# US 2022/0045895 A1 · Apparatus and method for receiving quadrature amplitude modulated "qam" symbol > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2022/0045895 A1 - Document ID: US20220045895A1 - Status: Published application - Kind: A1 - Application number: 17/374,483 - Filed: 2021-07-13 - Published: 2022-02-10 - Earliest claimed: 2020-08-06 - Assignees: Cisco Technology, Inc. - Applicants: Cisco Technology, Inc. - Inventors: Andreas Bernhard Bisplinghoff; Stefan Helmut Müller-Weinfurtner - Web page: https://patentgrep.com/patent/US20220045895A1 ## CPC - H04L 27/3863: {Compensation for quadrature error in the received signal} - H04L 27/3818: {using coherent demodulation, i.e. using one or more nominally phase synchronous carriers (H04L27/227 and H04L27/389 take precedence)} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract Techniques are presented for receiving Quadrature Amplitude Modulated (QAM) symbols from a transmitter via a transmission path. In one example, a demodulator is configured to down-convert an incoming Radio Frequency (RF) signal to a baseband signal and convert the baseband signal to digital samples, and output the digital samples. A demapper is configured to receive the digital samples output from the demodulator and output data encoded in QAM symbols. The demapper is further configured to: determine from a constellation of QAM symbols a subset of QAM symbols that a digital sample from the demodulator may represent; apply an offset to each QAM symbol in the subset of QAM symbols of the constellation to result in a subset of offset QAM symbols; determine which QAM symbol in the subset of offset QAM symbols the digital sample most likely represents; and output data representing a determined QAM symbol. ## Claims ### Claim 1 A receiver for receiving Quadrature Amplitude Modulated (QAM) symbols from a transmitter via a transmission path, the receiver comprising: a demodulator configured to down-convert an incoming Radio Frequency (RF) signal to a baseband signal and convert said baseband signal to digital samples, and output said digital samples; and a demapper coupled to receive the digital samples output from the demodulator and configured to output data encoded in QAM symbols, wherein the demapper is configured to: determine from a constellation of QAM symbols a subset of QAM symbols that a digital sample from said demodulator may represent; apply an offset to each QAM symbol in the subset of QAM symbols of the constellation to result in a subset of offset QAM symbols; determine which QAM symbol in the subset of offset QAM symbols the digital sample most likely represents; and output data representing a determined QAM symbol. ### Claim 2 (depends on 1) The receiver of claim 1, wherein the offset represents characteristics of any of the transmitter and the receiver. ### Claim 3 (depends on 1) The receiver of claim 1, wherein the offset represents characteristics of the transmission path. ### Claim 4 (depends on 1) The receiver of claim 1, wherein the offset for each QAM symbol is adaptive. ### Claim 5 (depends on 1) The receiver of claim 1, further comprising memory and a look-up table of the offset for each of the QAM symbols stored in the memory. ### Claim 6 (depends on 1) The receiver of claim 1, further configured to receive QAM symbols associated with a probabilistically-determined constellation. ### Claim 7 (depends on 6) The receiver of claim 6, wherein the offset applied to each QAM symbol in the subset of QAM symbols is associated with a probability of the QAM symbol occurring in the probabilistically-determined constellation of QAM symbols. ### Claim 8 A method of receiving Quadrature Amplitude Modulated (QAM) symbols from a transmitter via a transmission path, the method comprising: down-converting an incoming Radio Frequency (RF) signal to a baseband signal and converting said baseband signal to digital samples; determining from a constellation of QAM symbols a subset of QAM symbols that a digital sample may represent; applying an offset to each QAM symbol in the subset of QAM symbols of the constellation to result in a subset of offset QAM symbols; determining which QAM symbol in the subset of offset QAM symbols the digital sample most likely represents; and outputting data representing a determined QAM symbol. ### Claim 9 (depends on 8) The method of claim 8, wherein the offset represents characteristics of any of the transmitter and a receiver. ### Claim 10 (depends on 8) The method of claim 8, wherein the offset represents characteristics of the transmission path. ### Claim 11 (depends on 8) The method of claim 8, wherein the offset for each QAM symbol is adaptive. ### Claim 12 (depends on 8) The method of claim 8, further comprising storing the offset for each of the QAM symbols stored in a look-up table in memory. ### Claim 13 (depends on 8) The method of claim 8, further comprising receiving QAM symbols associated with a probabilistically-determined constellation. ### Claim 14 (depends on 13) The method of claim 13, further comprising applying the offset to each QAM symbol in the subset of QAM symbols, wherein the offset applied to each QAM symbol in the subset of QAM symbols is associated with a probability of the QAM symbol occurring in the probabilistically-determined constellation of QAM symbols. ### Claim 15 A non-transitory computer-readable medium comprising instructions that, when executed by a computer, cause the computer to: determine from a constellation of Quadrature Amplitude Modulated (QAM) symbols obtained from a Radio Frequency (RF) signal that is down-converted to baseband and converted to digital samples, a subset of QAM symbols that a digital sample may represent; apply an offset to each QAM symbol in the subset of QAM symbols of the constellation to result in a subset of offset QAM symbols; determine which QAM symbol in the subset of offset QAM symbols the digital sample most likely represents; and output data representing a determined QAM symbol. ### Claim 16 (depends on 15) The non-transitory computer-readable medium of claim 15, wherein the offset represents characteristics of any of a transmitter that transmitted the RF signal, a transmission path over which the RF signal is transmitted, and a receiver that receives the RF signal. ### Claim 17 (depends on 15) The non-transitory computer-readable medium of claim 15, wherein the offset for each QAM symbol is adaptive. ### Claim 18 (depends on 15) The non-transitory computer-readable medium of claim 15, wherein the instructions further cause the computer to store the offset for each of the QAM symbols stored in a look-up table in memory. ### Claim 19 (depends on 15) The non-transitory computer-readable medium of claim 15, wherein the instructions further cause the computer to receive QAM symbols associated with a probabilistically-determined constellation. ### Claim 20 (depends on 19) The non-transitory computer-readable medium of claim 19, wherein the instructions further cause the computer to apply the offset to each QAM symbol in the subset of QAM symbols, wherein the offset applied to each QAM symbol in the subset of QAM symbols is associated with a probability of the QAM symbol occurring in the probabilistically-determined constellation of QAM symbols.