# US 9,521,579 B1 · Method and apparatus for rate adaptation in a wireless communication system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,521,579 B1 - Document ID: US9521579B1 - Status: Granted - Kind: B1 - Application number: 13/783,277 - Filed: 2013-03-02 - Granted: 2016-12-13 - Earliest claimed: 2013-03-02 - Assignees: Redpine Signals, Inc. - Applicants: Sriram Mudulodu - Inventors: Sriram Mudulodu - Web page: https://patentgrep.com/patent/US9521579B1 ## CPC - H04W 74/085: {collision avoidance} - H04L 1/0003: {by switching between different modulation schemes} - H04L 1/0009: {by adapting the channel coding (H04L1/1812 takes precedence)} - H04L 1/0015: {characterised by the adaptation strategy} - H04L 27/00: Modulated-carrier systems - H04W 72/0446: Resources in time domain, e.g. slots or frames - H04L 1/1867: Arrangements specially adapted for the transmitter end - H04L 27/0008: {arrangements for allowing a transmitter or receiver to use more than one type of modulation (negotiating modulation type for two-way transmission paths H04L5/1453)} - H04W: WIRELESS COMMUNICATION NETWORKS (broadcast communication H04H; communication systems using wireless links for non-selective communication, e.g. wireless extensions H04M1/72) - H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M) ## Abstract A method for selection of a particular modulation coding selection (MCS) from a plurality of available MCS selects a particular MCS after obtaining SNR_d, SNR_high, SNR_low, and if SNR_d>SNR_high, selecting the highest available MCS, and if SNR_dSNR_d>SNR_low, selecting MCS based on computing the function/table for each MCS according to the formula: f(MCS)=(1−PER(length_packet,MCS,SNR_d))/length_packet(packet_size,MCS), and thereafter selecting the MCS that maximizes the f(MCS) function. Further the neighboring MCS values are characterized for throughput in a throughput characterization step, and compared in throughput to the above determined throughput. In an embodiment of the invention, SNR_high, SNR_low are found by finding the SNR that satisfies: PER(length_packet,MCS_lowest,SNR_low)=PER_thresh PER(length_packet,MCS_highest,SNR_high)=PER_thresh Where PER_thresh is a design parameter, and MCS_lowest is the lowest MCS and MCS_highest is the highest available MCS. ## Claims ### Claim 1 A method for the selection of a particular Modulation and Coding Selection (MCS) from a plurality of available MCS in a wireless communications system, the method having the steps: obtaining a derived signal to noise ratio (SNR_d); establishing threshold values SNR_high, SNR_low; if SNR_d>SNR_high, selecting the highest MCS; if SNR_dSNR_d>SNR_low, selecting MCS based on: obtaining a table of the product of f(MCS) and f_m corresponding to each MCS, where f(MCS) is an estimate of throughput in the absence of collisions or interference, and f_m is a correction factor for the effects of collisions or interference; selecting the MCS that maximizes said product of f(MCS) and f_m; said plurality of MCS including at least a modulation type and a coding rate; and where said method steps are repeated when a change in SNR_d of more than 2 dB since a previous transmission occurs. ### Claim 2 (depends on 1) The method of claim 1 where f ⁡ ( MCS ) = 1 - PER ⁡ ( length_packet , MCS , H_hat , noise_power ) length_packet ⁢ ( packet_size , MCS ) ; where f(MCS) is an estimated throughput for a particular MCS in the absence of collisions or interference where: PER is a packet error rate; length_packet is the length of the packet; MCS is a particular Modulation and Coding Selection; H_hat is an estimate of the channel matrix H; noise_power is an estimated noise level in the absence of collisions or interference. ### Claim 3 (depends on 1) The method of claim 1 where SNR_d, SNR_high, SNR_low are derived from receive signal strength indication (RSSI). ### Claim 4 (depends on 3) The method of claim 3 where SNR_high is selected such that PER(length_packet, MCS_highest, SNR_high)=PER_thresh, where: PER is the packet error rate of the communications channel and excludes the effect of collisions, and said PER is a function of said length_packet which is the time duration of a packet, said MCS_highest is an MCS corresponding to the highest data rate, and said PER_thresh is less than or equal to 1%. ### Claim 5 (depends on 3) The method of claim 3 where SNR_low is selected such that PER(length_packet, MCS_lowest, SNR_low)=PER_thresh, where: PER is the packet error rate of the communications channel, and said PER is a function of said length_packet which is the time duration of a packet, said MCS_lowest is an MCS corresponding to the lowest data rate, and said PER_thresh has a value which is equal to or less than 1%. ### Claim 6 (depends on 1) The method of claim 1 where SNR_d is derived from a channel characterization matrix, and SNR_high and SNR_low are derived from a packet error rate. ### Claim 7 (depends on 5, 6) The method of claim 6 or claim 5 where a packet error rate threshold (PER_thresh)=alpha* the ratio of collisions on a channel to total packets on a channel, and where alpha is less than or equal to 0.25. ### Claim 8 (depends on 1) The method of claim 1 where said length_packet is computed from said MCS, a guard interval, a payload length, and a preamble length. ### Claim 9 (depends on 1) The method of claim 1 where said length_packet is computed from said MCS, a guard interval, a payload length, a preamble length, and an inter-packet gap. ### Claim 10 (depends on 1) The method of claim 1 where said f(MCS) is derived from measurement of the number of transmitted packets that did not get acknowledged but were not the result of collisions. ### Claim 11 (depends on 1) The method of claim 1 where said f(MCS) is derived from measurement of packets in a communications channel which were not acknowledged and lost or not decoded due to thermal noise of said packet. ### Claim 12 (depends on 1) The method of claim 1 where said SNR_d is derived from an unsuccessfully decoded SIGNAL field of a packet header and successfully decoded SIGNAL field of other packet headers. ### Claim 13 (depends on 1) The method of claim 1 where said f(MCS) is multiplied by a f_m(MCS) factor derived from a peak information rate and packet length. ### Claim 14 (depends on 1) The method of claim 1 where said f(MCS) associated with a particular remote station is computed from information which includes retransmission requests from said particular remote station. ### Claim 15 A method for selection of a Modulation and Coding Selection (MCS) from a plurality of available MCS in a wireless communications system, the method having the steps: obtaining a derived signal to noise ratio (SNR_d); establishing threshold values SNR_high, SNR_low; if SNR_d>SNR_high, selecting the highest MCS; if SNR_dSNR_d>SNR_low, selecting MCS based on: obtaining a table of the product of f(MCS) and f_m corresponding to each MCS, where f(MCS) is an estimate of throughput in the absence of collisions or interference, and f_m is a correction factor for the effects of collisions or interference; selecting the MCS that maximizes said product of f(MCS) and f_m; and where said method of selection repeats when a change in SNR_d is detected. ### Claim 16 A method for the selection of a particular Modulation and Coding Selection (MCS) from a plurality of available MCS in a wireless communications system, the method having the steps: obtaining a derived signal to noise ratio (SNR_d); establishing threshold values SNR_high, SNR_low; if SNR_d>SNR_high, selecting the highest MCS; if SNR_dSNR_d>SNR_low, selecting MCS based on: obtaining a table of the product of f(MCS) and f_m corresponding to each MCS, where f(MCS) is an estimate of throughput in the absence of collisions or interference, and f_m is a correction factor for the effects of collisions or interference; selecting the MCS that maximizes said product of f(MCS) and f_m; said plurality of MCS including at least a modulation type and a coding rate where f ⁡ ( MCS ) = 1 - PER ⁡ ( length packet , MCS , H hat , nosie power ) length_packet ⁢ ( packet size , MCS ) where f(MCS) is an estimated throughput for a particular MCS in the absence of collisions or interference and where: PER is a packet error rate; length_packet is the length of the packet; MCS is a particular Modulation and Coding Selection; H_hat is an estimate of channel matrix H; Noise power is an estimated noise level in the absence of collisions or interference. ### Claim 17 A method for the selection of a particular Modulation and Coding Selection (MCS) from a plurality of available MCS in a wireless communications system, the method having the steps: obtaining a derived signal to noise ratio (SNR_d); establishing threshold values SNR_high, SNR_low; if SNR_d>SNR_high, selecting the highest MCS; if SNR_dSNR_d>SNR_low, selecting MCS based on: obtaining a table of the product of f(MCS) and f_m corresponding to each MCS, where f(MCS) is an estimate of throughput in the absence of collisions or interference, and f_m is a correction factor for the effects of collisions or interference; selecting the MCS that maximizes said product of f(MCS) and f_m; said plurality of MCS including at least a modulation type and a coding rate; where SNR_d, SNR_high, SNR_low are derived from receive signal strength indication (RSSI) where SNR_high is selected such that PER(length_packet, MCS_highest, SNR_high)=PER_thresh, where: PER is the packet error rate of the communications channel and excludes the effect of collisions, and said PER is a function of said length_packet which is the time duration of a packet, said MCS_highest is an MCS corresponding to the highest data rate, and said PER_thresh is less than or equal to 1%. ### Claim 18 A method for the selection of a particular Modulation and Coding Selection (MCS) from a plurality of available MCS in a wireless communications system, the method having the steps: obtaining a derived signal to noise ratio (SNR_d); establishing threshold values SNR_high, SNR_low; if SNR_d>SNR_high, selecting the highest MCS; if SNR_dSNR_d>SNR_low, selecting MCS based on: obtaining a table of the product of f(MCS) and f_m corresponding to each MCS, where f(MCS) is an estimate of throughput in the absence of collisions or interference, and f_m is a correction factor for the effects of collisions or interference; selecting the MCS that maximizes said product of f(MCS) and f_m; said plurality of MCS including at least a modulation type and a coding rate; where SNR_d, SNR_high, SNR_low are derived from receive signal strength indication (RSSI) where SNR_low is selected such that PER(length_packet, MCS_lowest, SNR_low)=PER_thresh, where: PER is the packet error rate of the communications channel and excludes the effect of collisions, and said PER is a function of said length_packet which is the time duration of a packet, said MCS_lowest is an MCS corresponding to the lowest data rate, and said PER_thresh is less than or equal to 1%.