Method and apparatus for frequency tracking in a space time transmit diversity receiver
View Patent ↗A system and method for obtaining a frequency error estimate representing the difference between a reference frequency and the frequency of a space-time transmit diversity signal is disclosed. The method includes taking the correlation of total sums, comprised of partial sums taken in defined first and second intervals, to represent the frequency error as the imaginary component of the correlation function.
1. A frequency discriminator comprising:
memory configured to input, from a receiver, first and second sequences of symbols that were wirelessly received by the receiver from respectively first and second transmit antennae, wherein each sequence has two sets of first and second intervals, and the contents of the second interval of the second received sequence are an additive inverse of the contents of the first interval of the second received sequence;
a set of adders configured to
calculate two sets of first and second partial sums as the sum of the contents of the first and second intervals, respectively, for each set;
calculate total sum functions for the first and second sets by summing the first and second partial sums for each set;
calculate an auto-correlation function based on the total sum functions for the first and second sets; and
a splitter configured to isolate an imaginary part of the auto-correlation function as a frequency error estimate.
2. The frequency discriminator of claim 1 wherein the auto-correlation function is calculated as a time average of the product of the first total sum function and the conjugate of the second total sum function.
3. The frequency discriminator of claim 1 wherein isolating by the splitter includes adding the auto-correlation function to a correlation of a second set of total sum functions calculated by summing the first partial sum with an additive inverse of the second partial sum.
4. The frequency discriminator of claim 1 wherein the first and second interval in each set are adjacent.
5. The frequency discriminator of claim 1 wherein the first and second sets of intervals are interleaved with each other.
6. A frequency discriminator comprising:
memory configured to input, from a receiver, first and second sequences of symbols that were wirelessly received by the receiver from respectively first and second transmit antennae, wherein each sequence has two sets of first and second intervals, and the contents of the second interval of the second received sequence are the additive inverse of the contents of the first interval of the second received sequence;
a set of adders configured to
calculate two sets of first and second partial sums as the sum of the contents of the first and second intervals, respectively, for each set;
multiply the second partial sum for each set by −1;
calculate total sum functions for the first and second sets by summing the first and second partial sums for each set;
calculate an auto-correlation function based on the total sum functions for the first and second sets; and
a frequency error estimator configured to extract a frequency error estimate from the auto-correlation function.
7. The frequency discriminator of claim 6 wherein the auto-correlation function is calculated as a time average of the product of the first total sum function and the conjugate of the second total sum function.
8. The frequency discriminator of claim 6 wherein extracting includes adding the auto-correlation to a correlation of a second set of total sum functions calculated by summing the first partial sum with an additive inverse of the second partial sum.
9. The frequency discriminator of claim 6 wherein the first and second interval in each set are adjacent.
10. The frequency discriminator of claim 6 wherein the first and second sets of intervals are interleaved with each other.
11. A frequency discriminator comprising:
memory configured to input, from a receiver, first and second sequences of symbols that were wirelessly received by the receiver from respectively first and second transmit antennae, wherein each sequence has two sets of first and second intervals, and the contents of the second interval of the second received sequence are an additive inverse of the contents of the first interval of the second received sequence;
a set of adders configured to
calculate two sets of first and second partial sums as the sum of the contents of the first and second intervals, respectively, for each set;
calculate total sum functions for the first and second sets by summing the first and second partial sums for each set;
calculate an auto-correlation function based on the total sum functions for the first and second sets;
a frequency error estimator configured to extract a frequency error estimate from the auto-correlation function; and
a multiplyer configured to multiply the frequency error estimate by an average of a signal-to-noise-ratio of the received sequences.
12. The frequency discriminator of claim 11 wherein the auto-correlation function is calculated as a time average of the product of the first total sum function and the conjugate of the second total sum function.
13. The frequency discriminator of claim 11 wherein the first and second interval in each set are adjacent.
14. The frequency discriminator of claim 11 wherein the first and second sets of intervals are interleaved with each other.
15. The frequency discriminator of claim 11 wherein the extracting includes adding the auto-correlation to a correlation of a second set of total sum functions calculated by summing the first partial sum with an additive inverse of the second partial sum.
16. A communication device comprising:
the frequency discriminator of claim 11 ;
first and second receiving antennas; and
the receiver, the receiver being configured to generate the first sequence from a component received from the first antenna and to generate the second sequence from a component received from the second antenna and provide the first and second sequences to the discriminator.