Interpolating bandpass filter for packet-data receiver synchronization
Assignee2Wire, Inc.
InventorsCarl H. Alelyunas, Philip DesJardins
Life of this patent
Estimating the term…
Abstract
An interpolating bandpass filter for packet-data receiver synchronization comprises a single delay line that delays the passband-sampled data from the analog-to-digital converter, and a convolving structure that uses the delay line to implement a L-times oversampling bandpass filter. A separate accumulator accumulates a fractional phase difference that represents the frequency offset between the remote transmitter's frequency and the receiver's sampling frequency. The integer portion of the accumulator is used to determine the number of samples to delay the input of the filter, while the fractional portion is used to choose two coefficient sets closest to the desired delay and to interpolate between these two filter sets.
Claims17
An interpolating bandpass filter in a receiver, the filter comprising:
- a delay line configured to receive samples of a received signal;
- a convolving structure configured to receive delayed samples from the delay line, wherein an integer portion of a phase difference between a transmitter's clock and the receiver's clock determines an amount of delay in the delay line;
- and
- a coefficient generator configured to generate filter coefficients using a fractional portion of the phase difference, the coefficient generator inputting the filter coefficients to the convolving structure which convolves the filter coefficients and the delayed samples to produce filtered samples.
A method for generating interpolating bandpass filter coefficients, comprising the steps of:
- storing a predetermined set of filter coefficients as a set of coefficients for even indexed subfilters and a set of coefficients for odd indexed subfilters;
- determining a phase difference between a remote transmitter's clock and a receiver's clock;
- selecting a fractional portion of the phase difference;
- selecting an upper K+F bits of the fractional portion of the phase difference;
- using the K bits to determine an even coefficient index and an odd coefficient index;
- using the even coefficient index to select an even subfilter from the set of coefficients of even indexed subfilters and using the odd coefficient index to select an odd subfilter from the set of coefficients of odd indexed subfilters;
- and
- interpolating between the even subfilter and the odd subfilter using the F bits to produce the interpolating bandpass filter coefficients.
A system for efficient storage of filter coefficients, comprising:
- an even subfilter coefficient storage configured to store even subfilter coefficients;
- an odd subfilter coefficient storage configured to store odd subfilter coefficients;
- an index generator configured to generate an even subfilter index and an odd subfilter index;
- and
- a linear interpolator configured to interpolate between even subfilter coefficients selected according to the even subfilter index and odd subfilter coefficients selected according to the odd subfilter index.
Dependencies are inferred from the claim text.