Cycle slip compensation in coherent receiver
View Patent ↗A receiver architecture and method recovers data received over an optical fiber channel in the presence of cycle slips. In a first cycle slip recovery architecture, a receiver detects and corrects cycle slips based on pilot symbols inserted in the transmitted data. In a second cycle slip recovery architecture, a coarse cycle slip detection is performed based on pilot symbols and a cycle slip position estimation is then performed based on carrier phase noise. The receiver compensates for cycle slips based on the position estimation.
1. A method for compensating for cycle slips in a coherent receiver, the method comprising:
receiving a sequence of frames, each frame comprising a data symbol block and a pilot symbol block, the pilot symbol block comprising one or more pilot symbols;
performing a comparison of a sequence of received pilot symbol blocks from the sequence of frames to an expected sequence of pilot symbol blocks;
estimating a phase rotation of the sequence of received pilot symbol blocks relative to the expected sequence of pilot symbol blocks based on the comparison;
applying the estimated phase rotation to a target data symbol block in a target frame of the sequence of frames to generate a compensated data symbol block; and
outputting the compensated data symbol block.
2. The method of claim 1 , wherein estimating the phase rotation comprises selecting from a predefined set of possible phase rotations, the predefined set of possible phase rotations corresponding to phases of a symbol space of pilot symbols in the expected sequence of pilot symbol blocks.
3. The method of claim 2 , wherein selecting from the predefined set of possible phase rotations comprises:
determining a likelihood of each of the possible phase rotations based on the received sequence of pilot symbol blocks and the expected sequence of pilot symbol blocks; and
selecting the phase rotation having a maximum likelihood.
4. The method of claim 3 , wherein the determining the likelihood comprises computing a Euclidean distance between the received sequence of pilot symbol blocks and the expected sequence of pilot symbol blocks.
5. The method of claim 3 , wherein the determining the likelihood comprises:
slicing pilot symbols of the received sequence of pilot symbol blocks to map each of the pilot symbols to a nearest constellation point; and
computing a Euclidean distance between the sliced sequence of pilot symbol blocks and the expected sequence of pilot symbol blocks.
6. The method of claim 1 , further comprising:
removing a received pilot symbol block from a target frame prior to outputting the target data symbol block from the target frame.
7. The method of claim 1 , wherein the target frame comprises a center frame of the sequence of frames.
8. The method of claim 1 , wherein the sequence of received pilot symbol blocks and the expected sequence of pilot symbol blocks each have a length of 16 blocks.
9. The method of claim 1 , wherein the pilot symbol block has a length P=1, and wherein the data symbol block has a length D=L−P, where L is a frame length, the method further comprising:
receiving via a configuration control signal of the receiver, a parameter S for configuring the frame length L of the receiver, wherein the frame length L=4*S, and wherein S is programmable and comprises an integer value between 5 and 40,
wherein each frame in the sequence of frames has the configured frame length L.
10. A non-transitory computer-readable storage medium storing instructions for compensating for cycle slips in a coherent detection based receiver, the instructions when executed by a processor causing the processor to perform steps including:
receiving a sequence of frames, each frame comprising a data symbol block and a pilot symbol block, the pilot symbol block comprising one or more pilot symbols;
performing a comparison of a sequence of received pilot symbol blocks from the sequence of frames to an expected sequence of pilot symbol blocks;
estimating a phase rotation of the sequence of received pilot symbol blocks relative to the expected sequence of pilot symbol blocks based on the comparison;
applying the estimated phase rotation to a target data symbol block in a target frame of the sequence of frames to generate a compensated data symbol block; and
outputting the compensated data symbol block.
11. The non-transitory computer-readable storage medium of claim 10 , wherein estimating the phase rotation comprises selecting from a predefined set of possible phase rotations, the predefined set of possible phase rotations corresponding to phases of a symbol space of pilot symbols in the expected sequence of pilot symbol blocks.
12. The non-transitory computer-readable storage medium of claim 11 , wherein selecting from the predefined set of possible phase rotations comprises:
determining a likelihood of each of the possible phase rotations based on the received sequence of pilot symbol blocks and the expected sequence of pilot symbol blocks; and
selecting the phase rotation having a maximum likelihood.
13. The non-transitory computer-readable storage medium of claim 12 , wherein the determining the likelihood comprises computing a Euclidean distance between the received sequence of pilot symbol blocks and the expected sequence of pilot symbol blocks.
14. The non-transitory computer-readable storage medium of claim 12 , wherein the determining the likelihood comprises:
slicing pilot symbols of the received sequence of pilot symbol blocks to map each of the pilot symbols to a nearest constellation point; and
computing a Euclidean distance between the sliced sequence of pilot symbol blocks and the expected sequence of pilot symbol blocks.
15. The non-transitory computer-readable storage medium of claim 10 , further comprising instructions for:
removing a received pilot symbol block from a target frame prior to outputting the target data symbol block from the target frame.
16. The non-transitory computer-readable storage medium of claim 10 , wherein the target frame comprises a center frame of the sequence of frames.
17. The non-transitory computer-readable storage medium of claim 10 , wherein the sequence of received pilot symbol blocks and the expected sequence of pilot symbol blocks each have a length of 16 blocks.
18. A receiver comprising:
a carrier phase recovery block configured to output a sequence of frames based on a received signal, each frame comprising a data symbol block and a pilot symbol block, the pilot symbol block comprising one or more pilot symbols;
a cycle slip detector configured to perform a comparison of a sequence of received pilot symbol blocks from the sequence of frames to an expected sequence of pilot symbol blocks, and to estimate a phase rotation of the sequence of received pilot symbol blocks relative to the expected sequence of pilot symbol blocks based on the comparison; and
a phase corrector configured to apply the estimated phase rotation to a target data symbol block in a target frame of the sequence of frames to generate a compensated data symbol block.
19. The receiver of claim 18 , wherein the cycle slip detector is further configured to select the phase rotation from a predefined set of possible phase rotations, the predefined set of possible phase rotations corresponding to phases of a symbol space of pilot symbols in the expected sequence of pilot symbol blocks.
20. The receiver of claim 19 , wherein the cycle slip detector is further configured to determine a likelihood of each of the possible phase rotations based on the received sequence of pilot symbol blocks and the expected sequence of pilot symbol blocks, and select the phase rotation having a maximum likelihood.