KR19990067371A - Transmitter Identification System and Method for Improved Multiple Data Transmission Detection - Google Patents

Abstract

The present invention provides a method and apparatus for improving the probability of identifying multiple transmitters 1, typically transponders, which transmit data to a receiver. The present invention includes a plurality of systems including a passive radio frequency transponder system, a system in which multiple self-powered transmitters must be identified by a receiver, or a system in which multiple transmitters broadcast using randomly delayed "back and retry" algorithms. Applicable to Each transmitter 1 is adapted to transmit at regular intervals and is random or pseudo-random about the operating frequency of the means for generating the transmission, the means for calculating the duration of the interval between successive transmissions and the local timing means 21. Means 20 for enabling the transmitter at intervals. In a passive RFID system, the frequency of the local timing means is unclear and is not specified until the transmitter is in operation.

Description

Transmitter Identification System and Method for Improved Multiple Data Transmission Detection

Identification systems are known in which a plurality of transmitters, typically transponders, are operated by interrogation signals to transmit response signals comprising identification data to a receiver, which typically forms part of an interrogator. The signal can be transmitted in a variety of ways, including acoustic waves such as ultrasound, interfering light, infrared (IR), and electronic energy, such as radio frequency (RF). For example, transmission is achieved by actual radiation of RF energy by the transmitter, or by modulating the reflectance of the antenna of the transmitter, thereby changing the amount of RF energy of the interrogation signal that is reflected or backscattered from the transmitter antenna. Can be.

In general, if transmissions of two transmitters overlap or collide, transmissions are lost because the receiver cannot distinguish between individual transmissions. Thus, the system must provide each transmitter for repetitive transmission until the transmission of the transmitter occurs at a "quiet" time and is successfully received by the interrogator. GB 2,116,808 A discloses an identification system in which individual transponders are programmed for retransmitting data in a pseudo-random manner. In this identification system, the timing signal for the transponder is derived from the crystal oscillator, which makes the manufacturing of the transponder more expensive.

EP 467,036 A discloses another identification system that uses a pseudo-random delay between transponder data transmissions. In this example, the linear recursive sequence generator completes the sequence by transponder identification address to make the pseudo-random delay as random as possible.

It is an object of the present invention to provide an alternative system that enhances the detection of multiple transmissions in this kind of system.

EP 494,114 A and EP 585,132 A disclose an identification system in which a transponder can be programmed with the same data. It is an object of the present invention to provide an improved system for generating pseudo-random delays between transponders.

The present invention relates to a method of identifying a plurality of transmitters, each transmitting data to a receiver at regular intervals. The present invention relates to an identification system comprising a plurality of transmitters and a receiver, and to the transmitter itself. The present invention relates to a method and apparatus for improving the identification system disclosed in EP 494,114 A and in particular EP 585,132 A.

1 is a block schematic diagram of a radio frequency transponder in accordance with the present invention;

2 is a block schematic diagram of the transmission controller block of FIG.

3 is a schematic diagram illustrating transmission timing of two transponders or tags.

A method of identifying a plurality of transmitters, each transmitting to a receiver at regular intervals in accordance with a first aspect of the present invention, each randomly or pseudo-randomly calculated and at an interval associated with an operating frequency of a local timing means associated with the transmitter. And altering the duration of the interval between successive transmissions from each transmitter by enabling the transmitter of.

The interval is preferably varied between the maximum interval duration and the minimum interval associated with the predetermined number of cycles of the local timing means.

In this method, the interval duration between transmissions periodically generates a pseudo-random number, by comparing the pseudo-random number with the output of the counter means clocked by the local timing means, and the pseudo-random number of the counter means. It can be calculated by enabling the transmitter when the number of outputs matches.

An identification system, each of which is adapted to transmit at regular intervals in accordance with a second aspect of the invention and comprises at least one receiver and a plurality of transmitters for receiving transmissions from the transmitter, comprising: means for each transmitter to generate a transmission; The identification system is provided comprising means for calculating the duration of the interval between successive transmissions and means for enabling the transmitter at random or pseudo-random intervals associated with the operating frequency of the local timing means.

Means for generating a transmission in accordance with a third aspect of the invention, means for calculating the duration of the interval between successive transmissions and means for enabling the transmitter at random or pseudo-random intervals associated with the operating frequency of the local timing means. There is provided a transmitter adapted to include and to transmit at regular intervals.

Since the local timing means are preferably oscillators of the transmitter, with unspecified clock frequencies affected by relatively large tolerances, oscillators of different transmitters tend to run at different frequencies.

The enabling means includes a pseudo-random number generator tuned to generate a pseudo-random number, a counter means tuned to count at a rate associated with the oscillator frequency, and an output of the pseudo-random number generator and an output of the counter means. Comparator means adapted to enable the transmitter when these outputs match.

The transmitter may be a radio frequency identification (RF / ID) transponder. In the transponders embodying the "anti-collision protocol" disclosed in EP 494,114 A and EP 585,132 A, the identification codes of each transponder need not be different, and the transponders can be identical and can be manufactured very inexpensively in large quantities. Can be. When this anti-collision protocol is used, there is an advantage that there is a better response to this collision. However, reading of a plurality of transponders can be achieved at higher speeds if unique seeds are used in the pseudo-random number generator.

The present invention extends to a method of operating an integrated circuit and a transmitter in which the transmitter of the present invention is customized.

It is an object of the present invention to provide a method and system for improving the identification probability for multiple transmitters, typically transponders, which transmit data to a receiver. Although the embodiments described below relate to passive radio-frequency transponders driven and operated by interrogation signals received from interrogators, the invention is applicable to other systems. For example, the present invention can be employed in systems where multiple self-powered transmitters must be identified by the receiver, or systems where multiple transmitters broadcast using randomly delayed "back-off and retry" algorithms.

The present invention draws attention to this requirement by having a transmitter or transponder that transmits at different times at random or pseudo-random intervals rather than at regular intervals.

In addition, the randomness of successive transmissions from each transponder is improved by deriving random or pseudo-random timing from each transponder's local timing means, typically an oscillator. Transponders may be of the type described in EP 494,114A and EP 585,132A, the entire contents of which are incorporated herein by reference. Large tolerances at the operating frequencies of the oscillators of the nominally identical transponders increase the randomness of these transmissions.

Referring now to FIG. 1, a passive RF transponder is shown schematically. This transponder has an antenna 10 which receives energy from an RF interrogation signal transmitted from an interrogator, a portion of which is switched to charge a capacitor C which acts as a power supply for the transponder. . The transponder has on-board oscillator 12 that operates at the same nominal frequency as other transponders nominally. However, due to the manufacturing tolerances of the preferred low cost integrated circuit transponder, the output frequency of the oscillator 12 typically has a manufacturing tolerance of ± 25%. The output frequency is also affected by the supply voltage VDD from the capacitor C, which is influenced by the strength of the energy received from the interrogation signal due to proximity to the interrogator, antenna direction and other factors. Thus, each tag has an oscillator whose frequency depends on significant uncertainty, depends on supply voltage and manufacturing tolerances, and depends on the received RF field strength. Therefore, the frequency of each oscillator is indeterminate and not specified until the tag is active.

The thick black solid line 1 represents the components of a transponder that can be integrated into a monolithic integrated circuit.

Transponders typically store the configuration information for programming the transponder for code data transmission frequencies (bit rates) that differ from the transponder's identification code, the maximum delay time (Nmax. T), and the seed for the pseudo-random time delay circuit. A nonvolatile memory element 14 that is an EEPROM. The transponder further comprises an output driver 16 which modulates its reflectivity by modulating the load applied to the antenna 10 in the described embodiment but may be an active transmitter. The control logic circuit 18 controls the operation of the output driver 16 and reads data from the memory element 14 in response to the signal from the transmission control circuit 20 shown in detail in FIG. The power on reset circuit 22 initializes the control logic circuit 18 to a predetermined start-up state when a voltage is applied to this circuit.

2, the transmission control circuit 20 is shown in more detail. This circuit receives a clock signal from the oscillator 12 and sequencer 24 which derives from it a frequency that may be lower to produce a "memory read" signal that is applied to the control logic circuit 18 with the clock signal. It includes. The "memory read" signal is a continuous sequence of pulses with a period T and of constant frequency. Each of these pulses causes the control logic block 18 to command the memory element 14 via a " read command " signal to sequentially output the identification code stored in the memory element 14 to the control logic circuit. However, the code is not transmitted to the output driver 16 by the control logic circuit for transmission unless the transfer controller 20 also outputs a " transmit enable " signal to the control logic circuit 18 simultaneously with each " memory read " pulse. Not delivered. This only happens occasionally with pseudo-random time intervals, as described below.

The output of the sequencer circuit 24 is output to the code cycle counter 26 so it is incremented each time and the identification code output sequence from the memory element 14 is started. The code cycle counter 26 never resets, but counts upwards to its maximum count, counts to the maximum count, then returns to zero and counts upward again. Pseudo-random number generator circuit 28 sometimes generates a pseudo-random number, and the output of pseudo-random number generator circuit 28 and the current output of code cycle counter 26 are supplied to comparator 30. Comparator 30 provides an output each time the two numbers being compared are the same, which is the "transmit enable" signal described above. The transmit enable signal also triggers a pseudo-random number generator to generate a new pseudo-random number. When the "transmit enable" signal goes high at the same time as in "memory read", the code read out from the memory element 14 by the control logic circuit 18 is output to the output driver 16 and transmitted.

Referring to FIG. 3, the transmissions or tags (tag 1 and tag 2) of the two transponders are compared. Tag 1 has an oscillator run that is slightly faster than Tag 2. Tag 1 and Tag 2 both have the same Nmax programmed therein, but at a particular time in the diagram shown in FIG. 3, Tag 1 will be in manual (non-transmitted) mode for N1.T periods, and Tag 2 Will be in passive mode for N2.T periods, where N1 changes with each transmit / quiet cycle (0 <= N <= Nmax). T for tag 1 is not the same as T for tag 2, but is subject to the same deviation as the frequency described above. Moreover, the T1, T2, T3 ... TN for any tag are not exactly the same due to time-dependent deviations in the supply voltage for that particular tag. Thus, there is a frequency deviation between the tags and between different times in the same tag. The anti-clash system used in the present invention, as in the case of other RF identification systems, is inexpensive to implement and provides for a crash if the tag clock signal is derived from the RF carrier frequency (eg by frequency division). A better protection system is achieved.

The value of Nmax is determined by the number of bits compared by the comparator 30. Nmax = 255 for 8-bit comparison. Nmax is configured at the time of manufacture or programming of the transponder. For a certain number of Nmax, it has been experimentally determined that there is a practical limit on the number of transponders or tags that can be read simultaneously in the same RF query field. When compared to the time taken for all transponders where the number of transponders in the same RF query field must be successfully identified, this time is due to collisions between transponder transmissions until the number of transponders reaches Nmax / 2. It is roughly proportional to the number of transponders. If the number of transponders is increased beyond Nmax / 2, the time taken to identify the tags is rapidly increased with no transponders identified, as all transmissions result in collisions.

Due to the various advantageous aspects of the design of the transponder described above, a large degree of randomness is obtained from the data transmission from each transponder, although the transponder programmed with the same value of Nmax is necessarily the same. This means that only values that need to be adjusted from one transponder to another transponder are transponder identification codes. Those skilled in the art will appreciate that the present invention may be effective in many different systems. In systems where the deviation of the local timing means is not an inherent feature, this deviation may be included in this system design. For example, many different crystal oscillator circuits can be used that drive at different speeds. Each transmitter may be equipped with a different oscillator circuit, although it is not necessary to supply a natural frequency for the transmitter set. Alternatively, the transmitter can dynamically change the frequency of the local timing means, for example by switching between oscillator circuits. In the same spirit, local timing means, in which the frequency depends on external factors such as temperature, incident light, can provide the necessary deviation in frequency.

Claims (30)

A method of identifying a plurality of transmitters, each transmitting to a receiver at regular intervals, Varying the duration of the interval between successive transmissions from each transmitter by enabling each transmitter at intervals that are randomly or pseudo-randomly calculated and related to the operating frequency of the local timing means associated with the transmitter. Method comprising a. 2. A method according to claim 1, wherein the interval varies between a maximum duration and a minimum interval associated with a predetermined number of cycles of local timing means. 2. A method according to claim 1, wherein the operating frequency of the local timing means is indeterminate frequency. The method of claim 1, wherein the interval duration between transmissions generates a pseudo-random number, compares the output of the counter means clocked by the local timing means with the pseudo-random number, and compares the pseudo-random number with the counter means. And can be calculated by enabling the transmitter only when the outputs match. 5. The method of claim 4 wherein the pseudo-random number is generated periodically. A plurality of transmitters each adapted to transmit at regular intervals and at least one receiver for receiving transmissions from said plurality of transmitters, each of said plurality of transmitters comprising means for transmission generation, between successive transmissions; Means for calculating an interval duration and means for enabling the transmitter at random or pseudo-random intervals associated with the operating frequency of the local timing means. 7. The system of claim 6, wherein the means for calculating changes the interval between a maximum duration and a minimum interval associated with a predetermined number of cycles of local timing means. 7. The system of claim 6, wherein the local timing means is an oscillator. 10. The system of claim 8, wherein the clock frequency of each oscillator is subject to relatively large tolerances. 10. The system of claim 8, wherein oscillators of different transmitters operate at different frequencies. 10. The system of claim 8, wherein the operating frequency of the transmitter is an indeterminate frequency. 7. The identification system of claim 6, wherein the means for calculating comprises a pseudo-random number generator tuned to generate a pseudo-random number and a counter means adapted to count at a rate associated with a frequency of local timing means. . 13. The identification system of claim 12, wherein the enabling system compares the output of the pseudo-random number generator and the output of the counter to enable the transmitter only when the pseudo-random number matches the output of the counter means. . 14. The system of claim 13, wherein the pseudo-random number is generated periodically. Means for generating a transmission, means for calculating the interval duration between successive transmissions, and means for enabling the transmitter at random or pseudo-random intervals associated with the operating frequency of the local timing means. Transmitter adapted to transmit. 16. The transmitter of claim 15 wherein the means for calculating changes the interval between a maximum duration and a minimum interval associated with a predetermined number of cycles of local timing means. 16. The transmitter of claim 15 wherein the local timing means is an oscillator. 18. The transmitter of claim 17 wherein the clock frequency of each oscillator is subject to relatively large tolerances. 16. The transmitter of claim 15 wherein the means for calculating comprises a pseudo-random number generator tuned to generate a pseudo-random number and a counter means adapted to count at a rate associated with a frequency of local timing means. 20. The transmitter of claim 19 wherein the enabling system compares the output of the pseudo-random number generator and the output of the counter to enable the transmitter only when the pseudo-random number matches the output of the counter means. 21. The transmitter of claim 20, wherein the pseudo-random number is generated periodically. In a method for generating transmissions from a transmitter at random intervals, Varying the interval duration between successive transmissions from each transmitter by enabling each transmitter at intervals that are randomly or pseudo-randomly calculated and related to the operating frequency of the local timing means associated with the transmitter. Method comprising a. 23. The method of claim 22, wherein the interval is varied between a maximum duration and a minimum interval associated with a predetermined number of cycles of local timing means. 23. The method of claim 22, wherein the interval duration between transmissions generates a pseudo-random number, compares the pseudo-random number with the output of the counter means clocked by the local timing means, and outputs the pseudo-random number and the counter means. And can be calculated by enabling the transmitter only when this matches. 25. The method of claim 24, wherein the pseudo-random number is generated periodically. Local timing means, means for calculating the interval duration between successive transmissions and means for enabling the transmitter at random or pseudo-random intervals associated with the operating frequency of the local timing means. For integrated circuits. 26. The integrated circuit of claim 25, wherein the local timing means is an oscillator. 28. The integrated circuit of claim 27, wherein the clock frequency of each oscillator is subject to relatively large tolerances. 26. The integrated circuit of claim 25, wherein the computing means comprises a pseudo-random number generator tuned to generate a pseudo-random number and a counter means adapted to count at a rate associated with a frequency of local timing means. 30. The integrated circuit of claim 29, wherein the enabling means compares the output of the pseudo-random number generator and the output of the counter to enable the transmitter only when the pseudo-random number matches the output of the counter means. .