well as the rain and ice crystals depolarization valid for a frequency reuse system. In the present paper, an existing model, predicting the degradation of the total carrier‐to‐interference ratio under rain fade conditions, is properly modified considering interference effects by two adjacent satellites. The method is based on a convective rain cell model and the lognormal assumption for the point rain rate statistics. The obtained numerical results indicate the significant impact of the second interfering satellite on the aggravation of radio interference effects. Also presented are some simple mathematical formulas for the prediction of the carrier‐to‐interference ratio, based on the above theoretical results, appropriate for use by the system designer for back of the envelope computations.

Consistent surface albedo retrieval from two adjacent geostationary satellites

Monitoring and understanding climate changes of the Earth require the generation of long‐term and consistent global data set from observations. In this context, geostationary satellite observations could play a significant role thanks to the long duration of the missions and the corresponding archives. In particular, their frequent acquisition cycle throughout the day can be used to document the surface anisotropy and therefore surface albedo. This paper investigates the possibility to generate a consistent surface albedo maps from two adjacent geostationary satellites, namely Meteosat‐5 and ‐7. The analysis relies on the comparison of albedo values derived over the common observed area. These values agree favorably between the two spacecrafts.

Offshore Absolute Calibration of Space-Borne Radar Altimeters

Absolute calibration of sea level measurements collected from space-borne radar altimeters is usually performed with respect to collocated sea level in situ records from tide gauges or GPS buoys (Ménard et al. 1994; Haines et al. 1996; Bonnefond et al. 2003; Haines et al. 2003; Schum et al. 2003; Watson et al. 2003; Watson et al. 2004). Such a method allows regular and long-term control of altimetric systems with independent records. However, this approach is based on a single, geographically dependent point. In order to obtain more significant and accurate bias and drift estimates, there is a strong interest in multiplying the number of calibration opportunities. This article describes a method, called the “offshore method” that was developed to extend the single-point approach to a wider regional scale. The principle is to compare altimeter and tide gauge sea level data not only at the point of closest approach of an overflying pass, but also at distant points along adjacent satellite passes. However, connecting sea level satellite measurements with more distant in situ data requires a more accurate determination of the geoid and mean ocean dynamic topography slopes, and also of the ocean dynamical changes. In this demonstration experiment, 10 years of averaged TOPEX/Poseidon mean sea level profiles are used to precisely determine the geoid and the mean ocean circulation slope. The Mog2d barotropic ocean model (Carerre et Lyard 2003) is used to improve our estimate of the ocean dynamics term. The method is first validated with Jason-1 data, off Corsica, where the dedicated calibration site of Senetosa provides independent reference data. The method is then applied to TOPEX/Poseidon on its new orbit and to Geosat Follow On. The results demonstrate that it is feasible to make altimeter calibrations a few tens to hundreds of kilometers away from a dedicated site, as long as accurate mean sea level altimeter profiles can be used to ensure the connection with reference tide gauges.

A model for the estimation of the carrier-to-noise plus total interference ratio between two adjacent dual polarized satellite links sharing the same frequency band

In modern satellite communications, matters such as frequency congestion, transmission of dual polarized carriers and increase of the number of geostationary satellites in use, necessitate the implementation of interference analysis in neighbouring networks so as to ensure satisfactory quality of service. In this paper, a recently proposed model for the prediction of the degradation of the carrier-to-interference ratio due to differential rain attenuation and cross-polarization, which is applicable only for the noise-dominant case, has been properly modified to include the general case. The proposed model is based on the lognormal assumption for the point rainfall rate statistics and the convective raincell model. Due to complexity of the proposed analysis, some simple regression-derived formulas have been generated forming a very useful tool for the system engineer. The elaborations of numerical results examine the influence of various parameters upon the total availability performance and the optimum utilization of the geostationary orbit. Copyright © 2005 John Wiley & Sons, Ltd.

The Heather Field, Block 2/5, UK North Sea

abstract The Heather oil field is located in Block 2/5 in the Northern North Sea. Oil is produced from sandstones of the Middle Jurassic Brent Group. at depths between 9500ft and 11600 ft below sea level. The field has been in production for over 20 years, and to date 120 MMSTB of oil have been produced out of an oil-in-place volume of 464 MMSTB. Although approaching non-commercial flow rates, an ambitious programme of field re-evaluation has been conducted since 1997 to identify remaining infill potential, and to investigate the development potential of satellite accumulations. New 3D seismic surveys shot in 1995 and 1997 have been combined to produce a continuous top reservoir map of the main field and adjacent satellite structures. The new mapping and an updated reservoir description were integrated with reservoir simulation models to identify zones of unswept oil. Main field infill projects have been identified which target the unswept oil, allowing extension of field life to be planned in conjunction with satellite field development. An additional 57 MMSTB of recoverable oil are expected to be produced from Middle Jurassic reservoirs in the main field and in satellite areas.

Prediction of the degradation of the carrier‐to‐noise plus interference ratio concerning a site diversity system suffering from differential rain attenuation

Rain‐induced attenuation is a factor of utmost importance in designing a satellite link since it can strongly deteriorate the availability and performance of an Earth‐space path. Availability and performance are key criteria for the reliable design process. In the present paper the statistics of carrier‐to‐noise plus interference ratio under rain fade conditions are examined, given that the interference is caused by an adjacent satellite operating at the same frequency, and taking also under consideration double site diversity protection as a countermeasure technique. The method presented herein is based on a model of convective rain cells and the lognormal assumption for the point rainfall statistics. Numerical results have been obtained for heavy rain climatic regions and very large availability times, to examine how effective site diversity can be, not only for lowering fade margins but for compensating severe interference effects. Moreover, the elaboration of the numerical results has revealed how the optimum design of the satellite link can be achieved by selecting proper values for some critical parameters of the system.

Adjacent satellite interference effects as applied to the outage performance of an earth- space system located in a heavy rain climatic region

Interference effects are of utmost importance to the reliable design of modern satellite communication systems operating at Ku and Ka bands. In these frequencies rain attenuation is the dominant fading mechanism particularly for Earth-space systems located in subtropical and tropical regions. On the other hand, the main propagation effect on interference between two adjacent satellite systems is considered to be the differential rain attenuation. The subject of the paper is the development of a procedure for the prediction of carrier-to-noise plus interference ratio (cnir) statistics, under the presence of rain fading conditions, applied to heavy rain climatic regions. The method is based on a model of convective raincells and the gamma distribution assumption for point rainfall rate statistics, which fits better than lognormal distribution in subtropical and tropical regions. A tropical raindrop size distribution is also adopted for the calculation of the power-law parameters of specific rain attenuation. The numerical results are concentrated on the analytical examination of various operational parameters upon the CNIR statistics and the subsequent outage performance of the system. Comparison of the proposed model with an already existing one is attempted and the necessity of the present procedure for application to locations belonging to subtropical/tropical zones becomes obvious.

The Implementation of Maintaining Constant Distance Between Satellites in Coplanar Elliptic Orbits

A strategy for maintaining separation distances between several satellites in a coplanar elliptical orbiting constellation is developed. A possible scientific application of such a system would be in measuring the curl ofthe Earth's magnetic field by taking simultaneous measurements along the elliptical orbit. The strategy involves maneuvers which would cause small shifts in the direction of the four semimajor axes. With this approach for Keplerian type orbits, the separation distance between adjacent satellites remains within a few percent of the nominal separation distance. This paper emphasizes problems of implementation: 1. Initial deployment. It is assumed that the satellites are launched by a single vehicle. The method to distribute the satellites into their positions using the least maneuver energy is studied. 2. Maintenance of the separation distance. Since the mathematical model is nonlinear and time-variant, a nonlinear control law based on a Lyapunov function is applied to the osculating orbital elements of the daughter satellites. The simulation results with this control show that with perturbations (mainly caused by J 2 ), the response to initial errors converges smoothly and the control energy spent is at a very low level.

Analysis of the Degradation of the Carrier-To-Noise Plus Total Interference Ratio Concerning a Dual Polarization Site Diversity System Suffering From Differential Rain Attenuation

For the modern satellite systems where frequency and orbital congestion will be an expectable fact the analysis of the interference effects is considered to be of utmost importance. In this paper, the differential rain attenuation from an adjacent satellite system as well as the rain cross-polarization (valid for frequency re-use systems) are assumed to be the dominant interference sources. A method to predict the carrier-to-noise plus total interference ratio statistics applied to a single-site system is extended to include systems operating under a site diversity protection scheme. The method is based on a model of convective raincells and the lognormal assumption for the point rainfall statistics. The numerical results examine the influence of various parameters upon the total availability performance and it is expected to be useful toward the optimum system design in the future.

Ice crystals and raindrop canting angle effects applied to satellite interference prediction with respect to heavy rain climatic zones

For frequencies above 10GHz the performance of the operating satellite systems is mainly aggravated because of the potential existing severe rain attenuation. As a result of the above fading mechanism, the dominant interference sources encountered in this frequency band are the following: differential rain attenuation induced by an adjacent satellite system operating in the same frequency, and cross talk between orthogonally polarized signals. The latter source concerns of course satellite systems employing the dual polarization mode. In the present paper, an already existing method to predict interference statistics, due to above reasons, is properly modified to include ice crystals and raindrop canting angle effects. The assumption that the point rainfall rate statistics follows a gamma form, valid for heavy rain climatic regions such as J, M, N, P, Q zones, is also adopted. The sensitivity of various parameters affecting the interference performance, after introducing the novel assumptions, is finally investigated.

A Generalized Gaussian User Distribution and a Modified Traffic Power Control (MTPC) for LEO Systems

This paper proposes the use of the generalized Gaussian as a user distribution model in LEO satellite communication systems. Evaluating the signal to interference ratio (SIR) for this more general function depicts the performance of a LEO system. It is shown that the performance of the system is sensitive to the assumed user distribution. Furthermore, since the discrepancy between the SIR of adjacent satellites is large especially in severe non-uniformity of the traffic, the use of a modified power control (MPC) is essential. A slight modification of this MPC is also suggested.

Multiply Charged Ions from Aromatic Molecules Following Irradiation in Intense Laser Fields

It is well-known that aromatic molecules, when irradiated by UV laser beams in the nanosecond pulse width regime, yield exclusive parent ions at laser intensities of 107 W cm-2 (soft ionization). As the laser intensities increase up to 109 W cm-2, however, extensive fragmentation takes place such that small mass fragments dominate the spectra at the expense of parent signature ions. The reason for this is that the dissociative lifetimes are shorter than the laser pulse width and ladder-switching fragmentation takes place. With the development of high power femtosecond lasers, these dissociative lifetimes can often be bypassed. Presently, at laser intensities up to the order of 1015 W cm-2 with pulse widths as short as 50 fs at near-infrared (IR) wavelengths (790 nm), soft ionization again takes place. This has been seen using a technique known as femtosecond laser mass spectrometry (FLMS). Under such conditions, stable multiply charged parent and adjacent satellite ions are observed and the fragmentation ...

Availability and performance of satellite links suffering from interference by an adjacent satellite and rain fades

An analysis is presented relating rain attenuation statistics to BEP performance of Earth-space links subjected to interference by an adjacent satellite operating in the same frequency band. A systematic design method is proposed that takes into account the BER objectives specified by the ITU for the design of satellite links. Numerical results based on the proposed method have been obtained to investigate the combined effect of rain and interference for the Ku and Ka bands and for various data rates and climatic zones.