1. Field of the Invention
The present invention relates to communications systems, and more particularly to carrier tracking in communications systems.
2. Description of the Related Art
In a typical orthogonal frequency division multiplexing (OFDM) communications system, a carrier frequency oscillator used to modulate a baseband signal in a transmitter of the communication system is independent from a carrier frequency oscillator used by a receiver to demodulate the baseband information from a received modulated signal. In addition, channel effects introduce frequency offset (i.e., a difference in frequency of a transmitted subcarrier and a received subcarrier) into a received OFDM signal. A frequency offset between a received subcarrier and a frequency of a transmitted subcarrier may result in amplitude reduction of a received symbol and loss of orthogonality between subcarriers of the received OFDM signal, which results in inter-carrier interference. To avoid severe system performance degradation, any uncompensated frequency offset must not exceed a small fraction of the subcarrier signaling rate. However, small carrier offsets (i.e., on the order of a percentage of the subcarrier spacing) can severely degrade OFDM demodulation.