# US 10,320,489 B2 · Channel estimation using intra-symbol frequency domain averaging > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,320,489 B2 - Document ID: US10320489B2 - Status: Granted - Kind: B2 - Application number: 15/853,449 - Filed: 2017-12-22 - Published: 2018-06-28 - Granted: 2019-06-11 - Earliest claimed: 2016-12-22 - Assignees: Zte Corporation - Applicants: ZTE Corporation - Inventors: Xin Xiao; Jianjun Yu - Web page: https://patentgrep.com/patent/US10320489B2 ## CPC - H04B 10/6972: {using passive filtering} - H04B 10/0795: {Performance monitoring; Measurement of transmission parameters} - H04B 10/11: Arrangements specific to free-space transmission, i.e. transmission through air or vacuum - H04B 10/548: Phase or frequency modulation - H04L 25/0204: {of multiple channels} - H04L 25/024: {channel estimation algorithms} - H04L 27/3854: {using a non - coherent carrier, including systems with baseband correction for phase or frequency offset} - H04B: TRANSMISSION - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A channel estimation technique suitable for implementation at a digital communication receiver such as an optical signal receiver apparatus includes receiving, over a communication channel, a transmission comprising a sequence of modulated symbols, estimating, at multiple frequencies, estimated values of a channel transfer function of the communication channel and selectively revising the estimated values of channel transfer function by reducing glitches in the estimated values of the channel transfer function. ## Claims ### Claim 1 A method of digital communication, implementable at a receiver-side in a digital communication network, comprising: receiving, over a communication channel, a transmission comprising a sequence of modulated symbols; estimating, at multiple frequencies, estimated values of a channel transfer function of the communication channel; and selectively revising the estimated values of channel transfer function by reducing glitches in the estimated values of the channel transfer function by: comparing, at the multiple frequencies, a corresponding estimated value of the channel transfer function with smoothened values of the channel transfer function at the multiple frequencies; and replacing, in a revised estimated channel transfer function, the corresponding estimated value of the channel transfer function with the smoothened value when a difference between the corresponding estimated value and the smoothened value is greater than a threshold. ### Claim 2 (depends on 1) The method of claim 1, wherein the smoothened value of the channel transfer function is computed by averaging a number of values of the channel transfer function in a frequency domain window around the multiple frequencies. ### Claim 3 (depends on 2) The method of claim 2, wherein the threshold is in a range of between 5 percent and 15 percent of the estimated value of the channel transfer function. ### Claim 4 (depends on 2) The method of claim 2, wherein a size of the window is dependent on a number of multiple frequencies at which the channel transfer function is estimated. ### Claim 5 (depends on 4) The method of claim 4, wherein the number of multiple frequencies is 2048 and wherein the size of window is 31 frequency domain samples. ### Claim 6 (depends on 2) The method of claim 2, wherein the smoothened value of the channel transfer function used to be compared with the corresponding estimated value is calculated based on the number of values of the channel transfer function including the corresponding estimated value. ### Claim 7 (depends on 6) The method of claim 6, wherein the smoothened value of the channel transfer function replacing the corresponding estimated value is calculated based on the number of values of the channel transfer function excluding the corresponding estimated value. ### Claim 8 (depends on 7) The method of claim 7, further comprising, after replacing the corresponding estimated value of the channel transfer function, recalculating the smoothened value of the channel transfer function based on the number of values of the channel transfer function including the replaced smoothened value of the channel transfer function. ### Claim 9 (depends on 8) The method of claim 8, further including: recovering information bits from the optical transmission based on the revised estimated channel transfer function and recalculated smoothened value of the channel transfer function. ### Claim 10 (depends on 2) The method of claim 2, wherein the threshold is in a range of between 0.05 and 0.2 of a maximum absolute value of the estimated value of the channel transfer function. ### Claim 11 (depends on 1) The method of claim 1, wherein the smoothened value of the channel transfer function is calculated by lowpass filtering frequency domain estimate values and thresholding an output of the lowpass filtering. ### Claim 12 (depends on 1) The method of claim 1, further including: recovering information bits from the optical transmission based on the revised estimated channel transfer function. ### Claim 13 An optical communication receiver apparatus, comprising: an optical receiver front end; a memory storing instructions; and a processor; wherein the processor reads instructions from the memory and implements a method of estimating a channel transfer function using a transmission signal received by the optical receiver front end, the method comprising: estimating, at multiple frequencies, estimated values of a channel transfer function of the communication channel; calculating, at a given frequency from the multiple frequencies, a first value based on a first number of estimated values of the channel transfer function at frequencies lower than the given frequency; calculating, at the given frequency, a second value based on a second number of estimated values of the channel transfer function at frequencies higher than the given frequency; calculating a candidate replacement value at the given frequency from the first value and the second value; comparing a difference between the candidate replacement value and the estimated value of the channel transfer function at the given frequency with a threshold; and replacing, in a revised estimated channel transfer function, the estimated value of the channel transfer function estimate with the candidate replacement value when the difference is greater than the threshold. ### Claim 14 (depends on 13) The apparatus of claim 13, wherein the first value is calculated by averaging the first number of estimated values of the channel transfer function and the second value is computed by averaging the second number of estimated values of the channel transfer function. ### Claim 15 (depends on 14) The apparatus of claim 14, wherein the first number and the second number are dependent on a number of multiple frequencies at which the estimated values of the channel transfer function are estimated. ### Claim 16 (depends on 15) The apparatus of claim 15, wherein the number of multiple frequencies is 2048 and wherein the first number and the second number are 15, respectively. ### Claim 17 (depends on 13) The apparatus of claim 13, wherein the first number and the second number are equal to each other. ### Claim 18 (depends on 13) The apparatus of claim 13, wherein the threshold is in a range of between 0.05 and 0.15. ### Claim 19 (depends on 13) The apparatus of claim 13, wherein the calculating the first value based on the first number of estimated values of the channel transfer function includes lowpass filtering followed by and thresholding an output of the lowpass filtering. ### Claim 20 (depends on 13) The apparatus of claim 13, wherein the processor further performs: recovering information bits from the optical transmission based on the revised estimated channel transfer function.