Receiver architecture for pilot based OFDM systems

A method for reducing phase error in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, the method comprising:

• simultaneously rotating the plurality of pilot sub-carriers and the data sub-carrier by an accumulated phase offset associated with a carrier frequency offset between the FDM receiver and the remote source;
• calculating a residual phase offset for each of the plurality of rotated pilot sub-carriers;
• determining a mean residual phase offset for the calculated residual phase offsets of the plurality of rotated pilot sub-carriers;
• updating the accumulated phase offset using the mean residual phase offset;
• detecting sample timing errors, said detecting sample timing errors comprising:
• determining a phase gradient, and comparing the phase gradient to a predetermined reference phase gradient;
• and
• adjusting samples of the received FDM symbols responsive to detecting sample timing errors.

A method for reducing phase error in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, the method comprising:

• calculating a phase offset for each of the plurality of pilot sub-carriers;
• applying a threshold discriminator to the plurality of pilot sub-carriers;
• determining a mean phase offset using the threshold discriminated pilot sub-carriers;
• and
• rotating the data sub-carrier using the determined mean phase offset.

A method for reducing sample timing errors in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, the method comprising:

• calculating a phase offset for each of the plurality of pilot sub-carriers;
• calculating a phase gradient using the calculated phase offsets, the phase gradient representative of the change in phase versus frequency for the plurality of pilot sub-carriers;
• comparing the calculated phase gradient to a predetermined threshold phase gradient;
• and
• adjusting samples of the FDM symbol responsive to the comparison of the calculated phase gradient to the predetermined threshold phase gradient.

An apparatus for correcting phase error in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, comprising:

• an accumulator storing an accumulated phase offset associated with a carrier frequency offset between the FDM receiver and the remote source;
• a first multiplier continuously coupled to the accumulator, the multiplier receiving a plurality of pilot sub-carriers and rotating the plurality of pilot sub-carriers by the accumulated phase offset;
• a phase error processor coupled to the first multiplier and the accumulator, to calculate a residual phase offset for each of the plurality of rotated pilot sub-carriers, to determine a mean residual phase offset for the calculated residual phase offsets of the plurality of rotated pilot sub-carriers, and to provide the mean residual offset to the accumulator, for updating the accumulated phase offset;
• a second multiplier continuously coupled to the accumulator, the second multiplier receiving the data sub-carrier and rotating the data sub-carrier by the accumulated phase offset;
• and
• a threshold discriminator determining the magnitude of each of the plurality of pilot sub-carriers, comparing the determined magnitude to a predetermined threshold magnitude, and selectively using the pilot sub-carrier to determine the mean residual phase offset if the determined magnitude is greater than the predetermined threshold, and using all of the plurality of pilot sub-carriers, regardless of their respective magnitudes, if the determined magnitude of less than two of the plurality of pilot sub-carriers is greater than the predetermined threshold magnitude.

An apparatus for reducing phase error in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, comprising:

• a phase error processor receiving the plurality of pilot sub-carriers and calculating a respective phase offset for each;
• the phase error processor comprising:
• a threshold discriminator receiving the calculated phase offsets;
• a mean function determining the mean phase offset using the threshold discriminated pilot sub-carriers;
• and
• a multiplier coupled to the phase error processor, multiplying the received data sub-carrier by a phasor having an argument related to the determined mean phase offset.

An apparatus for reducing sample timing errors in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, comprising:

• a phase error processor, calculating a phase offset for each of the plurality of pilot sub-carriers and a phase gradient using the calculated phase offsets, the phase gradient representative of the change in phase versus frequency for the plurality of pilot sub-carriers;
• a comparator coupled to the phase error processor comparing the calculated phase gradient to a predetermined threshold phase gradient;
• and
• a synchronizer coupled to the comparator, adjusting samples of the FDM symbol responsive to the comparison of the calculated phase gradient to the predetermined threshold phase gradient.

A system for reducing phase error in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, the method comprising:

• means for calculating a phase offset for each of the plurality of pilot sub-carriers;
• means for applying a threshold discriminator to the plurality of pilot sub-carriers;
• means for determining a mean phase offset using the threshold discriminated pilot sub-carriers;
• and
• means for rotating the data sub-carrier using the determined mean phase offset.

A system for reducing sample timing errors in a pilot-based, frequency-division-multiplexing (FDM) receiver configured to receive FDM symbols from a remote source, each symbol including a data sub-carrier and a plurality of pilot sub-carriers, the method comprising:

• means for calculating a phase offset for each of the plurality of pilot sub-carriers;
• means for calculating a phase gradient using the calculated phase offsets, the phase gradient representative of the change in phase versus frequency for the plurality of pilot sub-carriers;
• means for comparing the calculated phase gradient to a predetermined threshold phase gradient;
• and
• means for adjusting samples of the FDM symbol responsive to the comparison of the calculated phase gradient to the predetermined threshold phase gradient.