Theoretical Capacity Analysis Research Articles

Ultra-Dense LEO Satellite Constellations: How Many LEO Satellites Do We Need?

Recently, the ultra-dense low Earth orbit (LEO) satellite constellation over high-frequency band has served as a potential solution for high-capacity backhaul data services. In this paper, we consider an ultra-dense LEO-based terrestrial-satellite network where terrestrial users can access the network through the LEO-assisted backhaul. We aim to minimize the number of satellites in the constellation while satisfying the backhaul requirement of each user terminal (UT). We first derive the average total backhaul capacity of each UT, based on which a three-dimensional constellation optimization algorithm is proposed to minimize the number of satellites in the constellation. Simulation results verify our theoretical capacity analysis and show that for any given coverage ratio requirement, the corresponding optimized LEO satellite constellation can be obtained by the proposed three-dimensional constellation optimization algorithm. Given the same number of deployed LEO satellites, the average coverage ratio of the proposed LEO satellite constellation is at least 10 percentage points higher than that of Telesat constellation.

Single‐carrier frequency domain equalisation for microwave LOS‐MIMO systems and its performance analysis

The authors analyse and investigate the effectiveness of frequency domain equalisation (FDE) for single-carrier (SC) transmission over a line-of-sight multiple-input multiple-output (LOS-MIMO) channel with frequency selective fading. For this purpose, they propose a 2 × 2 LOS-MIMO system model employing SC-FDE techniques together with a data frame structure having a cyclic prefix and postfix (CPP) overhead. The channel capacity of the proposed system is derived taking into account system design parameters, such as symbol rate and roll-off factor, as well as multipath fading channel parameters. An efficient channel estimation method is also proposed for implementing and simulating the proposed system. Signature curves estimated in simulations are consistent with those expected from the theoretical capacity analysis. The simulation results show that the SC-FDE approach to the LOS-MIMO system can, with small CPP overhead, effectively reduce intersymbol and interstream interference.

Performance of time reversal precoding technique for MISO-OFDM systems

Time reversal (TR) is considered as a promising technique for green and multi-user communications thanks to its time and space focusing properties. TR can be viewed as a precoding scheme which can be combined with orthogonal frequency division multiplexing (OFDM) and easily carried out in a multiple transmit antenna context. This paper analyzes the performance of TR for a multiple-input single-output (MISO) OFDM system and provides a comparison with maximum ratio transmission (MRT) and equal gain transmission (EGT) precoding techniques. The analytical performance of the three precoding techniques is derived by computing the capacity and the bit error rate (BER) as a function of the transmit signal-to-noise ratio (SNR). First, the capacity analysis highlights the ability of the TR system to provide higher bit rates than the MRT system at low SNRs, while the capacity of the MRT system is the highest at high SNRs. From the obtained BER analytical expressions, the diversity exploitation of each system is discussed. In particular, it is shown that the TR system only exploits half the available diversity, while the systems using EGT or MRT exploit the full diversity. Hence, contrary to what is expected from the theoretical capacity analysis, the TR system is shown to underperform the other precoding schemes in terms of BER. To overcome such a drawback, the combination of TR with classical adaptive modulation techniques is studied, allowing the achievable throughput to be increased without destroying the focusing properties of TR. It is then observed that TR takes advantage of adaptive modulations and outperforms the other schemes at low SNRs. In this study, analytical results and closed-form expressions of capacity and BER performance are provided and confirmed through Monte Carlo simulations.

Finite Element Numerical Simulation Analysis on Strengthening High Gravity Abutment Using Carbon Fiber Sheet

Gravity abutment widely uses for substructure part of the bridge structure. For many reasons, there are many damages take place in the parts of abutment. The objective of this study is to evaluate the strengthening effects on the performance of highly structure of Gravity abutment. ANSYS ver.10 software is used in the theoretical analysis of capacity of abutment structure .There are two experimental models. The first model uses one ring of carbon fiber sheet and the second uses two rings of carbon fiber sheet .The results of theoretical analysis show that there are good effects when using carbon fiber sheet strengthening method.

Serine alkaline protease overproduction capacity of Bacillus licheniformis

A comprehensive metabolic network that considers 147 reaction fluxes and 105 metabolites is used in a mass-flux-balance-based stoichiometric model for Bacillus licheniformis for serine alkaline protease (SAP) overproduction. The theoretical capacity analysis leading to optimized SAP overproduction was carried out by using a linear constrained optimization technique for several specific growth rates and the variation of the fluxes were calculated by fixing the sole carbon source citrate’s uptake rate at 10 mmol/gDW/h. The theoretical data-based capacity analysis was conducted by using the model in combination with the off-line extracellular analyses of the dry cell and the metabolites that were citrate, organic acids, amino acids, and SAP; and the variations in the intracellular fluxes were obtained for the three periods of the batch bioprocess. The flux distribution maps of the analyses showed that the tricarboxylic acid cycle was active and the cells utilized the gluconeogenesis pathway, the pentose phosphate pathway, and the anaplerotic reactions; nevertheless, the glyoxylate shunt and the glycolysis pathway were inactive. The theoretical capacity analysis showed that SAP synthesis flux increased with the decrease in the specific growth rate, and was the highest at μ = 0 h −1 as 0.0260 mmol/gDW/h. Both in the theoretical capacity and the theoretical data-based capacity analyses, among the fluxes towards the amino acid groups, aspartic acid group had the highest value and aromatic acid group had the lowest flux value; the flux distributions are similar. The flux values towards SAP was maximum in Period II, whereas it was minimum in Period I. In Period II of the theoretical data-based capacity analysis, the fluxes of alanine and valine are higher than the other amino acid fluxes; and the pyruvate branch point seems to be the potential metabolic engineering site. The results reveal that SAP production can theoretically be increased 1.09, 16.68, and 7.21 folds, respectively, in Periods I, II, and III. The diversions in the pathways and certain metabolic reactions depending on the bioprocess periods and potential strategies for improving SAP production are also discussed.

Experimental and theoretical capacity analysis of space-division multiple access (SDMA) with adaptive antennas

The paper focuses on TDMA air interface techniques combined with spatial multiplexing through the space division multiple access (SDMA) method. First, results from field trials performed for a variety of operational scenarios provide experimental proof of the SDMA concept for two users. Then, the capacity of the space and time division multiple access scheme is studied with the help of simulations, but from the more general and practical point of view of the produced/achieved radiation-pattern characteristics. Up to now, the analyses for the capacity of SDMA systems have ignored the critical effects that parameters, such as the scattering of the environment, the mutual coupling among the array elements or signal mismatches, have on the produced radiation pattern. The straightforward method employed in the analysis presented here takes into account these effects and hence produces a more realistic capacity assessment. The presented results for different radiation pattern beamwidths and average sidelobe levels, different frequency reuse distances and additional interference cancellation techniques highlight the trade-offs between different performance criteria and the implications to the overall system design.