Augmentation Methods for GNSS Integrity and Precision Enhancement in Difficult Environment

The topic of the paper is to describe influences of the difficult environment to the GNSS and SBAS signals and consequences for signal processing. At first, the issues related to signal reception in difficult environment are discussed, namely signal attenuation and shadowing, multipath propagation and effects related to user receiver movement. The satellite line of sight shadowing influence to signal reception is discussed for various environments together with proposed shadowing model. The model is derived from two state Markov model. The experimental measurements of mobile reception of EGNOS signal has shown the need of supporting SBAS signals in several environment by complementary transmission. Such concept of supporting system with data transmitted by separate channel is discussed in the paper both for DGNSS and SBAS case. The possibility and analysis of use of Internet for real time distribution of augmentation data is presented in the paper, namely questions of data latency and augmentation influence to user position in difficult environment. INTRODUCTION The satellite navigation systems are now frequently used in wide range of applications and environments. The plan of combination of in the future available Galileo system with modernized GPS and restored GLONASS will bring to the sky more than 60 satellites whose ranging signal can be used. The concept of Global Navigation Satellite System (GNSS) together with the development of the integrated chipsets for all systems for mobile equipment open broad spectrum of possible applications. It can be various Location Based Services (LBS), for example hazardous material transport monitoring, public transport services optimization and synchronization, position based lock of the classified data or position based advertising, or incorporation of GNSS to position determination for E112 emergency calls. A lot of present and future mobile phones and handhelds will have built in navigation receivers intended for personal oriented LBS use. All the mentioned cases are characteristic by one common attribute: navigation receivers are supposed to work under various circumstances, even under the difficult conditions or indoors. For example journey passing through terrain cuts or urban canyons, inside of the store-house, high-rise building or roofed station, virtually any place where the position demand occurs. The users of all applications expect the stable quality of LBS no matter to the environment the service is used in. That's why the use of GNSS in difficult environment brings new challenges in the GNSS signal processing and receiver design. Moreover, safety critical applications need high level of GNSS integrity information and highest