| 摘要 |
The subject invention relates to a system for reading from and for writing data into electronic tags which may be associated with objects which are moving with respect to an interrogator, or may be located in fixed positions in the path of a moving interrogator. The interrogator, which is stationary if the tag is moving, sends a continuous RF signal to the remote tag. The tag backscatter-modulates the received RF signal with data temporarily or permanently stored in the tag, including, for example, data associated with the object to which the tag is attached, for example, its identity or contents. The system of this invention uses a very efficient encoding technique for the data which is backscatter-modulated by the tag and received by the interrogator. The backscatter-modulated signals are made up of signals of first and second frequencies f1 and 2f1, respectively, where the second frequency 2f1 is twice the first frequency f1, and where one of the two binary bits ONE and ZERO is represented by one-half period of a signal of the first frequency followed by one period of the second frequency, and the other of the two binary bits is represented by one period of a signal of the second frequency followed by one-half period of a signal of the first frequency. The signals also contain FRAME MARKERS made up of five periods of frequency 2f1 followed by one-half period of frequency f1. The WRITE-by-RF signals sent to the tag by the interrogator are made up of pulses of three different frequencies, one being frequency f2, the next 2f2 and the third 4f2. Either a ZERO or a ONE can be one period of pulses of either 2f1 or 4f2 with the other bit being the other frequency, and with the FRAME MARKER being one period of frequency f2. The MODE signal is four periods of frequency f2.
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