Joint sample rate offset and symbol timing offset correction
A receiver has a sample rate converter that outputs samples of orthogonal frequency division multiplexing symbols. The receiver includes a fast Fourier transform engine that receives the samples and converts them into a plurality of frequency domain sub-carriers. A timing control circuit generates a timing error and controls the sample rate converter to adjust a sample rate of the orthogonal frequency division multiplexing symbols based at least in part on the timing error.
1. A receiver configured to jointly correct sample rate offset and symbol timing offset, comprising:
a sample rate converter configured to output one or more samples of one or more orthogonal frequency division multiplexing symbols;
a first buffer configured to store first samples of the one or more samples corresponding to a current symbol;
a fast Fourier transform engine configured to receive the first samples from the first buffer and convert the first samples into a plurality of frequency domain sub-carriers;
a second buffer configured to store second samples of the one or more samples corresponding to: a current symbol, a portion of a prior symbol, and a portion of a future symbol; and
a timing control circuit configured to generate a timing error using the second samples and to jointly correct sample rate offset and symbol timing offset by control of the sample rate converter to adjust a sample rate of the one or more orthogonal frequency division multiplexing symbols based at least in part on the timing error, and further configured to generate the timing error based at least in part on a difference between a first correlation sum for a first portion of a cyclic prefix of a first one of the one or more symbols and a second correlation sum for a second portion of the cyclic prefix.
2. The receiver of claim 1 wherein the timing control circuit is configured to control the sample rate converter to adjust the sample rate according to a difference between the first correlation sum and the second correlation sum of the one or more orthogonal frequency division multiplexing symbols received via a multi-path channel.
3. The receiver of claim 1 wherein the timing control circuit is configured to control the sample rate converter to adjust the sample rate until the first correlation sum is at least substantially equal to the second correlation sum.
4. The receiver of claim 1 wherein the timing control circuit includes a cyclic prefix correlator configured to calculate first cyclic prefix correlations for the first portion of the cyclic prefix and second cyclic prefix correlations for the second portion of the cyclic prefix, and to calculate first guard band correlations for one or more first guard band samples adjacent the first portion of the cyclic prefix and second guard band correlations for one or more second guard band samples adjacent the second portion of the cyclic prefix.
5. The receiver of claim 4 further comprising a summer configured to calculate the first correlation sum based on the first cyclic prefix correlations and the first guard band correlations, and to calculate the second correlation sum based on the second cyclic prefix correlations and the second guard band correlations.
6. The receiver of claim 1 wherein the timing control circuit is configured to determine a timing error based on a comparison of the first correlation sum and the second correlation sum.
7. The receiver of claim 1 wherein the timing control circuit is further configured to maintain a first count and a second count based on the timing error for a plurality of comparisons of the first correlation sum and the second correlation sum.
8. The receiver of claim 1 wherein the timing control circuit generates the timing error using a number of samples from the second buffer sufficiently large to correct a desired symbol timing offset impairment but not so large as to extend into a cyclic prefix correlation region of the prior symbol or the future symbol.
9. The receiver of claim 1 wherein adjustment of the sample rate converter causes movement of a pointer of the second buffer to jointly correct sample rate offset and symbol timing offset sample rate offset, without moving a pointer of the first buffer.
10. A wireless communication device comprising:
an antenna;
transceiver circuitry in communication with the antenna and configured to configured to receive one or more orthogonal divisional multiplexing signals from the antenna, the transceiver circuitry including: a sample rate converter configured to output one or more samples of one or more orthogonal frequency division multiplexing symbols; a first buffer configured to store first samples of the one or more samples corresponding to a current symbol; a fast Fourier transform engine configured to receive the one or more samples from the first buffer and convert the first samples into a plurality of frequency domain sub-carriers; a second buffer configured to store second samples of the one or more samples corresponding to a current symbol, a portion of a prior symbol, and a portion of a future symbol; and a timing control circuit configured to generate a timing error using the second samples, and to jointly correct sample rate offset and symbol timing offset by control of the sample rate converter to adjust a sample rate of the one or more orthogonal frequency division multiplexing symbols based at least in part on the timing error, and further configured to generate the timing error based at least in part on a difference between a first correlation sum for a first portion of a cyclic prefix of a first one of the one or more symbols and a second correlation sum for a second portion of the cyclic prefix.
11. The wireless communication device of claim 10 wherein the timing control circuit is configured to control the sample rate converter to adjust the sample rate according to a difference between the first correlation sum and the second correlation sum of the one or more orthogonal frequency division multiplexing symbols received via a multi-path channel.
12. The wireless communication device of claim 10 wherein the timing control circuit is configured to control the sample rate converter to adjust the sample rate until the first correlation sum is at least substantially equal to the second correlation sum.
13. The wireless communication device of claim 10 wherein the timing control circuit includes a cyclic prefix correlator configured to calculate first cyclic prefix correlations for the first portion of the cyclic prefix and second cyclic prefix correlations for the second portion of the cyclic prefix, and to calculate first guard band correlations for one or more first guard band samples adjacent the first portion of the cyclic prefix and second guard band correlations for one or more second guard band samples adjacent the second portion of the cyclic prefix.
14. The wireless communication device of claim 13 further comprising a summer configured to calculate the first correlation sum based on the first cyclic prefix correlations and the first guard band correlations, and to calculate the second correlation sum based on the second cyclic prefix correlations and the second guard band correlations.
15. The wireless communication device of claim 10 wherein the timing control circuit is configured to determine a timing error based on a comparison of the first correlation sum and the second correlation sum.
16. The wireless communication device of claim 10 wherein the timing control circuit generates the timing error using a number of samples from the second buffer sufficiently large to correct a desired symbol timing offset impairment but not so large as to extend into a cyclic prefix correlation region of the prior symbol or the future symbol.
17. The wireless communication device of claim 10 wherein adjustment of the sample rate converter causes movement of a pointer of the second buffer to jointly correct sample rate offset and symbol timing offset sample rate offset, without moving a pointer of the first buffer.
18. A method of receiving orthogonal division multiplexing symbols, the method comprising:
receiving, in a receiver, a radio frequency signal;
processing, in the receiver, the radio frequency signal to obtain a plurality of orthogonal division multiplexing symbols, each of the plurality of orthogonal division multiplexing symbols including cyclic prefix samples and information samples;
storing in a first buffer first samples corresponding to a current symbol of the plurality of symbols, and converting the first samples from the buffer into a plurality of frequency domain sub-carriers;
storing in a second buffer second samples corresponding to a current symbol of the plurality of symbols, a portion of a prior symbol of the plurality of symbols, and a portion of a future symbol of the plurality of symbols;
using the second samples, determining a timing error based at least in part on a difference between a first correlation sum for a first portion of a cyclic prefix of a first one of the plurality of symbols and a second correlation sum for a second portion of the cyclic prefix; and
controlling a sample rate converter to adjust a sample rate of the plurality of orthogonal division multiplexing symbols based at least in part on the timing error, and to jointly correct sample rate offset and symbol timing offset.
19. The method of claim 18 wherein the timing error is determined using a number of samples from the second buffer sufficiently large to correct a desired symbol timing offset impairment but not so large as to extend into a cyclic prefix correlation region of the prior symbol or the future symbol.
20. The method of claim 18 wherein adjustment of the sample rate converter causes movement of a pointer of the second buffer to jointly correct sample rate offset and symbol timing offset sample rate offset, without moving a pointer of the first buffer.