林芝机场GBAS信号完整性监控可用性预测与分析

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本文主要探讨了在林芝机场安装GBAS（Ground-Based Augmentation System）时，对GBAS信号完整性监控可用性进行预测与分析的重要性。GBAS是一种地面增强导航系统，对于提升飞行安全和精确度至关重要。研究者们利用现有的标准文档和已发表的研究成果，开发了一种软件工具，专门用于预测GBAS在林芝机场的服务可用性。模拟实验涵盖了单点、单一进近路径以及同一进近路径的多次重复，旨在深入理解GNSS（全球导航卫星系统）信号在不同场景下的可靠性。具体来说，针对GBAS的两种服务类型——C级（GASTC）和D级（GASTD），分析结果显示： 1. 对于GASTC，典型单点沿进近路径的长期（24小时）服务可用性高达99.999%，这表明系统在大部分时间里能够提供高度稳定的服务。 2. 而对于GASTD，在三个典型单点处，其服务可用性低于99.8%，这意味着尽管整体性能良好，但存在一定的不稳定因素。在24小时内，GASTC的不可用百分比为0.76%，而GASTD的不可用百分比则更高，达到2.40%。这些数据揭示了不同GBAS服务类型对信号完整性的实际影响。此外，敏感性测试还探究了遮挡角和纬度等因素对GBAS可用性的影响。通过这些测试，研究者们得以评估环境变化和系统参数调整如何影响GBAS的运行效率，并据此优化系统的部署策略和维护计划。这篇研究论文为林芝机场GBAS的安装和运营提供了关键的数据支持，强调了对GBAS信号完整性监控可用性预测的必要性和细致的分析工作，这对于提高机场导航系统的可靠性和安全性具有重要的实践指导意义。

where x

air

is the slant range distance (in meter) between current aircraft location and the reference point,

i is the index of ranging sources used in the position solution, P

k_x

is the broadcast ephemeris

decorrelation parameter for the j

ranging source, which is set to 0.00015 meters/meter in Section F3.4

of RTCA DO245A (2004), and K

md_e_x

is the appropriate broadcast ephemeris missed detection

multiplier for the approach associated with the satellite constellation for the j

ranging source. In Table

B-3 of RTCA DO246D (2009), the suggested values for K

md_e_C,GPS,

and K

md_e_D,GPS

are 5.0 and 5.6,

respectively.

According to Section 2.3.11.5.2.1 of RTCA DO253C (2008), the airborne GBAS system will raise a

flag as being unavailable if VPL

Apr

or VPB

Apr_e

exceeds the vertical alert limit. Therefore, VPL is defined

as the maximum of VPL

Apr

and VPB

Apr_e

User differential range error models

SIS pseudorange accuracy model σ

pr_gnd_x,i

depends on the Approach Service Type that is currently in

use. However, there is no model available for GAST D in the standard documents or published studies.

Additionally, the ground accuracy bound should not be really impacted by the change in code carrier

smoothing time constant because it is a bound to several errors sources (Neri et al. 2010). Therefore, for

GAST C and D, the same model is used in our simulations and is given as

()

pr gnd i

aae











(9)

where M

is the number of reference receivers, i is the i

ranging source, θ

is the ranging source

elevation angle for ground station receivers, and a

, a

and θ

depend on the level of Ground

Accuracy Designators (GAD) (i.e., A, B and C) as defined in Table 3-1 of RTCA DO245A (2004).

The residual tropospheric uncertainty is defined in Section 2.3.12.2 of RTCA DO253C (2008) as

() 1

0.002 sin ( )

tropo i N



















(10)

where θ

is the elevation angle, σ

is the refractivity uncertainty transmitted by the ground subsystem,

and h

is the troposphere scale height transmitted by the ground subsystem (in meter). The values for σ

and h

are set to 34 and 7600 m, respectively, as in Section F3.4 of RTCA DO245A (2004). The

difference Δh in altitude between airborne and ground subsystems (in meter) changes with time.

Similar to σ

pr_gnd_x,i

, the residual ionospheric delay uncertainty σ

iono,i

also depends on the Approach

Service Type. For GAST C the value for σ

iono,i

is set based on σ

vert_iono_grad

broadcast in Message Type

(MT) 2; for GAST D it is set based on σ

vert_iono_grad_D

transmitted by the MT 2 additional data block. The

parameter σ

vert_iono_grad_D

differs from σ

vert_iono_grad

in that the former should include no adjustment to

address overbounding of anomalous errors according to Section 2.4.4.2 of RTCA DO246D (2009).

However, since there is no reference value for σ

vert_iono_grad_D

, an increased value of 4mm/km is used in

our simulations, similar to the strategy adopted by DLR (Dautermann et al. 2012). The residual

ionospheric uncertainty for a given satellite is thus (RTCA DO245A 2004, RTCA DO253C 2008):,





iono pp vert iono grad air air

 

   (11)

where F

is the vertical-to-slant obliquity factor (unitless) for a given satellite, χ

air

is the same as the

one in equation (8), τ equals to 100 seconds both for GAST C and GAST D as in Table 2-18 of RTCA

DO253C (2008), and v

air

is the aircraft horizontal approach velocity, which is assumed to be 77 m/s for

GAST C and 72 m/s for GAST D as in Section F3.3 of RTCA DO245A (2004).

For GAST C, the total aircraft contribution includes the receiver contribution and a standard

allowance for airframe multipath as

22 2

() () ()

air i i receiver i multipath i



  

 (12)

(/ )

()

receiver i

aae







 (13)

(/ )

()

multipath i

aae







 (14)

where i is i

ranging source, θ

is the ranging source elevation angle for the i

ranging source, and a

, a

and θ

depend on either the level of Airborne Accuracy Designators (AAD) (equation (13)) or Airborne

Multipath Designators (AMD) (i.e., A and B) in equation (14)) as defined in Sections 3.3.1.1 and 3.3.1.3

of RTCA DO245A (2004).

For GAST D, in addition to the contributions of receiver and multipath, the σ

air,i

should also include

the effects of code-carrier divergence. Since no standardized model is available, the model proposed by

Neri et al. (2010) is used in the simulations,

_, ,

100 / 30

air GASTD i air i



 (15)

This model takes into account the different code carrier smoothing time constant.

Model of the B value

Since the simulation of pseudorange corrections is complex and not necessary to analyze PLs, models

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林芝机场GBAS信号完整性监控可用性预测与分析

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