Precoded Cluster Hopping for Multibeam GEO Satellite Communication Systems

Beam hopping (BH) and precoding are two trending technologies for high-throughput satellite (HTS) systems. While BH enables the flexible adaptation of the offered capacity to the heterogeneous demand, precoding aims at boosting the spectral efficiency. In this study, we consider an HTS system that employs BH in conjunction with precoding in an attempt to bring the benefits of both in one. In particular, we propose the concept of cluster hopping (CH), where a set of adjacent beams are simultaneously illuminated with the same frequency resource. On this line, we propose an efficient time–space illumination pattern design, where we determine the set of clusters that shall be illuminated simultaneously at each hopping event along with the dwelling time. The CH time–space illumination pattern design formulation is shown to be theoretically intractable due to the combinatorial nature of the problem and the impact of the actual illumination design on the resulting interference. For this, we make some design decisions on the beam–cluster design that open the door to a less complex still well-performing solution. Supporting results based on numerical simulations are provided which validate the effectiveness of the proposed CH concept and a time–space illumination pattern design with respect to benchmark schemes.

Fault diagnosis with adaptive kalman filters and CMG design for picosatellite ACS

Picosatellites have only recently become a viable research topic thanks to the creation of the cubesat standard in 1999 and improvements in technology. However they are still limited in application because there are no high performance active actuators available in the market that can satisfy the mass/power/budget constraints of a picosatellite. Space and power are limited in these satellites which means that hardware redundancy is not very practical. If actuator faults occur, analytical redundancy techniques should be employed to determine if, where, and how the fault(s) occurred. This thesis focuses on enhancing picosatellite actuator tehnologies, as well as presenting an alogrithm for fault detection, isolation, and identification of ACS actuators. A CMG cluster design is proposed to demonstrate the feasibility of using CMGs in picosatellites to enhance their performance. The proposed CMG cluster design weighs less than 100g, occupies less than 25% of a cubesat's volume, and theoretically consumes less than 1.5W and 1W of peak and average power respectively. Furthermore, it is capable of providing sufficient torque and momentum storage for picosatellite attitude control in LEO. Next a novel adaptive Kalman filter algorithm is presented that can be implemented with the EKF and UKF for linear and non-linear systems respectively. The algorithm performs parameter estimation with sequential adaptive estimation and fading memory mechanisms that allow it to track changes in faulty parameters even in the presence of high levels of measurement noise. Furthermore, it is capable of tracking continuously varying and instantaneous changes in parameters. Numerical simulations are carried out to verify the performance of the propsed CMG cluster design as well as the fault diagnosis algorithm. The capabilities of the filter are further demonstrated via its application to a systems identification problem for a nonosatellite RW prototype being developed at SSDC group.

Fault diagnosis with adaptive kalman filters and CMG design for picosatellite ACS

Picosatellites have only recently become a viable research topic thanks to the creation of the cubesat standard in 1999 and improvements in technology. However they are still limited in application because there are no high performance active actuators available in the market that can satisfy the mass/power/budget constraints of a picosatellite. Space and power are limited in these satellites which means that hardware redundancy is not very practical. If actuator faults occur, analytical redundancy techniques should be employed to determine if, where, and how the fault(s) occurred. This thesis focuses on enhancing picosatellite actuator tehnologies, as well as presenting an alogrithm for fault detection, isolation, and identification of ACS actuators. A CMG cluster design is proposed to demonstrate the feasibility of using CMGs in picosatellites to enhance their performance. The proposed CMG cluster design weighs less than 100g, occupies less than 25% of a cubesat's volume, and theoretically consumes less than 1.5W and 1W of peak and average power respectively. Furthermore, it is capable of providing sufficient torque and momentum storage for picosatellite attitude control in LEO. Next a novel adaptive Kalman filter algorithm is presented that can be implemented with the EKF and UKF for linear and non-linear systems respectively. The algorithm performs parameter estimation with sequential adaptive estimation and fading memory mechanisms that allow it to track changes in faulty parameters even in the presence of high levels of measurement noise. Furthermore, it is capable of tracking continuously varying and instantaneous changes in parameters. Numerical simulations are carried out to verify the performance of the propsed CMG cluster design as well as the fault diagnosis algorithm. The capabilities of the filter are further demonstrated via its application to a systems identification problem for a nonosatellite RW prototype being developed at SSDC group.

Advancements in Step Down Tests to Guide Perforation Cluster Design and Limited Entry Pressure Intensities - Learnings from Field Tests in Multiple Basins

This paper presents advancements in step-down-test (SDT) interpretation to better design perforation clusters. The methods provided here allow us to better estimate the pressure drop in perforations and near-wellbore tortuosity in hydraulic fracturing treatments. Data is presented from field tests from fracturing stages with different completion architectures across multiple basins including Permian Delaware, Vaca Muerta, Montney, and Utica. The sensitivity of near-wellbore pressure drops and perforation size on stimulation distribution effectiveness in plug-and-perf (PnP) treatments is modeled using a coupled hydraulic fracturing simulator. This advanced analysis of SDT data enables us to improve stimulation distribution effectiveness in multi-cluster or multiple entry completions. This analysis goes much further than the methodology presented in URTeC2019-1141 and additional examples are presented to illustrate its advantages. In a typical SDT, the injection flowrate is reduced in four or five abrupt decrements or "steps", each with a duration long enough for the rate and pressure to stabilize. The pressure-rate response is used to estimate the magnitude of perforation efficiency and near-wellbore tortuosity. In this paper, two SDTs with clean fluids were conducted in each stage - one before and another after proppant slurry was injected. SDTs were conducted in cemented single-point entry (cSPE) sleeves, which present a unique opportunity to measure only near-wellbore tortuosity using bottom-hole pressure gauge at sleeve depth, negligible perforation pressure drops, and less uncertainty in interpretation. SDTs were conducted in PnP stages in multiple unconventional basins. The results from one set of PnP stages with optic fiber distributed sensing were modeled with a hydraulic fracturing simulator that combines wellbore proppant transport, perforation size growth, near-wellbore pressure drop, and hydraulic fracture propagation. Past SDT analysis assumed that the pressure drop due to near-wellbore tortuosity is proportional to the flow rate raised to an exponent, β = 0.5, which typically overestimates perforation friction from SDTs. Theoretical derivations show that β is related to the geometry and flow type in the near-wellbore region. Results show that initial β (before proppant slurry) is typically around 0.5, but the final value of β (after proppant slurry) is approximately 1, likely due to the erosion of near-wellbore tortuosity by the proppant slurry. The new methodology incorporates the increase in β due proppant slurry erosion. Hydraulic fracturing modeling, calibrated with optic fiber data, demonstrates that the stimulation distribution effectiveness must consider the interdependence of proppant segregation in the wellbore, perforation erosion, and near-wellbore tortuosity. An improved methodology is presented to quantify the magnitude of perforation and near-wellbore tortuosity related pressure drops before and after pumping of proppant slurry in typical PnP hydraulic fracture stimulations. The workflow presented here shows how the uncertainties in the magnitude of near-wellbore complexity and perforation size, along with uncertainties in hydraulic fracture propagation parameters, can be incorporated in perforation cluster design.

Innovation-Centric Cluster Business Model: Findings from a Design-Oriented Literature Review

How should a cluster be designed to foster the innovativeness of its members? In this article, we view self-aware and organised clusters as “meta-organisations” which can deliberately shape their internal structures through design-based interventions. To formulate interventions for cluster design fostering its innovativeness, we adopt a methodology combining a systematic literature review and a design-oriented synthesis. We distinguish between six cluster business model elements: actors and their roles, resources and capabilities, value flows, governance, value propositions and value-creating activities. To gain insight into the properties of these elements conducive to cluster innovativeness, we review literature at the intersection of cluster, meta-organisation, business model and innovation studies. Our study allows to consolidate the extant research into “organised” clustering and the drivers of the cluster actors’ innovativeness. It also helps identify several important unanswered questions in the literature and to suggest potentially fruitful directions for further work.

The network architecture optimization based on the server load balancing technology

The paper takes the authentication gateway system for internal office network as the research object, for the performance bottleneck and single point of failure problem of the single authentication gateway deployed in the existing primary and standby modes, chooses an authentication gateway integration method based on CA certificate. The practical results show that: through implementing the authentication gateway cluster design and introducing load balancing mechanism, this method solves the performance, stability and single point of failure of the authentication gateway, and improves the resource utilization of the authentication gateway device. This method introduced in this paper can be used for reference for the network architecture optimization based on the server load balancing technology.

Identification of Potential Medicinal Plants in Tawang Selubang Forest in Kelam Permai Subdistrict, Sintang Regency, West Kalimantan

The Tawang Selubang Forest, located in the Other Use Area (APL) is determined by the regional government of Sintang Regency, West Kalimantan as the Hutan Tutupan (forest cover). This forest has great benefits for the community, one of which is as a source of medicinal plants. This research aims to identify the potential species of medicinal plants in the Tawang Selubang Forest Cover. Inventory of potential medicinal plants is done by making a square (0.5 Ha) cluster design (100 mx 100 m) in which there are 5 circular plots. Each plot contained several circular subplots that functioned for observation of seedling level (r= 1 m), stake (r= 2 m), pole (r= 5 m) and tree (r= 17.8 m). The number of plant species found in the Tawang Selawang Forest Cover were 47 species and 27 species were medicinal plants. Some species of medicinal plants that have a high density and important value index are Xanthophyllum amoenum Chadat, Antidesma montanum Blume, Nephelium maingayi Hiern, Palaquium gutta (Hook.) Baill and Syzygium lineatum (DC.) Merr. & J.Parn .