1. Field of the Invention
The present invention relates to carrier recovery systems and carrier recovery methods.
2. Description of the Related Art
In communication systems using Quadrature Amplitude Modulation (QAM), such as OpenCable and DVB-C communication systems, receivers have to compensate for frequency offset and phase offset by blind methods since a transmitted signal has no pilot and training sequence. The blind methods are named carrier recovery.
There are many solutions for carrier recovery. One conventional carrier recovery technique compensates for frequency and phase offsets at the output terminal of the equalizer. This conventional technique provides a wide frequency offset estimation range (such as up to 300 KHz) but has a bad performance at the equalizer since the signal inputted into the equalizer includes the uncompensated frequency offset. Another conventional carrier recovery technique compensates for frequency and phase offsets at the input terminal of the equalizer. This conventional technique provides a good performance equalizer but limits the frequency offset estimation range (only up to 40 KHz for example).
Thus, novel carrier recovery techniques providing good performance equalizer and wide frequency offset estimation range are called for.