# US 11,121,769 B2 · Fast estimation of chromatic dispersion > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,121,769 B2 - Document ID: US11121769B2 - Status: Granted - Kind: B2 - Application number: 17/019,491 - Filed: 2020-09-14 - Published: 2021-05-20 - Granted: 2021-09-14 - Earliest claimed: 2019-11-18 - Assignees: Ciena Corporation - Applicants: Shahab Oveis Gharan; Lukas Jakober - Inventors: Shahab Oveis Gharan; Lukas Jakober - Web page: https://patentgrep.com/patent/US11121769B2 ## CPC - H04B 10/07951: {Monitoring or measuring chromatic dispersion or PMD} - H04B 10/6161: {Compensation of chromatic dispersion} - H04B 10/0799: {Monitoring line transmitter or line receiver equipment} - H04B 10/2513: due to chromatic dispersion - H04B 10/50: Transmitters - H04B 10/61: Coherent receivers - H04B: TRANSMISSION ## Abstract A receiver is configured to calculate a representation of a received signal conveying symbols at a frequency fS, the representation comprising a first frequency band and a second frequency band which are disjoint and have non-zero correlation. The receiver calculates a first term comprising a function of a phase difference between the representation at a first pair of frequencies separated by a gap Δ and comprised within the first frequency band, and a second term comprising a function of a phase difference between the representation at a second pair of frequencies separated by the gap Δ and comprised within the second frequency band, wherein the higher frequency of the first pair and the higher frequency of the second pair are separated by a gap G. An estimate of chromatic dispersion in the received signal is calculated based on the first term and the second term. ## Claims ### Claim 1 A receiver apparatus comprising: a communication interface configured to receive a communications signal conveying symbols at a symbol frequency fS; and circuitry configured to calculate a representation of the communications signal, wherein the representation comprises a first frequency band and a second frequency band which are disjoint and have non-zero correlation; calculate a first term comprising a function of a phase difference between the representation at a first pair of frequencies separated by a gap Δ and comprised within the first frequency band; calculate a second term comprising a function of a phase difference between the representation at a second pair of frequencies separated by the gap Δ and comprised within the second frequency band, wherein the higher frequency of the first pair and the higher frequency of the second pair are separated by a gap G; and calculate an estimate of chromatic dispersion (CD) in the communications signal based on the first term and the second term. ### Claim 2 (depends on 1) The receiver apparatus as claimed in claim 1, wherein G=fS. ### Claim 3 (depends on 2) The receiver apparatus as claimed in claim 2, wherein the first frequency band is centered at fS/2 and wherein the second frequency band is centered at −fS/2. ### Claim 4 (depends on 1) The receiver apparatus as claimed in claim 1, wherein the communications signal comprises N subcarriers, wherein N>1, and wherein G=fS/N. ### Claim 5 (depends on 1) The receiver apparatus as claimed in claim 1, wherein the circuitry is configured to calculate a complex metric using the first term and the second term; and calculate the estimate of CD in the communications signal based on an angle of the complex metric. ### Claim 6 (depends on 5) The receiver apparatus as claimed in claim 5, wherein the circuitry is configured to calculate the complex metric using complex conjugate multiplication. ### Claim 7 (depends on 1) The receiver apparatus as claimed in claim 1, wherein the circuitry is configured to calculate the first term and the second term using complex conjugate multiplication. ### Claim 8 (depends on 1) The receiver apparatus as claimed in claim 1, wherein the circuitry is configured to calculate a plurality of different versions of the first term at a respective plurality of different first pairs of frequencies; calculate a plurality of different versions of the second term at a respective plurality of different second pairs of frequencies; and calculate the estimate of CD in the communications signal based on a combination of the plurality of different versions of the first term and the plurality of different versions of the second term. ### Claim 9 (depends on 8) The receiver apparatus as claimed in claim 8, wherein the combination applies different weights to the different versions of the first term based on respective magnitudes of the different first pairs of frequencies, and wherein the combination applies different weights to the different versions of the second term based on respective magnitudes of the different second pairs of frequencies. ### Claim 10 (depends on 5) The receiver apparatus as claimed in claim 5, wherein the circuitry is configured to calculate a plurality of different representations of the communications signal corresponding to a respective plurality of time intervals; calculate a plurality of different versions of the complex metric corresponding to the respective plurality of different representations; and calculate the estimate of CD in the communications signal based on the plurality of different versions of the complex metric. ### Claim 11 A method performed at a receiver apparatus, the method comprising: receiving a communications signal conveying symbols at a symbol frequency fS; calculating a representation of the communications signal, wherein the representation comprises a first frequency band and a second frequency band which are disjoint and have non-zero correlation; calculating a first term comprising a function of a phase difference between the representation at a first pair of frequencies separated by a gap Δ and comprised within the first frequency band; calculating a second term comprising a function of a phase difference between the representation at a second pair of frequencies separated by the gap Δ and comprised within the second frequency band, wherein the higher frequency of the first pair and the higher frequency of the second pair are separated by a gap G; and calculating an estimate of chromatic dispersion (CD) in the communications signal based on the first term and the second term. ### Claim 12 (depends on 11) The method as claimed in claim 11, wherein G=fS. ### Claim 13 (depends on 12) The method as claimed in claim 12, wherein the first frequency band is centered at fS/2 and wherein the second frequency band is centered at −fS/2. ### Claim 14 (depends on 11) The method as claimed in claim 11, wherein the communications signal comprises N subcarriers, wherein N>1, and wherein G=fS/N. ### Claim 15 (depends on 11) The method as claimed in claim 11, further comprising calculating a complex metric using the first term and the second term; and calculating the estimate of CD in the communications signal based on an angle of the complex metric. ### Claim 16 (depends on 15) The method as claimed in claim 15, further comprising calculating the complex metric using complex conjugate multiplication. ### Claim 17 (depends on 11) The method as claimed in claim 11, further comprising calculating the first term and the second term using complex conjugate multiplication. ### Claim 18 (depends on 11) The method as claimed in claim 11, further comprising calculating a plurality of different versions of the first term at a respective plurality of different first pairs of frequencies; calculating a plurality of different versions of the second term at a respective plurality of different second pairs of frequencies; and calculating the estimate of CD in the communications signal based on a combination of the plurality of different versions of the first term and the plurality of different versions of the second term. ### Claim 19 (depends on 18) The method as claimed in claim 18, wherein the combination applies different weights to the different versions of the first term based on respective magnitudes of the different first pairs of frequencies, and wherein the combination applies different weights to the different versions of the second term based on respective magnitudes of the different second pairs of frequencies. ### Claim 20 (depends on 15) The method as claimed in claim 15, further comprising calculating a plurality of different representations of the communications signal corresponding to a respective plurality of time intervals; calculating a plurality of different versions of the complex metric corresponding to the respective plurality of different representations; and calculating the estimate of CD in the communications signal based on the plurality of different versions of the complex metric.