Determining vehicle orientation based on GNSS signals received by three antennas that are logically combined into two pairs, with one antenna common for both pairs. GNSS receiver measures first carrier phase difference within each pair of antennas, represented as sum of an integer number of periods of the carrier frequency and a fractional part of the period. The fractional parts are used to compute orientation of the vector connecting the antennas phase centers within each pair, excluding integer ambiguity resolution. Vehicle attitude is calculated from the orientation of two non-collinear vectors with a common origin, measured by two pairs of antennas. Each antenna has an RF front end. All RF front ends, heterodynes, digital navigation processors of this receiver are clocked from one common clock oscillator. All carrier phase measurements of the three antennas are performed on a common time scale.