# US 2018/0324858 A1 · Collision detection and avoidance mechanism using distributed radio heads in a wireless network > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2018/0324858 A1 - Document ID: US20180324858A1 - Status: Published application - Kind: A1 - Application number: 15/585,400 - Filed: 2017-05-03 - Published: 2018-11-08 - Earliest claimed: 2017-05-03 - Assignees: Cisco Technology, Inc. - Applicants: Cisco Technology, Inc. - Inventors: David Kloper; Brian D. Hart; Matthew A. Silverman; Paul J. Stager - Web page: https://patentgrep.com/patent/US20180324858A1 ## CPC - H04W 74/0816: with collision avoidance - H04L 1/0002: {by adapting the transmission rate} - H04L 1/0007: {by modifying the frame length} - H04W 74/004: {in the uplink, i.e. towards network} - H04W 74/006: {in the downlink, i.e. towards the terminal} - H04L 2001/0092: {Error control systems characterised by the topology of the transmission link} - H04W 88/085: {Access point devices with remote components} - 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 central processor subsystem controls multiple transceivers. Each transceiver transmits protocol data units from antennas of that transceiver and produces receive waveforms from wirelessly received signals at the one or more antennas. A transmit waveform, including a frame addressed to one or more wireless client devices, is sent through a first transceiver to be transmitted wirelessly by the first transceiver on a frequency channel. A receive waveform, representative of the transmission by the first transceiver and wirelessly received at a second transceiver, is received from the second transceiver. While the transmit waveform is being sent to the first transceiver: a level of collision between the receive waveform and another transmission on the frequency channel is detected; and if the level of collision exceeds a threshold prior to an end of the receive waveform, the transmit waveform being sent to the first transceiver is modified to reduce the collision. ## Claims ### Claim 1 A method comprising: at a central processor subsystem configured to control multiple transceivers separated from each other in a coverage region of a wireless network, each transceiver configured to transmit protocol data units (PDUs) wirelessly from one or more antennas of that transceiver and convert wirelessly received signals at the one or more antennas to receive waveforms: sending a transmit waveform representative of a PDU, the PDU including a frame addressed to one or more wireless client devices, through a first transceiver of the multiple transceivers to be transmitted wirelessly by the first transceiver on a frequency channel; receiving from a second transceiver of the multiple transceivers tuned to receive on the frequency channel a receive waveform representative of the PDU transmitted by the first transceiver that is wirelessly received at the second transceiver; and while sending the transmit waveform to the first transceiver: beginning with a start of the receive waveform, detecting a level of collision between the receive waveform and another transmission on the frequency channel; and if the level of collision exceeds a threshold prior to an end of the receive waveform, modifying the sending of the transmit waveform or modifying sending of a sequence of transmit waveforms representative of PDUs to reduce or avoid the collision. ### Claim 2 (depends on 1) The method of claim 1, wherein the detecting the level of collision includes determining one of a signal-to-interference ratio (SIR), a frequency offset estimate, or a time offset estimate associated with the receive waveform as the level of collision, and wherein the threshold represents one of an SIR threshold, a variance of the frequency offset estimate from an expected frequency offset estimate, or a variance of the time offset from a time offset estimate, respectively. ### Claim 3 (depends on 1) The method of claim 1, further comprising, while sending the transmit waveform through the first transceiver: beginning with the start of the receive waveform, decoding the receive waveform, wherein if the detected level of collision exceeds the threshold prior to decoding an entirety of the receive waveform, performing the modifying. ### Claim 4 (depends on 1) The method of claim 1, further comprising: if the detected level of collision exceeds a first threshold prior to the end of the receive waveform, reducing a data rate at which a remainder of the transmit waveform yet to be transmitted is to be transmitted by the first transceiver; and if the detected level of the collision exceeds a second threshold greater than the first threshold prior to the end of the receive waveform, terminating the sending of the transmit waveform prior to the end of the transmit waveform. ### Claim 5 (depends on 1) The method of claim 1, wherein the modifying the sending the transmit waveform includes: inserting an invalid cyclic redundancy check (CRC) into a remainder of the transmit waveform representative of the PDU that is being transmitted by the first transceiver; and sending the remainder of the transmit waveform that includes the invalid CRC through the first transceiver to be transmitted by the first transceiver. ### Claim 6 (depends on 1) The method of claim 1, further comprising: performing digital beam forming on the transmit waveform so that the one or more antennas of the first transceiver form a signal null directed to one or more antennas of the second transceiver. ### Claim 7 (depends on 1) The method of claim 1, wherein the PDU includes a training field, a header defining transmission parameters used for decoding the PDU, and a payload including the frame, wherein the method further comprises, while sending the transmit waveform through the first transceiver: decoding the receive waveform beginning with the start of the waveform, wherein if the detected level of collision exceeds the threshold prior to an indication in the header of a duration of the PDU, the modifying includes changing the duration of the PDU from an initial intended duration to a different duration. ### Claim 8 (depends on 1) The method of claim 1, wherein the PDU includes a training field, a header defining transmission parameters used for decoding the PDU, and a payload including the frame, wherein the method further comprises, while sending the transmit waveform through the first transceiver: decoding the receive waveform beginning with the start of the waveform, wherein if the detected level of collision exceeds the threshold prior to an indication in the header of a data rate, the modifying includes reducing the data rate from an initial intended data rate to a reduced data rate. ### Claim 9 (depends on 1) The method of claim 1, wherein, as part of a wireless request-to-send (RTS)/clear-to-send (CTS) protocol, the sending includes sending the transmit waveform representative of the PDU such that the frame of the PDU includes a RTS-to-self frame, and the method further comprises: if the level of collision does not exceed the threshold prior to the end of the receive waveform, sending a second transmit waveform representative of a second PDU that includes a CTS-to-self frame through the first transceiver to be transmitted wirelessly by the first transceiver; and if the level of collision is detected above the threshold and at the time prior to the end of the receive waveform, not sending the second transmit waveform representative of the second PDU that includes the CTS-to-self frame. ### Claim 10 (depends on 1) The method of claim 1, further comprising, as part of a modified wireless request-to-send (RTS)/clear-to-send (CTS) protocol: bypassing sending a transmit waveform representative of a PDU including an RTS frame to the first transceiver for transmission by the first transceiver, wherein the sending includes sending the transmit waveform representative of the PDU such that the PDU includes a CTS-to-self frame in place of the RTS frame in order to detect collisions. ### Claim 11 (depends on 1) The method of claim 1, wherein the PDU is a physical layer convergence procedure (PLCP) PDU (PPDU) formatted as a Very High Throughput (VHT) PPDU, a High Throughput (HT)-mixed format PPDU, a non-HT format PPDU, or a High Efficiency (HE) format PPDU. ### Claim 12 An apparatus comprising: a central processor subsystem configured to control multiple transceivers separated from each other in a coverage region of a wireless network, each transceiver configured to transmit protocol data units (PDUs) wirelessly from one or more antennas of that transceiver and convert wirelessly received signals at the one or more antennas to receive waveforms, the central processor subsystem configured to: send a transmit waveform representative of a PDU, the PDU including a frame addressed to one or more wireless client devices, through a first transceiver of the multiple transceivers to be transmitted wirelessly by the first transceiver on a frequency channel; receive from a second transceiver of the multiple transceivers tuned to receive on the frequency channel a receive waveform representative of the PDU transmitted by the first transceiver that is wirelessly received at the second transceiver; and while sending the transmit waveform to the first transceiver: beginning with a start of the receive waveform, detect a level of collision between the receive waveform and another transmission on the frequency channel; and if the level of collision exceeds a threshold prior to an end of the receive waveform, modify the sending of the transmit waveform or modify sending a sequence of transmit waveforms representative of PDUs to reduce or avoid the collision. ### Claim 13 (depends on 12) The apparatus of claim 12, wherein the central processor subsystem is configured to detect the level of collision by determining one of a signal-to-interference ratio (SIR), a frequency offset estimate, or a time offset estimate associated with the receive waveform as the level of collision, and wherein the threshold represents one of an SIR threshold, a variance of the frequency offset estimate from an expected frequency offset estimate, or a variance of the time offset from a time offset estimate, respectively. ### Claim 14 (depends on 12) The apparatus of claim 12, wherein the central processor subsystem is further configured to, while sending the transmit waveform through the first transceiver: beginning with the start of the receive waveform, decode the receive waveform, wherein if the detected level of collision exceeds the threshold prior to decoding an entirety of the receive waveform, perform the modify operation. ### Claim 15 (depends on 12) The method of claim 12, wherein the central processor subsystem is further configured to: if the detected level of collision exceeds a first threshold prior to the end of the receive waveform, reduce a data rate at which a remainder of the transmit waveform yet to be transmitted is to be transmitted by the first transceiver; and if the detected level of the collision exceeds a second threshold greater than the first threshold prior to the end of the receive waveform, terminate the sending of the transmit waveform prior to the end of the transmit waveform. ### Claim 16 (depends on 12) The apparatus of claim 12, wherein the PDU includes a training field, a header defining transmission parameters used for decoding the PDU, and a payload including the frame, wherein the central processor subsystem is further configured to, while sending the transmit waveform through the first transceiver: decode the receive waveform beginning with the start of the waveform, wherein if the detected level of collision exceeds the threshold prior to an indication in the header of a duration of the PDU or prior to an indication in the header of a data rate, the central processor subsystem is configured to modify by reducing the duration of the PDU from an initial intended duration to a reduced duration or reducing the data rate from an initial intended data rate to a reduced data rate, respectively. ### Claim 17 (depends on 12) The method of claim 12, wherein the central processor subsystem is further configured to: perform digital beam forming on the transmit waveform so that the one or more antennas of the first transceiver form a signal null directed to one or more antennas of the second transceiver. ### Claim 18 A non-transitory computer readable storage medium encoded with instructions that, when executed by a processor of a central processor subsystem configured to control multiple transceivers separated from each other in a coverage region of a wireless network, each transceiver configured to transmit protocol data units (PDUs) wirelessly from one or more antennas of that transceiver and convert wirelessly received signals at the one or more antennas to receive waveforms, cause the processor to perform: sending a transmit waveform representative of a PDU, the PDU including a frame addressed to one or more wireless client devices, through a first transceiver of the multiple transceivers to be transmitted wirelessly by the first transceiver on a frequency channel; receiving from a second transceiver of the multiple transceivers tuned to receive on the frequency channel a receive waveform representative of the PDU transmitted by the first transceiver that is wirelessly received at the second transceiver; and while sending the transmit waveform to the first transceiver: beginning with a start of the receive waveform, detecting a level of collision between the receive waveform and another transmission on the frequency channel; and if the level of collision exceeds a threshold prior to an end of the receive waveform, modifying the sending of the transmit waveform or modifying sending of a sequence of transmit waveforms representative of PDUs to reduce or avoid the collision. ### Claim 19 (depends on 18) The non-transitory computer readable storage medium of claim 18, further comprising instructions to cause the processor to perform, while sending the transmit waveform through the first transceiver: beginning with the start of the receive waveform, decoding the receive waveform, wherein if the detected level of collision exceeds the threshold prior to decoding an entirety of the receive waveform, performing the modifying. ### Claim 20 (depends on 18) The non-transitory computer readable storage medium of claim 18, further comprising instructions to cause the processor to perform: if the detected level of collision exceeds a first threshold prior to the end of the receive waveform, reducing a data rate at which a remainder of the transmit waveform yet to be transmitted is to be transmitted by the first transceiver; and if the detected level of the collision exceeds a second threshold greater than the first threshold prior to the end of the receive waveform, terminating the sending of the transmit waveform prior to the end of the transmit waveform.