# US 2012/0237204 A1 · System and Method for Blind Frequency Recovery > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2012/0237204 A1 - Document ID: US20120237204A1 - Status: Published application - Kind: A1 - Application number: 13/048,630 - Filed: 2011-03-15 - Published: 2012-09-20 - Earliest claimed: 2011-03-15 - Assignees: AT&T Intellectual Property I, L.P. - Inventors: Xiang ZHOU - Web page: https://patentgrep.com/patent/US20120237204A1 ## CPC - H04B 10/6165: {Estimation of the phase of the received optical signal, phase error estimation or phase error correction} - H04B 10/0795: {Performance monitoring; Measurement of transmission parameters} - H04B 10/6164: {Estimation or correction of the frequency offset between the received optical signal and the optical local oscillator} - H04L 7/0075: {with photonic or optical means} - H04L 27/0014: {Carrier regulation (of chaotic carriers H04L27/001; for multicarrier receivers H04L27/2657)} - H04L 2027/0028: {at passband only} - H04L 2027/0034: {using hypothesis testing} - H04L 2027/0065: {Frequency error detectors (H04L2027/0067 takes precedence)} - H04L 2027/0067: {Phase error detectors} - H04L 2027/0085: {with no special signals for synchronisation} - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Described herein are systems and methods for accurately estimating and removing a carrier frequency offset. One exemplary embodiment relates to a system comprising a frequency offset detection circuit detecting a carrier frequency offset in an optical signal, and a frequency testing circuit calculating an estimated frequency offset value of the carrier frequency offset, wherein the frequency testing circuit removes a carrier phase based on the estimated frequency offset value and recovers the optical signal. Another exemplary embodiment relates to a method comprising detecting a carrier frequency offset in an optical signal, calculating an estimated frequency offset value of the carrier frequency offset, removing a carrier phase based on the estimated frequency offset value, and recovering the optical signal. ## Claims ### Claim 1 A system, comprising: a frequency offset detection circuit detecting a carrier frequency offset in an optical signal; and a frequency testing circuit calculating an estimated frequency offset value of the carrier frequency offset, wherein the frequency testing circuit removes a carrier phase based on the estimated frequency offset value and recovers the optical signal. ### Claim 2 (depends on 1) The system of claim 1, wherein the frequency offset detection includes a parallel processing architecture for multi-stage frequency detection. ### Claim 3 (depends on 2) The system of claim 2, wherein the parallel processing architecture includes a plurality of frequency testing units performing multiple tests simultaneously, and the frequency testing circuit determines a minimum mean square error for each of the multiple tests simultaneously. ### Claim 4 (depends on 1) The system of claim 1, wherein the frequency offset detection includes a sequential processing architecture for single-stage frequency detection. ### Claim 5 (depends on 4) The system of claim 4, wherein the sequential processing architecture includes a single frequency testing unit performing multiple tests at different intervals, and the frequency testing circuit determines a minimum mean square error for each of the multiple tests at different intervals. ### Claim 6 (depends on 1) The system of claim 1, wherein the frequency offset detection includes a combination architecture having a parallel processing architecture and a sequential processing architecture for multi-stage frequency detection. ### Claim 7 (depends on 6) The system of claim 6, wherein the combination architecture implements an adjustable frequency tracking speed. ### Claim 8 (depends on 1) The system of claim 1, wherein the frequency testing circuit removes the carrier phase based on a phase rotation operation to generate a phase rotated signal. ### Claim 9 (depends on 1) The system of claim 1, wherein the frequency offset detection circuit implements digital coherent detection to detect the carrier frequency offset. ### Claim 10 A method, comprising: detecting a carrier frequency offset in an optical signal; calculating an estimated frequency offset value of the carrier frequency offset; removing a carrier phase based on the estimated frequency offset value; and recovering the optical signal. ### Claim 11 (depends on 10) The method of claim 10, wherein the carrier frequency offset detection includes parallel multi-stage frequency detection. ### Claim 12 (depends on 11) The method of claim 11, wherein the parallel multi-stage frequency detection includes performing multiple tests simultaneously and determining a minimum mean square error for each of the multiple tests simultaneously. ### Claim 13 (depends on 10) The method of claim 10, wherein the carrier frequency offset detection includes sequential single-stage frequency detection. ### Claim 14 (depends on 13) The method of claim 13, wherein the sequential single-stage frequency detection includes performing multiple tests at different intervals and determining a minimum mean square error for each of the multiple tests at different intervals. ### Claim 15 (depends on 10) The method of claim 10, wherein the carrier frequency offset detection includes parallel multi-stage frequency detection and sequential single-stage frequency detection. ### Claim 16 (depends on 15) The method of claim 15, wherein the carrier frequency offset detection includes an adjustable frequency tracking speed. ### Claim 17 (depends on 10) The method of claim 10, wherein the removing the carrier phase includes performing a phase rotation operation to generate a phase rotated signal. ### Claim 18 (depends on 10) The method of claim 10, wherein the carrier frequency offset detection is based on digital coherent detection. ### Claim 19 A circuit, comprising: a detecting means detecting a carrier frequency offset in an optical signal; a calculating means calculating an estimated frequency offset value of the carrier frequency offset; a phase removal means removing a carrier phase based on the estimated frequency offset value; and a signal recovering means recovering the optical signal. ### Claim 20 (depends on 19) The circuit of claim 19, wherein the detecting means includes one of a parallel processing architecture for multi-stage frequency detection, a sequential processing architecture for single-stage frequency detection, and a combination architecture for multi-stage frequency detection.