Synchronization and frequency correction for a receiver
View Patent ↗A receiver and a method for providing block synchronization of symbols and integral frequency offset correction of subcarriers are provided. Samples of a received signal are transformed into the frequency domain. Subcarrier extraction is performed to extract selected subcarriers. The extracted subcarriers are differentially demodulated using subcarriers from the previous symbol and coherently combined with reference subcarrier values to obtain sample vectors. The sample vectors are obtained over a number of symbols preferably equal to the number symbols in a block. Cyclic correlation is performed on those sample vectors relative to a known synchronization (sync) pattern. A maximum magnitude search is performed over sample vectors obtained from the cyclic correlation to determine an integral frequency offset and a block boundary of the received signal. The integral frequency offset and the block boundary can be used to tune and synchronize the receiver for proper reception of the received signal.
1. A method in a receiver, the method comprising:
performing correlation of a synchronization pattern to a received orthogonal-frequency-division-multiplexed (OFDM) signal;
identifying a block boundary of a data block of the received OFDM signal according to the correlation;
synchronizing the receiver to the received OFDM signal according to the block boundary;
determining an integral frequency offset value; and
tuning the receiver to receive the received OFDM signal according to the correlation.
2. The method of claim 1 wherein the determining the integral frequency offset value comprises:
performing a maximum magnitude search of correlation values of the correlation.
3. The method of claim 2 wherein the identifying the block boundary of the data block of the received OFDM signal is performed using the maximum magnitude search of the correlation values of the correlation.
4. The method of claim 1 further comprising:
selecting a range of subcarrier indices, including a specified reference subcarrier index over which the correlation is to be performed, wherein the tuning adjusts the receiver for a frequency difference between a nominal frequency of the specified reference subcarrier index and an actual frequency of a corresponding reference subcarrier of the received OFDM signal.
5. The method of claim 4 wherein the correlation is a cyclic correlation.
6. The method of claim 4 wherein the selecting the range of subcarrier indices comprises:
selecting multiple ranges of the subcarrier indices for multiple specified reference subcarrier indices.
7. The method of claim 1 wherein the synchronization pattern consists of eleven synchronization bits of a 32-bit control data sequence.
8. A receiver comprising:
an analog-to-digital converter (ADC);
a correlation module coupled to the ADC, the correlation module configured to perform correlation of a synchronization pattern to a received orthogonal-frequency-division-multiplexed (OFDM) signal
a frequency correction module coupled to the correlation module, the frequency correction module configured to determine an integral frequency offset value for tuning the receiver to receive the received OFDM signal according to the correlation; and
a block synchronization module coupled to the correlation module, the block synchronization module configured to identify a block boundary of a data block of the received OFDM signal for synchronizing the receiver with the received OFDM signal according to the correlation.
9. The receiver of claim 8 wherein the correlation module is further configured to perform a maximum magnitude search of the correlation values of the correlation to determine the integral frequency offset value.
10. The receiver of claim 9 wherein the block synchronization module is further configured to identify the block boundary of the data block of the received OFDM signal according to the maximum magnitude search of the correlation values of the correlation.
11. The receiver of claim 8 wherein the correlation module is further configured to select a range of subcarrier indices including a specified reference subcarrier index over which the correlation is to be performed.
12. The receiver of claim 11 wherein the correlation is a cyclic correlation.
13. The receiver of claim 11 wherein, to select the range of subcarrier indices, the correlation module is configured to select multiple ranges of the subcarrier indices for multiple specified reference subcarrier indices.
14. The receiver of claim 8 wherein the synchronization pattern consists of eleven synchronization bits of a 32-bit control data sequence.
15. A method in a receiver, the method comprising:
searching over a time range and a frequency range of a OFDM signal to obtain symbol synchronization for symbols of the OFDM signal and a fractional frequency offset estimate for subcarriers of the OFDM signal;
searching over the time range and the frequency range of the OFDM signal to obtain block synchronization for symbols of the OFDM signal and an integral frequency offset estimate for subcarriers of the OFDM signal; and
receiving the OFDM signal according to the symbol synchronization, the fractional frequency offset estimate, the block synchronization, and the integral frequency offset estimate.
16. The method of claim 15 wherein the searching over the time range and the frequency range of the OFDM signal to obtain the block synchronization and the integral frequency offset estimate is performed using cyclic correlation.
17. The method of claim 16 wherein the searching over the time range and the frequency range of the OFDM signal to obtain the block synchronization and the integral frequency offset estimate is performed using a maximum magnitude search.
18. The method of claim 15 wherein the time range comprises a number of symbols in a data block of the OFDM signal, and the frequency range comprises a plurality of subcarrier indices proximate to reference subcarrier indices of the OFDM signal.
19. The method of claim 18 wherein the plurality of subcarrier indices are selected based on a previously determined integral frequency offset estimate.
20. The method of claim 15 wherein the searching over the time range and the frequency range of the OFDM signal to obtain block synchronization for symbols of the OFDM signal ends before a number of symbols in a data block of the OFDM signal are searched in response to determining a correlation value greater than a threshold.