# US 2021/0279433 A1 · Collaborative rfid reader using code divisional multiple access (cdma) and methods for same > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0279433 A1 - Document ID: US20210279433A1 - Status: Published application - Kind: A1 - Application number: 17/055,974 - Filed: 2019-05-14 - Published: 2021-09-09 - Earliest claimed: 2018-05-14 - Assignees: Cornell University - Applicants: Cornell University - Inventors: Edwin C. KAN; Xiaonan HUI - Web page: https://patentgrep.com/patent/US20210279433A1 ## CPC - G06K 7/10019: {resolving collision on the communication channels between simultaneously or concurrently interrogated record carriers. (collision between the communication channels used by wireless communication devices, where the solution is not particularly adapted for RFIDs or the like, H04W74/08)} - G06K 19/0724: {the arrangement being a circuit for communicating at a plurality of frequencies, e.g. for managing time multiplexed communication over at least two antennas of different types} - H04B 5/79: for data transfer in combination with power transfer - H04B 7/216: Code division or spread-spectrum multiple access {[CDMA, SSMA]} - H04B 5/20: characterised by the transmission technique; characterised by the transmission medium - H04B 5/45: Transponders - G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS - H04B: TRANSMISSION ## Abstract The present disclosure provides collaborative radiofrequency identification (RFID) readers that employ code division multiple access (CDMA) encoding to simultaneously broadcast to and read responses from tags in an overlapping reading zone with improved data synchronization and read yield rates. In some embodiments, a harmonic backscattering scheme is used to enable the system to have a much higher signal-to-noise ratio (SNR) and sensitivity, while the reader CDMA protocol can be integrated with an initial TDMA polling process or alternative tag CDMA scheme. ## Claims ### Claim 1 A method for collaborative RFID readers, comprising: providing an RFID reader, the RFID reader having a baseband frequency and being a member of a group of participating RFID readers each being synchronized to the baseband frequency, and wherein the RFID reader is assigned an orthogonal code to produce a code division multiple access (CDMA)-encoded signal, and a set of mutually-orthogonal codes for all participating RFID readers is known to the RFID reader; transmitting, using the RFID reader, a CDMA-encoded signal to RFID tags within a reading range of the RFID reader; receiving a response signal from an RFID tag within the reading range, wherein the response signal comprises data encoded with an orthogonal code of an RFID reader of the group of participating RFID readers; and decoding the data of the response signal using the known set of mutually-orthogonal codes. ### Claim 2 (depends on 1) The method of claim 1, wherein the response signal is decoded using the assigned code of the RFID reader or using the assigned code of another participating reader. ### Claim 3 (depends on 1) The method of claim 1, further comprising transmitting a polling signal to RFID tags within the reading range, the polling signal comprising the set of the orthogonal codes for all participating RFID readers. ### Claim 4 A collaborative RFID reader, comprising: a transmitter having a Tx baseband frequency, wherein the Tx baseband frequency is configured to be synchronized to a Tx baseband frequency of participating RFID readers; a non-transient memory configured to store an assigned orthogonal code and a set of mutually-orthogonal codes assigned to all participating RFID readers; a processor in electronic communication with the transmitter and the non-transient memory, wherein the processor is programmed to: encode data according to the assigned orthogonal code to produce a CDMA-encoded signal; and transmit the CDMA-encoded signal using the transmitter. ### Claim 5 (depends on 4) The collaborative RFID reader of claim 4, further comprising: a receiver having an Rx baseband frequency, wherein the Rx baseband frequency is synchronized to the Tx baseband frequency; wherein the processor is further programmed to: receive a response signal from an RFID tag, wherein the response signal comprises encoded data; and decode the encoded data using the assigned orthogonal code and/or one or more codes of the set of mutually orthogonal codes. ### Claim 6 (depends on 5) The collaborative RFID reader of claim 5, wherein an Rx carrier frequency is separated from a Tx carrier frequency to reduce receiver interference. ### Claim 7 (depends on 6) The collaborative RFID reader of claim 6, wherein the Rx carrier frequency is twice the Tx carrier frequency. ### Claim 8 An RFID tag, comprising: a non-transient memory configured to store a unique identification code and a set of mutually-orthogonal RFID reader codes; and an antenna configured for a signal at a first frequency; a receiver in electronic communication with the non-transient memory and the first antenna, the receiver configured to receive and decode a reader CDMA-encoded signal from the first antenna using a code of the mutually-orthogonal RFID reader codes. ### Claim 9 (depends on 8) The RFID tag of claim 8, further comprising an energy-harvesting circuit configured to harvest RF energy from a signal received from the first antenna. ### Claim 10 (depends on 8) The RFID tag of claim 8, further comprising: a second antenna configured for a signal at a second frequency, wherein the second frequency is separated from the first frequency to reduce receiver interference at a reader; and a frequency conversion unit configured to convert a portion of a received signal to a signal at a second frequency to backscatter the signal using the second antenna.