Improving Sensitivity and TTFF

J A N U A R Y / F E B R U A R Y 2 0 1 4 www.insidegnss.com The structure of current GNSS open service signals is the result of a design trade-off between several performance figures of merit. The most relevant are position accuracy, receiver sensitivity (for signal acquisition, tracking, and data demodulation), and the time to first fix (TTFF). Signal performance generally results from a compromise among those. However, if one concentrates on the signal acquisition phase, the last two factors assume a much higher relevance. Also, the design of the navigation message has to take into account many needs, and the information transmitted has to serve different services and/or classes of users. Again, of all the information present in a typical navigation message, only a portion is relevant to obtain the first position fix within a reasonable amount of time. The main goal of the work described in this article is to propose the design of an acquisition-aiding signal and to discuss the benefits of adding such a signal to the current GNSS baselines. Our work has focused on the Galileo E1 Open Service (E1-OS), but many of the concepts that we will introduce can be easily extended to any GNSS signal. The discussion presented here clearly does not pretend to be a proposal for an actual system implementation.