OFDM pilot tone tracking for wireless lan
First Claim
1. A pilot phase tracking loop for an orthogonal frequency division multiplexed (OFDM) receiver comprising:
 a phase rotator for receiving and phase derotating an incoming signal;
a fast Fourier transform coupled to an output of the phase rotator for processing a signal output from the phase rotator;
a pilot phase error metric including a discrete Fourier transform portion, the discrete Fourier transform portion coupled to the output of the phase rotator, wherein the pilot phase error metric determines a phase error estimate associated with a received OFDM symbol of the signal output from the phase rotator;
a loop filter coupled to an output of the pilot phase error metric; and
an oscillator coupled to an output of the loop filter and having an output coupled to the phase rotator such that the phase rotator adjusts the phase of subsequent OFDM symbols of the incoming signal arriving after the received OFDM symbol by the phase error estimate.
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Accused Products
Abstract
A pilot phase tracking loop for an OFDM receiver including a phase rotator receiving an incoming signal, a fast Fourier transform coupled to a phase rotator output, and a pilot phase error metric including a discrete Fourier transform portion coupled to the phase rotator output. The pilot phase error metric determines a phase error estimate associated with a received OFDM symbol, e.g., a data symbol, from the phase rotator output. A loop filter is coupled to the pilot phase error metric output and an oscillator is coupled to the loop filter output. The oscillator output is coupled to the phase rotator to adjust the phase of subsequent OFDM symbols of the incoming signal. Phase noise introduced by a radio portion of the OFDM receiver and OFDM transmitter is reduced by the baseband portion of the OFDM receiver improving OFDM signal tracking under poor SNR conditions.
89 Citations
59 Claims

1. A pilot phase tracking loop for an orthogonal frequency division multiplexed (OFDM) receiver comprising:

a phase rotator for receiving and phase derotating an incoming signal;
a fast Fourier transform coupled to an output of the phase rotator for processing a signal output from the phase rotator;
a pilot phase error metric including a discrete Fourier transform portion, the discrete Fourier transform portion coupled to the output of the phase rotator, wherein the pilot phase error metric determines a phase error estimate associated with a received OFDM symbol of the signal output from the phase rotator;
a loop filter coupled to an output of the pilot phase error metric; and
an oscillator coupled to an output of the loop filter and having an output coupled to the phase rotator such that the phase rotator adjusts the phase of subsequent OFDM symbols of the incoming signal arriving after the received OFDM symbol by the phase error estimate.  View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 30, 31, 32)


16. A method of pilot phase tracking in an orthogonal frequency division multiplexed (OFDM) receiver comprising:

receiving a baseband signal corresponding to an OFDM preamble waveform at a discrete Fourier transform portion of the OFDM receiver, wherein the discrete Fourier transform is a separate processing operation than a fast Fourier transform of the OFDM receiver;
determining pilot reference points corresponding to a plurality of pilots of an OFDM preamble waveform;
receiving a baseband signal corresponding to an OFDM symbol at the discrete Fourier transform portion;
determining complex signal measurements corresponding to each of the plurality of pilots of the OFDM symbol;
determining a phase error estimate corresponding to the OFDM symbol based on the pilot reference points and the complex signal measurements;
filtering the phase error estimate; and
rotating a phase of an incoming signal corresponding to subsequent OFDM symbols to be received at the fast Fourier transform after the OFDM symbol by a filtered phase error estimate;
wherein a phase noise of the incoming signal corresponding to the subsequent OFDM symbols to be received at the fast Fourier transform is reduced.


29. A method of pilot phase tracking in an orthogonal frequency division multiplexed (OFDM) receiver comprising:

receiving a signal representing an OFDM waveform at a discrete Fourier transform portion of the OFDM receiver, wherein the discrete Fourier transform is a separate processing operation than a fast Fourier transform of the OFDM receiver that also receives the signal;
determining a phase error estimate corresponding to an OFDM symbol of the OFDM waveform;
filtering the phase error estimate; and
rotating a phase of the signal for subsequent OFDM symbols to be received at the fast Fourier transform after the OFDM symbol by the filtered phase error estimate, wherein a phase noise of the signal for the subsequent OFDM symbols to be received at the fast Fourier transform is reduced.


33. A pilot phase error metric for an orthogonal frequency division multiplexed (OFDM) receiver comprising:

a discrete Fourier transform portion for receiving an incoming signal corresponding to an OFDM waveform, wherein the discrete Fourier transform portion outputs complex signal measurements corresponding to each of a plurality of pilots of a preamble portion of the OFDM waveform and complex signal measurements corresponding to each of a plurality of pilots of a subsequent OFDM symbol of the OFDM waveform, wherein the discrete Fourier transform portion is separate from a fast Fourier transform operation of the OFDM receiver;
a maximum likelihood phase error/weighting processor coupled to the discrete Fourier transform portion for processing the complex signal measurements corresponding to each of the plurality of pilots of the subsequent OFDM symbol in comparison to the pilot reference points; and
a phase error estimator coupled to the maximum likelihood phase error/weighting processor for estimating a phase error of the subsequent OFDM symbol relative to a phase corresponding to the preamble portion based on the processed complex signal measurements and the pilot reference points.  View Dependent Claims (34, 35, 36, 37, 38, 39, 40, 41)


42. A method of pilot phase error estimation in an orthogonal frequency division multiplexed (OFDM) receiver comprising:

determining pilot reference points corresponding to a plurality of pilots of an OFDM preamble waveform;
processing, in a parallel path to the determining step, the OFDM preamble waveform with a fast Fourier transform;
determining a phase error estimate of a subsequent OFDM symbol relative to the pilot reference points; and
processing, in the parallel path to the determining steps, the subsequent OFDM symbol with the fast Fourier transform;
wherein the determining the phase error estimate step is completed prior to the completion of the processing the subsequent OFDM symbol with the fast Fourier transform in the parallel path.  View Dependent Claims (43, 44, 45, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59)


46. A method of pilot phase error estimation in an orthogonal frequency division multiplexed (OFDM) receiver comprising:

determining, in a separate processing path parallel to a fast Fourier transform processing path of the OFDM receiver, pilot reference points corresponding to a plurality of pilots of an OFDM preamble waveform; and
estimating, in the separate processing path, an aggregate phase error of a subsequent OFDM symbol relative to the pilot reference points using complex signal measurements corresponding to each of the plurality of pilots of the subsequent OFDM symbol and the pilot reference points.

1 Specification