Gerçek-Zamanlı Çoklu-GNSS Hassas Nokta Konumlama (Multi-GNSS RT-PPP) Tekniğinin Performansının İncelenmesi (Performance Analysis of Real-Time Multi-GNSS Precise Point Positioning Technique)

Abstract

The Single-baseline Real-time Kinematic method was used in applications where real-time high accurate positioning is required. Studies carried out to eliminate some of the limitations in this method have brought up the idea of adding real-time positioning feature to Continuously Operating Reference Stations, thus Network-RTK (Network-RTK) method has emerged. The Network-RTK method offers a homogeneous accuracy in the centimeter level. However, in the Network-RTK method, it is necessary to have a reference network consisting of reference stations whose position is known with high accuracy, as well as a strong communication infrastructure is required to transmit the data of the stations to the control center and to transmit the obtained corrections to the rover receiver. Studies to eliminate these requirements in both RTK methods have led to the emergence of the technique called Precise Point Positioning (PPP). An average of 10-30 minutes of convergence time is required in order to achieve centimeter-decimeter accuracy with this method. This is a major shortcoming of PPP and significantly limits its usability in real-time applications.
Within the scope of the IGS-RTS (The International GNSS Service-Real-Time Service) project launched in 2013, the production of real-time precise satellite orbit and clock corrections and code/phase biases in addition to broadcasted ephemeris was started, as a result of that real-time PPP (RT-PPP) concept emerged. The IGS-RTS products used in this method are calculated by IGS analysis centers, formatted according to the RTCM State Space Representation (SSR) standard, and streamed real-time via the Internet with the NTRIP (The Networked Transport of RTCM via Internet Protocol) protocol. In the RT-PPP method, users need a computer/receiver connected to the internet and with a suitable software installed in order to take real-time corrections and GNSS measurements. Therefore, various interruptions in the data and correction retrieval process may limit real-time positioning or cause it to be impossible at all. For RT-PPP applications, real-time products in SSR format are offered by other institutions besides IGS. In this context, in addition to IGS Analysis Centers such as BKG, CAS, CNES, DLR, GFZ, GMV and WHU, real-time satellite orbit and clock correction services such as NAVCAST and MADOCA are available.
In this study, approximately 10 hours of real-time PPP application was carried out using the data of ISTA station, which is the only IGS-RTS point streaming real-time data in Türkiye. Correction products of IGS-RTS's CNES and BKG analysis centers and NAVCAST service were used in the study. RT-PPP solutions was done by using the aforementioned correction products with GPS-only, Galileo-only, and combination of both satellite systems. According to the results obtained from the study, it has been seen that it is possible to reach 1 dm horizontal and 2 dm vertical accuracies in the solutions obtained from all correction products. It has been seen that the RT-PPP accuracy and convergence performance
obtained by using GPS and Galileo systems together are more successful than the results obtained by using a single system. On the other hand, the solutions obtained using only the Galileo satellite system could not provide the cm-dm accuracy expected from the RT-PPP technique. In general, the obtained results show that the performance of the RT-PPP method depends on the used service, the analysis center and also the software and monitoring network used in the production of corrections. As a result, it has been seen that the most important key factor in obtaining real-time PPP solution by using the correction products of services such as IGS and NAVCAST is a stable, uninterrupted and high-quality internet connection.

Full text

Türkiye Ulusal Jeodezi Komisyonu 2022 Yılı Bilimsel Toplantısı, 02-04 Kasım 2022, Gebze
Turkish National Geodesy Commission 2022 Scientific Meeting, 02-04 November 2022, Gebze
Gebze Teknik Üniversitesi, Harita Mühendisliği Bölümü http://tujk2022.gtu.edu.tr
Gebze Technical University, Department of Geomatics Engineering
Gerçek-Zamanlı Çoklu-GNSS Hassas Nokta Konumlama (Multi-GNSS RT-PPP)
Tekniğinin Performansının İncelenmesi
Performance Analysis of Real-Time Multi-GNSS Precise Point Positioning Technique
Serdar Erol1, Bilal Mutlu1,, Reha Metin Alkan1
1İstanbul Teknik Üniversitesi, Sarıyer, İstanbul
mutlubil@itu.edu.tr
Özet
Gerçek-zamanlı yüksek doğruluklu konum belirlemenin gerekli olduğu uygulamalarda ilk olarak klasik
Real-time Kinematik (Tekli-RTK) ölçme yönteminden yararlanılmıştır. Bu yöntemdeki bazı kısıtları
ortadan kaldırmak üzere yapılan çalışmalar, sürekli gözlem yapan GNSS ağlarına gerçek zamanlı
konumlama özelliğinin eklenmesi fikrini ortaya çıkarmış, böylelikle Network-RTK (Ağ-RTK) yöntemi
geliştirilmiştir. Ağ-RTK yöntemi, santimetre mertebesinde, homojen bir doğruluk imkânı sunmaktadır.
Bununla birlikte, Ağ-RTK yönteminde konumu yüksek doğrulukla bilinen sabit istasyonlardan oluşan
bir GNSS ağına ve aynı zamanda sabit istasyonların verilerinin hesap merkezine iletilmesi ve elde edilen
düzeltmelerin gezici alıcıya iletilmesi için güçlü bir iletişim altyapısına gereksinim duyulmaktadır. Her
iki RTK yöntemindeki bu gereksinimleri ortadan kaldırmak için yapılan çalışmalar, Hassas Nokta
Konumlama (Precise Point Positioning-PPP) adı verilen tekniğin ortaya çıkmasını sağlamıştır.
Yöntemle santimetre-desimetre mertebesinde doğruluğa ulaşabilmek için ortalama 10-30 dakikalık
yakınsama süresine gereksinim duyulmaktadır. Bu durum PPP’nin önemli bir eksikliği olup, gerçek-
zamanlı uygulamalarda kullanılabilirliğini de önemli ölçüde kısıtlamaktadır.
2013 yılında hayata geçirilen IGS-RTS (The International GNSS Service-Real-Time Service) projesi
kapsamında yayın efemerisine ek olarak gerçek-zamanlı hassas uydu yörünge ve saat düzeltme ürünleri
ile kod/faz sapmalarının üretimine başlanılmış, bunun sonucunda da gerçek-zamanlı PPP (RT-PPP)
konsepti ortaya çıkmıştır. Bu yöntemde kullanılan IGS-RTS ürünleri, IGS analiz merkezlerince
hesaplanmakta, RTCM State Space Representation (SSR) standardına göre formatlanmakta ve NTRIP
(The Networked Transport of RTCM via Internet Protocol) protokolü ile internet aracılığıyla anlık
olarak yayımlanmaktadır. RT-PPP yönteminde gerçek zamanlı düzeltmelerin ve GNSS ölçülerinin
alınabilmesi için kullanıcıların internete bağlı ve uygun bir yazılımın yüklü olduğu bilgisayara (veya bu
özelliğe sahip alıcıya) ihtiyaçları bulunmaktadır. Dolayısıyla veri ve düzeltme alım sürecinde meydana
gelen muhtelif aksaklıklar gerçek-zamanlı konum belirlemeyi kısıtlayabilmekte veya hiç
yapılamamasına neden olabilmektedir. RT-PPP uygulamaları için IGS’ in dışında başka kurumlar
tarafından da SSR formatında gerçek zamanlı ürünler kullanıma sunulmuştur. Bu kapsamda BKG, CAS,
CNES, DLR, GFZ, GMV ve WHU gibi IGS Analiz Merkezlerine ek olarak, NAVCAST ve MADOCA
gibi servisler, gerçek-zamanlı uydu yörünge ve saat düzeltme bilgilerini kullanıcılarına sunmaktadır.
Bu çalışmada, ülkemizde gerçek-zamanlı veri yayımlayan tek IGS noktası olan ISTA istasyonu verileri
kullanılarak yaklaşık 10 saatlik gerçek-zamanlı PPP uygulaması gerçekleştirilmiştir. Çalışmada IGS-
RTS’ nin CNES ve BKG analiz merkezlerinin ve NAVCAST servisinin düzeltme ürünleri
kullanılmıştır. RT-PPP çözümleri; sadece GPS, sadece Galileo ve her iki uydu sisteminin kombinasyonu
ile, anılan düzeltme ürünleri kullanılarak gerçekleştirilmiştir. Çalışmadan elde edilen sonuçlara göre,
tüm düzeltme ürünlerinden elde edilen çözümlerde, yatayda 1 dm, düşeyde de 2 dm’ lik doğruluklara
erişmenin mümkün olduğu görülmüştür. GPS ve Galileo kombinasyonu ile elde edilen RT-PPP
doğruluk ve yakınsama performansının, tekli sistem kullanımı ile elde edilen sonuçlara göre daha
başarılı olduğu görülmüştür. Diğer yandan sadece Galileo uydu sistemi kullanılarak elde edilen
çözümler, RT-PPP tekniğinden beklenen cm-dm doğruluğu sağlayamamıştır. Genel olarak söylenecek
olursa, elde edilen sonuçlar RT-PPP yönteminin performansının kullanılan servise, analiz merkezine ve
düzeltmelerin üretiminde kullanılan yazılıma ve izleme ağına bağlı olduğunu göstermiştir. Diğer yandan
gerçek zamanlı PPP yönteminin başarılı bir şekilde uygulanabilmesinin sağlam, kesintisiz ve kaliteli bir
internet bağlantısına bağlı olduğu da anlaşılmıştır.
Anahtar Kelimeler: Tekli-RTK, Ağ-RTK, PPP, RT-PPP, IGS-RTS, NAVCAST

Türkiye Ulusal Jeodezi Komisyonu 2022 Yılı Bilimsel Toplantısı, 02-04 Kasım 2022, Gebze
Turkish National Geodesy Commission 2022 Scientific Meeting, 02-04 November 2022, Gebze
Gebze Teknik Üniversitesi, Harita Mühendisliği Bölümü http://tujk2022.gtu.edu.tr
Gebze Technical University, Department of Geomatics Engineering
Abstract
The Single-baseline Real-time Kinematic method was used in applications where real-time high
accurate positioning is required. Studies carried out to eliminate some of the limitations in this method
have brought up the idea of adding real-time positioning feature to Continuously Operating Reference
Stations, thus Network-RTK (Network-RTK) method has emerged. The Network-RTK method offers a
homogeneous accuracy in the centimeter level. However, in the Network-RTK method, it is necessary
to have a reference network consisting of reference stations whose position is known with high accuracy,
as well as a strong communication infrastructure is required to transmit the data of the stations to the
control center and to transmit the obtained corrections to the rover receiver. Studies to eliminate these
requirements in both RTK methods have led to the emergence of the technique called Precise Point
Positioning (PPP). An average of 10-30 minutes of convergence time is required in order to achieve
centimeter-decimeter accuracy with this method. This is a major shortcoming of PPP and significantly
limits its usability in real-time applications.
Within the scope of the IGS-RTS (The International GNSS Service-Real-Time Service) project
launched in 2013, the production of real-time precise satellite orbit and clock corrections and code/phase
biases in addition to broadcasted ephemeris was started, as a result of that real-time PPP (RT-PPP)
concept emerged. The IGS-RTS products used in this method are calculated by IGS analysis centers,
formatted according to the RTCM State Space Representation (SSR) standard, and streamed real-time
via the Internet with the NTRIP (The Networked Transport of RTCM via Internet Protocol) protocol. In
the RT-PPP method, users need a computer/receiver connected to the internet and with a suitable
software installed in order to take real-time corrections and GNSS measurements. Therefore, various
interruptions in the data and correction retrieval process may limit real-time positioning or cause it to
be impossible at all. For RT-PPP applications, real-time products in SSR format are offered by other
institutions besides IGS. In this context, in addition to IGS Analysis Centers such as BKG, CAS, CNES,
DLR, GFZ, GMV and WHU, real-time satellite orbit and clock correction services such as NAVCAST
and MADOCA are available.
In this study, approximately 10 hours of real-time PPP application was carried out using the data of
ISTA station, which is the only IGS-RTS point streaming real-time data in Türkiye. Correction products
of IGS-RTS's CNES and BKG analysis centers and NAVCAST service were used in the study. RT-PPP
solutions was done by using the aforementioned correction products with GPS-only, Galileo-only, and
combination of both satellite systems. According to the results obtained from the study, it has been seen
that it is possible to reach 1 dm horizontal and 2 dm vertical accuracies in the solutions obtained from
all correction products. It has been seen that the RT-PPP accuracy and convergence performance
obtained by using GPS and Galileo systems together are more successful than the results obtained by
using a single system. On the other hand, the solutions obtained using only the Galileo satellite system
could not provide the cm-dm accuracy expected from the RT-PPP technique. In general, the obtained
results show that the performance of the RT-PPP method depends on the used service, the analysis center
and also the software and monitoring network used in the production of corrections. As a result, it has
been seen that the most important key factor in obtaining real-time PPP solution by using the correction
products of services such as IGS and NAVCAST is a stable, uninterrupted and high-quality internet
connection.
Keywords: Single-baseline RTK, Network-RTK, PPP, RT-PPP, IGS-RTS, NAVCAST