GNSS radio signal for improved synchronization

#The present invention concerns the technological field of satellite radionavigation. The invention is concerned with a global navigation satellite system (“GNSS”) positioning method that is based upon the radionavigation signals transmitted by satellites (hereafter “GNSS radio signals” or “GNSS signals”), in particular with the navigation message communicated by these signals to the user receivers in order to enable or facilitate geopositioning by said receivers.

#GNSS signals (the “Signal-in-Space” segment) are the main interface between a GNSS (“Global Navigation Satellite System”) spatial infrastructure and the various user segments thereof. In this respect, it plays a major part in the performance which will be available to a user in a given environment and use context. This is because performance is the result of the receiving algorithms used (a function of the use context) and of the quality of the signal which reaches the user (affected by propagation conditions).

#The spectral and temporal characteristics of the signal, such as carrier frequency, power or modulation (PRN, BPSK, BOC rate) parameters, substantially determine performance in terms of interoperability, tracking and interference and multipath robustness, etc.

#Other distinctive features and characteristics of the invention will emerge from the detailed description of some advantageous embodiments given below by way of illustration with reference to the appended drawings, in which:

#FIG. 1: is a diagram of the structure of a Galileo I/NAV radionavigation signal provided on the E1-B signal component;

#FIG. 2: is a diagram of the structure of a subframe of the I/NAV radionavigation message on the E1-B signal component;

#The embodiment of the invention discussed below is based on the I/NAV navigation message transmitted on the E1-B component (data channel of the E1 OS signal) of the Galileo navigation system, which said embodiment proposes to modify. It should, however, be noted that this choice has been made purely for the purposes of illustrating the invention, which can also be carried out on other GNSS signals (from Galileo, GPS, Glonass, Compass etc.). Further information about the I/NAV message may be obtained by consulting the document “European GNSS (Galileo) Open Service Signal in Space Interface Control Document” (hereafter Galileo OS SIS ICD), version 1.1, September 2010, published by the European Commission on the site: http://ec.europa.eu/enterprise/policies/satnav/galileo/open-service/index_en.htm.

#The Galileo I/NAV message consists of a frame of 720 seconds, divided into 24 subframes each of 30 seconds. The latter are composed of 15 pages of 2 seconds, each page being composed of an even part and an odd part lasting 1 second. The structure of the I/NAV message is schematically illustrated in FIG. 1.

#The even and odd parts of a page are composed of 120 bits of useful data, a complete page therefore containing 240 bits of useful information. These bits are encoded with a convolutional code (of constraint length L=7 and of coding rate R=½). The 120 bits of useful data are converted into 240 symbols after encoding, to which a 10-symbol synchronization header is added. A half-page therefore contains 250 symbols.