# US 2008/0187032 A1 · Systems and methods for efficient channel classification > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0187032 A1 - Document ID: US20080187032A1 - Status: Published application - Kind: A1 - Application number: 12/024,029 - Filed: 2008-01-31 - Published: 2008-08-07 - Earliest claimed: 2007-02-02 - Assignees: Texas Instruments Incorporated - Inventors: Tarkesh PANDE; Deric W. WATERS; Srinath HOSUR; Anuj BATRA - Web page: https://patentgrep.com/patent/US20080187032A1 ## CPC - H04L 25/0204: {of multiple channels} - H04B 7/0417: Feedback systems - H04B 7/066: {Combined feedback for a number of channels, e.g. over several subcarriers like in orthogonal frequency division multiplexing [OFDM]} - H04L 2025/03426: {transmission using multiple-input and multiple-output channels} - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) - H04B: TRANSMISSION ## Abstract Embodiments provide a system and method for efficiently classifying different channel types in an orthogonal frequency division multiplexing (OFDM) system. Embodiments quantify the frequency selectivity in a channel by measuring the variation in a particular channel statistic across sub-carriers in an OFDM system, involve minimal complexity in implementation, and can be used in a variety of scenarios. One embodiment is a method for classifying channels in an OFDM system, comprising measuring variation of at least one channel statistic across sub-carriers, quantifying the variation to determine a measurement value, and applying the measurement value to at least one threshold to classify the channel. ## Claims ### Claim 1 An orthogonal frequency-division multiplexing (OFDM) system, comprising: a translation unit for translating at least one channel statistic received from each of a plurality of sub-carriers to a set of channel statistics that represents variation in the at least one channel statistic. a measuring unit for mapping the set of statistics to a measurement value; and a processor for comparing the measurement value to at least one threshold to classify a channel. ### Claim 2 (depends on 1) The system of claim 1, wherein the OFDM system is a multiple-input, multiple-output (MIMO) OFDM system. ### Claim 3 (depends on 1) The system of claim 1, wherein the variation in the channel statistics comprises a rate of variation in the at least one channel statistic. ### Claim 4 (depends on 1) The system of claim 1, wherein the translation unit translates the channel statistic for every Mth sub-carrier where (M>1). ### Claim 5 (depends on 1) The system of claim 1, wherein the translation unit determines the peaks (maxima) and the valleys (minima) in the at least one channel statistic across sub-carriers. ### Claim 6 (depends on 1) The system of claim 1, wherein the translation unit calculates a difference in the at least one channel statistic between adjacent sub-carriers. ### Claim 7 (depends on 1) The system of claim 1, wherein the translation unit calculates a mean in the at least one channel statistic across a set of all sub-carriers. ### Claim 8 (depends on 7) The system of claim 7, wherein the translation unit calculates a difference from the resulting channel statistic mean between adjacent sub-carriers. ### Claim 9 (depends on 1) The system of claim 1, wherein the translation unit is a high pass filter. ### Claim 10 (depends on 1) The system of claim 1, wherein the measurement value is a sum of zero-crossings. ### Claim 11 (depends on 1) The system of claim 1, wherein the measurement unit is a moments-based estimator. ### Claim 12 (depends on 1) The system of claim 1, wherein the at least one threshold is computed offline. ### Claim 13 (depends on 1) The system of claim 1, wherein the processor classifies the channel on the basis of variation in frequency selectivity. ### Claim 14 (depends on 1) The system of claim 1, wherein the at least one channel statistic is selected from the group of: magnitude, phase, singular values, steering matrices' angular information, matrix distance norm, distance of the steering matrices from a reference matrix, and a combination thereof. ### Claim 15 (depends on 1) The system of claim 1, wherein the processor determines an amount of information to transmit to a beamformer based on the channel classification. ### Claim 16 (depends on 15) The system of claim 15, wherein the amount of information comprises a modulation and coding scheme (MCS) the transmitter is to use. ### Claim 17 (depends on 15) The system of claim 15, wherein the amount of information comprises a number of feedback bits required to convey steering matrix information. ### Claim 18 (depends on 15) The system of claim 15, wherein the amount of information comprises steering matrices to be used. ### Claim 19 A method for classifying channels in an OFDM system, comprising: measuring variation of at least one channel statistic across sub-carriers; quantifying the variation to determine a measurement value; and applying the measurement value to at least one threshold to classify the channel. ### Claim 20 (depends on 19) The method of claim 19, wherein the measuring variation further comprises measuring a rate of variation. ### Claim 21 (depends on 19) The method of claim 19, wherein the measuring further comprises taking the difference of the channel statistic between adjacent sub-carriers. ### Claim 22 (depends on 19) The method of claim 19, wherein the applying further comprises classifying the channel on the basis of variation in frequency selectivity. ### Claim 23 (depends on 19) The method of claim 19, wherein the counting further comprises determining a value which is a sum of zero-crossing counters. ### Claim 24 (depends on 19) The method of claim 19, wherein the measuring further comprises measuring variation of at least one channel statistic selected from the group of: magnitude, phase, singular values, steering matrices' angular information, matrix distance norm, distance of the steering matrices from a reference matrix, and a combination thereof. ### Claim 25 (depends on 19) The method of claim 19, further comprises determining, by a beamformee, an amount of information to transmit to a beamformer based on the channel classification.