36 InsideGNSS OCTOBER 2010 www.insidegnss.com I n the irst article in this series ( Inside GNSS, July/August, 2010) we looked at the range of tasks that require GNSS signal simulation during design, manufacturing, certification, and maintainence of GNSS equipment. he second installment (Inside GNSS, September/October, 2010) described a range of simulation solutions. In this inal article, we try to ind a simulation solution that best suits a par- ticular task. Live Satellites Versus Simulation Until this point in the series we haven’t really discussed the possibility of using live satellites for testing. he main dis- advantage in using live satellites is that a user has much less control over the test environment. With live satellite testing the user can only to some extent determine the GNSS user equipment’s antenna location and operating environment and has no control over the signal parameters them- selves. Therefore, using a live satellite type of testing at R&D, design, certi i- cation, and maintenance stages is much less deterministic than use of an RF sim- ulator, and even during manufacturing and QA testing the latter approach has the advantage. Let’s look, for example, at a few tests that we may wish to do during a receiver design process and see if they can be done using live satellites. We used our sotware receiver to conduct these tests in combination with a high-end RF simulator for GPS and GLONASS. We also have conducted a number of tests for Galileo, as far as Galileo is supported by the receiver. Figure 1 shows a screen shot of the total satellite constellation that we simu- lated during the test. Our tests mirrored a few general tests and may be described as follows: 1. After receiver tracking loops are designed, we would need to check if they deliver correct observations, such as code phase, carrier phase, Doppler, and carrier-to-noise ratio (C/N 0 ). Using a simulator we know the true observations and directly compare them with those measured epoch by epoch. his test may be possible to do with live satellites, but with much greater efort and less usable results. Such a test would require us to survey the antenna position in advance, collect the predicted ephemerides, and cal- culate a predicted range to a satellite and Doppler shit. his procedure, however, would not guarantee deinitive results. For instance, the satellite orbits can be This article concludes our series about the use of simulators and simulation techniques in developing GNSS receivers. Part 3 examines various simulator designs and wheth- er the specifications of any given simulator equpment is suitable for a particular test. IVAN PETROVSKI, IP-SOLUTIONS TOSHIAKI TSUJII, JAXA JEAN-MICHEL PERRE, THALES AVIONICS BRYAN TOWNSEND, ROBERTON ENTERPRISES LTD. TAKUJI EBINUMA, UNIVERSITY OF TOKYO GNSS Simulation: A User’s Guide to the Galaxy