TABLE OF CONTENTS The general topic of digital signal processing has filled a number of books, and to cover any substantial portion is far beyond the scope of our discussion here. We shall limit ourselves to a few remarks specific to RFID.
Because of the modest computational capabilities of passive tags, only relatively simple modulation schemes are used for passive RFID, and data rates are low relative to most other communications technologies. When simple ASK symbols are used, the transmitter can be based on a simple switch (equivalent to a 1-bit digital-to-analog converter), with optional analog filtering to smooth transitions and reduce spectral width. Filtering can also be performed in the digital domain using standard techniques such as finite-impulse-response filters (FIR) in this case requiring a more sophisticated DAC with multiple bit resolution. It is important to note that the DAC can then be a source of amplitude noise, and it may be useful to bypass or fix the DAC output during the CW portion of operation, when the receiver is attempting to decipher a possible tag reply.
On the receive side, the optimal approach for signal processing depends on the protocol in use. As we shall see in Chapter 8, the EPCglobal class 0 protocol uses subcarrier-modulated frequency-shift keying, with frequencies of 2.2 or 3.3 MHz, for the tag reply to the reader. The relatively high frequency means that one can use a conventional analog FM discriminator, which produces a simple binary output (either 1 or...
