Patent Application
20110205025
This application relates to converting between different radio frequencies.
In some cases, an RFID reader operates in a dense reader environment, i.e., an area with many readers sharing fewer channels than the number of readers. Each RFID reader works to scan its interrogation zone for transponders, reading them when they are found. Because the transponder uses radar cross section (RCS) modulation to backscatter information to the readers, the RFID communications link can be very asymmetric. The readers typically transmit around 1 watt, while only about 0.1 milliwatt or less gets reflected back from the transponder. After propagation losses from the transponder to the reader the receive signal power at the reader can be 1 nanowatt for fully passive transponders, and as low as 1 picowatt for battery assisted transponders. At the same time other nearby readers also transmit 1 watt, sometimes on the same channel or nearby channels. Although the transponder backscatter signal is, in some cases, separated from the readers' transmission on a sub-carrier, the problem of filtering out unwanted adjacent reader transmissions is very difficult.
The present disclosure is directed to a system and method for converting between different radio frequencies. In some implementations, a method includes receiving a request from a Radio Frequency Identification Device (RFID) reader configured to communicate with a first type of RFID tag. Independent of digital signal processing, the received request is automatically converted to a request compatible with a second type of RFID tag different from the first type of RFID tag. The converted request is transmitted to an RFID tag of the second type of RFID tag.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference symbols in the various drawings indicate like elements.
At a high level, the system 100 can, in some implementations, include one or more RFID tags 102 and 104, a reader 106 and a slave transceiver 108. The RFID tags 102 may be a different type of tag than RFID tags 104. For example, the RFID tags 102 may communicate at a first frequency and the RFID tags 104 may communicate at a second frequency different from the first frequency. The RFID tags 102 and/or 104 may directly or indirectly communicate with the RFID reader 106 through an antenna 110. In certain implementations, the RFID tags 104 can communicate with the RFID reader 106 using the slave transceiver 108 and the antenna 112. For example, the slave transceiver 108 may convert wireless communication between signals compatible with the reader 106 and signals compatible with the tags 104. During the conversions, the transceiver 108 may modify or otherwise update one or more attributes of a signals such as frequency, phase, amplitude, and/or other attributes. In these instances, the conversions may be transparent to the tags 104 and/or the reader 106. The transceiver 108 communicates with the reader 106 through the connection 107. The connection 107 may be a wired and/or wireless connection. For example, the connection 107 may be a wired connection (e.g., coaxial cable) to the antenna 110, wireless connection with the antenna 110, wired connection to a port (e.g., serial), and/or other type of connection.
The RFID tags 102 and/or 104 can include any software, hardware, and/or firmware configured to directly or indirectly, i.e., via transceiver 108, respond to communication from the RFID reader 106. These tags 102 and/or 104 may operate without the use of an internal power supply. Rather, the tags 102 and/or 104 may transmit a reply to a received signal using power stored from the previously received RF signals, independent of an internal power source. This mode of operation is typically referred to as backscattering. In some implementations, the tags 102 and/or 104 can alternate between absorbing power from signals transmitted by the RFID reader 106 and transmitting responses to the signals using at least a portion of the absorbed power. In passive tag operation, the tags 102 and/or 104 typically have a maximum allowable time to maintain at least a minimum DC voltage level. In some implementations, this time duration is determined by the amount of power available from an antenna of a tag 102 and/or 104 minus the power consumed by the tag 102 and/or 104 and the size of the on-chip capacitance. The effective capacitance can, in some implementations, be configured to store sufficient power to support the internal DC voltage when there is no received RF power available via the antenna. The tag 102 and/or 104 may consume the stored power when information is either transmitted to the tag 102 and/or 104 or the tag 102 and/or 104 responds to the RFID reader 106 (e.g., modulated signal on the antenna input). In transmitting responses back to the RFID reader 106, the tags 102 and/or 104 may include one or more of the following: an identification string, locally stored data, tag state, internal temperature, and/or others. For example, the tag 102 and/or 104 may transmit information including or otherwise identifying vehicle information such as type, weight, vehicle height, tag height, account number, owner information (e.g., name, license number), and/or other information. In some implementations, the signals can be based, at least in part, on sinusoids having frequencies in the range of 902-928 MHz, 2400-2483.5 MHz, or about 5.9 Ghz. In some implementations, an RFID tag 102 and/or 104 may be of a type manufactured to support the ISO 18000-6C standard. An RFID tag manufactured to ISO 18000-6C standard may support dual states: an A state, in which the RFID tag is responsive to RF interrogation, and a B state, in which the RFID tag is temporarily unresponsive to RF interrogation. Under the ISO 18000-6C standard, an RFID tag may typically remain in an unresponsive B state for between 0.8 seconds and 2.0 seconds even without any further power being supplied to the RFID tag 102 and/or 104.
The RFID reader 106 can include any software, hardware, and/or firmware configured to transmit and receive RF signals. In general, the RFID reader 106 may transmit a request for information within a certain geographic area, or interrogation zone 113, associated with the reader 106. The reader 106 may transmit the query in response to a request, automatically, in response to a threshold being satisfied (e.g., expiration of time), as well as other events. The interrogation zone 113 may be based on one or more parameters such as transmission power, associated protocol, nearby impediments (e.g., objects, walls, buildings), as well as others. In general, the RFID reader 106 may include a controller, a transceiver coupled to the controller, and at least one RF antenna 110 coupled to the transceiver. In the illustrated example, the RF antenna 110 transmits commands generated by the controller through the transceiver and receives responses from RFID tags 102, RFID tags 104 and/or antennas 110 in the associated interrogation zone 113. In certain cases such as tag-talks-first (TTF) systems, the reader 106 may not transmit commands but only RF energy. In some implementations, the controller can determine statistical data based, at least in part, on tag responses. The reader 106 often includes a power supply or may obtain power from a coupled source for powering included elements and transmitting signals. In some implementations, the reader 106 operates in one or more of frequency bands allotted for RF communication. For example, the Federal Communication Commission (FCC) has assigned 902-928 MHz and 2400-2483.5 MHz as frequency bands for certain RFID applications. In some implementations, the reader 106 may dynamically switch between different frequency bands. For example, the reader 106 may switch between European bands 860 to 870 MHz and Japanese frequency bands 952 MHz to 956 MHz. Some implementations of system 100 may further include an RFID reader 106 to control timing, coordination, synchronization, and/or signal strength of transmissions by inhibitor antenna and RFID antenna.
In some implementations, the reader 106 can include a receiver module 114, a Digital Signal Processor (DSP) 116 and a transmission module 118. The receiver module 114 can include any software, hardware, and/or firmware configured to receive RF signals from the tags 102 and/or the transceiver 108 and can down convert the received signal to digital signals for the DSP 116. For example, the receiver module 114 may convert an RF signal to a baseband signal and, in turn, convert the baseband signal to a digital signal using, for example, an ADC. In some implementations, the baseband signal is a low frequency signal (e.g., DC to 400 KHz). In addition, the receiver module 114 may perform other functions such as amplification, filtering, conversion between analog and digital signals, and/or others. The receiver module 114 may produce the baseband signals using a mixer and low pass filters (not illustrated). In some implementations, the receiver module 114 includes a low noise amplifier (LNA), a mixer, a low pass filter (LPF), and a dual ADC (not illustrated).
The receiver module 114 passes or otherwise directs the baseband signals to the digital signal processor (DSP) 116. The DSP 116 can include any software, hardware, and/or firmware operable to process the digital signal. For example, the DSP 116 may generate control signals for adjusting a cancellation signal used to compensate for leakage signal. In some implementations, the DSP 116 compensates the baseband signals for DC offset and/or phase offset. As mentioned above, the reader 100 may include elements that subtract DC offsets and/or de-rotate phase offsets in the baseband signals. Otherwise, these offsets can reduce the efficacy of the cancellation signal in reducing the leakage signal. In other words, the DSP 116 may eliminate, minimize, or otherwise reduce the DC offset and/or the phase offset to reduce error in the cancellation signal. In the case of DC offset, the DSP 116 can, in some implementations, subtract estimates of the DC offsets in the baseband signals such as the in-phase signal and the quadrature signal. For example, the DSP 116 may determine samples (e.g., hundreds of samples) of the DC offset for the baseband signals and generate an average for each baseband signal based, at least in part, on the samples. In this example, the DSP 116 may subtract the DC offset from the corresponding baseband signal during steady state. In regards to the phase offset, the DSP 116 may introduce a phase shift in the baseband signals to minimize, eliminate, or otherwise reduce the phase shift generated by the elements in the reader 100. In some cases, varying a control value on one baseband signal (e.g., in-phase signal) can produce a change on the other baseband signal (e.g., quadrature signal). This cross-coupling between the two baseband signals can, in some implementations, lead to a more complex control algorithm for compensating for the phase shift offset. In addition, the DSP 116 may analyze the received information such as detecting the signal from a background noise including unwanted DC level shifts and/or signal changes outside the baseband of interest.
The transmitter module 106 can include any software, hardware, and/or firmware operable to generate transmission signals for RFID tags 102. In the illustrated implementation, the transmitter module 106 can include a digital-to-analog converter (DAC), a LPF, a transmission mixer, a power amplifier, and/or other elements. The DAC may receive a digital signal from the DSP 116 and converts the digital signal to an analog baseband signal. For example, the digital signal can encode queries for tags 102 to identify associated information. The DAC may pass the analog signal to an LPF to attenuate frequencies higher than a cutoff frequency from the analog signals. The LPF may pass the analog signals to the transmission mixer to upconvert the baseband signals to an RF signals. In this case, the transmission mixer may receive a signal from a frequency synthesizer and mix this signal with the analog signal to generate the RF signal.
In some implementations, the transceiver 108 can provide internetworking between the reader 106 and tags 104. For example, the transceiver 108 may internetwork signals compatible with a first standard and signals compatible with a second standard. As appropriate, the transceiver 108 can include any software, hardware, and/or firmware operable to convert between a first type of wireless signal and a second type of wireless signal. In some implementations, the transceiver 108 can receive a wireless message from the reader 106 at a first frequency, automatically convert the wireless message to a second frequency, and transmit the converted message to the tag 104. In a first example, the auxiliary transceiver 108 may convert the reader signals from one carrier frequency to another carrier frequency by converting to/from baseband as an intermediate step (e.g.,
In some implementations, the transceiver 108 may emulate or otherwise represent itself as a tag 102 to the reader 106 and/or a compatible reader to the tags 104. Thus, the reader 106 may query the transceiver 108 like any other tag 102 in the system 100. In addition, the tags 104 may transmit replies to the transceiver 108 as if transmitting replies to a compatible reader. In these instances, the transceiver 108 can include any software, hardware, and/or firmware operable to provide foreign communications to the reader 106 and/or the tags 104. For example, the transceiver 108 may provide the reader 106 communications from the tags 104. In providing foreign communications, the transceiver 108 may perform one or more of the following: identify the reader 106 requesting the communication; identify the tag 104 associated with requested communication; determine whether the communication is foreign; and/or translate or otherwise convert communications to forms compatible with the reader 106. As previously mentioned, the transceiver 108 may convert messages between different standards independent of digital signal processing. For example, the transceiver 108 may convert a received wireless signal to baseband and the baseband signal to a different type of wireless signal without digitally processing the signal. In some implementations, the transceiver 108 may convert communications independent of any digital elements such as ADCs, DACs, DSPs, and/or others. In doing so, the transceiver 108 may eliminate, minimize, or otherwise reduce the cost of upgrading the system 100 to communicate with new and/or different tags 104. In addition, the transceiver 108 may passively convert communications. For example, the transceiver 108 may use power from received wireless signals to convert the signals to different types of communications without relying on external power supplies, international batteries, and/or other elements.
In the illustrated implementation, the transceiver 108 includes a receiver module 120 directly to a transceiver module 122 through the connection 124. The receiver module 120 can include any software, hardware, and/or firmware configured to receive wireless signals from the reader 106 and/or the tags 104 and downconvert the signals to baseband. The receiver module 120 passes the baseband signal directly to the transceiver module 122 using the connection 124. In some implementations, the baseband signal is passed to the transmitted module 122 independent of digital signal processing. For example, the receiver module 120 may pass the baseband signal to the transmitted module 122 independent of ADC, DAC, and/or other digital processing elements. The transmitter element 122 upconverts the baseband signal to signals compatible with the reader 106 and/or the tags 104.
In some aspects of operation, the RFID reader 106 transmits a request for information from tags 102 and/or 104 in the interrogation zone. The receiver 120 receives the request and downconverts the request to a baseband signal. In some implementations, the receiver 120 passively downconverts the received request independent of a power supply. The receive 120 may directly pass the baseband signal to the transmitter module 122 through the connection 124. The transmitter module 122 upconverts the baseband to a signal at frequency different from the received signal and transmits the converted request to the interrogation zone. In some implementations, the transmitter module 122 may convert the request to a different protocol such as from GEN2 to DSRC. The tags 104 receive the converted request and transmit a reply compatible with the perceived reader. Again, the transceiver 108 may convert the reply to a form compatible with the reader 106 and transmits the converted reply to the reader 106.
Method 300 begins at step 302 where a request for information is received from an RFID reader. For example, the transceiver 108 of
In some implementations, the reader 106 may include any software, hardware, and/or firmware configured to communicate with RFID tags using RF signals. In general, the reader 106 may perform functions such as amplification, filtering, conversion between analog and digital signals, digital signal processing, noise reduction, and/or others. In illustrated implementation, the reader 106 includes a modem 502, mixers 504a and 504b, a local oscillator 506, a power amplifier (PA) 508, a UHF TX-RX coupling network 510, a multiplexer (MUX) 512, and a low noise amplifier (LNA) 514. In the transmit path, the modem 502 passes baseband signals to the mixer 504, and the local oscillator 506 passes a UHF signal to the mixer 504a. The mixer 504a modulates the baseband signal using the UHF signal to generate transmission signals for a first type of tag or signals for conversion by the converter 108. The PA 508 amplifies the modulated signals and passes the signals to the coupling network 510. The coupling network 510 serves to separate the transmit signal going out to the antenna port from the receive signal coming in from the antenna port. The MUX 512 receives the signal and directs the signal to one of a plurality of outputs. For example, the MUX 512 may dynamically switch the input between the plurality of outputs based, at least in part, on the type of received signal. In some examples, example, the MUX 512 may switch the input to the transmission antenna 110 based, at least in part, on the received signal being compatible with a first type of RFID tag. In some examples, the MUX 512 may pass the signal to the converter 108 based, at least in part, on the signal being compatible with RFID tags that are foreign to the reader 106. For example, the MUX 512 may pass signals having a specified frequency to the converter 108. In the receive path, the MUX 512 receives signals from the antenna 110 and/or the converter 512. For example, the antenna 110 may receive signals from a first type of tag, and the converter 108 may receive signals from a second type of tag that communicates using a different frequency. The MUX 512 passes the received signal to the coupling network 510. The coupling network 510 serves to separate the transmit signal going out to the antenna port from the receive signal coming in from the antenna port. The LNA 514 amplifiers the received signal and passes the amplified signal to the mixer 504b. The mixer 504b demodulates the received signal by mixing the signal with the signal generated by the oscillator 504b and passes the baseband signal to the modem 502 for digital signal processing.
In some implementations, the converter 108 includes a microwave synthesizer 516, mixers 518a and 518b, microwave bandpass filter 520a and 520b, PA 522, coupling network 524, MUX 526, and LNA 528. In the transmit path, the reader 106 passes signals to the mixer 518a, and the microwave synthesizer 516 passes a microwave signal to the mixer 518a. The mixer 518a modulates the UHF signal using the microwave signal to generate transmission signals for a second type of RFID tag. The bandpass filter 520a substantially blocks frequencies outside a specified range of frequencies and pass the remaining frequencies to the PA 522. The PA 522 amplifies the modulated signals and passes the signals to the coupling network 524. The coupling network 524 serves to separate the transmit signal going out to the antenna port from the receive signal coming in from the antenna port. The MUX 526 receives the signal and directs the signal to one of a plurality of outputs. For example, the MUX 526 may dynamically switch the input between different antennas. In some examples, example, the MUX 526 may switch the input to the transmission antenna 112 based, at least in part, on an attribute of the transmission signal. In the receive path, the MUX 526 receives signals from an antenna. For example, the antenna 112 may receive signals from a second type of tag. The MUX 526 passes the received signal to the coupling network 524. The coupling network 524 serves to separate the transmit signal going out to the antenna port from the receive signal coming in from the antenna port. The LNA 528 amplifiers the received signal and passes the amplified signal to the filter 520b. The bandpass filter 520 passes a portion of the signal in a specified frequency range to the mixer 518b. The mixer 518b demodulates the received signal by mixing the signal with the signal generated by the oscillator 516 and passes the UHF signal to the reader 106. In some implementations, the separate receive and transmit lines between the RFID reader 106 and the transceiver 108 can be combined through a circulator such that a single line is connected to the reader 106. In some implementations, the system 500 may include a control line 530 between the reader 106 and the converter 108. In these instances, the reader 106 may dynamically modify the synthesizer 516 to update the communication frequency of the converter 108. For example, the 5.9 GHz may be updated to change frequencies using the control line 530.
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
