is used to process the down-converted digital signal to retrieve essential data for a wireless digital system. The baseband processing block in GNSS receivers is responsible for providing observable data: that is, code pseudo-ranges and carrier phase measurements, as well as navigation data. Equivalent baseband signal An equivalent baseband signal or equivalent lowpass signal is—in analog and digital modulation methods for (passband) signals with constant or varying carrier frequency (for example ASK, PSK QAM, and FSK)—a complex valued representation of the modulated physical signal (the so-called passband signal or RF signal). The equivalent baseband signal is where is the inphase signal, the quadrature phase signal, and the imaginary unit. In a digital modulation method, the and signals of each modulation symbol are evident from the constellation diagram. The frequency spectrum of this signal includes negative as well as positive frequencies. The physical passband signal corresponds to where is the carrier angular frequency in rad/s. Modulation A signal at baseband is often used to modulate a higher frequency carrier signal in order that it may be transmitted via radio. Modulation results in shifting the signal up to much higher frequencies (radio frequencies, or RF) than it originally spanned. A key consequence of the usual double-sideband amplitude modulation (AM) is that the range of frequencies the signal spans (its spectral bandwidth) is doubled. Thus, the RF bandwidth of a signal (measured from the lowest frequency as opposed to 0 Hz) is twice its baseband bandwidth. Steps may be taken to reduce this effect, such as single-sideband modulation. Conversely, some transmission schemes such as frequency modulation use even more bandwidth. The figure below shows AM modulation: See also Complex envelope Broadband In-phase and quadrature components Narrowband Wideband References Signal processing