Method and device for frame synchronization and coarse frequency offset estimation (CFE)
View Patent ↗A device for Frame Synchronization and coarse frequency offset estimation (CFE) and a method thereof is provided. The method may include the step of receiving a communication signal in a matched filter. The matched filter may be configured for selecting one or more blocks from the communication signal. The matched filter may be further configured for filtering the blocks to obtain an output of the matched filter. The method may also include the step of providing the output of the matched filter to a frame synchronizer and to a coarse frequency estimator. The method may include the step of obtaining substantially simultaneously a symbol boundary using the frame synchronizer and a plurality of metrics using the coarse frequency estimator. Each of the metric may be an indicative of an estimate of coarse frequency offset. The method may further include a step of selecting one of the metric from the plurality of metrics according to the symbol boundary for obtaining an estimate of the coarse frequency offset. The method further provides a step of obtaining the estimate of the coarse frequency offset by performing an inverse tangent operation on the selected metric.
1. A method comprising the steps of:
receiving a communication signal in a matched filter, the matched filter being configured for selecting one or more blocks from the communication signal and for filtering the blocks to obtain an output of the matched filter;
providing the output of the matched filter to a frame synchronizer and to a coarse frequency estimator;
obtaining substantially simultaneously a symbol boundary using the frame synchronizer and a plurality of metrics using the coarse frequency estimator, wherein each of the metric being indicative of an estimate of coarse frequency offset, wherein obtaining the plurality of metrics comprises:
receiving output of the matched filter in a first memory and in a correlator;
obtaining a metric by performing a sliding correlation using the correlator on a first sample obtained from the first memory and a second sample obtained from the output of the matched filter, the first and the second samples being separated from one another by a predetermined time;
storing the metric in a second memory;
repeating above steps for each of the samples of a block; and
executing the step of receiving the samples of a following block, and obtaining the metric;
accumulating the obtained metric in the second memory; and
repeating the steps of executing and accumulating for a number of subsequent blocks; and
selecting one of the accumulated metric from the plurality of metrics corresponding to a location indicated by the symbol boundary for obtaining an estimate of the coarse frequency offset.
2. The method as claimed in claim 1 , wherein the method further comprises a step of obtaining the estimate of the coarse frequency offset by performing an inverse tangent operation on the selected metric.
3. The method as claimed in claim 1 , wherein the block may include a plurality of samples.
4. The method as claimed in claim 1 , wherein the matched filter being configured for selecting one or more blocks such that number of samples in a block is equal to the number of elements in a Pseudo Noise (PN) sequence.
5. The method as claimed in claim 4 , wherein the output of the match filter is obtained by performing a sliding correlation operation of the communication signal, with a time reversed PN sequence, wherein the PN sequence is a Barker sequence, and wherein the output of the matched filter is obtained using the equation:
y
k
=
∑
n
=
0
N
-
1
x
(
k
÷
n
)
b
n
wherein, y k is the output of the matched filter, x k is k th sample of the block, b n is n th element of the PN sequence and N is the length of the PN sequence.
6. The method as claimed in claim 5 , wherein the Barker sequence is an upsampled Barker sequence.
7. The method as claimed in claim 1 , wherein the step of obtaining symbol boundary includes a step of obtaining a power value corresponding to power of the communication signal.
8. The method as claimed in claim 7 , wherein the step of obtaining the power value may include step of obtaining power value of samples used for obtaining output of the matched filter.
9. The method as claimed in claim 8 , wherein the step of obtaining symbol boundary includes a step of confirming receipt of a valid frame by comparing the magnitude of output of matched filter with a predetermined threshold value.
10. The method as claimed in claim 9 , wherein the step of confirming includes a step of obtaining a normalized value of the magnitude of output of the matched filter with respect to the power value and comparing the normalized value with the predetermined threshold value.
11. The method as claimed in claim 9 , wherein the predetermined threshold is set according to a valid frame detection probability.
12. The method as claimed in claim 1 , wherein the step of obtaining symbol boundary includes the step of confirming receipt of a valid frame by examining for periodicity of the samples having maximum value.
13. The method as claimed in claim 1 , wherein the step of obtaining symbol boundary includes accumulating magnitudes of the filtered samples in consecutive blocks and finding a maximum value.
14. The method as claimed in claim 1 , wherein the step of accumulating the metric includes the step of accumulating the first metric of a block with the first metric of the subsequent block and so on for the subsequent metrics of the blocks.
15. The method as claimed in claim 1 , wherein the predetermined time is equal to time-length of the PN sequence.
16. The method as claimed in claim 1 , wherein the number of subsequent blocks is 8.
17. A device comprising:
a matched filter being configured for receiving a communication signal, and for selecting one or more blocks of the communication signal, and for filtering the blocks to obtain an output of the matched filter;
a frame synchronizer coupled to the output of the matched filter, wherein the frame synchronizer being configured for obtaining a symbol boundary; and
a coarse frequency estimator coupled to the output of the matched filter, wherein the coarse frequency estimator being configured for obtaining a plurality of metrics, wherein each of the metric being indicative of an estimate of coarse frequency offset, wherein the frame synchronizer and the coarse frequency estimator are configured to obtain substantially simultaneously the symbol boundary and the plurality of metrics respectively, and wherein the coarse frequency estimator comprises:
a first memory for receiving the output of the matched filter;
a correlator for receiving output of the first memory and the matched filter, the correlator is configured for obtaining a metric by performing a sliding correlation on a first sample obtained from the first memory and a second sample obtained from the output of the matched filter, the first and the second samples being temporally separated from one another by a predetermined time; and
a second memory receiving output from the correlator for storing the metric,
wherein the coarse frequency estimator repeats above steps for each of the samples of a block, executes the step of receiving the samples of a following block, obtains the metric, accumulates the obtained metric in the second memory, and wherein the coarse frequency estimator repeats the steps of executing and accumulating for a number of subsequent blocks, and
wherein the coarse frequency estimator being configured for selecting an accumulated metric amongst the plurality of metrics corresponding to a location indicated by the symbol boundary for obtaining an estimate of the coarse frequency offset.
18. The device as claimed in claim 17 , wherein the device is further configured for obtaining the estimate of the coarse frequency offset by performing an inverse tangent operation on the selected metric.
19. The device as claimed in claim 17 , wherein the matched filter is configured for selecting the blocks such that number of samples in a block is equal to the number of elements in a Pseudo Noise (PN) sequence, and wherein the block includes a plurality of samples.
20. The device as claimed in claim 19 , wherein the output of the match filter is obtained by performing a sliding correlation operation of the communication signal, with a time reversed PN sequence, wherein the PN sequence is a Barker sequence, and wherein the output of the matched filter is obtained using the equation:
y
k
=
∑
n
=
0
N
-
1
x
(
k
÷
n
)
b
n
wherein, y k is the output of the matched filter, x k is k th sample of the block, b n is n th element of the PN sequence and N is the length of the PN sequence.
21. The device as claimed in claim 20 , wherein the Barker sequence is an upsampled Barker sequence.
22. The device as claimed in claim 17 , wherein the frame synchronizer is configured for obtaining a power value corresponding to power of the samples used for obtaining output of the matched filter.
23. The device as claimed in claim 22 , wherein the frame synchronizer is configured for confirming receipt of a valid frame by comparing the magnitude of output of matched filter with a predetermined threshold.
24. The device as claimed in claim 23 , wherein the frame synchronizer is configured for confirming receipt of the valid frame by obtaining a normalized value of the magnitude of output of the matched filter with respect to the power value and comparing the normalized value with the predetermined threshold.
25. The device as claimed in claim 23 , wherein the predetermined threshold is set according to a valid frame detection probability.
26. The device as claimed in claim 17 , wherein the frame synchronizer is configured for obtaining symbol boundary in the frame by accumulating magnitudes of the filtered samples in consecutive blocks and finding a maximum value.
27. The device as claimed in claim 17 , wherein the frame synchronizer is configured for confirming receipt of a valid frame by examining for periodicity of the samples having maximum value.
28. The device as claimed in claim 17 , wherein the correlator is configured for enabling accumulation of the first metric of a block with the first metric of the subsequent block and so on for the subsequent metrics of the blocks.
29. An article comprising the device of the claim 17 .
30. A non-transitory computer readable storage medium operable with a computer system, the computer-readable medium having stored thereon instructions operable with an architectural simulator environment supported by the computer system, the medium comprising instructions that, when executed by the computer system, cause the computer system to perform the method of the claim 1 .
31. An article comprising the computer readable medium of the claim 30 .
32. The method of claim 1 , wherein obtaining the symbol boundary using the frame synchronizer comprises:
processing the one or more blocks from the matched filter;
comparing a peak sample value in each of the blocks with a predetermined threshold;
declaring that there is a valid frame detected when a certain number of the peak values in consecutive blocks exceed the predetermined threshold and the peak values are repeated periodically;
accumulating magnitudes of the filtered samples at each corresponding position in consecutive blocks in the valid frame; and
identifying a maximum value from the accumulated values as the symbol boundary.