Downlink acquisition
View Patent ↗The subject matter disclosed herein provides methods and apparatus, including computer program products, for detecting a preamble to enable acquisition of a downlink. In one aspect, there is provided a method. The method may include receiving a plurality of symbols. From an autocorrelation of the received symbols, a guard interval may be detected. The guard interval may represent a receive/transmit transition gap (RTG). A metric may be used to verify whether at least one symbol positioned after the detected guard interval is a preamble. Related systems, apparatus, methods, and/or articles are also described.
1. A method comprising:
receiving a plurality of symbols;
detecting, from an autocorrelation of the received symbols, a guard interval representative of a receive/transmit transition gap (RTG); and
verifying, based on a modulation type, whether at least one symbol positioned after the detected guard interval is a preamble.
2. The method of claim 1 further comprising:
determining the modulation type, wherein the determined modulation type provides a value representative of whether the at least one symbol was transmitted using binary phase shift key (BPSK) modulation.
3. The method of claim 1 further comprising:
determining the modulation type based on a first magnitude of at least one real component of the at least one symbol and a second magnitude of at least one imaginary component of the at least one symbol, the determination using a Fast Fourier Transform (FFT) of the at least one symbol.
4. The method of claim 3 , wherein determining the modulation type further comprises:
determining the modulation type by calculating a ratio of the first magnitude to the second magnitude.
5. The method of claim 4 , wherein determining the modulation type further comprises:
providing an indication that the at least one symbol is likely the preamble, when the ratio is greater than about 1.
6. The method of claim 1 , wherein verifying further comprises:
determining the modulation type based on the following equation:
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L
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real
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imag
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7. The method of claim 1 , wherein detecting further comprises:
determining at least one distance between at least two peaks detected from the autocorrelation of the received symbols, the autocorrelation implemented as a cyclic prefix (CP) autocorrelation.
8. The method of claim 7 further comprising:
indicating a location of the RTG, when the at least one distance exceeds a threshold.
9. The method of claim 8 further comprising;
transforming the at least one symbol positioned after the location of the RTG.
10. The method of claim 9 , wherein transforming further comprises:
transforming using a Fast Fourier Transform (FFT).
11. The method of claim 10 further comprising:
compensating, before performing the transformation, for at least one of a frequency offset and a phase rotation;
providing a timing estimation to enable the transformation; and
searching for a preamble identifier by searching a set of preamble identifiers.
12. The method of claim 1 , wherein receiving further comprises:
receiving the plurality of symbols as a complex signal comprising an I signal and a Q signal.
13. A system comprising:
a processor; and
a memory, wherein the processor and the memory are configured to perform a method comprising:
receiving a plurality of symbols;
detecting, from an autocorrelation of the received symbols, a guard interval representative of a receive/transmit transition gap (RTG); and
verifying, based on a modulation type, whether at least one symbol positioned after the detected guard interval is a preamble.
14. The system of claim 13 further comprising:
determining the modulation type based on a first magnitude of at least one real component of the at least one symbol and a second magnitude of at least one imaginary component of the at least one symbol, the determination using a Fast Fourier Transform (FFT) of the at least one symbol.
15. The system of claim 13 further comprises:
a buffer; and
a cyclic prefix autocorrelator for correlating at least one of the plurality of symbols.
16. The system of claim 13 further comprising:
determining a timing offset representing phase rotation of the plurality of symbols.
17. An article comprising a non-transitory machine-readable medium embodying instructions that when performed by one or more machines result in operations comprising:
receiving a plurality of symbols;
detecting, from an autocorrelation of the received symbols, a guard interval representative of a receive/transmit transition gap (RTG); and
verifying, based on a modulation type, whether at least one symbol positioned after the detected guard interval is a preamble.
18. The article of claim 17 further comprising:
determining the modulation type, wherein the determined modulation type provides a value representative of whether the at least one symbol was transmitted using binary phase shift key (BPSK) modulation.
19. The article of claim 17 further comprising:
determining the modulation type based on a first magnitude of at least one real component of the at least one symbol and a second magnitude of at least one imaginary component of the at least one symbol, the determination using a Fast Fourier Transform (FFT) of the at least one symbol.
20. The article of claim 19 , wherein determining further comprises:
determining the modulation type by calculating a ratio of the first magnitude to the second magnitude.