Simulating Ionospheric Effects on GPS Signals in Space Teddy M. Surco Espejo (1)* , Emanoel Costa (1) , Alison de O. Moraes (2) , Eurico R. de Paula (3) , João Francisco Galera Monico (4) (1) Centro de Estudos de Telecomunicações, Pontifícia Universidade Católica do Rio de Janeiro (CETUC PUC-Rio); Rua Marquês de São Vicente 225; 22451-900 Rio de Janeiro, RJ, Brazil; teddy@cetuc.puc-rio.br (*presenting author), epoc@cetuc.puc-rio.br (2) Instituto de Aeronáutica e Espaço/Instituto Tecnológico de Aeronáutica, Praça Marechal Eduardo Gomes 50; 12228-900 São José dos Campos, SP, Brazil; aom@ita.br (3) Instituto Nacional de Pesquisas Espaciais (INPE), Av. dos Astronautas, 1.758 - Jardim da Granja, 12227-010 São José dos Campos, SP, Brazil, eurico.paula@inpe.br (4) Universidade Estadual Paulista Júlio de Mesquita Filho - UNESP, R. Roberto Símonsen, 305, 19060-900 Presidente Prudente, SP, Brazil, galera.monico@unesp.br The Global Positioning System (GPS) is extensively used for navigation and positioning in static or kinematic condition in a large number of applications, such as Air Traffic Control. The ionosphere affects the propagation of the signal GPS and can reduce the accuracy of positioning by tens of meters particularly in the equatorial and low-latitude regions. Auxiliary systems have been developed to meet the safety requirements of aviation. For example, Ground Based Augmentation Systems (GBAS) provide higher accuracy for differential corrections. The propagation and degradation of signals in space due to ionospheric effects are important and are the focus of this work, which describes a simulation model of the GPS observables for future GBAS applications. For completeness, non ionospheric effects will also be considered. For each active communication channel between satellite i and receiver j, the following expressions apply for the pseudorange (,) , carrier phase (,) , and received power (,) of the GPS L1 signals: (,) = (,) + [△ () −△ () ]+ (,) + (,) + PR(,) + PR(,) (,) = (,) + [△ () −△ () ]− (,) + (,) + (,) + 1 (,) + (,) + (,) (,) = () +G () + (,) + () + C(,) + 20log[ (,) ] where (,) is the geometric range; △ () and △ () are the receiver and satellite clock errors, respectively; (,) and (,) represent the ionospheric and tropospheric delays, respectively; ,,(,) are associated with multipath effects on the pseudorange, carrier phase, and power, respectively; ,(,) represents random errors in the pseudorange and carrier phase, respectively; 1 = 1 ⁄ is the L1 wavelength, c is the velocity of light in free space, and 1 is the L1 frequency; (,) is an integer number representing the cycle ambiguity, which considers effects from cycle-slips; (,) and (,) represent phase and amplitude ionospheric scintillation effects; () is the effective isotropic radiated power of each satellite transmitter; () and () are the gains of the satellite and receiver antennas in the pertinent directions, respectively; and (,) is the free-space path loss, represented by: