carrierfase

Carrierfase, or carrier phase, is the instantaneous phase angle of a carrier signal in a modulated communications signal. It represents the angle of the sinusoidal carrier relative to a reference oscillator and can carry information through phase modulation or serve as a reference for coherent demodulation. The carrier phase is typically denoted φ(t) in mathematical models of the transmitted signal s(t) = A cos(2π f_c t + φ(t)).

In modulation schemes, the carrier phase plays a central role. For amplitude modulation, the carrier phase is usually constant, while in phase modulation and quadrature modulation, the data modulates φ(t). In coherent detection, knowledge of the carrier phase allows the receiver to correctly demodulate the transmitted symbols. Practically, receivers estimate and track the carrier phase using devices such as phase-locked loops (PLL), Costas loops for polar modulation, or more advanced carrier-recovery algorithms, to maintain synchronization with the transmitter.

Applications and implications of the carrier phase are prominent in both wireless communications and navigation systems. In GPS and other high-precision receivers, the carrier phase of the received signal is tracked to extract measurements with very fine resolution. The phase observation includes a receiver- and transmitter-specific phase offset and an integer ambiguity corresponding to the number of whole carrier cycles; resolving this ambiguity is essential for absolute phase determination and accurate positioning.

Common challenges to accurate carrier phase tracking include phase noise of the oscillator, rapid phase changes due to mobility, scattering and fading, interference, and occasional phase slips. Robust estimation and tracking techniques are employed to mitigate these effects and preserve coherent demodulation.