A positioning method of BDS receiver under weak signal circumstances based on Compressed Fractional-Step

U ovom se radu predlaže sažeta metoda frakcijskog koraka koja se odnosi na pozicioniranje BDS prijemnika u uvjetima slabog signala. Zatim se analiziraju karakteristike BDS konstelacije i poboljšava originalni algoritam zasnovan na dinamičkim uvjetima miješane konstelacije raznih satelita. U odnosu na neodređenost decimale tisućinke sekunde nastale zbog greške sata prijemnika pri izračunu, ovaj rad razvija način obrade proširenja dimenzija pretrage i korištenja metode frakcijskog koraka implicirane informacije o elevaciji prijemnika koja se zatim substituira u jednadžbu kao promatrana količina kako bi se smanjila izračunata količina neodređenosti. U zaključku se kaže da u najnepovoljnijim uvjetima ova metoda može smanjiti gotovo polovicu količine izračuna čitave druge fuzzy pretrage vremena emisije signala. U radu se također predlaže metoda skraćenja proračuna kako bi se smanjio raspon između približnog položaja i greške na satu zasnovana na karakateristici da je dinamika ne-MEO satelita među BDS satelitima mala. Uključujući ne-MEO satelite u računanje, sateliti mogu smanjiti potrebe za točnošću lokalnog sata prijemnika. Teorijski, računanje uporabom čistih GEO satelita može proširiti potrebu od 187,5 s na 1500 s. Imajući u vidu rezultate simulacije, proizlazi da kada je informacija o elevaciji poznata i točna, prvim se korakom računanja frakcijskog koraka može zadovoljiti potreba za pozicioniranjem. Inače, drugim se korakom računanja može dobiti točno pozicioniranje i postići rapidno pozicioniranje u uvjetima slabog signala.This article puts forward the compression fractional-step method which applies to the positioning of BDS receivers under weak signal circumstances. It then analyses the features of BDS constellation and improves the original algorithm based on various satellites’ dynamic conditions of mixed constellation. With respect to the ambiguity of the decimal of milliseconds arising from the clock error of receivers in the process of calculation, this article advances a processing mode of extending search dimension and a fractional-step method of employing the implied elevation information of receivers which is then substituted into the equation as the observed quantity to reduce the calculation amount of ambiguity. It concludes that in the most adverse circumstances this method can reduce nearly half of the calculation amount of the whole second fuzzy search of signals’ emission time. This article also brings forward the compression calculation method to compress the range between the approximate position and clock error based on the feature that the dynamic of non-MEO satellites among BDS satellites is small. Taking non-MEO satellites as calculation, satellites can reduce the accuracy requirements of the local clock of receivers. In theory, calculation through using pure GEO satellites can broaden the requirement from 187,5 s to 1500 s. In the light of simulation results, it turns out that when the elevation information is known and precise, the first step of fractional-step calculation is capable of meeting the requirement of positioning. Otherwise, the second step of calculation can obtain the accurate positioning and achieve the rapid positioning under weak signal circumstances

A Quick Location Method for High Dynamic GNSS Receiver Based on Time Assistance

Traditional A-GPS positioning method when quickly calculate a position, need a condition that the approximate position must not exceed 150km, otherwise the calculation will be very complex. This paper proposes a time-assisted fast positioning method for high dynamic GNSS receiver, effectively solving the problem of large search calculation in traditional method, even if exact position is unknown after the signal is recaptured. According to the known auxiliary time information and implied  elevation information, this paper put forwards a custom coordinate system for building twodimensional search space, which could reduce the number of search-dimensions. It proposes a search method based on receiver clock calculated by analyzing the influence of time auxiliary accuracy. By using GPS ephemeris data provided by the IGS, it builds a simulation environment and analyzes the influence of different preferred satellites based on the custom coordinate system on the calculation, and thus puts forward a principle for choosing the preferred satellites. Simulation examples show that through the rational combination of satellites to create a custom coordinate system, and when time auxiliary accuracy is less than 60us, the calculation can 100% guarantee to restore a complete satellite signal emission time and obtain an accurate position

The positioning method of BDS receiver with auxiliary clock under the weak signal circumstance

Tradicionalni algoritam za pronalaženje vremena odašiljanja ne može se primijeniti u praksi zbog drastičnog povećanja izračuna kada je nepoznat približan položaj prijemnika. U ovom se radu predlaže metoda za određivanje položaja prijemnika temeljena na pomoćnom satu, koja se može primijeniti kada je približan položaj prijemnika nepoznat. Kako bi se odredilo područje traženja, u radu se koriste dva GEO satelita za dobivanje polarnih koordinata, i reduciraju se nepoznati brojevi pretraživanja na osnovu informacija o dometu elevacije uključenih u prijemniku. Nadalje, prema ograničenjima područja pokrivenog satelitskim signalom, preporučuje se izabrati dva najudaljenija GEO satelita za stvaranje uobičajenog koordinatnog sustava te dodati bilo koji broj satelita zbog verifikacije i selekcije, da bi se vrijeme prijenosa signala uspjelo vratiti do tisućinke sekunde. Ta se metoda provjerava simulacijskom analizom, točnije, statistička analiza točnosti algoritma pomoćnog sata provodi se jedino u uvjetima GEO konstelacije u Kini i susjednim područjima. U zaključku se pokazuje da kada je greška na pomoćnom satu ispod 100 us, a broj satelita za provjeru je dovoljan, prijemnik se može brzo pozicionirati u uvjetima slabog signala čak i kada mu je približni položaj nepoznat.The traditional time-of-transmission recovery algorithm cannot be applied to practice due to a drastic calculation increase when the approximate position of receiver is unknown. This paper puts forward a receiver positioning method based on auxiliary clock, which can be used when the receiver’s approximate position is unknown. To determine search scope, the paper makes use of double GEO satellites to build custom polar coordinates, and reduces unknown searching numbers on the basis of elevation range information implied in the receiver. Furthermore, according to the restraints of satellite signal coverage scope, it is advocated to choose two farthest GEO satellites to build the custom coordinate system, and add any validation satellites for verification and selection, so as to realize the restoration of millisecond integer of signal transmission time. This method is verified through simulation analysis. To be specific, statistical analysis of the algorithm’s precision requirements of auxiliary clock is made under the application circumstance of only GEO constellation in China and neighbouring areas. The conclusion shows that, when the auxiliary clock error is below 100 us and the number of validation satellites is enough, the receiver can be rapidly positioned under the weak signal circumstance even when the approximate position is unknown

Amplified role of potential HONO sources in O3 formation in North China Plain during autumn haze aggravating processes

Co-occurrences of high concentrations of PM2.5 and ozone (O-3) have been frequently observed in haze-aggravating processes in the North China Plain (NCP) over the past few years. Higher O-3 concentrations on hazy days were hypothesized to be related to nitrous acid (HONO), but the key sources of HONO enhancing O-3 during haze-aggravating processes remain unclear. We added six potential HONO sources, i.e., four groundbased (traffic, soil, and indoor emissions, and the NO2 heterogeneous reaction on ground surface (Het(ground))) sources, and two aerosol-related (the NO2 heterogeneous reaction on aerosol surfaces (Het(aerosol)) and nitrate photolysis (Phot(nitrate))) sources into the WRF-Chem model and designed 23 simulation scenarios to explore the unclear key sources. The results indicate that ground-based HONO sources producing HONO enhancements showed a rapid decrease with height, while the NO C OH reaction and aerosol-related HONO sources decreased slowly with height. Photnitrate contributions to HONO concentrations were enhanced with aggravated pollution levels. The enhancement of HONO due to Phot(nitrate) on hazy days was about 10 times greater than on clean days and Phot(nitrate) dominated daytime HONO sources (similar to 30 %-70% when the ratio of the photolysis frequency of nitrate (J(nitrate)) to gas nitric acid (JHNO(3)) equals 30) at higher layers (>800 m). Compared with that on clean days, the Phot(nitrate) contribution to the enhanced daily maximum 8 h averaged (DMA8) O-3 was increased by over 1 magnitude during the haze-aggravating process. Phot(nitrate) contributed only similar to 5% of the surface HONO in the daytime with a J(nitrate) =JHNO(3) ratio of 30 but contributed similar to 30 %-50% of the enhanced O-3 near the surface in NCP on hazy days. Surface O-3 was dominated by volatile organic compound-sensitive chemistry, while O-3 at higher altitudes ( >800 m) was dominated by NOx-sensitive chemistry. Phot(nitrate) had a limited impact on nitrate concentrations (Peer reviewe

Dust emission reduction enhanced gas-to-particle conversion of ammonia in the North China Plain

Liu et al. found that the formation rate of particulate ammonium is slower in the atmosphere than that observed in the laboratory, while it is sped up due to an increase in aerosol acidity driven by an emission reduction of dust in North China Plain.Ammonium salt is an important component of particulate matter with aerodynamic diameter less than 2.5 mu m (PM2.5) and has significant impacts on air quality, climate, and natural ecosystems. However, a fundamental understanding of the conversion kinetics from ammonia to ammonium in unique environments of high aerosol loading is lacking. Here, we report the uptake coefficient of ammonia (gamma(NH3)) on ambient PM2.5 varying from 2.2 x 10(-4) to 6.0 x 10(-4) in the North China Plain. It is significantly lower than those on the model particles under simple conditions reported in the literature. The probability-weighted gamma(NH3) increases obviously, which is well explained by the annual decrease in aerosol pH due to the significant decline in alkali and alkali earth metal contents from the emission source of dust. Our results elaborate on the complex interactions between primary emissions and the secondary formation of aerosols and the important role of dust in atmospheric chemistry.Peer reviewe