Adjusting receiver frequency to compensate for frequency offset during a sounding sequence used for fractional time determination

A method for determining a fractional timing value associated with measuring a distance between a first communications device including a receiver and a second communications device including a transmitter, the method comprising:

• receiving a sounding sequence at the receiver from the second communications device, the sounding sequence containing a positive tone and a negative tone;
• providing frequency offset estimates of frequency offset between the transmitter and the receiver;
• generating frequency offset corrections based on the frequency offset estimates;
• adjusting a frequency used by a mixer in the receiver to down convert a receiver signal based on a current one of the frequency offset corrections to thereby better center the positive tone and the negative tone around 0 Hz;
• and
• determining the fractional timing value based on respective phases of the positive tone and the negative tone.

A communications device comprising:

• a receiver to receive a sounding sequence and supply a baseband signal having a positive tone and a negative tone present in the sounding sequence;
• wherein the receiver includes,
• a frequency offset estimator to generate frequency offset estimates of frequency offset between the communications device and a second communications device;
• a frequency offset correction circuit coupled to the frequency offset estimator to generate frequency offset corrections based on the frequency offset estimates;
• a frequency adjustment circuit coupled to the frequency offset correction circuit to supply an adjusted frequency control signal to adjust a frequency used by a mixer in the receiver based on a current one of the frequency offset corrections to thereby better center the positive tone and the negative tone around 0 Hz;
• a first discrete Fourier transform (DFT) circuit and a second DFT circuit to perform respectively single bin discrete Fourier transforms centered on a nominal value of the positive tone and a nominal value of the negative tone;
• and
• an arctangent function to generate respective phase values of the positive tone and the negative tone based on outputs of the first and second DFT circuits;
• wherein the frequency offset correction circuit includes a shift circuit responsive to a first value of a control signal to use a first scaling factor on a first plurality of representations of the frequency offset estimates received by the shift circuit;
• and
• wherein the shift circuit is responsive to a second value of the control signal to use a second scaling factor on a second plurality of representations of the frequency offset estimates received by the shift circuit, the second scaling factor reducing the second plurality of representations of the frequency offset estimates.