A frequency offset estimator is employed that estimates the frequency
offset in signal frames that include only binary Phase-Shift Keying
(BPSK) carriers in OFDM systems. Specifically, the offset frequency
estimator takes advantage of those OFDM systems in which some OFDM
symbols only have carriers with either zero or the BPSK constellations.
In many WLAN systems such as the system described in standard
IEEE802.11a, transmission frames include only BPSK symbols, which are
used for training and other services. By making use of these BPSK symbols
in each frame, a very accurate estimate of frequency offset can be
obtained. By advantageously employing the frequency offset estimator of
this invention, a carrier recovery system can achieve high performance
even under strong ISI and low SNR. In a specific embodiment of the
invention, BPSK carriers spread to be on a line in a complex plane at an
angle to the real axis. An estimate of the angle of the line including
the BPSK carriers is then employed to obtain an estimate of the frequency
offset.