Carrier frequency recovering apparatus using phase shift and method thereof

A method for recovering a carrier frequency based on phase shift of a receiving signal, comprising the steps of:

• a) differentially decoding and estimating a phase shift value caused by a frequency offset based on a received preamble signal of the receiving signal into a down sampled currently decoded signal and providing a complex conjugate of the estimated phase shift value, wherein the phase shift estimation step a) includes the steps of:
• a1) receiving preamble symbols of a receiving signal, which are referred to as the preamble signal;
• a2) delaying the preamble signal of the receiving signal by a symbol length and acquiring a complex conjugate of the preamble signal as the currently decoded signal;
• a3) acquiring a complex phase shift value by multiplying a currently inputted preamble signal by the complex conjugate;
• and
• a4) estimating a phase shift value as the currently decoded signal by acquiring an average of the complex phase shift values of the preamble symbols such that the phase shift estimation step a4) includes the steps of:
• a4-1) accumulating the complex phase shift values as many as the length of a spread code, acquiring an average thereof, and performing down-sampling to decrease a symbol clock rate as many as the length of the spread code;
• a4-2) summating complex phase shift values of the down-sampled signal of the preamble symbols, acquiring an average thereof, and estimating a phase shift based on the average;
• and
• a4-3) acquiring a complex conjugate of the estimated phase shift value;
• b) compensating the decoded signal based on the complex conjugate of the estimated phase shift value after differential decoding;
• and
• c) recovering the compensated signal;
• wherein the step b) compensates the currently decoded signal by multiplying the currently decoded signal by the complex conjugate of the phase shift value estimated in the step a).