Robust OFDM carrier recovery methods and apparatus

An apparatus for processing a multi-tone signal including a preamble, a signal field following the preamble, and a data field following said signal field, the apparatus comprising:

• a fine frequency error estimation module for generating a fine carrier frequency offset correction estimate from at least a portion of said preamble;
• a decision directed frequency error correction module for generating decision directed carrier frequency error correction estimates from said signal field and from said data field;
• a frequency error correction module coupled to said fine frequency error estimation module and said decision directed frequency error estimation module for generating a frequency error corrected signal;
• and
• a fast Fourier transform module for performing a fast Fourier transform operation on said frequency error corrected signal.

A receiver for receiving a burst orthogonal frequency division multiplexing signal, comprising:

• means for generating a coarse frequency correction estimate from a first portion of a preamble included in said signal;
• means for generating a fine frequency correction estimate from a second portion of said preamble;
• means for generating decision directed frequency correction estimates from a signal portion of said signal and from a data portion of said signal, said means for generating a decision directed frequency correction estimate using both data symbol values and pilot values when processing said data portion of said signal to generate frequency correction estimates;
• and
• means, coupled to each of said means for generating said fine frequency correction estimate and said means for generating said decision directed frequency estimates, for selecting which of said generated frequency correction estimates to use at any given point in time to perform a frequency correction operation on said signal.

A method of performing a frequency correction operation on an orthogonal frequency division multiplexing (OFDM) signal including a preamble portion and additional portions, each additional portion including pilot symbols and data symbols, the method comprising the steps of:

• generating a first frequency correction signal from the preamble portion of said orthogonal frequency division multiplexing signal;
• generating a second frequency correction signal from one of said additional portions, the step of generating a second frequency correction signal including:
• generating frequency error indicator values corresponding to pilot symbols included in said one of said additional portions;
• generating frequency error indicator values corresponding to data symbols by performing decision directed error estimation operations on data symbols included in said one of said additional portions;
• and
• generating a weighted average from said frequency error indicator values corresponding to pilot symbols and said frequency error indicator values corresponding to data symbols.