Low-complexity doppler estimator

A Doppler estimator for data packets to be received over a time-varying transmission medium, comprising:

• a receiver configured to receive a first plurality of data packets over a downlink channel of the time-varying transmission medium;
• a processer configured to analyze the received first plurality of data packets for at least one of constructive or destructive superposition as a function of time, predict a condition of the downlink channel for a subsequent transmission interval based on the analysis, and estimate whether the time-varying nature of the downlink channel is likely to be one of low, high, or very high based on the prediction;
• and
• a transmitter configured to construct a mid-amble periodicity request based on the estimated nature, and transmit the constructed request over an uplink channel of the time-varying transmission medium;
• wherein the receiver is further configured to receive a second plurality of data packets over the downlink channel, at least one of the second plurality comprising a mid-amble responsive to the transmitted request;
• wherein the processor is further configured to compensate at least the second plurality of data packets for Doppler shift based on the mid-amble;
• and
• wherein the processor is further configured to analyze by sampling a channel magnitude at substantially regular time intervals, setting a threshold magnitude relative to a mean magnitude, identifying positive-going threshold crossings, and measuring for the positive-going threshold crossings a magnitude difference between the sampled channel magnitude and the threshold magnitude.

A program storage device tangibly embodying a non-transitory program of instructions executable by a processor to implement Doppler estimation for a signal to be received over a time-varying transmission medium, the program instructions comprising:

• receiving the signal over a channel of the time-varying transmission medium;
• sampling a magnitude of the received signal repeatedly over time;
• identifying unidirectional threshold crossings based on the sampled magnitude;
• measuring differences between the sampled magnitude and a threshold magnitude for the identified crossings;
• analyzing the measured differences over time;
• estimating the time-varying nature of the channel based on the analyzed differences;
• and
• transmitting a signal indicative of the estimated time-varying nature.